During five months of troubleshooting, Voyager's ground team continued to receive signals that the spacecraft was still alive. But as of Saturday, they still had no insight into the specifics of Voyager 1's condition.
“That's pretty much the way we've always done it,” Spilker said. “We are still in the early stages of analyzing all channels and looking at their trends. Some temperatures dropped a bit during this time, but we saw almost everything we had hoped for. And that's always good news.”
Migration code
Through the investigation, Voyager's ground team discovered that a chip responsible for storing part of the FDS memory had stopped working, possibly due to a cosmic ray strike or an old hardware failure. This affects some of the computer's software code.
“That took away some of the memory,” Spilker said. “What they have to do is move that code into another part of memory, then make sure that everything that uses those codes, those subroutines, knows to go to the new location of memory, so Go in and run it.”
Only about 3% of FDS memory fails due to bad chips, so engineers need to implant that code in another part of the memory bank. But no location is large enough to hold the entire code, NASA said.
So the Voyager team divided the code into parts to be stored in different places in the FDS. This is not just a copy and paste job. Engineers needed to modify some code to ensure it would all work together. “Any references to the location of that code in other parts of the FDS memory should also be updated,” NASA said in a statement.
Newer NASA missions have on-the-ground hardware and software simulators where engineers can test new processes to make sure they don't cause harm when linking commands to a real spacecraft . Due to its age, Voyager does not have any ground simulators, and much of the mission's original design documents remain in paper form and have not been digitized.
“It's really only the eyes that can see the code,” Spilker said. “So we had to recheck three times. Everyone is looking at it and making sure we have all the connections together.”
This is just the first step in restoring full functionality to Voyager 1. “We're pretty sure it will work, but until it actually happens, we don't know for sure,” Spilker said. %.
“The reason we didn't do everything in one step is because the amount of memory we could find quickly was very limited, so we favored one data mode (engineering data mode ) and just move the code to restore that mode, said Jeff Mellstrom, the JPL engineer who heads the Voyager 1 “tiger team” tasked with fixing the problem.
“The next step, to relocate the three remaining actively used scientific data regimes, is essentially the same,” Mellstrom said in a written response to Ars. “The main difference is that the available memory constraints are now even tighter. We have ideas about possibly migrating the code but we have not yet fully evaluated the options or made a decision. These are the first steps we will begin this week.”
