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NASA contracted with the Armour Research Foundation for an investigation of conditions likely to be found on the lunar surface. Research would concentrate first on evaluating the effects of landing velocity, size of the landing area, and shape of the landing object with regard to properties of the lunar soils. Earlier studies by Armour had indicated that the lunar surface might be composed of very strong material. Amour reported its findings during the first week of November.
Grumman began fabrication of a one-tenth scale model of the LEM for stage separation tests. In launching from the lunar surface, the LEM's ascent engine fires just after pyrotechnic severance of all connections between the two stages, a maneuver aptly called "fire in the hole."
Also, Grumman advised that, from the standpoint of landing stability, a five-legged LEM was unsatisfactory. Under investigation were a number of landing gear configurations, including retractable legs.
At a mechanical systems meeting at MSC, customer and contractor achieved a preliminary configuration freeze for the LEM. After "considerable discussion," Grumman agreed to begin designing systems and subsystems based on this configuration, bearing in mind that certain unresolved areas (the docking system scanning telescope location and function, and the outcome of visibility studies) would have a substantial effect on the final configuration. Several features of the design of the two stages were agreed upon:
At a meeting on mechanical systems at MSC, Grumman presented a status report on the LEM landing gear design and LEM stowage height. On May 9, NASA had directed the contractor to consider a more favorable lunar surface than that described in the original Statement of Work. Accordingly, Grumman recommended an envelope of LEM S-IVB clearance of 152.4 centimeters (40 inches) for a landing gear radius of 457 centimeters (180 inches). Beyond this radius, a different gear scheme was considered more suitable but would require greater clearances. The landing gear envelope study was extended for one month to establish a stowed height of the LEM above the S-IVB for adapter design.
MSC Director Robert R. Gilruth reported to the MSF Management Council that the LEM landing gear design freeze was now scheduled for August 31. Grumman had originally proposed a LEM configuration with five fixed legs, but LEM changes had made this concept impractical. The weight and overall height of the LEM had increased, the center of gravity had been moved upward, the LEM stability analysis had expanded to cover a wider range of landing conditions, the cruciform descent stage had been selected, and the interpretation of the lunar model had been revised. These changes necessitated a larger gear diameter than at first proposed. This, in turn, required deployable rather than fixed legs so the larger gear could be stored in the Saturn V adapter. MSC had therefore adopted a four-legged deployable gear, which was lighter and more reliable than the five-legged configuration.
Grumman built a full-scale cardboard model of the LEM to aid in studying problems of cockpit geometry, specifically the arrangement of display panels. This mockup was reviewed by MSC astronauts and the layout of the cockpit was revised according to some of their suggestions.
Also Grumman reported that a preliminary analysis showed the reaction control system plume heating of the LEM landing gear was not a severe problem. [This difficulty had been greatly alleviated by the change from five to four landing legs on the vehicle.
MSC began a study to define the stability limits of a 457-centimeter (180inch) radius LEM gear configuration. The study, in two phases, sought to examine factors affecting stability (such as lunar slope, touchdown velocity and direction, and the effects of soil mechanics) in direct support of the one-sixth model and full-scale drop test programs and to complete definition of landing capabilities of the LEM.
At a LEM Mechanical Systems Meeting in Houston, Grumman and MSC agreed upon a preliminary configuration freeze for the LEM-adapter arrangement. The adapter would be a truncated cone, 876 centimeters (345 inches) long. The LEM would be mounted inside the adapter by means of the outrigger trusses on the spacecraft's landing gear. This configuration provided ample clearance for the spacecraft, both top and bottom (i.e., between the service propulsion engine bell and the instrument unit of the S-IVB).
At this same meeting, Grumman presented a comparison of radially and laterally folded landing gears (both of 457-centimeter [180-inch] radius). The radial-fold configuration, MSC reported, promised a weight savings of 22-2 kilograms (49 pounds). MSC approved the concept, with an 876-centimeter (345-inch) adapter. Further, an adapter of that length would accommodate a larger, lateral fold gear (508 centimeters [200 inches]), if necessary. During the next several weeks, Grumman studied a variety of gear arrangements (sizes, means of deployment, stability, and even a "bending" gear). At a subsequent LEM Mechanical Systems Meeting, on November 10, Grumman presented data (design, performance, and weight) on several other four-legged gear arrangements - a 457-centimeter (180-inch), radial fold "tripod" gear (i.e., attached to the vehicle by three struts), and 406.4-centimeter (160-inch) and 457-centimeter (180-inch) cantilevered gears. As it turned out, the 406.4-centimeter (160-inch) cantilevered gear, while still meeting requirements demanded in the work statement, in several respects was more stable than the larger tripod gear. In addition to being considerably lighter, the cantilevered design offered several added advantages:
Because OMSF had requested OSSA to provide lunar surface microrelief and bearing strength data to support LEM landing site selection and to permit LEM landing-gear design validation, the Ad Hoc Working Group on Follow-On Surveyor Instrumentation met at NASA Headquarters. Attending were Chairman Verne C. Fryklund, Clark Goodman, Martin Swetnick, and Paul Brockman of the NASA Office of Space Sciences and Applications; Harry Hess and George Derbyshire of the National Acadamy of Sciences; Dennis James of Bellcomm (for OMSF); and Milton Beilock of the Jet Propulsion Laboratory (JPL). The group proposed "a fresh look at the problem of instrumenting payloads of Surveyor spacecraft that may follow the currently approved developmental and operational flights, so that these spacecraft will be able to determine that a particular lunar site is suitable for an Apollo landing." The study was assigned to JPL.
Bendix Products Aerospace Division was awarded a 99973 contract by MSC to study crushable aluminum honeycomb, a lightweight, almost non-elastic, shock-absorbing material for LEM landing gears. Bendix would test the honeycomb structures in a simulated lunar environment.
NASA conducted a formal review of the LEM mockup M-5 at the Grumman factory. This inspection was intended to affirm that the M-5 configuration reflected all design requirements and to definitize the LEM configuration. Members of the Mockup Review Board were Chairman Owen E. Maynard, Chief, Systems Engineering Division, ASPO; R. W. Carbee, LEM Subsystem Project Engineer, Grumman; Maxime A. Faget, Assistant Director for Engineering and Development, MSC; Thomas J. Kelly, LEM Project Engineer, Grumman; Christopher C. Kraft, Jr. (represented by Sigurd A. Sjoberg), Assistant Director for Flight Operations, MSC; Owen G. Morris, Chief, Reliability and Quality Assurance Division, ASPO; William F. Rector III, LEM Project Officer, ASPO; and Donald K. Slayton, Assistant Director for Flight Crew Operations, MSC.
The astronauts' review was held on October 5 and 6. It included demonstrations of entering and getting out of the LEM, techniques for climbing and descending the ladder, and crew mobility inside the spacecraft. The general inspection was held on the 7th and the Review Board met on the 8th. Those attending the review used request for change (RFC) forms to propose spacecraft design alterations. Before submission to the Board, these requests were discussed by contractor personnel and NASA coordinators to assess their effect upon system design, interfaces, weight, and reliability.
The inspection categories were crew provisions; controls, displays, and lighting; the stabilization and control system and the guidance and navigation radar; electrical power; propulsion (ascent, descent, reaction control system, and pyrotechnics ; power generation cryogenic storage and fuel cell assemblies ; environmental control; communications and instrumentation; structures and landing gear; scientific equipment; and reliability and quality' control. A total of 148 RFCs were submitted. Most were aimed at enhancing the spacecraft's operational capability; considerable attention also was given to quality and reliability and to ground checkout of various systems. No major redesigns of the configuration were suggested.
As a result of this review, the Board recommended that Grumman take immediate action on those RFC's which it had approved. Further, the LEM contractor and MSC should promptly investigate those items which the Board had assigned for further study. On the basis of the revised M-5 configuration, Grumman could proceed with LEM development and qualification. This updated mockup would be the basis for tooling and fabrication of the initial hardware as well.
To ensure that the redesigned landing gear on the resized LEM would be consistent with earlier criteria, MSC sent to Grumman revisions to those design criteria:
From MSC, Grumman received updated criteria to be used in the design of the LEM's landing gear. The gear must be designed to absorb completely the landing impact; it must also provide adequate stability for the vehicle under varying surface conditions, which were spelled out in precise detail.) Maximum conditions that MSC anticipated at touchdown were:
vertical velocity - 3.05 m (10 ft) per sec
horizontal velocity - 1.22 m (4 ft) per sec
pitch - 3 degrees
roll - 3 degrees
yaw - random
attitude rates - 3 degrees per sec
At touchdown, all engines (descent and reaction control would be off. "It must be recognized," MSC emphasized, "that the vertical and horizontal velocity values . . . are also constraints on the flight control system."
In response to MSC's new criteria for the landing gear of the LEM, Grumman representatives met with Center officials in Houston to revise the design. Grumman had formulated a concept for a 419-cm (165-in) radius, cantilever-type configuration, In analyzing its performance, Grumman and Structures and Mechanics Division (SMD) engineers, working separately, had reached the same conclusion: namely, that it did not provide sufficient stability nor did it absorb enough of the landing impact. Both parties to this meeting agreed that the gear's performance could be improved by redesigning the foot pads and beefing up the gear struts. Grumman was modifying other parts of the spacecraft's undercarriage accordingly.
At the same time, Grumman advised MSC that it considered impractical a contrivance to simulate lunar gravity in the drop program for test Mockup 5. Grumman put forth another idea: use a full-sized LEM, the company said, but one weighing only one-sixth as much as a flight-ready vehicle. SMD officials were evaluating this latest idea, while they were reviewing the entire TM-5 program.
Evaluations of the three-foot probes on the LEM landing gear showed that the task of shutting off the engine prior to actual touchdown was even more difficult than controlling the vehicle's rate of descent. During simulated landings, about 70 percent of the time the spacecraft was less than 0.3 m (1 ft) high when shutdown came; on 20 percent of the runs, the engine was still burning at touchdown. Some change, either in switch location or in procedure, thus appeared necessary to shorten the delay between contact light and engine cutoff (an average of 0.7 sec).
Louis Walter, Goddard Space Flight Center geochemist, reported that his research with tektites indicated the lunar surface may be sandlike. Waiter had discovered the presence of coesite in tektites, believed to be particles of the moon sent into space when meteorites impact the lunar surface. Coesite, also found at known meteorite craters, is a form of silicon dioxide - a major constituent of sand - produced under high pressure. "If we accept the lunar origin of tektites," Walter said, "this would prove or indicate that the parent material on the moon is something like the welded tuft that we find in Yellowstone Park, Iceland, New Zealand, and elsewhere." Welded tuft was said to have some of the qualities of beach sand.
MSC's Structures and Mechanics Division was conducting studies of lunar landing conditions. In one study, mathematical data concerning the lunar surface, LEM descent velocity, and physical properties of LEM landing gear and engine skirt were compiled. A computer was programmed with these data, producing images on a video screen, allowing engineers to review hypothetical landings in slow motion.
In another study, a one-sixth scale model of the LEM landing gear was dropped from several feet to a platform which could be adjusted to different slopes. Impact data, gross stability, acceleration, and stroke of the landing gear were recorded. Although the platform landing surface could not duplicate the lunar surface as well as the computer, the drop could verify data developed in the computer program. The results of these studies would aid in establishing ground rules for lunar landings.
An evaluation was made of the feasibility of utilizing a probe-actuated descent engine cutoff light during the LEM lunar touchdown maneuver. The purpose of the light, to be actuated by a probe extending 0.9 m (3 ft) beyond the landing gear pads, was to provide an engine cutoff signal for display to the pilot. Results of the study indicated at least 20 percent of the pilots failed to have the descent engine cut off at the time of lunar touchdown. The high percentage of engine-on landings was attributed to
After further design studies following the M-5 mockup review (October 5-8, 1964), Grumman reconfigured the boarding ladder on the forward gear leg of the LEM. The structure was flattened, to fit closer to the strut. Two stirrup-type steps were being added to ease stepping from the top rung to the platform or "porch" in front of the hatch.
William F. Rector, the LEM Project Officer in ASPO, replied to Grumman's weight reduction study (submitted to MSC on December 15, 1964). Rector approved a number of the manufacturer's suggestions:
Apollo Program Director Samuel C. Phillips told ASPO Manager Joseph F. Shea that Bellcomm, Inc., was conducting a systems engineering study of lunar landing dynamics to determine "functional compatibility of the navigation, guidance, control, crew, and landing gear systems involved in Apollo lunar landing." Phillips asked that he be advised of any specific assignments in these areas which would prove useful in support of the ASPO operation.
Shea replied, "We are currently evaluating the LEM lunar landing system with the Apollo contractors and the NASA Centers. We believe that the landing problem is being covered adequately by ourselves and these contractors." Shea added that a meeting would be held at Grumman April 21 and 22 to determine if there were any deficiencies in the program, and that he would be pleased to have Bellcomm attend the meeting and later make comments and recommendations.
Grumman and MSC engineers discussed the effect of landing impacts on the structure of the LEM. Based on analyses of critical loading conditions, Grumman reported that the present configuration was inadequate. Several possible solutions were being studied jointly by Grumman and the Structures and Mechanics Division (SMD):
Also Grumman representatives summarized the company's study on the design of the footpads. They recommended that, rather than adopting a stroking-type design, the current rigid footpad should be modified. The modification, they said, would improve performance as much as would the stroking design, without entailing the latter's increased weight and complexity and lowered reliability. SMD was evaluating Grumman's recommendations.
MSC completed contract negotiations with Westinghouse Electric Company on gear for the LEM's television camera (cables and connectors, stowage containers, and camera mockups). Because of technical requirements, the idea of using the same cable in both spacecraft was abandoned.
MSC completed a cursory analysis of LEM landing gear load-stroke requirements at touchdown velocities of 2.43 m (8 ft) per sec vertical and 1.22 m (4 ft) per sec horizontal. This study was conducted to determine the lowest crush loads at 8-4 velocity to which the gear could be designed and still meet its landing performance requirements.
William A. Lee, ASPO, pointed out to the MSC Thermo-Structures Branch that Grumman was engaged in a strenuous weight reduction effort and that, when feasible, MSC should accept the proposed changes. In the area of thermal control, Grumman was investigating the use of etched aluminum surfaces to replace thermal paint. It was expected that the change was feasible and that approximately 11 kg (24 lbs) of inert weight would be saved on each stage of the LEM. In addition, Grumman was investigating the applicability of this technique to the landing gear components.
Grumman was also studying substitution of an aluminum-mylar nonrigid outer heatshield with plastic standoffs for current rigid ascent and descent heatshields. The potential inert weight saving would be about 84 kg (185 lbs). Lee requested that Thermo-Structures Branch stay in close contact with these developments.
Maj. Gen. Samuel C. Phillips, NASA Apollo Program Director, approved the deletion of the LEM TM-5 from the ground test program. He requested that MSC consider the following recommendations:
The LEM landing gear subsystem was reviewed during the LEM Critical Design Review at MSC and Grumman. The review disclosed no major design inadequacies of the landing gear. The review included: lunar landing performance, structural and mechanical design, structural and thermal analysis, overall subsystem test program including results of tests to date, and conformance of landing gear design to LEM specifications.
Handling and installation responsibilities for the LM descent stage scientific equipment (SEQ) were defined in a letter from MSC to Grumman Aircraft Engineering Corp. The descent stage SEQ was composed of three basic packages:
Donald K. Slayton said there was some question about including extravehicular activity on the AS-503 mission, but he felt that, to make a maximum contribution to the lunar mission, one period of EVA should be included. Slayton pointed out that during the coast period (simulating lunar orbit) in the current flight plan the EVA opportunity appeared best between hour 90 and hour 100. Two primary propulsion system firings would have been accomplished and the descent stage of the LM would still be attached.
Slayton specified that EVA should consist of a crewman exiting through the LM forward hatch and making a thorough orbital check of the LM before reentering through the same hatch. He said EVA on AS-503 would provide:
C. H. Bolender, ASPO Manager for the lunar module, wrote Joseph G. Gavin, Jr., Grumman LM Program Director, that recent LM weights and weight growth trends during the past several months established the need to identify actions that would reduce weight and preclude future weight growth. He pointed out that the Configuration Control Board (CCB) at MSC had emphasized such actions, while recognizing the specific weight increases associated with design change actions resulting from the AS-204 accident. Several other design corrections or improvements had been implemented, such as increased plume protection, ascent engine reflection protection, descent stage upper-deck structural repair, and landing gear shielding. Bolender told Gavin, "We cannot afford to exercise ultraconservatism as an expedient to problem solving. The modification of the descent stage skin panels may be a case in point. . . . We have already asked that in consideration of minimum weight design, you reassess your recommendation to change to a uniform panel thickness." He requested that the objectives of the recent Super Weight Improvement program (a weight saving "tool" employed by Grumman) be reiterated in design activity and that weight reduction suggestions be solicited and evaluated for implementation. Bolender requested a biweekly review of weight reduction candidate changes and told Gavin he was asking Systems Engineering Division to maintain close coordination with Grumman and to report progress of the weight reduction and control activity at the regular CCB meetings.
Grumman President L. J. Evans wrote ASPO Manager George M. Low stating his agreement with NASA's decision to forego a second unmanned LM flight using LM-2. (Grumman's new position - the company had earlier strongly urged such a second flight - was reached after discussions with Low and LM Manager G. H. Bolender at the end of January and after flight data was presented at the February 6 meeting of the OMSF Management Council.) Although the decision was not irreversible, being subject to further investigations by both contractor and customer, both sides now were geared for a manned flight on the next LM mission. However, Evans cited several spacecraft functions not covered during the LM-1 flight that would have to be demonstrated before attempting a lunar mission, notably control by the primary navigation and guidance system of the descent propulsion system burn as well as control of stage separation and firing of the ascent propulsion system. To demonstrate these functions fully, he said, some modifications in mission plans for the next two manned flights might be necessary.
About 30 small aluminum brackets and fittings were replaced or reinforced in Apollo lunar modules to rule out the possibility of cracking from stress corrosion. Stress corrosion monitoring began in December 1967 when small cracks were discovered in LM landing gear struts. Nine fittings were replaced in LM-3, scheduled for the Apollo 9 mission, and six fittings were repaired in LM-4, scheduled for the Apollo 10 flight. About 25 fittings were being replaced on LM-5 and LM-6 and 8 fittings on each of these vehicles were being reinforced.