ASTEX An In-Situ Exploration Mission to two Near-Earth-Asteroids A. Nathues 1, H. Boehnhardt 1, A. W. Harris 2, W. Goetz 1,C. Gritzner 3, C. Jentsch 4, N. Schmitz 2, S. Schaeff 6, F. Weischede 5, A. Wiegand 6 1 MPI for Solar System Research, 37191 Katlenburg-Lindau, Germany; 2 DLR, 12489 Berlin, Germany; 3 DLR, 53227 Bonn, Germany; 4 Astrium GmbH, 88039 Friedrichshafen, Germany; 5 DLR, Oberpfaffenhofen, 82234 Weßling, Germany; 6 Astos Solutions 78089 Unterkirnach, Germany Image: JAXA
The NEA Links The origin link: asteroids are remnants from the planetary formation disk of the early solar system preserved information about the time of disk accretion The planet link: asteroids contributed to the formation of the terrestrial planets and to the core accretion of the gas giants constrain disk & planetesimal properties at 2-5 AU by time of planet formation The population evolution link: asteroids have a wide envelope of planetary evolution phenomena primitive to differentiated bodies The Earth link: main Belt erosion produces continuous flow of Near-Earth Asteroids (NEAs) collisions with Earth, mass extinctions, disastrous consequences for our modern civilization in case of a mega impact
Scientific Motivations: Motivations of ASTEX NEAs have intimate links to the original primitive planetesimals to the evolved population in the asteroid belt to the Earth environment the diversity of NEAs is still unexplored the inner structure of NEAs and main-belt asteroids is less investigated Technological Motivations: Rendezvous and autonomous landing maneuvers are sophisticated Long lasting ion propulsion system required Only relatively low ΔV values are required to reach some NEAs high payload mass or the use of a cheap launcher is possible
ASTEX Immediate Scientific Goals Exploration of a primitive (C, D, P, B, F) NEO and a fragment of an evolved asteroid (E, V, Q, S, A, R, M ) Explore the origin and evolution history of NEAs Determination of the inner structure of NEAs Determination of the morphology, geology, chemistry, mineralogy as well as the age of the surface Search for bounded water Determination of physical parameters (spin vector, size, shape, mass, density, rotation period) Determination of the physical properties of the surfaces (thermal conductivity, roughness, material strength) Establish the link between the asteroids and the meteorite classes
Study Goals (1) Identification of suitable NEAs for a double rendezvous and landing mission (2) Identification of optimized trajectories and launch dates (3) Selection of suitable instrumentation to meet the scientific mission goals (4) Preparation of a realistic mission timeline (5) Propose appropriate propulsion systems (6) Propose suitable and affordable spacecraft and lander systems (7) Propose suitable launcher (8) Evaluate the required ground segment for mission operations and support The study is funded by the German Aerospace Agency (DLR), performed by the German industry and research institutes under guidance of MPI for Solar System Research Current Status: tasks (1) to (6) almost done, (6) (7) to be completed until Aug 08
Basic Mission Concept Launcher for about 1.6 t S/C mass (Soyuz type) Electric propulsion for transfers and rendezvous manoeuvres Single spacecraft Two lander approach (one per target)
Mission Concept & Technology Propulsion system: chemical propulsion system is not suitable for the mission (excessive fuel mass) electric propulsion system required Fuel Mass [kg] 1500 1200 900 600 300 Fuel Mass of a 1500 kg Spacecraft Chemical Propulsion System (Isp = 350s) Electric Propulsion System (Isp = 4500s) Criteria low fuel consumption (Isp ~ 4500s) high thrust (T~150mN) long engine lifetime at least 4 engine types available 0 0 2 4 6 8 10 Delta-V [km/s]
Lander Design Concept (1) Total lander mass: 64.1 kg Shovel or rake possible About 100g regolith mass can be removed
Lander Design Concept (2) Controlled descend: Radar Ranger Guide Camera Momentum wheel Thruster for orbit and attitude control
Target Selection (1) Data Base Preparation of Excel spreadsheets containing the orbit elements of ~5000 NEOs (adopted from NASA s Near Earth Object Program data base) Further information about the physical properties of the NEOs added (e.g., adopted from the EARN data base)
Target Selection (2) Target Pre-Selection Step 1: Amor s removed NEOs with absolute magnitude H 22.5 mag rejected 2115 NEOs left Step 2: NEOs with delta-v 7 km/s rejected 207 NEOs left Step 3: NEOs with unknown taxonomy have been given lower priority 46 NEOs
Target Selection (3) Combinations Step 4: Computation of the required min. mission delta-v for 2070 target combinations Optimal Hohmann transfers assumed Inclination change at nodes assumed Step 5: Mission scenarios with a total delta-v > 11 km/s were rejected 1210 combinations left Step 6: Detailed mission delta-v computations for 1210 combinations Patched Conic Approach with target ephemeris considered Impulsive maneuvers assumed Introduction of further constraints: 1. Mission time slot between 2015 and 2040 2. Mission duration max. 15 years 212 combinations left
Target Selection (4) Scientific Selection Step 7: Selection of combinations consisting of a primitive NEA (C, D, P, B, F) and a fragment of an evolved body (E, V, M, S, A, Q, R) 71 combinations left Step 8: Prioritizing E and V-types Min. stopover time 6 months Max. mission duration < 10y Rotation period between 2h and 80h 29 combinations left Step 9: Low thrust cases computed for 29 missions
Target Selection (5) Prime Missions Step 10: 4 primary (and 4 secondary) missions were selected for further elaboration total Delta-V < 11 km/s Min solar distance > 0.7 AU (thermal constraint) Max solar distance < 2.0 AU Launch date Target taxonomy Delta-V (km/s) 10 8 6 4 2 NEA Update 12/2007: 5000 Objects NEA Accessibility H-Plot Hohmann Rendezvous 11500 1996 FG3 162173 Asteroid Main Belt 65679 3361 ORPHEUS 99942 APOPHIS Mars Venus Hohmann Flyby Selected (primary) Target Combinations 1 st Asteroid 99942 Apophis 65679 162173 2 nd Asteroid 1996 FG3 3361 Orpheus 3361 Orpheus Depart ure Date 2023-05-12 2017-03-06 2020-12-03 Missi on Durati on (year s) 8.61 7.46 6.70 Total Δv (km/s) 9.088 10.811 9.848 1 st Asteroi d Taxono my Sq B C 2 nd Asteroi d Taxono my C S, V S, V 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Aphelion Distance (AU) 162173 11500 2019-12-18 9.36 10.885 C S
99942 Aphophis and 1996 FG3
162173 and 3361 Orpheus
65679 and 3361 Orpheus
162173 and 11500
Operations at ASTEX Targets Our orbit stability investigations around very small bodies revealed: 1. For most ASTEX targets no stable orbit was found only hovering or/and flyovers are possible 2. Polar terminator orbits may be stable for the asteroids 3361 Orpheus and 162173
Scientific Payload (1) Orbiter Radio Reflection Tomographer Marsis DAWN FC Cameras LEO VISNIR Spectrometer Total mass: 12 kg Volume electronics: 160 x 250 x 110 mm Dipole Antenna: ~30 m length Frequency: between 5-30 MHz (choise after target selection) Power: DC power active 60 W Daily data volume: 30 Mbits Mass: 5.5 kg Volume: 160 x 190 x 380 mm Detector: 1024 x 1024 CCD Wavelength range: 250 1020 nm FoV: 5.5 x 5.5 Resolution: 93 mrad/pixel Power: 18 W 7 color filters + clear filter Telemetry rate: 2.1 MB per frame Telemetry volume: ~5 GB for one NEA Mass: 6.4 kg Volume: 300 x 300 x 180 mm Detector: HgCdTe (256 x 500 pix) Wavelength range: 0.4 3.0 μm FoV: 6.87 Spectral resolution λ/δλ: 394 295.4 Power: 30 W Spatial resolution 0.2 m @10 km distance Telemetry rate: 1.1 MB per spectrum Telemetry volume: ~10 GB for one NEA
Scientific Payload (2) Lander MARSIS Panoramic Camera Mass: 0.8 kg Detector: CCD or APS FoV: 70 x 70 Power: 5W Volume: 100 x 100 x 100 mm 3 Wavelength range: ca. 400 950 nm Pixel FoV: 0.9 mrad Telemetry volume: 250 MB for one NEA VNIR Microscope Beagle 2 Mass: 0.3 kg Detector: CCD FoV: 4 x 4 mm (in 12 mm distance to surface) Power: 3W Volume: 125 x 60 x 50 mm 3 Wavelength range: ca. 400 950 nm Spatial resolution: 4 μm /pixel Iluminating LEDs of different wavelength Telemetry volume: 700 MB for one NEA Close-up Camera ROLIS Mass: 0.5 kg Detector: CCD FoV: 3.6 Power: 2.2 W / 6 W with LEDs Telemetry rate: 1.1 MB per spectrum Volume: 90 x 60 x 80 mm 3 Wavelength range: 0.3 1 μm Spatial Resolution: 17μm/pix Telemetry volume: 250 MB for one NEA
Scientific Payload (3) Lander Electron Microscope Mass: 0.5 kg Detectors: Electron multiplier, Photo-cell, X- ray detector FoV: 100 x 100 mm (in 100 mm distance to surface) Power: 3W Volume: 50 x 50 x 80 mm 3 Energy range: X-Ray > 30 kev Pixel FoV: > 0.2 mm x 0.2 mm Telemetry volume: 700 MB for one NEO Moessbauer Spectrometer Mass: 0.8 kg Detectors: 5 Si-PIN diodes FoV: circular area of about 2 cm diameter Mass: 5 * 20 g = 100 g Power: 0.1W each Volume: 90 x 50 x 40 mm 3 Energy range: either 14.4 kev and/or 6.4 kev Power: 3 W TM volume for one NEO:~2MB Volume: 10 x 10 x 3 mm 3 Telemetry volume: 250 kb for one NEO Thermistor Common DPU/PSU Power: 12W Volume: 120 x 120 x 60 mm 3 Mass: 1.5 kg
Reference Mission Timeline extraction Lander descend Start of lander operations
Conclusion The ASTEX study investigates several mission scenarios, compiles suitable instrument options for a scientific exploration mission to two mineralogically different Near-Earth Asteroids The mission could be launched around the middle of the next decade at the earliest The ASTEX study complements other NEA mission studies like ESA s Marco Polo mission with a similar launch window. It provides thus a basis for a mutually beneficial exchange of scientific and technological ideas.