Daniel Jacobs

CubeSats developed at universities seldom have propulsion due to cost and complexity constraints and are very commonly deployed from the ISS into orbits where atmospheric drag is significant. Without propulsion, the time to re-entry is a function of the cross section to mass ratio and the space weather. Many cubesats have limited ways of decreasing ram cross section, e.g. pointing into the wind. Hard radiation from solar activity inflates the atmosphere and increases drag. Since the beginning of the cubesat era, the Sun has been unusually quiescent, at a level not seen for 200 years, which has biased expectations for mission lifetimes. The current solar maximum is higher than the previous and has reduced the lifetime of LEO satellites. DORA was a joint mission supported by NASA, JPL, ASU’s Low frequency Cosmology and the Interplanetary Lab with help from Amateur radio operators. The satellite was a platform for experiments in the related fields of communications and radio astronomy. The spacecraft was built by students and amateur radio operators local to the Phoenix area and launched in August of 2024, as the solar max was well underway. The spacecraft was released in October and before the end of November 2024, it had re-entered. This paper investigates the DORA’s trajectory as it descended from the ISS orbit to re-entry in 54 days. We compare the actual trajectory to various analyses including the Space Mission Analysis and Design method, STK simulation and compare with estimates provided by NASA CSLI/KSC DAS. We find that, while these models all perform well, they do rely on forecasts of solar activity. Such a forecast must be made at the mission formulation phase, which for DORA was done when solar maximum was five years in the future. We recommend that future missions deploying below 500 km consider space weather variability as a risk to mission success and include a worst-case level.

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ABSTRACT Detection of the faint 21 cm line emission from the Cosmic Dawn and Epoch of Reionization will require not only exquisite control over instrumental calibration and systematics to achieve the necessary dynamic range of observations but also validation of analysis techniques to demonstrate their statistical properties and signal loss characteristics. A key ingredient in achieving this is the ability to perform high-fidelity simulations of the kinds of data that are produced by the large, many-element, radio interferometric arrays that have been purpose-built for these studies. The large scale of these arrays presents a computational challenge, as one must simulate a detailed sky and instrumental model across many hundreds of frequency channels, thousands of time samples, and tens of thousands of baselines for arrays with hundreds of antennas. In this paper, we present a fast matrix-based method for simulating radio interferometric measurements (visibilities) at the necessary scale. We achieve this through judicious use of primary beam interpolation, fast approximations for coordinate transforms, and a vectorized outer product to expand per-antenna quantities to per-baseline visibilities, coupled with standard parallelization techniques. We validate the results of this method, implemented in the publicly available matvis code, against a high-precision reference simulator, and explore its computational scaling on a variety of problems.

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