Apollo Mission mode selection Lunar orbit rendezvous

apollo 11 lunar module rendezvousing command module in lunar orbit

when apollo moon landing program started in 1961, assumed three-man command , service module combination (csm) used takeoff lunar surface, , return earth. therefore have landed on moon larger rocket stage landing gear legs, resulting in large spacecraft (in excess of 100,000 pounds (45,000 kg)) sent moon.

if done direct ascent (on single launch vehicle), rocket required have extremely large, in nova class. alternative have been earth orbit rendezvous, in 2 or more rockets in saturn class launch parts of complete spacecraft, rendezvous in earth orbit before departing moon. possibly include separately launched earth departure stage, or require on-orbit refueling of empty departure stage.

tom dolan proposed alternative of lunar orbit rendezvous, had been studied , promoted jim chamberlin , owen maynard @ space task group in 1960 apollo feasibility studies. mode allowed single saturn v launch csm moon smaller lunar excursion module (lem). when combined spacecraft reaches lunar orbit, 1 of 3 astronauts remains csm, while other 2 enter lem, undock , descend surface of moon. use ascent stage of lem rejoin csm in lunar orbit, discard lem , use csm return earth. method brought attention of nasa associate administrator robert seamans langley research center engineer john c. houbolt, led team develop it.

besides requiring less payload, ability use lunar lander designed purpose advantage of lor approach. lem s design gave astronauts clear view of landing site through observation windows approximately 15 feet (4.6 m) above surface, opposed being on backs in command module lander, @ least 40 or 50 feet (12 or 15 m) above surface, able see through television screen.

developing lem second manned vehicle provided further advantage of redundant critical systems (electrical power, life support, , propulsion), enabled used lifeboat keep astronauts alive , them home safely in event of critical csm system failure. envisioned contingency, not made part of lem specifications. turned out, capability proved invaluable in 1970, when such critical failure occurred on apollo 13 mission when oxygen tank failure disabled service module.

advocacy

john houbolt explains lunar orbit rendezvous

dr. john houbolt not let advantages of lor ignored. member of lunar mission steering group, houbolt had been studying various technical aspects of space rendezvous since 1959 , convinced, several others @ langley research center, lor not feasible way make moon before decade out, way. had reported findings nasa on various occasions felt internal task forces (to made presentations) following arbitrarily established ground rules. according houbolt, these ground rules constraining nasa s thinking lunar mission—and causing lor ruled out before considered.

in november 1961, houbolt took bold step of skipping proper channels , writing private letter, 9 pages long, directly robert c. seamans, associate administrator. voice in wilderness, houbolt protested lor s exclusion. want go moon or not? langley engineer asked. why nova, ponderous size accepted, , why less grandiose scheme involving rendezvous ostracized or put on defensive? realize contacting in manner unorthodox, houbolt admitted, issues @ stake crucial enough unusual course warranted.

it took 2 weeks seamans reply houbolt s extraordinary letter. associate administrator agreed extremely harmful our organization , country if our qualified staff unduly limited restrictive guidelines. assured houbolt nasa in future paying more attention lor had time.

in following months, nasa did that, , surprise of many both inside , outside agency, dark horse candidate, lor, became front runner. several factors decided issue in favor. first, there growing disenchantment idea of direct ascent due time , money going take develop 50-foot (15 m) diameter nova rocket, compared 33-foot (10 m) diameter saturn v . second, there increasing technical apprehension on how relatively large spacecraft demanded earth-orbit rendezvous able maneuver soft landing on moon. 1 nasa engineer changed mind explained:

the business of eyeballing thing down moon didn t have satisfactory answer. best thing lor allowed build separate vehicle landing.

the first major group break camp in favor of lor robert gilruth s space task group, still located @ langley move houston. second come on von braun team @ marshall space flight center in huntsville, alabama. these 2 powerful groups of converts, along original true believers @ langley, persuaded key officials @ nasa headquarters, notably administrator james webb, had been holding out direct ascent, lor way land on moon 1969. key players inside nasa lined behind concept, webb approved lor in july 1962. decision officially announced @ press conference on july 11, 1962. president kennedy s science adviser, jerome wiesner, remained firmly opposed lor.

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