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. 19 / 39
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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
Ò 25 / 39
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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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