Moon Is Too Dry for Astronauts

NASA is counting on water ice in shadowed craters on the moon,
but there may be none. And there are other hazards.

 

The first test launch of the massive Space Launch System (SLS) for the Artemis mission is scheduled for no earlier than November 16, writes Elizabeth Howell at Space.com. Her article accompanied by a stunning photo of the Artemis megarocket under the Nov 8 lunar “blood moon” eclipse.

The rocket launch has suffered several delays so far over weather and safety concerns, which is par for the course, says professor of space studies Michael Dodge today at The Conversation. Scrubbing launches at the last minute is a long tradition, he says, coming from hard lessons on crew safety. But if the program reaches NASA’s goal of returning humans to the moon after the Apollo 17 crew left its last bootprint on the surface, launch safety may be the easiest problem to solve.

Surviving the lunar night can be a challenge for astronauts on the moon (Leonard David, Space.com, 13 Nov 2022).

The old Apollo missions were timed to have men on the moon during the relatively mild hours of low sunlight during the lunar day. Even so, the astronauts survived only by living within their carefully-sealed space suit cocoons that kept their bodies within the narrow limits of temperature, pressure and oxygen required for human life.

Historical note: Eugene Cernan and Harrison Schmitt spent the longest time on the lunar surface—75 hours—during the Apollo 17 mission 50 years ago next month (they left the moon on December 14, 1972). The two also spent the most time in moonwalks (22 hours), one of them for 7 hours and 35 minutes.

Artemis, however, hopes eventually to maintain a lunar base on the surface operated by humans spending extended periods of time. This raises several new risks not experienced by Apollo. One is the chance of getting hit by a blast of solar wind from a flare, which could kill a man within minutes, even one inside a spacecraft.

Another risk is temperature. Without an atmosphere to moderate temperatures, the lunar surface boils in sunlight and freezes in shade. There will be two-week periods of both, Leonard David reminds readers: “The moon’s lunar day/night cycle means fourteen days of continuous sunlight followed by fourteen days of constant darkness” during which it will be profoundly cold—too cold to do geology work outside. At the equator, lunar temperatures can rise to 250° F and fall to -290° F. It gets even colder at the poles.

Imagine the toll on human psychology spending two weeks at a time in darkness and profound cold. Without a well-equipped base able to supply reliable electric lights and heat, and perhaps TV, such a lifestyle could cause panic very fast. And there won’t be light for two-week periods for solar power. Battery technology will have to advance substantially to survive lunar nights.

Even during the day there will be unearthly risks:

Regarding moonwalking suit systems, including boots, gloves and the backpack-like portable life support system, the thermal design issues will be severe, [Dean] Eppler of The Aerospace Corporation said.

“For instance, say you’re standing ankle deep in a very cold, shadowed area, but your legs, torso, etc., are in direct sunlight. You’ll need to ensure that the boots and pressure garment material don’t freeze and break, while ensuring that the upper parts of the suit system don’t become so hot that serious heat stress to the crewmember is a significant issue,” Eppler said. “It’s real problem.”

Eppler believes these are challenges that can be solved. Great is Artemis of the Envisions, he trusts. But one thing these articles do not address is water. Up to now, everyone has been assuming that water can be mined from ice deposits in permanently shadowed regions (PSRs) near the poles.

In fact, craters within permanently shadowed regions are sun-shy spots on the moon in which quantities of water ice could reside. Those deposits would be ideal for processing into oxygen, water, even rocket fuel.

Moon exploration planners are laying out what has to happen to operate successfully on the moon, particularly at the lunar south pole, loaded with PSRs and conceivably a rich haven for harvesting water ice. 

But is that true? The Artemis planners should read a new paper from the American Geophysical Union:

The Arid Regolith of the Moon (Hodges and Farrell, Geophysical Research Letters, 31 Oct 2022, open access).

The hoped-for water to maintain a lunar base may not exist. The lunar surface is arid.

Whether vast deposits of water ice have accumulated in lunar polar cold traps may hinge on an unproven hypothesis that water acquired from meteor impacts and possibly other sources is moved to polar cold traps by the dynamic transport process of the lunar exosphere (a rarefied, collisionless atmosphere). Movement of exospheric molecules over the lunar surface is a two-dimensional random walk process in which the steps are random segments of ballistic trajectories that begin with thermal desorption from soil grains and end with adsorption at distances measured in hundreds of kilometers. Obviously, trajectories that end in cold traps must create ice deposits. However, the upper bound for exospheric water derived here from data collected in 2013–2014 by the neutral mass spectrometer on the Lunar Atmosphere and Dust Environment Explorer spacecraft, about three molecules/cc, pales in comparison to the concentration of ∼15,000 molecules/cc needed to sequester the meteoritic water influx. The only pragmatic conclusion is that the hypothesis for water ice accumulation at the poles due to exospheric transport is false. This conclusion forces the question of the fate of water that accretes on the lunar surface.

Houston, we have a problem.

The key experimental finding of this report is that the LADEE mass spectrometer data show no evidence of exospheric water on the Moon. More important, the upper bound for exospheric water falls short by several orders of magnitude of allowing the exosphere to be the conduit for transferring the meteoritic water influx to polar cold traps. This conclusion eliminates meteoritic water from the possible sources of polar ice deposits, but appears to leave open the possibility of trapped cometary water.

OK; what about those comets? The paper continues,

On the other hand, it is possible that one or more comets have impacted the moon and deposited significant amounts water in polar cold traps (Stewart et al., 2011). However, the only certain source of water on the moon is meteorites, and the only route to polar traps is exospheric transport.

If meteorites can create a “rain” of water molecules over the entire lunar surface, why was so little detected by the spacecraft? The solar wind is capable of accelerating water molecules (or ions, like OH^–) to escape velocity. In short, it got blasted away. According to their calculations (and there are uncertainties—see details near end of paper), the solar wind removes water nine times faster than meteorites bring it in. The same solar sweeper would have removed comet water, too.

News release 2029: “First Artemis astronauts land on the moon, find the well is dry. Trillions of dollars wasted. Landing site found to be an arid zone.” They should have settled for Arizona.

So much for Artemis. She’s always been just a dumb idol.