SmallSat Aerocapture to Enable a New Paradigm of Planetary Missions

Abstract

This paper presents a technology development initiative focused on delivering SmallSats to orbit a variety of bodies using aerocapture. Aerocapture uses the drag of a single pass through the atmosphere to capture into orbit instead of relying on large quantities of rocket fuel. Using drag modulation flight control, an aerocapture vehicle adjusts its drag area during atmospheric flight through a single-stage jettison of a drag skirt, allowing it to target a particular science orbit in the presence of atmospheric uncertainties. A team from JPL, NASA Ames, and CU Boulder has worked to address the key challenges and determine the feasibility of an aerocapture system for SmallSats less than 180kg. Key challenges include the ability to accurately target an orbit, stability through atmospheric flight and the jettison event, and aerothermal stresses due to high heat rates. Aerocapture is a compelling technology for orbital missions to Venus, Mars, Earth, Titan, Uranus, and Neptune, where eliminating the propellant for an orbit insertion burn can result in significantly more delivered payload mass. For this study, Venus was selected due to recent NASA interest in Venus SmallSat science missions, as well as the prevalence of delivery options due to co-manifesting with potentially many larger missions using Venus for gravity assist flybys. In addition, performing aerocapture at Venus would demonstrate the technology's robustness to aerothermal extremes. A survey of potential deployment conditions was performed that confirmed that the aerocapture SmallSat could be hosted by either dedicated Venus-bound missions or missions performing a flyby. There are multiple options for the drag skirt, including a rigid heat shield or a deployable system to decrease volume. For this study, a rigid system was selected to minimize complexity. A representative SmallSat was designed to allocate the mass and volume for the hardware needed for a planetary science mission. In addition, a separation system was designed to ensure a clean separation of the drag skirt from the flight system without imparting tipoff forces. The total spacecraft mass is estimated to be 68 kg, with 26 kg of useful mass delivered to orbit for instruments and supporting subsystems. This is up to 85% more useful mass when compared to a propulsive orbit insertion, depending on the orbit altitude. Key to analyzing the feasibility of aerocapture is the analysis of the atmospheric trajectory, which was performed with 3 degree-of-freedom simulations and Monte Carlo analyses to characterize the orbit targeting accuracy. In addition, aerothermal sizing was performed to assess thermal protection system requirements, which concluded that mature TPS materials are adequate for this mission. CFD simulations were used to assess the risk of recontact by the drag skirt during the jettison event. This study has concluded that aerocapture for SmallSats could be a viable way to increase the delivered mass to Venus and can also be used at other destinations. With increasing interest in SmallSats and the challenges associated with performing orbit insertion burns on small platforms, this technology could enable a new paradigm of planetary science missions.

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