Hubble's Last Hurrah

Hubble's Last Hurrah

The Skies' Eyes
The Hubble Space Telescope, pictured here during its 4th repair mission, will be serviced a final time in 2008. The upgrades should extend Hubble's operational life through 2013, and its orbit should be stable for another decade or so after that.

If it is true that what does not kill you makes you stronger, the final incarnation of the Hubble Space Telescope may fundamentally change what is known about existence.

After reversing a decision to cancel a shuttle servicing mission to Hubble, NASA is putting the finishing touches on a flight planned for August to overhaul the world's most popular observatory one last time.

The expectations seem giddily high. Astronomers want to use the refurbished telescope to peer back to when the universe was a mere 460 million years old -- a fraction of its current 13.7 billion years. They plan to hunt down supernova explosions to serve as bookmarks in time and space in an attempt to figure out why the expansion of the universe has sped up in the last 4 to 5 billion years or so.

Some scientists are even putting forth most audacious proposals to chemically analyze the atmospheres of planets circling other stars.

Were it not for Hubble's history, the dreams would be far-fetched. Written off as a boondoggle after scientists discovered its misshaped primary mirror, Hubble, outfitted with corrective optics during the first shuttle servicing mission in December 1993, was resurrected and spent the next 14 years making observations of the universe that drove astronomy textbooks into early retirement.

For example, in an ironic tribute to its namesake, the space telescope uncovered evidence that the universe's expansion is speeding up, not slowing down as predicted. Astronomer Edwin Hubble discovered in the 1920s that the galaxies are all flying apart and that the ones farthest away from Earth are flying the fastest.

"We've been able to use Hubble to probe the story farther back in time," said Adam Riess, a highly regarded 36-year-old astrophysicist at Johns Hopkins University in Baltimore, who developed techniques for using supernova explosions to ferret out the universe's steroid-like expansion rate.

Dark Mysteries

The force whipping the universe's spread has been termed dark energy, which is quite distinct from so-called dark matter.

"Dark matter are particles of matter that mostly reside in galaxies. Dark energy is smooth and spread evenly through space. Dark matter we've known about for 80 years or so. Dark energy is something new, only detected 10 years ago," Riess said.

Scientists don't know much about dark energy. But they do know that it is causing the universe to expand 20 percent faster today than it was 5 billion years ago. More data is expected once Hubble is outfitted with a new wide-field camera, one of two new science instruments to be installed by spacewalking astronauts during the upcoming shuttle flight.

The new camera will enable Hubble to detect and image an expanded chunk of the electromagnetic spectrum, with sensitivity spanning ultraviolet to near-infrared radiation. It also greatly increases the amount of information that can be collected during a single observation.

"We can take the same data 70 times faster and with 40 to 50 percent better resolution," said Sandra Faber, an astronomer at the University of California-Santa Cruz, who plans to use the new camera to image the universe's first galaxies.

Riess' study of dark energy hinges on surveys of supernovas. Hubble's new camera is expected to increase their rate of detection by a factor of 2.5, as well as find supernovas that are much farther away, according to a National Science Foundation report that prompted NASA to reinstate the Hubble servicing mission.

"The result would be much tighter constraints on the properties of dark matter," the report concludes.

Back From the Dead

The shuttle flight to Hubble was canceled by former NASA administrator Sean O'Keefe following the 2003 Columbia accident, due to safety concerns. His successor, Mike Griffin, reversed the decision after outside experts concluded a flight to Hubble was not significantly more risky than flying to the International Space Station, which offers shuttle astronauts a safe haven if their ship is too damaged to return to Earth.

To mitigate the risk of flying to Hubble, NASA plans to have a second shuttle at the launch pad ready to mount a rescue mission in case of an emergency.

The mission will be among the most ambitious NASA has attempted. Five spacewalks are planned during the 11-day flight.

In addition to installing the new wide-angle camera, astronauts plan to replace Hubble's corrective optics instrument, which is no longer needed (science instruments installed after Hubble's mirror flaw was discovered are manufactured to precisely match the misshaped glass), with an ultraviolet-sensitive spectrometer that can detect gases which individual light beams have encountered on their journeys from a radiating source to Hubble's eye.

Scientists plan to use the Cosmic Origins Spectrograph (COS) to probe the chemical composition of gas between galaxies for elements such as nitrogen, silicon, aluminum, oxygen, carbon, and iron, all of which somehow evolved from the hydrogen and helium created in the Big Bang. COS also will be used to probe the atmospheres of extrasolar planets, perhaps providing evidence of distant worlds with habitable environments.

A Long To-Do List

Before leaving Hubble, the astronauts will attempt to revive Hubble's visible light camera, which short-circuited last year, and repair a second spectrograph, which failed in 2004. They also plan to replace the observatory's guidance sensors and gyroscopes, which are needed to point and hold the telescope on targets, and install fresh batteries.

Finally, they will wrap Hubble with new layers of insulation and install a docking ring so a booster rocket can latch on at some point in the future to steer Hubble safely toward the atmosphere and its final resting place in the sea.

That won't happen anytime soon. The upgrades should extend Hubble's operational life through 2013, and its orbit should be stable for another 10 years or so after that.

Hubble has defied the odds many times before. Perhaps when another spacecraft locks on to Hubble's new docking port, it will be the shuttle replacement Orion, with a new crew to service the telescope once again.