Neil Armstrong and Robert Seamans Jr., "Engineering Aspects of a Lunar Landing” - MIT 25th Anniversary AeroAstro Gardner Lecture

[MUSIC PLAYING]

MURMAN: Good afternoon. My name is Earll Murman. On behalf of the Department of Aeronautics and Astronautics of the Massachusetts Institute of Technology and the New England section of the American Institute of Aeronautics and Astronautics, I'd like to welcome you to the 25th Lester Gardner lecture.

Lester Gardner was a graduate of the class of 1898, an air officer in World War I, publisher of aviation literature, a leader of the aeronautics profession, and an enthusiast for aeronautical engineering. In his will, he bequeathed a gift to sponsor an annual lecture on the history of aeronautics.

With today's lecture marking the 25th anniversary year of the landing on the moon, we are expanding the theme of the Lester Gardner lecture to include astronautics. If Academy Awards were to be given for this half century's greatest achievements, the Apollo program certainly would be nominated for an Oscar. And today's speakers would be nominated for the best producer and the best leading performer.

Dr. Robert C. Seamans Jr., a researcher, engineer, skillful administrator, professor, dean of engineering, and outstanding gentlemen will be the first speaker. A graduate of Harvard and MIT, Dr. Seamans joined NASA as associate administrator in 1960, after research and teaching at the instrumentation lab-- now the Charles Stark Draper Laboratories-- at MIT and five years with RCA.

In his position as associate administrator and then deputy administrator of NASA until 1968, he oversaw the historic Mercury, and Gemini, and Apollo programs. After leaving NASA, he served as Secretary of the Air Force, President of the National Academy of Engineering, administrator of the energy research and development administration agency, and Professor and Dean of Engineering at MIT.

His lovely wife, Jean, his partner for 52 years during this illustrious career is also with us today-- Jean.

[APPLAUSE]

Midway through this lecture, Dr. Seamans will pass the podium to Neil Armstrong, engineer, combat and test pilot, astronaut, professor, businessmen, and role model for a generation of youth around the world. A graduate of Purdue and USC, Mr. Armstrong joined NASA as a test pilot after serving in Korea. In 1962, he transferred to the astronaut corps and was the commander in 1966 of the Gemini 8 flight, the first to accomplish docking in space. His Gemini partner was David Scott, a graduate of our department here at MIT.

Mr. Armstrong is known throughout the world for the words, "That's one small step for man, one giant step for mankind," which he spoke as the first human to step on the moon on July 20th, 1969. His hiking partner on the Apollo 11 expedition, Dr. Buzz Aldrin, Jr., also a graduate of our department, is here with us today. Buzz, can you--

[APPLAUSE]

After leaving NASA-- sorry, Buzz I have to cut off the applause. After leaving NASA in 1971, Neil has been a Professor of Aerospace Engineering at the University of Cincinnati and is presently chairman of AIL Systems, Inc., an electronics manufacturer.

25 years ago, the attention of the world was focused on a race to put man on the moon. Such a feat seemed unbelievable to most humans. Today, mankind debates the wisdom of manned space program and the priorities for its funding. But since Neil and Buzz walked on the moon, how many times have we all heard someone say, if we can put a man on the moon why can't we-- whatever the problem is.

The Apollo program stands as the benchmark for what mankind can accomplish and a challenge to all those who follow. Today we will hear just how difficult this challenge was as our speakers tell us about engineering aspects of a lunar landing. Please join me in welcoming Dr. Seamans to the podium.

[APPLAUSE]

SEAMANS: Neil and I flipped a coin. I'm going to take the left hand side, and he's going to take the right.

[LAUGHTER]

It's certainly a great honor for me to be involved with the Gardner lecture and to be on the podium with Neil. And I can honestly say that it wouldn't have happened if it hadn't been for my former boss, my first boss, my mentor for 15 years here at the Institute, a person by the name of Doc Draper.

Now Doc, on occasion, used to use the analogy of fire engines, their power, their speed, their energy, when Air Force or Navy brass, complete with entourages, would visit the lab. He'd say, we're nothing but little boys on the sidewalk watching the fire engines go by.

And at this point, I'm going to show you what Doc liked to do best. Doc loved to work with equipment. He also liked people. But nothing better for Doc than to have a new design coming along, to test it, to try it, to take it up in an aeroplane, or put it through its paces.

And here you see my mentor, Doc Draper, up on the roof of his laboratory checking out the guidance and navigation system that was to be used going to the moon. And in the distance, you can recognize the Longfellow Bridge. You can see the Prudential Building

Now, in the late 1950s, NASA had reminded me very much of Doc's analogy. Keith Glennan, the fire chief up front, Bob Gilruth, there he was manning the life support vehicle for the seven astronauts. Wernher Von Braun was driving the hook and ladder. Fortunately, he had [? Eberhart ?] Reese back on the rear of the hook and ladder to keep on the road. He was a chief engineer.

Other engines were driven by people like Abe Silverstein and Tommy Thompson and all the various directors and program managers. There were a lot of engines. And there were a lot of fires to put out.

Now I was one of the small boys watching the armada approach one day, and sort of wishing I was aboard when all of a sudden, Keith Glennan, who was the fire chief, he swerved over the curb. And he opened the door. And he invited me to ride along with him and Dr. Dryden.

I asked about what's really going on. What's the rush? Why all this energy? What capabilities were needed? Before obtaining all the answers, Keith left. And Jim Webb became the chief. The fire intensified. It was no longer merely a 10 alarm fire. New facilities and kinds of equipment were required. We had only eight years to meet a major deadline of landing men on the moon and returning them safely to Earth.

Now we know we met the deadline-- although sometimes, I'll have to admit, when I see the moon coming up over the horizon, I really wonder if it actually happened. And I also find it sometimes hard to believe that it took place 25 years ago. I mean, Neil and Buzz haven't changed a bit.

[LAUGHTER]

But the magnitude of the effort required to achieve this goal was so great that no single person could possibly observe the total endeavor. I say this because-- there may be differing views of the mission, and so on-- but after all, there were 400,000 people involved. And there were many different jobs to be done. Now you're about to hear two accounts discussing the program from an engineering standpoint.

When I joined NASA in the late summer of 1960, the agency was $400 million apart from President Eisenhower's view of what we should be getting. Keith Glennan met with Maury Stands, director of OMB, soon after I arrived to reclamor 60 million of the $400 million difference.

Stands laughed at the idea. In desperation, Keith asked, what do you want in space? And Stands replied, a bargain basement figure-- $1.09 billion. Sometime later at a cabinet meeting, George Kistiakowsky, who was the present science advisor, presented the result of a study that indicated the cost of manned lunar landing would be between $20 and $40 billion. After the gasping subsided around the table, Eisenhower said, I wish someone could tell me the best $1 billion program for space.

After Jim Webb became chief I joined him in a visit to the new director of OMB, Dave Bell. We made a pitch for Saturn boosters and the Apollo manned exploration beyond the existing manned, operating on a shoestring, Mercury. When we proposed design studies for Apollo, there was no sale. And it was no sale a few days later when we met with President Kennedy.

However, Gagarin's flight around the world in one hour and 48 minutes a month later raised anew the question, why was the USA so far behind? The Congress went crazy looking for a scapegoat. Why wasn't NASA working 24 hours a day to get ahead of the Soviets? And let me say, at that time, people were working darn near 24 hours of the day to get Mercury into orbit.

President Kennedy had wanted to hear the evidence before weighing in on new space initiatives. However, the evidence had become clear. Whether by luck or careful planning the Soviets had scored big in the international arena. And Kennedy didn't propose hauling up the white flag.

But which goals would permit the US to gain greater respect in future years? Some counseled against further manned space in favor of intensified scientific research here on Earth or in space. Kennedy reached out beyond the staff to Vice President Johnson and ultimately to McNamara, Secretary of Defense, and to Jim Webb for the answers.

Now if I can find the right button-- here we go. What you have here is that Mercury vehicle up on top of the Redstone booster. This was really a wing and a prayer type operation. It was the vehicle that was being prepared for Alan Shepard at the Cape. Behind it you see the very large gantry which sort of overpowers it, which was backed off so that some tests could be run.

But when work was to be done on either Redstone or the Mercury vehicle, it would be rolled up into place. Now with some foreboding, the White House allowed the Mercury suborbital flight to proceed. And on May 5th, Alan Shepard became a world figure by traveling 630 miles downrange in 15 minutes.

The Webb-McNamara meeting that took place at the Pentagon the following day had the benefit of the world reaction to Shepard's completely open televised flight. It was agreed by the two of them that all missions should be conducted openly and also that prestige was a valid national goal.

It was felt that the Soviets would soon be able to fly with multiple crew. And that proved to be correct. They might soon be able to actually fly out around the moon, or even go into circumlunar flight around the moon. But it was also believed that they would not have the capability for an extended period, and with new equipment, to actually land on the moon.

So at this point, let me just show you what happened at just about the time that this report was to be handed in to the Vice President Johnson and then to Kennedy, there was a meeting out in the back of the White House where President Kennedy gave Alan Shepard the highest award that NASA can give. And behind Alan is his beautiful wife.

Now thanks, in part, to the success of Shepard's flight, the President and Vice President accepted the goal, as did the Congress following President Kennedy State of the Union address on May 25th, 1961. Now to achieve this goal, policy issues had to be resolved, and quickly. And one of them had to do with NASA personnel buildup.

And a decision was made that the necessary buildup and capability around the country would not come by increasing substantially the number of people at NASA. Rather, major support would be required from many other departments and agencies of government-- the Air Force, for example, played a major role-- from a large number of contractors-- and I forget the number, but it was staggering-- and from foreign nations, particularly those nations that were located where we wanted to put large tracking antennas.

Now the space task group, which had been 1,000 strong down at Langley Field where the astronauts were being trained, and where the design of the Mercury was taking place, was move to Houston, Texas and became the Manned Spacecraft Center, and now the Johnson Flight Center.

New operations were started in New Orleans for assembling the first stages of the Saturn booster, and in Mississippi for testing large rocket engines and boosters. A tremendous amount of engineering was required, obviously.

I believe it's true that every engineering discipline was brought into play, from pile driving in the Florida sands to support what was to become the second largest building in the world to a study of orbital mechanics for transfer of astronauts from lunar landing to, for example, the orbiting craft going around the moon-- with Mike Collins aboard, as it turned out.

Now I'm going to discuss for you three aspects of the engineering decisions that had to be made-- first, the mode selection for achieving lunar landing and return, second, the method for assembly and checkout at Cape Canaveral, and third, the strategy for evolving developmental hardware into flight-ready launch vehicles as rapidly as possible, and as safely and reliably as possible. Neil, on the other hand, is going to talk about the design requirements for the lunar landing. He'll get into the subject of the rocket engines. He'll get into guidance and navigation as well as the subject of training and of simulation and the special aids that were required for the crew before they made their first of a kind mission.

So now turning to the mission itself and how it was to be accomplished, the favored mode in those days followed the Jules Verne script of a takeoff with all equipment aboard. In this version, called direct ascent, you peeled off booster stages as you required more and more acceleration. So this happened as the trip progressed, arriving back home aboard the capsule that had been a home away from home for the whole journey.

A variant on this approach involved placing the hardware and propellants in Earth orbit through a series of two or more launches. Several stages, or modules, could be launched separately, connected together in Earth orbit after rendezvous and docking, much as the space station has been planned today. The astronauts, once they were in Earth orbit, would then proceed to the moon and back just as though they'd taken off direct ascent.

However, there was a strategy proposed by John Hubalt, the NASA research engineer, which was quite different. In this mode, the astronauts travel to the moon with two separate habitats. One spacecraft would stay in orbit around the moon. The other, the lunar lander, would separate from the spacecraft to land on the moon. After visiting the lunar surface, the astronauts would lift off from the moon, rendezvous, and transfer to the return spacecraft.

What did this seemingly more complex, and possibly more dangerous, approach have to offer? You know, supposing you don't rendezvous and dock? The obvious answer was to limit the launch requirement. The return spacecraft required a heavy heat shield to protect the astronauts during high speed reentry. The requirement to land, then accelerate the return spacecraft back into lunar orbit, if we'd done it that way, would have doubled the size of the launch vehicle at takeoff from Cape Canaveral.

More detailed design brought out additional advantages. The lunar lander could be configured for maneuverability and crew visibility in the vacuum and to approach the moon, where the visibility was clearly very important. And Neil will be discussing that with you shortly.

But obviously, all was lost if the astronauts failed to rendezvous. I didn't say dock, because the astronauts were trained to transfer the return capsule by EVA-- extra vehicular activity-- if docking failed. And the return vehicle would also be maneuvered for a rendezvous if the lunar lander happened to run out of gas or something went wrong assuming it was up in orbit.

These aspects of the mission were practiced extensively on Gemini missions that preceded Apollo and in simulated Apollo flights. At one flight, Gemini 6 rendezvoused with Gemini 7. But we flipped the numbers. It was much more fun to talk about the 76 mission rather than the 67 mission. Here you see Gemini 7 with Frank Borman and Jim Lovell aboard. And they took off from a pad. They were going to fly for 14 days anyway. And the idea was that in about seven days, if we work post-haste, night and day, we could get Gemini 6 and its titan booster on the pad. And it could take off. And we could demonstrate rendezvous but not docking.

Well, obviously this did take place. There was a little trouble at the takeoff. We had to delay a couple of days. But they not only were able to come reasonably close-- they differ as to how close they came, but I believe the measurement was made in centimeters.

Now, the extra vehicular was actually tested first on Gemini 4. And here you see Ed White outside the capsule. And he found that once he got outside, he had a little hand rocket gun, and he could aim it in different directions and move back and forth. And the idea here was that if all else failed, if he didn't dock, it would be possible for the transfer to take place by going out of one capsule and coming into the other.

Now finally, the added risk had to be viewed in the context of total risk, weighing the pros of a smaller launch vehicle at Cape Canaveral, maneuverability and visibility near the moon, and the advantage of two inhabitable vehicles, each with its own life support, against the greater risk associated with rendezvous of two vehicles in orbit around the moon.

Now there were many differing views on this, both within and without NASA, let me say. And Brainerd Holmes, who headed the manned program at that time, and Joe Shea, the systems architect who worked with him, ran all kinds of analyses to try to get a better feel for which was the best of these mission approaches. And while all this was going on, and before a decision had been made, President Kennedy and Vice President Johnson decided they'd like to go and visit the various centers involved in the program.

And the first stop was Huntsville. And we ended up very early on inside of the large assembly hangar that's there. And here you see the entourage with President Kennedy on the left. You can see Vice President Johnson looking a little gloomy facing us. And on his right is Jim Webb talking to Wernher Von Braun. There's a spy looking over somebody's shoulder there.

[LAUGHTER]

And then you have Secretary of Defense McNamara, Gary Wiesner and Howard Brown. Gary Wiesner at that time was President Kennedy's science advisor. And Kennedy was very interested in some of the intellectual aspects of things. And right on the floor here of this big building, he started asking about the pros and cons, the kind of thing we've just been discussing.

And it was a roped off area. And a whole bunch of press and everything on the other side of the rope. And they could see this earnest discussion. And needless to say, there was plenty of probing by the press after this had taken place.

But when all the dust settled and everything was taken into account, reason prevailed. And the Apollo mission was conducted by lunar orbit rendezvous.

Now all previous space vehicles had been assembled on a launch pad. And when launched, the ground team-- usually about 250 strong-- were as close as you could get them. And to have them close and have it safe, they had lots of reinforced concrete over their heads. So the only way they could get information as to what was really going on was by looking through a submarine type telescope or by reading a whole bunch of dials.

And in order to proceed, you had to take the vehicle stage by stage-- the first stage on the pad, then the next, and the next. Hook them altogether. Test it out. And while you're doing this, you might have tremendous sandstorms, rain, hail, lightning, all kinds of things. And it was just-- as we thought about it and then we tried to plan how we were going to assemble the Saturn V, which was many, many times larger and more complex than anything we'd done before, it was just daunting to think of doing it out of doors.

And for that reason, we thought we should assemble indoors. But of course, then you run up against the very obvious problem of how you're going to get it on the pad, and also how are you going to check it out?

And here you see the Saturn V and the Apollo on the transporter. Now how did the transporter come to look like that? Incidentally, in the distance, you can see the vertical assembly building, that very large building I mentioned earlier.

Now in the past, when we moved the gantry back and forth, it ran on wheels. And so we thought, why not. We just put a lot of track down, and wheels. And no matter how many wheels we put on, we found that if you stopped the transporter overnight you had flats on the wheel the next day, the loads were so great.

Then we thought, well, we've got a lot of water down at the Cape. And we could just build some canals. And we'll float it out. And there wasn't a marine type engineer who could figure out how to keep the whole [INAUDIBLE] stable if you tried it that way.

[LAUGHTER]

So things were starting to look pretty bleak. The whole concept of an assembly building appeared to be going out the window when the Von Braun team discovered the enormous drag lines that are used for surface mining of coal in Appalachia. The loads carried by the caterpillar tractors-- and you can see perhaps three or four of them there-- were carrying loads that were comparable to what Apollo's Saturn would weigh, along with its umbilical tower, and along with the platform itself. And the drag lines had automatic leveling, obviously an important feature, and particularly important since to get out to the pad three miles away, this whole assembly had to go up a three degree slope.

However, the use of a transporter introduced other problems. Until 1962, as I've described, everybody was in the block house. And what you used there for instrumentation is what you used practically at home. You had thermometers, and with wires perhaps coming out inside, volt meters to read, and so on. But there was no way that you could connect directly from the sensors on the Apollo and the Saturn directly into the large control here three miles away.

The solution necessitated the conversion of analog to digital signals. Never before had so many sensors and converters been required. The same devices were to be used for checkout and for launching, which was also important. At launch, on the order of 70,000 signals were automatically verified during the final two minutes before liftoff. And if the signals were not within tolerance, the launch crew would investigate and determine whether to scrub, or continue, or hold.

Extensive digital processing and computing equipment was installed in the base of the transporter to provide all the necessary information for the checkout and launch crews whether the vehicle was in assembly or sitting on the launch pad. And you can see their individual consoles. And at each console you had somebody who was a specialist in a particular area that the instruments were measuring.

And if anything appeared to be out of tolerance, the light would go on to tell a fella to get alert, or the gal to get alert. And by means of the computer, and so on, you could zero in and find what the fault was. Or if you couldn't find it, you certainly were going to hold or scrub. If you could find it, there were occasions that something would be slightly over tolerance and you could go ahead.

Now the last item I want to discuss is what are called all up testing. Technologies enters into design decisions in many obvious ways. But it also affects optimal developments, often in subtle fashion.

Rocket propelled vehicles have experienced many failures prior to success. Going back to the beginning, I understand it was the 71st firing of the V2 before the Germans achieved success at Peenemunde, and thank goodness that was the case.

As a consequence, the planning for the Saturn, with the Von Braun team in charge, called for four launches of the first stage before going to the second stage so that you'd get the first stage under control. And then you'd move on to the next. Now all four were successful.

And by the time Saturn, or as it was called SA3, and SA4 came along. The press got wind of this. We had quite a time with the media explaining why we had to spend all this money to carry tons of sand across the Atlantic Ocean. Because that's about all we were accomplishing.

Now just prior to the launching of SA5, President Kennedy, who was staying at Palm Beach, said he'd like to come over and see how things were going on with his friend Senator Smathers. And here you see him. That's a member of the Secret Service behind Wernher Von Braun. And here you see President Kennedy.

And President Kennedy is pointing up at the SA5. And a model of it was used for explanation. And that's right next to Werner. And if you want to see it in the flesh, you can go over to the Kennedy Library, where that very same model now rests.

But what we were explaining to President Kennedy was that the next launching, which actually occurred about six weeks later, had a live upper stage. It's called the S4 stage for very complicated reasons, but it's really the second stage. It would be the first time that we'd tried in a major way to make use of hydrogen as a fuel.

Now you can see that if we were going to proceed step by step this way, we had a long road to go before we got to a full scale launching with astronauts aboard of the Saturn V. Now George Miller, when he came aboard, answered these questions in a dramatic fashion.

He stated we couldn't reach our goal step by step. We must test as much hardware as possible on each mission. All up testing became the watchword. The first flight of Saturn V included all three rocket stages and the Apollo capsule with its service module. The official designation was Apollo 4 AS501. All systems were go at large right on time November 4th, 1967-- nobody aboard, of course. And all continued to perform essentially perfectly during the entire flight.

And there you see the first launch of the Apollo Saturn. And the bottom has almost reached the top of the umbilical tower. You can see those swing arms that are back away from the vehicle. And this is at the point when, since the three mile distance to the spectators and to the large control, when you could first hear the sound of those rocket motors. And it was really intense.

When I say hear, you didn't just hear them with your ears. You could feel it in your chest. You felt it all over. The roar of those engines and the vibrations were really fantastic.

But the principle of all up systems testing was established by this daring but essential plan made possible by greatly improved component reliability and comprehensive testing. It was one of the reasons that we had, of course, the Mississippi test facility.

Now as I have mentioned earlier, Neil Armstrong will discuss certain engineering aspects of the lunar landing from quite a different perspective than mine. Neil's view was that of a very interested and technically minded user.

[LAUGHTER]

He was the first to conduct a successful docking when he piloted Gemini 8 and docked with the Agena. And that's a whole story in itself. And that was a very exciting experience. He ended up spinning, when the thing went out of control, at two revolutions a second. And he pulled his way out of it.

He then landed eagle in the Sea of Tranquility with Buzz Aldrin at his side. They worked together as a team, obviously, followed by a docking with Mike Collins aboard the Apollo 11 spacecraft in lunar orbit. And then he went through a very high speed reentry to return back into the Earth's atmosphere.

And for his remarkable skills, demonstrated live before millions of people, he earned the privilege of addressing august groups like the one I'm showing you here-- a joint session of Congress. And here you see Neil, with Buzz on the right, Mike on the left, Vice President Agnew, and Speaker McCormack. And now the shoe is on the other foot. We here are privileged to have Neil with us today to tell us some of the engineering aspects of his flight. Thank you.

[APPLAUSE]

ARMSTRONG: Thank you. Thank you. That's a very kind welcome. And I'm most appreciative. I'm appreciative to be asked to give the Gardner lecture. As I look on the back of your program at the list of former lecturers, I'm struck that there are some of the most able and creative leaders in aviation and aerospace in our history. And I'm honored that Bob and I would be asked to add our names to that list.

Bob said I'm going to talk a little bit about the engineering aspects of the lunar landing. And you can, of course, find 1,000 kinds of engineering challenges and solutions to talk about. So I thought I would highlight just that part of the flight which was involved in getting from lunar orbit to the surface of the moon.

The requirements were relatively simple. Begin in lunar orbit, and end up parked on the surface, hopefully in a suitable condition to take off again.

[LAUGHTER]

It was desirable to be able to land at a preselected location without runways, without control towers, beacons, or any other aids on the surface. Each of the sites that we would like to go to would be selected to investigate different types of lunar topography, to photograph and sample the highlands, and the craters, and the mare.

I can see if the lights [INAUDIBLE]. After selecting a landing site, its longitude and latitude could be accurately determined from lunar maps drawn from astronomical photographs. Elevations relative to the mean surface level was considerably less certain. A landing site near the equator certainly has advantages. Equatorial orbits would pass over or near the landing area on every revolution and would give the flight planner a good deal of flexibility.

Because the landing site must lie underneath the orbital path, or near it, a site well north or south of the equator requires an inclined orbit. The moon's rotation about its axis is about a half a degree per hour. And so the landing site is always moving toward or away from an inclined orbit, adding constraints to the trajectory plan.

The fact that Earth-based radar could provide accurate spacecraft position and velocity information at lunar distance was a substantial engineering achievement. Of course, the rotation of the Earth meant that the radar itself was moving at substantial speed.

Additionally, half of the time, it was on the side of the Earth away from the moon and could not be utilized. So three giant radars were used, more or less equally spaced around the Earth so that at least one of them was always located in a position to give good coverage of the spacecraft.

Because the entire orbit around the moon subtended only a half a degree as seen from Earth, some amount of tracking time and mathematical smoothing was required to establish an accurate value for the three orthogonal components of position and the three orthogonal components of velocity.

These six vectors, with the associated time tag, was known as the spacecraft state or state vector. It could be accurately determined and projected ahead in coasting flight, but was unable to keep up whenever the spacecraft was changing its trajectory due to rocket thrust.

In 1966, the trajectory planners were given an unwelcome surprise. It happened during the flight of an American robot spacecraft named Lunar Orbiter, the first craft to fly around the moon. Its orbit, as recorded by the giant radars here on Earth, had some peculiar wiggles in it.

Whenever the spacecraft flew over one of the dark areas, or Mare, it was attracted inward toward the moon. The only known cause for such a phenomenon would be an extraordinarily strong gravitational pull due to the very heavy spots on the moon's surface. These mass concentrations, or mascons, were mapped by analyzing the orbit of the lunar orbiters, and later by mapping the orbit of Apollo 8, the first manned craft to fly around the moon, which occurred during the Christmas of 1968, and again on Apollo 10, the lunar landing dress rehearsal.

These orbit wiggles were quite pronounced, indicating that the mascons were quite near the lunar surface. There was substantial concern that these gravitational uncertainties would preclude landing at a precise location on the surface.

NASA's landing trajectory specialists in Houston ran many trajectories with varying levels of mascon influence. They concluded that the mascon effects were acceptable. Additionally, they considered dispersions in inertial guidance, alignment, and rocket engine performance.

Two possible conditions were to be considered-- a successful completion of the landing or a discontinuance of the approach during the descent for any one of a variety of reasons. The dispersions should not prevent the successful execution of either.

In the case of the abort back to orbit, the dispersion should not put the lunar module in a trajectory that would make a subsequent rendezvous with the command module impossible.

The rocket engine to be used in the descent was critical. There would be a substantial advantage in using a minimum weight system. Weight was at a real premium, as Bob has discussed. That would dictate high chamber pressure and high energy propellants.

Top candidates would be liquid hydrogen as the fuel and liquid oxygen as the oxidizer. These propellants were cryogenic-- that is, they had to be kept at very low temperatures to maintain the liquid phase. And it was a four day trip to the moon. And there was a chance of substantial evaporative loss during the trip.

An alternate possibility was to use propellants that were liquid at normal temperatures-- fuel such as alcohol, or kerosene, hydrazine, oxidizers such as hydrogen peroxide or nitrogen tetroxide. The combination that eventually was selected was a hydrazine UDMH blend as the fuel and nitrogen tetroxide as the oxidizer. Now both of those are liquid at normal atmospheric pressures and temperatures. But they're very toxic and nasty to work with. They had been in common use for rockets for decades, however. And their nature, however unpleasant was well known and understood.

The combination had an important advantage. They were hypergolic-- that is, the fuel burned whenever it came in contact with the oxidizer. They were self-igniting. So there was no need for spark plugs or other special ignition devices, or other systems.

Additionally, the combination had reasonable specific impulse or energy efficiency at relatively low chamber pressures. That permitted a pressure-fed rocket that did not require the weight and complexity of a turbo pump to boost the pressure.

The resulting combination was conceptually simple and reliable. However, there was one other requirement that was everything but simple. Somehow, this rocket needed to provide a wide variation in thrust.

To efficiently decelerate from orbital velocity required a high thrust level. Landing required a relatively low thrust level. Orbital speed in lunar orbit is approximately 5,500 feet per second. Now some of you will be surprised by my archaic use of English units.

[LAUGHTER]

Although metric or SI was used in a few places, in NASA in those days English units were the predominant standard. And because this is an engineering history lecture, I'll use the English units that were the norm at the time.

Using Newton's law-- the second law-- and the definition of rocket specific impulse, one can readily determine the propellant required to decelerate a mass from orbit to zero velocity. We'll leave it as an exercise for the student.

[LAUGHTER]

For the lunar case, each pound to be delivered to the surface requires slightly more than a pound of our selected propellant. So the initial weight in orbit must be more than twice the landing weight. When the craft was landing or hovering above the surface preparing to land, the thrust would need to be equal to the landing weight plus some modulation to allow for increasing and reducing the rate of descent while maneuvering for landing.

Most rocket engines of that era were operated at essentially fixed thrust. Throttle-able engines were very rare. And those that had been tried had far less modulation than would be necessary. The engineering challenge was substantial.

Two contending approaches were tried. One concept inserted inert gas into the propellant line between the tanks and the rocket so that the thrust would be reduced while the total flow rates through the combustion chamber would be constant at all times. The competing idea used a mechanical throttling system using cavitating venturi flow control valves.

That engine, which was built by STL, later to become TRW, was selected for the lunar module. But actually, both approaches worked quite well-- surprisingly well. The engine had a maximum thrust of 10,000 pounds and could be modulated between 1,000 and 6,000 pounds. The thrust needed to hover before landing was about 2,500 pounds. And the variation available, then, 1,000 to 6,000, was adequate for that task.

In the thrust range between maximum thrust and the throttling range, the cavitating venturis would be intermittently cavitating or not and produce an unpredictable mixture ratio. That thrust range was prohibited to us due to the probability of excessive erosion of the nozzle.

Simplicity and reliability were selected over performance. The rocket used a simple pressure-fed system. The propellants were pushed into the rocket by gas pressure. Helium stored in a supercritical state at about 1,600 PSI, and that was used to pressurize the tanks at about 235 PSI. Maximum chamber pressure in the combustion chamber was a remarkably low 103 PSI at maximum thrust, and considerably less in the throttling range. There were many engineering accomplishments in the Apollo program, but many believe the descent engine was one of the most outstanding.

For guidance, navigation, and control, the lunar module had an inertial guidance system designed here at the Draper Lab, which at that time was called the Instrumentation Laboratory. The system included a three degree of freedom inertial measurement unit and a digital computer. The IMU was the navigation sensor, using accelerometers and gyros to sense attitude and velocity changes.

The computer, which included the navigation logic for calculating the guidance commands, was a 70 pound 16-bit machine. It had 36K of ROM and woven rope cores. It had no color monitor, not even a black and white monitor, no alphanumerics. All communication to and from the operator was through three registers of seven digits-- two for identification and five for data.

By today's workstation standards, or even in comparison with a Mac or a PC, it was a primitive device. But it was far advanced over anything we had had up to that time. And we were delighted to have it even though it cost more than a small country.

[LAUGHTER]

The orbital altitude selected to initiate the powered descent was 50,000 feet. Descents from altitude above 50,000 feet required increasing amounts of propellant, and altitudes below 50,000 feet increasingly reduced safety margins.

Altitude errors in either direction could prevent guidance equations from converging and would prevent a successful landing. The moon, of course, has no atmosphere. The normal flight instruments of an aircraft-- the altimeter, airspeed indicator, mach meter, rate of climb-- are all atmospheric sensing devices and will not operate in a vacuum. But clearly, such information, directly measured, would be of considerable use to the crew.

So a specially designed radar attached to the lunar module was used to determine altitude and velocity. The landing radar directed four beams to the lunar surface, a three beam Doppler velocity sensor and one beam for the determination of slant range.

With the appropriate coordinate transformations, the results could be converted into altitude and three components of velocity, all relative to the surface. Because the radar beams were traversing an irregular, and even mountainous surface, the radar data was jumping and required some smoothing within the guidance computer.

And I've mentioned a lot about two guys at the Draper Lab or the Instrumentation Lab who were in large way responsible-- Dick Batten and George Cherry. Dick's here today. And many of you here today, I'm sure, helped Dick and George with those projects. And we remember that work very well, and with a great deal of respect.

The descent trajectory was divided into three parts-- the braking phase, the approach phase, and the landing phase. The braking phase was intended to provide deceleration from orbital velocity down to something under 1,000 feet per second. The best fuel efficiency dictate that that be conducted at maximum thrust, as we've discussed. The breaking phase covered slightly more than 200 miles in about 8 and 1/2 minutes.

The last two minutes utilized the lower throttling region of the engine to allow for corrections of dispersions in engine thrust and trajectory. The braking phase was designed to place the lunar module at about 4 1/2 miles short of the landing site at an altitude of about 7,000 feet.

From this point, the approach phase was initiated. Here the crew should be able to pick up visual contact with the planned landing site. The guidance logic, which could be characterized as a downrange acceleration command, which was a quadratic function of time, was designed to bring the craft down to 500 feet just short of the landing point.

From this point, the autopilot could complete an automatic touchdown or the crew could maneuver to the preferred landing location. In actuality, the crews were reluctant to commit to an automatic landing. The autopilot had no way of picking out the smoothest landing area. And it was not protected against landing with one landing pad sticking in a crater.

Analytical studies had indicated 7% of automatic landings would overturn on touchdown. [LAUGHTER] So it's not surprising that the Apollo landings were flown manually.

Now, I put this diagram in because when I was teaching, these are the quality of the slides I used to use. [LAUGHTER] Because of the reduced gravity, a machine hovering over the moon, as shown in the middle there, would require only 1/6 of the vertical thrust it would need hovering over Earth, as on the left side.

So while slowing to a hover, the forward component of that thrust is consequently only 1/6 of its value on Earth. And likewise, the deceleration is only 1/6. So to obtain the same translational acceleration or deceleration as you would get on Earth on the left that requires attitude changes, as shown on the far right side, that are approximately six times larger than would be required on Earth.

Traversing large pitch or roll angles, of course, either requires more time or larger control powers. It was expected that the control characteristics ideal here on Earth would not at all be acceptable on the moon.

These concerns had been the subject of much attention in the years immediately prior to the landing attempt. A variety of studies and simulations had been conducted. Attitude changes in roll, and pitch, in yaw were assumed to be achieved by the use of small attitude control rockets.

In the ground-based flight simulators, pilots found that they could control attitude well with reaction control rockets. But they encountered difficulty in making precise landings and eliminating residual velocities at touchdown. It was clear that something nearer to the real flying experience was needed.

Helicopters were tried. They could hover. And they could duplicate the final lunar landing trajectory. Unfortunately, they were incapable of investigating the problems of most concern. They could neither replicate the consequences of the lunar gravity or the handling characteristics of reaction control system machines.

Fortunately, there were two projects which very effectively filled the void-- the Lunar Landing Research Vehicle, LLRV, and the Lunar Landing Research Facility LLRF.

The LLRV was developed by NASA's flight research center at Edwards California and built by the Bell Aircraft Company. In the lunar simulation mode, the turbo fan engine, mounted in a double gimbal, was aligned to the local vertical and the thrust adjusted to 5/6 of the LLRV weight. The equivalent of the lunar module descent engine was provided by a pair of throttle-able 500 pound thrust rockets fixed to the fuselage outside the gimbal ring. These were monopropellant rockets using hydrogen peroxide as a fuel.

The turbo fans angle and thrust could be modulated to compensate for aerodynamic drag so that the craft coasted as if it were flying in a vacuum. The LLRV had a very lightweight structure and encountered a variety of interactions between controls and low structural frequencies. After a number of development changes were incorporated, this cleverly compensated flying machine actually managed to closely duplicate flying as if it were over the moon, and became a very useful tool for understanding the needs of flying in the lunar environment.

At the NASA Langley Research Center, an alternate approach to lunar simulation was initiated in what they called the Lunar Landing Research Facility. I don't have a slide, I'm sorry, but you can imagine a craft like one of those stick figures I drew suspended by cables from a large gantry crane.

The idea, again, was to duplicate the lunar gravity and control characteristics. The method was to lower the vehicle apparent weight to its lunar equivalent by lifting upward on the vertical cables attached to a traveling bridge crane. And a complex electrohydraulic system kept the crane platform directly over the machine and with an upward force equal to 5/6 of the vehicle weight, even during translations, and angular motions, and weight changes during due to fuel usage.