Lunar orbit
In
Lunar orbit insertion (LOI) is an orbit insertion maneuver used to achieve lunar orbit.[1]
Low lunar orbit (LLO) is an orbit below 100 km (62 mi) altitude. These have a period of about 2 hours.[2] They are of particular interest in the exploration of the Moon, but suffer from gravitational perturbations that make most unstable, and leave only a few orbital trajectories possible for indefinite frozen orbits. These would be useful for long-term stays in LLO.[2]
Perturbation effects and low orbits
Most lunar low orbits, below 100 km (62 mi), are unstable.[2]
Gravitational anomalies slightly distorting the orbits of some Lunar Orbiters led to the discovery of mass concentrations (dubbed mascons) beneath the lunar surface caused by large impacting bodies at some remote time in the past.[2][3] These anomalies are large enough to cause a lunar orbit to change significantly over the course of several days. They can cause a plumb bob to hang about a third of a degree off vertical, pointing toward the mascon, and increase the force of gravity by one-half percent.[2] The Apollo 11 first manned landing mission employed the first attempt to correct for the perturbation effect (the frozen orbits were not known at that time). The parking orbit was "circularized" at 66 nautical miles (122 km; 76 mi) by 54 nautical miles (100 km; 62 mi), which was expected to become the nominal circular 60 nautical miles (110 km; 69 mi) when the LM made its return rendezvous with the CSM. But the effect was overestimated by a factor of two; at rendezvous, the orbit was calculated to be 63.2 nautical miles (117.0 km; 72.7 mi) by 56.8 nautical miles (105.2 km; 65.4 mi). [4]
Stable low orbits
Study of the mascons' effect on lunar spacecraft led to the discovery in 2001 of
Lunar high orbits
For lunar orbits with altitudes in the 500 to 20,000 km (310 to 12,430 mi) range, the gravity of Earth leads to orbit
Although the Moon's Hill sphere extends to a radius of 60,000 km (37,000 mi),[6] the gravity of Earth intervenes enough to make lunar orbits unstable at a distance of 690 km (430 mi).[7]
Orbits around Earth-Moon Lagrange points are options for stable lunar orbits, as with distant retrograde orbits, using two oppositional Lagrange points (L1 and L2), flying from one to the other around the Moon.
Relatively stable orbits above locations on the Moon are
Since 2022 (CAPSTONE) near-rectilinear halo orbits, using as well a Lagrange point, have been used and are planned to be employed by the Lunar Gateway.
Orbital transfer
There are three main ways to get to lunar orbit from Earth: direct transfer, low thrust transfer and low-energy transfer. These take 3–4 days, [word missing] months or 2.5–4 months respectively.[8]
History of missions to lunar orbit
First orbiters
The
Luna 10 became the first spacecraft to actually orbit the Moon and any extraterrestrial body in April 1966.[12] It studied micrometeoroid flux, and lunar environment until May 30, 1966.[12] A follow-on mission, Luna 11, was launched on August 24, 1966, and studied lunar gravitational anomalies, radiation and solar wind measurements.
The first United States spacecraft to orbit the Moon was
Crewed and later orbiters
The
See also
- Cislunar space
- List of orbits
- Orbital mechanics
- Distant retrograde orbit
- Near-rectilinear halo orbit
References
- ISBN 978-0-387-71675-6.
- ^ a b c d e f g
"Bizarre Lunar Orbits". NASA Science: Science News. NASA. 2006-11-06. Retrieved 2012-12-09.
Lunar mascons make most low lunar orbits unstable ... As a satellite passes 50 or 60 miles overhead, the mascons pull it forward, back, left, right, or down, the exact direction and magnitude of the tugging depends on the satellite's trajectory. Absent any periodic boosts from onboard rockets to correct the orbit, most satellites released into low lunar orbits (under about 60 miles or 100 km) will eventually crash into the Moon. ... [There are] a number of 'frozen orbits' where a spacecraft can stay in a low lunar orbit indefinitely. They occur at four inclinations: 27°, 50°, 76°, and 86° — the last one being nearly over the lunar poles. The orbit of the relatively long-lived
PFS-1had an inclination of 28°, which turned out to be close to the inclination of one of the frozen orbits—but poor PFS-2 was cursed with an inclination of only 11°. - ISSN 0019-1035.
- ^ "Apollo 11 Mission Report" (PDF). NASA. pp. 4–3 to 4–4.
- .
- NASA.gov. Greenbelt, MD: NASA Goddard Space Flight Center. Retrieved 23 July 2023.
- ^ "A New Paradigm for Lunar Orbits". Phys.org. 2006-12-01. Retrieved 2023-11-05.
- ^ The Aerospace Corporation (2023-07-20). "It's International Moon Day! Let's talk about Cislunar Space". Medium. Retrieved 2023-11-07.
- ^ Stein, Ben P. (August 23, 2011). "45 Years Ago: How the 1st Photo of Earth From the Moon Happened". Space.com. Retrieved October 7, 2020.
- ^ "Fifty Years Ago, This Photo Captured the First View of Earth From the Moon". August 23, 2016. Archived from the original on August 25, 2016.
- ^ a b c Wade, Mark. "Luna". Encyclopedia Astronautica. Archived from the original on 2012-01-11. Retrieved 2007-02-17.
- ^ a b Byers, Bruce K. (1976-12-14). "APPENDIX C [367-373] RECORD OF UNMANNED LUNAR PROBES, 1958-1968: Soviet Union". DESTINATION MOON: A History of the Lunar Orbiter Program. National Aeronautics and Space Administration. Archived from the original on 2021-01-26. Retrieved 2007-02-17.
- ^ a b Wade, Mark. "Lunar Orbiter". Encyclopedia Astronautica. Archived from the original on August 21, 2002. Retrieved 2007-02-17.
- ^ Byers, Bruce K. (1976-12-14). "CHAPTER IX: MISSIONS I, II, III: APOLLO SITE SEARCH AND VERIFICATION, The First Launch". DESTINATION MOON: A History of the Lunar Orbiter Program. National Aeronautics and Space Administration. Archived from the original on 2020-09-27. Retrieved 2007-02-17.
- ^ Jones, Eric M. (1976-12-14). "The First Lunar Landing". Apollo 11 Lunar Surface Journal. National Aeronautics and Space Administration. Retrieved 2014-11-09.