Humans Fast, Machines Slow

Rand Simberg talks about impedance matching. So I’d like to make a post of my comment there (I’ve always wondered why this obvious alternative gets mentioned so little…)

What to do when you arrive at Mars or Earth with your solar electric propelled vessel?

So, the problem with most low fuel demand velocity change schemes is that they only give slow accelerations. Low fuel high velocity change means solar or nuclear electric propulsion and aerocapture mainly.

High delta vee aerobraking is hard to do in one pass – it gets dangerous because of atmospheric variability and potentially other reasons.

Simple: detach a small capsule with the humans that goes directly to the surface (with only days of life support) and leave the untended craft to do multi-pass aerobraking. Hitting van Allen belts a few more times or taking a long time doesn’t matter that much with no humans onboard.

You could also potentially ultimately leave the long distance craft at some Lagrange point instead of LEO. (Cue some clever and complex maneuvers to save fuel – maneuvers that take long.)

Something similar could also be done when a long distance stack is assembled in LEO: send the humans there only after it’s through the belts. They can go with a smallish capsule again. Potentially at some Lagrange point, or in space without any fixed reference, just along the way. It could be dangerous though if the capsule doesn’t have much life support.

Many of these things have potential delta vee penalties as well as timing inflexibilities, but they could have enough other benefits that they should be considered.

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Jeff Greason

The Man. On Space Review. [EDIT: About a month ago, but I only just read it.] This is just excellent. So many things I agree with, that go against the stupid myths of spaceflight and space policy. If you read one space policy interview this year, this should be it!

“NASA is an organization that is dominated by fixed costs. In business terms everything is in the overhead,” he said. The committee found, with some effort, that the fixed cost of NASA’s human spaceflight program is $6–7 billion a year. “The bottom line is that they can’t afford to keep the doors open with they money they’ve got, let alone do anything with it.”

…

However, he said, if you’re trying to minimize costs, it makes more sense to use a smaller launch vehicle that flies more frequently and has other users and applications. The key to making that work for exploration architectures that require large amounts of propellant—and hence have driven the planning for heavy-lift vehicles like the Ares 5—is the use of propellant depots and in-space propellant transfer. “If you use in-space propellant transfer, it’s no longer true that you have to have a really big piece,” he said.

…

He said that while he had his own opinions on the right selection of launch vehicles, he didn’t have any insights on what direction the White House and Congress would go. “It’s really up to policymakers whether we have a space program or a jobs program.”

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JAXA’s HTV

It’s in orbit currently. Status updates on spaceflight now and an NSF forum thread. There’s some technical material on NSF L2 about the HTV, for anyone there.

Hope all goes well. This is also exciting, if everything works, there are soon four space agencies that have docked to a space station – a few years ago there were only two. Spacefaring is coming closer, although this is still baby steps in a sense – the vehicles as well as the rockets used to launch them are expendable, and have been developed with ultra expensive national programs.  They are the forerunners, grandparents of real spacefaring hardware that will hopefully come in the not too distant future, and be much easier and cheaper.

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