arXiv subjects

Simran Agarwal

Publications and source records attributed to Simran Agarwal.

4 recordsLinked to original sources

arXiv2026

Tiny Observatory for Telescope Optimization (TOTO): testing algorithms for autonomous on-orbit alignment for space-based telescope systems

The Tiny Observatory for Telescope Optimization (TOTO) is an optical testbed designed to evaluate the efficacy of autonomously driven alignment algorithms for space-based telescope systems. For space-based missions, active control of the telescope alignment on-orbit offers potential to relax passive alignment requirements and reduce on-ground verification activities. TOTO is used to evaluate and verify simulation work of two primary alignment algorithms, Stochastic Parallel Gradient Descent (SPGD) and focus-diverse phase retrieval (FDPR). Previous simulation work has confirmed that by using SPGD for coarse alignment followed by focus-diverse phase retrieval for fine alignment, we can reach diffraction-limited performance on-orbit. This paper presents the results of the autonomous alignment algorithm of a Cassegrain telescope using TOTO. We report the current status of TOTO as well as preliminary results from SPGD and phase retrieval on the testbed using monochromatic light source to simulate an on-axis point source.

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arXiv2026

Testing of machine learning wavefront sensing algorithms on the Tiny Observatory for Telescope Optimization (TOTO) testbed

Phase retrieval techniques are utilized to correct low order wavefront aberrations originating from misalignments of the optical system in space based telescope concepts. Traditional phase retrieval involves observation of the Point Spread Function (PSF) and a diversity measurement, usually focus diversity although other measures are possible, to reconstruct the incident wavefront at the science detector. We consider a Machine Learning model trained originally on simulated data, and then augmented with real focus diversity data from the Tiny Observatory for Telescope Optimization (TOTO) testbed at the University of Arizona. We then compare the wavefront sensing performance of the Machine Learning model with known truth values of the generated dataset. The model predictions for low order Zernikes on TOTO data after training and validation show a reasonable agreement with the true Zernike coefficients.

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arXiv2024

Optical alignment of contamination-sensitive Far-Ultraviolet spectrographs for Aspera SmallSat mission

Aspera is a NASA Astrophysics Pioneers SmallSat mission designed to study diffuse OVI emission from the warm-hot phase gas in the halos of nearby galaxies. Its payload consists of two identical Rowland Circle-type long-slit spectrographs, sharing a single MicroChannel plate detector. Each spectrograph channel consists of an off-axis parabola primary mirror and a toroidal diffraction grating optimized for the 1013-1057 Angstroms bandpass. Despite the simple configuration, the optical alignment/integration process for Aspera is challenging due to tight optical alignment tolerances, driven by the compact form factor, and the contamination sensitivity of the Far-Ultraviolet optics and detectors. In this paper, we discuss implementing a novel multi-phase approach to meet these requirements using state-of-the-art optical metrology tools. For coarsely positioning the optics we use a blue-laser 3D scanner while the fine alignment is done with a Zygo interferometer and a custom computer-generated hologram. The detector focus requires iterative in-vacuum alignment using a Vacuum UV collimator. The alignment is done in a controlled cleanroom facility at the University of Arizona.

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arXiv2022

FIREBall-2: flight preparation of a proven balloon payload to image the intermediate redshift circumgalactic medium

FIREBall-2 is a stratospheric balloon-borne 1-m telescope coupled to a UV multi-object slit spectrograph designed to map the faint UV emission surrounding z~0.7 galaxies and quasars through their Lyman-alpha line emission. This spectro-imager had its first launch on September 22nd 2018 out of Ft. Sumner, NM, USA. Because the balloon was punctured, the flight was abruptly interrupted. Instead of the nominal 8 hours above 32 km altitude, the instrument could only perform science acquisition for 45 minutes at this altitude. In addition, the shape of the deflated balloon, combined with a full Moon, revealed a severe off-axis scattered light path, directly into the UV science detector and about 100 times larger than expected. In preparation for the next flight, and in addition to describing FIREBall-2's upgrade, this paper discusses the exposure time calculator (ETC) that has been designed to analyze the instrument's optimal performance (explore the instrument's limitations and subtle trade-offs).

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