Credit: NASA/GSFC/Arizona State University

Late last year, sky watchers reported that a rocket body was heading towards a lunar collision, destined to make its demise on the Moon.

On March 4, 2022 that hardware smacked into the Moon near Hertzsprung crater.

Now thanks to the sharp-shooting NASA Lunar Reconnaissance Orbiter (LRO) spacecraft, the results of that grand slam have been spotted: a double crater roughly 92-feet (28 meters) wide in the longest dimension.

Double-dipping

“The double crater was unexpected and may indicate that the rocket body had large masses at each end,” reports Mark Robinson, the principal investigator for LRO’s Lunar Reconnaissance Orbiter Camera, or LROC, at Arizona State University in Tempe.

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

“Typically a spent rocket has mass concentrated at the motor end; the rest of the rocket stage mainly consists of an empty fuel tank. Since the origin of the rocket body remains uncertain, the double nature of the crater may help to indicate its identity,” Robinson adds.

No other rocket body impacts on the Moon created double craters.

Craters formed by impacts of the Apollo S-IVB stages: crater diameters range from 35 to 40 meters in the longest dimension.
Credit: NASA/GSFC/Arizona State University

 

Apollo upper stage craters

The four Apollo SIV-B craters that struck the Moon were somewhat irregular in outline (Apollos 13, 14, 15, 17) and were substantially larger than each of the double craters.

The maximum width of 95 feet (29 meters) of the double crater of the mystery rocket body was near that of the S-IVBs, Robinson reports.

 

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

Miss and hit predictions

First thought to be a SpaceX upper stage, it was later tagged by Bill Gray of Project Pluto as a leftover from China’s Chang’e 5-T1 lunar mission in 2014.

Gray says that before the actual March 4 impact he had computed a prediction for the impact location, as had the Jet Propulsion Laboratory. 

Those predictions differed by about 5 miles (8 kilometers) “which didn’t really surprise either off us,” Gray says in an email. “Their position was close enough to mine, and mine to theirs, to be consistent with the data we had.”

The actual impact location was uncertain, mainly because last observations were made about four weeks before impact. “After that, the object was too close to the Sun in the sky to be able to point a telescope at it.” Gray added. “The telescopic observations were of good quality and gave us an excellent idea of what the trajectory was at that time.”

Gray noted that the problem was that spacecraft and space junk are gently pushed by sunlight, in a way that depends on how the objects are oriented as they tumble end over end. It’s a small push, he said, but over the four weeks, observers knew it could push the object miles one way or the other,  in a poorly-determined direction. 

Credit: NASA

“It’s a bit like predicting where an empty trash bag will go in a windstorm. You know it’ll get blown downwind, but not exactly where it’ll go.”

Strange results

Indeed, the imaged impact crater was found 5 miles (8 kilometers) from where JPL put it and about 10 miles (16 kilometers) from where Gray put it.

“It is very difficult to be more accurate than JPL,” said Gray. “It’s a little further off than either of us had expected,  but not surprisingly so.”

Bottom line from Gray is that the object is pretty conclusively identified as the Chang’e 5-T1 booster.

“I’m a little puzzled by the double crater appearance. But I am in no way an expert on high-speed impacts,  except to know that they can have some very strange results,” Gray said.

The impact was about 15 degrees from being vertical, Gray added. “I vaguely recall reading about ‘twin craters’ being somewhat common on the Moon due to shallow-angle impacts. This wasn’t one. Still a puzzler.”

Strike Zone

The rocket body crater formed in a complex area (where ejecta from the Orientale basin event overlies the degraded northeast rim of Hertzsprung basin. Credit: NASA/GSFC/Arizona State University].

The LRO imagery of the strike zone has tossed up other discussion about this impact on the Moon.

Renu Malhotra is in the Department of Planetary Sciences at the University of Arizona in Tucson, reacting to the double crater might be the result of a rocket body having large masses at each end.

“Perhaps an alternative to the “large masses at each end” is that it is a single large mass that bounced and skipped, as in a low angle impact? This can be checked if the impact trajectory and impact velocity was computed already,” Malhotra said.

Upper stage details

According to Josh Hopkins, author of the International Reference Guide to Space Launch Systems, the object most credibly tied to this Moon impact is the upper stage from the Chang’e 5-T1 launch.

China’s CZ-3C GJ-II Y12 carrier rocket liftoff in 2014.
Credit: via Seger Yu

The Long March 3C booster’s third stage is about 41 feet (12.5 meters) long x 10 feet (3 meters) diameter, with an empty mass of probably around 2.5-3 tons. The upper stage has two YF-75 engines on the bottom, and a relatively stout vehicle equipment bay at the top with dense components like batteries and avionics boxes.

Hopkins said he doesn’t have a detailed mass breakdown but a reasonable estimate is that the engine bay could be 1,322 pounds to 1,763 pounds (600-800 kilograms) and the vehicle equipment bay could be a few hundred kilograms.

Oriented roughly sideways

“This double crater seems potentially consistent with a hypothesis that this upper stage impacted while oriented roughly sideways, with the mass concentrations on each end being about the right mass to create two craters of about the right size,” Hopkins said, which look to be roughly 39 feet 12 meters apart at their centers.

“However, the propellant tankage in between still made up a substantial fraction of the total stage mass,” said Hopkins. “So it’s not clear to me why such an impact would look like two adjacent craters instead of one broad one. Would the lower overall density of the empty tanks make their contribution to a crater so much less impactful?”

Edward Patrick, lead scientist of the Space Science & Engineering Division at Southwest Research Institute (SwRI) said the sun angles are different in LRO photos, “but it appears that a trench to the east of the impact was totally buried by overturned fines from the impact. Very cool! It would be nice to return to one or more similar sites to find out what contaminants persist after decades.”

Patrick told Inside Outer Space that there are some ulterior motives with his thoughts.

Surveyor spacecraft on display.
Credit: NASM

Far more mysterious

“With every breath of my being, I’m trying to understand how gases interact with lunar regolith grains. My lab experiments suggest that the lunar surface is far more mysterious than we currently know or understand, Patrick said. “My long-term plans for returning to the Moon would include returning to sites of previous landings and drilling under the spacecraft that landed there.”

Patrick’s top of his list would be NASA’s Surveyor VII that sat down on the Moon on January 10, 1968 on the ejecta blanket emanating from the bright Tycho crater in the south of the nearside. It was the seventh and last lunar lander of NASA’s robotic Surveyor program 

Patrick is the principal investigator for SwRI’s Southwest Research Institute’s Environmental Analysis of the Bounded Lunar Exosphere (ENABLE) project. It aims to return mass spectrometry to the lunar surface to identify materials present on the Moon.

Go to the Lunar Reconnaissance Orbiter Camera, or LROC, website:

“Mystery Rocket Body Found!” at:

http://lroc.sese.asu.edu/posts/1261

For more information on this incident, go to:

On-going Saga: What Will Crash into the Moon’s Far Side?

https://www.leonarddavid.com/on-going-saga-what-will-crash-into-the-moons-far-side/

Moon Slam Approaches: Out-of-control Rocket Stage

https://www.leonarddavid.com/31513-2/

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