Hubble 4-D: The telescope in space and time A conversation with Ed Weiler on the origins of servicing

Ed Weiler NASA Associate Administrator for the Science Mission Directorate. PhD, Northwestern, Post-doc, Princeton, as director of science operations for OAO-3 (Copernicus). HST Program Scientist, Chief, UV/Visible and Gravitational Astrophysics Division Director, Astronomical Search for Origins Program Associate Administrator, Space Science Enterprise, Director, GSFC,

Why was the Space Telescope built? 1977 Announcement of Opportunity mission objectives: Precise determination of distances of galaxies out to 10,000 km/s and calibration of distance criteria applicable at cosmologically significant distances. Determination of the rate of the deceleration of the Hubble expansion of the Universe. History of star formation and processing of matter in nearby galaxies. Stellar populations in early stages of galactic evolution. Resolution of the nuclei of globular clusters to find black holes. Optical/UV observations of faint x-ray and radio pulsars. High-resolution infrared observations of proto-stars. Direct imaging and astrometric search for planetary companions to nearby stars. Composition, density, etc. of Galactic halo gas, IGM. Precise mapping of the 100-micron flux sources in compact H II regions. Composition of clouds in the atmospheres of Jupiter, Saturn, Uranus, and Neptune. Surface mapping of the Galilean satellites of Jupiter and of asteroids. Comet chemistry in the UV.

1980s: A simpler time? ST and STS (Space Shuttle) were designed and built around each other. Shuttle flights were to be frequent and easily available. Launch of ST was to be in [N.B. AO for original instruments in March, 1977, had launch set for November, 1983.] The long-term strategy called for regular maintenance and refurbishment (M&R) of the satellite, plus a plan for new generations of instruments. Original strategy called for on-orbit repair of existing instruments to replace a detector, say, or replenish a cryogen. But there were many options for servicing: Shuttle vs. Space Station; repair of existing instruments vs. replacement, on-orbit or return to Earth, etc. Budget problems were leading to cuts in what was designated as an ORU (Orbital Replacement Unit). MSFC, GSFC, and LMSC all wanted a part of M&R. A noisy environment in which to make critical decisions!

The Weiler strategy In December, 1983, the ST Program Scientist wrote a white paper on a strategy for M&R of the instruments: Define a core set of instruments and capabilities. Prepare M&R plan to be able to repair a core instrument on the ground in a rapid-turnaround mode, or be able to replace on-orbit. Release AO for second-generation instruments ASAP. WF/PC is highest priority. Integrate M&R for instruments with overall M&R plan and emphasize on- orbit repair to avoid ground return.

The space station option As of July, 1984: ST was most clearly-defined customer for the Space Station. SS to be built starting 1987, to be launched in 1992 in low-inclination orbit, to last for 25+ years. Servicing of ST and other missions implied an Orbital Transfer Vehicle or Orbital Maneuvering Vehicle to take satellite to and from SS. These would have used chemical fuels. By 1986, SS was to have two servicing bays with thermal and contamination controls. Contamination a serious problem. Repair individual instruments within the SS? Axials would fit through airlock but a radial instrument (WF/PC) would not.

Shuttle servicing option (1) As of April, 1985: Only one axial instrument or spare solar arrays could be carried. 3 six-hour EVAs (+1 contingency) in a 12-day mission; one full day between EVAs. No JSC budget to support M&R. No spare solar arrays until 1989; will roll up and re-use originals. MSFC wanted 24- and 70-day turnarounds for quick missions; JSC says 6 months. Good news: JSC says Shuttle can reboost HST 17 miles, not the 2 miles calculated by MSFC; purely reboost missions not needed.

Shuttle servicing (2) Use one concept for all missions (eliminate contingency vs. planned). Same equipment for all missions. All procedures, crew training, hardware to be ready by time of launch. Cadre of trained Mission Specialists to be available. Dedicated orbiter for each mission (versus including other payloads). Reboost or Earth return possible on any mission. Use Remote Manipulator Arm in Shuttle cargo bay to secure ST if Space Support Equipment not available.

Questions ST vis-a-vis the Shuttle and how they interacted. Detector and technology development connected to ST: The TI 800 CCDs: NASA and NSF, CCD development. NASA UV detector program. HgCdTe IR arrays for NICMOS. What led to WFPC2 being built? Concrete plans for new instruments: STIS, HIMS, NICMOS, etc. The MSFC vs. GSFC divided management. Cepollina gets involved. The realization of spherical aberration. What was really involved in SM1? Snapshot exposures. Why have no other missions been serviced?