The flight instrument propsed here carried aboard an Earth satellite will measure the masses, fluxes, velocities and trajectories of incoming dust particles of man-made and natural origin. Man-made particles -- orbital debris -- will be distinguished from particles of natural (cosmic) origin -- i.e., from coments and asteroids, by means of the trajectory information. Specifically, it is proposed to design, develop and test a SPACE DUST (SPADUS) Experiment to the point where it is a flight-qualified deliverable flight experiment for incorporation aboard a near-Earth orbiting satellite. The SPADUS instrument will carry out measurements of the dynamical properties of the near-Earth dust complex over a particle size range (~2 µm to 200 µm diameter) for which there is little quantitative data at the present time.

Full development of the SPADUS instrument will result from collaborations between the University of Chicago, the Naval Research Laboratory and the Lockheed Palo Alto Research Laboratory. In addition to the funding from the Office of Naval Research requested in this proposal, we anticipate additional funding from the National Aeronautics and Space Administration, as well as a modest increment of funding from the State of Illinois. This joint funding, combined with the above collaborations, will permit the successful completion of the SPADUS instrument.

As presently conceived, the SPADUS instrument consists of a "trajectory" section and a "wire grid" section. The trajectory section consists of two Polyvinylidene Fluoride (PVDF) dust sensor arrays separated by a fixed distance. On the sides of the two arrays are located additional large area PVDF dust sensors to provide additional sensing area for measurement of particle flux. Dust masses and fluxes are determined from the detector signal amplitudes and impact rates, and particle velocity and trajectory are determined from electronic identification of the sensors impacted in the two trajectory arrays and from a time-of-flight (TOF) measurement.

The wire grid section will provide for a measurement of the magnitude and sign of the charge carried by an incident dust particle, and an additional TOF measurement (between the grid and first trajectory array) will provide an additional measurement of particle velocity.

Since the flux of orbital debris and cosmic dust is relatively low, the maximum collection area possible is highly desirable in order to abtain statistically meaningful measurements over space exposure time intervals of a year or so. The SPADUS instrument proposed here has the minimum instrument sensing area which will permit accurate measurement of the distribution of orbital debris and cosmic dust with respect to particle mass, flux, velocity and trajectory. With modest incremental cost, the sensing area of SPADUS could be greatly increased, which would then enhance the flux measurements for the rarer larger particles in the near-Earth dust complex.

The instrumentation also provides the opportunity for detection of transient increases in dust flux, either from man-made dust injections or from intersection of SPADUS with the orbits of interplanetary meteor streams.

The SPADUS instrument we propose is based on already developed, flight-proven technologies. The design of the PVDF detectors and associated electronics will use the heritage of the instrumentation developed at the University of Chicago and successfully flow on the VEGA 1/2 Comet Halley flyby missions. The specific objectives of SPADUS are:

1. To provide definitive measurements of the mass, flux, charge, velocity and arrival direction of individual particles in near-Earth space, both for man-made particles (orbital debris) and for particles of natural origin. These measurements would be carried out over the particle size range over which there is little quantitative data available.

2. To provide a survey map based on the above three-dimensional measurements which would establish a baseline of the present near-Earth dust distribution.

3. To improve our understanding of the dynamical properties and evolution of orbital debris.

4. To search for transient dust flux increases from man-made injections or from interplanetary dust streams.

5. To improve our understanding of the dynamical and physical characteristics of natural dust.

6. To obtain early flight experience for the SPADUS instrumentation, which contains sensors and electronics which are identical to those planned for:
   • Our future Space Station Freedom instrument which will measure the dynamical properties of near-Earth dust and return dust samples to Earth for analysis of composition, and
   • Our future Cassini instrument, which will measure dust in the Saturnian ring system.