BravoSat: Optimizing the Delta-V Capability of a CubeSat Mission with Novel Plasma Propulsion Technology ISSC 2013 Motivation Problem CAT Engine Feasibility Strategies Conclusions Sara Spangelo, NASA JPL, Caltech Benjamin Longmier, University of Michigan Interplanetary Small Satellite Conference, June 2013
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Optimizing the Delta-V Capability of a CubeSat Mission with Novel
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BravoSat:
Optimizing the Delta-V Capability of a CubeSat Mission
:, NASA (satellite constellation in measuring the Aurora Borealis over North America. Each ground station has an all-sky imaging white-light auroral camera and a magnetometer. The ground stations' radial coverage is rendered at 540km.)
Image Credit: Allison Craddock
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Sara Spangelo, NASA JPL, Caltech
Benjamin Longmier, University of Michigan
Interplanetary Small Satellite Conference, June 2013
Magnetic Field lines
BravoSat Orbit
How Far Can CubeSats Go (Alone)?
• Can CubeSats go beyond Low Earth Orbit (LEO)?
• Is there a fundamental size, mass, power, cost limitation? No!
• BravoSat: CubeSat with CAT engine designed to escape Earth orbit
• Enabling factors:
1. Miniaturized thruster technology with high ∆V capabilities
2. Heritage and experience operating CubeSats in LEO
3. Intelligent use of mass/ volume/ energy!
Photo Credit: NASA Website
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ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Is the Sky the Limit? Dream versus Reality
Image Credit: CubeSat Team Websites, Survey: http://gs.engin.umich.edu/sat_survey/
Dream (Goal):
• Can we escape Earth orbit? How far can we go?
• Maximize altitude increase on a CubeSat….. [Not equal to maximizing ∆ V]
Reality (Constraints)
• Maximum engine power (thrust)
• Initial orbital configuration (LEO)
• CubeSat or small satellite:
• Physical (mass/ volume)
• Limited potential to collect/ store energy
• Lifetime- degradation of batteries, solar panels, radiation, etc.
We can escape Earth’s Sphere of Influence in < 1 year!
Parameter Units
Destination
Maximum
LEO GEO
Mean
Moon
Earth's
SOI
Closest Mars
Approach
Distance from
Earth km 2,000 35,700 384,000 925,000 56,000,000
∆V km/ sec 0.6 4.4 6.5 6.9 7.4
I2 Fuel days 32 194 259 269 284
Ga Fuel days 36 226 308 321 341
H20 Fuel days 202 1,369 1,933 2,026 2,171
Constant thrust at 10 Watts
Let’s review different fuels and destinations
Note time is proportional to power because mass flow rate is linear with power!
10
102
103
104
105
106
107
108
0
1
2
3
4
5
6
7
8
Distance from Earth (Altitude), km
Vel
oci
ty, km
/sec
Maximum
LEOGEO
Closest Mars
Approach
Moon
Orbit
Earth
SOI
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Three Strategies for Trajectory Design
Case
# Description Consider
Energy?
Consider
Magnetics?
Exploit
Perigee?
1 Constant thrust along
velocity vector
100W: No
10/20W: Yes
No No
2 Phase 1: Thrust when
α<30 Phase 2: Pulse
thrust every 200 minutes
Yes Somewhat No
3 Thrust at perigee along
velocity vector2
Yes Yes Yes
and also thrust at apogee if perigee threatens to
crash into the Earth
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ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
1 α: Angle between the velocity vector and thrust vector (aligned with Earth’s magnetic field for passively stabilized craft) 2 Assume perigee is roughly when α is small
1-3: Consider additional realistic constraints and exploit environmental factors
Case 1: Constant Thrust Along Velocity Vector
Magnetic Field lines
BravoSat Orbit
Exhaust Vector
Velocity Vector
Thrust Vector
Work through Rocket Equation for I2 fuel and CAT
*Not to scale
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BravoSat Orbit
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Magnetic Field lines
BravoSat Orbit
13
Case 1: Constant Thrust Along Velocity Vector
2.5 kg fuel, 2.5 kg dry mass Initial 700 km circular orbit
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Add specs for this example
Starting altitude
Escape Earth’s Sphere
of Influence (SOI)
requires ~2.5 kg
Earth’s Sphere of Influence (SOI)
Requires ~2.5 kg!
Starting in 700km circular polar orbit with 2.5 kg dry mass
Desirable Configuration for Thrusting to Exploiting Passive Magnetic Stabilization
Velocity Vector
Thrust Vector
BravoSat Orbit
Body Z axis
Velocity Vector
Exploiting CAT’s Magnetic Dipole
α
Body Z axis
Velocity Vector
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Include Sim specs in STK
Short, high-powered (100W) burns
Example: Thrust only when α1 < 40o
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Exploiting CAT’s Magnetic Dipole
Body Z axis
Velocity Vector
α
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Include Sim specs in STK
Challenge: Once orbit grows, must be smarter about thrust duration (energy, thermal)
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Exploiting CAT’s Magnetic Dipole
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Short, high-powered (100W) burns
Strategy:
1. Phase 1: Thrust for 10 minutes when velocity and thrust vectors aligned
2. Phase 2: Thrust for 10 minutes every 200 minutes (pulsing)
Rationale:
• Exploit passive magnetic stabilization in Phase 1
• Thrust at perigee, where thrust vector ~parallel to velocity vector
• Energetically possible in both phases (thrust <10 minutes at a time)
Case 2: Multi-Staged Approach
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ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Case 2: Multi-Staged Approach
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Phase 1: Thrust <10 mins when aligned
Phase 2: Thrust every 200 mins for 10 mins
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Results sampled once a day
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Initial Fuel
Mass
Time to run out of fuel Radius when out of fuel
2 kg 320 days 1.39 ·106 km
2.5 kg 389 days 4.95 ·106 km
Case 2: Multi-Staged Approach
You could also stop thrusting when achieve desired radius and use remaining fuel for later fun!
Starting in 700km circular polar orbit with 2.5 kg dry mass
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Total ∆V when ran
out of fuel
5.8 km/ sec
6.9 km/ sec
Case 3: Exploiting Perigee to Escape Earth!
Strategy:
1. Start in elliptical orbit (assume 500km x 1500km)
2. Thrust at perigee (100W, 10mins), when α small
3. Continue until escape Earth orbit, or run out of fuel/time
Rationale:
• Exploit passive magnetic stabilization
• Energetically feasible (thrust once per orbit for 10 mins)
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ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Escaping with 1 kg fuel!
Case 3: Exploiting Perigee to Escape Earth!
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Possible if apogee is between L1 and L5 or between L3 and L4
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Interesting variations due to Earth-Moon interactions until escapes!
Case 3: Exploiting Perigee to Escape Earth!
Note results are sampled once a day
Case 3: Exploiting Perigee to Escape Earth!
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Starting in 500km x 1500km orbit with 2.5 kg dry mass
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Magnetic field still high at perigee
So can use passive stabilization
Interesting interactions with the Moon!
Case 3: Exploiting Perigee to Escape Earth!
Note results are sampled once a day
Something about magnet
Strength!!!
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Starting in 500km x 1500km orbit with 2.5 kg dry mass
ISSC 2013
Motivation
Problem
CAT Engine
Feasibility
Strategies
Conclusions
Consider 3 Different Approaches: Summary
# Description Power Fuel to
Escape
Time to
Escape
Challenges
1 Constant thrust
along velocity vector
10 W Constantly 2.5 kg 269 days Require attitude control
20 W Constantly 135 days
2 Phase 1: Thrust
when α1<30
Phase 2: Pulse thrust
every 200 minutes
100 W/
>1,000 times
2 kg 320 days Require attitude control
High number of battery
cycles
3 Thrust at perigee
along velocity
vector2
100 W/
~700 times
~1 kg < 3 years Require initial elliptical
orbit
Require (fine) active
attitude control
and also thrust at apogee if perigee threatens to
crash into the Earth
Disclaimer: These are not optimized, but rather representative results!
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1 α: Angle between the velocity vector and thrust vector (aligned with Earth’s magnetic field for passively stabilized craft) 2 Assume perigee is roughly when α is small
Best-case results assuming firing with 2.5 kg dry mass