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Japan Aerospace Exploration Agency

Technology for testing re-entry capsule aerodynamics

The future of Japan’s manned space activities hinges on safe, reliable technologies for re-entry and return procedures. With that need clearly in mind, researchers are working hard on an HTV-R that improves the functionality of HTV space station transfer vehicles in hopes of not only resupplying the International Space Station (ISS) but also securing recovery methods. HRV, the HTV-R’s atmospheric re-entry module, is a capsule that performs lifting re-entry to minimize the dispersion of the splashdown area. To develop a capsule-shaped atmospheric re-entry vehicle, engineers need to predict and evaluate the vehicle’s aerodynamic characteristics in the various conditions of the re-entry process.

This study aims to support HTV-R research by ensuring the necessary testing capabilities for predicting the wide array of aerodynamic characteristics that the phases of re-entry bring about.

The first steps are to create ways of predicting the aerodynamic interference characteristics created by RCS (reaction control systems) in re-entry capsules (Figure 1), establish support interference correction technologies for use in supersonic ranges, propose and verify Reynolds (Re) number correction methods for use in transonic and subsonic ranges (Figure 2), and determine the aerodynamic interference generated by model supports in supersonic ranges.

Figure 1: Using RCS interference field measurement technology to enhance CFD verification and improve predictions of actual aircraft characteristics

Figure 2: A transonic wind tunnel test for improving evaluations of aerodynamic characteristics in actual aircraft at high Reynolds numbers; using this data, JAXA proposes and verifies correction methods

The second steps are to assess the aerodynamic dynamic stability that re-entry capsules often experience at transonic speeds. Even with a statically stable configuration, small angular oscillation around a trim angle might grow infinitely by aerodynamic moment induced by the dynamic motion of the capsule. This is a phenomenon called dynamic instability. Although the capsule deploys the recovery parachute to land on the earth, it is difficult to deploy it in supersonic speed. A lifting capsule with an offset center of gravity from its symmetric axis can perform accurate guidance and control for the landing point. However, it requires flight control down to transonic speed, which makes it necessary to estimate dynamic stability characteristics at transonic speed. To estimate dynamic stability of the capsule, wind tunnel tests, ballistic range-based free flight tests, and unsteady CFD are attempted and their effective combination is discussed.

A wind tunnel test to estimate the dynamic stability
characteristics of the HTV-R reentry capsule