BIRDY-T : Focus on propulsive aspects of an iCubSat to small bodies of the solar system
Gary Quinsac, PhD student at PSL | Supervisor: Benoît Mosser | Co-supervisors: Boris Segret, Christophe Koppel
iCubeSat, Cambridge, 31/05/2017
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Outline
● Mission context
● Trajectory Correction Maneuvers (TCM)
– Concepts
– Description
– Comparison
– TCM loop control law
● CubeSat propulsion systems comparison
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Mission contexts
Interplanetary trajectory corrections
Earth-Mars-Earth free return trajectory
(trajectory from Boris Segret, inspired by Dennis Tito for 2018)
Earth at launch
Earth at the end of the mission
CubeSat
Sun
Mars
Proximity operations
Asteroid investigation
AIM
CubeSat
DART
65803DidymosBinarySystemEarth
Models © ESA (Galvez/Carnelli)
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Proximity operation context
AIM
CubeSat
DART
65803DidymosBinarySystemEarth
Models © ESA (Galvez/Carnelli)
Science case: radio-science experiment
● In-situ geodesy using radio science of NEA such as Didymos-A and -B
● 2-way radio-link between the mothercraft and the spacecraft for Doppler and range measurements
● Precise orbit determination leading to the parameters of geophysical interest
Main trajectory requirements
● Low orbit at low velocity
● Alternance of free-fall and Trajectory Correction Maneuvers (TCM)
GNC & ADCS main requirements
● Autonomous in-flight orbit determination
● Multi-axis thrusters for TCM and attitude control / reaction wheel desaturation
Semimajor axis 1.64 AU
Eccentricity 0.384
Inclination 3.4°
Diameter 0.780 km
Mass 5.278.1011 kg
SOI 9 kmFictional asteroid parameters derived from Didymos A
“Flying legs” illustration
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TCM concepts (1)
Issue
● Orbiting such a small body is tricky:
– Perturbations (SRP) make it unstable
– Long orbiting period
Concept
● Orbit segment at ~ constant velocity
– V ≈ 1 m/s => ~ 86 km per day
– Small acceleration due to perturbations
● TCM mode to obtain a 90° direction change or correct trajectory shifts due to perturbations
– andV⃗ ini=(10) V⃗ out=(01) CircularTCM
LoopTCMCubeSat
Asteroid
“Simple”TCM
v⃗ini
v⃗outv⃗out v⃗out
Illustration of TCM concepts
102 4 6 81 3 5 7 9
0.2
0.1
0.04
0.06
0.08
0.12
0.14
0.16
0.18
0.22
0.24
10
2
4
6
8
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Orbiting a Dydimos-A-like asteorid
Velocity and orbital period arround a small body
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TCM description
Circular TCM
● Constant acceleration / Inertial acceleration direction (orthogonal to the velocity)
“Simple” TCM
● Constant acceleration / Non-inertial acceleration direction (fixed)
“Loop” TCM (imagined by Boris Segret)
● Mathematical curve : rosette (k=2)
● Trajectory:
● Perimeter:
● Acceleration:
O⃗M=r⋅sin (k θ)⋅(cos(θ)sin (θ))
a⃗M=d2 V⃗M
dθ2=2⋅r⋅k⋅cos(k⋅θ)(−sin (θ)
cos(θ) )−r(1+k2)sin (k⋅θ)(cos (θ)sin (θ))
Δ s=2⋅r∫0
π2 √ 1−(1− 1k2)sin2(t)dt “Loop” TCM
geometry
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TCM comparisonCircular TCM
LoopTCMCubeSat
Asteroid“Simple”TCM
v⃗ini
v⃗outv⃗out v⃗out
Circular TCM “Simple” TCM “Loop” TCM
Duration [days] 1 1 1
Distance [km] 86.4 85.5 66.8
ΔV [m/s] 4.71 1.41 3.55
Average force [N] 2.2x10-4 6.5x10-4 1.6x10-4
Horizontal shift [km] -18.5 43.6 0
Vectical shift [km] 18.5 -42.8 0
Concept
● 1-day of science mode at constant velocity
– V ≈ 1 m/s => ~ 86 km per day
● TCM mode to obtain a 90° direction change
– and
Assumptions
● 3U-CubeSat (4 kg)
● No perturbation
Conclusion
● Simple missiondesign with “loop” TCM
Comparison of TCM concepts
V⃗ out=(01)V⃗ ini=(10) Illustration of TCM concepts
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Requirements:
●
● 3-axis control during maneuver
● Thrust modulation (< 25%)
● Power consumption < 10 W
● Volume < 1U
Fmin=F0max⋅ΔT 0ΔT
Reference thrust value and direction (F0 and α
0) for a 1-day maneuver
“Loop” TCM control law
“Loop” TCM geometry
0 20 40 60 8010 30 50 70 905 15 25 35 45 55 65 75 85
100
60
80
120
70
90
110
65
75
85
95
105
115
1.6e-04
1.8e-04
1.5e-04
1.7e-04
1.55e-04
1.65e-04
1.75e-04
TCM loop control law
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101
102
103
0
0.2
0.4
0.1
0.3
0.5
0.05
0.15
0.25
0.35
0.45
0.55ACS (CGT)
MEPSI MiPS (CGT)
Standard MiPS (CGT)
BGT-X5 (mono)
ADN MiPS (mono)
PM400 (bi)
CHIPS warm gas (elec-therm)
PPTCUP (elec-mag)
L-μPPT (elec-mag)
μCAT (elec-mag)
TILE-1 (elec-stat)
Typical delta-V performances of SP
CubeSat small propulsion systems
Zone of interest
© L-μPPT project, L-μPPT
Low Power Resistojet, © SSTL
PM400, © Hyperion Technologies
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10-4
10-3
10-2
10-1
100
101
0
200
400
100
300
50
150
250
350
ACS (CGT)
MEPSI MiPS (CGT)
Standard MiPS (CGT)
BGT-X5 (mono)
ADN MiPS (mono)
PM400 (bi)
CHIPS warm gas (elec-therm)
PPTCUP (elec-mag)
L-μPPT (elec-mag)
μCAT (elec-mag)
TILE-1 (elec-stat)
SP performances for TCM loop
CubeSat small propulsion systems for “loop” TCM
5.4 W 1 W10 W
20 W
15 W
30 W
2 W
2,5 W
25 W
6 W
3 W
Conclusions:
● Many CubeSat SP systems are missing
● Although, it seems that some SEP systems provide sufficient specific impulse and thrust
● With such systems a several month-mission using “loop” TCM would be feasible
● However, systems providing 3-axis attitude control are rare (usually cold gas) for 3U-CubeSats
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Conclusion and perspectives● A TCM loop for asteroid exploration is being studied
- It simplifies mission design and minimizes shifts due to small propulsion- Control laws are easy to implement
● Existing or in development SEP should provide the requested performances● Simulations taking into account perturbations will start soon● Tests on a frictionless bench (including gyroscopes, reaction wheels and a
propulsion system) are considered
Thank you for your attention
Gary Quinsac, PhD student at PSL | Supervisor: Benoît Mosser | Co-supervisors: Boris Segret, Christophe Koppel
iCubeSat, Cambridge, 31/05/2017
