Give me meth, or give me death
Methane, that is.
NASA recently dropped a requirement that the Crew Exploration Vehicle use methane and liquid oxygen for its propulsion system. The space blogs are up in arms about this, and rightly so.
When President Bush proposed his Vision for Space Exploration, he made it clear that the moon was a short-term goal, meant to prepare us for an even greater challenge--putting humans on Mars. The challenge was to show traceability between living on the moon and an eventual Mars mission.
Over the past 15 years, astronautical engineers have come to embrace the idea that, in order to live on Mars, you will need to live off the land. Part of this is making your own fuel by combining carbon dioxide from the Martian atmosphere with hydrogen (brought from earth) to make methane and water. The methane would be used for fuel, while water could be consumed by the crew, or electrolyzed into oxygen for breathing and fuel.
In the initial draft for the CEV's requirements, NASA wanted to use methane for the main propulsion system. The analogue here was obvious: develop methane-fueled rockets now, then apply them on the Mars mission later.
Methane has other benefits, too. Amongst chemical rockets, it's specific impulse is beaten only by hydrogen (and fluorine, but the stuff is too toxic for use in rockets.) It's also considered "space storable," as it doesn't boil away in space as fast as hydrogen does (due to its higher boiling point.) Storability will be important, as the Earth Departure Stage will have to wait in earth orbit until the CEV can successfully launch and dock with it.
NASA's reasons for eliminating methane as a requirement are quite specious, as it will not significantly shorten the development time or budget for the CEV. It's doubtable that an off-the-shelf engine can be used for the CEV. Methane doesn't present any real challenges; existing hydrogen engines like the RL-10 and Russian RD-0120 have been modified to run on methane in tests.
While there's nothing in the CEV's requirements that forbids Lockheed-Martin or Northrop Grumman/Boeing from using methane propulsion, it's unlikely that the big contractors will do anything other than meet the bare minimum requirements. Sadly, America's shattered aerospace industry can't be counted on to deliver a product that is forward-thinking and loaded with growth potential. LockMart and NorthGrum/Boeing have no incentive to pursue methane as a fuel; they have invested billions of dollars in hydrogen and kerosene, while most of the current work on methane-fueled rockets is being done by small companies like XCor.
The big contractors will likely go with hydrazine or one of its derivatives (monomethyl hydrazine or aerozine) as the fuel, and nitrogen tetroxide as the oxidizer. This fuel combination was used for the Apollo spacecraft, and its biggest advantage was the storability of the fuels. It has many major drawbacks, including low Isp and being lethally toxic. Personally, I wouldn't shed a tear if hydrazine was abolished as a rocket fuel.
Much like the Space Shuttle's troubled development, NASA is saving a little bit of money in near-term CEV costs, while losing fistfulls of money and creating more problems in the long run. While methane is not essential to landing on the moon, it will result in a smaller, more capable spacecraft, and it will remove an early hurdle in the human exploration of Mars. NASA Administrator Michael Griffin would be wise to listen to the space bloggers and get the methane requirement put back in the CEV specifications.
NASA recently dropped a requirement that the Crew Exploration Vehicle use methane and liquid oxygen for its propulsion system. The space blogs are up in arms about this, and rightly so.
When President Bush proposed his Vision for Space Exploration, he made it clear that the moon was a short-term goal, meant to prepare us for an even greater challenge--putting humans on Mars. The challenge was to show traceability between living on the moon and an eventual Mars mission.
Over the past 15 years, astronautical engineers have come to embrace the idea that, in order to live on Mars, you will need to live off the land. Part of this is making your own fuel by combining carbon dioxide from the Martian atmosphere with hydrogen (brought from earth) to make methane and water. The methane would be used for fuel, while water could be consumed by the crew, or electrolyzed into oxygen for breathing and fuel.
In the initial draft for the CEV's requirements, NASA wanted to use methane for the main propulsion system. The analogue here was obvious: develop methane-fueled rockets now, then apply them on the Mars mission later.
Methane has other benefits, too. Amongst chemical rockets, it's specific impulse is beaten only by hydrogen (and fluorine, but the stuff is too toxic for use in rockets.) It's also considered "space storable," as it doesn't boil away in space as fast as hydrogen does (due to its higher boiling point.) Storability will be important, as the Earth Departure Stage will have to wait in earth orbit until the CEV can successfully launch and dock with it.
NASA's reasons for eliminating methane as a requirement are quite specious, as it will not significantly shorten the development time or budget for the CEV. It's doubtable that an off-the-shelf engine can be used for the CEV. Methane doesn't present any real challenges; existing hydrogen engines like the RL-10 and Russian RD-0120 have been modified to run on methane in tests.
While there's nothing in the CEV's requirements that forbids Lockheed-Martin or Northrop Grumman/Boeing from using methane propulsion, it's unlikely that the big contractors will do anything other than meet the bare minimum requirements. Sadly, America's shattered aerospace industry can't be counted on to deliver a product that is forward-thinking and loaded with growth potential. LockMart and NorthGrum/Boeing have no incentive to pursue methane as a fuel; they have invested billions of dollars in hydrogen and kerosene, while most of the current work on methane-fueled rockets is being done by small companies like XCor.
The big contractors will likely go with hydrazine or one of its derivatives (monomethyl hydrazine or aerozine) as the fuel, and nitrogen tetroxide as the oxidizer. This fuel combination was used for the Apollo spacecraft, and its biggest advantage was the storability of the fuels. It has many major drawbacks, including low Isp and being lethally toxic. Personally, I wouldn't shed a tear if hydrazine was abolished as a rocket fuel.
Much like the Space Shuttle's troubled development, NASA is saving a little bit of money in near-term CEV costs, while losing fistfulls of money and creating more problems in the long run. While methane is not essential to landing on the moon, it will result in a smaller, more capable spacecraft, and it will remove an early hurdle in the human exploration of Mars. NASA Administrator Michael Griffin would be wise to listen to the space bloggers and get the methane requirement put back in the CEV specifications.
posted by Mr. X at
7:49 PM
