Design of a Close-Proximity Observation Mission for 99942/Apophis
- Paper number
IAC-07-A3.5.09
- Author
Mr. Paolo de Pascale, European Space Agency/ESOC, Germany
- Coauthor
Mr. Michael Khan, Germany
- Year
2007
- Abstract
99942/Apophis, an Aten-class asteroid with a probable diameter of around 250 m, will pass close by the Earth in April 2029, after which there are at least two further close encounters in 2036 and in 2037, for which the risk of an Earth impact is small but non-negligible. The asteroid’s orbit is being determined with Earth-based observations (optical and radar), but additional data from a spacecraft orbiting it for extended periods at close quarters would provide additional high-quality independent data types. These would not only allow determination and long-term prediction of the trajectory of Apophis with a degree of accuracy otherwise impossible to achieve, but also contribute to a characterization of natural non-gravitational perturbative effects on small body orbits such as the Yarkovsky effect. Such knowledge would improve the orbit determination accuracy and predictability also of other asteroids, some of which may also be identified as potentially hazardous objects (PHOs). A design is proposed that is consistent with a small launch vehicle and a low-cost mission. Following launch into a low Earth orbit, escape is achieved with a solid-rocket stage, possibly including a moon swingby. During interplanetary transfer, solar electric propulsion drives the spacecraft. An Earth swingby can be employed to raise the payload mass. Typically, the dry mass of the spacecraft will be between 400 and 450 kg. A feasible baseline scenario and several backups are proposed, all of which are consistent with existing technology. Alternative missions to other asteroids are also discussed. After arrival at the asteroid, the spacecraft is inserted into a self-stabilizing orbit around the asteroid. Such an orbit does not require stationkeeping maneuvers and makes use of the main perturbing force, solar radiation pressure. On the observation orbit, the spacecraft would be continuously tracked by terrestrial ground stations; the range and Doppler measurements would serve to obtain a precise orbit determination. The paper gives an indication of the measurements to be expected, analyzes the geometrical aspects and also assesses the achievable accuracy. Additionally, some options for a deflection mission facilitated by the enhanced orbit determination accuracy are listed. Such a deflection mission would involve a high velocity impact with the aim of imparting a change in impulse and changing the semi-major axis of the asteroid’s heliocentric orbit.
- Abstract document
- Manuscript document
IAC-07-A3.5.09.pdf (🔒 authorized access only).
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