IAC-18-B4.2.7 AAReST Autonomous Assembly Reconfigurable Space Telescope Flight Demonstrator Craig Underwood a , Sergio Pellegrino b , Hari Priyadarshan c , Harsha Simha c , Chris Bridges a , Ashish Goel d , Thibaud Talon b , Antonio Pedivellano b , Christophe Leclerc b , Yuchen Wei b , Fabien Royer b , Serena Ferraro b , Maria Sakovsky b , Michael Marshall b , Kathryn Jackson b , Charles Sommer b , Aravind Vaidhyanathan c , Sooraj Vijayakumari Surendran Nair c , John Baker d a Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH, UK, c.underwood@surrey.ac.uk, c.p.bridges@surrey.ac.uk b GALCIT, California Institute of Technology (Caltech), Pasadena, CA 91125, USA, sergiop@Caltech.edu, ashishg@Caltech.edu, ttalon@Caltech.edu, apedivel@Caltech.edu, cleclerc@Caltech.edu, ywei@Caltech.edu, froyer@Caltech.edu, sferraro@Caltech.edu, msakovsk@Caltech.edu, mamarsha@Caltech.edu, Kathryn.Jackson@nrc-cnrc.gc.ca, csommer@Caltech.edu c Indian Institute of Space Science and Technology (IIST),Valiamala P.O., Thiruvananthapuram - 695 547, Kerala, India, priyadarshnam@iist.ac.in, harshasimhams@iist.ac.in, aravind7@iist.ac.in, sooraj@iist.ac.in d Jet Propulsion Laboratory (JPL), California Institute of Technology, 4800 Oak Grove Dr. Pasadena, CA 91109, USA, ashish.goel@jpl.nasa.gov, john.d.baker@jpl.nasa.gov 69 th International Astronautical Congress (IAC), Bremen, Germany, 1-5 October 2018. 1
The Vision Autonomous Assembly of Reconfigurable Large Aperture Space Telescopes Using Multiple Deformable Mirror Elements... Demonstrator - 2020 Operation ~2025 2
AAReST Objectives • Demonstrate all key aspects of autonomous assembly and reconfiguration of a space telescope based on multiple mirror elements – including the use of adaptive mirrors . • Demonstrate the capability of providing high-quality (astronomical) images . • Provide new opportunities for education in space engineering to undergraduate and post-graduate students and to foster academic collaboration between the project partners. • Use this demonstration to provide outreach activities worldwide, to encourage participation of young people in science, technology, engineering and International Academic Team: mathematics . Caltech (USA), Surrey (UK), IIST (India) 3
AAReST Concept • An astronomical telescope comprising a camera and 2 active Deformable Mirror Payloads (DMPs) and 2 passive Reference Mirror Payloads (RMPs). • Fly as a ~30kg composite spacecraft based on CubeSat technologies. • Spacecraft comprises 2 MirrorSats (Surrey, IIST) and 1 CoreSat (Caltech). AAReST Launch Configuration (solar panels not shown) • On orbit, the camera package deploys to form a direct viewing telescope (Caltech). • MirrorSats un- dock from “narrow” configuration and re- dock in “wide” configuration using Surrey’s EM Docking and Optical Relative Navigation System. • DMP mirrors change shape to maintain focus on stellar targets. Narrow Configuration Wide Configuration 4
Telescope Payload • The AAReST telescope payload represents a segmented sparse aperture comprising four circular mirror elements of 10cm diameter each – two rigid and two deformable. • It is a prime focus telescope, operating in the visible band (465-615nm wavelength bandpass) and has a 0.34 o field of view and 1.2m focal length. Note: the apertures quoted are geometric. As the images are not co-phased in AAReST, the optical • Each mirror is supported on a apertures remain as 4 ⨯ 0.1m tip/tilt/piston mount allowing 3 rigid-body motions. • Actuation is via three picomotors. These can provide course scale or fine scale adjustments (of order 10 -3 ~10 -6 m). 5
Deformable Mirrors • The deformable mirrors are based on 200 m m thick Schott D263 glass substrates. • They are electrostatically actuated using a special pattern of 41 high voltage ( ± 500V) piezoelectric actuators. • Imaging sensors and Shack-Hartmann Wavefront Sensors (SHWSs) in the Camera Package (CP) provide the feedback for active control and calibration of the telescope in flight . 6
Camera and Boom • The Camera Package meets the design requirements of having a mass <4kg, a volume < 10cm ⨯ 10cm ⨯ 35cm and a power consumption < 5W. • DMP mirrors have been manufactured and extensively tested using a Reverse Hartmann Test Bed. • Mirror control algorithms have been developed and tested. • A new “slotted hinge” CFRP boom of 38.8mm diameter, 1.45m length and 200 m m thickness with a mass of just 65g has been developed and tested using a bespoke deployment test rig. • It is located in a kinematic mount. • Its straightness is 5mm in 1.45m (0.34%) 7
EM Docking System Drogues • Surrey Electro-Magnetic Docking System (EMDS) developed for AAReST. • Comprises four PWM controlled, H- bridge-driven, dual polarity electro- magnets, each of over 900 A-turns. • These are coupled to three “probe and drogue” (60 o cone and 45 o cup) type mechanical docking ports. Probes • Kinematic constraint is established using the Kelvin Clamp principle (3 spheres into 3 V-grooves arranged at 120 o ). • Provides 6DOF force and torque control for proximal operations within ~30-50cm separation distance. Kelvin Clamp 6DOF Rendezvous & Docking 6DOF Constraint Control 8
EMDS Testing • Prototypes of the docking ports have been manufactured and tested on SSC’s air bearing table. • These experiments verified the docking port “capture cone” force field concept, and demonstrated that we could capture and dock, from a distance of up to 50cm. • We could also undock, repel, stop and hold the MirrorSat in alignment at the required 25cm distance. • Force measurements were compared to both our semi-analytical (Gilbert model) and finite element mathematical model (FEMM) simulations and were found to be in good agreement with the latter. • More experiments are planned with closed loop control via the ORNSS. 9
Relative Nav. System • Surrey has developed an optical relative navigation sensor system (ORNSS) based on a miniature COTS lidar and a LED pattern/machine vision camera. Dual R-Pi • Compute For AAReST, we have taken the Softkinetic DS325 Lidar Module – Softkinetic DS325 Lidar/Camera system Payload and modified it for use in space. Interface Computer • The lidar provides pose and range out to (PIC) ~1.6m – but is affected by strong sunlight. NIR LED Pattern (in Lab) • We have therefore also developed a Outside test with highly filtered NIR LED/camera system the Sun in direct Sun view of the that works well even in bright sunlight. camera. The NIR • LED pattern was These sensors are connected to two R- still observable Pi Compute modules, which can provide LED Pattern and pose/range pose/range data at 10’s of Hz. data were obtained. 10
MirrorSats • Surrey and IIST have each developed their own design of MirrorSat, albeit both carrying a common set of mission critical systems: − Deformable Mirror Payload (DMP) (Caltech) − Payload Interface Computer (PIC) (Surrey) − Lidar/MVS Relative Navigation Sensor Surrey MirrorSat (Surrey) − Upper and Lower Docking Ports (Surrey) − Frangibolt Interface (Caltech) • The Surrey MirrorSat is a mixture of COTS and bespoke systems. • The IIST MirrorSat is all bespoke. • Both carry a butane propulsion system IIST MirrorSat of 5-10 mN thrust range. 11
CoreSat • The Caltech CoreSat comprises a bespoke ~9U structure with bespoke solar panels, COTS EPS and Battery (P60 unit from GOMSpace), COTS ADCS Unit (3-axis unit from CubeSpace) with 3 magnetorquers, 3 reaction wheels, 2 magnetometers and a star tracker for precision pointing. Caltech • There is also a VHF Uplink and UHF CoreSat Downlink (He-100 from AstroDev). • The CoreSat provides the interface to the launch vehicle through a standard fitting compatible with the Indian PSLV rocket. • At launch the 2 MirrorSats are rigidly held on to the CoreSat via frangibolts. • On orbit, the attachment is magnetic. AAReST Spacecraft Side View and Isometric View 12
SQM Testing • In June, the Caltech, Surrey and IIST teams each produced mass dummies of their AAReST spacecraft, and these were successfully assembled into a single Structural Qualification Model (SQM) for initial vibration testing. • Unfortunately, the SQM did not pass the vibration test with the PSLV loads. • The Frangibolt interface plate on the MirrorSats deformed and this led to excessive displacements and impacts between the deformable mirror and rigid mirror boxes. • Analysis shows that relatively small adjustments to the structures will fix these problems and further tests are planned for January 2019. AAReST SQM on Vibration Table 13
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