Ham Satellite Suffers Failures, Is Silent

Bruce Perens writes "The Phase 3-D satellite, renamed Oscar 40 once it reached orbit, has suffered multiple failures and has stopped transmitting telemetry. It is not yet known if the satellite is responding to commands. The main telemetry beacon on 145.898 MHz was operating poorly after separation and now may be transmitting a weak unmodulated carrier. A fuel valve appears to be sticking closed and appeared to be only 10% open after multiple operation commands. Then, the first flight burn was 3 minutes too long due to another, not-yet-understood problem, boosting the craft into a higher orbit than expected (not yet a problem in itself as the final orbit is to be even higher). A backup flight computer, itself an experiment to see if the CPU would be radiation-hard enough to survive, has its RAM corrupted every 1 or 2 days in orbit as it crosses radiation belts and currently is not set up to reboot automaticaly. The primary flight computer may have crashed. An expected watchdog timer reset did not occur, but this would be the case if the satellite was receiving some commands."

"We may have to wait until after Christmas for another reset. Controllers have not transmitted a hard reset command yet, which would work even with the flight computer crashed, as they wish to explore other options. The satellite would automaticaly cycle through a number of frequencies and antennas if it does not get any commands for 10 orbits, and controllers hope to re-establish control as this happens. A hard reset could delay that option.

"The satellite waited several years for launch due to Arianne 5's early failures and a revised accelleration profile for the booster that required a redisign of the satellite frame to take additional stress. Aging may have effected components such as the fuel valves. Telemetry stopped suddenly during work on the 400 Newton kick motor, leading to speculation that the satellite may have suffered physical damage, but NORAD radar profiles indicate that it has not exploded.

Problems with Phase 3-D are bad news for hams, who raised $1 Million for the satellite, the 40th in the series of Amateur satellites launched since 1962. Phase 3-D has been criticized for pu ting too many eggs in one basket, unlike other small ham satellites built on a low budget and more easily launched as hitch-hikers with other payloads than the multi-ton Phase 3-D.

"The core development team urges patience. The satellite is in a stable orbit in one piece, just where it is expected to be, as confirmed by NORAD. They can take lots of time to debug it where it is, and hope to restore its functionality.

"For bulletins, see the AMSAT web site.

"A number of other ham satellites remain operational, and astronauts are currently using a ham station on the International Space Station to speak with people on the ground."

Comments

UPDATES

[Bruce Perens]

Someone please moderate this up. Here are the updates to this story.

The RAM corruption on the experimental backup flight computer is a normal feature until the EDAC software "scrubbing" routine is enabled. This constantly scans RAM for errors and corrects them before they grow too large to be correctible. That software has not been loaded yet.

The 145.898 beacon was not damaged, a 440 MHz one was. The 145.898 beacon runs from the backup flight computer while the 440 MHz one runs from the primary one. That's why the backup flight computer could cause a loss of telemetry.

There have been a good deal more than 40 Amateur satellites, only the ones that actually reached orbit and transmitted get numbers, and there are Amateur satellites outside of this numbering series.

Insiders tell me to relax, have patience, and that it is really jumping the gun to think the bird is lost.

Thanks

Bruce

*Before* posting!

[maggard]

PLEASE - before asking 100 times the same questions regarding Ham sats remember you're on the web. Spend the 30 seconds BEFORE you post and see if you can find the answer yourself.

Google, Yahoo, Metacrawler, etc. are all more efficient then asking every time someone else to explain it for you.

ps Also check the links in the article itself.

Re:Storage mediums in space.

[IronChef]

I can actually answer some of this. I used to work at JPL on spacecraft computers, back when I was a EE student. I did stuff like writing bootstrap code in assembler that was particular to the custom chips that comprised the computer. I also designed PCBs for the test platform.

Space is a brutal environment. Even out in the deep black between the outer planets, there are a lot of gamma rays and charged particles that would play hell with a conventional computer. Spacecraft computers are built of relatively old-fashioned components, and they are made with a special radiation hardening process. There are no 1GHz CPUs in space. We don't really need them, either; the tasks performed by robotic spacecraft are pretty simple, compared to say running Windows.

Shielding isn't the answer. Imagine a metal box around a computer. Now imagine a proton or some other relatively heavy charged particle is fired into the metal. The particle can hit an atomic nucleus and shatter it, flinging MORE particles into the hapless computer. Bad news. And shielding thick enough to protect against this is heavy, and that's bad for spacecraft too.

So they use simple, rugged components, that can usually resist a proton zipping through them. And for the times when a bit gets flipped by a particle -- this is called a Single Event Upset or SEU -- there is a TON of error correction & detection bits allocated in these computers. The system I worked on, which is the computer in the Cassini craft, used a modified Hamming code. I think that almost 1/2 the bits in every 16-bit word were allocated to EDAC.

Unfortunately I do not remember the details of how you fab a chip to be radiation resistant. Some special substrate, special transistors... I'm sure you can Google for it.