posted 10-10-2006 09:15 AM
Lunar landing training was ‘touch and go’
by Ed Hengeveld
Spaceflight, vol. 34, December 1992One of the most remarkable accomplishments of the last 25 years is no doubt the landing of men on the Moon. Between 1969 and 1972, six pairs of American astronauts captured the imagination of millions of spectators by exploring an alien landscape while sending live television pictures back to Earth.
In the very early stages of Project Apollo, NASA realized that a lunar landing would need to be simulated here on Earth before astronauts could be committed to such a risky undertaking. Fixed-base flight simulators alone would not be realistic enough to practice the specific skills that would be needed to make a successful touchdown on an unknown and potentially hostile planet. Several ways were proposed to let astronauts simulate the final portion of the descent to the Moon in a free-flying vehicle.
Complicating factors were that the Moon has no atmosphere and that its gravity field is only one-sixth of that on Earth. A vehicle designed to fly in a lunar environment, such as the Apollo Lunar Module, could not fly on Earth without significant design changes and so other solutions had to be found.
Engineers at NASA’s Flight Research Center in California (1) had been thinking about simulating a lunar landing almost from the moment Project Apollo was born. When they recommended to NASA Headquarters in Washington that a free-flying simulator be built, they learned that studies along the same lines had been conducted independently by the Bell Aerosystems Company in Buffalo, New York. Consultations between FRC and Bell led to a joint proposal to NASA Headquarters and on January 18, 1963, it was announced that a $3.61 million contract for the design and construction of two manned lunar landing research vehicles (LLRVs) was awarded to Bell. The vehicles would be able to take off and land under their own power, reach an altitude of about 1200 meters, hover and fly horizontally. A flight test program at FRC would investigate the problems associated with landing a manned vehicle on the Moon and it was hoped that this would lead to the development at a later stage of a similar trainer for use by the Apollo astronauts.
”FLYING BEDSTEADS”
Bell’s design for the LLRV was based on the so-called “flying bedsteads” that were flown in the 1950s to study the potential of jet lift-off for vertical take-off and landing (VTOL) aircraft. As the name implies, these vehicles consisted of an open framework supporting the engine, fuel tanks, cockpit and other systems necessary to take off and land vertically. The first “flying bedstead”, built by British aviation pioneer Alan Arnold Griffith, made its maiden flight on August 2, 1954.
Bell completed the first LLRV on April 7, 1964, and it was formally turned over to NASA the next day. The vehicle consisted essentially of a down-pointing jet engine, four landing legs and a pilot seat. The General Electric CF-700-2V turbofan engine was mounted vertically in the center of the four aluminum landing legs and provided 18.850 Newtons of thrust. The engine was constantly throttled to support five-sixth of the total 1815 kg weight of the vehicle, thus simulating the gravity field of the Moon. Lift for the remaining one-sixth of the LLRV’s weight was provided by two 2250 Newton hydrogen-peroxide lift rockets. These engines were operated by the pilot to simulate the engine that the Lunar Module would use during its descent to the Moon.
Six additional lift rockets were provided for emergency use, in case the jet engine would fail. A closed-loop acceleration-sensing system automatically controlled the jet engine’s attitude and throttle setting to cancel out any aerodynamic forces. The LLRV had 16 hydrogen-peroxide control thrusters, just like the LM, mounted in groups of four on the four corners of the vehicle. This combination of propulsion systems allowed the pilot to hover, fly horizontally, perform pitch and roll maneuvers and yaw a full 360 degrees.
The LLRV was slightly more than three meters high and the landing legs stood four meters apart. The open cockpit extended forward from the upper half of the vehicle. The pilot sat between two plexiglass windscreens on a Weber zero-zero ejection seat. He controlled the LLRV by using a conventional control stick and two rudder pedals. To practice a lunar landing, the pilot would take off and climb to an altitude of about 100 meters. He would then select a landing spot and push a button to initiate the automatic control mode of the jet engine. Using the two lift rockets and the 16 control thrusters he would then try to make a soft touchdown in the selected spot.
The two LLRVs arrived at FRC on April 16, 1964, and preparations for the flight test program started immediately. Attention centered on the no. 1 vehicle, which was installed on a fixed “tilt-table” to enable it to fly without actually leaving the ground. Once these tests were successfully completed the support team and the vehicle were ready to try something more ambitious.
MAIDEN FLIGHT
The first flight in LLRV no. 1 was made on October 30, 1964, by NASA test pilot Joseph A. Walker, at an area of FRC called South Base. Walker was a veteran of such programs as the X-15 hypersonic research aircraft and he had been assigned as project pilot for the test phase of the LLRV. He lifted the vehicle off the ground for several meters using the thrust from the CF-700 jet engine, while holding his balance by using the reaction control thrusters. He described taking off in the LLRV as “just like going up in an elevator” and made three separate lift-offs and landings in a little over four minutes.
For the initial flights the LLRV’s landing legs were equipped with small wheels to facilitate ground handling. This caused some unexpected problems on Walker’s second flight, on November 16. He had to abort his first lift-off because a stiff breeze threatened to blow him to the rear. When the LLRV was turned around, Walker took off and drifted forward with the wind during his hovering flight. This motion caused the vehicle to roll forward upon touchdown and took it over a pit covered by iron doors. One door blew off but the LLRV was not damaged. At least that was one hazard that would not be encountered on the Moon.
Walker made five more flights during November and demonstrated that an experienced pilot could easily learn to handle the strange craft, although proficiency in helicopters was a must. Altitudes on these initial flights ranged between 15 and 20 meters and flight duration was usually about three minutes. The open cockpit did present some problems, other than making the pilot feel a little uncomfortable. The noise level from the jet engine was fairly high and tended to wash out any radio communications with the ground control van. Sunlight reflecting off the control panel would on some flights prevent the pilot from reading his instruments properly, but that problem was usually solved by turning the craft slightly.
A second NASA pilot, Donald L. Mallick, was checked out in the LLRV in December. He said that “the LLRV possesses nice handling characteristics and is an easy vehicle to fly”. On the 9th of the month, after ten flights, the vehicle was temporarily grounded for a detailed checkout. By then it had reached an altitude of 90 meters and a maximum forward velocity of 12 meters per second.
LUNAR SIMULATIONS
Flights were resumed in February of 1965 and on the 26th of the month the first landing was made with the design footpads on the landing gear, instead of the wheels. During the spring the LLRV’s flight envelope was gradually expanded. A special building had been set up at South Base to support the flights and to minimize interference with other base operations. On September 9 Mallick made the first flight in the so-called lunar simulation mode, with five-sixth of the vehicle’s weight neutralized by the jet engine, the descent controlled by the lift rockets and the attitude controlled by the 16 thrusters.
In December a third pilot was checked out. Army Lt. Col. Emil E. (“Jack”) Kluever made flights 73 and 74, both on the same day. Afterwards he reported that flying the LLRV felt like balancing on top of a ball. In early 1966 the cockpit was modified slightly, moving the display and control panel to the pilot’s right to make it look more like that of the LM. Also, the control stick was moved from between the pilot’s knees to the side of the seat.
After the initial series of qualification flights in the LLRV, Kluever and Mallick had started to check out experienced pilots from the Manned Spacecraft Center in Houston (2). Joseph S. Algranti and Harold E. (“Bud”) Ream would in turn act as instructors for the astronauts when LLRV operations would be moved to Ellington Air Force Base near MSC in the fall of 1966. Following one of his first flights Ream landed with severely irritated eyes and had to be rushed to an “eye bath” by ground crews. This was caused by the hydrogen-peroxide exhaust from the control jets. Don Mallick had also experienced this on one of his early flights when he had forgotten to close his helmet visor.
In addition to the two LLRVs, three improved versions of the trainer, called LLTV for Lunar Landing Training Vehicle, were ordered by MSC from the Bell factories. These would more closely simulate the actual Lunar Module’s handling characteristics and have a partially enclosed cockpit to give the pilot an LM-type window. That would also reduce the pilot’s apprehension when looking down, as Jack Kluever liked to joke. The two LLRVs would be brought up to LLTV standards later.
Discussions with NASA’s Langley Research Center in early 1966 resulted in an agreement to let astronauts use Langley’s Lunar Landing Research Facility for a full week before checking out in the LLRV. The LLRF was basically a tethered version of the LLRV, suspended from a giant support gantry, that allowed an LM-type vehicle to practice the final 50 meters of a lunar landing while hanging from moving cables. The LLRF had primarily been used by Langley pilots to test instruments and software designed for the LM. The helicopter-like cockpit would be modified to allow the pilot to stand upright, as he would during a real lunar landing, so he could get used to flying in that unusual position. The LLRVs and LLTVs could not let a pilot practice while standing up, for one thing because they were equipped with ejection seats.
MOVING TO HOUSTON
Meanwhile back at FRC, LLRV no. 1 had made 198 flights, completing its test program on November 30, 1966. It was shipped to Ellington AFB on December 12, where it was received the next day. Jack Kluever made the maiden flight in the no. 2 vehicle at FRC in January 1967. It was the first in the series to feature the partially enclosed cockpit. After five more flights it was also moved to Ellington on January 17. Kluever made the first flight there in the no. 1 vehicle in March. While no. 2 was undergoing a series of ground tests, Kluever, Algranti and Ream continued the flights in no. 1 in preparation for astronaut training to begin.
The planned delivery schedule for the three LLTVs could not be maintained because X-ray inspections at the factory had revealed cracks in certain parts that required repair. Also, the hydrogen-peroxide tanks had to be refabricated because the walls were found to be too thin. The first LLTV was finally delivered to MSC on October 9, 1967, where it started an extensive series of ground tests before it would be released for flight. LLTVs no. 2 and no. 3 arrived on December 8 and December 11, respectively.
In the meantime, preparations for the first manned Apollo mission were picking up speed and in November 1967 the prime and backup crew assignments for the second and third flights were announced. It was part of the normal crewing policy that a backup team would skip the next two flights and then be assigned to a prime crew. This made the backup crews for the second and third Apollo flights eligible for assignment to a possible lunar landing mission further down the line. Therefore, the backup commanders of these flights, Pete Conrad and Neil Armstrong, respectively, were the first astronauts to begin training in the LLRV in early 1968.
The ungainly-looking vehicles were by now considered essential to lunar landing training. Plans were made to move two of the LLTVs to the Kennedy Space Center, so astronauts would have access to them until just before launch. They would be operated from the so-called Skid Strip, an old landing strip at nearby Cape Canaveral Air Force Station.
DISASTER
By early May 1968, Conrad had made 13 flights in LLRV no. 1, still the only craft being flown at Ellington. On May 6, Neil Armstrong made his 21st flight in the vehicle and it ended in disaster.
Armstrong lifted off and flew to an altitude of about 150 meters, where he began a simulated lunar landing. When he had descended to about 70 meters, the LLRV began to pitch forward while picking up speed. Armstrong tried to halt this forward velocity by using his attitude control thrusters, but they did not respond properly and the vehicle started tilting to the right. When he was flying on his right side, Armstrong realized that he would not be able to stop this motion and he wisely ejected. Seconds later the LLRV crashed in a field and burned. Armstrong landed by parachute and walked away without injuries. The only damage, he said later, was that he bit his tongue…
Initially there was great concern that the accident would have a serious impact on the design of the actual Lunar Module. LM-1 had made an unmanned space flight in January 1968 and it would not be good news if a serious design flaw were to be found this far along in the program. While the LLRV was grounded, MSC Director Robert R. Gilruth appointed a five-man board of investigation to track down the cause of the crash. Among its members were pilots Joe Algranti and Don Mallick, as well as astronaut Bill Anders, who was in training as lunar module pilot for the third Apollo mission. On May 16, NASA Headquarters in Washington took the unusual step of forming a second review board to work with the team from Houston.
After a thorough investigation that lasted all summer, both groups reported on October 17, 1968, that the cause of the crash was not related to the design of the LM. It was found that helium in the propellant tanks had been depleted earlier than normal, resulting in insufficient pressure to force the hydrogen peroxide fuel to the attitude control rockets. A number of improvements was recommended and the boards concluded that the accident would have no bad effects on the lunar landing program.
FIRST LLTV FLIGHT
Two weeks earlier, on October 3, 1968, the first LLTV had made its maiden flight at Ellington AFB. Joe Algranti made a four-minute checkout, during which he reached a maximum altitude of about 15 meters. The three LLTVs incorporated changes that were the result of the initial LLRV test program at FRC and their systems were more like that of the real LM. Each one had cost about $2.5 million.
During October and November, Algranti and Ream made 14 flights in the no. 1 vehicle. Astronaut training in the LLRV and LLTV had been suspended after the crash and it was important that it be resumed as soon as possible. Apollo-7 had flown in October and now Apollo-8 was about to be launched. If all went well, men would try to land on the moon in seven months.
On December 8, Algranti took off in LLTV no. 1 for a final checkout of the vehicle before it would be released for astronaut training. It was the 15th flight for this particular craft. About four minutes into his planned six-minute flight, when he had descended from 160 to about 65 meters, Algranti suddenly experienced stability problems. He ended the simulated lunar landing to regain control of his craft. That caused severe lateral oscillations, after which the LLTV began to fall like a brick. Algranti wasted no time and ejected, one second before the vehicle crashed and exploded. He landed safely nearby, his only injury being thigh bruises from the force of ejection.
The implications of this second crash were potentially serious. Had something vital been overlooked? Was the vehicle unsafe? If it was, there was not enough time to redesign it. Astronaut Wally Schirra, who had just commanded the Apollo-7 mission, was named head of the investigating team in Houston. On January 8, 1969, NASA Administrator Tom Paine asked the review board from NASA Headquarters that had studied Armstrong’s accident to review its findings and determine if there was any connection between the two crashes. Next day, the crew for the Apollo-11 mission was named. If Apollos 9 and 10 were successful, astronauts Armstrong, Collins and Aldrin would be launched in July on the first lunar landing mission. Time was beginning to run out.
With the LLTV grounded, NASA began preparations to shift the important lunar landing training to Langley’s tethered LLRF, in case findings of the Schirra commission would point to a serious problem with the LLTVs. A number of astronauts had made familiarization flights in the LLRF, but only Armstrong and Aldrin were qualified to fly it in the lunar simulation mode. It was not comparable to the LLTV when it came to giving the pilot a realistic “feel” of flying the LM, but there was no alternative.
TRAINING RESUMES
In the meantime, preparations at Ellington AFB continued for resumption of qualification flights in LLTV no. 2. Wally Schirra’s investigation had soon focused on wind conditions during the December 8 accident. Since Joe Walker’s first flight in 1964 there had been strict flight rules for LLTV operations. Winds were not to exceed 7m/s during takeoff or 9m/s at maximum altitude. Surface winds had been calm when Algranti took off, but later wind velocities of up to 15m/s had been measured at altitude. It was possible that this had caused the LLTV to become unstable.
No immediate connection between the two accidents was found and on April 7, 1969, Bud Ream successfully completed a six-minute flight in LLTV no. 2. For safety reasons the thrust level of the attitude control thrusters had been increased. About a dozen flights were planned before astronauts would be allowed to fly the vehicle again. Plans to use the LLTVs at the Kennedy Space Center just before Apollo-11 had been abandoned because of the fast-approaching launch date.
On June 5, Schirra’s team presented its findings. They concluded that “the primary cause of the accident was that the vehicle entered a region of flight where aerodynamic moments overpowered the control system in use, such that attitude control was lost”. In other words, a gust of wind had probably thrown the LLTV out of control. No systems malfunctions were found. As a result of the investigation the cabin roofs on the other LLTVs were removed to provide an outlet for trapped air.
These findings cleared the way for astronaut training to resume and on June 14, with about a month left before the Apollo-11 launch, Neil Armstrong made his first flight in the LLTV since his crash more than a year before. Over a period of three days he completed eight flights in the vehicle, for a total flight time of 40 min. 14 sec. During these eight flights he made 14 takeoffs and landings, six of which were in the lunar simulation mode.
Armstrong stressed the importance of the LLTV when he talked to news media after the flights. “We are very pleased with the way it flies”, he said. “It’s a sifgnificant improvement over the LLRV, which we were flying here a year ago. I think it does an excellent job of actually capturing the handling characteristics of the Lunar Module in the landing maneuver”.
He added that “it’s really a great deal different than any other kind of aircraft that I’ve flown. The simulation of lunar gravity has some aspects that make this type of flight sufficiently different from anything else we’ve done to make this vehicle very worthwhile, and I’m very pleased that I’ve had the opportunity to get some flights in it here just before the Apollo-11 flight.”
FLIGHTS CONTINUE
The first lunar landing mission was launched on July 16, 1969, and four days later Neil Armstrong successfully flew the LM Eagle to its designated landing spot on the Moon. However, the job of the LLTV was by no means complete. On July 9, one week before the Apollo-11 launch, Apollo-12 commander Pete Conrad had resumed flying the trainer in preparation for the next mission, scheduled for November. After a number of familiarization flights he flew the vehicle again in October and completed the series on October 26, 1969, with his 27th flight (including the 13 LLRV flights in 1968).
Conrad echoed Armstrong’s praise of the vehicle when he remarked: “This is, like Neil said, the frosting on the cake as far as simulations are concerned. The LLTV is a tricky vehicle. So is the Lunar Module”.
It became standard practice for Apollo commanders and their backups to fly a series of simulations in the LLTV about one month prior to the scheduled launch date. Apollo-13s Jim Lovell flew the trainer in March 1970 and Apollo-14s Al Shepard in December of that year. In between these flights the LLTVs were regularly taken aloft by MSC pilots to keep them in perfect flying condition. On one of these trials, on January 29, 1971, pilot Stuart M. Present lost his attitude control because of a failure in the electrical system of LLTV no. 2. The vehicle started flipping over backwards and when he was facing straight up, Present ejected and parachuted to safety.
The incident came two days before the Apollo-14 launch, but NASA hastened to say it would not affect the mission, since the LLTV’s electrical system was totally different from that in the LM. There was some talk of ending the LLTV flights altogether because they were too risky. However, the astronauts strongly disagreed because experience had shown that the vehicles accurately forecast the LM’s handling characteristics during the final descent to the Moon. Chief astronaut Deke Slayton said there was “no other way to simulate Moon landings except by flying the LLTV”. NASA management concurred and the flights continued.
FINAL FLIGHT
On November 13, 1972, three weeks before the final mission in the Apollo program, Apollo-17 commander Eugene A. Cernan made the last flight in LLTV no. 3 before it was retired. Despite the fact that three of the five training vehicles crashed, the program was very successful. Hundreds of LLTV flights had given the Apollo crews the confidence they needed to make a total of six flawless landings on the Moon. The LLRV/LLTV was absolutely essential to this record of success.
Two of the vehicles still exist today. LLRV no. 2 is displayed at the Dryden Flight Research Center, where it made its maiden flight in 1967. LLTV no. 3 had been on display at the Alabama Space and Rocket Center for 12 years when it was returned to Houston for the 20th anniversary of the Apollo-11 mission in 1989. It can now be seen at the Johnson Space Center’s visitor center.
(1) The two principal locations featuring in ths article appear under the names they had during the sixties and early seventies. FRC is now called the Hugh L. Dryden Flight Research Center, while the Manned Spacecraft Center is now the Lyndon B. Johnson Space Center.
(2) Joe walker had been killed on June 8, 1966, in a crash that was not related to the LLRV program. He made his 35th and final LLRV flight on November 5, 1965.
ACKNOWLEGDEMENTS
Special thanks are due to Carol Homan of JSC’s History Office and Bunny Dean, the Freedom of Information Act Coordinator at JSC’s Office of Public Affairs. Mike Gentry and Debbie Dodds of Media Services and Don Haley of DFRC’s Office of Public Affairs provided me with some unique photos and so did Campbell Martin and Keith Henry of Langley’s Office of Public Affairs. NASA’s Audio Visual Section in Washington was also very helpful.
posted 10-07-2006 03:38 AM
.
advertisement