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Hubble Repairs Hindered By Antiquated Computer Systems
Andrew Moseman writes "Part of the trouble NASA is encountering while fixing the Hubble Space Telescope comes from the fact that it's been up there for nearly two decades, and therefore carries computer systems long outdated here on Earth. 'One of the main computers that the Goddard team has been struggling with during the repair attempts runs on an Intel 486 chip, the height of 1989 technology.' Many of NASA's long-running missions rely on antiquated systems — the Voyager probes each have about 32k of memory — but the scientists say they can manage."
in such a small space by a good programmer. Most systems today are so encumbered by having been built by toolkits built on toolkits built on metalanguages ad nauseum that a simple "hello world" program now can run hundreds of K of memory.
My compliments to the programmers who still know how to get the most out of the little resources they're working with on these scientific probes.
A quote from the famous "Real programmers don't use Pascal" article written in 1983. Some of the most awesome Real Programmers of all work at the Jet Propulsion Laboratory in California. Many of them know the entire operating system of the Pioneer and Voyager spacecraft by heart. With a combination of large ground-based Fortran programs and small spacecraft-based assembly language programs, they are able to do incredible feats of navigation and improvisation-- hitting ten-kilometer wide windows at Saturn after six years in space, repairing or bypassing damaged sensor platforms, radios, and batteries. Allegedly, one Real Programmer managed to tuck a pattern matching program into a few hundred bytes of unused memory in a Voyager spacecraft that searched for, located, and photographed a new moon of Jupiter. The current plan for the Galileo spacecraft is to use a gravity assist trajectory past Mars on the way to Jupiter. This trajectory passes within 80 +/- 3 kilometers of the surface of Mars. Nobody is going to trust a Pascal program (or Pascal programmer) for navigation to these tolerances. If you have never read it, it's still a great read (at least for us old-timers). http://www.pbm.com/~lindahl/real.programmers.html
Actually, some sorts of shielding make things worse. Moderate amounts of shielding just end up providing targets for the really high energy particles, which releases a big cloud of moderate energy particles on impact. The secondary radiation is both more abundant and more likely to interact with the stuff on the inside, and so causes a bigger problem. For space applications, there are intermediate amounts of shielding that will actually *increase* the total dose. (This is the case for cosmic rays, not solar flares; the latter can be fairly effectively shielded against, but is frequently less of a concern.) If you're not willing to put *large* amounts of mass around the thing to be shielded, it's often impossible to improve things all that much.
Hardening often consists of simple changes that are nonetheless expensive because they involve changes to the whole production line -- things like rating all the transistors for a noticeably higher voltage, to reduce the likelihood of a radiation-induced latchup event. As chip voltages get lower, this gets harder. Other changes include things like using isotopically pure boron in your dopants -- boron comes in two common isotopes, 10B and 11B. 11B is relatively immune to cosmic radiation, but 10B will fision when hit -- releasing secondary ionizing particles that cause a much greater problem than the cosmic ray by itself would. So rad-hard chips end up made with (expensive) depleted boron.
Combine these, and you see why it's difficult to find a decent selection of rad-hard chips, and also why an up-to-date radiation hardened CPU can cost over $100k each -- and also why you nonetheless need them, and can't really substitute anything short of a few tons of shielding.