Fill 'er up ... in space?

Posted: Friday, July 31, 2009 5:10 PM by Alan Boyle

NASA

An artist's conception from 1971 shows an orbital fuel depot in action.

The panel reviewing NASA's long-range plans is giving a new boost to the old idea of setting up orbital fueling stations for spaceflight. If the space agency and the White House go down that route, it would mark a dramatic change in direction for future journeys beyond Earth orbit.

Some would say that's just what the nation's space effort needs.

The idea of setting up a permanent infrastructure for travel in deep space was floated on Thursday during a hearing in Cocoa Beach, Fla., conducted by the Review of U.S. Human Space Flight Plans Committee.

Panel members who have been focusing on future travel beyond Earth orbit spoke favorably of the fuel-depot idea, and it's likely to appear as one of the options in a final report that's due by the end of August. It will be up to NASA and the White House to decide which option to pursue and how much money to spend. (The current ballpark figure is $80 billion over 10 years.)

Basically, here's how a fuel-depot system would change the spaceflight situation:

Spaceships currently have to carry all the fuel they'd need for an entire trip at once. That was the case for the Apollo-Saturn missions of the 1960s and the space shuttle missions of the past 28 years.

If fuel depots were built in orbit, however, spaceships coming up from Earth's "gravity well" could fill 'er up and continue their journey with a full tank of gas (or, say, liquid oxygen and hydrogen). Alternatively, you could design a different sort of transfer vehicle, optimized for making the trip from one orbital spaceport to another rather than launching and landing. 

That would lighten the load for launch vehicles leaving Earth, since they wouldn't have to carry all the fuel for a long trip at once. And it might reduce the need to develop a new heavy-lift vehicle like the Ares V. You could get by instead with a smaller booster, launched empty and fueled up in orbit.

"It really is a game changer," Jeff Greason, chief executive officer of California-based XCOR Aerospace and a member of the review panel, was quoted as saying in a New York Times report on the hearing.

The idea has been floated before. As the Apollo program was winding down, planners at NASA's Marshall Space Flight Center in Alabama touched upon orbital fuel depots as a key piece of space infrastructure for deep-space flights. At the time, the space shuttle was little more than a twinkle in the space agency's eye.

"An orbital modular propellant storage depot, supplied periodically by the space shuttle or Earth-to-orbit fuel tankers, would be critical in making available large amounts of fuel to various orbital vehicles and spacecraft," NASA said in 1971. (The artwork above conceptualized how the system might look.)

NASA's space ambitions didn't pan out the way those planners planned. The cost of building the infrastructure for those deep-space trips was deemed too high, with too little payoff. As a result, no manned spacecraft has gone beyond Earth orbit since Apollo was shut down.

Five years ago, when President George W. Bush announced a new goal of returning to the moon by 2020, NASA turned to an "Apollo on steroids" approach that passed up orbital refueling. The plan did call for a maneuver that would link up moon-bound crews with their fueled-up transfer vehicles, however.

Now the Bush-era vision is being reviewed by Obama-era officials, and many of the previously laid plans are open for discussion again. Panel members laid out five scenarios for future trips beyond Earth orbit (which I previewed earlier this month):

• Lunar base: Basically the current return-to-the-moon plan, which calls for setting up a permanent base.
  
  
• Lunar global: No manned base, but a combination of quick visits to the moon ("sorties")  plus robotic missions.
  
  
• Moon to Mars: Lunar landings conducted primarily as rehearsals for Mars landings.
  
  
• Mars first: Just focus on eventual Mars landings, don't return to the moon.
  
  
• Flexible path: Start out by sending astronauts to platforms that are at stable points spread from Earth orbit to lunar orbit to Martian orbit (on Mars' moons, for example), plus near-Earth objects. Then send robots from those manned platforms to the surfaces of other worlds (down into the "gravity wells"). Don't send astronauts down onto the moon or Mars right off, but see how things go.

The last option sounds most conducive to the fuel-depot approach, and it also meshes best with the international space station's current role. In fact, Transterrestrial Musings' Rand Simberg suggests that using the space station as a fuel-depot test bed is such an attractive idea it might be worth the cost of changing the station's orbit.

Simberg also links to a host of other commentary about the panel hearing in general and the fuel-depot idea in particular. One of the best links goes to a white paper at Selenian Boondocks discussing how the concept could boost American industry and commercial space development. You'll find still more to sink your teeth into over at RLV and Space Transport News as well as the Space Coalition Blog.

For a skeptical view of the fuel-depot idea, check out Rob Coppinger's comments on the Hyperbola blog.

In addition to the "how" and "where" questions surrounding human spaceflight, the panel members took on the question of "why" - something we've talked about in the past. (You do remember the five E's, don't you?)

Here's how MIT aerospace professor Edward Crawley answered the "why" question during Thursday's hearing:

"Our ultimate objective should be viewed as the exploration and eventual extension of human civilization within the solar system. We have to keep our eye on the big prize. This will take a long time, but the time has come. The political alignment is here to allow this to be a goal for our nation, and it's a goal worthy of a great nation."

XCOR's Greason added a kicker to that comment, according to Irene Klotz's account for Discovery.com: "I know this sounds terribly ambitious and dramatic, but if that is not the point of human spaceflight … then what the hell are we doing?" Greason asked.

What the heck should we be doing in space? I'm going to be a bit out of the loop this weekend, discussing this subject and many others at the SpoCon science-fiction convention in Spokane - but if you leave a comment below, I'll try to add it to the mix as soon as I get a chance.

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