by contributing writers for The Conversation
Pasadena CA (The Conversation) May 16, 2017
Forty-five years have passed since humans last set foot on an extraterrestrial body. Now, the moon is back at the center of efforts not only to explore space, but to create a permanent, independent space-faring society.
Planning expeditions to Earth's nearest celestial neighbor is no longer just a NASA effort, though the U.S. space agency has plans for a moon-orbiting space station that would serve as a staging ground for Mars missions in the early 2030s. The United Launch Alliance, a joint venture between Lockheed Martin and Boeing, is planning a lunar fueling station for spacecraft, capable of supporting 1,000 people living in space within 30 years.
Billionaires Elon Musk, Jeff Bezos and Robert Bigelow all have companies aiming to deliver people or goods to the moon. Several teams competing for a share of Google's US$30 million cash prize are planning to launch rovers to the moon.
We and 27 other students from around the world recently participated in the 2017 Caltech Space Challenge, proposing designs of what a lunar launch and supply station for deep space missions might look like, and how it would work.
The raw materials for rocket fuel
Any rocket leaving Earth has to carry all the fuel it will ever use to get to its destination and, if needed, back again. That fuel is heavy - and getting it moving at such high speeds takes a lot of energy. If we could refuel in orbit, that launch energy could lift more people or cargo or scientific equipment into orbit. Then the spacecraft could refuel in space, where Earth's gravity is less powerful.
The moon has one-sixth the gravity of Earth, which makes it an attractive alternative base. The moon also has ice, which we already know how to process into a hydrogen-oxygen propellant that we use in many modern rockets.
Those locations would be tricky to mine because they are colder and offer no sunlight to power roving vehicles. However, we could install big mirrors on the craters' rims to illuminate solar panels in the permanently shadowed regions. Rovers from Google's Lunar X Prize competition and NASA's Lunar Resource Prospector, set to launch in 2020, would also contribute to finding good locations to mine ice.
Imagining a moon base
One rover, which we call the Prospector, would explore the moon and find ice-bearing locations. A second rover, the Constructor, would follow along behind, building a launch pad and packing down roadways to ease movements for the third rover type, the Miners, which actually collect the ice and deliver it to nearby storage tanks and an electrolysis processing plant that splits water into hydrogen and oxygen.
The Constructor would also build a landing pad where the small near-moon transport spacecraft we call Lunar Resupply Shuttles would arrive to collect fuel for delivery as newly launched spacecraft pass by the moon. The shuttles would burn moon-made fuel and would have advanced guidance and navigation systems to travel between lunar bases and their target spacecraft.
A gas station in space
The depot would have large solar arrays powering an electrolysis module for melting the ice and then turning the water into fuel, and large fuel tanks to store what's made. NASA is already working on most of the technology needed for a depot like this, including docking and fuel transfer. We anticipate a working depot could be ready in the early 2030s, just in time for the first human missions to Mars.
To be most useful and efficient, the depot should be located in a stable orbit relatively near both the Earth and the moon. The Earth-moon Lagrangian Point 1 (L1) is a point in space about 85 percent of the way from Earth to the moon, where the force of Earth's gravity would exactly equal the force of the moon's gravity pulling in the other direction. It's the perfect pit stop for a spacecraft on its way to Mars or the outer planets.
Then, the spacecraft and its cargo could be towed from Low Earth Orbit to the depot at L1 using a solar electric propulsion tug, a spacecraft largely propelled by solar-powered electric thrusters.
This would let us triple the payload delivery to Mars. At present, a human Mars mission is estimated to cost as much as US$100 billion, and will need hundreds of tons of cargo. Delivering more cargo from Earth to Mars with fewer rocket launches would save billions of dollars and years of time.
A base for space exploration
By helping us escape both Earth's gravity and dependence on its resources, a lunar gas station could be the first small step toward the giant leap into making humanity an interplanetary civilization.
Editor's Note: An earlier version of this article had an error in the text relating to Earth Orbital and Escape velocities.
This article was written by Gary Li, Danielle DeLatte, Jerome Gilleron, Samuel Wald and Therese Jones for The Conversation and is republished with permission.
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