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Electric Propulsion in Small Satellites
Ulisses Pereira Sampaio
05/09/2019
1º Workshop Brasileiro em Propulsão Elétrica Espacial
Pesquisa e Aplicação
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Summary
Motivation
Electric vs Chemical
Case Studies
State of the Art
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Motivation
This information is property of Visiona and cannot be used or reproduced without written permission.
Motivation
“So there’s no question in my mind, whatsoever, that all
transport with the ironic exception of rockets, will go
fully electric. Everything, planes, trains, automobiles…”
-Elon Musk* Tesla and SpaceX co-founder
What about satellites?
*https://singjupost.com/elon-musk-interview-2017-the-future-the-world-technology-transcript/?pdf=5870&singlepage=1
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Motivation
On one hand, spacecraft are becoming smaller, cheaper and more numerous
In addition, big constellations are coming…
“In 2017 62% of all satellite launches fell under the “nanosat” category (...)
Forecasts show that the balance will shift even more towards small spacecraft in the near future.”
-NASA, State of the Art of SmallSpacecraft Technology
**
*
*https://sst-soa.arc.nasa.gov/10-integration-launch-and-deployment**https://www.nanosats.eu/
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Motivation
On the other, Rocket launches are still very expensive
Single-spacecraft launches are a “luxury”
Big rockets are more “cost-efficient”.
Falcon 9 FT22800 kg to LEOUS$ 50M/launch*
US$ 2.2K / 1kg
Pegasus443 kg to LEO
US$ 40M/launch*
US$ 90.3K / 1kg
Electron225 kg to LEO
US$ 6M/launch*
US$ 26.7K / 1kg
( And Rockets cannot “go electric” )*https://en.wikipedia.org/wiki/Comparison_of_orbital_launch_systems
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Motivation
Today’s dilemma:
“Big-rockets vs large number of small satellites”
For large constellations, launch several satellites together
For others, a cost-effective solution is Ridesharing:
“
However, this implies that precise orbital injection is not feasible for all:
Depending on launch, spacecraft might require large orbital maneuver capabilities ( )
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Electric vs Chemical
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Electric vs Chemical All propulsion work by ejecting mass ( ) to produce change in
velocity ( )*:
Efficiency parametrized by Specific Impulse ( ). The amount of propellant ( ) needed for given
The higher the , less mass is needed to produce given amount of .
*https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
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Electric vs Chemical Propulsion is mainly characterized by thrust (N) and 𝒔𝒑 (s)
High thrust is required for fast maneuvers or overcome large forces (e.g. Launch)
High 𝒔𝒑 means large performance in terms maneuver capability versus mass
Electric propulsion tends to have low thrust, and large 𝒔𝒑 and consume lots of power.
*
*https://sst-soa.arc.nasa.gov/04-propulsion
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Electric vs Chemical
Case scenario:
Perform 180deg plane phasing of two spacecraft launched together
Strategy:
1. Increase altitude of the first and decrease altitude of second.
2. Let planes drift due to difference in orbital perturbations (J2).
3. Once desired phasing is achieved, bring both to initial altitude again.
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Electric vs Chemical
Assumptions:
a. Circular orbits
b. Start in 𝑎 = 7078.14/ 𝑘𝑚 (750km altitude); 𝑖 = 25 𝑑𝑒𝑔; 𝑒 ≈ 0
c. Simplified Δ𝑉 computation: both satellites spend Δ𝑣/2 in step 1 and Δ𝑣/2 in step 3.
d. Disregard drag
e. 100kg of dry mass
J2 perturbation:
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Electric vs Chemical
Electric: vs Chemical:
2% of S/C dry mass
20% of S/Cdry mass
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Electric vs Chemical
In addition to having high efficiency, electric propulsion has several additional advantages.
low-thrust enable several technologies to produce low impulse bits, making then suitable for attitude control
In addition, low-thrust makes it suitable for very fine orbital maneuvering
Suitable automated orbital station keeping allowing maintenance of very small windows
Thrusters can often be accommodated in very small form factors.
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Case Studies
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Case Studies
GOCE• Operated at 250km altitude, experiencing high drag decay forces
• Used Xenon Ion Thruster with 40kg tank ( of total dry mass)
• Perform closed-loop low-thrust orbital corrections to automatically compensate atmospheric drag.
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Case Studies
SpaceX’s Starlink*
Thousands of satellites to be launched.
Compact design required for launch
optimization
Krypton Ion thrusters for orbit acquisition,
maintenance and de-orbitCan autonomously perform maneuvers for collision avoidance using DoD inputs
*https://www.starlink.com/
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Case Studies
NanoFEEP*• 26th February: First activation of electric propulsion system on a
1U CubeSat
• Thrusters fit inside the rails of CubeSat structure
• Mission to test attitude and orbit control capabilities
*https://digitalcommons.usu.edu/smallsat/2019/all2019/52/
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Case Studies
BRICSat-P*: • 1.5U launched May 20, 2015
• µCAT system (Vacuum Arc Thrusters):
Capability to perform Attitude control (detumbling)
System mass of 200g
𝚫𝐕 of 300m/s for a 4kg spacecraft (𝑰𝒔𝒑 between 2000-3000s)
*https://directory.eoportal.org/web/eoportal/satellite-missions/b/bricsat-p
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State of The Artfor Small Satellites
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State of the Art
Electric Propulsion Technologies for Small Satellites from NASA small satellite state of the art Report:*
*https://sst-soa.arc.nasa.gov/04-propulsion
Type How it works Thrust SpecificImpulse
TRL for smallsats
Pulsed Plasma and Vacuum Arc Thrusters
Pulsed Electric arc vaporizes solid propellant and
accelerates resulting plasma
1 – 1300 μN500 – 3000 7
Electrospray Propulsion
Extraction and acceleration of ions from propellant w/
negligible vapor pressure
10 – 120 μN500 – 5000 7
Hall Effect Thrusters
Electric/magneticfields accelerate ions
in plasma (Hall effect)
10 – 50 mN1000 – 2000 7
Ion EnginesElectric field
accelerates ionized propellant
10 – 50 mN 1000 – 3500 7