At some point in my life I learned that anything left in lunar orbit either (1) crashed into the moon (due to its non uniform gravity) or (2) fell into heliocentric orbit.

But recently a youtube video entitled Is Apollo 11’s Lunar Module Still In Orbit Around The Moon 52 Years Later? suggested that this might not be entirely true…

Frozen vs. Unstable Lunar Orbits

The article Bizarre Lunar Orbits describes how “the Moon is extraordinarily lumpy, gravitationally speaking.” Some of the flat areas of the moon made up of solidified lava (aka maria) contain mass concentrations (aka mascons). These mascons cause the local gravity to be much stronger than the remainder of the lunar surface.

The article says that the gravity from such a mascon is so great that it would be measurable by an astronaut standing on the edge of a maria:

If you were standing at the edge of one of the maria, a plumb bob would hang about a third of a degree off vertical, pointing toward the mascon.

The consequence of these mascons is that most low lunar orbits are 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.

This is because the orbits become more eccentric with time. As the perilune (i.e. point of an elliptical lunar orbit where the distance between the satellite and the Moon is at its minimum) gets lower and lower, the orbiting object eventually collides with the surface of the Moon.

But not all low lunar orbits share this problem:

There are actually a number of ‘frozen orbits’ where a spacecraft can stay in a low lunar orbit indefinitely.

Fates of the Apollo Lunar Module Ascent Stages

The NASA webpage entitled Current locations of the Apollo Command Module Capsules (and Lunar Module crash sites) describes the fates of the Apollo Lunar Modules.

The ascent stage of the Apollo 10 Lunar Module Snoopy was jettisoned into a heliocentric orbit. The recently discovered Earth-crossing asteroid 2018 AV2 is believed to be this ascent stage with 98% certainty.

The ascent stages for Apollo 12, 14, 15, and 17 were all deliberately crashed into the moon to provide data for the seismometers that were left on the surface.

Apollo 13’s ascent stage burned up in Earth’s atmosphere (it had been used as a lifeboat due to a malfunction in the Command Module which ultimately aborted the mission).

The webpage says that Apollo 16’s Lunar Module “Orion:”

Released 24 April 1972, loss of attitude control made targeted impact impossible. Impact site unknown.

Of Apollo 11’s Lunar Module, it says:

Jettisoned from the Command Module on 21 July 1969 at 23:41 UT (7:41 PM EDT). Impact site unknown.

Apollo 11’s Lunar Module Ascent Stage

The youtube video I cite is based on a paper entitled Long-term Orbit Stability of the Apollo 11 Eagle Lunar Module Ascent Stage authored by a James Meador that demonstrates the possibility that the ascent stage is still orbiting the moon.

The video describes how James Meador decided that he would look for the impact site of the Apollo 11 ascent module.

Meador used software called General Mission Analysis Tool (aka GMAT) to determine what parts of the Moon the ascent module was likely to have impacted. This is free software provided by NASA that allows one to design and simulate missions.

The Gravity Recovery and Interior Laboratory mission (aka GRAIL) provided high resolution maps of the Moon’s gravitational field.

The New Atlas article entitled The Apollo 11 Ascent Stage may still be orbiting the Moon described Meador’s process:

Using the GRAIL gravity model and the General Mission Analysis Tool (GMAT) simulator, Meador expected to find the LM’s orbit destabilizing very quickly. What he found – and was verified by a third party using different methods – was that the Ascent Stage had a feedback mechanism that caused the orbit to stabilize itself over a period of every 24 days. When he ran the simulation forward, the orbit remained stable until the present day.

So, maybe the ascent stage of Eagle is still in orbit?

Potential Visibility of the Apollo 11 Ascent Module

The Discover magazine article New Evidence Suggests Apollo 11’s Lunar Ascent Module Could Still Be Orbiting the Moon suggests that:

the spacecraft might still be visible from Earth to anybody willing to look hard enough to find it.

The article points out that the spacecraft may have succumbed to other problems, such as an explosion due to unused fuel, but:

Back in 2009, the Indian Space Research Organization lost contact with the Chandrayaan-1 lunar orbiter, a cube-shaped spacecraft less than half the size of Eagle.

And yet in 2016, scientists at NASA’s Jet Propulsion Laboratory in Pasadena found it again using radar aimed at a point in space just above the lunar surface where the spacecraft was expected to pass.

Meador suggests that a similar technique could find Eagle

Questions:

  1. What do you think? Is it still in orbit? How cool would that be?

  2. Apollo 16’s Lunar Module is also listed as “impact site unknown.” Wikipedia says of the Apollo 16 LM ascent stage, “…ascent stage left in lunar orbit, crashed on Moon.” The Wikipedia Apollo 16 page also says: “The lunar module ascent stage separated from the CSM on April 24, 1972 but NASA lost control of it. It orbited the Moon for about a year. Its impact site remains unknown.” Could James Meador’s analysis of the Apollo 11 LM ascent stage also apply to the Apollo 16 LM ascent stage? I.e. could it still be orbiting the moon?

Links:

Is Apollo 11’s Lunar Module Still In Orbit Around The Moon 52 Years Later? youtube video:

https://youtu.be/dBHbLV7xEhc

The Apollo 11 Ascent Stage may still be orbiting the Moon article:

https://newatlas.com/space/apollo-11-ascent-stage-orbiting-moon/

New Evidence Suggests Apollo 11’s Lunar Ascent Module Could Still Be Orbiting the Moon article:

https://www.discovermagazine.com/technology/new-evidence-suggests-apollo-11s-lunar-ascent-module-could-still-be-orbiting

Part of the Apollo 11 Spacecraft May Still Be Orbiting the Moon article: https://www.smithsonianmag.com/smart-news/part-apollo-11-may-still-be-orbiting-moon-180978352/

Apollo 11 Lunar Module / EASEP NASA page:

https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1969-059C

Bizarre Lunar Orbits NASA article:

https://science.nasa.gov/science-news/science-at-nasa/2006/06nov_loworbit

Current locations of the Apollo Command Module Capsules (and Lunar Module crash sites) NASA page:

https://nssdc.gsfc.nasa.gov/planetary/lunar/apolloloc.html

A New Paradigm for Lunar Orbits article:

https://phys.org/news/2006-12-paradigm-lunar-orbits.html

Lunar Module Eagle wikipedia page:

https://en.wikipedia.org/wiki/Lunar_Module_Eagle

List of artificial objects on the Moon wikipedia page:

https://en.wikipedia.org/wiki/List_of_artificial_objects_on_the_Moon

Lunar frozen orbits wikipedia page:

https://en.wikipedia.org/wiki/Frozen_orbit#Lunar_frozen_orbits

GMAT - General Mission Analysis Tool

https://sourceforge.net/projects/gmat/

Scripts and other files relevant to simulating the Apollo 11 Lunar Module orbit github page:

https://github.com/RogerTwank/Eagle