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.