ENHANCING SCIENTIFIC RECONNAISSANCE OF SMALL BODIES USING RADIOISOTOPE

Introduction: In the last two decades, a number of small bodies have been explored to differing degrees by spacecraft (Table 1). The majority of these missions have involved flybys, and only one, the NEAR mission, has involved extended observations at a small body. While the data acquired during flybys has greatly enhanced our knowledge of small bodies, the knowledge gained from the year-long study of the asteroid 433 Eros has clearly demonstrated the value of spending extended periods of time carrying out reconnaissance of an object [1]. For example, the data obtained at Eros enabled the determination of an appropriate site for landing, and could equally well have enabled the optimal choice of sampling sites or locations for landed packages such as geophones. In order to undertake comprehensive reconnaissance of a small body to determine its interior structure, we would argue that flybys are insufficient, and that only extended orbital missions can enable the appropriate science return. In many cases, radioisotope power supplies are enablers for small-body missions, especially those further out in the solar system, and propulsion is the significant technical driver. Radioisotope-Electric Propulsion (REP) can enable many of these missions by combining a small (~500 kg dry mass) spacecraft with a focused payload (~50 kg) and advanced radioisotope power sources for a mission cost on the order of that for a New Frontiers mission [2]. REP systems may, in addition, allow extension of the science goals in the recent report published by the National Research Council "New Frontiers in the Solar System: An Integrated Exploration Strategy" (the “Decadal Survey”) [3] by enabling orbital missions of bodies for which only flyby missions are possible with chemical propulsion. REP systems can also enable an interstellar precursor mission, the subject of a more recent NRC report “Exploration of the Outer Heliosphere and the Local Interstellar Medium” [4]. The key reason why REP spacecraft would be ideal for characterization of small bodies such is their capability of orbiting more than one body in a single mission. Rather than sending numerous spacecraft, with the associated development, assembly, test, launch and operations costs for each, a REP spacecraft could visit at least 2, and possibly more, bodies for the cost of only one mission. Furthermore, most technology for this class of missions already exists; the only technology development required is that of the next generation Stirling Radioisotope Generator (SRG), which is currently in NASA’s technology plan, and so is already underway. With continued development, REP missions could be available for small body characterization within the next decade.