ORFEUS-SPAS (Orbiting & Retrievable Far & Extreme UV Spectrometer - Shuttle
Palette Satellite) is a joint NASA - DARA (the German space agency) project. The
ORFEUS-SPAS 1 payload carried three ultraviolet instruments mounted on the free-flying
Astro-SPAS module. The reusable Astro-SPAS platform is designed to be deployed from the
Space Shuttle cargo bay for up to 2 weeks of free-flying science observations.
The
ORFEUS-SPAS I mission was flown in September 1993. The mission acquired astronomical data
on numerous targets during 5 days of observations. A second, 14 day flight (ORFEUS SPAS II) took place on STS-80 in November 1996.
The three ORFEUS-SPAS 1 instruments performed astronomical ultraviolet spectroscopy
over the wavelength range 400 - 1250 Å. These instruments were:
- Far Ultraviolet (FUV) Spectrometer
An off-axis paraboloidal mirror can be driven into the light path from the primary mirror
of the 1 meter ORFEUS telescope, collimating the beam and directing it into the FUV
spectrometer. This is an Echelle spectrometer provided by AIT and the Landessternwarte
Heidelberg (LSW). This instrument is designed to provide of point sources over the range
900 - 1350 Å with a resolving power of R = 10,000. Unfortunately, this instrument failed
to produce scientifically useful data during the ASTRO-SPAS I flight.
- Extreme Ultraviolet (EUV) Spectrometer
The Berkeley EUV spectrometer is positioned at the prime focus of the 1 m ORFEUS
Telescope. It is designed to provide high-resolution(lambda/5000) spectroscopy of point
sources between 390 and 1200 Å, with an effective area of ~ 4-6 cm. Due to various
problems, its effective resolution during the ASTRO-SPAS I mission was ~ lambda/3300.
- Interstellar Medium Absorption Profile Spectrograph (IMAPS)
IMAPS was mounted parallel to the ORFEUS optical axis. It consists of an objective grating
and an echelle spectrograph that can record very high resolution (~ 1.25 km/s) ultraviolet
spectra of stars over the wavelength interval 950-1150 Å.
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