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NASA To Repair Hubble By Remote Control
Matt_dk writes "NASA says it plans to fix the Hubble Space Telescope by remote control this week.
The Hubble stopped beaming information to Earth about two weeks ago, when a data unit on the telescope completely failed.
Scientists on Tuesday said they will bypass the failed unit and switch to a back-up system to restart the flow of information.
The computer glitch forced NASA to postpone a shuttle mission this month to repair the Hubble.
That shuttle mission has been postponed until next year."
Update - 10/15, 17:45 by SS: Readers have pointed out further details from Spaceflight Now and the NASA press release.
Actually, the part that failed has a backup, it's almost like a two-sided cassette tape, and that second side needs to be loaded into the device that is responsible for transmitting data.
The broken part right now stops any and all data transmission from Hubble. Performing the fix (flipping the tape) will restore all performance, with no degradation, other than no backup.
When the next shuttle mission launches to repair the Hubble, they will be replacing this part so that there is, again, redundancy.
It's pretty amazing that these parts are still working after...how many years?
I'm curious, I presume somebody knows this.
I don't work on hubble but I know something about this stuff and I'll try and answer your questions directly
Do they have several mock ups?
Yes, for hubble there are several mock-ups, from ones that are fairly low fidelity that are used by the software developers (maintainers) for code/debug/test to a very high fidelity full scale electrical and mechanical mock-up of the aft end of the vehicle called the VEST, when the astronauts practice the repair tasks on dry land before they move to the pool at JSC to learn to do them in a simulated 0g environment.
A complete computer model of the whole thing, emulated right down to hardware and software?
When HST was built we were still doing spacecraft control simulations on hybrid analog/digital computers. For all missions in the last 20 years or so there are computer models of all the control modes built using products like matlab/simulink long before any metal is cut. I wouldn't be surprised if there is a matlab (or similar) model of hubble now as the hybrid computer is long gone. In fact, I'm almost positive, as I don't see any way they could have come up with the 2 gyro science controller otherwise.
How are reboot/reprogram sequences like this handled/practiced/tested?
Not to be a wise guy, but reboot and reprogramming are handled very carefully. This is why switching to a backup system is going to take 2 weeks, most of which were used for analysis and a formal review before the decision to swap to the B side was made. It probably takes 5 minutes to send the actual commands to switch to the B side of the data formatter, but they will double, triple or quadruple check everything as they go thru the process. Remember, they are switching to hardware that hasn't been used since 1990. They expect it to take about 40 hours to switch to the B side and plan to be done by Friday.
Even at design stage I imagine failure modes are extensively analyzed and multiple redundancy built in.
There are failure modes and effects analysis done at each design step. Before launch there would have been a peer review of the final failure detection and correction design.
A lot of the NASA standards are available to the public. If you go to http://standards.nasa.gov/ and click on the public button it takes you to the listing of them.