[david-given]

You can --- you use a thing called a magsail.

The short version is: remember the old Bussard ramscoop idea? You use a magnetic field to collect interstellar hydrogen which you then fuse for thrust? Turns out that in our part of the galaxy, you get more drag from the sail than you do from the fusion thrust, so the idea was scrapped.

An embarrassingly long time later people finally realised that they'd invented a fuelless brake, and the idea was resurrected (but without the fusion drive). The maths are quite plausible and the sail itself trivially simple --- just a wire loop.

http://www.centauri-dreams.org/?p=22138

However, I don't think they'd be compatible with this idea --- I suspect you wouldn't get one big enough to be useful in a one gram package. But estimating the numbers is beyond me. Here's the paper if you want it. http://www.niac.usra.edu/files/studies/final_report/320Zubri...

[mrfusion]

Very fascinating! I had no idea we had such a viable option for braking.

Two questions for you if you're up for it.

Could we use this concept for braking during earth re entry to depend less on complex heat shields?

Why is the idea of a bussard ramscoop not viable?