My first computer ran at 87 kHz (!) - an IBM 1401. I wrote a compiler for a Python-like language for it, as well as an Operating System.

You kids today are spoiled with multi-GHz machines.

You can go through the exercise of building your own hardware, operating system, OO language, and writing programs on the resulting platform.

http://www.youtube.com/watch?v=JtXvUoPx4Qs

Everything is virtualized. The software is Open Source, and much of the courseware is available free. The book you still have to pay for, but it's very cool nonetheless.

Lots of the cost has to do with being radiation and temperature hardened. The methods are one-off for programs like this. There is little to stop it from scaling though - it's just a matter of getting the economies of scale.

From the Wikipedia page, the RAD6000 was used in the Mars Rovers. I believe that the Mars Rovers used Java, partly because of static analysis that can be performed on source and object code and partly due to the garbage collection.

I would be shocked if the actual rovers used Java. Perhaps Java is used in the tools used to control them (that send the signals), but not the little guys themselves.

Yep:

"The places where NASA scientists have used Java for this mission is all on the ground side right now."

http://www.sun.com/aboutsun/media/features/mars.html