Leonard David's INSIDE OUTER SPACE

A high-definition image of the Mars Australe lava plain on the Moon taken by Japan’s Kaguya lunar orbiter in November 2007.
Credit: JAXA

There is increasing interest in that wayward SpaceX Falcon 9 upper stage and its impact on the Moon next month.

In 2015 the Falcon 9 placed the National Oceanic and Atmospheric Administration’s (NOAA) DSCOVR climate observatory around the L1 Lagrange point.

That’s one of five such gravitationally-stable points between Earth and the Sun. Having reached L1, the mission’s upper stage ended up pointed away from Earth into interplanetary space.

Artist’s impression of DSCOVR on the way to L1 atop its Falcon 9 upper stage in 2015.
Credit: SpaceX

“This rendered a deorbit burn to dispose of it in our planet’s atmosphere impractical, while the upper stage also lacked sufficient velocity to escape the Earth-Moon system. Instead it was left in a chaotic Sun-orbiting orbit near the two bodies,” according to the European Space Agency.

Regulatory regime

Human-made objects have intentionally impacted the Moon before, starting as early as the 1950s, including Apollo upper stages used to induce “moonquakes” for surface seismometers. The SpaceX upper stage slamming into the Moon marks “the first time that a human-made debris item unintentionally reaches our natural satellite,” ESA has pointed out.

Credit: ESA

“The upcoming Falcon 9 lunar impact illustrates well the need for a comprehensive regulatory regime in space, not only for the economically crucial orbits around Earth but also applying to the Moon,” says Holger Krag, Head of ESA’s Space Safety Program.

“For international spacefarers, no clear guidelines exist at the moment to regulate the disposal at end of life for spacecraft or spent upper stages sent to Lagrange points,” said ESA in a statement. “Potentially crashing into the Moon or returning and burning up in Earth’s atmosphere have so far been the most straightforward default options.”

Credit: Advanced Space/Michael Thompson

Credible forecasts

There are credible forecasts when the upper stage will strike the Moon: March 4 at 12:25:39 UTC at a point on the lunar far side near the equator. Follow-up observations should sharpen the accuracy of forecasts.

One such calculation comes from astrodynamics engineer, Michael Thompson, of Advanced Space in Westminster, Colorado. He’s generated a plot and visual to capture where the upper stage may crash.

Thompson built upon the work by Bill Gray of projectpluto.com who collects and aggregates optical observations on near Earth objects. It was Gray that discovered the crash course of the SpaceX upper stage.

ProjectPluto.com posts (a subset) of raw observations from users around the world​

Using these observations, Thompson performed his own orbit determination process in addition to the processes run by Bill Gray​.

The lunar far side as imaged by NASA’s Lunar Reconnaissance Orbiter using its LROC Wide Angle Camera.
Credit: NASA/Goddard/Arizona State University

Advanced Space generated predicts (and samples of uncertainty) currently showing an impact west of the Sea of Tranquility​, very similar to the predict generated by Bill Gray​.

Impact is near the lunar limb as viewed from Earth – most of the distribution lays slightly on the Moon’s far side​. Based on current data, the impact is not expected to be near any NASA Apollo or China lunar exploration sites.

Looking back to Earth from DSCOVR’s Falcon 9 upper stage on the way to L1.
Credit: SpaceX

Uncertainties: attitude, solar radiation pressure

Thompson notes that this upper stage impact may or may not be visible from Earth.

The center of the distribution is (9.31, -95.86), which is pretty far off from the current location of China’s Chang’e-4 lander/rover  (-45.46, 177.59) and much closer to the lunar limb than fully over on the far side.

But even with large uncertainties in the attitude of the spacecraft and the resulting uncertainties in the solar radiation pressure that can affect the upper stage, an impact much further south towards Chang’e-4 would be unlikely, Thompson adds.

The uncertainty will come down a good bit more once there are additional observations this month.

NASA’s Lunar Reconnaissance Orbiter (LRO).
Credit: NASA/GSFC

Assessing observations

“NASA’s Lunar Reconnaissance Orbiter (LRO) will not be in a position to observe the impact as it happens,” a NASA statement sent to Inside Outer Space explains.

“However, the mission team is assessing if observations can be made to any changes to the lunar environment associated with the impact and later identify the crater formed by the impact. This unique event presents an exciting research opportunity,” the NASA statement adds.

“Following the impact, the mission can use its [LRO] cameras to identify the impact site, comparing older images to images taken after the impact. The search for the impact crater will be challenging and might take weeks to months.”