BOULDER, Colo. — A strikingly simple concept would provide efficient water provisions for human outposts and even bases on the moon. The idea is to clobber our already crater-rich neighbor repeatedly with tons of water ice — to establish an "anywhere, anytime" delivery system.
Not only could chucking a payload of water ice to the moon help sustain an expeditionary crew there, the impact would mimic — in experimental form — a comet strike. Therefore, it’s a double-whammy: A science mission wrapped within an exploration capability test mission.
Spearheading the speculative ploy — called SLAM — is Alan Stern, executive director of the Space Science and Engineering Division here at Southwest Research Institute. He’s the lead scientist on another "far-out but on the way" endeavor: the New Horizons spacecraft that is bound for Pluto.
"I hope the SLAM idea stimulates thought and gets people thinking a little bit more out of the box," Stern told Space.com. "When we have people on the moon, they are going to need water. This is an exceptionally efficient, low-cost way to get it there."
Cold traps, lukewarm thoughts
One perplexing issue for scientists and lunar exploration planners is just how much water ice is at the moon’s poles in the first place.
Spacecraft that orbited the moon — the Pentagon’s Clementine (1994) and NASA’s Lunar Prospector (1998-1999) — relayed data that hydrogen, arguably in the form of water ice, might be stashed at the lunar poles within permanently shadowed craters, called "cold traps."
If water ice is there, that resource could be used by visiting astronauts to make rocket fuel and oxygen. But is it there or not? And if so, how much water ice is available, and in what condition for processing?
NASA’s back-to-the-moon thinkers are anxious to sort out the truth about this possible lunar water inventory.
For instance, joining in on the robotic assault on the moon by several nations over the coming years is NASA’s Lunar Reconnaissance Orbiter, or LRO.
On LRO’s 2008 mission, a newly announced "secondary payload" is the Lunar Crater Observation and Sensing Satellite, or LCROSS. The LCROSS will monitor the impact of a spent upper stage from the same mission, leftover hardware that would impact a crater in the moon’s south pole area. A plume of material should be tossed high above the moon’s desolate landscape — then sensor-scanned in a look for lunar water ice.
If found, getting at that water ice at the poles won’t be easy. Having people and machinery work in those cold-trap climes would be tough. Light and power reserves aren’t easy to come by. Communications in and out of those locales is an issue, too.
And that’s where SLAM meets these difficulties, head on.
SLAM needs no midcourse correction en route to the moon — nor does it need a spacecraft, for that matter. All that’s necessary is a thermal jacket for the water ice payload that’s flung by rocket booster toward any selected spot on the moon.
"It appears to be entirely feasible, simple and really cheap," Stern said. A proprietary technique would be utilized to keep the water ice ball from being buried too deep on impact.
At lunar impact speeds, virtually all of the ice will come to rest less than 5 feet (1.5 meters) below the surface, if properly pre-fractured. Also, work done on the concept indicates that a majority of the water ice that is slammed into the moon is retained, with only 15 percent vaporized.
Clean water act
SLAM could even serve as an emergency, launch-on-demand service, Stern continued, for lunar-situated crews in need of a rapid recharge of oxygen, hydrogen or liquid water to drink.
SLAM is also, in a way, a "clean water act" for the moon. There's no telling what the quality of water ice, bacteriawise, might be in those darkened polar craters — if indeed it’s there.
Another ballistic bonus of SLAM is creation of a calibrated comet impact crater. The shot-to-the-Moon ball of ice is a little comet, Stern noted.
Moreover, scientists could study the transport efficiency of water on the moon. Molecules of water that are introduced into the lunar environment from outside sources hop around like droplets on a griddle — but some of those molecules make their way to the poles. The survival rate of those water molecules is a great scientific question, Stern said.
"SLAM is a nexus of three or four things in exploration and science," Stern said. "I defy you to find a space mission that’s cheaper or simpler" than a mission that essentially involves just two things: a rocket and a garden hose left behind at the pad.
Cutting the Gordian knot
Rockets lifting thousands of gallons of water skyward has been part of U.S. space history.
In the early 1960s, test missions for the Saturn 1 booster involved hurling water-filled upper stages into space, even dumping loads of water into Earth’s upper atmosphere under Project Highwater.
"SLAM was designed to take advantage of the high-performance and precision-injection capability of the existing Atlas 401," said Bernard Kutter, manager of advanced programs at Lockheed Martin Space Systems in nearby Denver.
Kutter explained to Space.com that, by utilizing existing Atlas capabilities, SLAM can provide a low-cost, low-risk, novel lunar science mission furthering our understanding of the moon and water transport around the moon.
The Southwest Research Institute’s Stern emphasized that SLAM is the output of roughly a dozen people that tackled a set of issues … to cut the Gordian Knot that's tangled up the value of polar volatiles and the difficulty of polar operations.
"To us it made a lot of sense. We couldn’t find an obvious flaw in it … not to say that it doesn’t have pros and cons," Stern explained. One constraint is that an Earth-to-moon ice ball strike must take place during lunar night, he said, with mining recovery necessary before sunrise to prevent ice sublimation after impact.
That’s a practical, real-world problem, Stern observed, just as deep ocean drilling here on Earth has its problems, too. In exchange for those troubles there are great rewards, he said.
"We’re proud of the SLAM idea," Stern concluded. "It’ll be up to others to see if this concept, I guess you could say, 'holds water.'"
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