REQUIREMENTS AND RISKS OF A SWEEPING DEVICE FOR REMOVING SMALL DEBRIS

摘要

Near-Earth space is an extremely important resource both for commercial and scientific purposes. However, its useis threatened by the growing problem of space debris. In particular, operational spacecraft in low Earth orbit (LEO)are vulnerable to impacts from debris in the 1 to 10 cm size range which has the potential to terminate missions,possibly in a catastrophic manner. Spacecraft cannot manoeuvre to avoid this debris because it is not trackedroutinely and the necessary shielding can be costly to implement. Therefore, remediation, whereby debris isremoved from the LEO environment, is now being widely considered to reduce the hazard to spacecraft. In thiswork, we investigate some of the requirements and risks of a 'sweeping' device, operating in LEO and targeted atcentimetre debris. The investigation was conducted using the Meteoroid and Space Debris Terrestrial EnvironmentReference (MASTER) 2009 model and the University of Southampton's Debris Analysis and MonitoringArchitecture for the Geosynchronous Environment (DAMAGE). Firstly, the sweeping area required to stabilise thegrowth of the ≥ 1 cm debris population between 700 km and 900 km altitude was identified under two futurescenarios: business as usual and mitigation. The sweeping area required was estimated to be 16.8 sq. km for thebusiness as usual case and 0.8 sq. km for the mitigation case. Clearly, sweeping areas of these magnitudes wouldneed to be divided over several thousand spacecraft. One approach to achieve this would be to mount a sweepingdevice on new spacecraft and to deploy the device at the end of the spacecraft mission. This would enable deorbiting,through drag augmentation, in addition to the sweeping capability. In the second step of the analysis, thenumber of collisions with objects ≥ 10 cm was quantified and found to be 218 per year for the business as usualcase and 10 per year for the mitigation case. Therefore, we conclude that the sweeper spacecraft would need toretain some form of orbit or attitude control. In addition, the number of sweeper spacecraft required is, perhaps,difficult to achieve at present. However, a more modest application of this type of passive sweeper, whereby thetotal number of such devices in the LEO region is kept below a certain threshold, should still be a viableproposition. Although remediation will be limited in this scenario, it could nevertheless be considered a usefulsecondary benefit of a carefully designed drag augmentation de-orbit device.