ASTEX An In-Situ Exploration Mission to two Near-Earth-Asteroids

Transcription

1 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, Katlenburg-Lindau, Germany; 2 DLR, Berlin, Germany; 3 DLR, Bonn, Germany; 4 Astrium GmbH, Friedrichshafen, Germany; 5 DLR, Oberpfaffenhofen, Weßling, Germany; 6 Astos Solutions Unterkirnach, Germany Image: JAXA

2 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

3 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

4 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

5 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

6 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)

7 Mission Concept & Technology Propulsion system: chemical propulsion system is not suitable for the mission (excessive fuel mass) electric propulsion system required Fuel Mass [kg] 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 Delta-V [km/s]

8 Lander Design Concept (1) Total lander mass: 64.1 kg Shovel or rake possible About 100g regolith mass can be removed

9 Lander Design Concept (2) Controlled descend: Radar Ranger Guide Camera Momentum wheel Thruster for orbit and attitude control

10 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)

11 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

12 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 Mission duration max. 15 years 212 combinations left

13 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

14 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) NEA Update 12/2007: 5000 Objects NEA Accessibility H-Plot Hohmann Rendezvous FG Asteroid Main Belt ORPHEUS APOPHIS Mars Venus Hohmann Flyby Selected (primary) Target Combinations 1 st Asteroid Apophis nd Asteroid 1996 FG Orpheus 3361 Orpheus Depart ure Date Missi on Durati on (year s) Total Δv (km/s) st Asteroi d Taxono my Sq B C 2 nd Asteroi d Taxono my C S, V S, V Aphelion Distance (AU) C S

15 99942 Aphophis and 1996 FG3

16 and 3361 Orpheus

17 65679 and 3361 Orpheus

18 and 11500

19 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

20 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: 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: μm FoV: 6.87 Spectral resolution λ/δλ: Power: 30 W Spatial resolution 0.2 km distance Telemetry rate: 1.1 MB per spectrum Telemetry volume: ~10 GB for one NEA

21 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 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 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: μm Spatial Resolution: 17μm/pix Telemetry volume: 250 MB for one NEA

22 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

23 Reference Mission Timeline extraction Lander descend Start of lander operations

24 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.