Entry Navigation Sensor (ENS)

Hypersonic entry at Mars relies exclusively on IMU (Inertial Measurement Unit) measurements for onboard navigation.  Enabling precision landing of human-class and high-mass robotic Mars vehicles will require improved navigation from longer ranges to enable earlier decisions within guidance systems to trigger phase transitions and executive control maneuvers that steer out landing dispersions.  The purpose of this study is to investigate the potential for using off-body optical sensing techniques during entry to provide direct measurement of freestream density and/or wind speed to use within onboard navigation.  Part of this study will focus on the technology advancements necessary to reduce the size, weight, and power of sensing technologies for deployment onboard an entry vehicle.  The research will also determine and then improve the performance specifications of this Entry Navigation Sensor (ENS), including measurement accuracy, precision, spatial resolution, latency, repetition rate and operational regimes (altitudes and atmospheres).  Furthermore, locating placement of the sensor on different vehicle types (e.g. capsule vs mid L/D) will be assessed.  These studies will be coupled with predictive models used to assess vehicle entry trajectories to determine how to optimize the impact of the new sensor technology to enhance vehicle performance.   This study directly addresses a technology gap within a highly-ranked LAND shortfall and has applicability to Artemis and science missions to Mars or any atmospheric body, including Earth hypersonic re-entry.  Entry into Uranus' atmosphere is also a potential application mission.  The outcome of this study will inform a follow-on project formulation to implement and flight test an entry navigation sensor.

In missions involving atmospheric entry, aero-breaking or aerocapture, the atmospheric density and the vehicle speed relative to the surrounding atmosphere are not directly measured owing to lack of suitable instrumentation.   On Earth, the atmospheric density can vary by as much as 80% depending on the day, time of day, and on solar activity. Mars has similar swings in gas density which vary by an order of magnitude at high altitudes (e.g. 70-130 km).  These large density –  and also velocity – excursions affect vehicle drag and lift characteristics and are recognized by NASA as one of the major challenges to aerocapture.   Onboard sensors that can measure gas density and/or relative velocity in real time, for the purpose of navigation and control, would reduce mission risk and improve vehicle performance.  Real-time measurements would improve landing precision in Martian and Earth entries and potentially enable new missions to enter into unknown or unknowable atmospheres.

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