Didymos Explorer and PANIC: Asteroid Concept Studies of the S4P Program at NASA Ames
Rozitis, Ben1; Bellerose, J.2; Cook, A.3; Fahnestock, E.4; Mester, C.5; Murdoch, N.6; Olds, P.7; Reddy, V.8; Schindler, K.9; Thomas, C.10; Yamaguchi, T.11; Asphaug, E.12
1The Open University; 2JAXA/JSPEC; 3Rensselaer Polytechnic Institute; 4University of Michigan; 5Stanford University; 6ESTEC/ESA; 7UARC/NASA Ames; 8University of North Dakota; 9University of Dresden; 10Massachusetts Institute of Technology; 11The Graduate University for Advanced Studies; 12University of California
In the last few decades, there has been an increasing interest in small bodies since they are made of the fundamental building blocks of our solar system. At the same time, there has been an increasing effort to assess near-Earth asteroids (NEAs) impact threats. In both cases, more information on their surface composition, interior, and response to external perturbations is necessary in order to better understand their role, and to design proper impact mitigation and countermeasures. The successful asteroid missions such as NEAR to (433) Eros, and Hayabusa to (25143) Itokawa have gathered a wealth of new information on the surface and interior of NEAs. Still, a lot of questions remain.
Recent developments in the field of NEAs may provide answers and add scientific motivation. In particular, the discovery of a large portion of binary or multiple systems, while identifying rare classes in this population, may give better insights on asteroid evolution, interior, and space weathering. To date, a few studies have investigated and modeled possible formation paths of binary systems, involving fission through flybys, capture of other large debris, and asteroid spin up due to solar radiation and heating. In addition to provide insights on small scale system formation, investigating binaries may be a more efficient way to understand the building blocks of small bodies.
In the summer 2008, the Small Spacecraft Summer Study Program (S4P) brought together 11 graduate students to further develop and contribute to the international effort in small body exploration. The S4P objectives were driven by these current questions on asteroid origin, impact threats, and on the formation of our solar system at large.
Considering low Delta V available targets, the potentially hazardous binary system (65803) Didymos has been chosen as the target of the Didymos Explorer. Didymos is a binary asteroid system with a primary diameter of 0.75 ± 0.1 km and a 0.15 ± 0.05 km secondary. Spectroscopic measurements show that Didymos is an Xk-type in the Bus taxonomic classification. The orbital period of the secondary is 11.91 ± 0.01 hrs while the primary spins at about 2.26 ± 0.0001 hrs. Hence, sending a spacecraft to Didymos offers a "2 for 1" science opportunity, allowing study of both slow and fast rotators, while investigating an unvisited asteroid class.
The Didymos Explorer mission is an interesting concept as it only has two-year lifetime, with an overall cost and wet mass less than $140M and 310 kg respectively. The mission can be launched in Fall 2014, with corresponding target arrival scheduled in Spring 2016. This leaves several months for science operations. In addition, the trajectory also includes a flyby of asteroid 2001XY10 15 days after a close approach to Earth at 0.12 AU. Then, after an intensive campaign of surface and shape characterization, using visible and near-infrared imaging, spectroscopic and thermal observation, and LIDAR topography sensing, the mission will conclude with deployment of a tetrahedral picolander for in situ compositional characterization on the secondary's surface. In this work, we also lay out the basic mission phases and spacecraft subsystems.