Post on 30-May-2018
transcript
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
2
– 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
3
• 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
4
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
5
• 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
Triton
Atmosphere – Surface pressure: 1.4–1.9 Pa – (1/70000 the surface pressure on Earth)
• Composition: nitrogen; methane traces.
7
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
9
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 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
14
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
Radioisotope Thermal Rocket engine
• Thermal energy from Pu-238 isotope heats gas • Heated gas expanded through nozzle • Two approaches:
16
• 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
17
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 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
24
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
25
Les BalkanyiJulie KleinhenzDavid ChatoStan GrisnikVikram ShyamIan DuxWaldy SjauwLaura Burke
Mike BurMike MartiniJames FittjeJohn GyekenyesiTony ColozzaPaul SchmitzJeff Woytach