2017.A.3.4. What is a rubble pile asteroid? A CubeSat Mission to find out
Patrick Bambach (1)
Jakob Deller (1)
Sampsa Pursiainen (2)
Hans Braun (3)
Mika Takala (2)
- Max-Planck-Institute for Solar System Research, Germany
- Tampere University of Technology, Finland
- RST Radar Systemtechnik, Germany
Swarm, Asteroid, radar, navigation
Most smaller asteroids in the size range of around 100 m to 3 km in diameter are not monolithic bodies, but rather ‘rubble pile’ aggregates, but little is known about the exact configuration of their inner structure. Anyhow, the internal configuration of rubble pile asteroids is fundamental to understand the collisional evolution of the solar system, and also it is of high importance for the design of future asteroid deflection concepts.
A conceptual design was performed for a tandem 6U cubesat mission to answer this question. An off-the-shelf electric propulsion system would offer a dv of more than 2.6km/s for the mission. Together with one of the many proposed launcher platforms going into a lunar transfer orbit reaching NEAs with a dv up to 4 km/s is possible. Various NEAs approaching closer than 20LD in a size range of 50 – 1000 m are reachable with this dv budget. In order to image the interior of an asteroid, a dual-use 20 MHz radio instrument is proposed. It is used for navigation and serves as penetrating and surface radar. Using a configuration of two identical satellites enables the measurement through the asteroid.
The full wave information can be inverted through an advanced computed radar tomography (CRT) approach  originating from medical imaging applications. Full-wave inversion is a computationally intensive imaging technique which allows for robust volumetric reconstruction of targets that are penetrable by a waveform signal. In CRT, the 3D dielectric permittivity distribution of the interior can be recovered. The resulting data will therefore be able to answer the question of the interior structure of rubble pile asteroids.
The Radar itself will be a one-cube element carrying a 2 x 3.75 m dipole antenna. It uses a stepped frequency modulation with programmable number of frequency lines between 256 and 2048 providing a bandwidth of about 2 MHz. This keeps the data rate at an acceptable limit. The stepped frequency technique was developed in an ESA technology program and is ready for application. Operating with an RF-output power of 10 W the pulse length is adaptable to the expected range to the target allowing to operate over large distances as required in asteroid detection and research.
- Will be made available for download after the workshop