Proposal:

The objective of CATS (Composition of Asteroids Transequitone Survey) is to image and catalogue the main belt asteroids believed to be located between the orbits of Phlebas and Equitone. The spacecraft is equipped with high and low resolution cameras for imaging of the asteroids, a spectro-photometer for reflectivity measurements. CATS is equipped with heavy micro-meteorite shielding to protect against small particles likely to be found in the belt (even though the density is small), and light radiation shielding for its close passage by Equitone.

Injection into the asteroid belt is to be accomplished by gravity assist from a close passage to Equitone. This will make an elliptical orbit with aphelion of 3.8 AU (at Equitone) and a perihelion of 2.0 AU (probably near the inner edge of the belt) and in the plane of the ecliptic. This orbit will have a semi-major axis of

an eccentricity of

and a period of

The gravity assist maneuver at Equitone will be at high speed and will utilize aerobraking in the outer atmosphere to slow the velocity of the probe which will be entering the system at high velocity. This is hazardous, and the heavy shielding will be of use, providing some heat shield and ablative protection in the braking maneuver. The light radiation shield will provide some shielding during passage of Equitone's magnetosphere, and for extra protection only the low-res imager will be turned on until this maneuver is completed. Other than these rough images, no data will be available from the Equitone encounter. There will be a backup DPU in case of failure of the main processor.

The orbit will carry CATS out to Equitone's orbit every 4.8 years unless an encounter with a large asteroid in the belt can be effected to help circularize the orbit (this is unlikely). Thus, over the course of a number of orbits, resonances with Equitone (period 7.2 years) will begin to perturb the orbit and will likely capture or eject the probe. However, CATS should survive on order of at least 15 years (3 orbits) and likely much longer, barring a close encounter of the crashing kind. The probe will have only limited maneuvering capability once on its elliptical belt-crossing orbit. Although solar power would be effective in this orbit, it was deemed that damage to panels during the Equitone passage, and probable impact damage in the belt would compromise the mission, so a nuclear generator is used for power. The lifetime of the generator (>100yrs) will likely long outlast the spacecraft.

The main science instruments are the high-resolution imager (HRI) which is equipped with a filter wheel with a polarizer and color filters (note: these do not require extra DPU slots), and the spectro-photometer. The combination of high-resolution imaging with color filters and polarimetry and the spectro-photometry will allow rough determination of composition, primarily from albedo and reflection spectrum measurements. We can compare this with studies of our own solar system asteroids and meteors to find whether the proto-planetary nebula that formed the Eliot system was similar to that in our own system, and wheter the same processes of differentiation occured.

Eliot Homepage ---

smyers@nrao.edu   Steven T. Myers