Testing

Testing of descent control systems is notoriously difficult, since it is hard to reach the conditions of aerodynamic similarity (Mach and Reynolds number). Arguably more important even than these, since parachute inflation relies on interactions between the flowfield and the parachute itself, is dynamic pressure.

Validation of the aerodynamic stability of the DS-2 entry vehicles was performed largely by computational fluid dynamics studies, augmented by only a couple of wind-tunnel tests.

Note that good sets of aerodynamic coefficients, as a function of incidence angle and Mach number, are required not only for accurate trajectory predictions, but also for precision in the recovery of the atmospheric density profile from entry accelerometer measurements.

Mars - retro-rockets in atmosphere

Full parachute systems tests therefore require lofting the test assembly to considerable altitude (40 km). Such range tests require extensive preparation of the test articles and range instrumentation, as well as good luck with the weather. If the test fails, isolation and elimination of the failure mechanism may take time and require one or more further tests, putting the project schedule in jeopardy.

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