The Deep Impact Discovery Mission

1 The Deep Impact Discovery Mission M. F. A’Hearn , L.A. McFadden, C.M. Lisse, D.D. Wellnitz (U.Md), M.J.S. Belton, (Belton Space Initiatives), A. Delamere (Ball Aerospace and Technologies Corp), K.P. Klaasen (JPL), J.Kissel (MPI), K.J. Meech (U.Hawaii), H.J. Melosh (U. Arizona), P.H. Schultz (Brown U.), J.M. Sunshine (SAIC), J. Veverka (Cornell U.), and D.K. Yeomans (JPL) The Deep Impact mission, two spacecraft, a flyby and an impactor, will explore beneath the surface of comet 9P/Tempel 1. The impactor will excavate a crater. Imagers and a spectrometer observe the collision, ejecta curtain and the crater, making a direct comparison of the newly excavated interior to that previously emitted into the comet’s coma. Launching together in January, 2004, for a 1.5 year cruise, encounter and impact will be July, 2005. Twenty-four hours before, the two spacecraft will separate. The flyby spacecraft will be slowed and diverted to miss the comet by 500 km. Closest approach occurs ~14 minutes post impact. The impactor, a mostly copper mass of 370 kg, continues under autonomous guidance to hit the comet in a sunlit area. Telescopic observations complement the spacecraft data. The flyby includes a medium resolution imager with narrow-band and medium-band filters and 10 mrad fov monitoring the comet nucleus at high time resolution during and following impact determining fundamental nucleus properties. The high resolution imager with medium -band filters, follows crater formation (spatial resolution 17 m/pixel at impact and 1.4 m/pixel final image). The infrared spectral imaging module will collect spectra between 1-4.8 microns continuously before, during and after impact comparing compositions and looking for spatial variations. The impactor targeting sensor, a white light imager collects high speed images until just before impact. Highest resolution will be 20-30 cm/pixel. An S-band transmitter sends the images to the flyby, then relays them back to Deep Space Network receivers on Earth. We will determine the comet’s shape, morphology, albedo and crater density. We will time and map the crater ejecta curtain and debris to determine surface properties (porosity and compressibility) and gravitational force at the comet. We will analyze spectral maps for photometric and compositional variations both before and after impact. With laboratory simulations of the impact we have explored the range of possible crater sizes (diameter and depth) and ejecta evolution. If gravity controls crater growth (strengthless particulate surface), the crater may be as large as 120m and 25m deep. Smaller diameters will occur if the surface is highly compressible or exhibits strength. Ball Aerospace designed and is building the spacecraft and instruments. Mission design and operations is carried out at JPL under its project management.