Planetary Entry Probes In the Foreseeable Future: Destinations, Opportunities, and Techniques

1. Planetary Entry Probes In the Foreseeable Future:Destinations, Opportunities, and Techniques Thomas R. Spilker Jet Propulsion Laboratory, California Institute of Technology, USA International Workshop on Planetary Probe Atmospheric Entry and Descent Trajectory Analysis and Science Lisbon, Portugal Oct. 8, 2003

2. NASA Implementation Options • NASA has multiple programs for implementing missions • Roadmap “Flagship” missions • NASA is responsible for the mission • PIs propose instruments & investigations • Generally, large budgets for complex missions with broad science scope • Non-US participation negotiated by NASA, approved by US Gov’t • “Community-based” mission programs • PI responsible for the entire mission) • Cost-capped, simpler missions with more focused science • Generally, the smaller the cost cap, the more focused the science • Non-US participation is encouraged • Negotiated by PI, approved by NASA & US Gov’t • Current programs • New Frontiers • $700M cost cap; specified destinations & science objectives options • Discovery • $350M cost cap; much looser restrictions on destinations & science objectives • Mars Scouts • Mid-size Explorers (MidEx)

3. Solar System Exploration (SSE) Theme high-priority mission Mission Objectives Enter Venus’ atmosphere, descend to surface Measure atmospheric pressure, temperature, composition Collect a surface sample Document context, make in situ composition measurements Balloon ascent above clouds, analyze sample Make atmospheric pressure, temperature, composition, and wind measurements while ascending Venus In-Situ Explorer New Frontiers Program candidate Mission Requirements • Sciencecraft requirements • Payload • Neutral mass spectrometer • Meteorological package • Multispectral near-IR imaging • Elemental geochemistry (XRFS?) • Mineralogy (UV fluorescence?) • Imaging microscope (petrographic?) • Mass, power, datavolume TBD • Driving observation accommodations • Protect components from extreme Venus environment • Thermal, pressure, chemical Architectures / Transportation challenges • Ballistic or SEP to Venus • Direct aero entry to atmospheric descent • Ventry >10 km/s for ballistic approach Transportation options • Rigid aeroshell or ballute aero entry Adapted from NASA ISP Technology Reprioritization Task mission list

4. Venus Aeronomy Probe • Mission Description • Example Mission Design: • - Small Delta II • - 1-Year Flight Time, 1year Ops • - High Inclination Elliptical Orbit • Orbit altitudes 150 km x 12,000 km • Flight System Concept • - Spin-Stabilized Platform • - Floating Potential Neutralization • - Solar array power • - Mass unknown, probably tens of kg science payload Sun-Earth Connection (SEC) Theme mission • Architectures/ Transportation Challenges • Launch direct to Venus • Aerocapture (attractive due to orbit) or propulsive capture into elliptic orbit • Options • Aerocapture • Advanced Chem • MXER Tether/Adv. Chem Science Objectives • Determine Mechanisms for Energy Transfer From Solar Wind to Ionosphere and Upper Atmosphere • Measure Charged Particles Responsible for Auroral-Type Emissions and Infer their Acceleration Mechanisms • Determine Formation Processes for Ionospheric Magnetic Flux Ropes, Ionospheric “Holes” on the Nightside and the Loss of Ionospheric Plasma in the Form of Streamers, Rays and Clouds Adapted from NASA ISP Technology Reprioritization Task mission list

5. SSE long-term mission (after 2013) Mission Objectives Return samples of Venus’ surface to Earth Estimated Flight System Characteristics Advanced chem should deliver ~2400 kg to Venus orbit 600 kg descent stage + sample collector 600 kg ascent stage + balloon Venus Sample Return Flagship Mission concept Mission Requirements • Sciencecraft requirements • Driving observation accommodations • Sample mass, number of samples not specified • Context documentation requirements not specified • Cooled IR focal plane • Low Venus orbit (300 km?) to minimize ascent ∆V Architectures / Transportation Challenges • Interplanetary craft (IC) uses advanced chemical or SEP to Venus orbit • Sampling craft performs aeroshell/parachute descent to surface, acquires samples • Balloon lofts ascent vehicle, it ascends to Venus orbit • Advanced chemical propulsion, multi-stage • IC performs rendezvous, retrieves sample • IC returns to Earth with advanced chemical or SEP • Advanced chem uses aero entry at Earth, Vrel > 11 km/s Transportation Options • SEP or advanced chemical for interplanetary transfer • Advanced chemical for ascent to Venus orbit Adapted from NASA ISP Technology Reprioritization Task mission list

6. Mars Exploration • NASA has a dedicated Mars Exploration Program • Easier to access than most other solar system locations • C3 requirement for direct transfer are low • Launch vehicles can deliver relatively large masses • Trip times are short • Many spacecraft have visited Mars already • More mature exploration destination than other solar system locations • High-priority science objectives call for platforms other than entry probes • Some typical entry probe instruments could ride along on landers • Several avenues for implementing missions • Roadmap “Flagship” missions • Mars Scouts

7. Mission Objectives Jupiter near-polar orbit, very low perijove Gravity field & dynamo magnetic field Auroral zone fields & particles, imaging Low-res global water, ammonia abundances May serve as relay for entry probes Multiple atmospheric entry probes Penetration to 100-bar level 3 different latitudes between +/- 30 deg Composition, dynamics, clouds, energy flux Jupiter Polar Orbiter With Probes New Frontiers Program candidate Mission Requirements • Sciencecraft requirements • Payload mass, power TBD • Probe data volumes ~4 Mbits per probe • Driving observation accommodations • Several orbits (≥5) with inclination ≥ 85 deg • F&P, microwave radiometer prefer spinning platform • Probe descent takes ~1.5 hr or more; need relay visibility • Magnetically clean S/C • ≥1 year in Jupiter orbit • Perijove < 1.1 Rj, near equator • Best for gravity & magnetic fields, microwave measurements • Avoid highest-flux parts of jovian radiation field Architecture / Transportation Challenges • Inner solar system gravity assists to Jupiter • Cruise time 2-8 years; depends on S/C mass, launch vehicle • SEP to Jupiter • Separate probe data relay satellite, or orbiter relay • Orbiter relay requires large post-insertion ∆V Transportation Options • Gravity assist or SEP to Jupiter • Advanced chemical propulsion for probe targeting, orbit insertion, post-insertion orbit adjustments High-priority Solar System Exploration Theme mission; could merge with Sun-Earth Connection Theme’s Jupiter Polar Orbiter mission Adapted from NASA ISP Technology Reprioritization Task mission list

8. Io Electrodynamics SEC Theme Mission • Mission Description • • Example Mission Design • - Delta launch: direct trajectory • - 5.9 Rj x 71 Rj Io-resonant equatorial orbit • - Approx 1 month orbital period • • Two-year flight time, 3-year operations • • Flight System Concept • - Rad-hard spin-stabilized platform • - Chemical bi-propellant, advanced RTGs • - Payload: • Fields & Particles instrumentation (plasma, energetic particle, magnetic & electric fields) • UV imager Science Objectives • Investigate the energy conversion processes in a magnetized plasma • Understand mass transport in a rapidly rotating magnetosphere • Determine how intense parallel electric fields are generated in a magnetized plasma • Determine how momentum is transferred through field-aligned current systems • Determine the role of Io in radio wave generation at Jupiter • Transportation Options • SEP with smaller launch vehicle • Advanced Chem, small cryo stage (launch • topoff plus insertion) Adapted from NASA ISP Technology Reprioritization Task mission list

9. Notional “Io Electrodynamics” Orbit andEntry Probe Trajectory

10. Jupiter Icy Moons Orbiter (JIMO) Fission-Powered Vehicle • Turbine-generated electric power, ~100 kWe • Ion propulsion (probably Xenon propellant) • ISP 6000 - 9000 s • Delta-V capability tens of km/s • When propulsion system is not active, high power is available for science instruments • Extremely high data rates • Launch 2011-2013? • Some mission designs might allow delivering Jupiter entry probes • Significant impact to mission • Payload mass • Mission duration Never Mind!

11. Solar System Exploration Theme long-term mission Mission Objectives Non-Keplerian “ring hover” orbit About 3 km from ring plane Visit diverse parts of A and B rings Observe individual ring particles: size, shape, composition, texture, dynamics Observe group particle behavior: clumping shepherding, ringlet & wave formation Magnetic & electric fields near rings Saturn Ring Observer Flagship Mission concept Mission Requirements • Sciencecraft requirements • Payload mass, power TBD • Driving observation accommodations • ~1 cm resolution images of ring particles • Image frequency ~1 per minute • Observe areas where average particle is stationary with respect to the spacecraft • ≥1 month in science orbit (ring hover) • Visit at least 4 different radial positions in the rings Architecture / Transportation Challenges • Gravity assists or SEP to Saturn • Initial equatorial aerocapture into slightly inclined Saturn orbit • Entry Vrel = 36-38 km/s, ∆V >7 km/s • Advanced chemical trajectory correction immediately afterward, ∆V up to 0.5 km/s • 1/2 orbit later, advanced chemical insertion into ring hover orbit • ∆V ~3 km/s • Pulsed chemical thrusters maintain ring hover Transportation Options • Gravity assist or SEP; aerocapture and advanced chemical • NEP Adapted from NASA ISP Technology Reprioritization Task mission list

12. Mission Objectives Orbiter and in situ element at Titan Detailed investigation of Titan and its organic environment Global high-resolution IR & SAR mapping Global measurements of gross surface morphology, composition, chemistry Atmospheric composition, structure, dynamics Composition & distribution of organics, organic chemical processes, context, & energy sources Pre- & proto-biological chemistry Titan Explorer Flagship Mission concept Mission Requirements • Driving observation accommodations • Telecom • Cooled IR focal plane • SAR • Delta IV-med/SEP can deliver ~1600 kg • Orbiter 1200 kg, entry vehicle 400 kg, including aeroshells • ≥2 years in near-polar Titan orbit, 1700 - 2000 km alt • High altitude driven by atmospheric drag • One year in situ element lifetime Architectures / Transportation Challenges • Inner SS / Jupiter gravity assists to Saturn • Cruise time for most trajectories 8 years or less • SEP transfer to Saturn; arrival V∞ ≥ (?) km/s • Aerobraking Ventry 6 - 10 km/s, ∆V > 4 - 8 km/s Transportation Options • Gravity assist or SEP (solar sail? tether?) to Saturn system • Rigid aeroshell or ballute aerocapture • Aeroshell mission studied by Aerocapture Systems Analysis Team SSE mid-term mission (Project start after 2005) Adapted from NASA ISP Technology Reprioritization Task mission list

13. Mission Objectives Orbit Neptune, visit all major parts of the Neptune system Cassini-like science investigation of the Neptune system Neptune interior, atmosphere (entry probes included), magnetosphere Many Triton flybys/gravity assists Nereid flyby upon approach Rings & small inner satellites Significant orbit evolution over mission lifetime: “Tour” Neptune Orbiter With Probes Flagship Mission concept Mission Requirements • Sciencecraft requirements • Driving observation accommodations • Deliver and support atmospheric entry probes • NAC pointing & stability during ≥ 500 km Triton flybys • Telecom • Cooled IR focal plane • At least 2 years in Neptune orbit • Cruise “not much more than 10 years” • Initial aerocaptured orbit 4000 x 430,000 km Architecture / Transportation Challenges • Inner SS / Jupiter gravity assists to Neptune • Cruise time for most trajectories well over 10 years • Some as little as 8 years (JGA, JSGA) • SEP for fast Neptune transfer; arrival V∞ ≥ 15 km/s • Aerocapture Ventry 25 - 31 km/s, ∆V > 5 km/s Transportation options • Gravity assist, SEP, or solar sail to Neptune • Rigid aeroshell or ballute aerocapture • Aeroshell mission study in progress • Momentum exchange tether + advanced chem? • Candidate for post-JIMO NEP SSE Theme long-term mission; could combine with SEC Theme Neptune Orbiter Adapted from NASA ISP Technology Reprioritization Task mission list

14. New Techniques for Atmospheric Entry Probes Multiple-Descent-Module Data Relay Strategies • Useful for atmospheres with radio-absorbing species (ex. NH3, H2O) • Shallow penetrator descends more slowly, stays in “clear” atmosphere • Deep penetrator descends more rapidly, enters more opaque atmosphere • Opacity plus distance to data relay craft greatly reduces data rate • Deep penetrator sends data via nearby (100-200 km) shallow penetrator • Disadvantage: Doppler Wind Experiments are more complex

15. New Techniques for Atmospheric Entry Probes Ballute Decelerators • CDA can be orders of magnitude larger than that of a rigid aeroshell • Surface heating rates greatly diminished • Might allow using new types of materials, save mass • Deceleration in a given atmosphere occurs higher • Would allow post-deceleration access to regions now unavailable • Lower-density regions of deeper atmospheres • Bodies with tenuous atmospheres • Io, Triton, Pluto, Charon?

16. New Technologies for Atmospheric Entry Probes Many potentially advantageous technological developments • Wind turbine generators • Potential for high power for data relay • Phase-change material for cooling • Data signal reception at multiple locations • Multi-vector Doppler Wind Experiments

17. Concluding Remarks Many future opportunities for entry probe missions • Many science objectives at many potential destinations • Multiple means for implementing missions • Project scales from relatively small to “Flagship” Much room for methodological & technological innovation • Can expand the envelope of science addressed Realizing missions requires significant community consensus about mission objectives