Assignments for Servicing Mission 3B
New solar panels
Replacement of the Power Control Unit
Nicmos was originally installed onboard Hubble during the second Servicing Mission (SM2) in February 1997. Designed to operate at infrared wavelengths, Nicmos had to be cooled so that its own heat did not interfere with the infrared detectors. In the case of Nicmos, cooling is produced by solid nitrogen at -196 °C, encased in an advanced thermos flask system.
Unfortunately Nicmos' lifetime was reduced from the expected 4.5 years to about 2, due to a problem in the cooling system. The sides of the thermos flask touched and as a result the solid nitrogen inside heated up and evaporated, so that by January 1999 all the coolant nitrogen had disappeared and Nicmos could no longer operate.
Once the problem was recognised the Space Telescope scheduling was adjusted in such a way that Nicmos observations were assigned to as much as 40-50% of the total observing time during the first period of observations after the instrument was installed. In this way the Nicmos science programme was completed despite the instrument's dramatically shortened lifetime.
But at last, after this enforced shutdown, Nicmos has been revived. Astronauts retrofitted it with a new, experimental cooling system that returned it to active duty. By fitting Nicmos with this refrigerator-like cooling system, it is again possible to re-cool the detectors to -196 ºC (77 K), thereby reawakening their infrared vision and extending the instrument's life by several years.
The super-quiet cooler (called the Nicmos CryoCooler - NCC) uses ultra-high-speed microturbines, spinning up to more than 400 000 rpm (revolutions per minute)- over 100 times the revolutions of a typical car engine). Hubble's engineering team successfully demonstrated this technology in 1998 during another Shuttle mission in the first on-orbit test of this high-performance, high-efficiency, mechanical cryocooler.
In the past Nicmos has produced excellent science and astronomers are looking forward to working with this top class instrument again.
A new coat for the telescope
Space debris has both a natural and an artificial origin. Naturally arising space debris has dimensions ranging from a thousandth of a millimetre to a few centimetres and resembles tiny stones. The artificial debris is of human origin and includes used rocket parts, small pieces of old satellites and fragments from explosions. To protect critical systems, Hubble and other satellites are placed at safe altitudes that minimise the risk of microcollisions.
Nevertheless, some deterioration is inevitable, so the Multi Layer blankets must be repaired to keep the telescope thermally insulated and protected. The Multi Layer Insulation has flaked in places and there is some concern that the particles might find their way into the telescope and cause a contamination problem. Repairs to this blanket began during Service Mission 3A and continued during Service Mission 3B.
A little boost
Hubble has no on-board propulsion, so the only way to restore lost altitude is by the creative use of Shuttle jets during servicing missions. Hubble's altitude was increased before the last spacewalk during SM3B, as it was done during both SM1 and SM2.
The Servicing Mission 3B astronauts
Michael J. Massimino, who will be making his first space flight, will join three veteran astronauts, John M.Grunsfeld, James H. Newman, and Richard M. Linnehan. Scott Altman, a two-time shuttle veteran, will command the mission. Pilot Duane Carey, making his first space flight and flight engineer Nancy Currie will join him on the flight deck. Currie has three previous space flights to her credit.