Propulsion Options For Missions To Nearearth Objects

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Propulsion Options For Missions To Near-Earth
Objects
P.M. Sforza University of Florida
Magellans view of Venus, Courtesy
NASA/JPL-Caltech
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Gaspra is an irregular body with dimensions about
19 x 12 x 11 kilometers (12 x 7.5 x 7 miles).
Photo courtesy NASA

• Earth-crossing asteroids (ECA) and comets (ECC)
  are NEOs
• Trajectories are capable of intersecting Earths
  capture cross-section
• There are more than 180 known ECAs
• Distribution 10 with dgt5km, 103 with dgt1km, and
  105 with dgt100m

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Meteor Crater in Arizona
1.2km
. Between 20,000 to 50,000 years ago, a small
asteroid about 80 feet in diameter impacted the
Earth and formed the crater.
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Asteroid 1998 KY26 was discovered in 1998 as it
passed 800,000 kilometers (half a million miles)
from Earth
1998 KY26, about the diameter of a baseball
diamond, may contain about a million gallons of
water, an oasis for future space explorers. Its
optical and radar properties suggest a
composition which contains complex organic
compounds that have been shown to have nutrient
value. These could be used as soil to grow food
for future human outposts.
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Classification of missions
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Spacecraft mass breakdown
Initial mass payload mass propellant
mass propulsion system mass
structural mass
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Rocket thrust, impulse, and power
Thrust (N)
Impulse (s)
Power in exhaust (kW)
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Specific impulse and specific power
Propulsion system mass (kg) Specific mass
(kg/kW) conversion efficiency
prime power (kW)
Power in exhaust (kW) Jet conversion
efficiency
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Thrust to weight ratio
The propulsion system is characterized by its
thrust to weight ratio
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Mass ratios and rocket burn time
O(1) since mpl, ms ltlt1
Then the rocket burn time is
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Propulsion systems characteristics
Type II Nuclear electric
Solar electric
Type I Gas core fission Solid core
fission Chemical
F/W010 1 10-1 10-2
10-3
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Type I NERVA Nuclear Engine for Rocket Vehicle
Application (NTP)
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NTP rocket configuration
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Type II Prometheus Nuclear Electric Propulsion
(NEP)
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Electrostatic propulsion system Ion Rocket
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Xenon Ion rocket for Deep Space 1
Solar electric I4000s tp 678 days P2.1kW
Nuclear electric I6000s Under test for Prometheus
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Mission trajectories Type I propulsion
flyby
intercept point
rendezvous
return
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Range-time relations for type I and II propulsion
systems (free space)
Type I propulsion
Type II propulsion
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Range-time graph for flyby mission
NI 5000 2000 1000 (Type I)
Jupiter
a/N0.1 1 10 (Type II)
Project NEAR
V10km/s
Mars
NEOs approaching Earth
V50km/s
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Range-time graph for return mission
NI 5000 2000 1000 (Type I)
Jupiter
a/N0.1 1 10 (Type II)
V10km/s
Mars
V50km/s
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Range of mission suitability
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Velocity change for Type I systems
N identical stages
kstructure mass/propellant mass
For kms/mp ltlt1 and mpsltlt1
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Type I Velocity boost
Gas core (NTP)
Solid core (NTP)
LH2-LOX (Chemical)
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Type I LEO payload possibilities
mpl10-N for stage mass ratio Mi1/Mi0.1
Spacecraft mass 20Mg Launch vehicle SSTO or
Titan IV N1 Mpl2000kg N2 Mpl200kg N3 Mpl
20kg
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Type I Range to Intercept
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Type I Range to rendezvous
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Conclusions

• Nuclear propulsion is best suited to NEO missions
  in terms of flight time
• NTP is best for mitigation and rendezvous
  missions up to 1 or 2 AU from Earth
• NEP is best for return missions beyond about
  0.5AU
• NTP has been demonstrated and can be applied
• NEP development should be brought to the
  demonstration stage

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Rendezvous in 4 years Flyby in
2.8 years
Courtesy NASA
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NTP Experience

• 20 reactors were designed, built, and tested from
  1953-1973 (1.4B). The Demonstrated performance
  included
• Power (MWt) 1100 (NRX) to 4100 (Phoebus-2A
• Thrust (klb) 55 (NRX) to 210 Phoebus-2A
• Fuel temperature (K) 2750 (PEWEE)
• Specific Impulse (s) 850 (vac, PEWEE)
• Burn endurance 1 to 2 hours
• Start/Stop cycles 28 automatic cycles (XE)

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The KIWI experimental nuclear reactor
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The KIWI experimental nuclear reactor
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Candidate NTP propellants