A rogue rocket expected to collide with the moon on March 4 was wrongly identified as a SpaceX Falcon rocket stage and, instead, is likely from a past Chinese lunar mission, according to NASA.
The object now on target to hit the moon was first made public by Bill Gray, an independent researcher focused on orbital dynamics and the developer of astronomical software. He identified it in 2015 as the second stage of a SpaceX Falcon rocket, used that same year to launch the .
The object, initially called WE0913A by asteroid spotters, had gone past the moon two days after DSCOVR's launch, he said.
"I and others came to accept the identification with the second stage as correct. The object had about the brightness we would expect, and had showed up at the expected time and moving in a reasonable orbit," Gray said on his website.
His assessment was widely accepted by .
A NEW IDENTIFICATION
Over the weekend, however, Gray said he had gotten the object's origins wrong after communicating with Jon Giorgini of NASA's Jet Propulsion Laboratory, which doesn't track space junk but does keep careful track of a lot of active spacecraft, including DSCOVR.
"Jon pointed out that JPL's Horizons system showed that the DSCOVR spacecraft's trajectory did not go particularly close to the moon. It would be a little strange if the second stage went right past the moon, while DSCOVR was in another part of the sky. There's always some separation, but this was suspiciously large," Gray said.
"Analysis led by NASA's Jet Propulsion Laboratory's Center for Near-Earth Object Studies indicates the object expected to impact the far side of the Moon March 4 is likely the Chinese Chang'e 5-T1 booster launched in 2014," according to a NASA statement released Monday.
"It is not a SpaceX Falcon 9 second stage from a mission in 2015 as previously reported. This update results from analysis of the object's orbits in the 2016 -- 2017 timeframe."
Gray said he subsequently reviewed his data and has now landed on a different explanation: He said that the object was the third stage of the Chinese Long March 3C rocket.
The rocket stage is expected to hit the moon at 7:26 a.m. ET on March 4. However, the impact will be on the far side of the moon and not visible from Earth. The rocket will likely disintegrate on impact and create a crater about 10 to 20 meters (32.8 feet to 65.6 feet) across.
NEED FOR OFFICIAL MONITORING OF SPACE JUNK
Jonathan McDowell, an astronomer at , said identifying space junk is "never easy" in deep-space orbit, but he said Gray's new identification was likely right. "I'd give at least 80 per cent and maybe 90 per cent odds."
He explained, "It's especially hard for these things in chaotic deep space orbits where you pick something up several years after it was last seen and try and backtrack it to match it with a known mission."
McDowell said the confusion over the identity of the rocket stage highlighted the need for NASA and other official agencies to be monitoring deep space junk more closely, rather than relying on limited resources of private individuals and academics.
There are about 30 to 50 lost deep-space objects like the rocket stage that have been missing for years, but no space agencies have systematically kept track of space debris so far away from Earth, he said.
"It's not like LEO (low Earth orbit) stuff where the traffic is high so junk is a danger to other spacecraft. But you'd think it would be a good idea to know where we have dumped things."
He added, "It's not a very high priority, but you would think the world could afford to hire at least one person to do this properly, and maybe require space agencies to make public their deep space trajectories."
More spacecraft are going into this sort of orbit in the future, Gray said, and some thought should be put into keeping "outer space clean." There are simple steps that government agencies and corporations launching rockets could take such as making the last known orbital data elements publicly available.
