46th Lunar and Conference (2015) 1386.pdf

AIDA: IMPACT & DEFLECTION ASSESSMENT. A. F. Cheng1, C. Reed1, I. Carnelli2, P. Michel3, S. Ulamec4, 1JHU/APL, Laurel, Maryland ([email protected]). 2 ESA Headquarters, Paris, France. 3Lagrange Laboratory, Univ. Nice, CNRS, Côte d’Azur Observatory, France. 4 DLR, Cologne, .

Introduction: On Feb. 15, 2013, an exceptionally tion will be measured to higher accuracy, and addition- close approach to by the small asteroid 2012 al results of the DART impact, like the impact crater, DA14 was eagerly awaited by astronomers around the will be studied in great detail by the AIM mission. world, but a different small asteroid unexpectedly im- AIDA will return vital data to determine the momen- pacted Earth over Chelyabinsk, Russia the same day tum transfer efficiency of the kinetic impact and key without warning. The released physical properties of the target asteroid. The two mis- several hundred kilotons TNT of energy and injured sion components of AIDA, DART and AIM, are each over 1500 people. This dramatic reminder of the - independently valuable, but when combined they pro- oid impact hazard re-emphasized the importance of vide a greatly increased knowledge return. discovering hazardous and learning how to The main objectives of the DART mission, which mitigate the hazards. The Asteroid Impact & Deflec- includes the spacecraft kinetic impact and Earth-based tion Assessment (AIDA) mission will be the first observing, are to: demonstration of a mitigation technique to protect the • Impact the secondary member of the Didymos bi- Earth from a potential asteroid impact, by performing a nary system during its close approach to Earth in spacecraft kinetic impact on an asteroid to deflect it October, 2022 from its trajectory. • Demonstrate asteroid deflection by kinetic impact AIDA is an international cooperation entering and measure the period change of the binary orbit Phase A study at NASA and ESA, consisting of two resulting from the impact mission elements: the NASA Double Asteroid Redi- • Determine the impact location on the target aster- rection Test (DART) mission and the ESA Asteroid oid, the local surface topography and the geologic Impact Mission (AIM) rendezvous mission. The pri- context mary goals of AIDA are (i) to test our ability to per- DART is targeted to impact the smaller secondary form a spacecraft impact on a potentially hazardous component of the binary system [65803] Didymos, near-Earth asteroid and (ii) to measure and characterize which is already well characterized by radar and opti- the deflection caused by the impact. The AIDA target cal instruments [1,2]. The impact of the >300 kg will be the (65803) Didymos, with the DART spacecraft at 6.27 km/s will produce a velocity deflection experiment to occur in October, 2022. The change on the order of 0.3 mm/s, which leads to a sig- DART impact on the secondary member of the binary nificant change in the mutual orbit of these two ob- at ~6 km/s will alter the binary orbit period, which can jects, but only a minimal change in the heliocentric be measured by Earth-based observatories. The AIM orbit of the system. This is because the target’s veloci- spacecraft will characterize the asteroid target and ty change from the impact is significant compared to monitor results of the impact in situ at Didymos. AIDA its orbital speed ~15 cm/s, although it is quite small will return fundamental new information on the me- compared to the heliocentric orbit speed ~23 km/s. chanical response and impact cratering process at real Thus the change in the binary orbit is relatively easy to asteroid scales, and consequently on the collisional measure compared with the change in the heliocentric evolution of asteroids with implications for planetary orbit. To maximize the orbit change, the impact should defense, , and near-Earth object sci- be close to the ’s perihelion [3, 4], although the ence and resource utilization. AIDA will return unique eccentricity of the Didymos secondary is very low. information on an asteroid's strength, surface physical The momentum transfer from the kinetic impact properties and internal structure. Supporting Earth- depends on momentum carried away by ejecta that are based optical and radar observations, numerical simu- not retained by the moon’s gravity [5]. The momentum lation studies and laboratory experiments will be an transfer is parameterized by β, which is the ratio of part of AIDA. momentum transferred to the incident momentum. AIDA=AIM+DART: The target of the AIDA Complete transfer of the kinetic impactor momentum mission will be a binary asteroid, in which the NASA to the target is indicated by β=1. Numerical simula- DART mission will target the secondary, smaller tions of asteroid fragmentation resulting from the im- member in order to alter its orbit around the primary. pact of a kinetic impactor as well as numerical integra- The resulting period change can be measured to within tions of the momentum carried away by impact ejecta, 10% by Earth-based observations. The asteroid deflec- 46th Lunar and Planetary Science Conference (2015) 1386.pdf

accounting for gravitational bending of ejecta trajecto- • Study the shallow subsurface and deep-interior ries, yielded similar β estimates of 1.28 to 2.52 for a structure of the secondary after the impact to variety of low strength, high strength, low cohesion characterize any change. and high cohesion target materials [6,7]. Hence, AIM will measure the size and shape of the The DART mission will use ground-based observa- impact crater and will image the ejecta plume, provid- tions to make the required measurements of the orbital ing valuable data to validate impact models. deflection, by measuring the change of AIM is a small mission of opportunity to explore the binary asteroid. The DART impact is expected to and demonstrate new technologies for future science change the period by ~0.5%, and this change can be and exploration missions while addressing planetary determined to 10% accuracy within months of observa- defense and asteroid science objectives. The AIM pay- tions. The DART target is specifically chosen because load consists of remote sensing instruments, a landed it is an eclipsing binary, which enables accurate deter- package and technology demonstrations. A Visual Im- mination of small period changes by ground- based aging System (VIS) is part of the guidance, navigation optical measurements. In an eclipsing bina- and control system of the spacecraft. The AIM straw- ry, the two objects pass in front of each other (occulta- man payload also includes a Thermal IR Imager tions), or one object creates eclipses seen by the (TIRI), a monostatic High-Frequency Radar (HFR), a other, so there are sharp features in the lightcurves bistatic Low-Frequency Radar (LFR), the Optel-D which can be timed accurately. optical communication terminal, the MASCOT-2 The DART payload consists of a high-resolution , and opportunity payloads (COPINS). visible imager to support the primary mission objective Thus, AIM will determine the Didymos secondary of impacting the target body through its center. The asteroid orbital and rotation state, size, mass and shape DART imager is required to support optical navigation and analyze geology and surface properties. In the on approach and autonomous navigation in the termi- AIDA mission together with the DART kinetic impact, nal phase. The imager is derived from the New Hori- AIM will observe the impact crater and derive colli- zons LORRI instrument [8] which used a 20 cm aper- sion and impact properties.. ture Ritchey-Chretien telescope to obtain images at 1 Mission Designs: The DART spacecraft, the in- arc sec resolution. The DART imager will determine terceptor, can be launched on a small class launch ve- the impact point within 1% of the target diameter, and hicle for the baseline mission in December 2021 to it will characterize the pre-impact surface morphology impact Didymos in Oct 2022, targeted to the secondary and geology of the target asteroid and the primary to member of the binary system. There are multiple inter- <20 cm/px. cept opportunities for both the 2022 and 2024 close The ESA AIM mission will use a small spacecraft approaches providing program flexibility. For all demonstrating a number of technologies including AIDA mission options, the interceptor is on a low- deep-space optical communication and inter-satellite energy trajectory and the impact occurs close to Earth. network in deep-space with a number of CubeSats de- The AIM launch opportunity is identified in Oct ployed in the vicinity of the Didymos system and 2020 with a transfer duration of around 19 months (i.e. lander on the surface of the secondary. arriving in mid-2022). This trajectory is based on a The AIM mission objectives are to: launch with a Soyuz 2.1b/Fregat MT from • Characterize the Didymos secondary component allowing a 21-day launch window and will lead the by analyzing its dynamical state, mass, geophysi- spacecraft to a maximum Sun distance of up to 2.2 AU cal properties, surface and subsurface structure. and a maximum Earth range of 3.2 AU. • Demonstrate deep-space optical communication Acknowledgement: We thank NASA for support technology and perform inter-satellite communi- of the AIDA study at APL. cation network with CubeSats and lander. References: [1] Pravec, P. et al. (2003), IAU Circular • Deploy the MASCOT-2 lander on Didymos sec- 8244. [2] Pravec, P., et al. Icarus, 181, pp. 63–93, 2006. [3] ondary asteroid and sound its interior structure. Ahrens, T. J. and A.W. Harris, (1994) In Hazards due to When AIM is operated together with DART, the & Asteroids, Univ. Ariz. Press, pp. 897-927. [4] mission covers supplementary objectives: Galvez, A. & Carnelli, I. (2006 In 57th IAC, Valencia, Spain. • Determine the momentum transfer resulting from i, 1, 11, 19. [5] Holsapple, K. A., and K. R. Housen (2012), DART’s impact by measuring the dynamical state Icarus, 221(2), 875–887. [6] Jutzi, M., and P. Michel (2014). of Didymos after the impact and imaging the re- Icarus 229, 247-253. [7] Cheng, A. F. (2013) 44th LPSC sulting crater. 2013, paper 2985. [8] Cheng A. F. et al., (2008) Space Sci- ence Reviews, 140, 189.