Space debris observed in daylight*
Researchers at the University of Bern have succeeded for the first time worldwide in determining the distance to a space debris object using a geodetic laser in daylight. The distance determination on June 24, 2020 was carried out at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald. Thanks to the new possibility to observe space debris during the day, the number of measurements can be multiplied. Possible collisions with satellites can thus be detected early and evasive maneuvers can be initiated.
In the afternoon of February 10, 2009, the active telephony satellite Iridium 33 collided with the disused communications satellite Kosmos 2251 over Siberia at an altitude of around 800 kilometers. The impact occurred at a speed of 11.7 kilometers per second and produced a cloud of debris consisting of over 2000 fragments larger than 10 centimeters. Within a few months these debris spread over a large area and since then threatens to collide with other active satellites. This event was a wake-up call for all satellite operators, but also for politicians. "The problem of so-called space debris - disused artificial objects in space - took on a new dimension," says Professor Thomas Schildknecht, head of the Zimmerwald Observatory and deputy director of the Astronomical Institute of the University of Bern.
In near-Earth space it gets tight
In certain orbital areas, the risk of collisions is already so high that active satellites must regularly perform maneuvers to avoid scrap parts. The European Space Agency ESA processes thousands of collision warnings per satellite and year for its fleet of satellites and carries out dozens of maneuvers per year. In most cases, the potential collision partner is one of about 20,000 known space debris objects. "Unfortunately, the orbits of these disused satellites, upper stages of launchers or fragments of collisions and explosions are only very imprecisely known, i.e. only to a few hundred meters," explains Schildknecht. It is therefore often impossible to decide whether an evasive maneuver, which is very expensive in each case, is even necessary and really reduces the risk.
Accurate trajectories thanks to laser distance measurements
The measurement of distances to such objects by means of the so-called "Satellite Laser Ranging" method is an effective technology to improve the path accuracy to a few meters. "We have been using this technology at the Zimmerwald Observatory for years to measure objects equipped with special laser retroreflectors. To date, only a few observatories worldwide have succeeded in determining distances to space debris with special, powerful lasers," Schildknecht continues. Moreover, for technical reasons, these measurements were previously only possible at night.
The breakthrough - daytime observations with geodetic laser
On June 24, 2020, researchers from the University of Bern succeeded for the first time ever in making daylight observations of space debris using a geodetic laser at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald. Geodetic laser systems are at least one order of magnitude less powerful than highly specialized space debris lasers. Furthermore, the detection of the individual laser photons diffusely reflected by the space debris objects in the flood of background photons of the bright daytime sky is a special challenge. The success at the Zimmerwald Observatory was only possible thanks to the combination of active tracking of the scrap object using a highly sensitive scientific CMOS camera with real-time image processing and a real-time digital filter to detect the photons reflected by the object.
Thomas Schildknecht comments: "The possibility to observe during the day allows to multiply the number of measurements. There is a whole network of stations with geodetic lasers, which could in the future help to build up a high-precision orbit catalog of space debris. More accurate orbits will be essential in the future to avoid collisions and improve safety and sustainability in space.
(* translation of the press release from University Bern: https://www.unibe.ch/aktuell/medien/media_relations/medienmitteilungen/2020/medienmitteilungen_2020/weltraumschrott_erstmals_am_tag_beobachtet/index_ger.html)