Passively Activated Parachute for Satellite Deorbiting - MEng Project

Department of Mechanical Engineering
FACULTY OF ENGINEERING AND DESIGN
FINAL YEAR MEng PROJECT REPORT
A Passively Activated Parachute for Deorbiting Inoperative Satellites
Thomas Hale
Date of submission
Word count: 10525
[1]
“I certify that I have read and understood the entry in the Student Handbook for the Department of
Mechanical Engineering on Cheating and Plagiarism and that all material in this assignment is my
own work, except where I have indicated with appropriate references.”
Author’s signature:
Supervisor: James Scobie
Assessor: Gary Lock
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Abstract
Space debris is a growing concern in Low Earth Orbit (LEO), with the potential to pose a threat to all
active satellites and spacecraft. One of the key ways to mitigate this problem is to ensure objects in
LEO are deorbited, meaning they are removed from orbit at the end of their useful lifetimes. Due to
the low atmospheric drag on satellites in LEO, deorbiting can take upwards of 100 years naturally,
despite their lifetimes being much smaller due to the harsh space environment. As such, a reliable
way to deorbit satellites is required.
With large satellite constellations increasing each year, Liou et al. (2018) simulated that a post-
mission disposal reliability of 99.9% should be aimed at for reducing growth. In the years 2000-2016,
35.2% of small satellites failed during their operational lifetimes. With many more likely to fail during
the deorbit period, the satellite cannot be relied upon to conduct the disposal itself, necessitating
the use of an external device. Current drag sail simulations and experiments fail to demonstrate
passive stability, therefore requiring an active attitude control system for years post End-Of-Life
(EOL), to swiftly deorbit. Thrusters and electrodynamic tethers also require functional subsystems,
and therefore cannot reach the required reliability, meaning a novel device must be designed.
Various shapes and materials for a 3D, attitude-independent drag device are explored as part of this
study, simulated through CNES STELA and ESA DRAMA, to find the optimal configuration. The device
aims to enable deorbiting for tumbling, out of control satellites, while staying mass efficient. It will
also incorporate a backup timing mechanism to start deployment after a set period, removing the
reliance on as many subsystems as possible.
Based on the analysis, an open tetrahedron was found to be the optimal solution, deploying with
inflatable, rigidisable aluminium cylinders, allowing it to survive small debris impacts. CFRP or metal
booms were found to have a similar mass, but with a higher area density, potentially causing
catastrophic collisions if they impacted a satellite. A cool gas generator was included to inflate the
cylinders, which has been previously stored for a combined 7 years on the ground and in space
before correctly generating.
The device requires further testing to validate the reliability and feasibility for practical
implementation but offers a promising, implementable solution for reducing the collisional debris
growth, and solving one of the largest current issues in space.

Table of Contents
1. Introduction .................................................................................................................................... 4
1.1. Background ............................................................................................................................. 4
1.2. Aims and Objectives ................................................................................................................ 6
2. Literature Review ............................................................................................................................ 6
2.1. Concepts.................................................................................................................................. 6
2.1.1. Natural decay .................................................................................................................. 6
2.1.2. Onboard thrusters ........................................................................................................... 7
2.1.3. Tethers ............................................................................................................................ 8
2.1.4. Drag augmentation - Mass .............................................................................................. 8
2.1.5. Drag augmentation - Area ............................................................................................... 9
2.2. Current work ......................................................................................................................... 11
2.3. Summary ............................................................................................................................... 14
3. Computational Methods ............................................................................................................... 15
3.1. Deorbit Simulation ................................................................................................................ 15
3.2. Code ...................................................................................................................................... 15
4. Results, Analysis and Discussion ................................................................................................... 16
4.1. Concept Selection ................................................................................................................. 16
4.1.1. Non-Drag Augmentation ............................................................................................... 16
4.1.2. Drag Augmentation ....................................................................................................... 17
4.2. Concept Design ..................................................................................................................... 18
4.3. Deployment........................................................................................................................... 22
4.3.1. Booms ........................................................................................................................... 22
4.3.2. Timing methods and Activation .................................................................................... 24
4.3.3. Load analysis ................................................................................................................. 24
4.4. Sizing and Scope .................................................................................................................... 25
4.5. Finalised Design .................................................................................................................... 28
5. Conclusions ................................................................................................................................... 29
6. Future Work .................................................................................................................................. 30
7. References .................................................................................................................................... 31
8. Appendices .................................................................................................................................... 36

List of Abbreviations
LEO
Low Earth Orbit
MMOD
Micrometeorites and Orbital Debris
EOL
End-Of-Life
ADR
Active Debris Removal
IADC
Inter Agency Debris Committee
SRP
Solar Radiation Pressure
ECS
European Cooperation for Space Standardisation
ADCS
Attitude Determination and Control Systems
GOLD
Gossamer Orbit Lowering Device
SPOUA
South Pacific Ocean Uninhabited Area
ESA
European Space Agency
ATP
Area-Time Product
DAS
Debris Assessment Software
DRAMA
Debris Risk Assessment and Mitigation Analysis
STELA
Semi-Analytic Tool for End-of-Life Analysis
EMR
Energy to Mass Ratio
CuBe
Copper Beryllium
CGG
Cool Gas Generator
1. Introduction
1.1. Background
Rockets are becoming increasingly commercialised, with many private companies designing their
own to launch satellites into orbit. This has greatly driven the price down allowing more business
models to become profitable, and therefore bringing additional companies and universities into the
sector. In 1960, the price per kg to LEO was more than $100k but has been reduced to $1.5k per kg
with the newer SpaceX rockets [2].
2613 satellites were launched into orbit in 2022, compared to 221 launched in 2016, with the rate
only increasing [3]. The biggest growth has come from the large satellite internet constellations, such
as OneWeb and Starlink. Starlink already represents almost half of the active satellites with nearly
3900 currently working in orbit [4], and up to 42,000 planned [5].
While the US tracks every object in space larger than 10cm [6], so they can be avoided by active
satellites, Micrometeorites and orbital debris (MMOD) pieces smaller than this can easily impact,
potentially catastrophically. An average collision happens at a velocity of around 10kms-1 [7],
creating thousands of small pieces of debris, as a 1cm projectile is comparable to 7 kg of TNT [8]. The
USA, Russia, China, and India have also completed anti-satellite tests, purposefully causing collisions
to simulate how it would work in a military scenario, which contributes more than half of the large
debris in LEO [9].
As active satellites reach the end of their useful lifetimes and become uncontrollable, which can be a
matter of months [10], there is nothing to stop them colliding with any MMOD or even other
satellites. Two uncontrolled satellites have already collided, scattering many large debris pieces into
orbit [11] (Figure 1). As more collisions happen, more debris is ejected into orbit, which increases the
chances of further collisions. This phenomenon is called Kessler syndrome, where collisions creating
debris, exponentially cause further collisions and making various orbits unusable.

Figure 1. Monthly Number of Objects in Earth Orbit by Object Type (Tracked objects only) [12]
A NASA report predicts there is as much as 10,000 tons of debris currently in orbit, in as many as 100
million pieces bigger than 1mm In LEO [6]. This has led to predictions that the MMOD population is
already self-sustaining, with further launches speeding up the process and limiting spacecraft
lifetimes [13]. As such, a reliable way to deorbit satellites is needed.
For satellites already in orbit, Active Debris Removal (ADR) missions need to be carried out. These
missions will rendezvous with a tracked piece of debris and attach via a robotic arm, net, harpoon, or
one of another few novel solutions [14]. The satellite then moves the debris to a lower altitude and
deorbits it, either deorbiting itself in the process, or gaining altitude to rendezvous and deorbit
another debris piece. Astroscale and ClearSpace are in the design stages of their missions, with both
companies on course to remove actual debris from orbit by 2026 [15]. However, ADR is a very
expensive method to deorbit every satellite, as each large piece would require an individual satellite
as well as many human hours monitoring the operations.
Satellites orbits naturally decay due to the atmospheric drag in LEO, but can take more than a
thousand years depending on the satellites altitude as well as its mass and drag area. Many larger
satellites save propellant, for their thrusters, to speed up the deorbit at the end of their natural
lifetime, as they must meet the Inter Agency Debris Committee (IADC) guidelines of staying a
maximum of 25 years in orbit post EOL [16].
Thrusters require a functional satellite to work, and so cannot deorbit all satellites. A few satellites,
such as EO-1, designed and launched by NASA, have even used this fuel to lengthen the mission
rather than to deorbit, with that specific satellite only deorbiting in 2056 despite being
decommissioned in 2017 [17]. Therefore, just having the fuel onboard to deorbit is no guarantee of
it being used for that purpose. A more effective solution would be to develop a low weight, mass
producible, and easily-implementable deorbiting device, which would force compliance.