ACS
The Advanced Camera for Surveys (ACS) was installed in Hubble by the crew of the Space Shuttle Columbia (STS-109) during Servicing Mission 3B, which took place March 1 to March 12, 2002. With its wide field of view, superb image quality, and exquisite sensitivity, the Advanced Camera for Surveys (ACS) has 10 times more discovery power than the camera it superceded (WFPC 2). ACS became mostly inoperable in January 2007, but is slated for repairs in SM4.
COS
The Cosmic Origins Spectrograph (COS) is a medium resolution spectrograph specifically designed to observe into the far and near ultraviolet regions of the electromagnetic spectrum. The ultraviolet region is particularly interesting for observing high energy objects such as young hot stars and quasi-stellar objects (QSO's). It is also well-suited for determining the composition and character of the intergalactic medium (IGM) and interstellar medium (ISM). The COS will be mounted in the space currently occupied by COSTAR, which has not been needed since the Faint Object Camera was replaced in 2002.
FGS
The Fine Guidance Sensors (FGS) are optical sensors used on the Hubble Space Telescope to provide pointing information for the spacecraft and also as a scientific instrument for astrometric science.
An FGS houses a collection of mirrors, lenses, servos, prisms, beam-splitters and photomultiplier tubes.
There are three fine guidance sensors on Hubble located at 90-degree intervals around the circumference of the telescope. Two FGSs are used to lock onto "guide stars" and point the telescope at an astronomical target, and hold that target in a scientific instrument's field of view. The third FGS can then be used as a scientific instrument for astrometry.
NICMOS
The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) provides imaging capabilities in broad, medium, and narrow band filters, broad-band imaging polarimetry, coronographic imaging, and slitless grism spectroscopy, in the wavelength range 0.8-2.5 microns. NICMOS has three adjacent but not contiguous camera channels, each with a different field of view (FOV) on the sky.
STIS
The Space Telescope Imaging Spectrograph is a powerful general-purpose spectrograph that is complementary to - not superseded by - the Cosmic Origins Spectrograph (COS). STIS was installed during Servicing Mission 2 on February 12, 1997. STIS performed on-orbit operations for approximately 65,000 hours (7 years, 171 days) before failing on August 3, 2004. The instrument remains in safe mode.
WFC3
Wide Field Camera 3 (WFC3) will be the last imaging camera to be installed on Hubble. WFC3 will replace WFPC2 which was installed during the 1993 Servicing Mission and will be nearly 15 years old by SM4. The new instrument contains two channels that will offer "panchromatic" coverage extending from the ultraviolet through the near-infrared. As a result of its unique capabilities, WFC3 will become Hubble's workhorse, imaging both the nearby and distant universe.
Batteries
Each of Hubble's six batteries consists of 22 cells in series along with heaters, heater controllers, pressure measurement transducers and electronics, and temperature-measuring devices and their associated electronics. Three batteries are packaged into modules measuring roughly 36 by 32 by 11 in. (91 x 81 x 28 cm) and weighing about 460 pounds (209 kg). Each of the two modules is equipped with two large yellow handles that astronauts use to maneuver the module in and out of the Telescope in space.
Gyros
The Gyroscopes are part of Hubble's pointing system. They report any small movements of the spacecraft to Hubble's Pointing and Control System. The computers then command the spinning reaction wheels to maintain the spacecraft at the desired location. A complete set of gyrosopes is six in number, housed in three Rate Sensing Units (RSUs), each containing two gyros.
NOBL
Hubble is protected by multi-layer external blankets. They maintain normal operating temperatures of Hubble's electronic equipment. Some damage to these external blankets was discovered during the second servicing mission in 1997, and additional wear and tear has been seen in each subsequent visit to the telescope.
Starting with servicing mission 3A in 1999 astronauts began covering Hubble with permanent sheets called the New Outer Blanket Layer (NOBL). The NOBLs are designed to protect Hubble's external blankets and are specially coated stainless steel foil trimmed to fit each particular door. Each cover is supported by a steel picture-frame structure. Expanding plugs, like common kitchen bottle stoppers, fit into door vent holes to allow quick installation.
SIC&DH
The Science Instrument Control and Data Handler (SIC&DH) unit is a collection of electronic components attached to a tray mounted on the door of Bay 10 in the SSM Equipment Section. Components of the SIC&DH unit are: The NASA Standard Spacecraft Computer (NSCC-I); Two standard interface circuit boards for the computer; Two control unit/science data formatters (CU/SDF); Two CPU modules; A Power Control Unit; Two Remote Interface Units; And various memory, data and command communications lines (buses) connected by couplers. These components are redundant so the system can recover from any single failure.
On 09/27/08 the failure of the A-side CU/SDF forced the postponement of the planned October servicing mission into mid-2009. While NASA engineers were able to switch over to the B-side CU/SDF, they could not leave such an important component unable to recover from a single point failure. Since a spare SIC&DH is available, its replacement will be added to the rescheduled SM4 mission.
SCM
The Soft Capture Mechanism (SCM) is a ring-like device that is to be attached to Hubble's aft bulkhead. It is designed for future use in safely de-orbiting the telescope at the end of its useful life by a next generation spacecraft vehicle.
It provides a Low Impact Docking System (LIDS) interface and associated navigation targets for future rendezvous, capture and docking operations.
Solar Arrays
The solar arrays (SA3) are rigid arrays, which do not roll up and therefore are more robust. Although one-third smaller than the first two pair (the original pair and the ones installed during SM1), they produce 30 percent more power. They are less susceptible to extreme temperatures and their smaller size reduces the effects of atmospheric drag on the spacecraft.
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