planetary entry probes in the foreseeable future: destinations, opportunities, and techniques thomas...

Planetary Entry Probes In the Foreseeable Future:

Destinations, Opportunities, and Techniques

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

Thomas R. Spilker 2003/10/08

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 scopeNon-US participation negotiated by NASA, approved by US Gov’t

–“Community-based” mission programsPI responsible for the entire mission)Cost-capped, simpler missions with more focused science

–Generally, the smaller the cost cap, the more focused the scienceNon-US participation is encouraged

–Negotiated by PI, approved by NASA & US Gov’tCurrent 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)


Venus In-Situ Explorer

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

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, data volume TBD

–Driving observation accommodations• Protect components from extreme Venus

environmentThermal, 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

New Frontiers Program candidate


Venus Aeronomy Probe

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

Sun-Earth Connection (SEC) Theme mission

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

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



Venus Sample Return

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


– Driving observation accommodationsSample mass, number of samples not specifiedContext documentation requirements not specifiedCooled 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


Flagship Mission concept


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


Jupiter Polar Orbiter With Probes

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


– 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 Thememission; could merge with Sun-Earth ConnectionTheme’s Jupiter Polar Orbiter mission


New Frontiers Program candidate


Io Electrodynamics

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

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

Transportation Options

•SEP with smaller launch vehicle•Advanced Chem, small cryo stage (launch topoff plus insertion)



Notional “Io Electrodynamics” Orbit andEntry Probe Trajectory

Io Orbit

Spacecraft orbit

Probe trajectory


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

NeverMind!


Saturn Ring Observer

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


– Payload mass, power TBD– Driving observation accommodations

~1 cm resolution images of ring particles Image frequency ~1 per minuteObserve 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 ringsArchitecture / 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 hoverTransportation Options• Gravity assist or SEP; aerocapture and advanced chemical• NEP




Titan Explorer

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

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)




Neptune Orbiter With Probes

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”


– Driving observation accommodationsDeliver and support atmospheric entry probesNAC pointing & stability during ≥ 500 km Triton flybysTelecomCooled 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




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

600 BPS

300 BPS

150 BPS


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 atmospheresIo, Triton, Pluto, Charon?


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

New Technologies for Atmospheric Entry Probes


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

Concluding Remarks

planetary entry probes in the foreseeable future: destinations, opportunities, and techniques thomas...

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