A Comparison of Nuclear Thermal to Nuclear Electric Propulsion for Interplanetary Missions Mike...
-
date post
21-Dec-2015 -
Category
Documents
-
view
220 -
download
1
Transcript of A Comparison of Nuclear Thermal to Nuclear Electric Propulsion for Interplanetary Missions Mike...
A Comparison of Nuclear Thermal to Nuclear Electric Propulsion for
Interplanetary Missions
Mike Osenar
Mentor: LtCol Lawrence
Overview
Introduction Objective Establish parameters NTR Design NEP Design Discussion and Conclusion
Introduction
NASA is developing Nuclear Electric Propulsion (NEP) systems for Project Prometheus, a series of interplanetary missions
What happened to Nuclear Thermal Rocket (NTR) systems? Should NASA only invest in NEP systems?
Objectives
Prove the feasibility of different nuclear propulsion systems for interplanetary missions which fit in a single launch vehicle
Compare NTR and NEP system designs for given missions
Method: take a set of inputs, use a series of calculations and SPAD process along with reasonable design assumptions to design a spacecraft to reach a given ΔV
Establish Parameters
Establish ΔV’s and flight times for both NEP and NTR systems to Jupiter and Pluto
Determine launch vehicle payload restrictions Obtain design points – inert mass fractions
based on thruster specific impulses
Establish Parameters
NTR ΔV (km/sec)
NEP ΔV (km/sec)
NTR TOF (years)
NEP TOF (years)
Jupiter 3.83 7.66 4.13 4.13
Pluto 6.70 13.40 19.00 19.00
•NEP ΔV’s and flight times based on AIAA 2002-4729 – low thrust gravity assist trajectories
•NTR data derived from NEP data
Establish Parameters
Relationship between NEP ΔV/TOF and NTR ΔV/TOF
Table shows that NTR has same TOF for 50% of the ΔV
NTR numbers based on AIAA 1992-3778
Mission ΔV (km/s) TOF (yrs)
Pluto NEP 13.4 19
Pluto NTR 6.52 16
Pluto NTR 12.9 10
Establish Parameters
Ariane 5 Payload Specifications
Mass to orbit (kg) 18000
Height (m) 12.5
Diameter (m) 4.5
Establish Parameters
Dumbkopff Chart - Jupiter NTR 1000 kg
0
18000
0 500 1000 1500Isp (sec)
Init
ial M
as
s (
kg
)
0.1 0.2
0.3 0.4
0.5 0.6
0.7 0.8
0.9
Dumbkopff Chart - Jupiter NEP 1000 kg
0
18000
0 1000 2000 3000 4000 5000Isp (sec)
Init
ial M
as
s (
kg
)
0.1 0.2
0.3 0.4
0.5 0.6
0.7 0.8
0.9
Dumbkopff Chart - Pluto NTR 500 kg
0
18000
0 500 1000 1500Isp (sec)
Init
ial M
as
s (
kg
)
0.1 0.2
0.3 0.4
0.5 0.6
0.7 0.8
0.9
Dumbkopff Chart - Pluto NEP 500 kg
0
18000
0 1000 2000 3000 4000 5000Isp (sec)
Init
ial M
as
s (
kg
)0.1 0.2
0.3 0.4
0.5 0.6
0.7 0.8
0.9
Establish Parameters
Design points established from Dumbkopff charts
Design Isp (sec) ΔV (km/sec) f-inert
Jupiter NTR 1000 3.83 0.65
Jupiter NEP (Ion) 3500 7.66 0.80
Jupiter NEP (Hall) 1500 7.66 0.60
Pluto NTR 1000 6.70 0.50
Pluto NEP (Ion) 3500 13.40 0.65
Pluto NEP (Hall) 1500 13.40 0.32
NTR Design
Size system so that it meets 3 specifications
1. Under max payload mass
2. Fits in payload fairing
3. Reaches required ΔV
NTR Design
Inputs from Dumbkopff: finert, ΔVAssumptions
Po = 7 MPa
Isp = 1000 s – hydrogen
Tc = 3200 KT/W = .3 – experimented, balance between
high thrust short burn time and low reactor mass (low power)
NTR Design
Equations for basic parameters
0
0
1
11
gI
V
inert
inert
gI
V
pay
prop
sp
sp
ef
fem
mimW
FF
0gI
Fm
sp
715417.5018061.0 TmP
NTR Design
Subsystem Sizing (note: volume constraint height)
Payload
1000 kg to Jupiter, 500 to Pluto
based on densities of actual space mission
sized as 2 m tall cylinder
Tank
biggest part – hydrogen has low densitynkta
totbk g
Vpm
.0tan
NTR Design
Turbo Pump Feed SystemNuclear Reactor
Radiation Shieldstandard SPAD design – 18 cm Be, 5 cm W, 5 cm LiH2
3549512 )10(1703.1)10(946.8)10(655.2 corecorecorecore PPPR 34.3132955.2)10(427.7 23
corecore PP
9883.171427.0)10(027.4 25 corecorecore PPH
NTR Design
NozzleColumbium, designed to be ideally expanded in space (ε=100)
MiscellaneousAvionicsReactor containment vesselAttitude thrustersStructural mass
NTR Design
Achievable ΔV verified with Rocket Equation
Vehicle height determined by stacking parts according to Figure
f
isp m
mgIV ln0
Pump
Shield
Reactor
Nozzle
Propellant Tank
Payload
NTR Design
Final Results of NTR Design
ΔV (km/s) f-inert
Initial Mass (kg)
Height (m)
Power (MWe)
TOF (years)
Jupiter NTR 4.191 0.6094 9100.41 7.23 281.23 4.13
Pluto NTR 8.103 0.4182 14853.83 12.29 281.23 19.00
NEP Design
Size system so that it meets 2 specifications1. Under max payload mass2. Reaches required ΔV
No size requirement – analysis showed that NEP systems would violate mass constraints before volume – no low-density hydrogen propellant
NEP Design
Power Source Nuclear Reactors (P>6 kWe)
– Critical reactors designed as small as 6 kWe
Radioisotope Thermoelectric Generators (RTG) (P<6 kWe)
Solar?
NEP Design
Solar Power proportional to inverse square of distance from sun
to receive power equal to 1 m2 solar panel in earth orbit, would need 27 m2 panel at Jupiter and 1562 m2 panel at Pluto
does not factor in degradation – significant for long lifetimes
engineering, GNC concerns with huge solar array
mass too much
NEP Design
Thrusters based on actual designed thrusters from SPAD
Baselines used: T6, XIPS-25, RIT-XT Design allowed thrusters to be clustered in
groups of up to 3 – proven to work, increases force and power appropriately
NEP Design
Use NTR equations for propellant mass, thrust, mass flow and power
NEP equations:
0gIV spe
2
21
eVmP
NEP Design
Subsystem Design Power system Propellant tank Thruster mass Power conditioning mass Other mass (structural, feed systems,
avionics, etc.)
NEP Design
NEP Design ResultsΔV
(km/s) f-inertInitial Mass
(kg)TOF
(years)Power (kWe)
# of thrusters
Jupiter (Kaufman) 15.860 0.5266 4068.58 4.13 10.258 2
Jupiter (MESC) 14.051 0.5685 3673.06 4.13 8.425 2
Jupiter (RIT) 15.433 0.5622 3768.34 4.13 9.555 2
Jupiter (Hall) 12.242 0.3351 6645.87 4.18 6.180 3
Pluto (Kaufman) 42.725 0.2656 9495.62 18.79 10.258 2
Pluto (MESC) 41.420 0.2849 8079.27 19.40 8.425 2
Pluto (RIT) 44.626 0.2826 8352.61 19.19 9.555 2
Pluto (Hall) 13.771 0.3433 6719 19.02 1.471 1
Discussion and Conclusion
Overall, ΔV’s were low – real science mission would need higher ΔV to capture orbit of planet, maneuver
Accurate data on EP trajectories was desired over ΔV’s for realistic missions
Discussion and Conclusion
NTR Design Almost failed Pluto design – tank volume High thrust, impulsive burn more reliable –
operates for short time Much less efficient then NEP Other applications? launch vehicle, human
Mars exploration
Discussion and Conclusion
NEP Design Low thrust, long trip times Lifetime analysis – electric thrusters tested to
3.5 years – less than Jupiter TOF Space Nuclear reactors require extensive
testing
Discussion and Conclusion
Testing – extensive testing needed for either system – facilities, money needed to test for operational lifetime
Safety – perennial concern with nuclear systems, real hazards to be considered
Radiological hazard – higher with NEP (low power but long burn time), must be addressed for either system
Discussion and Conclusion
NASA probably right to go with NEP for interplanetary missions
Much stands between now and operational nuclear propulsion system
Much to be gained from nuclear propulsion technology