Astronaut, IISc prof pitch for back-up control for safer re-entry

BENGALURU: Isro astronaut Group Captain Angad Pratap and Assistant Professor Jishnu Keshavan from IISc, are in the final phases of their research to demonstrate the viability of a manual control system as an additional safety measure during the critical atmospheric re-entry phase of a manned spacecraft returning to Earth.

The re-entry phase involves complex aerodynamics and narrow margins for error. Too steep an entry could lead to excessive heating, while too shallow a path risks the capsule skipping off the atmosphere. Pratap and Keshavan’s research focuses on a possible scenario of a failure in the primary automatic Navigation, Guidance and Control (NGC) system of a crew module during re-entry.

To address this, the team explored whether an astronaut could manually guide the spacecraft in such conditions with support from a partially degraded NGC system. Their system is not being designed to replace the primary NGC architecture but to complement it.

The objective of automated guidance during re-entry is to ensure accurate tracking of a predefined reference trajectory all the way to touchdown. This requires designing a guidance law capable of countering potential disturbances that could otherwise alter the spacecraft’s descent profile and cause deviations from the intended landing point—an outcome that must be avoided in practice.

As per the abstract of their research presented at the recently concluded Global Space Exploration Conference (GLEX-2025), to mitigate this possibility, the study explored the feasibility of incorporating “a novel bank-angle based manual control scheme in a manned spacecraft during re-entry in the atmospheric altitudes of 120km - 10 km”.

“Bank-angle manipulation” used here is the same fundamental principle employed by automated systems, but adapted for human operation, as per the abstract titled “Robust Manual Guidance Law For Manned Spacecraft Re-Entry Applications”.

Using sophisticated 6-DOF (six degree-of-freedom) modelling incorporating both translational and rotational dynamics, researchers demonstrated that human pilots could successfully guide a representative manned spacecraft from re-entry altitude to parachute deployment while maintaining all critical parameters within safe limits.

Manual mode is proposed as an additional backup to the multiple chains of automated modes of reentry control in case of the flight profile either exceeding predefined perturbation models, or identical failure across all automated control chains.

Incorporating this additional degree of manual redundancy may enhance mission reliability for the crew capsule. The manual control scheme was explored from the standpoint of guiding the manned spacecraft manually from a predefined reentry altitude to the terminal altitude thus guaranteeing subsequent touchdown at the predefined target location.

The study describes the design and testing of a “reduced-order” flight display and manual control setup intended for emergency use. Drawing from operational precedents such as Nasa’s Apollo missions, the system provides a pilot with essential information through an intuitive interface. This would allow the crew to steer the capsule towards a pre-designated landing area, even in the absence of automated controls.