NASA's Hubble Hurdles: Ancient 486 CPUs and 32k Memory

Scientists Fixing Hubble Contend With Antiquated Computers

NASA scientists trying to find out what went wrong during last week's repair of the Hubble Space Telescope find themselves dealing with 486 processors and other outdated computer technology. But sometimes, mission managers say, simple is good when you're out in space—as long as you know how to talk to decades-old computers.

The Hubble needs service—again. The space telescope has beamed gorgeous images of the universe down to Earth for 17 years and has undergone four servicing missions by space shuttles. A September 27 failure in the Science Data Formatter pushed back a planned fifth and final servicing mission aboard the space shuttle Atlantis from this month until February 2009. While trying to switch over some of the telescope's electrical systems to redundant backup versions remotely, the team at NASA's Goddard Space Flight Center in Maryland hit two anomalies that caused the telescope to enter "safe mode" and stop most science operations. Goddard scientists think they have found the cause, and hope that operations will resume this weekend. But perhaps finding a few problems should come as no surprise—not only have Hubble's backup systems sat idle for 18 years, but the telescope operates with computer systems long outdated here on Earth.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. Today most would balk at using such outdated processors in our homes or offices, but NASA scientists find ways to talk to and fix spacecraft that carry computing systems from a bygone era.

To help the NASA scientists repair Hubble, Goddard spokesperson Susan Hendrix told PM, they have an on Earth replica. The Vehicle Electrical System Test, located at Goddard's headquarters inside the world's largest "clean room," is a full duplicate of Hubble's computers. Astronauts planning to service the telescope train on this equipment, and any equipment that they will carry to the telescope must be tested on VEST to make sure it can communicate and work with Hubble's existing systems. However, Hendrix said, "We just can't go up there every time there's a glitch." So VEST also helps the scientists currently trying to figure out what went wrong. The Goddard team, led by Art Whipple, can try out its hypotheses about the cause of the electric failures on VEST and see whether they work.

Hubble certainly isn't the only long-lived spacecraft running on an antiquated processor. NASA launched the Chandra X-Ray Observatory in 1999, but its project manager, Roger Brissenden of the Harvard-Smithsonian Center for Astrophysics told PM that because spacecraft concepts are designed years in advance, Chandra carries computing technology that is even older than that. The observatory carries a VAX computing architecture, he said, and a 1750A processor that is roughly the equivalent of a 386, though it didn't occur to him until well after the launch just how quickly those systems would become outdated. The Chandra team has its own mock-up of the telescope's insides, just like Hubble has VEST, where scientists can train to interact with the real Chandra systems. But while most scientists associated with Hubble or Chandra are worried first about problems in the telescope, Brissenden said that he can't forget about problems on the ground, like damage to the duplicate here on earth or glitches in the software he uses to talk to Chandra. Once, he said, he and his colleagues had to rig up a VAX emulator on a LinuxBox computer to talk to Chandra. It worked—the machine didn't know it's talking to an emulator.

While Hubble and Chandra operators have to deal with outdated computer systems running their observatories, at least those craft are orbiting Earth (though Chandra is in high orbit and can't be serviced by a shuttle). Ed Massey is the manager of the Voyager Interstellar Mission, and both Voyagers are now approaching the boundaries of our solar system, billions of miles from Earth.

But Massey said the hardest part about running Voyager 1 and 2, besides the great distance, is that most of the people who designed and operated the Voyager craft in the late 1970s have now gone. "New people have to learn old technology," he said. That turns off some scientists from working on the mission, he said, but it draws in others who are excited about the opportunity to work with the vintage computing systems that operate two of the most famous space missions in history.

Each Voyager has three computer systems, with a combined total of around 64k of memory. "The amount of computing power it has is far less that the two gig memory stick you carry around," he told PM. Sometimes, he said, he wishes that the Voyagers carried modern computer chips and memory. That would make his life a lot easier, he said, and the Voyager mission might have been able to take far more photographs if the crafts had more memory and could store images digitally, rather than on tape. But, he said, the old-fashioned computers get the job done, beaming the first close-ups of Jupiter, Saturn, Uranus and Neptune back to Earth.

Brissenden agreed: "Sometimes simple is good." Chandra's two-decades old computer system has only 768k of memory, he said, but with all the things that could go wrong with a machine in space, that's not such a bad thing. And Hendrix said the Hubble team is on the same page. Even though NASA can send astronauts up to Hubble, we can't exactly upgrade the system to 2008 computer and electrical technology. When the space shuttle Atlantis finally reaches Hubble, the crew plans to install a backup version of the Science Instrument Control and Data Handling unit (SICDH) and a slate of other upgrades, but the 486 chip will remain. While Hubble's dated hardware probably couldn't run World of Warcraft, Hendrix says that the telescope's computer systems do exactly what they need to do. "It's really reliable," she said. "There really is no need to upgrade it."