The observatory got off to a disastrous, blurry, and embarrassing beginning. Emergency on-orbit corrective optics had to be installed within HST by astronauts in 1993. Subsequently, service mission 2 to HST was accomplished in February 1997; service mission 3A took place in December 1999; and HST servicing mission 3B is up next.
With each visit to Hubble, astronauts have left it newer and better than they found it.
It's a kind of technological and celestial symmetry: To help Hubble peer back over billions of years, you replace equipment suffering from old age.
New workhorse
The star equipment to be hooked to Hubble during service mission 3B is the Advanced Camera for Surveys (ACS). It replaces the Faint Object Camera - the last of Hubble's original instruments.
The size of a large phone booth, and weighing in at 870-pounds (395-kilograms), ACS is expected to increase Hubble's discovery prowess by a factor of ten.
So powerful is ACS there exists an outside chance it may directly image planets in other, neighboring solar systems. ACS can spot celestial objects far beyond the reach of current Hubble instruments and in a fraction of the time. Working in wavelengths ranging from ultraviolet to the far red, ACS's picture taking tasks include monitoring weather and looking at other features on planets within our solar system.
Destined to be a Hubble workhorse, the ACS earns that rank thanks to cutting-edge, super-sensitive digital detectors, said Paul Volmer, program manger for aerospace systems at Ball Aerospace & Technologies Corporation here.
"That makes this instrument the great discoverer that it is," Volmer told SPACE.com. "It was a real challenge packaging those chips, building that detector, and assembling it all into a package to meet all the power, thermal, and optical requirements," he said.
Ball manufactured the ACS instrument. By the HST's final service mission in 2004, the firm will have produced seven of the observatory's science instruments.
Reach out into the future
The detectors in the Advanced Camera for Surveys are better known as charge coupled devices, or CCDs, similar to those used in home digital cameras. The CCDs gathers the light from an astronomical object, then records the image.
The Wide Field Channel of ACS allows it to observe very old, very distant objects whose spectra are red-shifted due to the expansion of the universe. The instrument's High Resolution Channel can pick out the inner regions of galaxies, and search neighboring stars for planets and planets-to-be. A Solar Blind Channel can search for hot stars and quasars, and will study aurora and weather on planets in our solar system.
"It would be difficult today to go find scientific detectors with a larger format than what we're flying on ACS. So it's going to be a state-of-the-art instrument," Volmer said. "Everyone reached out into the future, just far enough that we got there. It was a challenge…but we got there," he said.
Astronomer Holland Ford of The Johns Hopkins University, and leader of the team that built ACS over a five-year period, has noted that the instrument will keep Hubble "on the astronomical forefront that the public has come to expect of the Space Telescope."
Volmer said the tenfold upgrade is a huge leap. "That's what scientists typically like to see…an order of magnitude improvement from instrument to instrument. They'll be able to do Earth-shaking science if they get that order of magnitude," he said.
Cool experiment
Labeled as an experiment, astronauts will plug in a spiffy new cooling system into Hubble's now dormant Near Infrared Camera and Multi-Object Spectrometer, NICMOS in NASA lingo.
Stocked with infrared detectors that beg for very cold temperatures to work, NICMOS petered out when its cache of nitrogen ice was consumed faster than planned. A tiny heat leak in the thermos-like container that held the super-cold ice cut short NICMOS operations in 1999.
Astronauts will retrofit the high-tech cryocooler onto NICMOS, perhaps returning the Hubble instrument to active duty. The cooling system technology was first tested aboard STS-95 (John Glenn's return to flight) in 1998. The high-performance, high-efficiency, mechanical cryocooler proved to be the right stuff too.
The NICMOS Cryocooler uses neon gas as a coolant. At the very heart of the refrigeration device, however, is a miniature cryogenic circulator, replete with ultra-small turbines.
"They are, in fact, somewhat of a miracle of modern fabrication," said Ed Cheng, lead scientist for the NICMOS cooling system at Goddard Space Flight Center in Greenbelt, Maryland.
The ultra-high speed microturbines and a compressor remove heat from NICMOS. That heat is transported to the cryocooler. The small circulator turns at up to 7,000 revolutions per second, roughly 400,000 turns per minute. That's equal to some 50 to 100 times the speed of your automobile engine - depending on what kind of car you drive, Cheng said.
Developed jointly by NASA and the U.S. Air Force, the NICMOS Cryocooler runs virtually vibration-free. That's a must for shake-free shots of the cosmos and Hubble's clarity of purpose.
Moreover, bringing NICMOS back from the dead, and have it work in tandem with the ACS, should permit unprecedented insight into astrophysical issues of the day.
Next page: Lights out!
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