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 Mission Objectives - Part 3 of 3

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NICMOS Cooling System (NCS): Astronauts retrofitted an existing but dormant instrument called the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) with a new, experimental cooling system to return it to active duty. NICMOS was placed on Hubble in 1997, but 2 years later, after depleting the coolant needed to maintain low temperatures for its infrared detectors, it became dormant.

By fitting NICMOS with the experimental cryogenic system, the detectors were re-cooed lto below -315 ° F (-193 ° C or 80 K), reviving its infrared vision, and extending its life by several years.

The NCS consists of separate components such as the NICMOS Cryo-Cooler (NCC) and a radiator which is run along the length outside of Hubble's body.

At the heart of the NCC is a turbo-machine, consisting of a compressor and tiny turbines, turning at up to 400,000 rpm (about 100 times the operating speed of a typical car engine). Hubble's engineering team successfully demonstrated this technology in 1998 aboard STS-95 in the first on-orbit test of a high-performance, high-efficiency, mechanical cryocooler.
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Reaction Wheel Assembly (RWA): One of four reaction wheel assemblies (RWA), which is part of Hubble's pointing control system, was replaced by a refurbished unit. The four RWAs onboard Hubble are a very important component of the telescope's Pointing Control Subsystem (PCS).

The spinning of the RWAs (3000 rpm) cause rotational, or angular momentum to point the telescope from one target to another (this motion is called "slewing"), and to keep it stably pointed once the target is acquired.

Astronauts also performed the following "get ahead" tasks. These were not urgent or primary tasks, but accomplishing them on this mission freeed up time and resources for the next visit to Hubble.
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Gyroscopes: The gyroscopes, or gyros, are part of Hubble's sophisticated pointing system. They measure attitude when Hubble is changing its pointing from one target (a star or planet, for example) to another, and they help control the telescope's pointing while scientists are observing targets.

To conduct science at the time, Hubble needed three working gyros. The telescope carries six; three serve as backups. The gyros are paired in boxes called Rate Sensor Units (RSUs). It is the RSU that astronauts change when they replace gyros, so gyros are always replaced two at a time. The crew replaced one RSU.

New Outer Blanket Layers (NOBLs): Astronauts fitted Hubble with several, specially coated, stainless steel sheets to Hubble's exterior. These new outer layers prevent damage from sunlight and extreme temperature changes, and help maintain Hubble's normal operating temperature. NASA tested these covers to withstand at least 10 years of exposure to charged particles, X-rays, ultraviolet radiation, and thermal cycling. Astronauts installed several NOBL panels on Hubble in 1999.

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NCS - A New Cooler ::
The Nicmos Cooling System will allow Hubble's Near-Infrared Camera to be reactivated. Shown above is the cryo-cooler component.
NCS - Inner Workings ::
The cryo-cooler is shown here at an early stage. It uses revolutionary high speed turbines to function.
RWA - Steering Hubble ::
The reaction wheel assembly is needed to point Hubble. One of four RWA's will be replaced this mission.
RSU - Notice the Technique ::
Astronauts practice installing Hubble's Rate Sensing Unit on a Hubble test model.
RSU - The Gyro Component ::
The most essential part of an RSU, a gyro is shown here in its component parts.
NOBL - A New Blanket ::
Astronaut Massimino practices fitting a New Outer Blanket Layer in an underwater simulation.
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