Computational complexities of image plane algorithms for high contrast imaging in space telescopes

Abstract

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 10 9 . 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 ∼10 13 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 10 10 contrast might require up to several orders of magnitude more computational throughput than available on the most advanced radiation-hardened processor.

High-contrast Jacobian-free wavefront control: simulations, experimental results, and extensions to adaptive control

“…6 2.1 Computational demands of Jacobian-based and Jacobian-free algorithms and impact on Habitable Worlds Observatory Recently, Pogorelyuk et al completed a study of the computational demands of an assortment of HOWFSC algorithms relevant to HWO, under realistic assumptions about the number of DM actuators, controlled focalplane pixels, and hardware resources available to a radiation-hardened flight computer by a projected launch date of 2040. 19 A primary finding of this study was that Jacobian-based algorithms are most likely infeasible for deployment aboard HWO's flight computers, due to the constraints of implementation on radiation-hardened processors, which generally lag behind commercially-available hardware by a decade or more. Adoption of Jacobian-based methods as the baseline for HWO will necessitate a ground-in-the-loop architecture, as described in Section 1, or a more exotic computing architecture such as a collection of co-flying processors aboard separate spacecraft near HWO's nominal orbit at the L2 Lagrange point.…”

“…Conversely, for the most operation-lean implementation of Jacobian-based EFC, ADWC was estimated to require 5× fewer floating-point operations and 20,000× less storage. 19 There are both advantages and disadvantages to adopting an architecture in which HOWFSC processing is performed fully on flight computers as compared to a ground-in-the-loop scheme. With an on-orbit architecture, by eliminating the round-trip communication of ground-in-the-loop, the HOWFSC loop can theoretically update more frequently, and can also operate during communication blackouts where the telescope has no ground communications at all.…”

Evaluating embedded hardware for high-order wavefront sensing and control

“…Our previous work 13 has tabulated the expected computational requirements of HOWFSC onboard HabEx and LUVOIR and compared these requirements to the processing capability of the following CPU processors: BAE RAD5545, Teledyne LS1046-Space, SnapDragon855, NXP LX2160A. These processor represent a range of tolerance to radiation effects from radiation hardened by design (RHBD) to non-radiation-hardened commercialoff-the-shelf (COTS).…”

“…The range of parameters considered for this work is summarized in Table 1 and is based on the HabEx and LUVOIR studies. 13 Table 1: High contrast imaging system parameters for computational requirements 13…”

“…The RAD5545 has been a primary focus of previous analysis of HOWFSC computation on embedded processors. 13,37 The RTG4 FPGA manufactured by MicroSemi is a radiation tolerant FPGA released in 2015. The device has been tested up to 100s of krad(Si), 38 and is now used in standard spacecraft computing components.…”