IAC-18-B4.2.7 AAReST Autonomous Assembly Reconfigurable Space - - PowerPoint PPT Presentation

AAReST Autonomous Assembly Reconfigurable Space Telescope Flight Demonstrator

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Craig Underwooda, Sergio Pellegrinob, Hari Priyadarshanc, Harsha Simhac, Chris Bridgesa, Ashish Goeld, Thibaud Talonb, Antonio Pedivellanob, Christophe Leclercb, Yuchen Weib, Fabien Royerb, Serena Ferrarob, Maria Sakovskyb, Michael Marshallb, Kathryn Jacksonb, Charles Sommerb, Aravind Vaidhyanathanc, Sooraj Vijayakumari Surendran Nairc, John Bakerd

aSurrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH, UK, c.underwood@surrey.ac.uk,

c.p.bridges@surrey.ac.uk

bGALCIT, 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

cIndian 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

dJet 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

69th International Astronautical Congress (IAC), Bremen, Germany, 1-5 October 2018.

IAC-18-B4.2.7

The Vision

Autonomous Assembly of Reconfigurable Large Aperture Space Telescopes Using Multiple Deformable Mirror Elements...

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Demonstrator - 2020 Operation ~2025

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
• utreach activities worldwide, to

encourage participation of young people in science, technology, engineering and mathematics .

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International Academic Team: Caltech (USA), Surrey (UK), IIST (India)

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).

• 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.

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AAReST Launch Configuration (solar panels not shown) Narrow Configuration Wide Configuration

Telescope Payload

• The AAReST telescope payload

represents a segmented sparse aperture comprising four circular mirror elements

• f 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 0.34o field of view and 1.2m focal length.

• Each mirror is supported on a

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 10-3~10-6m).

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Note: the apertures quoted are geometric. As the images are not co-phased in AAReST, the optical apertures remain as 4 ⨯ 0.1m

Deformable Mirrors

• The deformable mirrors are based on

200mm 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 .

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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 200mm 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%)

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EM Docking System

• 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” (60o cone and 45o cup) type mechanical docking ports.

• Kinematic constraint is established using

the Kelvin Clamp principle (3 spheres into 3 V-grooves arranged at 120o).

• Provides 6DOF force and torque control

for proximal operations within ~30-50cm separation distance.

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Probes Drogues Kelvin Clamp 6DOF Constraint 6DOF Rendezvous & Docking Control

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.

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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.

• For AAReST, we have taken the

Softkinetic DS325 Lidar/Camera system and modified it for use in space.

• The lidar provides pose and range out to

~1.6m – but is affected by strong sunlight.

• We have therefore also developed a

highly filtered NIR LED/camera system that works well even in bright sunlight.

• These sensors are connected to two R-

Pi Compute modules, which can provide pose/range data at 10’s of Hz.

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Softkinetic DS325 Lidar Sun LED Pattern NIR LED Pattern (in Lab) Outside test with the Sun in direct view of the

• camera. The NIR

LED pattern was still observable and pose/range data were

• btained.

Dual R-Pi Compute Module – Payload Interface Computer (PIC)

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) − 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
• f 5-10 mN thrust range.

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Surrey MirrorSat IIST MirrorSat

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.

• There is also a VHF Uplink and UHF

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.

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AAReST Spacecraft Side View and Isometric View Caltech CoreSat

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.

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AAReST SQM on Vibration Table

Conclusions

• The AAReST project has now been running for almost a decade.
• In that time, a great body of work has been carried out by the teams at Caltech,

Surrey and IIST.

• The project has proven to be technologically challenging, but a fruitful source of

material for the education of students in our institutions.

• The international collaboration aspects have worked well, and all parties have

benefitted in bringing together different expertise.

• The SQM test failure has set the project back a few months, but we still expect

to deliver flight hardware in 2019, and look forward to a launch in 2020.

• In the mean time, further simulation and testing of the rendezvous and docking

system is taking place at Surrey and Caltech are continuing the optical testing

• f the telescope. IIST are developing and testing engineering models of their

flight systems, before production of the flight units.

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Acknowledgements

• We wish to acknowledge and thank the many people (especially students) who

have contributed to the AAReST project over the years, and in particular those whose work contributed to directly to this paper.

• The development of the optical systems for AAReST has been supported by

the California Institute of Technology and by the Keck Institute of Space Studies.

• The micro-porous carbon air-bearing table simulator, used in the earlier

rendezvous and docking experiments, was developed through funding from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/J016837/1.

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