Past studies: Earthguard I
More detailed information on the Earthguard I mission is available on the Executive Summary
The Earthguard-I mission, proposed by the Munich-based aerospace company Kayser-Threde and the German Aerospace Center (DLR) in Berlin, is one of the space missionsthe European Space Agency (ESA) has selected for further study in preparation for a possible future mission to studyNear Earth Objects. The goal of the study is to define a space mission and a dedicated payload concentrating on the detection of those NEOs whose orbits lie mostly or entirely within the orbit of the Earth. The former group of objects is known as Atens (named after asteroid 2062 Aten which was the first of this class to be discovered) while the latter are referred to as Inner-Earth-Objects, or, in short IEOs.
While these objects can occasionally come very close to our planet, they are very difficult to detect from the ground because this particular observing geometry places them at small angular distances from the Sun for most of the time, making them invisible against the bright sky background. It is exactly this difficulty that, until now, has prevented observers from discovering IEOs, although their presence in the inner regions of the Solar System has been predicted by dynamical studies and is generally accepted by planetary scientists.
The Earthguard-I mission overcomes this problem by making use of a compact search telescope mounted on a spacecraft in a heliocentric orbit in the inner Solar System. From this vantage point, not only would Atens and IEOs be more easily detected against a dark sky background, but they would also appear brighter due to the smaller solar phase angles in the same way that the full Moon appears much brighter than the crescent Moon.
In this way such an instrument could detect objects down to about 100 m in diameter, determine their orbits and estimate their sizes. The orbital and size distributions of such objects are of crucial importance not only for scientific reasons, but also for a better understanding of the hazard these objects pose to our civilization. For this reason this space-based detection system is to be seen ascomplementing the activities performed by the ground-based search programs. The compact search telescope could either fly "piggy-back" on a platform such as the BepiColombo Mercury orbiter scheduled for launch in 2010, or alternatively be mounted on adedicated spacecraft.
In the case of a dedicated spacecraft Earthguard-I could make use of a solar sail or an ion engine as a propulsion system to realize a low-thrust spiral transfer to an orbit closer to the Sun (in-between Earth and Mercury). The innovative solar sail technology, for which DLR has already developed functional models in cooperation with ESA, has the advantage of allowing a very compact spacecraft to be developed, compared to a conventional chemical propulsion system, therefore allowing a low-cost launch and reducing the total cost of the mission. The sailcraft possesses basically unlimited Dv capability for the orbit transfer from Earth to an orbit near the Sun, such as a circular orbit at 0.5 AU within the ecliptic plane. Here the sailcraft would “brake” against the solar pressure, such as a sailboat would tack against the wind, but in a 2-dimensional way orbiting the Sun.
Kayser-Threde GmbH is the designated prime contractor for a Solar Sail in-orbit deployment demonstration mission in Earth orbit, with alaunch date in early 2005. ESA and the German Aerospace Center (DLR) will co-fund this project. This mission will mark an important step to flight-validate solar sail technology, thus bridging the gap between laboratory models tested onground(see below) and a fully operational sailcraft mission such as Earthguard-I.