Ed Campion
Headquarters, Washington, D.C.                                                    
April 23, 1993
(Phone:  202/358-1780)
Kyle Herring
Johnson Space Center, Houston
(Phone:  713/483-5111)
RELEASE:  93-76
HUBBLE TELESCOPE SERVICING MISSION SCHEDULED FOR ELEVEN DAYS
   The December flight of Endeavour on Space Shuttle mission 
STS-61 to service the Hubble Space Telescope (HST) has been 
scheduled as an 11 day mission designed to accommodate a record 
five spacewalks with the capability for an additional two, if 
needed.
   The decision to schedule five extravehicular activities, or 
EVAs, was reached following extensive evaluations of underwater 
training, maneuver times required using the Shuttle's robot arm 
based on software simulations and actual EVA tasks on previous 
missions.
   "Basically what we've done by going to five EVAs rather than 
three is to repackage our margin so that we have the capability to 
respond to the dynamics, or unknowns, of spacewalks," Mission 
Director Randy Brinkley said.  "It improves the probabilities for 
mission success while providing added flexibility and adaptability 
for reacting to real-time situations."
   In laying out the specific tasks to be completed on each of the 
spacewalks, officials have determined that changing out the gyros, 
solar arrays and the Wide Field/Planetary Camera (WF/PC) and 
installing the Corrective Optics Space Telescope Axial Replacement 
(COSTAR) are priority objectives during the mission.
   "When we looked at accomplishing all of the tasks, highest 
through lowest priority, and recognizing that the major tasks -- 
gyros, solar arrays, WF/PC and COSTAR -- would consume most of the 
time set aside for each spacewalk, five EVAs were deemed 
appropriate," said Milt Heflin, Lead Flight Director for the 
mission.
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   While the five spacewalks will be unprecedented, the use of two 
alternating spacewalk teams will alleviate placing more stress on 
the crew than previous missions requiring two, three or four EVAs.
   "We have paid close attention to lessons learned during 
previous spacewalks and factored these into our timeline estimates 
for five EVAs," Heflin said.  "In planning for all Space Shuttle 
missions, it is necessary to formulate a work schedule that 
represents as realistic a timeline as possible to accomplish the 
mission objectives."
   Planning currently calls for at least five water tank training 
sessions that include support from the Mission Control Center, 
called joint integrated simulations, lasting between 10 and 36 
hours.  In addition, many stand alone underwater training "runs" 
will practice individual tasks in each spacewalk.
   Various refinements to the specific tasks on each spacewalk 
will be made based on actual training experience during the months 
prior to the mission.  Also, lessons learned from other spacewalks 
leading up to the flight will be valuable in assisting the STS-61 
crew in its training techniques.
   Endeavour's June flight and Discovery's July mission both will 
include spacewalks to evaluate some of the unique tools to be used 
on the HST mission.  The evaluations will help in better 
understanding the differences between the actual weightlessness of 
space and the ground training in the water tanks at the Johnson 
Space Center, Houston, and the Marshall Space Flight Center, 
Huntsville, Ala.
   Also, the inflight spacewalking experiences will assist in 
gaining further insight into the time required for the various 
tasks and expand the experience levels among the astronaut corps, 
the flight controllers and trainers.
   Designed to be serviced by a Space Shuttle crew, Hubble was 
built with grapple fixtures and handholds to assist in the capture 
and repair procedures.
   The telescope was launched aboard Discovery in April 1990.  At 
that time the NASA mixed fleet manifest showed the first revisit 
mission to HST in 1993 to change out science instruments and make 
any repairs that may have become necessary.
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