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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

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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