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Test Facilities Guide

Engineering Test Facilities Guide

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Radiant Heat Test Facility

    Photo credit: NASA

    The Johnson Space Center constructed the Radiant Heat Test Facility (RHTF) in 1975 to perform development and certification tests for the Orbiter thermal protection system (TPS). This facility has been maintained continuously to the present time to support sustaining engineering of the Orbiter and other NASA test programs such as the Aerobraking Flight Experiment and X-33. The facility has two test chambers, R1 and R2. These test chambers are both equipped with graphite element heaters that develop higher heat fluxes that those available with quartz lamp banks.

    Radiant Heat Test Chamber 1

    Radiant Heat Test Chamber 1
    Photo credit: NASA

    Radiant Heat Test Chamber 1 is 10’ in diameter and 18’ long. End bells on each end of the chamber add another 26” to its length. This facility can be configured to test wing panels with up to 22 separately controlled heater zones with the heaters arranged in a curved configuration to follow the wing contour. These heaters can also be arranged in a flat panel array, measuring 74” x 110”. The heaters are approximately 5” wide can be configured for either a 48” length or a 74” length. Since the heater elements are graphite they must be run in either a vacuum or Nitrogen environment. CVD silicon carbide coated heater elements have been used to allow operation in an air environment, but their use presents a very great increase in costs with diminished reliability. The heater arrays have the capability to easily achieve 2600 degrees F and well beyond, depending on the makeup of the test article.

    Radiant Heat Test Chamber 2

    Radiant Heat Test Chamber 2
    Photo credit: NASA

    R2 is 92” in diameter and 92” long. A graphite heater with a coated columbium susceptor is mounted in the top of the chamber with the heated source side oriented downward. This chamber/heater combination can simulate launch pressure decay, on orbit cold-soak, and re-entry heating and pressure environments. A water-cooled shutter may be inserted between the heater and test article to allow the heater to be pre-warmed before the test article is exposed or to assist in the more rapid cool down of the test article. Temperatures up to 2600 degrees F may be achieved with the susceptor in place, allowing the surrounding atmosphere to be air. If a Nitrogen atmosphere is used the susceptor may be removed and temperatures approaching 2900 degrees F can be induced, depending on the type of test article.

    The thermal responses of all Orbiter TPS tile materials have been determined in this chamber before they have been qualified to fly. Normally arrays of nine 6” x 6” tiles are run at constant surface temperature and pressure levels while the thermal gradients are recorded by in-depth thermocouple stacks that are installed in some of the tiles. Through an iterative analytical approach thermal properties for the tiles are postulated, then re-entry surface temperature and pressure profiles are applied to the array and the temperature responses of the tile back plates are then compared to the predicted values.

    This chamber was utilized heavily during the X-33 TPS development. Clipped hardware of Carbon-Carbon panels and metallic panels were run that were representative of joint interfaces and seals between Carbon-Carbon and Inconel honeycomb panels. Unique tests were performed that were unsuccessfully attempted by several other labs. Some of these tests were performed to determine the joint conductance of mounting hardware for Carbon-Carbon hardware thermal math models. During these joint conductance tests the interiors of the test articles were filled with fibrous insulation to block radiation heat transfer and the surface temperature was maintained constant within a few degrees for several hours until thermal equilibrium was reached. Other tests were run for curved metallic panels in which highly variable pressure differentials were applied across the panels while simultaneously following re-entry pressure/temperature profiles. Deflections of the curved panels were recorded with linear variable differential transformers (LVDT) along with numerous thermocouple connector readings.

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