Future planned space telescopes, such as the IR/O/UV Large Telescope, recommended by Astro2020 will be used to directly image exo-Earths. They will employ high-order wavefront sensing and control (HOWFSC) to correct static and slow wavefront errors in the image plane to achieve contrasts better than 109. Our work evaluates the computational requirements for HOWFSC algorithms and compares these to the capabilities of processors that are expected to be available during mission development. We find that HOWFSC creates unprecedented requirements for space-based computational power, such as the ∼1013 floating-point operations necessary to generate the dark hole, based on the Large UV/Optical/IR (LUVOIR) study. In our worst-case estimates, maintaining an LUVOIR-size dark hole at 1010 contrast might require up to several orders of magnitude more computational throughput than available on the most advanced radiation-hardened processor.
Microelectromechanical Systems (MEMS) Deformable Mirrors (DMs) are a key technology option for adaptive optics instruments for space applications because they provide high-precision wavefront control with small form-factor, low-power devices. The Deformable Mirror Demonstration Mission (DeMi) CubeSat demonstrated a MEMS DM in space for the first time in order to raise the Technology Readiness Level (TRL) of the technology for future space applications such as high-contrast imaging of exoplanets and optical communications. The DeMi payload demonstrated a 140-actuator MEMS DM from Boston Micromachines Corporation. DM performance was measured with a Shack Hartmann wavefront sensor (SHWFS). The DeMi CubeSat began on-orbit operations in July 2020 and has since met the mission goals of measuring individual actuator displacements to a precision of 12 nm and correcting wavefront errors in space to <100 nm RMS error. The DeMi mission has raised the TRL of MEMS DM technology from a 5 to a 9. This paper summarizes the DeMi payload design and the results from over a year of on-orbit operations. Individual actuator measurements from ground and space operations show the MEMS DM actuating in space with similar performance and measurement uncertainty to ground data with no dead or under-actuating actuators detected. Wavefront control experiments show the DeMi payload correcting thermal- and vibration-induced wavefront errors in space.
KEYWORDS: Space operations, Telescopes, Space telescopes, Computer architecture, Commercial off the shelf technology, Algorithm development, Radiation effects, Wavefront sensors, Satellites, Detection and tracking algorithms
Future planned space telescopes such as HabEx and LUVOIR will be used to directly image exo-Earths. These telescopes use coronagraph instruments to suppress starlight and resolve dim exoplanets. They will employ high order wavefront sensing and control (HOWFSC) to correct static and slow wavefront errors in the image plane to achieve contrasts above 109. This work evaluates architectures to meet the computational requirements for HOWFSC algorithms with available processors. We find that the computational requirements of HOWFSC will impose unprecedented requirements on space-based components and that typical combinations of computational resource and control architecture will consume significant observation time. Science yield from the space telescope can be improved, and mission risk and cost reduced, by using co-flying or ground-in-the loop computational offload architectures. In particular, a high-capability co-flying processor could use commercial components 104 times more powerful than typical radiation hardened options. This would enable key HOWFSC algorithms to run in seconds rather than hours or days, removing operational constraints on the science mission. While commercial processors may be more susceptible to total ionizing dose radiation effects over the expected mission lifetime of 5-10 years, the relatively low cost of development and replacement launches make these co-flying processors an attractive option. We evaluate three major co-flying architecture trades: (i) inter-spacecraft distance, (ii) risk classification, and (iii) processor selection. We find that one or more low-cost replaceable co-flying processors with COTS components and flying several kilometers from the telescope spacecraft can provide all needed computation.
Microelectromechanical systems (MEMS) deformable mirrors (DMs) can provide high-precision wavefront control with a small form-factor, low power device. This makes them a key technology option for future space telescopes requiring adaptive optics for high-contrast imaging of exoplanets with a coronagraph instrument. The Deformable Mirror Demonstration Mission (DeMi) CubeSat payload is a miniature space telescope designed to demonstrate MEMS DM technology in space for the first time. The DeMi payload contains a 50-mm primary mirror, an internal calibration laser source, a 140-actuator MEMS DM from Boston Micromachines Corporation, an image plane wavefront sensor, and a Shack–Hartmann wavefront sensor (SHWFS). The key DeMi payload requirements are to measure individual actuator wavefront displacement contributions to a precision of 12 nm and correct both static and dynamic wavefront errors in space to less than 100-nm RMS error. The DeMi mission will raise the technology readiness level of MEMS DM technology from a five to at least a seven for future space telescope applications. We summarize the DeMi optical payload design, calibration, optical diffraction model, alignment, integration, environmental testing, and preliminary data from in-space operations. Ground testing data show that the DeMi SHWFS can measure individual actuator deflections on the MEMS DM to within 10 nm of interferometric calibration measurements and can meet the 12-nm precision mission requirement for actuator deflection voltages between 0 and 120 V. Payload data from throughout environmental testing show that the MEMS DM and DeMi payload survived environmental testing and provides a valuable baseline to compare with space data. Initial data from space operations show the MEMS DM actuating in space with a median agreement between individual actuator measurements from space and equivalent ground testing data of 12 nm.
The Coronagraphic Debris Exoplanet Exploring Payload (CDEEP) is a Small-Sat mission concept for high contrast imaging of circumstellar disks. CDEEP is designed to observe disks in scattered light at visible wavelengths at a raw contrast level of 10-7 per resolution element (10-8 with post processing). This exceptional sensitivity will allow the imaging of transport dominated debris disks, quantifying the albedo, composition, and morphology of these low-surface brightness disks. CDEEP combines an off-axis telescope, microelectromechanical systems (MEMS) deformable mirror, and a vector vortex coronagraph (VVC). This system will require rigorous testing and characterization in a space environment. We report on the CDEEP mission concept, and the status of the vacuum-compatible CDEEP prototype testbed currently under development at the University of Arizona, including design development and the results of simulations to estimate performance.
The Deformable Mirror Demonstration Mission (DeMi) is a 6U CubeSat that will characterize the on-orbit performance of a Microelectromechanical Systems (MEMS) deformable mirror (DM) with both an image plane wavefront sensor and a Shack-Hartmann wavefront sensor (SHWFS). Coronagraphs on future space telescopes will require precise wavefront control to detect and characterize Earth-like exoplanets. High-actuator count MEMS deformable mirrors can provide wavefront control with low size, weight, and power. The DeMi payload will characterize the on-orbit performance of a 140 actuator MEMS Deformable Mirror (DM) with 5.5 μm maximum stroke, with a goal of measuring individual actuator wavefront displacement contributions to a precision of 12 nm. The payload will be able to measure low order aberrations to λ/10 accuracy and λ/50 precision, and will correct static and dynamic wavefront phase errors to less than 100 nm RMS. We present an overview of the payload design, the assembly, integration, and test process, and report on the development and validation of an optical diffraction model of the payload. Launch is planned for late 2019.
KEYWORDS: Sensors, Control systems, Infrared radiation, Satellites, Space operations, Error analysis, Telecommunications, Laser communications, Control systems design, Error control coding
The CubeSat Laser Infrared CrosslinK mission is a joint Massachusetts Institute of Technology (MIT), University of Florida (UF), and NASA Ames Research Center effort to develop laser communications (lasercom) transceivers. The terminals demonstrate full-duplex intersatellite communications and ranging capability using commercial components to enable future large constellations or swarms of nanosatellites as coordinated distributed sensor systems.
CLICK will demonstrate a crosslink between two CubeSats that each host a < 2U lasercom payload. Range control is achieved using differential drag in Low Earth Orbit (LEO), with attitude controlled using a three-axis reaction wheel assembly and attitude sensors, including star trackers.
The lasercom terminals are direct-detect and rate scalable, designed to achieve a 20 Mbps crosslink at ranges from 25 km to 580 km and operate full-duplex at 1537 nm and 1563 nm with 200 mW of transmit power and a 14.6 arcscecond (0.07 milliradian) full width half max (FWHM) beamwidth. The terminals also use a 976 nm, 500 mW, 0.75 degree FWHM beacon and a quadcell for initial acquisition, and a low-rate radio crosslink for exchanging orbit information.
The payload transmitter is a master oscillator power amplifier (MOPA) with fiber Bragg grating for pulse shaping and MEMS fast steering mirror (FSM) for fine pointing, modeled after the MIT Nanosatellite Optical Downlink Experiment. The transceiver leverages UF’s Miniature Optical Communications Transmitter (MOCT) including a chip-scale atomic clock (CSAC). The receiver implements both a time to digital converter (TDC) as well as pulse recovery and matched filtering for precision ranging.
Coronagraphs on future space telescopes will require precise wavefront correction to detect Earth-like exoplanets near their host stars. High-actuator count microelectromechanical system (MEMS) deformable mirrors provide wavefront control with low size, weight, and power. The Deformable Mirror Demonstration Mission (DeMi) payload will demonstrate a 140 actuator MEMS Deformable Mirror (DM) with 5:5 μm maximum stroke. We present the flight optomechanical design, lab tests of the flight wavefront sensor and wavefront reconstructor, and simulations of closed-loop control of wavefront aberrations. We also present the compact flight DM controller, capable of driving up to 192 actuator channels at 0-250V with 14-bit resolution. Two embedded Raspberry Pi 3 compute modules are used for task management and wavefront reconstruction. The spacecraft is a 6U CubeSat (30 cm x 20 cm x 10 cm) and launch is planned for 2019.
The Deformable Mirror Demonstration Mission (DeMi) was recently selected by DARPA to demonstrate in-space operation of a wavefront sensor and Microelectromechanical system (MEMS) deformable mirror (DM) payload on a 6U CubeSat. Space telescopes designed to make high-contrast observations using internal coronagraphs for direct characterization of exoplanets require the use of high-actuator density deformable mirrors. These DMs can correct image plane aberrations and speckles caused by imperfections, thermal distortions, and diffraction in the telescope and optics that would otherwise corrupt the wavefront and allow leaking starlight to contaminate coronagraphic images. DeMi is provide on-orbit demonstration and performance characterization of a MEMS deformable mirror and closed loop wavefront sensing. The DeMi payload has two operational modes, one mode that images an internal light source and another mode which uses an external aperture to images stars. Both the internal and external modes include image plane and pupil plane wavefront sensing. The objectives of the internal measurement of the 140-actuator MEMS DM actuator displacement are characterization of the mirror performance and demonstration of closed-loop correction of aberrations in the optical path. Using the external aperture to observe stars of magnitude 2 or brighter, assuming 3-axis stability with less than 0.1 degree of attitude knowledge and jitter below 10 arcsec RMSE, per observation, DeMi will also demonstrate closed loop wavefront control on an astrophysical target. We present an updated payload design, results from simulations and laboratory optical prototyping, as well as present our design for accommodating high-voltage multichannel drive electronics for the DM on a CubeSat.
The nanosatellite optical downlink experiment (NODE) implements a free-space optical communications (lasercom) capability on a CubeSat platform that can support low earth orbit (LEO) to ground downlink rates>10 Mbps. A primary goal of NODE is to leverage commercially available technologies to provide a scalable and cost-effective alternative to radio-frequency-based communications. The NODE transmitter uses a 200-mW 1550-nm master-oscillator power-amplifier design using power-efficient M-ary pulse position modulation. To facilitate pointing the 0.12-deg downlink beam, NODE augments spacecraft body pointing with a microelectromechanical fast steering mirror (FSM) and uses an 850-nm uplink beacon to an onboard CCD camera. The 30-cm aperture ground telescope uses an infrared camera and FSM for tracking to an avalanche photodiode detector-based receiver. Here, we describe our approach to transition prototype transmitter and receiver designs to a full end-to-end CubeSat-scale system. This includes link budget refinement, drive electronics miniaturization, packaging reduction, improvements to pointing and attitude estimation, implementation of modulation, coding, and interleaving, and ground station receiver design. We capture trades and technology development needs and outline plans for integrated system ground testing.
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