The proposed concept uses sensors to detect high-temperature plasma ingestion during entry through a breach in the thermal protection system (TPS) caused by a micrometeoroid orbital debris (MMOD) impact. It uses consumables usually available on human-rated spacecraft such as gaseous nitrogen (or helium) and water to maintain spacecraft structural integrity by keeping it within the temperature limits via an evaporative cooling effect and to equalize the internal and external pressures to prevent high-temperature plasma from flowing further into unintended areas. Once a breach was detected, the system could be activated autonomously or manually by the flight crew, or by telemetry from the ground crew.
The current technology to prevent ingestion of high-temperature plasma through a breach in the TPS is the repair method developed as part of return-to-flight after the Columbia accident. These on-orbit repair methods require significant support from the ground and the flight crews via training, detection, inspection, real-time analyses, and extra vehicular activities (EVAs).
A first proof-of-concept test was performed with gaseous nitrogen to prevent plasma ingestion in a relevant convective heating environment. Tests were performed on March 21, 2014 at Johnson Space Center’s Atmospheric Re-entry Materials and Structures Evaluation Facility on a test article designed with 0.25-in. (≈6.4-mm) diameter hole to simulate a TPS breach caused by an MMOD impact. Four constant heat flux and pressure conditions representative of a typical reentry environment were tested. Heat flux and pressure inside the cavity were measured. For all four conditions, immediately following injection of gaseous nitrogen into the cavity where internal pressures were slightly higher than those external, the heat flux inside the cavity dropped to near zero. The concept that ingestion of high-temperature plasma through a small breach could be prevented by providing adequate counter pressure was therefore validated. Water injection to provide additional cooling was out of scope for this first proof-of-concept test.
This technology would enhance crew survival probability where damage detection, inspection, repair, and/or crew rescue options are not available. By improving crew safety and overall vehicle reliability, this technology would enable routine and affordable access to space.
This work was done by Vuong T. Pham and Melissa D. Flores of Johnson Space Center, and James D. Milhoan and Geoffrey Degraff of Barrios Technology, Inc. MSC-25369-1