The STARLITE payload on STS-95

Preflight description:

Part of the International Extreme-Ultraviolet Hitchhiker 3 (IEH-3), Starlite comprises a 0.4-meter telescope with a spectrograph that will give significant new views of the hot Universe. Its silicon-carbide primary mirror maintains reflectivity beyond the range of traditional mirror coatings, down to the limit imposed on light from distant objects by hydrogen in our own neighborhood, at 912 Angstroms (0.0912 micrometers). What is really new is the combination of this deep-ultraviolet sensitivity with a large field of view, so that Starlite can observe nearby galaxies, supernova remnants, and similarly large targets much more efficiently than any of its precursors (such as HUT flown on STS-35 and STS-67 as part of the Astro payload) and upcoming missions such as the Far Ultraviolet Spectroscopic Explorer (FUSE).

The Principal Investigator is Dr. Jay Holberg of the University of Arizona in Tucson, with coinvestigators A. Lyle Broadfoot (Arizona), Roberto Stalio (Trieste, Italy), Jayant Murthy (Johns Hopkins), and William Keel (University of Alabama, Tuscaloosa). The Starlite payload was fabricated at the University of Arizona's Optical Sciences Center. The instrument package includes two star-tracking systems, one with a 4.5 by 6.5-degree field for initial acquisition, and a narrower-field tracker to maintain instrument pointing as the shuttle orbiter's attitude changes. The detector package includes a spectrograph designed to reject Lyman-alpha emission from the Earth's extended hydrogen envelope (geocorona) which can be a limiting factor for deep-UV observations from low Earth orbit. Our measurements will cover the 912-1150 Angstrom region, and will provide spatial as well as spectral information along a 30-arcsecond by 30-arcminute slit (long enough to cross the Moon, if we wanted to do that). The radiation is registered on a multianode microchannel array (MAMA), and downlinked to the instrument team at the Payload Operations Control Center, located at Goddard Space Flight Center in Greenbelt, Maryland.

Here are some views of the Starlite telescopes being assembled at the Optical Sciences Center in Tucson. Click for full-sized images:
Primary mirror Telescope optics Fully Assembled

Starlite is on a two-axis mounting angled slightly outward from the orbiter's centerline, to that it can observe all of the sky that is visible (that is, above the horizon and not behind some part of the orbiter structure) at any given time. There is a pointing limitation imposed by the orbiter's typical attitude for this mission - to avoid the interfering effects of "Shuttle glow" (an ultraviolet glow produced as the orbiter impinges on the rarefied remnant of our atmosphere), the bottom of the orbiter will generally face forward so that this glow doesn't show up in the IEH-3 instruments' field of view (an attitude known as "belly-to-ram"). Starlite is located at the back of the payload bay on the port side, with UVSTARS facing directly out the starboard side (which is "up" most of the time). This means that a typical target will be accessible for about 25 minutes at once. The instrument's location can be seen (as the gold-covered box pointing downward at lower left) in this image from KSC on October 23, just before the payload bay doors were closed:

Some of the science targets that are high priorities for observation by the Starlite team include:

  • The Cygnus Loop supernova remnant. Starlite will be able to map how various atomic species respond to the passing shock wave from the initial supernova (now about 14,000 years ago), showing details of how the gas cools which previous observations have left unclear.
  • The spiral galaxy M33. The nearest actively star-forming spiral galaxy, these data occupy an important niche in comparison to optical observations of the most distant galaxies. The expansion of the Universe has made the ultraviolet light from these galaxies arrive here as visible (or even infrared) radiation, so that ultraviolet observations of such nearby galaxies are of special interest as we attempt to unravel how galaxies formed and evolved. These data will complement an additional set of observations scheduled with the FUSE satellite next year, intended to probe the brightest individual star-forming regions in M33 for comparison with the more diffuse regions that will be well studied with Starlite.
  • Mercury. Pointing accurately so close to the Sun will require the orbiter pilot to set the its attitude so that the wingtip acts as a sunshade.
  • The newly discovered nova in Scorpius.
  • The plasma torus around Jupiter's volcanic moon Io.
  • Reflection nebulae. These clouds of dust, illuminated by neighboring stars, afford an unusually good chance to measure the scattering properties, and thus the physical nature, of the tiny grains of interstellar dust.
  • Hot evolved stars in globular clusters. Some of these rich star clusters contain unusual populations of very hot stars, which are best isolated and probed in the deep ultraviolet. This spectral region contains clues to the temperature and origin of these stars which are potentially much clearer than in any other band.
    Postflight roundup:

    Supporting Starlite turned out to be interesting. The azimuth bearing on the mount froze on orbit, so we had to find targets within a 1-by-160 degree slice of sky (passing through the stuck azimuth point in an outboard-tipped coordinate system) as we could. Spherical trig at 3 a.m. In any case, the telescope itself and detectors worked as well as expected. We did manage to fish some stars in, map a few regions of the Milky Way, and got the orbiter orientation changed for half an orbit to do a "drift scan" halfway around the sky. Here's a view of the telescope in action in the payload bay, taken from NASA TV by the staff of Florida Today's Space Online staff and posted by permission. It's the silver tube seen beyond the USC experiment package.

    Starlite telescope in STS-95 payload bay

    I think the Starlite team embarrassed some of the other ones in the operations center, because we'd tend to let out cheers when the spectrum of a recognizable target went through the slit. Alpha and Beta Muscae were especially good, since we got them one after the other in the same sequence (they're only about a degree apart).
    Last changes: August 16, 2000