The STS-95 Space Shuttle crew completed a series of successful tests on a new video guidance sensor component Tuesday, Nov. 3. The component - part of the Automated Rendezvous and Capture System - will allow spaceships to locate each other and rendezvous without human intervention. The sensor will be used by the International Space Station to simplify routine supply dockings and separations.
The video guidance sensor, developed by NASA's Marshall Space Flight Center in Huntsville, Ala., uses a combination of lasers, video and reflectors to measure the relative position and distance between spacecraft. For testing, reflectors were mounted on the SPARTAN solar observatory satellite that was carried into orbit by Discovery Oct. 29. During the STS-95 mission, the Shuttle-mounted video guidance sensor measured reflected laser light from SPARTAN to gather rendezvous data.
The satellite was deployed from the Shuttle's payload bay on Sunday, Nov. 1. The STS-95 crew used the Shuttle's robot arm to position SPARTAN 33 feet, or 10 meters, in front of the video guidance sensor mounted in the payload bay. The Shuttle's robot arm moved SPARTAN as close as 13 feet, or 4 meters, to the sensor to gather detailed tracking information prior to releasing SPARTAN into space for a two-day solar science mission.
On Nov. 3, after a successful SPARTAN science mission, the STS-95 crew began long-range testing of the Video Guidance Sensor during manual rendezvous and retrieval operations.
The video guidance sensor was activated and made contact when the Shuttle moved to within 480 feet, or 146 meters, of the satellite. During approach, at 360 feet, or 110 meters, the crew performed attitude maneuvers - changing the position of the Shuttle to determine the width of the sensor's field of view. "The video guidance sensor locked-on at 480 feet. That's 120 feet better than we designed the system to achieve," said Gene Beam, project manager for the video guidance sensor at Marshall Center.
The crew stopped attitude maneuvers at 246 feet, or 75 meters, from SPARTAN during the brief orbital nighttime to maintain observation of the nearby satellite. The Shuttle then moved away to a distance of 600 feet, or 82 meters, to gather more information on the maximum limits of long-range tracking. Completing the maneuver, the crew moved back into robot arm range of SPARTAN and successfully captured and re-stowed it in the Shuttle payload bay for return to Earth.
During long-range testing, data from the Shuttle's hand-held laser range finder was compared to information from the video guidance sensor. "The difference in readings between the hand-held laser and the sensor was well within acceptable levels," said an STS-95 crew member. "The data we collected looks comparable to the data from the earlier STS-87 mission where we first tested this sensor." The Space Shuttle Columbia carried the first test into orbit in November 1997. The operational version of the Automated Rendezvous and Capture System is expected to be accurate within one-tenth of an inch.