SPACE BASED OBSERVATIONS OF ORBITAL DEBRIS

摘要

An accurate knowledge of the population of debris orbiting the Earth is of prime importance to prepare the future missions in space. The observation of debris smaller than a few millimeters is not feasible using classical ground-based sensors such as radars or telescopes. The alternative solution is to implement instruments on-board satellites allowing the measurement of the environment on any orbit. CNES is currently investigating several techniques to observe in situ small particles. The first solution is to analyze spacecraft surfaces that were retrieved after a mission in space. New methods were developed to analyze impact craters on the solar panel of the Hubble Space Telescope and dedicated passive detectors are planned on the International Space Station (ISS). However this analysis gives only a general information concerning the average environment and is limited to very low Earth orbits. For the calibration and improvement of the flux models additional information is required, in particular the distribution of particles, function of time and location in space. This is the reason why active detectors were developed: thin dielectric capacitance sensors are made of 2 inches diameter silicon wafers. The devices are discharged upon impact and measure the time of impact and the amplitude of discharge to be compared with ground calibrations. This information is downloaded to the control center via telemetry. These detectors have low mass, low power consumption and can be easily implemented on-board any spacecraft allowing observations on different orbits. Prototypes were developed and calibrated with hypervelocity impact tests. Such sensors will be installed on the ISS and several micro-satellites, with a first flight scheduled on FBM in 2002. Typically these sensors are able to detect particles with a size between 1 and 100 microns. Larger particles represent high energy levels in case of impact. Another solution has to be found and the use of on-board optical sensors was considered. Such techniques, based on lidar are investigated in the frame of a feasibility study. The basic principle is to measure the back-scattered light of debris illuminated by one or several laser emitters to obtain information on position and velocity of the objects. The objective of this preliminary study is to determine the main characteristics of such an instrument: mass, volume, power consumption and the detection performances (limiting size, frequency of observations, type and accuracy of the measurements). The next step will be the definition of a small payload that could be implemented on-board a future micro satellite.