6.2. Hubble telescope servicing mission

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 (EVAs) was reached follo~~g extensive evaluations of underwater training, m~oeuvre times required using the Shuttle’s robot arm based on software simulations and actual EVA tasks on previous missions. Mission Director R. Brinkley commented: “Basically what we”ve done by going to five EVAs rather than three is to re-package our margin so that we have the capability to respond to the dynamics, or unknowns, of spacewalks. 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 FieldlPhmctary 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 recognized 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 M. Heflin, Lead Flight Director for the mission. “We have paid close attention to lessons learned during previous spacewalks and factored these into our time-line estimates for five EVAs. In planing for all Space Shuttle missions, it is necessary to form~ate a work schedule that represents as realistic a time-line as possible to accomplish the mission objectives.” 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 several EVAs. Plating currently calls for at least five water tank training sessions that include support from the Mission Control Center, called join? integrated simulations, lasting between 10 and 36 h. In addition, many stand-alone underwater training ‘runs’ will provide simulated practice for the individual tasks in each spacewalk. Various refinements to the specific tasks on each spacewalk will be 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. Both Endeavour’s June flight and Discovery’s July mission will include

~~)~~rnNASAN~ws,23Aprilf993.

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spacewalks to evaluate some of the unique tools to be used on the HST mission. The evaluations will improve underst~ding of 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. The inflight spacewalking experiences will also 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. The telescope was launched aboard Discovery in April 1990. At that time, the NASA mixed fleet manifest showed the first re-visit mission to HST in 1993 to change out scientific instruments and make any repairs that may have become necessary. As it was 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.

6.3. SEARCHING FOR GRAVIIY WAVES fN SPACEL31

Three interplanetary spacecraft, ES& Ulysses and NASA’s Mars Observer and Galileo, now quietly heading towards separate destinations (the poles of the Sun, Mars and Jupiter, respectively), may soon prove the existence of waves in the universe’s gravitational field by bobbing on ripples in space like corks bobbing on ripples in a pond. Such gravity waves have never been detected directly, athough their existence was predicted in Einstein’s theory of relativity and there is indirect evidence that they exist. The waves are believed to be produced by supernova explosions, collapsing black holes and like events. Past searches with ground-based equipment and single spacecraft have failed to discover them. This joint ESA/NASA experiment was scheduled to run from 21 March to 11 April when the three spacecraft were to have made observations simultaneously for the first time, greatly increasing the reliability of any detection, by ‘listening’ for passing very low frequency gravitational waves. Dr R. G. Marsden (Deputy Ulysses Project Scientists at E&A’s Research and Technology Centre, ESTEC in Noordwijk, The Netherlands) commented: “For Ulysses, it will be the second chance to search for these rare events. Last March, Ulysses ‘listened’ for a period of about four weeksI’ Xlthough no gravitational waves were found on that occasion, the experiment set new upper limits to their intensity, thereby excluding a number of possible sources,” said Professor Bnmo Bertotti, Principal Investigator of the Ulysses Gravitational Wave Experiment at the University of Pavia, Italy. ESA’s Ulysses spaceprobe was launched by Space Shuttle Discovery on 6 October 1990 to become the first probe ever to explore and circumnavigate the (‘)From ESA Press Release,

19 March

1993.

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