BIRDY-T : Focus on propulsive aspects of an icubsat to small bodies of the solar system

Transcription

1 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, 3/5/7

2 Outline Mission context Trajectory Correction Maneuvers (TCM) Concepts Description Comparison TCM loop control law CubeSat propulsion systems comparison

3 Mission contexts Interplanetary trajectory corrections (trajectory from Boris Segret, inspired by Dennis Tito for 8) CubeSat Proximity operations Earth at launch AIM CubeSat 6583 Didymos Binary System Sun Earth Earth at the end of the mission DART Mars Earth-Mars-Earth free return trajectory Models ESA (Galvez/Carnelli) Asteroid investigation 3

4 Proximity operation context Science case: radio-science experiment Semimajor axis.64 AU Eccentricity.384 Inclination 3.4 Diameter.78 km Mass kg SOI 9 km In-situ geodesy using radio science of NEA such as Didymos-A and -B -way radio-link between the mothercraft and the spacecraft for Doppler and range measurements Precise orbit determination leading to the parameters of geophysical interest Fictional asteroid parameters derived from Didymos A AIM Main trajectory requirements Low orbit at low velocity 6583 Didymos Binary System Alternance of free-fall and Trajectory Correction Maneuvers (TCM) GNC & ADCS main requirements CubeSat Autonomous in-flight orbit determination Multi-axis thrusters for TCM and attitude control / reaction wheel desaturation Earth DART Flying legs illustration Models ESA (Galvez/Carnelli) 4

5 TCM concepts () Issue Concept Orbiting such a small body is tricky: Orbit segment at ~ constant velocity Perturbations (SRP) make it unstable V m/s => ~ 86 km per day Long orbiting period Small acceleration due to perturbations Orbiting a Dydimos-A-like asteorid TCM mode to obtain a 9 direction change or correct trajectory shifts due to perturbations V ini = and V out = Circular TCM () () vini Loop TCM CubeSat Velocity and orbital period arround a small body Asteroid Illustration of TCM concepts Simple TCM 5

6 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=) π Perimeter: ) ( ) Δ s= r ( Trajectory: OM =r sin (k θ) cos(θ) sin (θ) am = Acceleration: d VM k sin (t) dt ( Loop TCM geometry ) ( ) = r k cos(k θ) sin (θ) r (+k )sin (k θ) cos (θ) cos(θ) sin (θ) d θ 6

7 TCM comparison Circular TCM Concept -day of science mode at constant velocity V m/s => ~ 86 km per day TCM mode to obtain a 9 direction change V out = V ini = and () Assumptions 3U-CubeSat (4 kg) No perturbation Conclusion vini Simple mission design with loop TCM () Loop TCM CubeSat Simple TCM Asteroid Illustration of TCM concepts Circular TCM Simple TCM Loop TCM Duration [days] Distance [km] ΔV [m/s] Average force [N].x-4 6.5x-4.6x-4 Horizontal shift [km] Vectical shift [km] Comparison of TCM concepts 7

8 Loop TCM control law TCM loop control law.8e e-4 5.7e e Loop TCM geometry.6e e-4 Requirements: 7.5e Reference thrust value and direction (F and α) for a -day maneuver ΔT F min= F max Δ T 3-axis control during maneuver Thrust modulation (< 5%) Power consumption < W Volume < U 8

9 CubeSat small propulsion systems Typical delta-v performances of SP.55 ACS (CGT) MEPSI MiPS (CGT) Standard MiPS (CGT) BGT-X5 (mono) ADN MiPS (mono) PM4 (bi) CHIPS warm gas (elec-therm) PPTCUP (elec-mag) L-μPPT (elec-mag) μcat (elec-mag) TILE- (elec-stat) PM4, Hyperion Technologies Low Power Resistojet, SSTL L-μPPT project, L-μPPT Zone of interest 9

10 CubeSat small propulsion systems for loop TCM SP performances for TCM loop 4 ACS (CGT) MEPSI MiPS (CGT) 5 W Standard MiPS (CGT) 35 Conclusions: BGT-X5 (mono) ADN MiPS (mono) PM4 (bi) 3 Many CubeSat SP systems are missing CHIPS warm gas (elec-therm) PPTCUP (elec-mag) L-μPPT (elec-mag) 5 μcat (elec-mag) TILE- (elec-stat) 5 6W 5 W,5 W W 5.4 W -4 3W 3 W -3 W W W 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 3UCubeSats

11 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, 3/5/7