Mission Overview and Objectives

1. Designing a New Frontiers-class Trojan/Centaur Reconnaissance Mission A JPL Planetary Science Summer School Study Alessondra Springmann1, C. Burke1, M. Cartwright2, R. Gadre3, L. Horodyskyj4, A. Klesh5, K. Milam6, N. Moskovitz7, J. Oiler8, D. Ostrowski9, M. Pagano8, R. Smith10, S. Taniguchi5, A. Townsend-Small11, K. U-yen10, S. Vance12, J. Wang3, J. Westlake13, K. Zacny14 1Massachusetts Institute of Technology, 2University of California, Los Angeles, 3Georgia Institute of Technology, 4Pennsylvania State University, 5University of Michigan, 6Ohio University, 7University of Hawaii Institute for Astronomy, 8Arizona State University, 9University of Arkansas, 10NASA Goddard, 11University of California, Irvine, 12Jet Propulsion Laboratory, 13University of Texas, San Antonio, 14University of California, Berkeley Mission Overview and Objectives Mission Design and Impactors Instruments Configuration The baseline mission design requires an Atlas V 531 launch vehicle and allows for three small body encounters. The trajectory brings the spacecraft within 900 km of 2001 HM10, which will provide the opportunity for a test run of the spacecraft systems. During the (624) Hektor encounter the spacecraft passes 700 km above the target at 8.2 km/s, while at 39/P Oterma it passes 800 km above the target at 9.1 km/s. Figure 1 is a visualization of the trajectory and shows the orbits of the target bodies in addition to other Solar System objects. Approximately six days prior to encounters with each target, the spacecraft will launch a 75-kg “dead” tungsten ball. Each impact will excavate a crater on the target, exposing the pristine subsurface and also producing a plume of material for analysis, allowing for more thorough morphology and composition investigations. Due to concerns of ejected material damaging the spacecraft, flybys will occur at a height too far away to perform onboard analysis of samples generated in the impacts. The impacts and resulting craters will help determine the extent of weathering on each object. • The spacecraft was designed within the constraints of the 2008 New Frontiers Announcement of Opportunity (AO) in terms of cost and mass. Our solution is a compact yet robust spacecraft and instrument package based on proven technology, which reduce the cost of the development phases. The instrument suite includes: • Multi-Spectral Imager (previous mission: NEAR) • Dust Secondary Ion Mass Spectrometer (Rosetta) • Thermal Infrared Spectrometer (Mars Global Surveyor) • Ultraviolet Imaging Spectrometer (Cassini) • Wide Angle Camera • Radio Science Experiment • Over a month prior to a target encounter, instrument check-out will begin and the imager begins running four hours per day. A week before encounter, radio science begins, the IR component of the imager turns on, and the the dust analyzer begins operating. Thirty minutes prior to the encounter, TIS and UVIS turn on and begin collecting data. • The science traceability matrix (Table 1) shows how the mission goals and science questions can be answered by different instruments and measurements, and how these will increase scientific understanding. The carrier spacecraft features a high-gain antenna and two solar arrays. This view shows the N2O4 (oxidizer) and NH (fuel) tanks as large red spheres, the tungsten impactors (20 cm diameter) in yellow, and the RCS thrusters in the corners. Instruments are in the grey box on the front lower right. Our mission objectives are the in situ reconnaissance of a Trojan asteroid and a Centaurs via conventional passive methods such as imaging and radio science in addition to the launch of two Deep Impact-style impactors (one for the Trojan target and the other for the Centaur target). Why study Jupiter Trojan asteroids and Centaurs? These primitive small bodies hold clues to the origin and evolution of the Solar System, in that they have avoided most of the processing experienced by larger bodies. Trojans were likely captured during Solar System formation, while Centaurs are believed to have originated in the Kuiper Belt and are similar to comets. Trojans and Centaurs are two major populations that have never been explored by spacecraft and have not been exhaustively studied by ground-based telescopes due to being both dim and distant. Centaurs, however, provide an accessible source of material from two more remote populations: the Kuiper Belt and comets. Targets were selected based on their science potential and low V requirements. Our mission involves a launch in 2015, followed by an encounter with main belt asteroid 2001 HM10 in 2016. In 2020, the spacecraft will encounter the Trojan target (624) Hektor, launch a single impactor, then continue on to the Centaur target 39/P Oterma and launch a second impactor. Our mission name, SHOTPUT, stands for Survey of Hektor and Oterma Through Pulverization of Unique Targets. Instruments Figure 2: Spacecraft bus configuration. Solar arrays are shown on either side. The high-gain antenna is located to the back. Conclusions The impact craters will have similar diameters (~100 m) and depths (~35 m) to the crater on Temple 1 created by the Deep Impact spacecraft. The New Frontiers AO caps missions at $650M; our mission is within the cap at $622.8M. SHOTPUT is also within the caps for both mass (1850 kg; max is 1890 kg) and power (max power is 700 W, within margins). SHOTPUT’s well-design spacecraft and trajectory would provide the first observations of a Trojan and a Centaur of both these targets’ surfaces and subsurfaces. The two impactors onboard both provide innovative science and add public interest to the mission. The robust suite of instruments utilize proven and reliable science capability to reduce the development time and mission cost. In addition to budgeting the mission below the AO limits, we have a descoping plan to ensure the potential science outcomes of the SHOTPUT mission are preserved. Table 1 (right) is the Science Traceability Matrix. In terms of scientific yield, green indicates a breakthrough; yellow a significant advance; while purple represents some advance. Our measurements intend to characterize the chemical composition and morphology of our targets by imaging and taking spectra in various wavelengths of the target surfaces and subsurfaces, including looking for organics, isotopes of hydrogen, the extent of weathering, bulk chemistry, ice presence, and dust properties. Fundamental properties, including the possibility of organic molecules, and the evolution of orbits, can only be addressed by sampling the small bodies up close, hence the importance of sending a varied suite of instruments to our targets. Results from the mission can be compared with formation scenarios, such as the Nice Model for consistency and accuracy. Figure 1 (left) shows the orbits of the inner planets and Jupiter relative to the SHOTPUT spacecraft during the (624) Hektor encounter. 39/P Oterma is at 6.2 AU during the encounter with the spacecraft, making it an accessible source of Kuiper Belt and cometary material. 39/P Oterma Jupiter (624) Hektor Acknowledgements We would like to thank the JPL Office of Informal Education, Anita Sohus, Amber Norton, JPL, the NASA Science Mission Directorate, Charles Budney, and the rest of Team X. For more information please visit http://pscischool.jpl.nasa.gov