The Hubble Space Telescope's main camera -- the ACS (advanced camera for surveys) -- has stopped working. It went into safe mode early Saturday morning, and engineers for the space telescope have little hope it can be fixed.
The ACS was installed in 2002 and increased the discovery capability of the telescope by a factor of 10. It consists of three electronic cameras, filters and dispersers that can detect light from the ultraviolet to the near-infrared end of the spectrum and had become the primary instrument of the telescope. The ACS was valuable to astronomers because it could take deep imaging surveys of clusters of galaxies, allowing scientists to study these environments. Hubble still has other cameras which look at different spectrums that are still operating.
NASA has scheduled a shuttle mission to fly to Hubble in September 2008, but that mission is so full already that Preston Burch, Hubble associate director at the Goddard Space Flight Center, says he doesn't believe a spacewalk to fix the camera is possible.
"It's not as easy or straightforward to fix ACS as it is to fix the STIS [space telescope imaging spectrograph] camera," he says. "In order to access the box cover and restore capability we would need to turn off the cooling system, and disconnect connections to the control module. It's a big job, the area is pretty limited; we are already challenged enough to do the other repairs and this spacewalk would be considerably more labor-intensive."
SMA 4, the shuttle flight to service Hubble, is scheduled for next year, and the crew of that mission has a long to-do list. Hubble needs six new nickel hydrogen batteries to keep it powered up and working, plus new units containing two gyroscopes to help the telescope lock on to targets.
While the astronauts are up there on what will be the last mission to Hubble, they will also install a new wide-field camera, a cosmic origins spectrograph and a new fine guidance sensor, as well as attach a new outer protective layer.
These fixes will increase Hubble's capability and keep Hubble running until its replacement, the Webb telescope, can be launched early next decade.
Under current NASA guidelines this mission will certainly be risky. Five intensive back-to-back spacewalks with two spacewalking teams will refurbish Hubble to extend the wildly successful telescope's lifespan through 2013.
This will be the fifth time the space shuttle has come to Hubble's rescue.
When Hubble was launched in the spring of 1990, its life expectancy was just 15 years, but thanks to four prior servicing missions by the space shuttle, Hubble's life and usefulness have been extended.
A Hubble mission had originally been scheduled for 2005, but was canceled following the February 2003 accident that killed the crew of the Space Shuttle Columbia. Retired shuttle Cmdr. Jim Wetherbee says the desire to save Hubble isn't just sentimental.
"Technically speaking, it is more risk. Is it worth taking that risk? I would say yes. If I were the administrator, I would go save Hubble. I can't even begin to tell you all the technological advances Hubble has given us. More importantly, think what we can gain in its future," Wetherbee says.
Hubble's pictures are so stunning because the telescope observes wavelengths, which are what the human eye sees. Therefore, Hubble occupies a unique position among the great space observatories launched by NASA.
Chandra observes X-rays, and SIRT observes the infrared band. Hubble's pictures are so spectacular that they are some of the most frequently downloaded photos on the Internet.
The failure of the ACS is disappointing to Burch. It was installed on Hubble in 2002 with an expected lifetime of five years, but engineers had hoped it would last longer. It was supposed to support several upcoming missions, and was in the middle of observing the northern and southern lights on Jupiter and Saturn when it failed.