Miniaturization of Planetary Atmospheric Probes Tony Colaprete NASA Ames
“Outline” • History of atmospheric entry probes and science • What probes have flown • What have they measured • What were their limitations • Building an entry probe • Survival First, Measure Later • Technological (and Physical) Limitations • Changing the paradigm • The curse of Galileo - Hand-me-down science • Enabling Sensors & Technology • Pico probes - New Architectures and Systems Credits: Gary A. Allen, Jr., William H. Ailor, James O. Arnold, Vinod B. Kapoor, Daniel J. Rasky, Ethiraj Venkatapathy
History of planetary entry “probes” • Since the 1960’s: • Mercury,Gemini, Apollo, Soyuz , etc. (Earth) • PAET (Earth) • Pioneer Venus, Vega, Venera (Venus) • Viking, Pathfinder, MER, DS-2 (Mars) • Galileo (Jupiter) • Huygens (Titan) • Future (on the books): • Phoenix Lander (Mars) • Mars Science Laboratory (Mars) • ExoMars – ESA (Mars) • Talked about: • Venus SAGE • Titan Aerobot/Rover • Jupiter, Saturn & Neptune
Atmospheric Science: PAET, Pioneer-Venus, Viking, Galileo and Huygens PAET (1971), An Entry Probe Experiment in the Earth’s Atmosphere M = 62 kg, Minst = 14 Kg, Rb = .914 m Viking (1976) Pioneer-Venus (1978) Galileo (1995 )
State-of-the-Art (16 years ago): Huygens • Probe specifics: • 2.7 m diameter heat shield • Total Probe mass of 349 kg • 6 instruments (49 kg or 14%)
In-Situ Mars Atmosphere Profiling • Viking 1 & 2: • Atmospheric state variables during entry (direct). • 5 minutes each • Pathfinder and MER: • Atmospheric state variables during entry (derived). • 5 minutes each • Phoenix: • Atmospheric state variables during entry (derived). • 5 minutes In All, about 25 minutes has been spent making measurements between the surface and 80 km.
And now for the rest of the data… Venus Profile Titan Profile 120 110 100 90 80 70 60 50 40 30 20 10 0 z (km) clouds ? 100 200 300 400 500 600 700 800 T (K) In all, planetary entry probes have measured ~14 individual profiles
The limitations of entry science • Up to this point it is very costly in terms of mass, and always mass = $$ • Can only afford to fly a few (if your lucky) and usually only one - Statistics of small numbers (e.g., Galileo) • Limited lifetime – poor temporal coverage The challenge is to change the way probes are done to overcome these limitations!
Payload Range: 5%-25% Aeroshell (TPS) Range: 3% - 50% Aeroshell (strcutures) Range: 5% - 12% Aeroshell Parachute Range: 2% - 5% Power/Thermal/Com Range: 5% - 20% Atmospheric Entry Mission & Probe Design Probe mass fraction • Mission Design Considerations: • Intended Science – Where are you headed? • Key Factors: Mass, Volume, Power, Design Complexities (risk) and Cost • Science payload (mass, power, etc) significantly impact both mission architecture and hardware (mass, power, complexity and cost) – Drives Probe Size Huygen Mission Design Spacecraft Mass fraction Cassini Spacecraft Components
Galileo – A flight through a nuclear blast About 50% of the probe was TPS
microprobe Designing for Hell Jovian Entry TPS Study • Calculations by Dr. G. Allen / M. Tauber, ELORET based on Engineering Code by Tauber, et. al. • Galileo entry conditions 48 Km/sec, - 6.64o E. angle, equatorial entry • Carbon Phenolic TPS - TPS mass fraction is insensitive to entry probe size • Science mass available for microprobe approx. 1 kg Galileo: Probe Mass: 338 kg, Science Mass: 8.3% of Entry Probe mass Base Radius: 1.28m The gas giants present extreme performance limits to TPS
Pascal – A Mars Network Mission Using Micro Probes Pascal Sample Network Configuration
Pascal – A Mars Network Mission Pascal Probe Deployment Sequence
Pascal – A Mars Network Mission Probe Entry System Science Station 0.5 m • - 70° half angle cone • - Hemispherical backshell • 20 kg entry mass • RHU powered
Pascal Carrier S/C accommodates 24 Probes with a Delta III or IV Launch Vehicle ADCS and Telecom Components MGA’s and LGA Spacecraft Bus Fixed Solar Array Probe Dispenser Panels (4) Hydrazine Thrusters Stowed in D3940 Fairing Power and C&DH Components
Entry • Speed = 6 km/s • Landing in 4 minutes Pascal EDL Sequence Selforientation Aft dome separates Parachute deployment separates entry probe from science package Q = 700 Pa M = 1.5 – 2.2 Airbag inflates immediately after chute deployment Airbag protects science station at impact – numerous bounces Jettison airbag and initiate landed operations Chute separates after first impact Pascal – A Mars Network Mission Pascal requires several enabling technologies/developments
Enabling Sensors - Venus SAGE Atmospheric Structure Investigation Wind Provides information on all atmospheric state variables, stability, and winds during descent and landing. Temperature Sensor Booms Landing Sphere Pressure IMU & Moutherboard Gyroscopes Accelerometers
Enabling Sensors -Amazing Shrinking Sensors A miniaturized mass spectrometer
The Pico Reentry Probe (PREP) • Modular reentry probe: • Conduct flight-testing of an integrated entry system • Flight qualification of subsystems such as TPS, innovative sensors and science instruments • Perform low cost atmospheric science experiments • Specifications: • ~ 20 cm in diameter • Total mass ~ 1 kg • Payload mass ~ 0.3 kg • Heatshield mass fraction < 7% (for Mars entry)
Possible mission architectures • Multiple atmospheric sounders • More valuable in atmospheres where remote sensing is difficult (e.g., thick or opaque) • …or for measurements that are difficult to make with remote sensing (e.g., methane on Mars, water in Jupiter) • “Ground” truth for remote sensing (e.g., winds, composition, state) • Landed Network • Hard landers would retain the most simplicity • Synoptic weather • Seismic networks • Penetrator (e.g., DS-2) • Crewed Descent • Forward observers to high-value descent vehicles
Micro Probe System Considerations • Science instrument design • Multiple integrated sensors • TPS • Rethink design • New materials for outer planets • Terminal descent & landing • Parachute? • Heat shield separation • Novel Shapes? • Thermal and power management • Extreme operational ranges • Data storage, processing, relay & comm. • Miniature & ruggedized transmitters
Micro Probe System Considerations Examples of integrated micro-systems ST5 micro-sat 3corner micro-sat
Concluding Thought “A personal impression is that more can and ought to be done with simple sensors : a shift of emphasis from exquisite construction to testing and analysis.”– Ralph Lorentz
Existence Proof – NASA V-Team • NASA V-Team Descent Probe • 4 accelerometers • 3-axis gyro • 2 external temperature • 2 external pressure • GPS • Total mass ~3kg The probe is no longer a vehicle but rather an instrument into itself.