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Sighting Aids

Sighting aids include all items used to aid the flight crew within and outside the crew compartment. The sighting aids include the crewman optical alignment sight, binoculars, adjustable mirrors, spotlights and eyeglasses.

The COAS is a collimator device similar to an aircraft gunsight. Two are installed in the crew compartment flight deck. One COAS is mounted during launch and entry over the positive X commander's forward window and on orbit is removed and mounted next to the aft flight deck overhead right negative Z window. The other COAS is mounted at the aft flight deck station for checking the alignment of the payload bay doors.

When the COAS is mounted at the commander's station, it allows the viewers to reassure themselves of proper attitude orientation during the ascent and deorbit thrusting periods. When the COAS is removed from the commander's station to the aft flight deck for on-orbit operations, it provides a backup to the orbiter star trackers for inertial measurement unit alignment. It is also used as the primary optical instrument for measuring range and rotational rates and allows the flight crew members to align the vehicles and dock.

The COAS consists of a lamp with an intensity control, a reticle, a barrel-shaped housing, a mount, a combiner assembly and a power cable. The reticle consists of a 10-degree circle, vertical and horizontal cross hairs with 1-degree marks, and an elevation scale on the right side of minus 10 degrees to 31.5 degrees.

For IMU alignments, the flight crew member at the aft flight deck station maneuvers the orbiter using the COAS at the right overhead negative Z window until the selected star is in the field of view. The crew member continues maneuvering the orbiter until the star crosses the center of the reticle. At the instant of crossing, the crew member makes a mark, which means he depresses the att ref (attitude reference) push button. At the time of the mark, software stores the gimbal angles of the three IMUs. The mark can be taken again if it is felt the star was not centered as well as it could have been. When the crew member feels a good mark was taken, the software is notified to accept it. Good marks for two stars are required for an IMU alignment.

By knowing the star being sighted and the COAS location and mounting relationship in the orbiter, software can determine a line-of-sight vector from the COAS to the star in an inertial coordinate system. Line-of-sight vectors to two stars define the attitude of the orbiter in inertial space. This attitude can be compared to the attitude defined by the IMUs, and if the IMUs are in error, they can be realigned to the more correct orientation by the COAS sightings.

The COAS requires 115-volt ac power for reticle illumination. The COAS is 9.5 by 6 by 4.3 inches and weighs 2.5 pounds.

The 10-by-40 binoculars are a space-modified version of the commercial Leitz Trinovid binocular noted especially for its small size, high magnification, wide field of view, and rugged sealed construction. The 7-by-35 binoculars are noted for close focal distance at high magnification. The 14-by-40 gyrostabilized binoculars contain a gyrostabilized system that enhances target acquisition and retention. When the crew member is subjected to ambient vibrations or hand tremor while using the gyrostabilized binoculars, the target image remains clear and stable. The gyrostabilized binoculars are electrically powered by six alkaline-type AA batteries and will operate continuously up to three hours on one battery pack.

Adjustable mirrors are installed before launch on handholds located between windows 2 and 3 for the commander and windows 4 and 5 for the pilot. During ascent and entry, the commander and pilot use the adjustable mirrors to better see controls that are in obscured areas of their vision. On orbit, the mirrors can be removed and stowed if desired. Each mirror is approximately 3 by 5 inches and weighs approximately 1 pound.

The spotlight is a high-intensity, hand-held flashlight powered by a battery pack consisting of five 1.2-volt one-half D size nickel-cadmium batteries. The spotlight produces a 20,000-candlepower output with a continuous running time of 1.5 hours. The lamp is a 6-volt tungsten filament and cannot be replaced in flight. A spare battery pack is available on board.

For those crew members requiring them, two pairs of eyeglasses are available on board.


Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 04/07/2002
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