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In-orbit Fuel Depots vs. NASA's Heavy Lift Space Launch System (SLS) for Dummies

Satellite Technology

Satellite Technology Feature Article

October 24, 2011

In-orbit Fuel Depots vs. NASA's Heavy Lift Space Launch System (SLS) for Dummies

By Doug Mohney, Contributing Editor

The New York Times has (belatedly) discovered NASA's examination of propellant depots. In November, NASA engineers will meet in Washington to discuss how to leverage propellant depots to get further into space and enable “more ambitious missions” using the agency's heavy lift Space Launch System (SLS) rocket, according to an October 22, 2011 piece.   But apparently NASA officials aren't interested in trying to convince/fight Congress about the time and cost savings a fuel depot architecture would offer deep space missions.

NASA has done an internal study on fuel depots that they've yet to officially release to the public or to Congress. A July 21, 2011 draft PowerPoint summary of the document was leaked to the NASA Watch website last week.  

“Not only was the fuel depot mission architecture shown to be less expensive, fitting within expected budgets, it also gets humans beyond low Earth orbit a decade before the SLS architecture could,” writes NASA Watch editor/gadfly Keith Cowling. “Moreover, supposed constraints on the availability of commercial launch alternatives often mentioned by SLS proponents, was debunked.  In addition, clear integration and performance advantages to the use of commercial launchers Vs SLS was repeatedly touted as being desirable: 'breaking costs into smaller, less-monolithic amounts allows great flexibility in meeting smaller and changing budget profiles.'“

Let me try to simplify the acronym-rich “Propellant Depot Requirements Study Status Report” into a simply model. Over 70 percent of conduction an exploration mission beyond low earth orbit is fuel (to be precise for the rocket scientists: propellant, which is fuel and oxidizer).   The study crunches the numbers for going out and starting to demonstrate and build a fuel-depot infrastructure today with existing rockets vs. spending years and billions of dollars to get a heavy lift rocket and then go off and explore an asteroid or the moon.

If you start using a fuel-depot architecture to get to an asteroid today, you can get astronauts there by 2024, at a rough cost of $60 billion to $86 billion.  You use a number of smaller rockets to put up a fuel depot, fuel, and hardware into orbit, put it all together, fuel up, and go explore.

If you have to build a heavy lift rocket – which doesn't exist today – you don't get the mission to 2029 and end up spending $143 billion. 

Building a heavy lift rocket takes at least five years and anywhere from $57 billion to $83 billion more.

If you look at the problem from how much it costs to put 100 metric tons (MT) into orbit vs. cost, it's very disturbing, even assuming you've magically washed away the tens of billions of dollars for doing the research and development on a SLS heavy lift rocket capable of putting that much stuff into orbit. 

Estimates on a single SLS launch for 100 MT to $1.86 billion, according to another NASA study conducted by Georgia Tech dated September 2, 2010 and published by NASA Watch on March 30, 2011. NASA won't publically say how much SLS is estimated to cost per launch, but leaked documents suggest a cost of around $2.8 billion to $3 billion to conduct a single 70 MT flight every other year -- that's the cost to just buy the rocket and do the launch.

The current existing workhorses of NASA and the Defense Department, the United Launch Alliance (ULA) Atlas V and Delta IV, can put up anywhere between 22 MT to 29 MT into low earth orbit. While not public, costs estimates per launch range between $140 million to $170 million. Assume it costs $170 million for a single launch to put 22 MT into orbit. Multiple by 5 to put roughly 100 MT into orbit at a cost of $850 million and five launches. Compare that to $1.86 billion to $3 billion for an estimate of a single SLS launch.

Yes, it's a simplistic pricing model; there's some upfront hardware costs to put a fuel depot into orbit and the hardware has to replaced every decade or so, but you're saving (literally) a ton of money.

Other advantages with using in-orbit refueling include fault tolerance (lose one SLS launch, you lose everything), creating a real/expanded market for commercial launch vehicles as well as competition to drive pricing down, providing a steady stream of business for the U.S. launch industrial base, and a path for international participation (more cost savings) by providing launch services and fuel .

Hopefully NASA Deputy Administrator Lori Garver will start looking at and talking about the advantages of fuel depots for saving money and creating commercial competition, like she has with a pitch to fully fund U.S. commercial crew development

Doug Mohney is a contributing editor for TMCnet and a 20-year veteran of the ICT space. To read more of his articles, please visit columnist page.

Edited by Jennifer Russell

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