[MTech(Res) Colloquium] Inflatable aerodynamic decelerators for atmospheric re-entry

Atmospheric re-entry is the most challenging part of human space flight. In the re-entry phase of flight, the crew module (or re-entry vehicle) is required to bring the onboard astronauts from orbital velocities, which are in the range of several kilometers per second, to near-zero velocity at touchdown, in a safe and controlled manner. The crew module experiences severe aerodynamic heating and large deceleration loads (g-forces) as it descends into the atmosphere at high hypersonic velocities. Re-entry poses formidable engineering challenges, and also places great physical and mental demands on astronauts.

The re-entry crew module of the Gaganyaan space program follows a positive L/D (aerodynamic lift to drag ratio) descent trajectory that is established through an offset CG (center of gravity) design. Reaction thrusters provide roll, pitch, and yaw control. The design and philosophy of the Gaganyaan crew module is similar to that of the Soyuz crew module. However, the Soyuz crew module additionally incorporates a ballistic descent mode for use during off-nominal (emergency) situations. Ballistic descent requires a zero L/D condition, which is achieved by Soyuz through a continuous rotation of the crew module at the rate of 13 degrees per second. The Gaganyaan crew module does not presently incorporate such a feature.

The present effort is aimed at developing the concept of inflatable aerodynamic decelerators (IADs) to achieve standby ballistic mode capability, and to also reduce deceleration and aerodynamic heating loads during routine re-entry (or entry to other planetary atmospheres). The aerodynamic characteristics of a canonical re-entry body – crew module with an IAD – at hypersonic Mach numbers is studied through flow computations (using Reynolds-averaged Navier–Stokes equations) and wind tunnel experiments. The L/D of the re-entry body is varied by changing its CG location, which is achieved by altering the relative position of the IAD with respect to the crew module. The default re-entry body configuration is set for a positive L/D, which significantly limits deceleration and aerodynamic heating loads. The L/D is brought to zero to achieve ballistic re-entry in an off-nominal situation. Using the aerodynamic data obtained from flow computations and experiments, the advantages of using an IAD for re-entry are quantitatively assessed and demonstrated through trajectory analysis. A preliminary engineering feasibility study for the proposed concept is also presented in this thesis.