Chang’e-4 lander on the Moon’s farside as imaged by Yutu-2 rover.
Credit: CNAS/CLEP

A recent posting by NASA has indicated that the U.S. space agency and the China National Space Administration (CNSA) are coordinating efforts focused on the farside landing of China’s Chang’e-4. That robotic spacecraft touched down in the South Pole-Aitken Basin on January 3rd.

In particular, NASA’s Lunar Reconnaissance Orbiter (LRO) is expected to image the Chang’e-4 landing site on January 31 in a manner similar to what was done on Chang’e-3, the NASA story explains.

NASA’s Lunar Reconnaissance Orbiter can use its super-powerful camera to spot the Chang’e-4 lander and rover, as it did in imaging China’s earlier Moon lander, Chang’e-3.
LROC NAC view of the Chang’e 3 lander (large arrow) and rover (small arrow) just before sunset on their first day of lunar exploration. Credit: NASA/GSFC/Arizona State University

NASA and CNSA are also exploring the prospect of observing a signature of the landing plume of the Chang’e-4, making use of the LRO-carried Lyman Alpha Mapping Project (LAMP), an ultraviolet imaging spectrograph instrument. LAMP was developed by the Southwest Research Institute.

Chang’e-4’s farside landing zone.
Credit: NASA/GSFC/Arizona State University

Plume residue

This isn’t the first time that a NASA lunar orbiter has searched for plume residue of a Chinese Moon lander.

The Chang’e-3 landing in northern Mare Imbrium in mid-December 2013 was surveyed by NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE).

LADEE controllers uploaded a command sequence that scheduled the science instruments for operations during the Chang’e-3 landing period, gathering data and gas species before and after the landing to provide the science team with a comparison.

The intent of using LADEE in this manner was to compare any results to theoretical predictions of gas and exhaust plume particle ejecta. Doing so would inform and update just how Moon lander propulsion systems interact with surface materials.

NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE).
Credit: NASA

Initial evaluation

Going over the LADEE data collected, the science teams’ initial evaluation of the data did not reveal any large effects attributable to Chang’e-3’s descent through the thin lunar atmosphere (an exosphere) and subsequent, rocket powered touchdown. LADEE instruments observed no increase in dust and no propulsion products were measured.

In reviewing the Chang’e-3 descent video, the interval of time that dust was launched by that December 2013 landing is very short, perhaps less than 15 seconds.

“It is actually an important and useful result for LADEE not to have detected the descent and landing. It indicates that exhaust products from a large robotic lander do not overwhelm the native lunar exosphere,” said Rick Elphic, Project Scientist for LADEE at NASA’s Ames Research Center, in outlining initial observations of the Chang’e-3 landing in a December 20, 2013 posting.

“LADEE would probably have had to be in just the right place at the right time to intercept it,” Elphic added. Also, significant amounts of exhaust products apparently cannot migrate to large distances, say hundreds and thousands of miles, and linger with sufficient density to be measured, he advised.

The mission of LADEE ended on April 18, 2014, with the spacecraft purposely crashed into the farside of the Moon.

LRO-carried Lyman Alpha Mapping Project (LAMP).
Credit: NASA/SwRI

Inform future missions

For the Chang’e-4 landing spot, LRO’s LAMP would scout for any signature of the landing plume of Chang’e-4.

NASA is still interested in possibly detecting the plume well after the landing, explains the January 19 space agency-posted article.

“Science gathered about how lunar dust is ejected upwards during a spacecraft’s landing,” the NASA story notes, “could inform future missions and how they arrive on the lunar surface.”

Relay satellite for handling farside operations.
Credit: CNSA’s Lunar Exploration and Space Engineering Center (CNSA-LESEC)

 

Farside politics

In a related development, the South China Morning Post last week reported that Wu Weiren, chief scientist of China’s lunar program, said that U.S. space scientists had asked permission to “borrow” China’s Chang’e-4 spacecraft and relay satellite to plan a mission to the farside of the Moon. That overture was made at an international conference a few years ago, citing Wu’s comments to state broadcaster China Central Television (CCTV).

Wu Weiren, general designer of China’s lunar exploration program.
Credit: SCIO

 

An essential aspect of the Chang’e-4 farside mission is use of a relay satellite launched last May and is now in a halo orbit at the L2 Lagrange point. It is needed to link Earth controllers with farside operations.

The story goes that American scientists had asked China to extend the Queqiao relay satellite’s lifespan and outfit a U.S.-supplied beacon on the Chang’e-4 mission, helping the U.S. in staging its own lunar landing strategy, Wu said.

“We asked the Americans why they wanted our relay satellite to operate longer,” Wu told CCTV. “They said, perhaps feeling a little embarrassed, that they wanted to make use of our relay satellite when they make their own mission to the farside of the Moon.”

To view the NASA-posting — NASA’s Campaign to Return to the Moon with Global Partners — go to:

https://www.nasa.gov/feature/nasa-s-campaign-to-return-to-the-moon-with-global-partners

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