Space Shuttle Discovery carried out shuttle mission STS 82, the second servicing mission for the Hubble space telescope. The successful mission lasted ten days, during which two instruments built at Ball Aerospace were exchanged with instruments already in the telescope. The two new "Next Generation" instruments, known as NICMOS and STIS have built in corrective optics, to account for Hubble's problem mirror, and don't depend on the corrective optics provided by the COSTAR instrument, installed during the first servicing mission, STS-61. COSTAR has the capability to permit retraction of the corrective optical mirrors over each instrument that it was designed to serve. One goal of the servicing missions is to eventually replace all of the instruments which depend on COSTAR -- including COSTAR itself -- with instruments capable of making the optical adjustments themselves. As an interesting side note, one of the instruments that was replaced during STS-82 was the Goddard High Resolution Spectrograph (GHRS) which was also built at Ball and was installed in the telescope before it's launch during shuttle mission STS-31 in April of 1990.   Another interesting note:  GHRS was near the end of it's operating life when the second servicing mission came due.  After the second servicing mission was launched, and during the approach to the Hubble, the GHRS instrument exhausted it's supplies and shut itself down.  It was almost as if the instrument knew it was time to be replaced, and was ready to come back to earth. 

STS-103 was mission 3A, originally unplanned, launched on December 9, 1999 to replace all of Hubbles six gyroscopes.  Normally these things wear out and are replaced during the planned service missions, like the one planned for June of 2000.  The Hubble relies on these six gyro's to maintain axial stability, with two gyro's per X, Y, or Z axis.  It uses two per axis to allow one to wear out and still have a backup to rely on.  Should four of the six gyroscopes fail, the Hubble will have insufficient control over it's axial stability, and can't be accurately pointed at it's intended targets.  The telescope would place itself in a "safe mode", which would allow no science observations, and thus cost lots of money and observing time for scientists on the ground.  The operating requirements for Hubble dictate that should a situation like this develop, a mission should be considered to replace the failing parts.  Hubble project directors decided to split the original third mission into two "half" missions.  Mission 3A (December of 1999) replaced the gyroscopes, the telescope's computer, a guidance sensor, installed a new data recorder, and the outer insulation which gets torn off by small meteor hits occasionally.  The mission's timing couldn't be better - three of the four gyroscopes had failed as of the fall of 1999, and a fourth gyroscope failed on November 13th, placing the Hubble in safe mode (it could still be maneuvered and collected by the shuttle for repairs).

If you're curious about what wears out the gyroscopes, it's because of thermal expansion and contraction of components on the telescope.  Specifically, it's due to thermal expansion & contraction of components in the solar panel structures.  As they heat up & cool down in space, they create vibrations.  Due to their massive size, these vibrations shake the telescope, and thus put stresses on the gyroscope bearings - which are trying to keep the telescope stable.  Eventually, the bearings fail and gyroscopes stop working.  It's pretty much that simple.

What was the third planned service mission, but now will be mission 3B,  is due to launch on June 8, 2000 (2001?).  Ball is developing the Advanced Camera ACS (Advanced Camera for Surveys) for installation during this mission.  The ACS is 10 times more powerful than the Faint Object Camera that it will be replacing.  In addition to the ACS, new solar panels will be installed, along with the Aft Shroud Cooling System, which will carry heat away from the scientific instruments and allow the instruments to  operate better at lower temperatures.  The new cooling system will allow multiple instruments to operate simultaneously, helping the science team maintain the space telescope's high productivity.  Another advanced cooling system will be installed onto NICMOS, which became dormant after its solid nitrogen coolant was exhausted in January 1999.  The telescope will be re-boosted back to a good orbit to maintain it's efficiency during this mission as well, along with whatever other maintenance is required, such as (the now standard procedure) thermal blanket repairs, etc. 

The fifth mission, which is actually the fourth "official" mission, is planned for November 2002, but little detail seems to be available about it right now.  Of course, by then we'll be finding large, black rectangular objects on the moon and we'll be sending manned missions to Jupiter with guys named Dave and psychotic computers named HAL... :-)

The operating goal calls for Hubble to work at least until 2005, but it's performing so well that a plan called the HST Second Decade Study looks at how to extend the telescope's use until at least 2010 [When, of course, we'll be sending another mission to Jupiter to revive a computer named HAL, to recover a ship named Discovery, and to see Jupiter turn into a sun at the hands of the aliens who are in charge of large, black, rectangular objects... :-) ]

Hubble, launched in 1990, is one of what are called the Great Observatories. It's slightly younger brother, the Compton Gamma Ray Observatory was launched in 1991, and lasted four years longer than it was expected to.  CGRO finally had too many of it's gyroscopes fail to maintain stability of the observatory, and is being readied to plunge back into earths atmosphere.  It's so big that not all of it will burn up on re-entry, so what little manueverability remaining is being used to position the telescope so that the parts that don't totally become more vapor in our atmosphere will splash down on or around June 1, 2000 in the Pacific Ocean.

A younger sibling to Hubble is the Chandra X-ray Observatory, formerly known as AXAF, which was launched on July 23, 1999.  Chandra was carried to space aboard the Space Shuttle Columbia on mission STS-93(95), commanded by astronaut Eileen Collins, the first woman to command a shuttle mission and at the same time make history for doing so.

This was the last of the giant telescopes to be carried into space on the shuttle.  AXAF and Hubble are so large that they filled the entire cargo bay with less than six inches at either end.  After AXAF was launched, Columbia was taken to California to be refitted with components needed to dock with the International Space Station.  This doesn't mean there won't be anymore telescopes launched using space shuttles, it means that the telescopes (or at least pieces that are assembled in space) will be small enough to fit in the cargo bay alongside the docking hardware.

Chandra consists of three major elements:  a spacecraft with an inertial upper stage rocket motor, a telescope, and a science instrument module.  The observatory is helping astronomers world-wide get a better understand the structure and evolution of the universe by studying powerful sources of X-rays such as exploding stars, matter falling into black holes and other exotic celestial objects.  X-ray astronomy can only be done from space because Earth's atmosphere blocks X-rays from reaching the surface.  Chandra provides images that are fifty to one hundred times more detailed than previous X-ray missions.  At more than 45 feet in length and weighing more than five tons, it will be one of the largest objects ever placed in Earth orbit by the Space Shuttle. 

Ball designed all of the instrumentation platforms for the Science Instrument Module (SIM), and some of the instruments that mount to these platforms: The Scanning Electronics Assy, the Processing Electronics Assy, and the star tracking camera that gathers directional information in real time to direct and point the main telescope, which contains the High Resolution Mirror Assembly (take a look at these - they're unlike any mirror you would expect to find in a telescope). In front of the star tracking camera is a very sophisticated light baffle that was designed to protect it from any stray light.