Apollo Lunar Module

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Lunar module Orion from Apollo 16 on the moon (1972)

The Apollo lunar module ( LM for Lunar Module , originally LEM for Lunar Excursion Module ) was a spacecraft developed from 1963 by the Grumman company for NASA as part of the Apollo program for landing on the moon . NASA's preliminary planning, however, goes back to 1960.

The LM is in two parts and consists of a descent and an ascent stage. A total of 16 lunar landing vehicles were produced. Of these, six made a moon landing, leaving the lower part with the feet and the descent engine (the descent stage) on the moon. After the astronauts had switched to the command module after the lunar stay to return to earth, the upper part of the lunar module (the ascent stage) was left in lunar orbit and later crashed onto the moon. Most of the other ten units built were used for tests on earth or were not used because their missions were canceled. The Apollo 13 lunar module was used to partially take over the tasks of the damaged service module and thus enable the space travelers to return to Earth. Some of the unused lunar landing vehicles are now on display in museums.

General

In order to get people to the moon , there were various technical designs that were thought through in the early phase of the Apollo project. NASA moved relatively quickly from a spacecraft landing completely on the moon to a split system in which an astronaut in the "return capsule" (the command and service module, CSM) orbits the moon and a separate " Landefahrzeug "is to be used with two astronauts for the moon excursion. This concept is mass-optimized, but technically complex, as both vehicles navigate independently and have to dock in lunar orbit after the ascent.

Mission profile

In the starting phase and until it reached the lunar transfer orbit, the lunar module was located in a conical adapter on the S-IVB, the third stage of the Saturn V , below the CSM. After being fired into the lunar transfer orbit, this adapter was opened and separated, and after a turning maneuver, which its pilot flew manually, the CSM docked on the now accessible lander. Aside from brief tests, the lunar module remained passive on most missions until after reaching a lunar orbit.

In the lunar orbit, the LM pilot and the mission commander then put the LM into operation, unfolded the landing legs and separated from the CSM. This gave the CSM pilot remaining in the CSM the opportunity to visually inspect the lander. The two astronauts in the LM then ignited the descent engine for about 30 s (Descent Orbit Insertion, DOI) with the aim of creating an elliptical transfer orbit with a lowest point (periselenum or pericynthion) at a height of about 15 km about 480 km "forward" (east) to reach the planned landing site. This maneuver took place on the back of the moon without radio contact with earth. Starting with Apollo 14 , this process was changed so that the DOI maneuver was carried out by the CSM and the separation only took place afterwards in order to have more fuel for the landing phase; the need to accelerate again was not a problem for the CSM, with its larger reserve.

The actual braking maneuver (Powered Descent Initiation, PDI) began in the periselenum (and again in radio contact with both the CSM and the earth). Primarily the speed of the LM was reduced; this flight phase took place entirely under computer control. At a height of around 3 km, at the so-called “high gate”, the LM was partially erected for the first time and allowed the astronauts to inspect the landing site. In this phase the commander was able to move the target point, which was still being flown to under computer control, with the aid of his reticle by moving his hand controller in the direction of flight or to the side. The computer indicated an angle for this (Landing Point Designator, LPD); Reading it and monitoring the other flight parameters (above all altitude and rate of descent) was the responsibility of the lunar module pilot, while the commander kept his eyes directed outwards. The final approach phase was initiated at a height of 200 to 300 m (“low gate”); All commanders took over one of the two partially manual control modes in order to select a suitable landing site themselves, although a fully automatic landing would have been possible. During this flight phase, fuel remained for about two minutes. It would have been possible to abort in any phase, the ascent stage would then have flown back into a lunar orbit. When the surface of the moon was reached, the sensors installed on three of the four legs reported contact with the ground by means of a blue signal lamp. The astronauts then switched off the engine manually, and the lunar module fell the last meter to the surface of the moon.

For the return start, the descent step was cut off, served as a launch platform and remained on the moon. The ascent level flew back into a lunar orbit and docked there again with the CSM. After the astronauts switched, the ascent stage was separated from the CSM and left in lunar orbit or brought to a controlled crash.

development

Lunar Module , the lunar module
Training lander at Edwards Air Force Base (1964)

In 1963, the Grumman company in Bethpage , New York , was commissioned to build the lander . Thomas J. Kelly , who accompanied the early studies for the development of the LM, is generally referred to as the father of the lander . As he himself said, however, the LM was a co-production of many. For example, the future Apollo astronauts were also involved in the development and construction, as they ultimately had to fly and land the LM. Mainly Scott Carpenter , Charles Conrad and Donn Eisele .

The LM was the largest manned spacecraft that had ever been developed and built until then. There had to be enough space inside the lander for two astronauts to fly and land the LM manually if necessary. The occupants had to put on and take off their space suits and get out of the vehicle to the surface of the moon. The need to save weight was even greater than with the CSM, since the landing on the moon and the ascent each required a change in speed of around 1800 m / s. There had to be space for the soil samples ( moon rocks ) that were brought with them , and the astronauts had to be able to live, eat, drink and sleep in the LM for several days.

The first plans were for seats similar to those in an airplane cockpit. These would not only have been bulky and heavy, but would also have required considerably larger windows. With the idea of ​​flying and operating the LM in a standing position, the astronauts were able to get much closer to the windows and therefore make them much smaller. The left window (that of the commander) received a reticle, which allowed the commander to identify the landing place on the lunar surface, calculated in the form of a numerical code.

Since the LM descended to the moon on its own, it also had to have an independent life support system and independent electrical systems including navigation. The companies that were awarded the contract to develop the life support system were different from those responsible for the CSM. During the Apollo 13 mission, this turned out to be a fatal error, as both systems were partially incompatible . Nevertheless, the Apollo 13 astronauts were also able to return to Earth by staying in the still functional LM for a long time after the explosion in the service unit. The LM served as a lifeboat, so to speak. The LM also used different fuels and engines than the SM, but the navigation unit was largely identical, and the navigation data could be transferred between the systems.

The landing legs presented a special problem. They should be as graceful and light as possible, but also as stable as necessary for a landing on the moon and be able to absorb the resulting shocks. In addition, they had to be retractable, as the diameter of the rocket stage had been determined relatively early. At the beginning of the planning, the developers provided for five landing legs. For reasons of space, only four were then implemented, which did not affect the stability.

Since the lunar module had to work in the gravitational field of the moon, it was not possible to properly test the flight characteristics of the LM on earth. Changes to the LM to include a floating engine turned out to be pointless. Tests with landers suspended from helicopters did not produce any usable results either. Finally, attempts were made to recreate the lunar gravity by giving specially built landing training devices , the LLTVs , a boost by means of additional engines . Since the lift and control nozzles influenced each other, the LLTVs were not very stable, and several crashes occurred, whereby the pilots, including Neil Armstrong , were able to save themselves with the ejector seat . As a result, the use of LLTVs was reduced and only the mission commanders were allowed. The LLRF was a special construction for practicing the last landing sequence until touchdown. In particular, simulators were used to a previously unknown extent.

Technical specifications

Lunar Module Eagle on the Moon (1969)

When fueled, the lander had a nominal total mass of 14,696 kg, which, however, differed from mission to mission, a total height of 6.40 m and a diameter of 4.30 m (9.50 m with extended landing legs). It consisted of about a million parts, had redundantly designed radio and radar equipment , the aforementioned life support and navigation computer . This complexity made new processes in planning, production and quality assurance necessary. The lack of an atmosphere on the moon also required protection against micrometeorites and thermal protection in the form of aluminum and gold vaporized Kapton foils .

The lunar module was developed from a purely functional point of view. The aerodynamics played no role because of the vacuum in space or on the moon. The system consisted of two stages: the descent stage (DS) and the ascent stage (AS), each of which was equipped with its own engine. This structure means that the center of gravity is very precisely on the engine axis, which was achieved through various design measures.

Level of relegation

The descent stage (DS for D escent S days) was the lower part and, in addition to the engine, contained the tanks for fuel, oxygen , water and helium . On the outside of the structure were the four landing legs and the equipment for the field missions. A not inconsiderable part of the total mass of the stage was ultimately accounted for by the batteries for the supply of the on-board network of 28 V and 115 V. These batteries were in principle rechargeable, but there was no system for recharging on board.

The landing legs gave the vehicle a spider-like appearance, which earned it the nickname “Spider” among astronauts. The step was 3.24 m high including the landing legs. A ladder was attached to the leg that was under the hatch for getting in and out. The EASEP or ALSEP and, for the J missions, also the Lunar Roving Vehicle were accommodated on the sides and accessible from the outside . After the exploration was completed, the descent stage served as the starting base for the ascent stage. An explosive mechanism separated the two stages, leaving the descent stage on the moon . If necessary, the separation could also be carried out during the descent phase in order to enable a landing to be aborted and a safe return to the CSM.

structure

Structurally, the descent stage consisted of a double cross with a central square and four box structures of equal size attached to the side surfaces. The individual panels consisted of milled and chemically processed aluminum plates that were riveted together. The engine was in the middle, the two tanks for the fuel and the oxidizer were located symmetrically on the four sides . The outer diagonals of the cross were braced and clad so that the descent step took the shape of an octagon. The other facilities were housed in the four triangular segments. The landing legs were tied to the outer corners with struts. They were constructed telescopically and contained a deformable element that took up a large part of the impact when touching down. The leg in front of the exit hatch carried the ladder that the astronauts could use to reach the lunar floor, the other three legs were fitted with sensors to detect touchdown. To protect against cooling down on the way to the moon, the descent stage was mostly clad with gold-coated mylar foil.

Descent stage engine

The descent propulsion system was pivotable and provided a thrust of 10,500  lbs (45 kN). The power of the engine could be throttled by the computer or manually in two ranges down to 1050 lbs (4.7 kN). A mixture of 50 percent hydrazine (N 2 H 4 ) and 50 percent asymmetrical dimethyl hydrazine , called Aerozin 50 , was used as fuel. In conjunction with the oxidizer dinitrogen tetroxide (N 2 O 4 ), the mixture is highly explosive and hypergolic , i.e. it ignites automatically on contact without the need for an ignition system. Another tank contained helium , which was used as a propellant to press the oxidizer and fuel into the combustion chamber.

specification

  • Height without landing legs: 2.62 m
  • Width without landing legs: 3.91 m
  • Width with extended landing legs: 9.4 m
  • Total mass, fueled: 10,334 kg (specified, exact value depending on the mission), significantly higher for the J missions
  • Water: a tank of 151 kg
  • RCS : none, control was based on the promotion level
  • Fuel of the DPS (Descent Propulsion System): 8200 kg Aerozin 50 and nitrous tetroxide (N 2 O 4 ) as oxidizer
  • Thrust of the DPS: 45.0 kN, adjustable between 10% and 60%; swivel nozzle
  • Printing on the DPS: a 22 kg helium tank under 10,700 kPa
  • Specific pulse of the DPS: 311 s
  • DPS Delta v : 2500 m / s
  • Batteries: four (five for the J missions) silver-zinc batteries 28–32 volts, 415 Ah, each weighing 61 kg

Advancement level

Ascent stage engine

The ascent stage (AS for A scent S day) contained the cylindrical cabin for two astronauts who were in the front part (left the commander, right the pilot, from the astronaut's point of view), a middle section with all controls and the ascent engine and a rear part that housed the electronics. The tanks, antennas, attitude control and the outer shell were built around the cylinder, which gave the ascent stage its characteristic appearance. To save weight, the two astronauts had to stand when landing. They were held in place by belts and cables. In the front foot area between the astronauts there was an almost square hatch about 82 cm wide and high, which was used to exit after landing. A large part of the steering, communication and printing systems were located in the middle section. The rock samples for return transport were also housed here. Another hatch about 84 cm in diameter was attached in the upper area of ​​the middle section and served as a connection between the lander and the command module. The ascent stage had three windows, two triangular ones to the front for observation of the landing (provided with a reticle in the commandant's window) and a small rectangular one in the top to control the approach to the mother ship. The position of the ascent step in space was controlled by 16 control nozzles , which were arranged in four groups (so-called "quads"). These were identical to the quads of the CSM - that is, had a comparatively high thrust - and were attached far out. The resulting major moments, especially when the tanks were empty, led to flight behavior that the astronauts described as "angular".

structure

The ascent stage is built around a lying cylinder that forms the pressurized cabin. The cylinder again consisted of milled aluminum plates, the front and back were particularly stiffened. In contrast to the plate structure of the descent stage, all other parts (tanks, attitude control nozzles, antennas and the rear instrument panel) were connected with struts. Again, attention had to be paid to the position of the center of gravity; since the ascent stage only has two tanks, the lighter fuel tank (on the left side as seen by the astronauts) was located significantly further out than that of the oxidizer. The buttress was hidden under the outer panel.

Ascent stage engine

The permanently installed - in contrast to the descent stage, non-swiveling - engine for the return start from the moon generated a non-controllable thrust of 3,500 lbf (15.6 kN). That was enough to bring the ascent stage, which weighs about 4.8 tons, back into lunar orbit. The fuels were the same as for the descent stage. The engine was designed to be as simple as possible and, apart from the valves, had no moving parts in order to achieve the highest possible reliability. Therefore, a pressurized gas feed was used. The engine could be re-ignited several times, so that changes in orbit in lunar orbit after the ascent, in particular the rendezvous maneuver with the CSM, were possible. The control during the ascent phase was carried out by a computer that had its own ascent program independent of the main navigation. However, manual control was also possible.

specification

  • Crew: 2
  • Habitable volume: 6.7 m 3
  • Height: 2.83 m
  • Width: 4.29 m
  • Depth: 4.04 m
  • Total mass, fueled: depending on the mission, approx. 4870–4990 kg
  • Atmosphere: 100% oxygen below 33 kPa
  • Water: two tanks of 19.3 kg each
  • Coolant: 11 kg ethylene glycol- water mixture (for the electronics)
  • Thermal control: an active evaporator
  • Fuel of the RCS (Reaction Control System): 287 kg of aerozine 50 and nitrous tetroxide (N 2 O 4 ) as oxidizer
  • RCS configuration: 16 nozzles with 45 N thrust, arranged on struts in four "quads"
  • Specific pulse of the RCS: 290 s
  • APS (Ascent Propulsion System) fuel: 2353 kg Aerozin 50 and nitrous tetroxide (N 2 O 4 ) as oxidizer
  • Thrust of the APS: 15,600 N, not adjustable
  • Printing on the APS: two helium tanks of 2.9 kg each under 21,000 kPa
  • Specific pulse of the APS: 311 s
  • APS Delta v : 2220 m / s
  • Thrust-to-weight ratio on the moon: 2.1: 1
  • Batteries: two silver-zinc batteries 28–32 volts, 296 Ah, each weighing 57 kg
  • Power supply: 28 V DC, 115 V 400 Hz AC

Moon car

As part of the Apollo program, Apollo 15 was the first of the three so-called J missions that provided for a longer stay on the moon. A battery-powered lunar roving vehicle, which was folded up and attached to the outside of the lunar module for transport, made it possible to move more freely over the lunar surface and to explore a larger area.

Climate system

The lunar module's climate system was so compatible with the astronauts' spacesuits that they could be recharged up to six times on the ferry.

The whereabouts of the lunar lander

No. Surname Apollo Whereabouts of the LM comment
01 - 5 burned up in the earth's atmosphere Unmanned test in earth orbit. The ascent and descent stages entered the atmosphere shortly after the mission was completed, 19 days apart.
02 - - National Air and Space Museum , redecorated to look like the Apollo 11 ferry Was intended for an unmanned test in Earth orbit, which was waived due to the success of LM-1.
03 Spider 9 burned up in the earth's atmosphere Manned test in earth orbit. The descent stage burned up shortly after the mission. The ascent stage remained in earth orbit for a few years.
04 Snoopy 10 Moon or sun orbit Manned test in lunar orbit. The descent remained in a low lunar orbit and later crashed in an unknown location. The ascent stage was specifically brought into a solar orbit. A group of British amateur astronomers believe that the ascent stage of the lunar module "Snoopy" was near Earth on January 15, 2018.
05 eagle 11 moon Successful moon landing. The ascent remained in lunar orbit and later crashed uncontrollably onto the moon.
06 Intrepid 12 moon Successful moon landing. The ascent stage was deliberately brought to crash on the moon near the landing site.
07 Aquarius 13 burned up in the earth's atmosphere Mission canceled. The LM served as a "rescue capsule". Ascent and descent were not separated.
08 Antares 14th moon Successful moon landing. The ascent stage was deliberately brought to crash on the moon near the landing site.
09 - - John F. Kennedy Space Center Was planned for a moon flight, which should have taken place between Apollo 14 and Apollo 15, but was canceled for reasons of cost.
10 Falcon 15th moon Successful moon landing. The ascent stage was deliberately brought to crash on the moon near the landing site.
11 Orion 16 moon Successful moon landing. The targeted crash maneuver failed. The ascent remained in a lunar orbit and later crashed uncontrollably onto the moon.
12 Challenger 17th moon Successful moon landing. The ascent stage was deliberately brought to crash on the moon near the landing site.
13 - - The Cradle of Aviation Museum , New York Was already under construction when further Apollo flights were canceled.
14th - - Franklin Institute , Philadelphia Was already under construction when further Apollo flights were canceled.
15th - - scrapped Was already under construction when further Apollo flights were canceled.

From Apollo 15, a modified lunar module was used, which allowed a longer stay and could carry a lunar car.

See also

literature

  • Thomas J. Kelly: Moon Lander: How We Developed the Apollo Lunar Module . Smithsonian Books, Washington, DC 2001, ISBN 1-56098-998-X .

Web links

Commons : Lunar Module  - collection of images, videos and audio files

Individual evidence

  1. ↑ Lunnar modules in the National Air and Space Museum .
  2. ↑ Astronomers Might Have Found Apollo 10's “Snoopy” Module . Accessed February 15, 2020