Hubble Huggers

An astronaut since 1992, Grunsfeld has served on a mission to the Russian Mir space station and one to carry out astronomical observations with ultraviolet telescopes, in addition to his three servicing trips to Hubble.

But as an astronomer by passion and education, he started staring at stars long before the telescope did. After earning three physics degrees (a bachelor’s from MIT and a master’s and PhD from the University of Chicago), Grunsfeld became a senior research fellow at Caltech, where he studied gamma-ray bursts–jets of high-energy radiation spewed our way by distant, rapidly spinning stars–before joining the astronaut corps. Following the first Hubble rescue ­mission, in 1993–when astronauts installed “contact lenses” to correct an error in the mirror’s curvature–Grunsfeld’s astronomical work relied on results from the telescope itself. So his own first Hubble visit, in 1999, was “a magical moment” that began a whole new relationship with the telescope, as he wrote in the journal he kept “on orbit,” posted online as the John Grunsfeld Reports.

Now Grunsfeld is a Hubble pro, and as leader of the spacewalking team on the final mission, he gave his team more than a few tips and hints. That included a top 10 list–with “about 35 items,” he says, laughing. The main one, he recalls, was “Don’t break the telescope!”

Upgrades on this mission included installing a wide-field camera that sees from the ultraviolet all the way into the near infrared–a new capability for the telescope–and adding a state-of-the-art ultraviolet spectrograph that will sniff out the chemical content of nearby stars and galaxies while helping scientists study how dark matter has molded the shape of the universe.

The team also replaced one of two computers, to ensure redundancy after the 2008 failure, and installed a docking system to help bring the telescope down when it finally peters out. Other fixes included replacing the 19-year-old nickel-hydrogen batteries and adding six new gyroscopes, which let the telescope “stare” at one spot for a long time. A new fine-guidance sensor was also added, to complement the only one of three original sensors still functioning.

In addition to replacing parts, the astronauts completed Hubble’s first-ever in-flight repairs. They fixed the advanced camera for surveys, which yielded the classic galactic snapshots associated with the telescope before failing in 2007, and the electronics board for Hubble’s older imaging spectrograph, which failed in 2004.

“Everyone said [repairs] wouldn’t work,” Grunsfeld says. The naysayers pointed out that it would be nearly impossible to keep track of lots of tiny screws in zero gravity (and any that got loose could damage Hubble’s sensitive instruments), and that astronauts would have to reach into parts of the telescope that were never meant for humans to access in space. But after hundreds of practice go-rounds on Earth and multiple hours of space walks, he and his team proved them wrong. Using special tools designed to remove the screws and trap them inside a clear casing during repair, the astronauts brought both instruments back online.