Comparison with other UV experiments
- IUE (International Ultraviolet Explorer; 1978)
- Telescope diameter: 3.5 times smaller
- Spectral range (115 nm - 320 nm): only somewhat smaller
- Spectral resolution (R =12000 - 13000): substantially lower
- Detector noise: The television camera of the VIDICON detector of IUE
causes a strong noise. Consequently the SNR reaches only 10-15.
In contrast, HIRDES of SUV has an extremely low noise only determined
by photon statistics and the background of the sky.
- HST (Hubble Space Telescope; 1990)
- Telescope diameter: 1.25 times larger. However, after installing
COSTAR for correcting the spherical abberation the effective area
of the main mirror is only somewhat larger than the one of the
T-170 telescope.
- Spectral range: larger (up to the near infrared)
- Spectral resolution: The presently active Goddard High Resolution
Spectrograph (GHRS) of HST has R=80000 and therefore a higher
resolution. The GHRS contains a DIGICON (line of 512 pixels) as a
low noise photon counting detector allowing only a small part
of the spectrum (5 - 15 nm) to be observed simultaneously.
In February 1997 the GHRS will be replaced by the Space Telescope
Imaging Spectrograph (STIS). The spectral range of STIS will be
from the ultraviolet to the near infrared
(115 - 10000 nm). In the UV (115 - 340 nm) the spectral resolution
will be twice as large as the one of HIRDES. The spectral range
which can be observed simlutaneously amount to 80 nm and 25 nm,
resp.. The corresponding range of HIRDES is twice and six times,
resp., larger.
- HUT (Hopkins University Telescope; 1990/91)
- Operation: only operated during flights of the space shuttle
(up to now twice, 1991 and 1995). The duration of these missions is
limited to 10 days.
- Telescope diameter: 90 cm
- Spectral range (42 nm - 186 nm): Overlapping with the range of
SUV at short wavelenghts.
- Spectral resolution (R = 600): Corresponding to the long slit
mode of HIRDES.
- WUPPE
(Wisconsin Ultraviolet Photo-Polarisation; 1990/91)
- Operation: similiarly to HUT operated during space shuttle missions.
- Spectral range (140 nm - 340 nm): somewhat smaller
- Polarisation observations: not possible with SUV
- ORFEUS
(Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer; 1993)
- Operation: similiarly to HUT operated during space shuttle missions.
The 2. flight will be in the fall of 1996, duration: 14 days.
- Telescope diameter: 1m.
- Spectral range: On board are two spectrographs covering the range
of 40 nm - 115 nm and 90 - 125 nm, resp. Only small overlap
with HIRDES.
- Spectral resolution: R = 3000 and 10000, resp. 5 times smaller than
the resolution of HIRDES, comparable to the one of the
Rowland spectrograph.
- FUSE (Far Ultraviolet Spectroscopic Explorer)
- Operation: This future mission will be operated by the NASA.
- Spectral range: 91 nm - 120 nm.
Like the Lyman channel of the Rowland spectrograph,
only small overlap with HIRDES.
- Spectral resolution: R > 30000. 3 times larger than the one of
the Rowland spectrograph
Summary:
- Concerning its efficiency (sensitivity and SNR), spectral resolution
and simultaneously observable spectral ranges, SPECTRUM UV is comparable
or even more powerful than existing UV missions.
- The STIS of HST will exceed the spectral resolution of SPECTRUM UV
by a factor of two. The lower resolution of SPECTRUM UV has been put
up with in order to maximize the spectral range which can be observed
simultaneously.
- The orbit of SPECTRUM UV is one of the main advantages of the mission.
The extremely elliptical orbit permits to carry out continous astronomical
observations for more than 30 hours. Mostly, the satellit is beyond
the radiation belt and the geo corona being less perturbed by
the scattered background light and corpuscular radiation.
- SPECTRUM UV and HST will be the most important astrophysical experiments
for the ultraviolet spectral range of 110 nm - 350 nm after the turn
of the century.
Other missions
like FUSE, HUT or ORFEUS are due to their specific conceptions
complementary to these experiments.
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Return to the Stellar Physics Mainpage
suv@aip.de - T. Bloecker - 20. Jan. 1996