Autonomous Navigation using Gravity Gradient Measurements

The proposal is to study the efficacy of a new orbit determination method, using gravity gradient measurements, for Low-Earth-Orbiting satellites. Based on the study of gravity gradient measurement error models, and orbit determination estimation techniques, we aim to apply Linear Covariance technique to determine the optimal onboard sensor requirement, and hence intend to improve the accuracy of the given method. Improvement in accuracy for this innovative technique can help usher a new autonomous satellite navigation system, which will be completely independent of GPS navigation system. Although, the technology involved in measuring gravity gradients has been in use, since 1960s, for many airborne and terrestrial surveys, the technology has matured over the recent years and, the requisite instruments have been improved and upgraded. Because of this, there has been a renewed interest in space applications for this technique. Recent missions like European Space Agency’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) launched in March 2009, and NASA’s Gravity Recovery and Climate Experiment (GRACE) launched in March 2002, are relevant example for this

Revolution in Autonomous Orbital Navigation (RAON)

Spacecraft navigation is a critical component of any space mission. Space navigation uses on-board sensors and other techniques to determine the spacecraft’s current position and velocity, with permissible accuracy. It also provides requisite information to navigate to a desired position, while following the desired trajectory. Developments in technology have resulted in new techniques of space navigation. However, inertial navigation systems have consistently been the bedrock for space navigation. Recently, the successful space mission GOCE used on-board gravity gradiometer for mapping Earth’s gravitational field. This has motivated the development of new techniques like cold atom accelerometers, to create ultra-sensitive gravity gradiometers, specifically suited for space applications, including autonomous orbital navigation. This research aims to highlight the existing developments in the field of gravity gradiometry and its potential space navigation applications. The study aims to use the Linear Covariance Theory to determine specific sensor requirements to enable autonomous space navigation for different flight regimes

Assessment of Evolving Conjunction Risk for Small Satellite Missions

This study presents an assessment of evolving conjunction risk for small satellite missions (5U or smaller) by using the suite of LeoLabs\u27 products. The aim is to (1) quantify the growth of small satellites population in the low Earth orbit (LEO), (2) assess the impact of on-orbit break-up events and small debris (sub-10 cm) objects on small satellite missions, and (3) present an optimal risk mitigation timeline for small satellite missions, based on conjunction alerts issued in 2023. The global network of S-band radars built and operated by LeoLabs provides a 24/7 data feed to power this assessment and help identify the evolution of this risk. The ability to access this enhances operational safety. Thus, a statistical assessment of the risk posed and quantification of the evolution of this risk over mission timeline is important. Further, understanding the optimal risk mitigation timeline for small satellite missions is critical as these missions have limited on-board resources and hence, knowing the severity of the risk and taking appropriate and timely mitigative action (attitude change or thrusting \u27n\u27 days before time of closest approach, i.e., TCA) is paramount. Although, the mitigative action (the level and duration of thrusting or the amount of attitude change) itself is not studied as these specifics often vary based on the event type, the optimal timeline (as in how many days before TCA?) of this mitigative action is reviewed by studying the conjunction events encountered by small satellites