LUNAR LANDING

When John F. Kennedy challenged his nation to land a man on the Moon before the decade was out, Hubert M. ‘Jake’ Drake at Edwards Air Force Base, who in the 1950s participated in the initial planning for the X-15 rocket plane, concluded that to provide realistic training for flying a lunar module it would be necessary to build a free-flying craft that accurately reproduced the stability and control issues involved in ‘flying’ in a vacuum and a reduced gravitational field. Drake set up a study group to design such a machine and enrolled Neil Armstrong as one of the team’s members. After reviewing 1950s research into vertical takeoff and landing (VTOL) aircraft, it was decided to mount a jet engine in a gimbal to provide vertical thrust. Its throttle would operate in two modes: in ‘terrestrial mode’ the jet would run conventionally in order to lift off vertically and climb to the altitude needed to simulate the lunar landing, and then be throttled back into ‘lunar mode’ in order to offset five-sixths of the craft’s weight. The rate of descent would be controlled by a pair of throttleable thrusters affixed to the airframe. The attitude control system was based on that developed for the X-15 at the top of its ballistic arc, where aerodynamic control surfaces are useless. It was decided to use 16 thrusters, arranged in pairs, to control roll, pitch and yaw. The project attracted interest precisely because aerodynamics played no part in the craft’s operation. To translate, it would have to tilt, and use the angled component of the thrust from the ‘descent engines’ to impart lateral motion, then tilt back to cancel this motion. By a remarkable coincidence, Bell Aerosystems in Buffalo, New York – which had built the X-1 rocket plane in which Charles E. Yeager had ‘broken the sound barrier’ on 14 October 1947, and was the only US

It was for this reason that the KC-135 aircraft used for such training was nicknamed the Vomit Comet.

aircraft manufacturer with experience of using jet engines for VTOL – independently submitted to NASA a proposal to develop a vehicle to be used to investigate the issues of making a landing on the Moon. When NASA sent Bell out to Edwards, Drake realised that the company was better placed to develop the vehicle and, as a result, on 18 January 1963 NASA issued Bell with a contract to supply two Lunar Landing Research Vehicle (LLRV) aircraft.

On 15 April 1964 the two LLRVs were shipped to Edwards Air Force Base in crates, because Drake’s team wished to do the assembly and install the instruments themselves. Each vehicle stood 10 feet tall on four legs spanning some 13 feet, and weighed 3,700 pounds. The General Electric CF-700-2V turbofan jet delivered a maximum of 4,200 pounds of thrust. The descent engines for ‘lunar mode’ were non­combustion rocket thrusters using pure hydrogen peroxide propellant, each of which could be throttled between 100 and 500 pounds of thrust in order to control the rate of descent and horizontal translations.[12] The pilot sat on a platform that projected forward between the front legs. In view of the fact that if a vehicle were to get into trouble it would be close to the ground, probably be falling, and certainly be within seconds of crashing, it was fitted with a lightweight ejection seat developed by Weber Aircraft that was not only capable of lifting its user clear of an aircraft on the ground but also from an aircraft that was at low level and falling at 30 feet per second. On 30 October 1964 NASA test pilot Joseph S. Walker, a former X-15 pilot, made three vertical ‘hops’ in LLRV-1, remaining within 10 feet of the ground for a total duration of 60 seconds to exercise the hydrogen peroxide attitude control thrusters, the steam from which nearly obscured the view of the spectators. Armstrong was no longer at Edwards, but having been assigned the task of overseeing the development of trainers and simulators he closely monitored the test program.

In 1963 NASA began to train astronauts to fly helicopters in the hope that this would enable them to gain a feel for the issues of making a landing on the Moon. However, while a helicopter could duplicate the trajectory of the final phase of a lunar landing, the basic aerodynamic requirements of helicopter flight meant that the controls could not simulate those of a spacecraft. In contrast, the ми-aerodynamic LLRV did accurately simulate control over the rate of descent, attitude, and lateral movement. On 26 January 1965, Warren J. North, who was in charge of training, ordered that astronauts must have 200 hours of helicopter training prior to trying to fly the LLRV. In October that year NASA drew up the preliminary specifications for a Lunar Landing Training Vehicle (LLTV). Based on the LLRV, this new vehicle was to have an upgraded jet and larger tanks of peroxide for longer endurance in ‘lunar mode’, a cabin with a similar field of view to that envisaged for the LM, a 3- axis hand controller (instead of the stick and pedals of the LLRV), instruments laid out as in the LM, and as much as possible of the LM’s built-in flight control logic in order to enhance its fidelity as a trainer. In August 1966 Armstrong and Joseph S. Algranti, chief of aircraft operations at the Manned Spacecraft Center, worked with Bell to implement these upgrades. To augment helicopter training, a cratered surface based on the highest resolution pictures from the Ranger probes was mocked up, and on climbing to 500 feet the astronauts would cut the throttle and land at various angles and rates of descent and in a variety of lighting conditions to familiarise themselves with visually gauging their height and sink rate over the alien landscape. Meanwhile, it had been decided that once Edwards completed its LLRV tests these vehicles should be sent to Ellington. When LLRV-1 arrived on 12 December 1966, Armstrong was present to watch Algranti perform the formal acceptance trial. LLRV-2 followed in mid-January 1967. In a rationalisation, the two LLRVs were redesignated LLTV A1 and A2, and the three new vehicles were to be B1, B2 and B3. Before being permitted to fly, an astronaut was required to undertake a 3-week helicopter refresher, 1 week of familiarisation with the Lunar Landing Research Facility at Langley,[13] spend 15 hours in a ground simulator and then be cleared by Algranti.

Armstrong made his first flight in LLTV A1 on 27 March 1967, but did not fly again until starting an intensive program of lunar landing rehearsals in early 1968. A typical flight involved using the jet at maximum thrust to lift off vertically and climb to 500 feet altitude, throttling back to balance five-sixths of the weight, and then, as when using the helicopter, flying a profile that would match the trajectory of a LM at that altitude, except that now the rate of descent and lateral manoeuvres were actively controlled employing the ‘descent engines’. As Armstrong reflected of his experience:[14]

‘‘The thing that surprises people on their initial flights in ‘lunar mode’ is the tendency of the vehicle to float far beyond where you think it is going to go. It takes practice to anticipate the distance required to slow down – you must start to brake much earlier, if you are to stop where you want to stop. Similarly, if you are in a hover, and change your mind, it takes a lot of effort to get moving again. The vehicle is sluggish in its translating ability, so it takes a long time, and big angles, to gain a little speed and translate 50 feet. We hope to have one – and-a-half to two minutes of fuel essentially in hover when we’re landing on the

Moon, but you can use that up really fast if you change your mind frequently about where you want to go.”

On 6 May 1968 LLTV A1 went out of control during a descent and he had to eject.

“I lifted the vehicle off the ground and climbed to an altitude of 500 feet in preparation for making the landing profile. I had been airborne for about 5 minutes, and was down to about 200 feet when the trouble began. The first indication was a decreasing ability to control the vehicle. It began to tilt sharply. There was less and less response. The trouble developed rather rapidly, but wasn’t an abrupt stop. It was a decay in attitude control. Without attitude control there is no way to remain upright. The vehicle does have two separate systems for doing this, but in this case both systems failed at their common point – the high-pressure helium to pressurise the propellant to the rockets. I was losing both systems simultaneously, and that’s where I had to give up and get off. I guess I ejected at 100 feet, plus or minus – we don’t have a way of measuring it accurately, even from photographs. How far the ejection throws you depends on your attitude at the time you leave, and also on your upward or downward velocity at the time. If you start from an upright attitude at a hover, it will take you up about 300 feet. The parachute ejector is automatic, although there is a manual override. I had always thought I might be able to match the automatic system, but when I was reaching for the D-ring the automatic system had already fired.’’