Aphrodite MISSION

1. Aphrodite MISSION AlpbachSummerschool 2014 Team GREEN

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3. Introduction “Venusonlylookslike the Earth, in the samesense that the evil Mr. Hyde resembles the good Dr. Jekyll” “As we search forterrestrial-like planets elsewhere, we need to find out the reasonsfor these differences and the conditions thatallows these diverse bodies (…) to form at all.” Why is Venusso different fromEarth?

4. How is Venus different? • Magnetic field • Tectonics and volcanism • Spin rate • Atmosphere

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6. ScientificObjectives

7. Tectonic & Volcanic Activity

8. Tectonic & VolcanicActivity

9. Activevolcanoeson Venus? GanikiChasma, AtlaRegio(5°N-25°N, 180°E-200°E) Geological map of theAtlaRegio, Venus. (Ivanov & Head (2011) Goal: SearchforactivevolcanoesingeologicallysimilarareasasGanikiChasmain thenorthernhemisphere of Venus.

10. Activevolcanoeson Venus? GanikiChasma, AtlaRegio(5°N-25°N, 180°E-200°E) Topographic map (a) and SAR albedo map (b) (Shalygin et al. 2014)

11. (Sub)surfaceTopography • Magellan (1990-1994) + Venera-D (2024?) • Scientificgoals: topographicalmapping of thesurface. • OurAim: • Studythe (sub)surfacetounderstandthevolcanic and tectonicprocesses • Structure and stratigraphy of lavaflows • Detectsubsurfacemagmaticbodies • Depth/structure of thecoronae, riftzones, wrinkleridges and tesseraregions

12. ThermalImaging • Magma chambers • Eruptions • Lava flows • Smallestvolcanoes • Coldest lava flows

13. Volcanic Signature Atmosphere Chemical and isotopic measurements of the atmosphere above, through and below the cloud layer (65-45 km). • understand the evolution of the atmosphere and its link to volcanic processes • gas species related to volcanic activity: H2O and SO2 • their respective isotopes: D/H, 16O/18O and 32S/34S • the variability of SO2 give clues to the rate of current volcanism • refined measurements, obtained in-situ, provide constraints on volcanism • link to volcanic processes via isotopic fractionation due to volcanic process • recent interior degassing and processes controlling the sulfur cycle on Venus Identification of a volcanic ash layer at the lower cloud base • study the nature of the layer at the base of the cloud • measure particle sizes of volcanic ash / dust particles • distinguish between H2SO4 aerosols measured chemically

14. Spin rate • Second complementing question:

15. Spin rate • ChangedfromMagellan to Venus Express • Even changedwithinMagellan • Period of 3 years • => improve absolute and temporal variability precision

16. Spin Rate • Atmospheric coupling to the surface • → spin influence • Observation in-situ & fromorbit • Temperature • Pressure • Wind Speed

17. Scientific objectives summary • Synergy between the two questions through special focus on interaction between surface and atmospheric markers • First time dedicated mission to revealing geophysical processes • => BONUS scientific question: preparing exoplanet geology by determining geophysical processes observable without lander or orbiter

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19. PAYLOAD • Needs slide to explain each payload package

20. Spin Rate measurement Package • Accurate accelerometer • Match orbitfluctuations • Shifts in orbitsafter 1 Venusday • Sum “errors” of everyorbit • Find spin changes and axischanges

21. Spin Rate measurement Package STAR Accelerometer: • Mass: < 15 kg (estimated) • Power: < 15 W (estimated) • Resolution: < 3 E-9 m/s^2 • Requires 3 star trackers

22. Spin Rate measurement Package APS Star tracker (x3): • Mass: 3 x 1.5 kg = 5 kg • Power: 3 x 5 W = 15 W

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24. STK mission

25. Timeline • Launch – 20/3/2025 using Soyuz from Kourou • Delivery to Venus - ???? Days (hohmann transfer) • Orbit period – 2.54 hours • Balloon separation – at 66,000km • Probe separates and lands on surface • Balloon altitude – 40-60km (day/night variation) • Balloon lifespan – 30 days • Orbiter lifespan – 3 years • Total mission – 4 years

26. Particular mission phases • Venus approach • Entry descent inflation • Orbit insertion

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29. Orbiter and Balloon design

30. Orbiter design • Design drivers: • Venus express bus to maximize heritage • As simple as possible • Twin solar arrays • Heat shield • Agility for balloon communication and instrument stability • Mass budget:

31. Balloon design • Design drivers • Entry descent and inflation

32. Balloon design: • Entry descent and inflation • Lifetime requirement =30 days:

33. Balloon design: • Stability: buoyancy/aerodynamics/height control gondola

34. Balloon design: • Power generation • Solar panels + battery • Relative wind + battery • Communication with orbiter through S-band • Thermal control • Passive probe release mechanism • Passive probe design: • (stephen)

35. Mass budget • Orbiter • Payload • Total dry mass : 85*5=425kg

36. Mass budget • Balloon: • Entry and Descent module: • Approximately 250 kg [Yves Langevin]

37. Power system (orbiter) • Power required • Payload: 100-115 W • Solar array • Large voltage range dueto the wide range of temperatures • Triple junctionGaAs • Efficiency EOL 24.3% • Power production 645.2 W/m² • Battery • Low-mass 24 Ah Li-ion • Specificmassdensity : 300 to 1500 W/kg

38. Power system (balloon) • Power required • Payload: 10 W (if all operating at the same time) • Cruise Entry and Descent (?) • Solar array • Battery • Low-mass 24 Ah Li-ion • Specificmassdensity : 300 to 1500 W/kg

39. Earth – Venus Transfer • Launch and entry into Earth parking orbit by launcher • Hohmann transfer to Venus sphere of influence with hyperbolic capture • B-plane targeting to Venus (perigee altitude / inclination specified) • Venus elliptical orbit by use of aerobreaking • Possible orbit change maneouvre (either lower or circular) Earth orbit ΔV1 Hohmann transfer RV RE ΔV2 Venus orbit

40. Venus orbit parameters • Periapsis – 250km • Apoapsis – 6000km • Semi-major axis – 9177 • Eccentricity - 0.31 • Period - 2.54 hours • Max velocity – 8228m/s • Min velocity 4303m/s • Ground speed at pericentre – 7902m/s From excel sheet orbital tools Dr Peter Falkner 250km 6000km

41. Aerobreaking • This is used to decrease the apocentre of the Venus orbit • It uses significantly less fuel, therefore increasing the delivered mass to Venus

42. Orbiter profile • Total launch mass possible – 1780kg • Balloon mass – 70kg • Payload (orbiter) – 71.6kg • Fuel – 538kg (for major manoeuvres) • Power – 115W (payload) • Comms – X-band (orbiter to Earth) ???? • OnBoard Data Handing – Radiation resistant processor, 2TB data storage • Fairing diameter – 4.11m • Overall length – 11.4m

43. Communication strategy • Period – 2.54 hours • Balloon period – 4 days Ground segment + operations: • ESA – ESTRACK • ESOC • NASA - DSN Communications are ensured every orbit. Time TBD

44. Data Handling System • - Radiation tolerant Processor • Data: ~100 Gbit/day • Max storage time: ~ 0.25 years • - Internal Data Storage: ~ 2TB

45. Altitude/OrbitControl - Star trackers - Inertialmeasurement units - 3-axis-stabilisation

46. Thermal Control Passive thermal control • Heat rejection towards space via radiators • Multi-Layer Insulation (MLI) blankets to minimise heat exchange and temperature fluctuations • Dedicated radiator for VIRTIS

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49. Extra slides

50. ThermalImaging