MISSION CONTROL CENTER STATUS REPORT # 2
STS-91
Wednesday, June 3,  1998 - 6:30 a.m. CDT

  Discovery's crew has begun its first full day in orbit, a day
devoted to preparations for Thursday's final docking between a
U.S. Space Shuttle and the Russian Mir space station.

  The crew was awakened this morning to "Shake, Rattle and Roll,"
performed by Huey Lewis and the News, in honor of Tuesday's flawless
liftoff.  At the day's start, the crew -- Commander Charlie Precourt,
Pilot Dom Gorie and Mission Specialists Franklin Chang-Diaz, Wendy
Lawrence, Janet Kavandi and Valery Ryumin -- were about 2,600 miles
behind Mir, closing the distance between the two spacecraft by about
260 miles with each hour and a half-long orbit of Earth.

  Later today, Precourt and Gorie will conduct additional planned
engine firings to refine Discovery's approach, and the crew will
install a centerline camera in Discovery's docking system to provide
Precourt with views of Mir docking targets during the rendezvous.  The
crew will then conduct a check of all the equipment they will use
during tomorrow's activities.  Discovery is planned to dock with Mir
at 11:58 a.m. CDT on Thursday.

  Flight controllers noted a problem yesterday with transmissions from
Discovery's KU-band communications system, a system that uses a
dish-shaped antenna aboard the Shuttle to provide high-rate
communications, including television, to the ground.  Although flight
controllers are continuing to troubleshoot the problem, at present the
system is unable to send television from the Shuttle or data from the
cargo bay experiments to the ground.  Other operational modes of the
KU-band system are working properly.  The system is able to receive
uplink transmissions from the ground and to operate as a rendezvous
radar system.  Flight controllers believe a circuit, required to turn
the communications downlink system on, may not be working properly.

  Late Tuesday, the crew powered up the Alpha Magnetic Spectrometer,
an astronomy instrument in Discovery's cargo bay that is planned to
look for "dark matter" that is theorized to comprise much of the
matter in the universe.  The communications problem will not affect
the instrument's investigations since the data it gathers can be
recorded onboard the Shuttle for study after a return to Earth.

  Flight controllers also are monitoring a water leak in a check valve
associated with one of Discovery's three fuel cells.  The fuel cells
combine hydrogen and oxygen to generate electricity for the Shuttle,
and, as a byproduct, create water. The water produced by the fuel
cell's operation is normally routed to storage tanks, but the valve
problem is allowing some water to leak overboard.  The valve problem
was known to controllers prior to Discovery's launch and is not a
problem for Thursday's docking with Mir.  Discovery is in a 207 by 200
mile orbit.

The next STS-91 status report will be issued at 6 p.m. Central time
Wednesday.