AIDA-DART Asteroid Impact & Deflection Assessment Double Asteroid Redirection Test

Transcription

1 AIDA-DART Asteroid Impact & Deflection Assessment Double Asteroid Redirection Test DART Andy Cheng [JHU/APL] Cheryl Reed [JHU/APL] Ian Carnelli [ESA, HQs.] Patrick Michel [Obs. Cote D Azur, Nice, France] Stephan Ulamec [DLR] AIM NASA Team: Goddard Space Flight Center Johnson Space Center Langley Research Center 1

2 Planetary Defense: Mitigation of Asteroid Hazards, a Global Concern Small asteroids that hit the Earth, Chelyabinsk-sized impacts (500 kilotons TNT) every few decades Tunguska-sized impacts (5 megatons TNT) every few centuries 2

3 What can be done, if a dangerous asteroid is discovered that can hit the Earth? AIDA/DART Multiple studies of impact threat deflection have cited three techniques: Kinetic Impactor, Gravity Tractor, Nuclear Device All techniques require some level of demonstration and validation before considered viable for implementation in impact emergency response Kinetic Impactor technology has been assessed as most mature and most capable of effecting adequate deflection except in cases of short term warning before impact - highest ranked as ready for flight demonstration International participation in any asteroid mitigation / deflection campaign is highly desirable if not essential to overall acceptability The AIDA/DART mission is an international collaboration to demonstrate asteroid deflection by kinetic impact 3

4 AIDA supports important goals of the Planetary Defense community Consistent with finding from SBAG 12, January 2015: AIDA/DART SBAG strongly supports the creation of a NASA Planetary Defense Coordination Office, a top recommendation of the 2010 NAC Task Force report. Furthermore, SBAG recommends that this new office (1) pursue goals specified in congressional direction, such as NEO population survey completion, (2) work towards development of NEO mitigation technologies through additional funded programs, including flight validation of the most promising mitigation system concepts, and (3) utilize cross-agency and international collaborations as warranted in accomplishing those goals. Consistent with recommendations from 2011 and 2013 Planetary Defense Conferences: Missions should be planned to demonstrate and validate the most promising deflection or disruption options (2011) Missions are being proposed that would use kinetic impactors to move an asteroid, and the impact and motion away from the original path would be verified by observer spacecraft. Designing these missions and developing the necessary tools and payloads for these types of actions would verify model predictions and build confidence in our abilities to deal with an actual threat. (2013) 4

5 AIDA international cooperation DART kinetic impactor (NASA) AIM rendezvous (ESA) AIM Radar Telescopes DART AIDA = AIM + DART Didymos Binary 5

6 AIDA: First Full Scale Test of Asteroid Deflection First mission to demonstrate asteroid deflection by a kinetic impactor Measure outcomes of a known impact on an asteroid at full scale AIDA combines US and European space experience and expertise to address an international concern, the asteroid impact hazard. First mission to study a binary asteroid and its origins Impact on to secondary allows Earthbased observations of changes to binary orbit First mission (AIM) to demonstrate interplanetary optical communication and deep-space inter-satellite links with CubeSats and a lander in deep-space Cheng AF et al. (2015). Acta Astronautica, 115: Radar image of Didymos L. Benner, Arecibo, Nov

7 AIDA is relevant for many disciplines Planetary Defense Deflection demonstration and characterization Orbital state Rotation state Size, shape, gravity Geology, surface properties Density, internal structure Sub surface properties Composition (mineral, chemical) Human Exploration Orbital state Rotation state Size, shape, gravity Geology, surface properties Density, internal structure Composition (mineral, chemical) Radiation environment Dust environment AIM DART Deflection demonstration and characterization Orbital state Rotation state Size, shape, gravity Geology, surface properties Density, internal structure Sub surface properties PDC 2015 Science Orbital state Rotation state Size, shape, gravity Geology, surface properties Density, internal structure Sub surface properties Composition (including isotopic) Resource Utilization Geology, surface properties Density, internal structure Sub surface properties Composition (mineral, chemical)

8 AIDA Investigation Summary AIDA = DART + AIM Planetary Defense Demonstrate kinetic impact mitigation technique, measure asteroid deflection Develop and validate models for momentum transfer in asteroid impacts Science and Exploration Understand asteroid collisions Infer physical properties of asteroid surface and subsurface, interior structure Data on impact cratering Test models of binary formation Demonstrate technologies: optical communication, cubesats, proximity operations 8

9 AIDA Joint Working Groups Welcome AIM DART AIM Advisory Team led by P. Michel DART Investigation Team co-led by A. Cheng, A. Rivkin Working Group 1 [Modeling and Simulation of Impact Outcomes] Angela Stickle, Paul Miller, Steven Schwartz Working Group 2 [Remote Sensing Observations] Andy Rivkin, Peter Pravec Working Group 3 [Dynamical Properties of Didymos] Derek Richardson, Kleomenis Tsiganis Working Group 4 [Science Proximity Operations] Stephan Ulamec, Olivier Barnouin 9

10 JHU/APL Proprietary DART: Double Asteroid Redirection Test NASA s DART, a kinetic impactor mission with supporting Earth-based observing campaigns Full-scale demonstration of asteroid deflection by kinetic impact, to learn how to mitigate an asteroid Understand impact effects, to infer asteroid physical properties and study long term dynamics of impact ejecta Ground-based observations to measure the binary period change from kinetic impact to within 10% Return high resolution images of target prior to impact to determine impact site and geologic context Target: Didymos binary in JHU/APL Proprietary

11 Didymos: Spectral Type and Composition Observations by Binzel et al. (2004) and de León et al. (2010) Pretty clearly S type Not exotic, new type Context for Eros/Itokawa Most common NEO type Dunn et al. (2013): L/LL chondrite best analog, very common 1.6 meteorite type Originally from Flora family? 1.3 LL chondrite parent family? Chelyabinsk link? 1 Gaspra link? 0.9 Normalized Reflectance 0.8 de León et al. (2010) Didymos (de Leon et al.) 433 Eros (Binzel et al.) Itokawa (Binzel et al) Wavelength ( m) 11

12 JHU/APL Proprietary DART: Double Asteroid Redirection Test Target: Didymos binary in September, 2022 Launch Date Dec 18, 2020 Launch C km 2 /s 2 Arrival Relative Speed 7.03 km/s Time of Flight 640 days Maximum Earth Distance 0.21 AU Solar Distance 0.95 AU 1.06 AU Earth Distance at Impact AU Solar Phase Angle 44 Impact Angle to Orbit Plane 27.5 DART payload is a single instrument, a high resolution imager derived from New Horizons LORRI Support optical navigation and autonomous targeting Determine impact site and geologic context 12 JHU/APL Proprietary

13 DART: 2022 Didymos Intercept DART trajectory remains near 1 AU from Sun, Earth distance < 0.2 AU. DART launch energy 6 km 2 /s 2 Impact velocity 7 km/s Impact event in Sept. 20, 2022 occurs under excellent Earth-based optical viewing conditions, with radar study of aftermath shortly thereafter SEP architecture may allow impact during radar observability window NEA flyby 10 months before Didymos encounter DART launches in Dec 2020 and intercepts Didymos on Sept 20,

14 DART Spacecraft Orbit Configuration Launch Configuration HGA LGA DRACO imager LGA Star Tracker Three-axis stabilized, thruster control only Monoprop propulsion Single payload instrument: DRACO imager 14

15 AIDA: DART+ AIM Objectives AIM mission objectives together with DART: Determine the momentum transfer resulting from DART s impact by measuring the dynamical state of Didymos after the impact and imaging the resulting crater Study the shallow subsurface and deepinterior structure of the secondary after the impact to characterize any change Study the impact response of the target asteroid and measure distributions of impact ejecta providing valuable data to validate impact models

16 Momentum Transfer Efficiency Full-scale measurement at an asteroid is defined as momentum transferred divided by momentum input If no ejecta, then = 1 Ejecta enhances momentum transfer, > 1 M is target mass, is velocity change Incident momentum ejecta ejecta Enhanced momentum transfer 16

17 Impact-Induced Binary Orbit Change The orbit changes depend on orbit phase of the impact DART targets close to maximal period change 1% variation in period change over 34 minute window. 17

18 Modeling and understanding the outcome of the DART kinetic impact Scaling law calculations, 300 kg at 7.0 km/s on Didymos secondary, accounting for ballistic trajectories of ejecta Basalt Weakly Cemented Basalt Perlite /Sand Sand / Fly Ash β R [m] β* Orbiting fraction <1% <1% 32% <1% Nonporous, strong Housen & Holsapple 2011 Holsapple & Housen 2012 Cheng 2012 Low porosity, moderate strength Very high porosity, weak High porosity, weak Porous target cases predict of ~1.1 to ~1.3 consistent with simulations, Jutzi & Michel (2014) Basalt case not expected to apply because of binary formation scenario Deflection result of kinetic impact is not appreciably affected by gravity of binary companion AIM measurement of crater radius is important for finding target properties is the contribution from ejecta fast enough to escape Didymos system, almost the same as Orbiting fraction is the ejecta mass fraction captured into temporary binary orbits 18

19 Post-Impact Observing Prospects Observation and Modeling of DART ejecta Didymos primary and secondary are separated by up to 0.02 arcsec when 0.08 AU from Earth Marginally resolvable with ALMA (sub-mm), Magellan adaptive optics Post-impact brightening and ejecta stream as extended object ( coma ) may be observable from Earth Nonporous, strong Low porosity, moderate strength Very high porosity, weak High porosity, weak Brightening [mag] Coma, integrated V mag Itokawa gravel size distribution; Miyamoto et al

20 Didymos Observations during 2015 Establishing preferred pole for system Apparition in spring. Reached V ~ 20.5 Several observers, using telescopes with 2-4 m apertures Bad weather limited useful data. Observations by Moskovitz and Thirouin with DCT show mutual event Observations This rules out one of two possible poles, favor low-obliquity, retrograde YORPy option Confirming is major goal of 2017 observations 20

21 Preparations for 2017 Didymos apparition Focusing on Jan-May Reaches V~20.3 Four goals for 2017 observing: 1. Confirming the preferred retrograde pole position 2. Gathering data to allow BYORP-driven changes in the mutual orbit to potentially be determined by later observations 3. Establishing whether or not the secondary is in synchronous rotation with the primary 4. Constraining the inclination of the satellite orbit Some of these goals met with a few nights of 4-m time, others require up to 6-m time Investigating whether HST proposal is warranted 21

22 Outline of 2022 Impact Observing Campaign DART impact during excellent apparition: Didymos at V ~ 14-15, very well placed for Chile, observable from other observatories Planetary Radar participation hugely useful Didymos primary and secondary are separated by up to 0.02 arcsec when 0.08 AU from Earth Marginally resolvable with ALMA (sub-mm), Magellan adaptive optics Post-impact brightening and ejecta stream as extended object ( coma ) may be observable from Earth White paper about observing campaign possibilities in preparation Debris cloud analogous to YORP-driven MBCs? P/2013 P5 ~250 m, observed at 1.1 AU distance from Earth 22

23 Didymos, Points 5 days apart Period of impact Motion with time

24 Modeling and Simulation of Impact Outcomes Working Group Goals (1) Determine the expected outcome of the DART impact and its sensitivity to initial impact conditions. (2) Assess the effect of the DART impact on the moon of Didymos, focusing on implications for asteroid deflection and properties. Preliminary Modeling Predicts: crater diameter of 5-10 m β values range from 1 5 using estimated target properties The DART impact will change the secondary s period by ~ 10 minutes Current Activities Benchmarking of hydrocodes and comparison to experimental data and analytical models Investigating sensitivity of momentum transfer to: target properties, impact conditions, shape effects (target and spacecraft) Investigating ejecta dynamics and evolution in the Didymos system following DART impact 24

25 Modeling and Simulation of Impact Outcomes Working Group Goals (1) Determine the expected outcome of the DART impact and its sensitivity to initial impact conditions. (2) Assess the effect of the DART impact on the moon of Didymos, focusing on implications for asteroid deflection and properties. Impact simulations and scaling rules predict β~1-5 for reasonable target strength and porosity conditions Analytical models and preliminary simulations predict crater diameters of 5-17 m Orbit evolution studies predict 8-10 minute period change For a two-body problem, it is most efficient to impact in direction parallel to orbit velocity For aggregate bodies (e.g., rubble pile), the disturbance of most orbit parameters (a and i) nearly identical to 2-body case. 25

26 Potential Future Opportunities for the Community Participating Scientist Program Modeling of Event (pre- and post-dart impact) Observing Campaign (pre-encounter, near-impact, and postimpact) Instruments on AIM 26

27 Conclusion DART successfully completed NASA s Pre-Phase A study milestone in May 2015, Mission Concept Review (MCR) DART is now officially in Phase A! This study phase continues through September Primary NASA milestone is System Requirements Review (SRR) and Mission Design Review (MDR), scheduled for August 2016 DART is in tandem with AIM s Phase A/B1 study phase, and supports their programmatic milestones DART will continue to support joint both AIM interfaces and reviews, and joint AIDA sessions The 2 nd International AIDA Community Workshop will be held in June 1-3, 2016 in Nice, France. You are all welcomed to attend!! Consideration underway for maximizing and optimizing community involvement in getting full success! 27