The Asteroid Geophysical EXplorer (AGEX) to explore Didymos

Transcription

1 CubeSat 2016, the 5th Interplanetary CubeSat Workshop The Asteroid Geophysical EXplorer (AGEX) to explore Didymos. Karatekin & AGEX TEAM. Karatekin, B. Ritter N. Gerbal, M. van Ruymebeke. Royal Observatory of Belgium, Brussels, Belgium. Mimoun, N Murdoch, A Cadu. Institut Supérieur de l Aéronautique et de l Espace, France. Carrasco, Javier Garcia de Quiros Embedded Instruments and Systems S.L., Spain.. Vasseur Antwerp Space, Belgium N.Rambaux IMCCE, Paris Observatory France, S. Tardivel (JPL, USA)

2 AIM MISSION AND AGEX Asteroid Geophysical Explorer (AGEX) is among the proposals selected by ESA as a response to a call for ideas for the CubeSat Opportunity Payloads for the AIM mission.

3 Asteroid Geophysical Explorer (AGEX) The proposed concept includes two 3U CubeSats that will land ballistically to the surface Didymoon to study its geophysical properties First CubeSat (SeisCube) will land geophysical instrument package including seismometer, and gravimeter to study the subsurface properties. Second CubeSat (Bradbury), will deploy miniaturized sensors Pixies (femtosats) to study the surface properties. Both Cubesats will be have radio transceiver, sun/thermal sensors to study the rotation and inertial measurement units to study surface mechanical properties..

4 Proposed Payload The Preliminary Payload for SeisCube is a geophysical instrument package including: 1. Geophones 2. Gravimeter 3. Accelerometer (MEMS) 4. Gyroscope (MEMS) 5. Cameras (always fun!) 6. Thermal sensors 7. Radio Link (ISL) TRL 4 The Preliminary Payload for Bradbury includes: 1. ~10 Pixies (Femtospacecrafts, 75 mm x 35 mm x 10 mm), set of instrument including temperature, magnetometer, sun sensor 2. Accelerometer (MEMS) 3. Gyroscope (MEMS) 4. Cameras 5. Thermal sensors 6. Radio Link (ISL) TRL 4 TRL 3

5 Asteroid Landing AGEX will use a passive descent (no power or attitude control) Bounces are part of the investigation + Release positions + First impact location + Final positions Tardivel et al CubeSat deployment will demonstrate autonomous landing in low-gravity

6 SEISMICITY: Evidence for seismic activity on asteroids Seismic shaking following impact is the most probable mechanism for crater erasure on Eros (Thomas and Robinson, 2005) Lack of craters on Itokawa implies a mechanism, such as seismic shaking, must be eroding craters (Saito et al., 2006) Thermal cracking may be an important regolith forming process on asteroids (Delbo et al., 2014) Extensive lineaments on Lutetia are suggestive of impact-induced seismic activity (Thomas et al., 2012) Plus other sources (tidal forcing,..) (see Murdoch at al)

7 GRAVITY Local Gravity Vector Perform first ever in-situ gravity experiment on an asteroid The local surface gravity measurements (~5 mgal) can provide mass and density (provided that the shape is known) The local surface acceleration is also sensitive to the rotational accelerations (~0.2 mgal) Mutual body tides; tidal accelerations ~10-1 g Didymoon on Didymoon on compared to ~10-7 g Earth on the Earth) The tilt (~10-3 rad on Didymoon on compared to ~10-7 rad on the Earth ) represents the horizontal component of the changing tidal acceleration in an elliptical orbit. Gravimeter acts as a long-period

8 ROTATIONAL KINEMATICS Changes in Spin Studying the orbit and rotational kinematics of Didymoon will shed light on its internal mass distribution as well as the tidal interaction with Didymain. Gravimeter, Thermal Sensors/Solar Panels, ISL, multi-point Pixie measurements,. An animation showing motion by both components of the 1999 KW4 system Expected forced librations of Didymoon by assuming an ellipsoidal shape After Dart impact, the synchronous rotation is conserved but Free librations are superimposed.

9 Geophysical surface properties Understanding the mechanical properties of the surface material has important implications for small body evolution (e.g., cratering) and for the interpreting the DART impact (with numerical simulations) Philae accelerometers provided information on the strength and layering of the comet s surface Biele et al., 2015

10 AIM PRIMARY SCIENCE OBJECTIVES PARAMETER S#1 Didymoon size, mass, shape, density RELEVANCE Mass => momentum size => shape, volume, gravity density => internal structure SUPPORTING AIM INSTRUMENTS Camera (VIS), LIDAR (OPTEL-D), radio tracking S#2 Didymoon dynamical state S#3 Geophysical surface properties, topology, shallow subsurface Momentum transfer Indirect constraints on interior structure Composition, mechanical properties, thermal inertia =>Interpretation of impact VIS VIS, Thermal Infrared Imager (TIRI), High Frequency Radar (HFR), Accelerometer on Lander (?) S#4 Deep-internal structure of the moonlet Interpretation of impact Origin of binary Low Frequency Radar (LFR)

11 AIM PRIMARY SCIENCE OBJECTIVES PARAMETER RELEVANCE SUPPORTING AIM INSTRUMENTS AGEX S#1 Didymoon size, mass, shape, density Mass => momentum size => shape, volume, gravity density => internal structure Camera (VIS), LIDAR (OPTEL-D), radio tracking Determines the Mass, & bulk density (for a given Volume) (Gravimeter,..) S#2 Didymoon dynamical state Momentum transfer Indirect constraints on interior structure VIS Determines the rotational state (Sun/Thermal sensors) S#3 Geophysical surface properties, topology, shallow subsurface S#4 Deep-internal structure of the moonlet Composition, mechanical properties, thermal inertia =>Interpretation of impact Interpretation of impact Origin of binary VIS, Thermal Infrared Imager (TIRI), High Frequency Radar (HFR), Accelerometer on Lander (?) Low Frequency Radar (LFR) Determines the mechanical properties (Accelerometer, Gyro) Contributes to thermal properties (Thermal sensors) Seismic analysis (Geophones) Density hetorogenities (with additional GM determination, Gravimeter) AGEX will address all AIM primary Science Objectives,

12 AGEX Science Matrix A ROBUST SCIENCE TIMELINE (1/2) Time from release Mission phase Goal Investigation Instruments Mission level Requirements ~few hours Descent and Landing Descent and Landing Preliminary Mass of Didymoon with 20 % Doppler ISL Preliminary Mass of Didymoon with 20 % Surface Mechanical properties Rebound Accelerometer /Gyroscopes Doppler Capability of ISL, Lineof sight Touchdown ~several hours Surface monitoring Surface monitoring Precise Mass of Didymoon Geophysical properties of subsurface Surface Gravity Seismic background Gravimeter Geophones Landing Landing, Coupling ~1 day/2 orbits Didymoon dynamical Surface state monitoring Mean values for Rotational kinematics & Orbital dynamic Solar Panels / Thermal Sensors ISL Gravimeter Pixies Landing, (LOS for ISL, unobstructed FOV for Solar planels/thermal sensors/pixies) Threshold Science ~1 Day

13 AGEX Science Matrix A ROBUST SCIENCE TIMELINE (2/2) Time from release Mission phase Goal Investigation Instruments Mission level Requirements ~ several days ~ weeks Surface Didymoon dynamical monitoring state Surface monitoring Surface monitoring Surface monitoring Geophysical properties of subsurface Geophysical properties of surface Geophysical properties of subsurface Surface Didymoon dynamical monitoring state Time Variable Rotation & Tidal interactions Average seismic properties of the sub-surface (<10m) Multi-point Temperatures, Remanent magnetisation Detailed seismic properties of the sub-surface Solar Panels / Thermal Sensors ISL Gravimeter Pixies Geophones Pixies Baseline Mission ~7 Days Precise Rotation & Tidal interactions Geophones Solar Panels /Pixies Thermal Sensors ISL Gravimeter Landing, LOS for ISL, unobstructed FOV for thermal sensors/pixies Landing, Coupling, Event detection Landing Landing, Coupling, event detection Landing,, LOS for ISL, unobstructed FOV for thermal sensors/pixies ~ months Dart Impact Characterization of Dart Impact & Deep Interior Seismicity, Rotational kinematics, Orbital dynamics Geophones Gravimeter Thermal Sensors Coupling,, LOS for ISL, unobstructed FOV for thermal sensors/pixies Full Mission : up to DART impact

14 Platform design : a thermal challenge Surviving the secondary surface more than a few hours requires a warm box enclosure Temperature maps of the far side of Didymoon for 1 AU Thermal analysis as a function of thermal insulation

15 SeisCube platform requirements Requirements for SeisCube platform: - To provide a platform that hosts the service and load modules and warrantee the maximum survivability time of the mission: at least up to several hours into Nominal Mission (on asteroid surface) - From the mechanical point of view to provide a structure that withstands the launch and efficiently transmits vibrations to the payloads (geophones, accelerometers and gyroscopes) while in operation (descent and surface operations). - Provide an operation environment for the Cubesat service and payload modules during hibernation (travel to Dydimos) and operation (after deployment). - From the electrical point of view provide power, platform management and data handling for the payloads, i.e. connection to the ISL.

16 SeisCube design drivers Design drivers for SeisCube platform: - Design a platform specifically adapted for the mission to hold the platform and payload electronics. - Implement a Warm Box concept that keeps the service an payload electronics within a reasonable working environment isolated from the extreme external temperatures. - Provide a flexible concept using primary/secondary batteries and solar arrays with independent MPPTs to guarantee a minimal mission and, if possible, extend the mission as much as possible. - Accommodate the platform and payloads. - Be as light as possible (less than 500g for the mechanical structure). - Inherit as much space experience as possible.

17 SeisCube Accommodation: warm box proposal Solar panel Upper lid Aluminium structure ISL Battery Secondary: 1s1p Saft MP Primary: 1s8p Saft LSH 14 Patch antenna Azurspace 3G28 cell Aluminium rings PAI rings Gravimeter Thermal Sensors (1 per face at centred position) PAI supports (4 at each side) 5 mm width MLI warm enclosure Inner supporting structure

18 SUMMARY & CONCLUSIONS AGEX provides, unique in-situ exploration in support of all AIM primary science mission goals. CubeSat operated in interplanetary environment, & soft landing on a very small body. In-situ investigations in low gravity environment in a binary system Qualification of new technologies and scientific instruments for future deep-space mission. The AGEX mission concept combines high science return, a low risk posture and will help secure AIM/AIDA primary mission goals by providing complementary investigations and a deployment strategy assessment. (The perfect test for MASCOT-2 Deployment)