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=--=--=START=--=--= NASA Spacelink File Name:6_2_2_46_3_12.TXT
STS-51 ORFEUS/SPAS RENDEZVOUS OPERATIONS
The ORFEUS/SPAS will be released by Mission Specialist Dan
Bursch using Discovery's mechanical arm on the second day of the
mission.
While Bursch works with the arm to release the satellite, fellow
crew member Jim Newman will oversee the mechanical operations of the
ORFEUS instrument and the SPAS. The majority of commands to ORFEUS,
however, will come from ground controllers.
Once Bursch has released the satellite, Commander Frank
Culbertson will fire Discovery's small steering jets twice to
separate from the vicinity of ORFEUS/SPAS, moving at least 13
nautical miles ahead of the satellite.
For ORFEUS/SPAS operations, science ground controllers require
at least 1 1/2 hours of communications with ORFEUS/SPAS out of every
4 1/2 hours (three orbits). For these transmissions, Discovery must
act as a relay station -- ground communications will reach
ORFEUS/SPAS via Discovery and vice versa.
ORFEUS/SPAS will fly free of Discovery for almost 6 days.
Discovery will move from being ahead of the satellite to trailing it
the day before it is recaptured. The actual maneuvers to recapture
the satellite will begin about 5 1/2 hours before ORFEUS/SPAS is
captured, with Discovery trailing 30 n.m. behind the satellite.
Discovery then will perform an engine firing to begin closing in on
to a point 8 n.m. behind the satellite at a rate of about 11 n.m. per
orbit. After two orbits and one fine-tuning burn once the
ORFEUS/SPAS is in sight of the electronic star trackers on the
Shuttle's nose, Discovery will reach the 8 n.m. point.
From 8 n.m., the final rendezvous sequence begins with the
Terminal Intercept (TI) burn. The TI burn, occurring less than 2
hours before capture, will send Discovery on a final approach to
ORFEUS/SPAS. As Discovery closes in, four mid-course correction
firings will be done, if needed, with the Shuttle's small steering
jets. The dish-shaped Ku-band antenna on the Shuttle will obtain a
radar lock on the satellite.
About 1 hour, 10 minutes before capture, when Discovery is
passing about 1 statute mile below ORFEUS/SPAS, Culbertson will take
manual control of the rendezvous. Around that time, two laser
ranging devices that measure distance and closing rate by bouncing a
laser beam off of the satellite, will be used for navigation as well.
One laser ranging unit is hand-held and will be pointed by Pilot Bill
Readdy through the Shuttle cockpit window at ORFEUS/SPAS. A second
laser ranging unit, being flown for the first time, mounted in the
cargo bay of Discovery, will be remotely operated. These two units
will supplement onboard radar information.
Culbertson will brake Discovery, flying with the control stick
on the flight deck as it moves toward ORFEUS/SPAS, finally reaching a
point a few hundred feet in front of the satellite. While Discovery
is closing in, Bursch will extend the mechanical arm. With
Culbertson moving Discovery to within 35 feet of ORFEUS/SPAS and
holding position, Bursch will grapple the satellite and reberth it in
the cargo bay for the trip back to Earth.
Source:NASA Spacelink Modem:205-895-0028 Internet:192.149.89.61
=--=--=-END-=--=--=