Cubesats and the challenges of Docking

Transcription

1 Cubesats and the challenges of Docking Luca Simonini Singapore Space Challenge 2017 Education outreaches, Thales Solutions Asia Pte. Ltd. August the 30 th 2017 September the 6 th

2 Challenges of Space What are the challenges of space? 2

3 Access to Space is challenging, rare and costly In launches performed (4 launch failures) and 60 more planned from 15000USD to 50000USD per kilogram of launched mass in Low Earth Orbit 3

4 Space is a harsh environment Galileo O3B SpaceBUS-NEO Jason, Jason-2, Globalstar 2 nd Gen Iridium Next Optical HR 4 Image Source: E.J. Daly, A. Hilgers, G. Drolshagen, and H.D.R. Evans, "Space Environment Analysis: Experience and Trends," ESA 1996 Symposium on Environment Modelling for Space-based Applications, Sept , 1996, ESTEC, Noordwijk, The Netherlands

5 No maintenance is possible after the launch most of the times 5 Hubble telescope serviced 5 times in 1994, 1997, 1999, 2002, 2009 Each mission cost between 300 and 400 MUSD with last costing 900MUSD Image Courtesy NASA

6 CubeSat - Definition 1U = 11.35cm x 10cm x 10cm = max 1.33kg Commercial Components -> Low Cost fly-learn-refly approach -> Reduced Test Campaign -> Low Cost 6 Satellites released outside the Kibo laboratory using a Small Satellite Orbital Deployer on Oct. 4, Credits NASA

7 CubeSat A class of Satellites Courtesy VELOX-I AOBA-VELOX-III Courtesy VELOX-PII VELOX-PIII VELOX-II Courtesy 7

8 CubeSat History of Success In percent have achieved full success (33 percent) or partial success (34 percent) In the period have been more successful at 71 percent, than in the previous 8 years ( ), at 35 percent In the last period there is a shift from University Research and Formation tools to Industry and Operational Systems with a global effort to increase the reliability, that is still far from institutional demands for big satellites The reliability also increases with the experience the design team has Education-only CubeSats have had a lower success rate of 45 percent for in-orbit performance compared to all CubeSats Source 8

9 CubeSat Design Functional Architecture All the high level functions of a Big Satellite Structure Thermal Control (Passive or Active) Power Production, Storage and Distribution Command and Control Attitude Determination and Control Telecommunications Payload -> I.e. why the satellite flies Sometimes Propulsion (as from 3U) Reduced Complexity Reduced low level functions set No redundancy No hardening 9

10 CubeSat Design Parts and Components A set of provider of flight proven CubeSat components, buses and lunch systems And Standards 10

11 Challenges of Cubesats What are the challenges of cubesats? 11

12 CubeSat Design Challenges Mass Development cost is roughly proportional to the mass - With a ratio that is higher than for big satellites Launch ~50.000USD per kg 12

13 CubeSat Design Challenges Power For a 1U CubeSat the power installed is about 12W (12 cells, 2 each face), but the power available for the bus may decrease to 1.5 to 2W as minimum and a average of between 3W and 4W in an orbit - For higher factors, the power can increase due to the possibility to introduce deployable solar arrays 1W ISS inclined scenario 13

14 CubeSat Design Challenges Power Batteries to store energy and release during eclipse (it counts for 1/3 of the orbit) are big and heavy - Consider 100Wh for kg and 300Wh per liter (1U) for the most advanced - Remember that the deepest you discharge the battery the lower the lifetime - The number of cycles is high - every day there are at least 15 cycles of charge / discharge 33mm 60mm Courtesy 14

15 CubeSat Design Challenges Data link to ground Generally UHF/VHF (Up/Downlink) is used with whip antennas - around 10kbps - 1 visibility is max 10minutes for LEO -> 6Mb -> 750kB per orbit - 1 W when receiving, 2W when transmitting - Noisy at low elevations S-Band starts to be used for payload data but also command and control - Up to 1Mbps -> 75MB per orbit - Up to 10 to 15W when transmitting Experiences for X and Ka-Band for Payload data transmission only higher consumption and Ka-band is very affected by rain - Higher bands use patch antennas S-Band patch antenna UHF/VHF whip antenna 55cm 70mm 70mm 15

16 CubeSat Design Challenges Attitude and Orbit (Propulsion) Control Goes from very simple gravity gradient control To high accuracy 3axes control Large impact on the flight software and on board computer choice Requires a large amount of hardware - Wrong choice can underperform or excite resonant frequencies of the spacecraft 16

17 CubeSat Design Challenges Attitude and Orbit (Propulsion) Control Reaction wheels to have fast maneuvering with high precision - Require adequate controller - Vibrations engendered may perturb some payloads requiring vibration dumpers - Energy consuming - At least 3 to control each axis Control momentum gyros even faster maneuvering, but high mechanical stresses Magneto-torquers to have a broad control, are however necessary to desaturate reaction wheels Thrusters to change or maintain precisely the orbit - Electrical low thrust, low propellant mass - Chemical higher hrust, higher propellant mass Electromagnetic tethers Sun Sail Star Tracker only for fine pointing, suffers from Earth and Sun view Sun Sensors for coarse pointing (>1deg), pay attention to obstructions IMU for eclipse and phases where the sun sensors not point the sun Magnetometer if magnetic coils are used as actuators GPS with adequate number of antennas for precise position 17

18 CubeSat Design References Consult catalogue of components of various providers Consult Space Mission Analysis and Design by Larsson and Wertz The Bible of the Space System Engineer 18

19 Docking - Definition VIDEO 19

20 Challenges of Docking What are the challenges of docking? 20

21 Space objects travel on curves 21

22 Docking - Challenges To select the approach strategy Many different strategies are possible - V-bar, R-bar, - Man in the loop or Delay as C = km/s - Autonomous and depending on the target dynamics: - Straight line approach for collaborative objects - Ellipse of inspection for non-cooperative ones ATV Strategy -> V-bar Keep safe at all time Clouds of debris are seen somehow negatively Not just threatening ISS and Astronauts lifes 22

23 Docking - Challenges Sentinel 1-A impact from a 1mm size particle causing a damage 100x its size 23

24 Docking - Challenges Rendez-Vous and docking strategy depends on the attitude and orbit control suite How do I adapt my trajectory in space? - Thruster embarked for performing the orbital parameters - Thrust influence the amplitude of the manoeuvers and their duration How do I adapt my orientation in space? - Reaction wheels, control momentum gyros, magnetotorquers, thrusters, Rendez-Vous and docking strategy depends on the navigation suite selected How do I know where I am? - STR, GNSS, Sun Sensors give the absolute position and attitude how do I know where is the target with respect to me? - Metrology, navigation and communication suites provide relative position and attitude Rendez-Vous and docking strategy depends on the target the chaser is aiming at Is the target cooperative? Is the target uncooperative? Is the target uncontrolled and with an unknown motion? Rendez-Vous and docking strategy depends also on how the functions are shared among the various players 24

25 Docking - Challenges Position requirements are associated with the size of the object 30cm object cannot have an error higher than a small percentage of its size - GNSS (GPS, Galileo, Beidou, Glonass constellations) does not generally give sufficient precision for docking (>1m) - STR can provide fine attitude, but in cubesats are difficult to accommodate and depending the strategy can be blinded by Sun, flares on target, Earth, Moon, To retrieve relative position and attitude Relative sensors trade-off with passive elements requiring demanding computations (e.g., cameras and Image processing) or active elements providing 3D mapping (e.g., scanning and flash LIDARs, TOF cameras) Prisma RF metrology Radar or Lidar Scanning - Car ISS Videometers 25

26 Docking - Challenges Docking mechanisms ATV, Soyuz and Progress cargo share the same mechanism with a direct mechanical interface 26

27 Docking - Challenges Docking mechanisms Other docking mechanisms are studied - Arms for berthing and docking with a clamping system, Harpoons, Nets, Magnetic systems, adhesive tapes. Orbital Express Capture Mechanism 27 DLR Electro-Mechanical Interface (3) LED (4) signal block (5) camera (7) Guiding pins (8) marker (9) bolt for latch mechanism (10) contact block and distance pins

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