EISCAT radar

In Tromsø, Norway, the EISCAT Scientific Association (European Incoherent Scatter Radar) is operating a 930-MHz UHF radar and a 225-MHz VHF radar. Furthermore, they own a 500-MHz radar system consisting of a steerable 32-metre dish and a fixed 42-metre dish in Longyearbyen, Svalbard.

ESA radar tracking: increase in debris after Chinese a-sat test

The primary mission of the EISCAT network is to perform ionospheric measurements. However, following the development of a dedicated space-debris computer to run at the back-end of the processing units, these radars are now capable of statistical observations of LEO debris down to 2 cm, without compromising the main EISCAT objectives.

The EISCAT radars now allow a continuous monitoring of the LEO debris population in a beam park-type configuration. As an example, EISCAT was able to monitor and characterise China's Feng-Yun 1C debris cloud, generated at 800-km altitude in January 2007, following the worst single fragmentation event in space history.

ESA's top-ranked telescope: detecting unknown objects

ESA operates a Zeiss telescope of 1-metre aperture that is used for the detection and survey of objects near the geostationary ring. The telescope is equipped with Ritchey-Crétien optics, with an FOV (field of view) of about 0.7º, and a liquid-nitrogen-cooled CCD camera with a 2 x 2 mosaic of 2k x 2k CCD chips.

ESA's 1-metre Zeiss space debris telescope

The telescope can detect and track near-GEO objects up to magnitudes of +19 to +21 (i.e. down to 15 cm in size). With this performance, the ESA telescope is top-ranked worldwide. During GEO observation campaigns, typically 75 percent of all detections are new objects that are not contained in the US Space Surveillance Catalogue.

The data provided by the telescope are a major input for space debris environment models, indicating a much larger number of GEO fragmentation events than confirmed so far (a Soviet Ekran 2 satellite explosion in 1978 and a US Titan Transtage break-up in 1992). Observations of highly eccentric orbits passing through GEO led to the discovery of a class of faint, lightweight objects with high area-to-mass ratios. Orbital characteristics indicate that they could be pieces of thermal blankets of satellites.

Retrieving hardware for hypervelocity impact studies

ESA also gains information on the small-size, sub-millimetre meteoroid-and-space-debris environment through the analysis of retrieved space hardware, such as the EURECA satellite, and the three solar arrays retrieved from the Hubble Space Telescope through the Space Shuttle.

The total exposed surface that was analysed exceeded 300 square metres. The samples contained several thousand impact craters from a few micrometres up to a 7 mm in diameter. An analysis of chemical residues in the craters allowed a discrimination of possible progenitors of the impacts.

Debris sensors in orbit

ESA-funded Geostationary Orbit Impact Detector (GORID), 1996

For orbits above 600 km, and for inclinations outside the Shuttle's reach, a retrieval of space hardware is not possible and active in-situ sensors are required to measure impact fluxes. In 1996, the ESA-funded Geostationary Orbit Impact Detector (GORID) was launched into GEO on board the Russian Ekspress-2 satellite. During five years of operation, an average of 2.4 impacts/day were detected, with peak counts of 50 per day.

DEBIE II in orbit with ESA's Columbus science lab

In 2001, a newly designed Debris in-Orbit Evaluator (DEBIE) was launched into LEO on ESA's PROBA-1 satellite. DEBIE used a combination of impact ionisation, momentum and foil penetration detection for the active monitoring of sub-millimetre particles impacting on the detector surfaces. In 2008, DEBIE II was launched together with the Columbus science module, now docked to the International Space Station (ISS). It is now operated via the EUTEF (European Technology Exposure Facility), one of the external Columbus payloads.

Objects in GEO orbit detected by ESA

Debris environment models require measurement data of well-defined regions in space - at specific observation times - to validate their predictions. On the other hand, the data return from measurement campaigns can be optimised with respect to search regions, observation times and sensor sensitivity if some a-priori information on the space debris population is available.

To support the planning of observation campaigns and the exploitation of data for improved debris environment models, ESA has sponsored the development of the PROOF software (Program for Radar and Optical Observations Forecasting).

PROOF simulates space debris observation campaigns for ground- and space-based sensors using available population data from the MASTER model. The simulation generates expected detection statistics and characteristics for given radar or telescope systems and for given campaign parameters. For catalogued objects, PROOF performs predictions with a level of accuracy that allows a clear correlation of recorded detections with catalogued objects.