The Hubble Space Telescope is returning to operation more than a month after its original payload computer shut down. NASA said it has successfully switched over to its backup computer — and while the process of bringing the system back online is slow, the agency has started to bring science instruments out of "safe mode."
"There was cheering in the control center" on Thursday night when word came that NASA had managed to restore the payload computer, James Jeletic, Hubble's deputy project manager, told NPR.
Hubble will likely resume science work this weekend
"There's a big sense of relief," Jeletic said.
"We believed that this all would work, but, you know, you're dealing with the space business and all kinds of surprises can come your way. But we didn't get any surprises."
As for when the telescope will beam its first breathtaking images back to Earth since the restart, the wait should be a short one.
"The first observations will hopefully be done over the weekend," Jeletic said. Accounting for the time it takes to receive and process the data, he predicted, "you probably would see the first images come out sometime in the beginning of next week."
Troubleshooting a tech issue in orbit
The relief and joy comes more than a month after the space telescope stopped collecting images and other data on June 13 when the payload computer that controls its science instruments suddenly shut down. (The computer that runs the Hubble spacecraft remained online.)
For weeks, NASA scientists worked on possible solutions to bring the payload computer back, but none of those ideas worked.
Initial system tests struggled to isolate the problem — a process complicated by the hundreds of miles separating the Hubble team from the computer and other components. But as every system failure stubbornly remained, the team came to believe that only one glitch would account for such widespread problems: the power control unit, which sends electricity to all the hardware.
To work through the problem, the team studied schematics of the original designs that date back decades.
"We even had people come out of retirement who were experts in these areas on Hubble to help us," Jeletic said.
The system's successful restart, he added, "has a lot to say for the people who designed the spacecraft 40 years ago."
Backup systems remain in place
Hubble's scientific payload is running on its backup computer system, he said, because the team had already set it up to run on secondary units while working on the outage. It opted to stay on the backup system, Jeletic said, to simplify the restart process.
Hubble carries backups of all its components, part of the original engineers' plans to cope with such problems. As of now, it's down to just one power control unit. But the Hubble team also thinks there's a chance the power unit might simply fix itself over time.
Outlining two ways that could happen, Jeletic said the unit may simply need to sit cold for a while to let electricity dissipate. There's also a chance it failed due to "circuit drift," he said, explaining that the circuit may have drifted out of its operational setting — and that it might simply drift back.
Exotic science relies on a 25 megahertz computer chip
The successful restart is just the latest comeback for Hubble, which was originally scheduled for only 15 years of service. It was placed into orbit in April 1990 after hitching a ride aboard the space shuttle Discovery.
Hubble's main onboard computer is an Intel 486 computer whose 25 megahertz speed was the best available (and rated for space travel) when astronauts upgraded the system around the turn of the century.
"It has about 2 megabytes of memory," Jeletic said. "So you can compare that to your latest iPhone. It's very, very primitive by today's standard of what you wear on your wrist, but it's more than enough for what we need to do."
Those components, which would be deemed vintage or simply obsolete in today's computer market, are responsible for sending more than 1.5 million observations of nebulae, galaxies and star clusters back to Earth's surface. And now that work will continue.
"Today, we still only use about 60[%] to 70% of its memory and its capacity to do all the things that Hubble does," Jeletic said.
But Hubble is now in a situation many smartphone users may identify with: While tech support is still available, hardware support has been discontinued since NASA completed its final servicing mission in 2009.