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Space Log: U.S. goes big, Japan small on propulsion

July 19, 2010

george.leopold-July 19, 2010


WASHINGTON -- The United States and Japan, close collaborators on space technology and exploration, are taking markedly different approaches when it comes to propulsion.

Some background: The Obama administration's proposed overhaul of NASA touched off a firestorm of criticism within the aerospace industry and its backers in Congress. After months of mud-slinging, a Senate panel last week reached what appears to be a meaningful compromise that could help placed the space agency on a new course to again send humans to explore the solar system.

Among other things, the NASA budget deal forged by the Senate Commerce, Science and Transportation Committee would accelerate development of a new U.S. heavy-lift rocket that could eventually transport crews to asteroids or Mars. The fiscal 2011 budget authorization package, which must still be approved by the full Senate, then reconciled with a House version, would begin development of a new heavy launcher as early as the end of this year. A new spacecraft would also be developed.

Both would replace the for-now canceled U.S. Constellation moon rocket program. Portions of the existing Ares spacecraft development program could end up as part of a new long-haul spacecraft. The House also could try to revive Constellation. Nevertheless, the White House has signaled that it approves the Senate compromise, which was approved unanimously.

If so, we can end the political posturing over the future direction of U.S. manned spaceflight and get on with the task of building the 21st century version of the mighty Saturn V rocket. The rocket scientists must now attempt to move beyond reliable but limited chemical propulsion to promising new technologies like xenon ion propulsion. As with most technical challenges, the big problem is scaling up a good idea into something big enough to take humans beyond Earth orbit.

Still, the Japanese space agency has demonstrated that ion propulsion works in spaceflight. Japan relied on ion engines to recover its Hayabusa space probe after it landed on the asteroid Itokawa, which orbits between Earth and Mars.

Ion engines use microwaves to heat xenon gas to propel a spacecraft. NASA scientists are likely interested in new, more powerful ion engine designs that could be used to power spacecraft once they've left Earth orbit.

Whether this approach would ever work in a booster remains to be seen. NASA also wants to look at new launch concepts like orbiting refueling depots that could be used by astronauts to gas up before heading out to distant points in the solar system.

(Had it not been for the end-of-the-decade deadline for a U.S. lunar landing during the space race of the 1960s, it's possible that the U.S. space program would have jumped from an orbiting space station to the moon and then on to Mars, using the orbiter and the moon as construction platforms for sending humans to the Red Planet.)

Meanwhile, the Japanese are also demonstrating a solar sail on its Ikaros probe. The sail will use "photon pressure" to help propel the probe to Venus. This rudimentary propulsion technology isn't fast, but it's cheap. And it will provide a practical demonstration of whether photons can be harnessed to help speed up spacecraft.

With NASA working with international partners, especially Japan, it can begin developing new concepts that can help humans reach that magic velocity of roughly 25,000 mph, the speed needed to escape Earth orbit.

NASA recently released a solicitation for new propulsion concepts.. The first industry proposals are due to NASA at the end of July. We'll take a closer look at them in a future post.

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