Friday, December 24, 1999 – 10 a.m. CST

The Hubble Space Telescope is scheduled to receive its final upgrades today as astronauts Steve Smith and
John Grunsfeld perform the last of three planned space walks to refurbish the orbiting observatory.

Today’s planned 7 ? hour-long space walk will see Smith and Grunsfeld install a transmitter that relays
Hubble’s scientific data from the telescope to the ground and an upgraded digital recorder replacing an
older mechanical version.

The transmitter to be installed today replaces one that failed in 1998. Since that time, the second on-board
transmitter has successfully carried the load without any disruption to Hubble operations. The transmitters
are considered very reliable, and unlike most of the equipment aboard Hubble, were not designed to be
changed out in orbit. Special tools were developed to enable astronauts to do the job more easily.

The digital Solid State Recorder being installed on the telescope will replace an older mechanical model and
provide more than 10 times the storage capacity. Smith and Grunsfeld also will apply some new insulation
on equipment bay doors to minimize any degradation of the telescope’s protective thermal coverings.

The space walk currently is scheduled to being at 1:20 p.m. Central Time and is expected to last about 7 ?

Mission Control awakened the crew at 8:50 a.m. today to the sounds of Steppenwolf’s “Magic Carpet
Ride” played for Smith and the children’s song “Skinnamarink” by Kimbo for Grunsfeld. Discovery
remains in excellent condition, in an orbit with a high point of 380 statute miles and a low point of 364

The next status report will be issued at 11 p.m. or as events warrant.