Poseidon - Trident Flying by Neptune
TEAM BLUE Alpbach, 2 August 2012 Outline
● Science Case
● Objectives & Requirements
● Payload
● Mission trade study & design
● System design
● Ground Segment Mission statement
● To explore the Neptunian system as an archetype for ice giants
● To investigate the nature of the moon Triton
ESA Cosmic Vision 2015-2025 Call Themes addressed ● 1.3 Life and habitability in the Solar System ● 2.1 From the Sun to the edge of the Solar System ● 2.2 The giant planets and their environments
1 Mission Profile
● Neptune and Triton Flyby
● Neptune Atmosphere Probe
● Launch date - June 2028
● Arrival at Neptunian system - Jan 2041
● Transit time 13.4 years
● Nominal mission duration: 15.4 years Neptunian System Rationale
● Limited knowledge about icy giants
● Planet formation process
● Link to Exoplanets
● Triton - possible KBO The Neptunian System
● Only visited by Voyager 2 (August 1989) ● Additional data taken from ground-based measurements and HST ● Icy giant (30 AU)
● 13 satellites (discovered so far) in the Neptunian system ● Ring Structure ● Very dynamic storm events (Suomi et al., 1991) Neptune's Atmospheric Composition
● Main species : H2 (~80 %), He (~18 %), CH4 (~2 %)
● We expect heavy elements (Z>3) O, C, N, S in the form:
○ S in H2S Troposphere ○ O in H2O
○ N in NH3
○ C in CH4
● Hydrocarbons, CO and HCN Stratosphere Atmospheric Structure
PRESSURE
The locations and densities of the various cloud layers in the atmosphere of Neptune. de Pater et al. (1991) Atmospheric Dynamics
Sromovsky et al., 2001 ● Large dispersion of zonal wind speeds & cloud features
● Wind velocity at different altitudes has not measured yet
● Cloud activity + heat excess => convection (not yet proven)
● Potentially new Great Dark Spot Planetographic latitude [deg] (GDS), smaller dark spot (DS2) ?
ZONAL VELOCITY [m/s]
Triton
● Neptune's largest moon (d=2700 km)
● Retrograde orbit (~ 6 day period)
● Possible Kuiper Belt Object
(Agnor and Hamilton, 2006)
● Mixture of rock and ice
● Triton seems to be geologically active Magnetosphere
● Complete magnetosphere reconfiguration in every planetary rotation ● No stable particle trapping expected (Paranicas et al., 1990) ● Triton as a source & sink in the magnetosphere (Krimigis et al., 1990; Richardson and McNutt 1990)
(Bagenal, 1992) Radio Emissions (NKR)
● What do we know from radio spectra measured by Voyager 2? 1) Rotation period of Neptune 2) First evidence for Neptunian magnetic field
● What will be added by our measurements?
1) Determination of location and source 2) More exact value for rotation period 3) Connection to Exoplanets
Satellites and Ring system
● Clumpy ring structure caused by small moons (Salo and Hänninen, 1998). ● The Liberté arc might disappear within a decade (Pater et al.,2005).
(Wikimedia Commons) (NASA Press Release #PIA02202) Outline
● Science Case
● Objectives & Requirements
● Payload
● Mission trade study & design
● System design
● Ground Segment Science Objectives & Requirements
1.1 To characterize the atmosphere of Neptune a. Bulk composition
Requirements
Objective Measure elemental abundances of
C, N, O, S and noble gases Constrain P < 50 bar, m/dm>3000 at 1% peak height, absolute planetary accuracy 10% formation Measure isotopic ratios D/H models Instruments
Reflectron time-of-flight (RTOF, probe) Science Objectives & Requirements
1.1 To characterize the atmosphere of Neptune a. Chemistry
Requirements
Objective Observe hydrocarbons in stratosphere & disequilibrium species in troposphere (e.g. CO, Photochemistry PH3,GeH4) & Convection absorption lines of PH3 (20-100 cm^-1;FAR-IR & MID-IR), GeH4 (2-17 um; FAR-IR & MID-IR), with a spectral resolution of 0.5-20 cm^-1.
Instruments
Infrared Spectrometer (IRS) Science Objectives & Requirements
1.1 To characterize the atmosphere of Neptune b. structure and dynamics
Requirements
Determine the pressure & temperature profile up to min 50 bars, Objective with 1% accuracy on pressure and 0.01 mbar resolution and, with 0.5 K accuracy on temperature and 0.02 K resolution. Structure Instruments
Pressure Sensor (PS, probe) Temperature Sensor (TS, probe) Science Objectives & Requirements
1.1 To characterize the atmosphere of Neptune b. structure and dynamics
Requirements
Measure the wind velocities & zonal wind speeds Objective troposphere and the stratosphere (at least 10 bars), with an accuracy of 1 m/s and a resolution of 0.1 m/s Dynamics Instruments
Doppler Wind Experiment (DWE, probe) Narrow Angle Camera (NAC) Science Objectives & Requirements
1.2 To characterize the interior of Neptune
Requirements Objective Determine the J2 & J4 gravity field
Understand ice component range-rate accuracy in the range of 0.015 giants formation mm/s and 0.1 mm/s at 60 sec integration time and evolution processes Instruments
X Ka Transponder (RSI) Science Objectives & Requirements
2.1 To investigate the interior structure of Triton
Requirements
Objective Determine the J2 gravity field component range-rate accuracy in the range of 0.015 Is Triton mm/s and 0.1 mm/s at 60 sec integration time differentiated? Determine ocean induced magnetic field?
Does it have a Instruments subsurface ocean? X Ka Transponder (RSI) Magnetometer (FGM) Science Objectives & Requirements
2.2 To investigate Triton's atmospheric composition
Requirements
Observe a stellar occultation Objective with 0.01°/s stability within 1 sigma accuracy Observe a solar occultation Atmospheric with 0.1°/s stability within 2 sigma accuracy
composition Instruments
UV Imaging Spectrometer (UVIS) Science Objectives & Requirements
2.3 To investigate Triton's geological activity (N2 geysers)
Requirements
Image the surface Objective global spatial resolution of 100m local interests at 10m/pix resolution Characterise Triton's Surface Instruments Features Narrow Angle Camera (NAC), Wide Angle Camera (WAC) Science Objectives & Requirements
3. To improve our current understanding of the magnetosphere
Requirements
Measure the magnetic field vectors Objective +/- 16384nT/magnetic component, 0.2 nT resolution, |min value|: 0.1 nT Magnetospheric Configuration Instruments
Magnetometer (FGM) Science Objectives & Requirements
3. To improve our current understanding of the magnetosphere
Requirements
Characterize the plasma content in
Objective the magnetosphere and interplanetary medium Plasma Transport E: 1eV - 5 MeV Sources & Sinks in magnetosphere Instruments
Plasma Spectrometers, (HPS, MPS)
Langmuir Probe (LAP) Science Objectives & Requirements
3. To improve our current understanding of the magnetosphere
Requirements
Objective Measure the possible auroral radio emissions Insight on the radio emission generation, its sources and location Instruments
Radio & Plasma Wave experiment (RPW) Outline
● Science Case
● Objectives & Requirements
● Payload
● Mission trade study & design
● System design
● Ground Segment Imaging Instruments & Spectrometers
● Camera: ● Narrow angle camera (NAC) 350-1050 nm ● Wide angle camera (WAC) 350-1050 nm
● Spectrometer ● UV Imaging Spectrometer (50-320 nm) ● VIR Hyperspectral Imaging Spectrometer (0.4-5.2 µm) ● Composite IR Spectrometer (MID, FIR, 7-1000µm) Environmental instruments
● 2 Fluxgate magnetometers + 10m boom (MAG) ● Radio Plasma Wave Experiment (RPW) ● Extreme Low Frequency Radio (ELFR) ● Particle package (PP): ○ Electron Spectrometer (ELS) ○ Hot Plasma Spectrometer (HPS) ○ Medium Plasma Spectrometer (MPS) ○ Energetic-charged particle spectrometer (EPS) ○ Langmuir Probe (LAP) ● Dust Analyser (DA) Probe Instruments
● Probe measurements crucial for fulfillment of Neptune atmosphere science objectives. ○ Mass spectrometer (RTOF) ○ Very low frequency radio ○ Doppler wind experiment (DWE) ○ Electric field sensor ○ Accelerometer ○ Pressure & temperature sensor Outline
● Science Case
● Objectives & Requirements
● Payload
● Mission trade study & design
● System design
● Ground Segment Going to Neptune...
● Several trade-off options for transfer: ○ Orbit vs. flyby ○ Slow vs. fast (11, 13, 22 years) ○ Ariane vs. Soyuz ● Dry mass in orbit/flyby:
Flyby with Flyby with Orbiter with Orbiter with Time-of-flight Soyuz [kg] Ariane 5 [kg] Soyuz [kg] Ariane 5 [kg] [years]
483_ 1788_ 148_ 554_ 11_
1028_ 3798_ 543_ 2020_ 22_
679_ 2481_ 182_ 670_ 13_ Comparing the options
● Selection driver is fulfillment of science objectives. ● Payload mass at Neptune must be compared. ● Orbiter options have greater propulsion system dry mass. ● Payload masses at Neptune (excluding probe): Flyby with Flyby with Orbiter with Orbiter with Time-of-flight Soyuz [kg] Ariane 5 [kg] Soyuz [kg] Ariane 5 [kg] [years]
-16_ 86_ -45_ -48_ 11_
21_ 257_ -9_ 79_ 22_
-3_ 143_ -43_ -40_ 13_
● Soyuz transfer infeasible. ● Final trade-off: ○ Flyby in 13 years traded-off against orbiter in 22 years. Flyby vs orbiter in numbers
Payload mass [kg] FLYBY option ORBITER option
NAC 12
WAC 5.4
MAG (x2) + boom 23
CIRS 42
UVIS 2.6
PP 13.2
RPW 5.6
DA 6
ELFR 2.4
VIRHIS 20.4
Total 132 kg 80 kg
Target 140 kg 80 kg Flyby vs orbiter in numbers
Decision Weight Orbiter Flyby matrix
Neptune 10.0 8.4
Triton 9.3 4.6
Magnetosphere 0.0 3.0
Science 60% 100 % 76 %
Cost 7.0 10.0
Time-of-flight 5.0 10.0
Engineering 40% 60 % 100 % Global result 94 % 100 % Why a flyby?
● We can successfully fulfil our main science goals. ● We can achieve a more cost-efficient and faster mission than with an orbiter ● We have the chance to have a full, state-of-the-art instrument package onboard, as opposed to an orbiter. ● Flyby mitigates orbiter data rate bottleneck ● Allows for anchoring of ground-based observations Selected transfer
● 13.4 years VEEJN transfer selected. ● Launch date June 2028 on Ariane 5. ● Main characteristics: ○ 4.7 km/s excess velocity at Earth departure ○ 14.0 km/s excess velocity at Neptune arrival ● Maximum wet mass: 2939 kg ○ Includes margin to account for orbit insertion errors. ● Transfer Delta V budget: ○ 523 m/s DSM (including margin). ○ 25 m/s per transfer leg for course corrections Selected transfer
● In-transfer targets-of-opportunity ● Three-axis stabilization. JUICE Mission requirements
● Required: ○ Close Neptune flyby (2000 km altitude selected). ○ Close Triton flyby (500 km selected). ○ Observe probe for 90 min while entering atmosphere ○ Earth-pointing high gain antenna during close approach of Neptune/Triton for radio science ● Desired: ○ High inclination Neptune and Triton flyby Flyby trajectory summary
● Probe targeting and release ~3 months pre-Neptunian system.
● Minimum Neptune altitude: 2000 km
● Maximum Neptune relative velocity: 27 km/s
● Minimum Triton altitude: 500 km
● Trajectory deflection angle ~60 degrees
● Orbit inclination wrt Neptune: ~30 degrees
● Triton flyby after Neptune flyby Selected flyby trajectory Flyby trajectory geometry & illumination Outline
● Science Case
● Objectives & Requirements
● Payload
● Mission trade study & design
● System design
● Cost, Risk, Public Outreach Instrument planning and mounting
● Several options for observation planning/system layout: ○ Instrument single/multiple pointing direction ○ Instrument turntable mounting ○ Payload/subsystem backup modes for risk mitigation Spacecraft (Poseidon)
● Driving system requirements: ○ Concurrent tracking and Neptune observation ○ Concurrent probe data collection and Neptune observation ○ Flyby tracking accuracy ○ Flyby power requirement ○ Long mission duration ○ Neptunian environment Concurrent design environment
● Concurrent design environment set up for spacecraft subsystem sizing ○ Automatic linking of subsystem mass, power, etc. System layout Mass budget
● Mass budget set up from subsystem design ○ Conservative margins applied (system and subsystem) Power budget
● Power usage at different mission arcs considered ● Concentrated power usage during flyby. Power system trade-off
● Main power provided by ASRG: 34 kg, 160 W each ● Power system architecture trade off: ○ More batteries vs. additional ASRG
● ASRGs are complex, expensive ● Result: ○ 3 ASRGs (BOL: 640W; 500W after 16.4yr) for normal operations ○ Supplemented by Li-Ion batteries for flyby Communications & tracking
● 4.0 m High gain antenna, X and Ka band Earth communications in outer solar system ○ Also used for spacecraft shielding near Venus flyby ○ Data rate at Neptune: 12 kbit/s ○ 0.15 degrees pointing requirement ○ Collected science data to be sent back post-flyby ○ X and Ka transponder for spacecraft tracking (gravity science) using Doppler, VLBI ● Yagi antenna used for communications with probe in UHF ● S-band low gain antenna for near-Earth communications Thermal subsystem
● Hot constraint: Venus flyby ○ 12.5 m2 white antenna as a shield ○ 1.84 m2 silvered teflon radiators ● Cold constraint: Neptune's environment ○ MLI coating ○ Heat piping from the ASRGs Other subsystems
● Attitude control: ○ Momentum wheels ○ Thrusters for desaturation, coarse/fast maneuvers ○ Achieves required pointing stability of 0.01 deg/s for occultation observations ○ Achieves required pointing accuracy for observations ○ Navigation camera for fine-tuning and adjustment ● Command and data handling: ○ Completely redundant to avoid single point of failure ○ 480 Gb flash memory ○ 4 132 MHz processors ○ 2 15 MHz processors on the probe Trident (probe)
● Probe provides in-situ investigation of Neptune's atmosphere structure & composition ● Total mass: 346 kg (including margins) ● Entry velocity: 22.6 km/s ● Peak power: 382 W ○ Provided by redundant batteries ● Data rate: 25 kbps ○ UHF communication for overcoming high attenuation ● TPS mass fraction: 28.2% ● TPS material: fully dense carbon phenolic ● Unique possibility for entry trail observation *CDF Study Report PEP July 2010 Probe entry and descent
CDF Study Report PEP July 2010 Targets of Opportunity
● Asteroids ● Jupiter & Io ○ 13 Jupiter radii flyby distance ○ Possible JUICE synergy ● Centaurs ○ Current observations are few ● Kuiper-Belt Objects ○ Comparable post-mission options as New Horizons ○ Possible comparison to Triton observations ● Interplanetary dust/magnetic field Open and critical items
Open issues ● Gravity field measurement accuracy ● Suitability of instruments at targets-of-opportunity
Critical technology ● European ASRGs ● ELFR & UVIS (TRL 4) ● Flash memory Risk assessment
Failures Likelihood (1- Consequence Priority 5) score
Launch 1 5 12
ASRG 3 3 15
Thruster 1 4 9
Reaction 3 3 15 wheels
On board 1 3 5 computer
Navigation 2 4 14 camera
High gain 1 5 7 antenna
Turntable 3 3 15
Instruments 3 2 10 Risk mitigation
General protection for critical subsystems : ● ASRG: ● In cruise phase : 1 spare ASRG ● In flyby phase : 1 spare Li-Ion battery ● Spacecraft design to prevent overheating ● Spare reaction wheel ● Redundant onboard computer/memory ● 2 onboard scientific cameras for navigation ● Ground tracking for the navigation ● Turntable fixed emergency position
Launch delay: ● Longer time-of-flight (15 yr) at later launch date (2 yr) Descoping options
● No turntable ● Smaller antenna dish ● IRS-lite instead of IRS ● Cut down Particle Package Cost estimate Development phases
Outline
● Science Case
● Objectives & Requirements
● Payload
● Mission trade study & design
● System design
● Ground Segment Downlink to Earth - Tracking
● ESTRACK or successor (ESA's Deep Space Network)
● DSN (or successor)
● Square Kilometer Array - possibly tracking of atmospheric probe
● Memorandum of Understanding (MOU) agreements in place
between ESA and NASA's Deep Space Network Ground based probe observation campaign
SKA, DSN for tracking spacecraft
complementary observatories (VLT, KECK, ELT, TMT) for Neptune & Triton
Frequency = 500 MHz Array resolution = 0.025" Extension radius = 3000 km Spatial resolution = 600 Km^2 Data & Knowledge Handling
● Knowledge handover ● Ground support equipment (maintenance) ● Preparation of guidelines for data archiving (Planetary Science Archive) ● ESA data distribution policy ● Knowledge Management in Support of Spacecraft Operations (R. Mugellesi Dow, 2012) COSPAR Planetary Protection
Category I: Flyby by Venus and Jupiter
Category II*: Triton flyby (review necessary, possible upgrade to III) Category III: Europa flyby (at safe distance)
Conclusion: Category III sterilization measures
The mission therefore either needs to demonstrate that the likelihood of collision with Europa / Triton is <10–4, or undergo active bioburden reduction to meet the requirement that the probability of inadvertent contamination is <10–4 (dry heat or plasma sterilization)
Public Outreach & Education Conclusions and summary
● A mission to study Neptune as a reference for icy giants
● Flyby allows primary science objectives to be achieved
● Flyby is faster (13 vs 22 years) and allows all instruments to be
flown, traded off against shorter observation time
● Data collection volume in short flyby time drives system and
mission design Thank you
Team Blue Flyby vs orbiter in numbers Decision matrix Competing Missions
Voyager 2 Pep study? Neptune explorer study Juice what can we do better? Photochemistry (back-up slide)
Photodissociation occurs only in the upper atmosphere and the stratosphere at pressures P<0.3 bar. ● Photolysis breaks up NH3, CH4, H2S, H2O and PH3 ● Methane photochemistry (UV; lambda < 160 nm) => hydrocarbons (models: C3H8, C4H10) ● Model: Hydrocarbons + N2 => HCN Atmospheric Dynamics (back-up slide)
Wind velocity at different altitudes has never been measured in Neptune's atmosphere.
Comparing to the other giant planets, the measured zonal wind speeds on Neptune have big uncertainties caused by unusual big degree of seasonal variations.
Voyager 2 detected the Great Dark Spot (GDS), a smaller dark spot (DS2), and a small bright cloud (Scooter). Several years later, all three features had vanished, as imaged by the Hubble Space Telescope.
Convection: Based on the cloud activity and the large heat excess Neptune is supposed to be active in terms of convection. This is supported by the presence of CH3 above the tropopause. Atmospheric Profile - Neptune Atmospheric Profile - Triton Particle Package
Heritage: Cassini, JUICE
Measure particle energies, densities and temperatures in plasma, as well as composition (TOF-time of flight)
Electron Spectrometer (ELS): 1eV-20keV Hot Plasma Spectrometer (HPS): 1eV-30keV Medium Plasma Spectrometer (MPS): 1eV - 10 keV Langmuir Probe ELFR
Extremely long frequency Radio Emissions (0 - 10 Hz)
Heritage: eg. Huygens
Determining water content, derive fraction of volatiles in presolar cloud Magnetometer - (MAG)
MAG is mounted on a 10m AstroMast boom weighing in total 19kg.
2 FGM's are located at: 5m and 10m of the boom.
Min Absolute measurement: 0.1nT Resolution: 0.2nT UVIS
The UV Imaging Spectrometer will provide occultation measurements of Triton's and Neptune's atmosphere.
Spectral range * 50-110 nm * 110-230 nm * 230-320 nm
Numerous heritages (BepiColombo, Mars/Venus Express)
Requirements: The Sun should be at least 30° away from the field of view of the instrument. The maximum angular speed of the spacecraft during operations is 0.1 deg/s. VIRHIS
The visible and infrared hyperspectral imager will measures the atmosphere composition and dynamics. Additionally it measures thermal emission in NIR.
● Heritage: VIRTIS (ROSETTA)
- Spectral Range: 0.4 - 5.2 um - 408 x 640 px - FOV 3.4° & IFOV 125 urad => 62m/px @ 500km altitude. => 250m/px @ 2000km altitude NAC/WAC
Narrow Angle Camera (NAC), Wide Angle Camera (WAC)
* high resolution images (in spectral range 350-1050 nm) with few m/pix res * used to investigate Triton's surface, monitor Neptune's atmosphere dynamics * can also be used to investigate the rings, lesser moons & potential KBOs * the WAC provides broader pictures to get context for other measurements CIRS Composite Infrared Spectrometer
● Measures absorption and emission features in infrared - Determines the gas composition - Determines the thermal emission from atmospheres, rings and surfaces => (e.g. vertical profiles in atmospheres)
● CASSINI heritage
Fourier Transform Spectrometer (FAR-IR, MID-IR) - Spectral range (um): 17-1000, 7-17 - Spectral resolution (cm^-1): both 0.5-20 cm^-1 - Pixel FOV (mrad): 3.9, 0.237 RPW (Radio Plasma Wave Experiment)
1. Remote and in-situ measurements of radio and plasma wave phenomena ● Study of local wave phenomena and identification of characteristic frequencies of the local plasma ● Direction finding to determine source and location of radio emission ● Detection of lightning 2. Heritage of Cassini/RPWS(Radio Plasma Wave Science) 3. Frequency range: fraction of a Hz to 20-40 MHz for electric fields and 100 kHz for magnetic fields Radio Emissions (NKR)
Zarka, 1998
RSI Radio Science Instrument
● - Characterises the internal structure (gravity field) of Neptune and Triton with Doppler shift - Distance determination from Earth ● Heritage from JUICE ● - Consists of one Radio Science Transponder (RST) and an Ultra Stable Oscillator (USO) - Triple link with Earth in the bands: X/X, X/Ka, Ka/Ka
Note: - The measurements are taken place at the Earth ground station, so the High Gain Antenna must be pointing at Earth during measurements Mission Payload
Payload Instruments Probe
NAC, WAC (Juice heritage) RTOF (ROSINA heritage)
MAG*2 & boom (Cassini, THEMIS, Juice Heritage, Pressure sensor Kaguya-SELENE)
IRS (CASSINI, Tandem) Temperature sensor
Doppler Wind Experiment (DWE)
UV Imaging Spectrometer (Juice) Accelerometer
Particle package - Ion Neutral Mass Spectrometer Very low frequency radio (Cassini, JUICE)
RPW (Radio Plasma Wave Experiment) Electric field sensor
SUDA (SUrface Dust Analyser) Mass budget Power Budget