let's get started. again, just putting things in perspective,professor cohen talked about how in a big engineering design project you work throughthe various stages. and the first stage is phase a where you comeup with the basic concepts. and i think the level of detail of the systemand subsystem lectures that he is giving, last lecture and today, we could sort of lookat as being on kind of the phase a level to show the basic feasibility and the overallstructure. those of you from aero-astro have certainlybeen familiar with our approach to systems engineering which we call cdio.
someone from aero-astro can tell me the cis conceive, design, implement, which actually means manufacture and test, and operate. so we're kind of dealing in these first fewlectures. and this could be looked at as phase a andthen the detailed design, that's your phase b. that ends with the critical design reviewafter which, in principle, you're supposed to be ready to cut hardware. and then you get into the phase cd where youactually build and test. and then, of course, we operate.
my sort of background, the way i got intoengineering, and i probably should have mentioned this at the beginning as sort of truth inadvertising is i was never trained as an engineer, unlike professor cohen. i was actually trained as an astrophysicist. but, when i went to nasa, i spent so muchtime working with all the technical systems and interacting with the engineers and thepeople who use them that i learned certainly a lot about the way these systems are designedand particularly operated. so my approach to a lot of these engineeringsituations is very much from an operator's point of view.
and i will try to emphasize that as we goalong. very important, right from the beginning ofthe design, i think that you think about how you're going to operate the system. we have had too many examples that i've comeacross and many people who have to actually operate systems where you build somethingwithout really thinking of how the system is going to be maintained and taken care of. one of the things that we have been doingfor the last few years is to take a group of undergraduates down to the kennedy spacecenter every january, an interim activities period, and have them spend a couple of weekswith the engineers and technicians who have
to maintain and operate the shuttle system. and they hear lots of stories from the engineersand particularly from the technicians who say, boy, i would like to have a chance totalk to the person who designed this little system. and i have to get my hand all the way around. and it takes five hours to turn the bolt orsomething more fundamental. and we will probably discuss this when wetalk about the main engines. the fact that originally the main engineswere supposed to be reusable without being taken out of the shuttle so that you couldcycle them many times.
well, it turns out that in order to get sufficientconfidence that the engines are ready to fly, we really do have to take them out after everyflight. and they are extensively borescoped when youlook inside. but some of the engineers in the main engineshop pointed out that, for instance, if certain diagnostic test equipment had been built intothe engine so that you could have taken data as the engines were shutting down over andabove the data that we actually get, possibly we would have been able to reduce considerablythe maintenance on those engines. again, the shuttle was the first time we hadreally tried to design reusability into a space vehicle and engines.
and we've learned an awful lot. so i think it's very important when we discussthe systems in the course of the term that we don't just look at the detailed designbut we also consider the operations. that's very important. in that spirit, professor cohen is going tocontinue his introduction to the shuttle systems. and, aaron, i will turn it over to you. ok. thank you. as professor hoffman said, i'm really givingyou what i would call a technical management
overview because, when we talk about structures,on the 22nd mr. moser is going to come and talk about structuresand he's really going to go into the details, how the loads were calculated, how the stressorswere calculated, how nastran was used, how we came up with the basic structure. but i'm just going to really give you sortof an overview on it. and i think it's interesting to note thatthe structures may be a very good system to look at for your project because it weighsa lot. we certainly didn't have all the tools forcalculations that you have today to make it a more efficient structure.
the materials are a lot different. but basically this structure, if you startat the front of it, the crew cabin, which i showed you a little bit about being made,a welded configuration, and the forward fuselage are basically an aluminum skin-stringer structure,very basic aluminum. if you go back down to the mid-fuselage, whichis the large part there, it's, again, a skinned structure. interestingly enough, the forward fuselageand the crew cabin where made by rockwell international in downey. the mid-fuselage was made by general dynamicsin san diego.
so we had various people putting the structureparts together. the wings were made by grumman. so we had this vehicle being built all overthe country coming to palmdale, california for assembly. and the aft thrust structure was built byrockwell. the vertical tail, i believe, was built byfairchild on long island. some of these places don't exist anymore. but then you go back to the vertical tail. again, it is machined skins with honeycomb.
the aft fuselage, as you can see, is verycomplicated. it has all the plumbing, all the wiring, allthe auxiliary power unit, so it is a maze of plumbing and wiring. you could get lost in there and they'd neverfind you again. but it is a maze of wiring and plumbing. and it's made basically of aluminum. but a lot of the support structure are boron/aluminumthrust structure panels with graphite epoxy skin panels. and then the payload bay doors, which wasour innovative material going into large composites,
we use graphite epoxy, that was the firsttime that really a large composite structure was used in a vehicle. now it's used quite commonly in the air forceand a lot of places, but graphite epoxy were the panels we used. and that saved a lot of weight. one of the problems we had, though, was whenwe built these panels we found we got moisture trapped in it. and, of course, the moisture, when you heatit up coming back it would pop the panels off.
so, on the pad, we had to go in and drilllittle holes in these panels to be sure we could get the moisture to escape. so those are things you learn when you donew technologies. but, as i said, mr. moser is going to go through a very detailedexplanation of this. this may be something you want to considerbecause there could be a real innovative way of reducing the weight and making the vehiclemore robust, so i suggest you think about that for the structure. now i'm going to talk a little bit about guidance,navigation and control.
and some people asked me yesterday where theycould find some information on it. actually, in those orange or yellow books,i've forgotten what color they are, that we showed you that are on-hold in the library,have a very detailed analysis and discussion of how the guidance, navigation and controlsystem was formulated. and it is probably as good as you're goingto find. it was very early in the program. it's a little bit different than it is today,but it's a very good description of the redundant computer set, the fail-operational, fail-safesystem. so i think you could really get a lot outof going through that book.
i should just say it turns out that we havetwo sets of those books in the library and they are on reserve so you can only use themfor two hours at a time. there really should not be any problem witheverybody in the class having access to those books when you need to go and look at them. that will probably be the best source, exceptwhen phil hattis from the draper labs comes and talks about the guidance system. i will talk a little bit more about that. this chart or this schematic or whatever youwant to call it was originated by the johnson space center and rockwell international.
it took us many hours but it basically isthe architecture, i am going to go through it in some detail, for the guidance, navigationand control system. now, this was the original one. it is a little bit different today, and iwill explain the differences that we have, but this was basically the guidance, navigationand control system main architecture. and you can see on the left side, and theleft side is what i would call sensors. first of all, in a very simplistic term, someof your experts in guidance, navigation and control, but guidance, navigation and control,navigation is actually determining where you are, guidance is getting to where you wantto go and control is controlling the vehicle
and its stability and its characteristicsaround the center of gravity. so that's basically control. this is for the total guidance, navigationand control system. interestingly enough, the contractor for thiswas ibm federal systems division. we used their computer and they did the software. much of the hardware was designed and builtby other contractors, and rockwell international basically did the integration. and they did the integration on a system calledthe shuttle avionics integration laboratory. it was basically a vehicle that was in thelaboratory that had all the electronics, the
cockpit and everything in it. it simulated the actuators. the hydraulic system was simulated and theengines were simulated, but basically all the hardware and software was in the shuttleavionics integration laboratory. i imagine you spent some time. we actually had two. we had one in houston and there was one outat rockwell. and, when professor cohen says that it wasa vehicle, you have to appreciate that it was actually laid out just like the shuttleso that they had the controllers, which were
in the aft end, like in the engine compartment,were a hundred feet away from the crew cabin and the computers and all the lines, the dataand power lines were laid out as closely as possible to physically duplicate the layoutin the shuttle because there was concern about the timing of signals going back and forth. and they wanted to run the simulation as accuratelyas possible. and then, of course, you have to have a setof simulation computers to try to determine the environment that the shuttle would beflying in so that it could make the inputs to the rate gyros and the other parts of themeasurement units to try to duplicate the flight regime.
and here is an explanation of the alphabetsoup of all the systems, subsystems, components. on this side you see really the sensors. that's the information that you need to doyour navigation part of it. and then, of course, that information thenis sent to the computer through a multiplexer demultiplexer, mdm, which basically is ananalog to digital converter, digital to analog converter. the computer does its computations and thensends it to the effectors which actually change, whether it's the rcs, reaction control system,whether it's the orbital maneuvering system, whether it's the aerosurfaces, the srb actuators,the solid rocket booster actuators, the main
propulsion system actuators. so you've got sensors, computation and effectors. let me talk a little bit about one sensorwhich probably many of you can relate to, and that's the imu or the inertial measurementunit. and draper labs is famous for its inertialmeasurement units. i worked with draper labs or mit instrumentationlab on apollo, and we had the original initial measurement developed by the mit instrumentationlab in that vehicle. the initial measurement unit has gyros onit to determine angles and it has accelerometers on it.
and it is aligned with the star tracker. it's basically a stable platform. it's aligned with the star tracker to geta reference system in inertial space. and when you make a maneuver you get accelerationand you send it to the computer. and you integrate it once, you get velocityand you integrate it twice and you get position. and it's also used during powered flight andit's used during entry but that then goes to the computer. so the inertial measurement unit is very critical. just to give you an example, here you havethree of them and you have four computers.
i'm going to talk about the computers in aminute. you have three of them. you have to recognize when we went to themoon on apollo we had one imu and one computer in the command and service module, and wehad one imu and one computer in the lunar module, except we did have a backup systemcalled a strap-down system. the primary system was built by draper labs,mit, and the backup system was trw. so we had two different contractors. then you have rate gyros and accelerometerassemblies primarily for ascent, for the stability of the bending of the vehicle.
here's the air data transducers that we talkedabout yesterday for entry. then you have the microwave landing system,the tactical navigation, radar altimeter, rendezvous radar. these are all sensors you use during variousphases of a mission, which again go through the mdms or multiplexer demultiplexers tothe computers and then to the effectors which change your position and velocity as needbe. let me talk about the computers for a moment. you see four computers. that was the real test of this system.
we had four computers that were synchronized. this vehicle, as we talked about yesterday,for aerodynamicists we decided to make it statically unstable. we saved a lot of weight. by that i mean a regular airplane, a normalairplane that's stable. when you get a disturbance it will still comeback. without any augmentation it will come backto its original position. with this vehicle, if you get a disturbanceit will diverge. so you had to continually have augmentation.
so you had to have a fail-operational, fail-safesystem. and that's why you have four computers. it's fail -operationa/ fail-safe you couldlose one computer and your fail-operational will use another computer. that means you have two left. and you're fail-safe and you come home. so that's what it is. now, the real concern about it is these computersare synchronized. they essentially communicate with each other440 times a second.
now, i'm recalling a lot of this from memory,but 440 times a second. and they actually vote on each other to simplisticform terminology. and if one computer is out, it votes it outand another computer takes over. basically that's it. but the concern we had was that in doing thiswe could have a generic failure and lose all computers or we could have what we call atwo on two split. and these would be sort of diabolical errorswhich would cause the vehicle to fail. so we decided, after this was made, to putin a backup flight system, a backup computer, a fifth computer.
now, it turns out there was an argument there. should we have the fifth computer a differentcomputer and different people or should we have a same computer with different people? and we argued long and hard on how to do it. and we had a lot of experience with the draperlabs. the draper labs just did an outstanding job. the mit instrumentation lab just did an outstandingjob on the apollo vehicle, both on the command and service module and lunar module. we went to the mit instrumentation lab, draperlabs, and asked them to actually take the
same computer but put it outside the loop. it's not part of the redundant set. it's outside the loop. i didn't show the schematic right becauseit gets all the same information that the other computers get, but it then can takeover if the primary system fails. now, phil hattis did this work for the draperlabs, for nasa in this backup system. he's going to give you a lecture. he's very good to lecture on this total system. he can tell you about the total system.
we thought we'd put the backup flight systemin just for a short period of time to give us confidence in the primary system, but itturns out that we started putting things in it that now we needed so we could not takeit out. so, it's really part of the major system. that is a very different part of the systemtoday. i don't think we ever really had a diabolicalproblem in flight. i think we did have one in the shuttle avionicsintegration laboratory one time when we had a two on two split. but when we did the approach and landing testwhere we had the orbiter on top of the 747
and we separated the orbiter and landed, iremember that first flight, i was sitting in the control station at edwards air forcebase, and at that time i smoked a pipe, and when we separated a big x came across thescreen because we lost the first computer. i guess the shock actually broke a solderjoint in the computer. the power shock from separating actually brokethe first computer so we had to go to the second computer. i bit my pipe in two. but it did prove that the redundant set didwork because it took over and landed. we had a very successful in-flight test, notplanned, but it turned out to be a very successful
in-flight test. now, when you make the computations, you getthe information on position that the computer computes, it sends it to the effectors. the effectors, during the high part of entry,may be to the reaction control system, the forward rcs system or to the aft, or it couldbe to the oms systems if you're trying to make a maneuver. or, when you get down lower in the atmosphere,it could be the aerosurface actuators. and then, during ascent, it's to the solidrocket boosters or the main propulsion system. so, those are the effectors.
the flight control system is a very interestingsystem for entry because, as you can envision early in the entry you don't have any aerodynamicsso your aerosurfaces aren't of any value to you, you use the reaction control system. but, as you get farther into the atmosphere,the loads become so high that the reaction control system becomes ineffective and thenyou have to use the aerosurfaces. so it's a blended system. and the system has to know when to handlethe aerosurfaces versus the reaction control and, of course, then you also have displaysto the crew and actually information that the crew could use to make certain decisions.
so that basically is the guidance, navigationand control system. there is one additional change, that i don'thave on this chart, which they have incorporated the global positioning system in the shuttle. the gps is now part of the system. it took a long time to do it because i rememberit wasn't done when i left. and were you still there when it was implemented? yeah, they did put it in. and gps you can essentially get position. if you could get attitude then theoreticallyyou could eliminate the inertial measurement.
and i don't think they do it that way. but theoretically, the gps, for you lookingat the guidance system change, this again becomes a very interesting system to lookat. would you do it different today? for example, the computer that was used, icannot remember all the characteristics of it, but it's basically the ibm 4 pi computer,which is a very old computer. it was probably made before many of you wereusing computers. or, weren't born. [overlapping voices] which i think was a designfrom the early `70s.
yeah, it is the early `70s. this would be a very neat system to take alook at for your system. not only that, you could probably get a lotof support from draper labs and that type of thing. so it would really be a good system to takea look at. and i'm sure you could make a lot of improvements. those improvements could theoretically beused on the new cev, the crew exploration vehicle. i think it would land a lot of merit of youvery smart people to take a look at the guidance,
navigation and control system. yes, sir. in the air data transducers, were there morethan just torpedo tubes and static cords? that's all there was, i believe. i think that was. we had a lot of problems with those. i think it's just very old technology. yes. i was going to ask, how you got position informationbefore gps.
position? well, i don't know exactly. but it's got 13 satellites going around. well, there were two ways. i mean the desire for gps, of course, wasto give the shuttle autonomous navigation capability. the shuttle with the star trackers and theimus, it has the autonomous ability to determine its attitude, but it doesn't know where itis because the inertial measurement units drift over time.
and so you need to be able to update the statevectors. originally, the only way you could do it wasradar tracking from the ground. you would track it. you would get a state vector. you would uplink the state vector and thenthe shuttle would know where it was. and then periodically you would have to updateit because of imu drift. once we got the tracking and data relay satellitesystem installed, you do get navigational information by the doppler navigation andfrom the signals coming back and forth through tdrss, but it was generally calculated onthe ground.
so it was not really until the advent of gpsthat we got autonomous capability. you need it for things like if you're goingto deploy a satellite, for instance, you need to know your position pretty accurately. because the satellite is going to take thatposition and has to do its burn accordingly. and, obviously, for your reentry burn or forrendezvous it's critical that you know your position. when you're doing a rendezvous, the shuttledoes have a rendezvous radar. i don't know if we'll deal with that in detail. once you get close enough to the object thatyou're rendezvousing with such that you can
get it either with your radar, or they actuallyuse the star trackers to optically track the object, then you can start getting your relativeposition with respect to the object, even though you may not know your absolute position. and so, from that point of view, the shuttlegets a certain degree of autonomy. maybe i'll just say one other thing aboutthe computers because people are amazed at how primitive the shuttle computers are. but, like i say, the original idea and theconcepts that we talked about, this was going to be an airplane-like vehicle. and originally they wanted to use some off-the-shelfhardware.
and, of course, the ap-101s, as they finallyused them, were not off the shelf. but these original computers had 128k of memory. and the memory they used, i don't know ifany of you have read back in the history of computing where they actually had the littlemagnetic ring cores with the wires going through. i mean this was really old stuff. and they did finally replace that with a solid-statememory with a whopping 256k. and, again, probably none of you have dealtwith overlay technology but, back when i was a graduate student and we were using computersto do complex astrophysical calculations, sometimes you would have a program that wastoo big for the computer memory so you would
have the whole program on a tape recorderand you'd segment it into what they would call overlays. and then you would load it one part at a timeand it would do its calculations. and then you would stop and load the nextbatch of software. well, that's the way we have to run a mission. the computers cannot hold enough softwareto do ascent, orbit and entry. there are three segments of flight software. you start the mission with the ascent softwareloaded. then, when you get up into orbit, you do whatthey call a major mode transition where you
basically punch a button and everything goesblank. and you sort of sit there saying i hope thisis going to load properly. and the tape recorder chugs away. and then it loads the orbit part. and the same thing when you're getting readyfor entry. now, the backup system they decided that theydidn't want to take that risk. that if something went wrong in a major waythey wanted the whole flight software on the backup system. and that meant it had to be scrubbed.
the backup system is capable of flying theshuttle and getting it home safely, but there are a lot of capabilities which the main computersystem can do which the backup system cannot do just because they're limited to the amountof software. the one other thing i'll say is putting togetherthis redundant set of four computers because, as professor cohen said, the shuttle willnot fly without the computers. i mean it's absolutely flight critical. hundreds of times a second, every computeris looking at the data from all the other computers. and they are all voting.
and so you have this matrix, just to makesure you understand the way the system works. if computer number one sees a problem withcomputer number three, it's likely that computer three is also going to see a problem withcomputer one because they're doing something different. but if computer number two sees a problemwith computer three and computer three sees a problem with computer two and computer foursees a problem with computer three, now you've got a three to one vote. and so computer three will recognize thatit is the problem and it will take itself out of the set.
and that's what happened, well, in that case,the computer actually shut down. i remember that big x. and, at the same time, all of this informationhas to go back and forth to the backup computer. because, if you're ever going to engage thebackup computer, it has to be ready to go at a split second's notice. and there are situations where you can geta two on two split. when we run through the simulations to learnhow to work this, actually learning the ins and outs of how to work the computer systemis probably one of the biggest trainings. the astronauts become more knowledgeable thanthe designers.
yes? if there is this danger of a two to two vote,was it ever thought about to have five computers then? well, that's why we put the backup systemin. oh, the backup system. yeah, the backup system. that was why we put the backup system in. it did a little bit more, too. it was programmed by different people.
even though it used the same computer, itwas actually programmed and formulated by different people. so, that was one way of saying take away any,you might say, systematic errors that were in the redundant set. in other words, they kept the same softwarerequirements document but the actual coding was done by draper rather than by ibm. that was the other problem. suppose all four computers are doing the samething but there was an error in the code which never turned out so that something startsto diverge, what's your protection against
that? there was a big argument in doing that. the real argument said should you really havethis or a different computer? should you really just say just do everythingdifferently? just have a different computer? a different everything? and, of course, there are advantages to thatand there are disadvantages to that. so, we settled on this. i think there was another question.
was there a question back there? you said this was the first fly-by-wire system. i was wondering what competing ideas therewere besides having [four computer systems?]. well, fly-by-wire means when you put an inputinto the control system, whether you do it manually or whether the computer does it,nevertheless, ultimately your command just goes into the computer. you put the stick to the left saying i wantto do a left bank, all you're doing is telling the computer you want to do a left bank. and now the computer has to figure out what'smy navigation state, where am i if i'm coming
down through the atmosphere, what's my altitude,what's the air pressure, what's my mach number? and then it's programmed with aerodynamiccontrol laws. this is one of the big challenges. because, as i mentioned the other day, youhit the top of the atmosphere at mach 25, you do your initial control with the rcs. as the dynamic pressure starts to increase,first the ailerons, the roll becomes active at about, i think, ten pounds per square inch,something like that. you blend the roll control into your aerosurfaces. at about 20, i think it's pounds per squareinch, you can do the pitch control.
but because the shuttle is coming in at a40 degree angle, the vertical stabilizer is pretty much shadowed. so for yaw control you actually have to keepusing the rcs all the way down to about mach one when the shuttle finally pitches downand the vertical stabilizer now has some effectivity. the computer calculates all this informationand it comes to the effectors, and you do the control laws on that. and the problem is that the flight controllaws, which the computer has to use in order to control the air surfaces in the rcs, arenot constant on your way down. i mean the flight control laws at mach 15are very different from at mach 5.
and there is part of the flight regime, forinstance, where if you want do a left bank, you actually have to start by commanding aright yaw. and then the cross-coupling terms in the aerodynamicsactually causes you to go in the other direction. it gets very complex. and the flight control system is continuallychanging as the entry progresses. and so the idea that maybe you should havea direct backup link between the pilot's inputs and the aerocontrol surfaces, although itmight give you a warm, fuzzy feeling, you could not fly the shuttle directly. because to be able to take into account thesechange in control laws on the way down, you
just cannot do it. in fact, the shuttle is uniquely, i mean,unless the shuttle knows where it is, if the navigation state goes bad the shuttle cannotfly. you could have the runway in sight, but ifthe shuttle's inertial nav state is wrong you will lose control and you cannot land. so it's a very complex system from that pointof view. this is a very, very, if you can envisionthe systems engineering that went into this system, it takes aeordynamics, it takes flightdynamics, it takes electrical signals, it takes guidance laws, navigation laws, hardware,software.
this is probably the biggest integration job,or systems engineering job. it requires everything. it also has to take into consideration aerodynamicheating. i'm going to show you that in a minute, becauseyou've got to be sure that you don't fly outside the regime that you were designed for aerodynamically. i think you had a question. just real quick, how big are those imus? because nowadays you can get a solid-stateone not quite that big. well, i don't recall.
it's a box, sort of like a shoebox. the apollo imu was about this big. that was built for the polaris vehicle. it was one imu and it was a three gimble platform. and i remember it was a big issue. a three gimble platform has a singularity,so you had to maneuver the apollo vehicle a certain way so you didn't get the singularityin it. and one of our astronauts, jim mcdivitt, quitea famous astronaut who was a good friend of mine, said he wanted a fourth gimble.
and there was no way we could get an imu inthat day in time with a fourth gimble. so, what i did was gave him a fourth gimbleto carry with him on his flight. a little gimble system so he had a fourthgimble. we didn't have the gimble lock problem onthe shuttle because it was a four gimble platform. but i remember we went through that with mitinstrumentation many times because all you could get at that time, because the imus wereso big, a fourth gimble was almost impossible. and mcdivitt was a very good astronaut buthe wanted the four gimbles. in fact, he wound up being my boss. before we go on, let me just mention one morething about the backup system.
sure. go ahead. the backup system actually takes a lot ofcare and maintenance and there's a lot of money that goes into that. and this is not a dead issue because in thedesign of the cev, nasa is going to have to make a decision. there were some guidelines which were produceda couple of years ago out of the johnson space center with a lot of astronaut office inputabout what are the requirements in the future for human space vehicles?
and they put in that you should have a backupcomputer system because basically that's the way we did the shuttle. and, actually, that was an afterthought. and yet now it's being listed as a requirement. and this is now being questioned for the cevbecause it's a huge financial impact. and so we're going to have to deal with theseproblems all over again. it's an interesting thing to think about ifsome of you want to delve a little bit more deeply. i think this could lead to a very interestingactivity for you.
do backup computers have their own sensoror are they reading the same sensors? the same sensors. i just didn't show this very accurately becausei looked at the chart, when i had it, i said my god this is the wrong chart. but this was the original chart before thebackup system so i quickly penciled in the backup system so i would remember to talkabout it. but, no, it has the same sensors. it has all the same information. but, again, most of those sensors are redundant.
yeah, they're redundant sensors. not all of them but most of them. any one of the four computers can read anyof these sensors. it's not like sensor one is dedicated [tothis computer?]. the sensor input is put on a data bus, andthey have multiple data buses. like four data buses in each of the computerscan read all four data buses. i mean there's just a tremendous amount ofredundancy built in. yes, go ahead. did they ever use the star tracker to updateyour gyros?
the platform? yeah, they do that. there is also a procedure if you totally loseattitude. then you have to go right back and manuallytake a star site and orient. and that we've only had to do in a simulator. to look at the failure history of this wouldbe very interesting. in my tenure, i know we lost one inertialmeasurement unit. we lost that one computer during the approachand landing test. i don't know what other failures we actuallyhad in this system.
the mdms, this box was made by sperry at thetime in phoenix, arizona. and i've visited that many times because thatis probably the most complicated electronics box of this whole system other than the computer. it's very, very complicated. computers have developed a lot faster so whydo you still think that it will be a major expense now? i don't think it will be a major expense now. as i recall, and you're absolutely right,nasa does not put a lot of money into development of this technology because other people havedone it.
it's so much more sophisticated than we havenow. we don't need it. it turns out, though, at one point in timestructures was the most expensive component of a space craft. then, of course, there was propulsion. and then there became avionics and software. and avionics and software for the shuttleis very, very expensive. it's probably one of the most expensive things. i think today, in today's environment, withthe technology we have in both software and
hardware, i think it won't be that expensiveanymore. so, i think you're right. that's why i'm saying in redoing it, you coulduse new technology and really show how much less it's going to weigh because the imusare probably going to be smaller. you could reduce the weight, you could reducethe electric power and you could reduce the cost. but you're going to have another detailedbriefing on this. and phil hattis, i know him very well, i thinkhe will do an outstanding job in explaining it to you.
let me just show you very briefly, we talkeda little bit about this yesterday, but here are some of the profiles that the guidancesystem has to be able to do. it certainly has to take care of launch. the abort modes, which are interesting, thereis an abort mode that is a return to launch site. and i guess you would use return to launchsite primarily for a main engine failure, i guess. if the main engine fails during ascent, youcan go to a return to launch site. or, a total loss of cabin pressurization,something like that.
and i guess that's never been tried. and i guess that's probably one of the mostdifficult maneuvers, most biggest fears the astronauts have if they ever have to comeback to return to launch site. but, of course, the guidance system has gotto be capable to take care of that. then you have abort once around. again, when you have main engine cutoff, youhave separation and you abort to once around. again, i guess that's primarily a main engineproblem. and then you have, of course, an abort toorbit. and those are the three abort regimes youhave.
transatlantic landing? transatlantic. yes, you have transatlantic abort. that's right. you do have transatlantic abort. yes, thank you. that actually drives the launch window, because[if they don't have clear weather overseas they don't launch?] . so, the guidance system has to take care ofall those abort modes.
again, i'm sure phil will go through thiswith you. but first stage guidance really consists ofattitude and throttle schedules as a function of relative velocity. it's not completely open-loop, it's almostan open-looped system, but you do control the thrust vectors of the engine and the solidrocket booster actuators. and the key thing, though, where systems engineeringcomes into play, it has to get maximum performance. but the angle tack history has got to be shapedto control aerodynamic loads. because some of the highest loads you have,and you will find out when moser talks about it, some of the highest loads you have onthe structure is during ascent.
control of maximum dynamic pressure. and you have to provide the flight angle atsrb staging to allow recovery of the spent boosters. these are some of the constraints that youhave. and, again, this comes out to be a real systemsengineering problem. and for entry, entry really becomes a taskin itself because one of the basic problems you have to control is thermal control. the thermal protection system, i should havepointed out on that structural slide that the back face temperature of the tiles haveto be at 350 degrees fahrenheit.
while the surface temperature may be 15 to2000 degrees fahrenheit the back face has to be at 350 degrees fahrenheit because that'sthe limit of aluminum, so you've got to control the guidance. the thermal control for guidance is to keepthe vehicle within the temperature constraints in the peak heating region. so, that's all got to be married togetherso that the tile system you design keeps the back face temperature to within 350 degreeson the aluminum structure. then you go into equilibrium glide. constant bank angle, we were talking about,is modulated for drag control.
and then the transition guides the vehiclefrom the high out braking to the lower angle of attack. and then you basically land. all this has to be tied together for yourguidance, navigation and control system. i have one more system that i'd like to talkabout briefly. now, you're going to have another very detailedbriefing on this. this is the hydraulic system. this ties in together with the other systemswe talked about, the flight control system, the guidance system, the department of flightcontrol, because the hydraulic system is three
systems. it's a 3000 pound per square inch system. and what does it do? it basically is used during ascent and entryfor it to control the thrust vector control of the engines, for the body flap, for theelevons, for the rudder speed brake, the actuators for the main engine, the doors for the externaltank separation, main landing gear, nose wheel steering and braking. so, that's what the hydraulic system does. if you lose your hydraulic system you hada bad day.
and there are three systems. i do believe there is one place where there'sa single point failure in the hydraulic system. it's pretty hard to eliminate all single pointphase. i believe that. when henry pohl talks, he's going to be doinga very detailed discussion on the hydraulic system, you might ask him that. i don't recall, but he'll tell you whetherthere is a single point failure in the hydraulic and this is a schematic of the hydraulic system. i am not going to go through the details ofit because i'm not sure i could explain it.
but basically this is the hydraulic systemthat shows how system one, system two and system three is tied into the right outboardelevon, the right inboard elevon and so forth and so on. the main engines. the external tank. and we've never had a loss in the hydraulicsystem. we did test the hydraulic system in what wecall the flight control hydraulics laboratory at downey where we had actually all the hydraulicsystems tied together with the computer system. and actually flew the vehicle, what we calledthis iron bird, with a hydraulic system.
and we did have a failure there one time. early in the program, we had a single pointfailure and lost all the hydraulic fluid. we had to go back and make a major changeto the actuator system, to the hydraulic system. i'm just wondering how the hydraulic systemon the shuttle compares to the hydraulic system on an aircraft? an airplane. yeah. i'm really not sure i can explain it. i think there's not much difference.
let me tell you the only difference. i think airplanes have three hydraulic systems. the shuttle started out with four hydraulicsystems. we actually started out with four, but itwas so heavy and so complicated we decided to go to three. and i think the airplanes have three hydraulicsystems, if i'm not mistaken. does anybody know? i at least know quite a few that have three. i don't know if all airplanes have three.
the big difference in it is that the hydraulicsystem in the shuttle is powered by what we call an auxiliary power unit. and that's what pressurizes the system. and i think on an airplane it's powered bythe engine itself. but this system is pressurized by what wecall an auxiliary power unit. an auxiliary power unit is a box about thisbig. it generates 135 horsepower. and it's got a ten inch turbine wheel thatgoes about 10,000 to 20,000 rpm. and actually it's fueled by hydrazine.
and it essentially pressurizes the systemto get you up to 3000 psi. again, if this auxiliary power unit doesn'twork, we have three of them, it's a bad day. and i think we did have some problems withone of the auxiliary power units at one time during ascent. but that's the major difference, i think,because i think we tried to copy pretty much aircraft designs using the same type of hydraulicfluid and everything else. so i think we copied their standard in usingthis, as i recall, except we're pressurized by the auxiliary power unit. again, not to belabor the point, you're goingto have a very detailed briefing or lecture
on the hydraulic system, the auxiliary powerunit and the reaction control system, the oms system by henry pohl. so, you will have more details on this. again, the hydraulic system might be anotherinteresting thing to take a look at. i hope what i'm trying to get across to youis how these systems all fit together. you cannot do the guidance, navigation andcontrol without the hydraulic system. you have the aerodynamics and you have theaerothermodynamics. you've got the structures and everything thathas to fit together. and you can imagine the systems engineeringproblem associated with trying to put all
that together. just to remind you of a few other things thatyou have to deal with. when you're working with a space system thatalso makes it a little bit different from designing for the ground. for instance, you have a fuel tank with thehydrazine inert. this is a generic problem with any liquidtank. once you're in weightlessness, how do youget the liquid to flow out? this is actually a fairly traditional old-fashioneddesign where they have a diaphragm in the tank.
and, on one side of the diaphragm, you pressurizeit with either helium or nitrogen. and that pushes the material. it's basically sort of like squeezing it outof a bag. the problem is that hydrazine is nasty stuff. and in the orbiter maneuvering and reactioncontrol systems they decided that, for reusability, they didn't want to use diaphragms. and so we'll probably learn more about someof the details. but there's a very elaborate screen mechanismwhich uses surface tension to collect the material.
and just getting liquids out of a tank intowhere you want to go is something you have to worry about in space. the second problem is a thermal problem. you're not flying through the atmosphere soyou don't have air cooling. as you see, you've got the gear box. you're generating a lot of heat. and, actually, in order to cool, they usewater spray boilers. and you essentially, we actually do this toget rid of heat from the orbiter as well before we open the payload bay doors which have radiators.
while those are closed, it has to be donewith a water spray boiler. and so you get rid of all your heat by puttingit into a heat exchanger. and you basically shoot liquid water. and, of course, in a vacuum the water flashevaporates and that takes the heat away. and so, although in essence the control systemis similar to airplanes, even there, there are a lot of special design features thathave to be put in because this is a system that has to work in space as well. that's a very good point. the cooling is one of the biggest differences.
and because this system is so complex andheavy and needs a lot of maintenance and uses hydrazine, which is very nasty stuff, therehave been, on various occasions, studies of could this system be replaced by an electromechanicalsystem? and as motors become more powerful and batteryand fuel cell systems are more efficient, i think just about two years ago we gave upon the last effort, but it always turned out to be too heavy. to get an electromechanical system which hadenough muscle to move these air surfaces around, it is just beyond what we can do. but that might be another good system to takea look at today.
it might be another good system. the other thing. you see where it has a speed control and safetyfor the apu controller? the interesting thing about this turbine wheel,i forget the exact rpm, but it's pretty high. i think it's at least 10,000 to 20,000 rpm. if this shaft should break off, it's a veryhard to control it in the box. i mean it will go right through the box it'sin and share the vehicle. we've tried everything we know. we've put protection around it.
we've put a lot of margin into the turbinewheel, into the shaft, but that's a very critical thing. and, as professor hoffman mentioned, therehave been many exercises to replace the auxiliary power unit. and i think again this would be another goodchallenge to take a look at seeing what you could do to come up with a different designfor the auxiliary power unit. but there will be other systems that you mightwant to look at. but i thought i'd just give you a little discussionof some that i personally think are very pertinent to look at.
that's the thermal protection system, thestructures, the guidance, navigation and control, the hydraulic system, including the apu. and these, i think, would be a very good system. now, you might pick others, but these mightbe very good ones to look at. let me wind up my discussion by talking toyou about what i think you ought to look for in the system. this is just a very simplistic chart, butthis is my way of thinking about what you do when you go about designing something. you need to look at the functions.
as we pointed out yesterday, the functionsare very important because, when we talked about a thermal protection system , we lookedat the functions of protecting the vehicle, maintaining that back surface temperatureto 350 degrees fahrenheit. we worked that to finite detail. we knew exactly how thick the tiles had tobe, what the characteristics had to be, but what did we? we forgot, oddly enough, that it had to beattached to the vehicle, which is sort of dumb. and you would think, my gosh, they ought tobe able to do that.
but you're infinitely smarter after you findout your problem. one thing you ought to do is really understandwhat functions have to be performed. and you might say that becomes your functionalrequirements. the whole thing is understanding your requirements. then you ought to understand what performanceis required. in other words, performance requirements. you ought to have a first order of magnitudecalculation of what kind of performance requirements you need. a lot of times this is going to have comefrom assumptions, talking to people, getting
experts involved. but what kind of performance requirements? it is going to have to be iterated, but whatkind of performance are you thinking about in this system? whatever the system may be, hydraulic system,thermal protection system, whatever. then we talk about the three-legged stool,as professor hoffman said. we talk about schedule, cost and output weightunder performance. because, as i told you before, the first thingyou're going to wind up, in designing a system, is that the weight is going to get too high.
then you're going to find out that performancegoes down. you have schedule slips. but the first thing that usually happens isyou wake up in the morning and you find out, my gosh, my system weighs a lot more, my subsystemweighs a lot more than they told me i could have. so, you've got to understand your weight. and then you need to think about what is theavailable technology? what is the technology available? as somebody pointed out, today the avionicstechnology is probably pretty high up on the
ladder. and you could probably pick something todayright off the shelf. although, in my experience of the 30 yearsi had in the space program, i never was able to find something that was off the shelf. space programs just don't usually allow youto take something off the shelf. people told me to go do it. and, once i went and did it, we changed everything. but today, in the technology we have in theavionics, you may be able to get a lot off the shelf.
so, what technology is available? and then one of the key things, one of thebiggest things you have to know is what are the interfaces? if you could see the multitude of interfacesthat are required for the guidance, navigation and control system, it takes into considerationall the interfaces you could think about. and so you need to think about interfaces,whether they be mechanical, whether they be electrical, whether they be functional. so, you need to think about what interfacesyou're talking about. and, to me, those are some guidelines youneed to think about.
of course then we talk about cost and schedule. usually your cost is going to grow, unfortunately,and usually your schedule is going to slip. and those are, what i would call, career limitingproblems. that's the best way to get fired, to haveyour costs go up and you schedule increase. so, these are some of my guidelines for thingsyou ought to look for when you try to design your system. i would be happy to answer any questions foryou that you may have. about taking technology off the shelf, i'mwondering, and i don't think, from what i know, it was really thought of much duringthe shuttle, but the idea of maybe putting
something on the shelf, so to speak, the ideaof designing something, a subsystem or something so it would have the flexibility to be usedin future systems. do you see where i'm going? no, i don't think i quite follow what you'resaying. try again. well, you said there wasn't really off theshelf technology available then but maybe there is now. the idea i'm thinking about is the idea ofdesigning something not so much just for the shuttle in this phase, but so that it couldbe used for other things.
well, that's a very possible thing to do andwould be a very good thing to do. in my experience, and we tried something likethat, usually this tends to start growing into it. you start saying, well, what is it reallygoing to cost you to do that? i know, when i was project manager, peoplewould come to me with something like that. and i used to be a pretty mean guy. i'm not quite as mean as i used to be. but that's the first thing i'd ask them, whatabout the cost, because that's what happens. when you start trying to make multiple usesout of something, you usually drive the cost
up. and that's what you have to be careful of. [unintelligible phrase] well, let me add tothat. i feel very strongly that had it not beenfor the mit instrumentation lab or the draper lab or the people they had there, the technologythey had there, we wouldn't have gone to the moon when we said we were going to doing it. i mean i worked very closely with them, andi feel very strongly that draper labs, i keep getting them mixed up, at that time the mitinstrumentation lab was really one of the
prime movers of the whole system. it was really fantastic. so the people working here, and you can takeadvantage of that, would be very useful for you to do that. any other questions? well, i will be back on the 22nd. and i look forward to working with you somemore. one more question. sorry.
it has not as much to do with the subsystemsbut to the overall concept of the shuttle. i was wondering why, if you know at all, themilitary thought it was important to have the ability to capture a satellite and bringit back? was it because satellites were so expensiveat the time and maybe they aren't as much? because i don't think we've really done that. well, it really wasn't the military. several satellites we did bring back. i cannot recall which ones. westar and palapa.
i have pictures of that a little later. and we retrieved those. and it turns out, interestingly enough, theywere insured by lloyds of london. and that was the biggest salvage operationlloyds of london ever achieved when they returned those satellites, bigger than anything inthe ocean they ever picked up. in fact, they rang the bell. when they have a big recovery, a big thingin lloyds of london they ring a bell. and they came down to serve somebody, whoeverhe was, i don't recall who he was, but he was head of lloyds of london.
and we had a big reception at the johnsonspace center after we retrieved westar and palapa. i don't think the air force really had thatmuch demand at the time, or it went away, whatever it was, for retrieving payloads,but commercials did. what the military was interested in was thepossibility of refueling satellites in orbit. we did do that. because when you have recognizant satellites,very often you have to change their orbit to get them over to the right place at theright time. and orbital maneuvering fuel is a limitingcommodity on satellites.
and these are very expensive satellites tobuild. so if you have the possibility of refuelingthen, in principle, you could extend the life of these very high value assets. and we did do a demonstration. of course, the fuel, in most cases, is hydrazinewhich is very nasty stuff. if you get it on your spacesuit you cannotcome inside until you bake it off. it's fairly dangerous. and so we actually did do a demonstrationjust in the shuttle's cargo bay, but we've never actually done a real refueling of asatellite in orbit.
but they're still working on it. now i think the military is still workingon possibly robotic refuelling technologies. for whatever the next version of the shuttleor crew vehicle would be, is it necessary or even a good idea to have this huge cargobay? well, i think that's what they're eliminating. i haven't been that close to it. but the cev is going to be really a passengercarrier. and then any cargo will be on an unmannedvehicle, i believe. so, that's what they're separating.
is that right? i mean i haven't really been that close toit. this is one of the guidelines now for futurespace vehicles, is to the maximum extent possible separate humans and cargo. if the original concept of the shuttle hadbeen realizable that the shuttle would be capable of flying frequently enough that itcould basically satisfy all of our launch needs then you can make the argument, well,all right, we're doing this and people are in it to fly it and we'll just do it thatway. but given the fact that we cannot fulfillthat goal then you have to ask why put humans
at risk just to take a satellite up in thecargo bay and launch it when we can launch satellites using unmanned vehicles? and, in fact, that was the decision afterthe challenger accident, was any payloads that are carried into space on the shuttlein general, i mean there were some exceptions for various reasons, but you ought to be usingthe shuttle to do things where you need people to do them. and some of those things, for instance, toservice in the hubble or the assembly of the space station, although even that could beargued that, had we planned it differently, we might have been able to do it without makingsuch extensive use of the shuttle.
but there we do make full use of the big cargobay. but future human space vehicles, the cev willbe basically a people carrier with a small amount of cargo. and any time you want to launch large amountsof cargo you will do it without people. let's take a one or two-minute break. i'm going to get my computer set up. let me put this down here. i want to give you a short presentation justto bring everybody up to a certain level of familiarity with what the shuttle does andwhat it looks like.
and, again, i tend to look at this from anoperational point of view. this will be informal, you know, ask questionsas we go through. as we've said, the two critical phases ofshuttle operations and what makes this such a unique vehicle is it launches verticallylike a spaceship with a tremendous amount of power. and it lands. you look at this, and you have to remind yourselfthat it looks like an airplane landing and, yet, a half an hour ago this was a spaceshipgoing in orbit around the earth. so it really has been a spectacular technologicalachievement.
let's go through some of the maintenance operations,what is actually done to the shuttle. we've talked about it a little bit, but ithink if you actually see some of the images it will help to give some reality to someof this. after the shuttle lands, here it's landingon the runway at the kennedy space center. and, as we mentioned, all of this is a birdsanctuary so sometimes you have to chase the birds away. and there's a problem from time to time withcrosswinds. there is only one runway so, if you get windblowing across the runway at more than 15 knots, you cannot land.
and so that's also a constraint sometimesto launch because when you take off you always have to be able to turn around and come backand land here, just like you have to be able to land over in europe or africa. and so there are a lot of launch constraints. what they do is, this was actually hookedup back on the runway, but they hook up air conditioning units. they have to purge. there's an ammonia boiler. remember we talked about getting rid of heatas you're coming in using water spray boilers.
but, once you get below 100,000 feet, thepressure is actually above the triple point of water and you cannot flash evaporate anymore. and so they switch from a water boiler toan ammonia boiler. and so, after the shuttle lands, there areammonia fumes all over the place. if you've looked at pictures of shuttle servicingon the runway, sometimes if there isn't actually wind blowing they bring around a big fan toblow the ammonia way. and everybody has to stay upwind of the ammonia. and there is also the possibility, of course,that there might be a hydrazine leak or who knows.
anyway, the orbiter has to be safe. and you have the people come out in what lookslike space suits. escape suits they call them. self-contained, i don't remember the acronym. but, in any case, we're bringing the orbiterback to the hanger area where it will undergo a lot more than 14 days of servicing. i remember, again, just to give you a senseof the state of mind before we were actually operating the shuttle, as a new astronautback in 1978. remember the shuttle didn't fly until '81.
we were getting a series of lectures on allthe shuttle systems. and i remember the lecture they gave us onturnaround, which was supposed to take 14 days. and we got a briefing from the people whowere planning the turnaround. and i remember they told us we've studiedthis really carefully, and we just don't think it's going to be possible to turn the shuttlearound in 14 days. we've cut out every unnecessary step and wethink it's impossible to do it in less than 16 days. [laughter] and that's kind of the way peoplewere thinking.
we were talking about it's supposed to make60 flights a year, and people were skeptical. there is no way they can make more than 40flights a year. people just didn't have a concept of how complexit was going to be to operate this vehicle because it is such a complex vehicle. to operate it safety is difficult. now sometimes it lands in california. and, in that case, you put it on the 747. this is the same bipod fitting, just to essentiallyduplicate the way that the orbiter is put on the external tank, and the tail pod is,of course, for aerodynamics.
and that was also the configuration for theapproach and landing tests. and, actually, later, i think, in the middleof october, gordon fullerton who was one of nasa's premier test pilots, he still flies,i mean i'll have to find out from him how many different types of airplanes he's flow,he's just an amazing guy, but he was actually in the shuttle during that first approachand landing test. so he can tell us about what it was actuallylike test flying the shuttle, as well as being on the third orbital flight test. were they carrying anything on the airplane? you mean inside here?
no, this is not your opportunity for a transcontinentalvacation trip. [laughter] i mean there are a few people whoride along with it because you need the maintenance people. they also have an airplane flying about 50miles in front of this checking for turbulence. and, in the early days, they had a chase airplaneas well. i told people they were crazy trying to getthem to do this because i thought it was the dumbest thing i heard of. [laughter] ok. now a look at some of the details.
remember we talked about how the engines aretaken out? you get a little bit of a view here insidethe engine compartment. i had the chance, on numerous occasions, toactually go inside the engine compartment. i mean it's just amazing. you get these huge big pipes. and it really helps when you're going to beusing a system like this. we spent a lot of time in the simulators. and you'll flip a switch, and that switchcontrols what they call the main fuel shutoff valve.
it's a big butterfly valve about 17 inchesin diameter inside this huge pipe. and you sit in the simulator and you flickthe switch and the talk back shows that the thing is closed. and then you actually go in the compartmentand you look and there's this huge pipe and this area. and you realize this huge thing that's movingaround. and it kind of gives a sense of realism. and, in fact, that's one of the big safetyconcerns. when the fuel is flowing, the butterfly valveis in a vertical position so the fuel flips
by it. obviously, it's an unstable situation. if it goes out just a little bit then thefuel flow can slam it closed and you've got an explosion on your hands. so that was a major consideration. this is the body flap. so, you can see all of the plumbing. and all these red things are removed beforeflight, stickers. it's a very, very complex process.
and they pull the engines out after everyflight now. that's the thing, all of the platforms haveto be designed so that they fold up and they fold down so that you can get access to allthe places. i mean it's a very complex system. and a lot of the equipment, the launch platformsand everything, as we mentioned, were adapted from the apollo program. but the hangers, which we call the opf, theorbiter processing facility was built specifically for the shuttle. the tiles we talked about.
i mean that's just a huge amount of work replacing,maintaining and testing the tiles. this is inside the cargo bay. you've got the fuel cells. you've got hydrogen and oxygen cryogenic tanks. helium pressurization tanks. nitrogen for your atmospheric system. this is the bulkhead in front of which onone side you have the engine compartment. on the other side you have the crew compartment. and, like we mentioned, this has to be doneessentially in clean-room conditions and yet
it's on the scale of a battleship. so, it's a real challenge. this is the forward window. on maybe one in every five flights we'll geta little ding on the windshield from a little piece of usually orbital debris. in fact, more often than not, it turns outto be little paint chips. whenever they do that they remove the window,they replace it and do a chemical analysis to see whether it was a micrometeorite ora piece of space debris. the windows, actually there are three panes.
there's a redundant pressure pane. the two panes on the inside are capable ofholding pressure and the outer is a thermal pane. this is one of the orbital maneuvering systempods. these are removable because, again, they containnitrogen tetroxide and hydrazine. and we mentioned the fact that these are calledhypergolic fuels. when you bring them together they ignite spontaneously,as opposed to hydrogen and oxygen you need a spark igniter. so, in that one sense, it's a nice systembecause when you want to use them in your
reaction control and you only want a verytiny tenth of a second pulse, you don't have to worry about an igniter which is a potentialfailure point. you just squirt in the hydrazine and the nitrogentetroxide. but they're very nasty stuff. they are extremely toxic and, of course, highlycombustible and they are very corrosive. so, these pods are serviced in a place faraway from where the other activities take place for the orbiter so just in case thereis a leak or an explosion it's not going to take down the rest of the critical facilities. this is the orbiter maneuvering engine, andthen they also have these smaller reaction
control engines. and there are two aft pods. and all the fuel tanks with the hydrazineand nitrogen tetroxide are in here. the aft system, the two pods, they actuallyhave inner connects so that you can actually cross-feed from one system to the other. and all of that stuff has to be hooked up. the forward system is independent. you cannot cross-feed to that. the landing gears.
we talked a little bit the other day aboutthe tires. these things sit up in space for two weeksat a time. you've got to worry about thermal control. i mean can you imagine if you had a slow leakand you found out that your tire was flat before you started your reentry? and then, of course, the problem of sealingthis against the hot gas. the tiles on the edge of the doors for thelanding gear, that's a very critical section. anyway, after typically about a three monthturnaround in the hanger they wheel the orbiter, actually, originally it was pulled over onits own wheels, but that required that they
then stow the wheels in this big verticalassembly building. this is the vertical assembly building. hopefully you've seen pictures of it. it's huge. it was actually built to assemble the saturnrockets. it's much taller than we need for the orbiterstack, but it has been adapted. so, what goes on here is it's wheeled intothe big vertical assembly building. there it is actually on the inside. you just don't get a sense of the size ofthis building from any picture that can be
taken. you have to be there and see it to reallyappreciate it. in the meantime, you remember the solid rocketboosters are recovered after every flight. and the liberty star and i think the freedomstar, that's the nasa navy. these boats are positioned out offshore. and they actually have divers who go downand put in plugs and floatation devices so that they actually float the boosters. and they drag them back where they're disassembledand cleaned up. the actual segments, which contain the fuel,are shipped back to utah to thiokol which
is now atk for cleaning, refilling. and the other parts, the nozzle and the top,which contains the electronics and the parachutes, those are serviced in florida. and then they're brought in segments intothe vehicle assembly building where they are stacked. and remember those are the segment sizes. some of these are assembled in the factory. those are the so-called factory joints. and then were these come together that's theso-called field joint, and that's the joint
that failed in the challenger accident. this gives you a sense of the size of thosesolid rocket motors in the way the solid fuel is put in. and they do all of these tests to look forthe roundness of the motor and the flatness of the propellant. yeah? is that the fuel itself? it is. although, what confuses me about this is i'mnot sure which segment this is because most
of the fuel is actually put in with a starpattern in it and they actually shape the way it's loaded so that you shape the thrustprofile. and i've not been able to get a good explanationof why that is not the case here. in any case, this is now the process wherethey lift one segment, they put it down on top of another. of course, all of these are hazardous activities. and nobody is allowed, except for the criticalpersonnel, nobody's allowed in the vab when they're doing this just in case there is aproblem. and then they actually put all of these boltsin to join up the field joint.
and now, of course, after challenger we havea new and improved o ring configuration. now we have the two solid rocket boosterssitting on the mobile launch platform. and, again, you can see you have to designall of these platforms so you have access. now, the external tank we talked about. this is in [unintelligible]. this has actually been damaged, not too heavily,but it did suffer damage from katrina. this is the oxygen tank upfront. notice how small this is compared to thisis the big hydrogen tank. and then this is actually the front side,but this is then turned around and the two
are joined together inside the outer shell. and, of course, the solids are joined to theexternal tank, the orbiter is joined to the external tank, so basically the external tankneeds a strong back mechanism inside it because that's ultimately what's tying the whole stacktogether. and the trust from the solids and the thrustfrom the main engines, ultimately they're linked together through the external tanks. so the tanks themselves, the hydrogen andoxygen tanks don't have a lot of beefy structure. but going through this is a very heavy structure. the hydrogen tank there is about the diameterof the overall structure?
that gives another idea of the scale. this is cleaning and polishing inside thebig hydrogen tank. i mean, again, the scale of all of this, it'simportant to get a sense of what's involved in taking care of these vehicles. do you know if they actually had to go inand scrub it by hand? i mean the scrubbing is only part of it. the inspection is the really critical thing,to see if there is anything that's not quite right. one thing that's interesting, the use of liquidoxygen, liquid hydrogen is wanted so much
because of its higher performance. but, on the other hand, if you would do somethinglike liquid oxygen and kerosene you would get a much smaller tank or some other propellant. and there is a tradeoff. i think today people are realizing, especiallyfrom the russians, the russians don't really use liquid hydrogen. you get a lower isp but your tanks becomeso much smaller to deal with. and hydrogen is very hard to deal with. it's very hard to find the hydrogen level,and hydrogen is very hard to deal with.
my second flight, do you remember? that was the one with the hydrogen leaks,remember that? we were supposed to launch in may of 1990. and we went down. and before they fill the system they do ahelium leak check. and, of course, helium, for those of you whohave worked with vacuum systems, helium will leak through anything. and, if the system is tight against helium,they figure it is tight. the problem is that that's done at ambienttemperature.
and, when you fill it with the cryogenic hydrogen,everything contracts. and so things which were vacuum-tight at ambienttemperature are not always vacuum-tight. but the problem is you don't know that untilyou fill it, which is only done a few hours before a launch. so, we had gone down to the cape. we were in medical quarantine. and we just got the message about six hoursbefore launch there's a hydrogen leak, launch is scrubbed. they did some checks.
they drained the tank. they did another helium leak check. it was fine. we had gone back to houston. we came back. the same thing happened. how long did it take? well, in the end, we made six trips over thecourse of six months. and we didn't launch until december.
and, actually, another one of the shuttlesalso had a hydrogen leak. they actually alternated us. they pulled us off the launch pad. they put somebody else on. i mean what had happened was they had somewhatchanged the procedure of installing some o rings in these big hydrogen lines, and itrequired a process where the workers were actually working in an area where they couldn'tsee. and the o rings were being installed slightlywrong. but it was just terribly difficult to trackthat down.
so, yeah, there are a lot of problems usingcryogenic fuel. now, the other thing is if you have a fullystaged vehicle with a separate first and second stage, one of the things that you learn inrocket propulsion classes is that in the first stage the specific impulse is not nearly asimportant. what's really important is to get a lot ofthrust. in your upper stages having a high isp becomesmuch more important in terms of the payload that you can carry. so, if you had a fully staged vehicle, and,in fact, that's the way saturn worked. the first stage of saturn was kerosene andliquid oxygen and the upper stages were cryogenic
with hydrogen and oxygen just for that reason. ok, let's move on. now we have the external tank, again, suspendedin the vertical assembly building. that's lifted up and joined between the twosrbs. this is the feed line where the oxygen comesdown and this is where these two feeds lines, this is the hydrogen. and then the orbiter has two correspondingfeed ports where the hydrogen and oxygen comes into the engine. and, actually, when you fill the tank on thepad, you actually put the hydrogen and oxygen
into the orbiter. and it flows from the orbiter back then intothe external tank. and it was on this oxygen fitting from thefoam that they put around this, was what fell off in the recent discovery flight where theydid get a big piece of foam. ok, so now we go back. remember we brought the orbiter over intothe vertical assembly building? now, you put this strong back to hold theorbiter. and this is really spectacular. i mean you lift the whole orbiter up off theground and tilt it up.
and you basically hang it and lower it. and these are big pieces of equipment andyet you need millimeters of accuracy. so, very skilled crane operators, to say theleast. now we have the orbiter and the strong backlaid down in position and all of the mating is done. and we're on the pad. excuse me, we're on the mobile launch platformand they put the crawler transporter underneath it and then they roll it on these speciallyprepared pads which have very, i don't know how deep it goes into the ground, but thisis heavy river gravel.
most of the boulders are about the size ofyour fist, but after one or two trips of the orbiter it's crushed down to the size of peagravel. and then they have to replace it with newstuff. and, of course, as you're going out to thepad, when you're rolling up to the launch pad, you're actually going up at an angle. and so this whole system, you can see thecrawlers down here, each one of these treads, each single piece of the tread weighs a ton. just to give you a sense, it goes about oneor two miles per hour top speed. it takes hours to get out there.
and it has to be capable of staying levelto within a few degrees, even as you're climbing the ramp up to the launch platform. what are those things supporting the [unintelligible]? the whole stack is basically sitting on thetwo srbs. the skirts of the srbs is taking the weight. these are the fuel inputs which are connectedthrough the other side where the hydrogen and the oxygen run into the shuttle. and, from there, the way i showed you before,it goes into the external tank. did they also keep it tilted back?
did it have the tendency to [unintelligible]? each of the srbs has four bolts. actually, they give us, as a souvenir aftera flight, they give us the big nuts that are explosive bolts. there are eight, four on each of the srbs. and, essentially, that's what gives it itsstability. again, this is a hill. it's a little hard to see the perspective,but keeping the whole thing steady. and we talked about how you can see this trackhere where the payload change-out room eventually
could come around and cover the shuttle togive it protection. this is actually going up the hill to getup. and it's just a pretty picture that i like. and here we are. this is nice because you have both shuttleson the launch pad. this is a big water tower. in order to protect the launch pad againstflame damage, and also to protect the shuttle against acoustic effects, they actually geta shockwave when you ignite the engines which can bounce back and do some damage.
shortly, about 15 seconds before t zero, theyopen up the valves. and all that water flows with little jets. if you've seen pictures of a launch, sometimesthey show that as part of the launch sequence. in fact, in another class, i will show yousome of the details of an actual launch picture. that's the water deluge, and that goes forabout 30 seconds. and that cushions the acoustic load reflectedback to the shuttle. ok, that's enough pictures on the pad. oh, i know what i wanted to show. this is called the white room.
and that's how the crew goes in. you take an elevator up to here. and then that actually joins up with the hatch. so the hatch is sitting open. and you put on your parachutes and the lastfew pieces of equipment to get in. and this is a view inside the white room. this is, i guess, from our last flight in1996. and, when you go out on launch day, the bigthing that you notice that's different is there are very few people on the pad, onlythe essential personnel.
and the whole stack is creaking because it'snow filled with the cryogens and everything is shrunk and it's sort of alive in a verystrange way. so, we talked about the mission profile. i won't deal with this. and i do want to talk about some of the shuttleaborts, but we will do that another time because i want to get finished with the slides. i did want to show you, after challenger theyintroduced a bailout. we did mention that the basic survivabilityfor the crew requires an intact orbiter. it used to be that it needed an intact orbiterlanding on the ground or ditching in the ocean,
which was kind of an unlikely survivabilitybecause you're going to hit the ocean at 200 knots and probably break up. so now there are circumstances where you canlose more than one engine during launch or you might have to do an emergency de-orbitwhere you basically can be flying along at 40,000 feet stably but with no place to land. and so that's really the only situation whichthe bailout system protects you against, but there is a collapsible poll. the reason for that is because the aerodynamicstudies show that if you just jumped out of the open hatch with a parachute the airflowwould carry you back on top of the wing and
you'd hit the oms pod, and that would notbe a good deal. so, you actually hook yourself to this escapepoll. and that takes you down below the wing, andthen you can open the parachute. and we actually practiced this where you goout into a swimming pool using the escape poll. these are some actual tests conducted by armyparachutists in, i think, a 141 transport. the system has been tested in flight, althoughnever with the shuttle. and that's the test where they have a simulatedhatch and you basically jump out into the swimming pool.
once again, into the white room. you can see the hatch out here. and that's the last thing that they'll do,is they close the hatch. then they pressurize the shuttle by about1.5 psi just to make sure that it has pressure integrity before a launch. and then we launch. as you can see, you're burning hydrogen andoxygen in the main engines. what's coming out there is just hot steam,not very visible. most of the smoke, the noise and everythingcome from the solid rocket boosters.
however, you do need these engines. in fact, people have calculated that if youtried to take off without these main engines pushing up on the shuttle that the attachmentbetween the shuttle and the external tank would probably fail. each of the main engines is about, well, it'sa half a million pounds of thrust in vacuum. it's slightly under 400,000 pounds at sealevel. you've got a little over a million poundscoming from the main engines, but these are putting out almost three million pounds apiece. so, most of your early thrusts in the firsttwo minutes are coming from the solid rocket
and it's a pretty rough ride. i mean there's a lot of vibration. when you go through mach 1, which is max q,maximum dynamic pressure, the vibrations are even more pronounced. the first time on my first flight, i reallythought the wings were going to come off, there was so much vibration. but, of course, they don't. but i'd love to get a hold of it. i actually saw a high-speed, well, a slowmotion picture actually looking at the tail,
as you go through max q. and you can actually see the tail flutteringback and forth like that. i mean the aerodynamic loads on the vehicleduring ascent are significant. and you do actually have to move your elevonsto what's called load relief in order to take the stress off that. i really like this. it gives a sense of the power that you'resitting on top of to get up there. and that's just a nice picture of riding thefire. ok, so you get up in orbit and you drop theexternal tank.
and, although now they're going out of theirway to take even better close-ups of the tank to look at the foam shedding. we've been doing that, in fact, throughoutthe history. now they especially time the launch so thatyou're guaranteed to drop the external tank with good lighting conditions. that didn't used to be a constraint to launchbut it is now. you can also, by the way, see how the atmospherequickly fades out into space. and that's a telephoto so it actually makesthe atmosphere look even thicker than it really looks.
ok, so there is the orbiter in space. that was actually after it had delivered apayload. this was taken from the space station. and just a quick reminder of all the differentthings that we've used the orbiter for. launching satellites, you've seen that picture. this is a payload assist module to take thesatellite from the shuttle orbit up to geosynchronous transfer orbit. we have used it extensively for satelliterepair in orbit. this is the intelsat where it was put intoorbit by an expendable rocket, but into a
bad orbit because of underperformance. and they managed to get it into a shuttlecompatible orbit. and i won't go through the whole history. why there happened to be three people outthere is a whole story in itself. this is one of the satellites. again, the satellites were put into orbitby the shuttle. and the shuttle deployment was fine, but thepayload assist module, which you saw before, did not perform properly. and so the two satellites were stranded ina useless orbit.
we actually brought them back to the ground. they were refurbished and re-launched againon expendable rockets. the shuttle has also been used as a spacestation with the space lab on in the inside to carry out scientific experiments. this is a large pressurized module which isput into the cargo bay. and the original idea, as professor cohenmentioned, was you could just take your laboratory equipment off the shelf, plug it in here,120 volts ac power, i guess, and it would be just like working on the ground. well, it never was.
but, having said that, i think the space labprogram, as a whole, was extremely successful. and then it's been used to service the mirspace station. we certainly added several years of usefullife to the mir station because we could carry up a lot more equipment than the russianscould themselves. and that also gave us an opportunity to getsome us astronauts on long duration space missions. and then, as you all know, we're using theshuttle to construct the international space station. and hopefully we'll get more of it built beforetoo long.
the shuttle is also an excellent platformfor performing evas, space walks. and that's a picture of when we went up andrepaired the hubble space telescope. i cannot overestimate the capability thatthe shuttle gives us as a work platform in orbit. we can do this sort of complex eva activityon the space station, but once we retire the shuttle we've essentially lost that capability. to have the manipulator arm and to be ableto use people and the robotic arm to move equipment around, it's just a very powerfulwork platform. that's one of my favorite pictures floatingup there.
this is a pretty picture of firing the orbitermaneuvering engines just to start your descent into the atmosphere. despite the fact that you're going at 18,000miles an hour, you only have to slow down by a few hundred feet per second in orderto lower your perigee down to essentially the surface of the earth so that half an orbitlater you intersect with the atmosphere. and, of course, that produces the aerodynamicheating which you can see on the outside. this is looking out to the front. that's kind of a dull glow. it starts out as a deep red and then it getsorange and yellow and finally white on the
outside. the most spectacular thing, you know, you'rea meteor. this is a picture that was taken from houston. this is at about 250,000 feet at about mach12 on the way to a landing at the kennedy space center. the shuttle is flying like this. if you look up at the overhead windows, youcan actually look back into the wake. and this is really spectacular because youhave these different colors, and it's sort of shimmering around.
and every once in a while, when i would belooking at this, you'd see a big bright light. and i would think boy, i hope that was nothingimportant. [laughter] what people said it probably waswere little bits of gap filler. you may have heard that on the last flightthey discovered that some gap fillers were protruding. and so steve robinson went around and actuallypulled some of them out. but they've probably been doing that the wholetime and just have come off. i mean this little point where you have theconvergence of the shockwaves, this is about 10,000 degrees fahrenheit, that's the surfacetemperature of the sun.
it's a spectacular visual view. and then, again, at this point we're justgoing subsonic flying like a glider and ready for touchdown. so, i hope that gives you some sense visuallyof what goes on in the course of a shuttle flight with an emphasis on the maintenanceoperations. without appreciating how complex it is tooperate this system, i think it's hard to really make the link between the originalconcept and the difficulties we've had in getting the shuttle to perform in terms ofthe turnaround maintainability. so, again, just wrapping up, that's kind ofmy farewell picture, the shuttle was an amazingly
ambitious concept. and, i think, what has been astounding ishow well the shuttle has been able to perform and do all the things that it was designedto do in terms of the satellite launching and being used as a science platform, performingeva, repairing satellites, building space stations. it has given us experience and capabilityto learn how to do things in earth orbit which we never had before. and, as i say, we may well miss them oncewe retire the shuttle. but where we really did get it wrong, andthis will be one of the things that we'll
look at when we deal with the individual subsystems,is in the operations. it turned out to be a lot more complex, expensiveand delicate to operate than had been anticipated. so hopefully there will come a time when weset out to design another reusable vehicle, possibly a reusable winged vehicle. and i think a lot of what we've learned fromthe shuttle will be folded into that. it still is a question of how re-usable thenext crew exploration vehicle, the cev will be. re-usability has been put in as a requirement,but that remains to be seen. and certainly the experience that we've gottenfrom the shuttle is going to make people look
really, really closely at what assumptionswe're making about the reusability whenever we do this again. next tuesday will be the last in kind of theconceptual part of what we're doing. professor john logsdon from george washingtonuniversity is a very well known space policy analyst. he did a seminal study on the apollo programand has also written a lot and done a lot of research on the origins of the shuttle. and so he'll talk to us then. let's see.
i had promised to post everybody's emailson the web, and i got diverted and didn't get that done. but i will do that before tomorrow, you know,in terms of forming your teams. put together an idea of what system you wouldlike to work at. if you're not able to form up as part of ateam between now and tuesday, just give me what your own personal preference is. and then we can look and see if differentpeople are interested in the same system. we'll let you all know and help you form upteams. i'll make sure your email is there in thestudent view.
[unintelligible phrase] if you've alreadyformed a group then just turn in something as a group. that's fine. if not, if you haven't hooked up with somebody,just let us know what system you're interested in working at and any ideas you might haveof what you're going to look at. really, this is just a very, very short write-upessentially to get you started. and that way, if you have any questions, wecan talk about it next tuesday.
