Geoffrey A. Landis 1

A Hopper for Exploring Neptune's moon Triton

Geoffrey A. LandisSteven R. Oleson

and the COMPASS concurrent engineering design team

NASA John Glenn Research CenterCleveland, OH

15th NASA Small Bodies Assessment Group (SBAG) meetingJune 28–30, 2016�

Johns Hopkins University Applied Physics Laboratory, Laurel, MD

Geoffrey A. Landis

Why Triton?

•  Visited once •  by the Voyager 2 fly-by in 1989

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–  One of the least-known places in the solar system

– … but one of the most interesting

Whole-disk color view of Triton from Voyager-2 approach

Geoffrey A. Landis

Triton

•  Visited once •  by the Voyager 2 fly-by in 1989

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•  A big moon –  1353 km across – … bigger than Pluto

Triton photomosaic from Voyager-2 images

–  One of the least-known places in the solar system

– … but one of the most interesting

•  And in a retrograde orbit

Geoffrey A. Landis

Triton Orbit

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Orbit:Retrograde orbit around NeptuneSemi-major axis: 354759 km

Eccentricity: 0.000016Orbital period: 5.877 daysInclination 156.9° (to Neptune's equator)

(= -23°)

Geoffrey A. Landis

Triton •  Visited once •  by the Voyager 2 fly-by in 1989

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•  A big moon –  1353 km across –  … bigger than Pluto

–  One of the least-known places in the solar system

– … but one of the most interesting

•  in a retrograde orbit

•  …and it’s pink

Whole-disk color view of Triton from Voyager-2 approach

•  That’s not a moon… it’s a captured Kuiper Belt Object!

Whole-disk color view of Pluto from New Horizons approach

Geoffrey A. Landis

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Triton photomosaic from Voyager 2

Geoffrey A. Landis

Triton

Atmosphere –  Surface pressure: 1.4–1.9 Pa –  (1/70000 the surface pressure on Earth)

•  Composition: nitrogen; methane traces.

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Geoffrey A. Landis Geysers and dust plumes on south pole

Geoffrey A. Landis

Why Triton?

•  Largest and closest of the Kuiper Belt Objects –  Pluto was exciting: Triton is similar, but bigger –  A whole class of worlds in our solar system which we are only

beginning to learn about –  Tholins: organic compounds characteristic of KBOs that may be

precursor compounds of life –  Easiest KBO to reach

•  Interesting geology –  Cantaloupe terrain –  Geysers –  Winds –  And many more science targets

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Geoffrey A. Landis

What’s on the Surface?

Mostly Nitrogen, plus CO, CO2, CH4

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Geoffrey A. Landis

Triton Project

•  Land on Triton –  First ever mission to land (or even

orbit!) a Kuiper Belt Object •  Mobility on Triton

–  Many targets of interest on Triton: need long-distance mobility to sample them all

•  Communications Relay in Neptune Orbit –  As a bonus, we will drop probes into

Neptune’s atmosphere and serve as a long-term platform for observing Neptune, the outermost of the giant planets--

Geoffrey A. Landis

Triton hopper visualization

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Geoffrey A. Landis

Triton Hopper some top level trade studies

•  Getting to Triton –  Technologies include chemical, solar electric

propulsion, nuclear electric propulsion –  Trajectory includes possible gravity assists –  Use aerobraking, aerocapture

•  Don’t want to take many decades to get there!

•  Triton Propellant Acquisition –  Acquire from atmosphere –  Acquire from surface ices

•  Engine –  Radioisotope provides thermal energy –  Store energy and transfer energy to propellant

•  Store energy in the propellant (heat the gas) •  Store thermal energy separately from the

propellant (“thermal capacitor”) •  Store energy in form of electrical energy

Geoffrey A. Landis

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Triton Hopper Delivery Trades

Chemical Capture

Solar Electric Propulsion/Chemical Capture

Solar Electric Propulsion/Aerocapture

Nuclear Electric Propulsion

Trip Time to Triton

~18 yrs ~ 15 yrs ~ 12 yrs ~ 17 yrs

Triton ∆V ~ 4 km/s ~ 3 km/s ~ 3 km/s ~ 1.2 km/s

Selection Pros

Customer for SLS?

Only requires new SEP stage

Trip Time excellent, Technologies being developed

Smallest Hopper landing stage ~

Selection Cons

Trip Time Landing stage ~ 3X mass of Hopper

Landing stage ~ 3X mass of Hopper

NEP not currently in development

Geoffrey A. Landis

Propellant Gathering Trades

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Geoffrey A. Landis

Radioisotope Thermal Rocket engine

•  Thermal energy from Pu-238 isotope heats gas •  Heated gas expanded through nozzle •  Two approaches:

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•  store thermal energy in the gas

•  warm, pressurized gas stored in insulated tank

•  "warm gas thruster"•  Lower Isp•  Simpler design- uses

waste heat from ASRG

•  store thermal energy in a separate thermal mass or phase-change material

•  gas is stored cold •  Higher chamber

temperature•  higher Isp, smaller tank•  more complex design

First approach chosen for point designSecond approach developed in parallel analysis

Geoffrey A. Landis

Specific impulse from warm gas thruster

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30.00$

35.00$

40.00$

45.00$

50.00$

55.00$

60.00$

65.00$

70.00$

0.00$ 0.10$ 0.20$ 0.30$ 0.40$ 0.50$ 0.60$ 0.70$ 0.80$ 0.90$ 1.00$

Isp$(sec)$

Propellant$Remaining$Frac5on$(n/d)$$$$[=$prop$remain$/$prop$load]$

CGR$N2$Model:$$Isp$vs$Popellant$Remaining$Frac5on$

Ini0al$Tank$Pressure$=$3,500$psia$

Ini0al$Tank$Pressure$=$2,000$psia$Liquefied$N2$B$not$usable$

$$$$$$$$

specific impulse decreases as gas exhausts due to Joule-Thomson cooling

Geoffrey A. Landis

Triton Hopper – Baseline Hop Summary

Sequence of events for each Hop –  Vertical takeoff followed by a pitch-over –  Ballistic coast –  Soft landing

Operational Hop SummaryFinal: acc= 0.11 (Earth) gPeak Alt= 1.3 km, Ballistic time= 118 secTotal time= 142 sec, Prop used= 122.5 kg

Heat Reservoir Rocket for Triton Hopper

HeatedBlock

InletTemperature

T=900⁰C

OutletTemperature=BlockTemperature

Nozzle

N2

schema>c

mul>plepassagesthroughheatedblock(notshown)

60

80

100

120

140

160

180

0 5 10 15 20 25 30

Isp(s)

MassofNitrogen(kg)

AverageIspvsTotalMassofNitrogen

Lithium LithiumFluoride Beryllium Copper Aluminum

Systems and subsystems Subsystem Components:!Communications!

GN&C!C&DH!

Science!

Thermal!

ASRG!Power Electronics!

Propellant Tank!

Structures!

Geoffrey A. Landis

Triton Hopper!Subsystem Components:

Communications

GN&C

C&DH

Science

Thermal

ASRG

Power Electronics

Propellant Tank

Structures

Geoffrey A. Landis

Triton Hopper Point Design Mass Summary

26% Propellant load

Geoffrey A. Landis

Triton Hopper Propellant Gathering

Radioisotope thermal hopper design for Triton: refueling allows multiple flightsSame principles could be used for other icy bodies:•  Jupiter moons-- Europa, Ganymede, Callisto•  Saturn moons– Enceledus, Tethys, etc•  Mars•  Other KBOs

Geoffrey A. Landis

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Point Design: 360 kg/110W Hopper can gather N2 and hop 5 km,

60 times in two years (300 km)

Summary and Next Steps Triton is the most readily accessible Kuiper Belt Object in our solar system!

We want to hop from pole to equator ~ 2000 km in 2 year Phase-1 point design from COMPASS ream provides a starting point for analysis Options to improve performance

Geoffrey A. Landis

Team

•  Sponsor: NASA Innovative Advanced Concepts (NIAC) Program •  Primary Investigators: Steve Oleson &Geoffery Landis •  Science Advisor: Ralph Lorenz (JHU/APL) •  Concept Design Integration Lead: Ian Dux •  Team members

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Les BalkanyiJulie KleinhenzDavid ChatoStan GrisnikVikram ShyamIan DuxWaldy SjauwLaura Burke

Mike BurMike MartiniJames FittjeJohn GyekenyesiTony ColozzaPaul SchmitzJeff Woytach