The goal of the proposed dust telescope mission is the in-situ characterization of galactic interstellar dust, in order to provide crucial information not achievable with astronomical methods. Galactic dust constitutes the solid phase of interstellar matter, from which stars and planetary systems form. Information on this fundamental material is extremely sparse. However, following the discovery by Ulysses (and recent confirmation by Cassini) that micron-sized galactic dust grains pass through the solar system, the analysis of galactic dust with an Earth orbiting spacecraft is now within our reach. Galactic DUNE establishes the next logical step beyond NASA's Stardust mission, to a full-fledged galactic dust analysis program, with an orbit being easily accessible for follow-up sample return missions. Galactic DUNE provides the following major advancements in interstellar dust research beyond Stardust:

• Reliable distinction between interstellar and interplanetary dust and other dust sources,

• Analysis of the elemental, molecular and isotopic composition of interstellar grains,

• Characterization of the interstellar dust flow through the planetary system,

• Determination of mass, speed and electrical charge of individual particles in order to derive the size distribution of interstellar dust from 0.1 to 10 |im.

The science payload is a dust telescope consisting of a complement of instruments that use various dust detection techniques (having heritage from instruments on Giotto, Vega, Cassini, Stardust, and Rosetta). They are selected for 1) large area impact detection and trajectory analysis of micron sized and larger dust grains, 2) determination of physical properties of small grains, like flux, mass, speed, electrical charge, and coarse chemical composition, and 3) high resolution chemical analysis of galactic dust. A plasma monitor supports the dust charge measurements. The viewing directions of all dust instruments shall be co-aligned with narrow fields of view. About 600 interstellar grains are expected to be recorded by this payload every year, with 30 or more providing high resolution mass spectra.

The total payload mass is 53 kg and the power consumption is 53 W. The mission requires a 3 axis stabilized spacecraft of 1° pointing accuracy. The orbit shall be outside the debris belts, orbits around LI or L2 being especially suitable. A mission duration of 2 years is required, with a possible 1 year extension. 50 Mbits of scientific data are transmitted to ground once every week. Monthly command uploads and spacecraft attitude changes are envisioned.

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