Meteor shower

NASA has selected 38 possible science investigations for the Comet Rendezvous Asteroid Flyby (CRAF) mission planned for launch in the early 1990s. The mission is designed to send an unmanned spacecraft to rendezvous with comet, fly in formation with it for three years and fire an instrumented penetrator into the comet's nucleus.

The spacecraft also will make close flybys of two asteroids on its way to the comet encounter.

The CRAF mission will conduct detailed study of the composition and physical properties of the comet nucleus and will observe changes that occur as the comet approaches the sun. It also will determine the size, shape and surface properties of the asteroids.

CRAF will carry 11 to 14 instruments including cameras, dust analyzers and nucleus penetrator. Results from two-year instrument accomodation study will determine the final payload.

Spacecraft instruments being considered are:

--Visual-infrared mapping spectrometer (VIMS) to study mineralogy, surface ices and coma gases.

--Telecommunications System (TCS), to measure gravity fields of the comet and asteroids.

--Infrared radiometer, to obtain temperature maps of the nucleus surface.

--Dust particle analyzer to determine chemical composition of individual dust grains.

--Ion and neutral mass spectrometers to determine composition and flow direction of gas and charged particles from the comet's nucleus.

--A magnetometer, an energetic particle analyzer and plasma wave analyzer to obtain data on high speed solar wind particles and cometary dust.

The penetrator will carry five instruments: gamma- ray spectrometer to measure elemental composition of both ice and non-volatile material; accelerometer to measure the strength and structure of the surface; thermometers; calorimeter to detect phase changes as an ice sample is heated; and gas chromatograph to determine types and amounts of gaseous molecules released from the ice sample.

CRAF is to be launched in late 1992, flyby the asteroid Malautra in mid-1993, and after an Earth gravity assist maneuver, reach the orbit of comet Tempel-2. Following flyby of the asteroid Hestia, it will rendezvous with the comet in late 1996 near the orbit of Jupiter.

It is to fly in formation with the comet for three years, first observing its quiet phase far from the sun, and then its coma, and dust and plasma tails as it nears the sun and become active. It will release the penetrator in 1997.

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