Engineering topics

Sood, Rohan

Publications and source records attributed to Sood, Rohan.

5 records

NASA NTRS2021

Design of Solar Sailing Trajectories Resilient to Safe Mode Events

Solar sails are an enabling technology for stand-alone small-satellite deep-space exploration. However, their always-on nature, combined with the time of flight required for deep-space missions, makes them particularly susceptible to safe mode events. Unlike missions using electric propulsion, exclusively solar sail- ing missions cannot carry extra propellant to make up for a safe mode event, and more powerful methods like expected availability cannot be directly applied. This work extends the expected availability and duty cycle approaches to solar sailing. Through an application to NASA’s Solar Cruiser mission, a 46 % increase in tra- jectory resilience is obtained at negligible change in the mission’s time of flight. Additionally, it is shown that when a safe mode event stops the spacecraft from reaching its target orbit, the developed methods reduce the expected final error by approximately an order of magnitude.

Johnson, Les↗

NASA NTRS2021

Expected Thrust Fraction: Resilient Trajectory Design Applied to the Earth Return Orbiter

Electric propulsion is an enabling technology for NASA’s Mars Sample Return mission that affords an order of magnitude reduction in fuel. Unfortunately, elec- tric propulsion’s low-thrust capabilities require long thrusting arcs that make space- craft susceptible to disturbances resulting in missed thrust events. One method for designing trajectories resilient to such missed thrust events is expected thrust frac- tion, which embeds their stochastic nature into a time-varying duty cycle. This paper investigates the application of expected thrust fraction to the Earth Return Orbiter’s outbound Earth-to-Mars trajectory and compares it with trajectories de- signed using traditional methods to mitigate missed thrust events. Through the use of expected thrust fraction, a trajectory with a baseline 65.4% success rate is im- proved to an 86.6% success rate at the cost of only a 12 kg reduction in delivered mass. Additionally, when expected thrust fraction is used in conjunction with a terminal coast, a 96.0% success rate is achieved, which is higher than any single mitigation technique.

Laipert, Frank↗

NASA NTRS2020

Designing Trajectories Resilient to Missed Thrust Events Using Expected Thrust Fraction

With the adoption of efficient low-thrust propulsion methods, the probability of a missed thrust event occurring has become a significant concern for short and long- duration missions. If the missed thrust events take place during a critical portion of the trajectory, the mission can be compromised. Therefore, it is essential to de- velop trajectories that are resilient to missed thrust events. This paper investigates the use of expected thrust fraction, which embeds the stochastic nature of missed thrust events into a deterministic optimal control problem. The performance of trajectories designed using expected thrust fraction is compared with traditionally designed trajectories to measure changes in resiliency to missed thrust events. In this investigation, trajectories designed using expected thrust fraction arrive with a median lateness half that of traditionally designed trajectories. Using expected thrust fraction can help astrodynamicists mitigate risks posed by the use of low- thrust propulsion.

Laipert, Frank E.↗

NASA NTRS2020

Using Reinforcement Learning to Design Missed Thrust Resilient Trajectories

From ion thrusters to solar sails, spacecraft continue to adopt new and more efficient forms of propulsion. As these low-thrust propulsion meth- ods have become more prevalent, new challenges have arisen. Depending on the mission, low-thrust propulsion elements may need to thrust con- tinuously for days/months. During these thrusting periods, external fac- tors, such as a micro-meteoroid impact or a software glitch, may cause the spacecraft to prematurely cease its thrust stage. Half of all deep space missions enter a safe mode where they cannot thrust every four months. These missed thrust events can result in the complete loss of a space- craft for time-dependent trajectories like planetary rendezvous. This paper demonstrates how neural networks, trained using reinforcement learning, can autonomously correct for missed thrust events during an interplanetary trajectory.

Laipert, Frank E.↗

NASA NTRS2019

Neural Network Based Optimal Control: Resilience to Missed Thrust Events for Long Duration Transfers

A growing number of spacecraft are continuing to adopt new and more efficient forms of in-space propulsion. One shared characteristic of these high-efficiency propulsion techniques is their limited thrust capabilities. This requires them to thrust continuously for long periods of time, making the spacecraft susceptible to potential missed thrust events. This work demonstrates how neural networks can autonomously correct for missed thrust events during a low-thrust long-duration transfer trajectory. The research applies and tests the developed method to au- tonomously correct a Mars return trajectory. Additionally, methods for improving the response of neural networks to missed thrust events are presented and further investigated.

Laipert, Frank E.↗