Inflatable Aerodynamic Decelerators for Atmospheric Re-entry
Abstract
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.
A typical re-entry crew module 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 Soyuz crew module is a good example of
this design philosophy. Additionally, the Soyuz crew module 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◦/s. It is noted that not all re-entry crew modules, past
and present, 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
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