Lunar orbit rendezvous
Lunar orbit rendezvous (LOR) is a process for landing humans on the Moon and returning them to Earth. It was utilized for the Apollo program missions in the 1960s and 1970s. In a LOR mission, a main spacecraft and a smaller lunar lander travel to lunar orbit. The lunar lander then independently descends to the surface of the Moon, while the main spacecraft remains in lunar orbit. After completion of the mission there, the lander returns to lunar orbit to rendezvous and re-dock with the main spacecraft, then is discarded after transfer of crew and payload. Only the main spacecraft returns to Earth.[1]
Lunar orbit rendezvous was first proposed in 1919 by Ukrainian engineer Yuri Kondratyuk,[2] as the most economical way of sending a human on a round-trip journey to the Moon.[3]
The most famous example involved Project Apollo's
Advantages and disadvantages
Advantages
The main advantage of LOR is the spacecraft payload saving, due to the fact that the propellant necessary to return from lunar orbit back to Earth need not be carried as dead weight down to the Moon and back into lunar orbit. This has a multiplicative effect, because each pound of "dead weight" propellant used later has to be propelled by more propellant sooner, and also because increased propellant requires increased tankage weight. The resultant weight increase would also require more thrust for lunar landing, which means larger and heavier engines.[4]
Another advantage is that the lunar lander can be designed for just that purpose, rather than requiring the main spacecraft to also be made suitable for a lunar landing. Finally, the second set of life support systems that the lunar lander requires can serve as a backup for the systems in the main spacecraft.
Disadvantage
Lunar-orbit rendezvous was considered risky in 1962, because space rendezvous had not been achieved, even in Earth orbit. If the LM could not reach the CSM, two astronauts would be stranded with no way to get back to Earth or survive re-entry into the atmosphere. Rendezvous was successfully demonstrated in 1965 and 1966 on six Project Gemini missions[Note 1] with the aid of radar and on-board computers. It was also successfully done each of the eight times it was tried on Apollo missions.[Note 2]
Apollo Mission mode selection
When the Apollo Moon landing program was started in 1961, it was assumed that the three-man command and service module combination (CSM) would be used for takeoff from the lunar surface, and return to Earth. It would therefore have to be landed on the Moon by a larger rocket stage with landing gear legs, resulting in a very large spacecraft (in excess of 100,000 pounds (45,000 kg)) to be sent to the Moon.
If this were done by
Besides requiring less payload, the ability to use a lunar lander designed just for that purpose was another advantage of the LOR approach. The LEM's design gave the astronauts a clear view of their landing site through observation windows approximately 4.6 metres (15 ft) above the surface, as opposed to being on their backs in a Command Module lander, at least 40 or 50 feet (12 or 15 m) above the surface, able to see it only through a television screen.
Developing the LEM as a second crewed vehicle provided the further advantage of redundant critical systems (electrical power, life support, and propulsion), which enabled it to be used as a "lifeboat" to keep the astronauts alive and get them home safely in the event of a critical CSM system failure. This was envisioned as a contingency, but not made a part of the LEM specifications. As it turned out, this capability proved invaluable in 1970, saving the lives of the Apollo 13 astronauts when an oxygen tank explosion disabled the Service Module.
Advocacy
Dr. John Houbolt would not let the advantages of LOR be ignored. As a member of Lunar Mission Steering Group, Houbolt had been studying various technical aspects of space rendezvous since 1959 and was convinced, like several others at Langley Research Center, that LOR was not only the most feasible way to make it to the Moon before the decade was out, it was the only way. He had reported his findings to NASA on various occasions but felt strongly that the internal task forces (to which he made presentations) were following arbitrarily established "ground rules." According to Houbolt, these ground rules were constraining NASA's thinking about the lunar mission—and causing LOR to be ruled out before it was fairly considered.[9]
In November 1961, Houbolt took the bold step of skipping proper channels and writing a nine-page private letter directly to associate administrator
It took two weeks for Seamans to reply to Houbolt's letter. The associate administrator agreed that "it would be extremely harmful to our organization and to the country if our qualified staff were unduly limited by restrictive guidelines." He assured Houbolt that NASA would in the future be paying more attention to LOR than it had up to this time.
In the following months, NASA did just that, and to the surprise of many both inside and outside the agency, LOR quickly became the front runner. Several factors decided the issue in its favor. First, there was growing disenchantment with the idea of direct ascent due to the time and money it was going to take to develop a 50-foot (15 m) diameter Nova rocket, compared to the 33-foot (10 m) diameter Saturn V. Second, there was increasing technical apprehension over how the relatively large spacecraft demanded by Earth-orbit rendezvous would be able to maneuver to a soft landing on the Moon. As one NASA engineer who changed his mind explained:
The business of eyeballing that thing down to the Moon really didn't have a satisfactory answer. The best thing about LOR was that it allowed us to build a separate vehicle for landing.
The first major group to change its opinion in favor of LOR was
Other plans using LOR
- The proposed Soviet lunar landing plan, using the N1 rocket, LK Lander and Soyuz 7K-LOK, would have used a similar LOR mission profile.
- The EORand LOR for Moon landing.
- The Artemis program plans to use LOR to land humans on the lunar south pole region.
In popular culture
Episode 5 of the 1998
See also
- Lunar orbit insertion
- Trans-lunar injection
- Trans-Earth injection
Notes
References
This article incorporates public domain material from websites or documents of the
Citations
- YouTube
- ^ Harvey (2007), pp. 6–7.
- ^ Wilford (1969), pp. 41–48.
- ^ Reeves (2005).
- ^ a b Godwin (2019).
- ^ Brooks (1979).
- ^ Gainor (2001), pp. 62–66.
- ^ Scheer, Julian W. (Assistant Administrator for Public Affairs, NASA). Memorandum from Project Designation Committee, June 9, 1966.
- ^ a b "The Rendezvous That Was Almost Missed: Lunar Orbit Rendezvous and the Apollo Program – NASA". www.nasa.gov. December 1992. Fact Sheet NF175. Archived from the original on 2020-12-23. Retrieved 2017-03-20.
- ^ Tennant (2009).
- ^ Hansen (1995).
- ^ Witkin (1962).
- ^ NASA (1962), p. 1.
- ^ Nelson (2009), pp. 209–210.
Bibliography
- Bergin, Chris (2013-01-03). "Golden Spike contract Northrop Grumman for Lunar Lander". Nasaspaceflight.com. London. Archived from the original on 2013-01-06. Retrieved 2013-01-04.
- Brooks; Grimwood; Swenson (1979). "Chariots for Apollo: A History of Manned Lunar Spacecraft". NASA. Archived from the original on 2004-11-18. Retrieved 2007-04-27.
- Gainor, Chris (2001). Arrows to the Moon. Burlington, Ontario: Apogee Books. ISBN 978-1-896522-83-8.
- Godwin, Robert (2019). Manned Lunar Landing And Return. Apogee Books. ISBN 978-1-926-83742-0.
- Hansen, James R. (1995). Enchanted Rendezvous: John C. Houbolt and the Genesis of the Lunar-Orbit Rendezvous Concept (PDF). Monographs in Aerospace History Series #4. Washington, D.C.: NASA. NASA-TM-111236.
- Harvey, Brian (2007). Russian Planetary Exploration: History, Development, Legacy and Prospects. New York: Springer. ISBN 978-0-387-46343-8.
- Laxman, Srinivas (2012-03-21). "China's Unmanned Moon Mission To Bring Back Lunar Soil To Earth". Singapore. Archived from the original on 2012-03-24. Retrieved 2013-01-04.
- ISBN 978-0-671-70625-8.
- NASA (1962). Lunar orbit rendezvous: news conference on Apollo plans at NASA headquarters on July 11, 1962. Washington, D.C.: NASA.
- Nelson, Craig (2009). Rocket Men: The Epic Story of the First Men on the Moon. New York: Viking. ISBN 978-0-670-02103-1.
- Reeves, David M.; Scher, Michael D.; Wilhite, Dr., Alan W.; Stanley, Dr., Douglas O. (2005). "The Apollo Lunar Orbit Rendezvous Architecture Decision Revisited" (PDF). National Institute of Aerospace, Georgia Tech. Archived from the original (PDF) on 2014-10-27. Retrieved 2012-06-08.
- Tennant, Diane (2009-11-15). "Forgotten engineer was key to space race success". HamptonRoads/PilotOnline. Archived from the original on 2010-11-18. Retrieved 2010-09-01.
- Witkin, Richard (1962-07-04). "Lunar Orbital Rendezvous: New Flight Plan to Moon Favored". The Globe and Mail. Toronto. New York Times Service. p. 1.
- Wilford, John (1969). We Reach the Moon; the New York Times Story of Man's Greatest Adventure. New York: Bantam Paperbacks.
- Woods, W. David (2008). How Apollo Flew to the Moon. New York: Springer. pp. 10–12. ISBN 978-0-387-71675-6.
External links