Other
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...18110101k&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #101.01; Bulletin of the American Astronomical Society, Vol. 24, p.1281
Other
Scientific paper
A solar orbit in which a spacecraft flies nearly in formation with the Earth will be stable for many years if the spacecraft drifts away from the Earth at a rate of several million km per year. There are many advantages of the solar orbit over an Earth orbit. The spacecraft will be completely out of the Van Allen radiation belt, although it will be more exposed to solar flares. There is no need for a propulsion system since the spacecraft is just drifting in space. Pointing and control, as well as fault protection are much simplified. Communications and operations can be geared to a 24 hour day, although a directional antenna is needed because of the increasing distance. For an astronomical telescope, additional advantages are the elimination of the need for Earth/Moon avoidance, greatly simplified baffles, and the ability to view large portions of the sky continuously for days or even months. We describe a mission concept that uses an Atlas IIAS to launch an 85 cm diameter infrared telescope with a 3 year minimum cryogenic lifetime into a solar orbit. This concept is radically different from other infrared missions such as IRAS and COBE which used low altitude (900 km) circular orbits, or the Infrared Space Observatory which will have a highly elliptical 24-hour orbit. The concept provides most of the scientific capabilities of the Space Infrared Telescope Facility (SIRTF), as launched by a Titan IV/Centaur into a 100,000 km altitude high Earth orbit (HEO). Two additional aspects of the solar orbit make the new concept viable. The first is that the solar orbit requires much less energy to achieve than does HEO. The Atlas IIAS can place 2500 kg into a solar orbit, vs. 1500 kg into HEO. The second is the absence of the Earth's thermal radiation which allows a colder outer shell temperature. Consequently, 60% of the cryogenic lifetime of the SIRTF HEO concept can be achieved with a helium dewar one quarter the size. All of these advantages result in tremendous size and cost reductions when compared to a similar system in Earth orbit.
Eisenhardt Peter
Kwok J.
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