CONFERENCE PRESENTATION - Design and Stability Analysis of a De-Orbiting System for Small Sats

Preliminary design and stability analysis of a de-orbiting system for CubeSats Guerric de Crombrugghe & Laurent Michiels Promoters: Pr. P. Chatelain (EPL) & Pr. Th. Magin (VKI) Supervisor: C. Asma (VKI) Ecole Polytechnique de Louvain, UCLouvain

January 29, 2012

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PART I: INTRODUCTION PART II: OBJECTIVES PART III: PROJECT STRATEGY PART IV: APPLICATION PART V: CONCLUSION AND PERSPECTIVES

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PART I: INTRODUCTION

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Origin of the idea: Two major concerns (1/3)

1. Atmospheric re-entry • Key for space exploration • human spaceflight • robotic exploration on Mars, Venus, and even Titan • Validation tools • costly • extended development timeline

2. Debris mitigation

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Origin of the idea: Two major concerns (2/3)

1. Atmospheric re-entry 2. Debris mitigation • Unexpected collisions between

satellites • Guidelines: on orbit

the mission’s end

25 years after

• difficult to respect • especially for small satellites

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Origin of the idea: Two major concerns (3/3)

1. Atmospheric re-entry

2. Debris mitigation

Ă‘ Need for CubeSat re-entry vehicle

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Opportunity: QB50 (1/2)

Mission • Initiated by the von Karman

Institute for Fluid Dynamics • Dedicated to in-situ exploration of

the lower thermosphere • Network of over fifty CubeSats • Some of them will experience a

controlled re-entry

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Opportunity: QB50 (2/2)

Breakthrough • QB50 opens a new type of

missions: very low Earth orbit • Allows for affordable in-orbit demonstration • New environment need for innovative stability and de-orbiting system

Credits: G. Bailet

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PART II: OBJECTIVES

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Objectives No spacecraft with such reduced dimension has ever performed a controlled re-entry.

The challenges • Communication: no recovery • De-orbiting: short timescale to avoid passing over the poles • Thermal loads: keeping the electronics below 70 C • Stability: heat shield facing the flow

Ñ satellite’s trajectory Earth

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Objectives No spacecraft with such reduced dimension has ever performed a controlled re-entry.

The challenges • Communication: no recovery • De-orbiting: short timescale to avoid passing over the poles • Thermal loads: keeping the electronics below 70 C • Stability: heat shield facing the flow

Ñ satellite’s trajectory Earth

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PART III: PROJECT STRATEGY

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Survey of de-orbiting techniques (1/3) Propulsion Satellite slowed down with an engine (chemical, cold gas, or electrical) providing thrust against its movement. • Integration issues • Manoeuvre complexity

Credits: ATK

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Survey of de-orbiting techniques (2/3) Tethers Satellite slowed down by electromagnetic interactions between a tether and the Earth’s magnetic field.

• Low Technology Readiness Level (TRL) • De-orbiting duration to count in years

Credits: NASA

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Survey of de-orbiting techniques (3/3) Aerodynamic drag Satellite slowed down by the atmosphere. • Fits the requirement enveloppe • Allows for passive stabilization if well-dimensionned

Credits: NASA

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2D re-entry stability model (1/2) Sum of forces: Sum of moments:

Fg er Bω M ez Bt J

m BBvt

D eD

L eL

z zz

G M2Earth m |r | v2 D ρphq CD ph, αq Aref 2 Fg

ρphq CL ph, αq v2 Aref 2

L

ρphq v2 Aref Lref pCMα ph, αq 2

Mz

p

q q

CMω h, α ω

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2D re-entry stability model (2/2)

Output Altitude, velocity, acceleration and angle of attack for every point of the object’s trajectory.

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Numerical computation (1/2) Rarefied flows vs continuum flows • the satellite will experience from free-molecular while on orbit to

continuum in lower altitudes • degree of rarefaction defined by the Knudsen number Kn

λL

• experimentation of rarefied flows: complex and expensive

Ñ numerical approach: Direct Simulation Monte Carlo (DSMC) Z

X

Z

Y

X

Mach 14 12 10 8 6 4 2

Kn = 30.2 Altitude = 130 km Flow direction Ð

Z

Y

X

Mach 22 18 14 10 6 2

Kn = 2.14 Altitude = 110 km Flow direction Ð

Y

Mach 25 21 17 13 9 5 1

Kn = 0.345 Altitude = 100 km Flow direction Ð 21 / 39

Numerical computation (2/2) X

Z

X

Y

Z

Y

Pressure (Pa) # collisions / particle / s 2600 2400 2000 1600 1200 800

Number of collision per unit of volume Altitude = 110 km Flow direction Ð

0.45 0.35 0.25 0.15 0.05

Pressure Altitude = 110 km Flow direction Ð

Output • Aerodynamic coefficient characterising the object as a function of

the altitude / angle of attack.

• Flow-field description (pressure, temperature, number of collisions, etc.) allows for defining the interesting geometrical features.

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PART IV: APPLICATION

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Geometry design

Basic Direction of flight:

Ò

Badminton Direction of flight:

Ò

Flower Direction of flight:

Plate Direction of flight:

Ò

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Aerodynamic characteristics

3 angle of attack: 0° angle of attack: 15°

2.8

Drag coefficient

2.6 2.4 2.2 2 1.8 1.6 −2 10

continuum regime

0

10

2

4

10 10 Knudsen number

transition

6

10

rarefied regime

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Flight characteristics: Basic geometry

satellite’s trajectory Earth

180 170

15 initial angle of attack: 0° initial angle of attack: 15°

107.7km

10 Angle of attack (°)

Altitude (km)

160 150 140 130

5 0 −5

120 −10

110 100 0

107.7 km 5 10 Time (hours)

15

−15

160

140 120 Altitude (km)

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Flight characteristics: Plate geometry

satellite’s trajectory Earth

170 7840 Absolute velocity (m/s)

160

Altitude (km)

150 140 130 120

115 m/s 7800

7760

110 100 0

satellite’s velocity orbital velocity 50 100 Time (minutes)

150

7720 170

150

130 110 Altitude (km)

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Geometry selection • better for de-orbiting but slightly less efficient for stabilization • more degrees of freedom • more likely to resist • less points of failure

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Design • Pressure is not a problematic issue • Passive deployment based on the drag is not possible • Materials should be chosen for their thermal properties • A 1 m link is optimal • A 1 m2 plate is enough, more is not interesting

0.09 m2

1 m2

2 m2

satellite’s trajectory Earth

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Flight characteristics: Influence of the mass plate of 0.09 m2

170 mass: 3kg mass: 2kg mass: 4kg

160

Altitude (km)

150 140 130 120 110 100 0

Re-writing sum of forces:

1 2 Time (hours)

Bv Bt

GM er |r| 2

3

D m

eD

L m

eL

Ă‘ The lower the mass, the greater the effect of the aerodynamic forces 33 / 39

Flight characteristics: Influence of the atmospheric model plate of 0.09 m2

170 160

Jacchia MSISE90 − medium activity MSISE90 − high activity MSISE90 − low activity

Altitude (km)

150 140 130 120 110 100 0

1 2 Time (hours)

3

Expected launch window during low solar activity

Ñ Longer re-entry duration 34 / 39

Flight characteristics: Influence of the trigger altitude plate of 0.09 m2

80 70

trigger altitude: 150km trigger altitude: 200km trigger altitude: 170km

Radial velocity (m/s)

60 50 40 30 20 10 0 200

180

160

140

120

100

Altitude (km)

Trigger altitude has only an influence in the beginning the trajectory.

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PART V: CONCLUSION AND PERSPECTIVES

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Achievements

• 2D re-entry simulation tool • more accurate • adaptable to every geometry • Design of a de-orbiting and stabilization device for QB50 re-entry

satellite

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Perspectives

• Further development of the system’s design • Upgrade of the Simulink program • Complete the aerodynamic coefficients databases • Investigation of the non-monotonic behaviour of the aerodynamic

coefficients

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THANK YOU Any questions?

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