Gravitational Tractor For Towing Asteroids

Paper number

IAC-07-E2.3.08

Author

Mr. Lisero Perez Lebbink, Technical University of Delft (TUDelft), The Netherlands

Year

2007

Abstract

The Technical University of Delft organizes the so-called Design Synthesis Exercise (DSE) for students to finish their Bachelor studies of Aerospace Engineering in a project team (10 students). One of the subjects of the DSE 2006 comprised the challenge to deflect an Earth bound asteroid with a “gravity tractor”. This technique has been proposed in an article published in Nature, describing the altering of an asteroid’s trajectory by making use of the attracting gravitational force of a surrounding satellite.

During the project research has been conducted in, for example, Earth threatening asteroids and the dynamics behind the proposed technique. Through several design trade-offs a feasible satellite design has been proposed based on existing technologies. It has also been proposed to use the technique to limited types of asteroids only. In the specific case of asteroid 99942 Apophis (2004 MN4), we have shown that it is possible to deflect the asteroid well enough to form no more threat to Earth. This sufficient deflection is possible due to the asteroid’s close fly-by of six Earth radii in 2029, well before its most threatening approach in 2036. Altering the orbit slightly before this fly-by, will have a major effect on the trajectory of the asteroid after the fly-by. 

The choice for this typical situation is validated by some scientific facts and calculations of the project team. Apophis, for instance, at the time of the DSE was one of the few asteroids with a serious risk level of impacting the Earth before 2050. Its diameter (320 m) enables it to destruct a large country, while it is small enough to design a credible satellite able to sufficiently deflect. It has been concluded by the project team that deflecting much larger asteroids or asteroids without a beneficial Earth fly-by, will be very challenging (if not impossible); even with a satellite mass of tens of thousands of kilograms and attracting for several months. 


Ten full-time weeks of research and design resulted in a 1000 kg satellite capable of sufficiently deflecting Apophis’ orbit. MATLAB/Fortran simulations showed the asteroid will miss Earth by some 6 Earth radii in 2036. It does so due to the hovering of the satellite in fixed position close to the asteroid, for approximately one month. The fixed position is maintained by four low thrust ion engines, burning continuously.

Although the proposed solution will be only viable for the specific case of Apophis, it does conclude that an asteroid can be deflected sufficiently by just applying gravitational attraction. It is therefore interesting to investigate whether more asteroids make close fly-by’s by the Earth before they might impact (this is something I would like to do the following months). When this is the case, the solution of our team might be very well feasible to these cases as well.

Abstract document

IAC-07-E2.3.08.pdf

Manuscript document

IAC-07-E2.3.08.pdf (🔒 authorized access only).

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