Analysis of Salient Events from the Two-Phase Flow (TPF) Thermal Control Flight Experiment

The Two Phase Flow (TPF) Thermal Control Flight Experiment is an integrated two-phase thermal control system designed to address capillary pumped loop (CPL) component and system performance issues in the microgravity environment of space. The TPF experiment was flown aboard the Space Shuttle Discovery (STS-85) in August 1997 as part of the Technology Applications and Science-01 (TAS-01) mission.

Ground and flight tests were performed to demonstrate reliable system start-up from the flooded state and sustained operation under various heat loads and conditions. Use of any of the large evaporator elements as a sacrificial starter pump in conjunction with the capillary vapor flow valve (CVFV) resulted in successful system start-up subsequent to which normal operation was demonstrated for an extended period of time. As expected, start-up from the flooded state with smaller evaporator elements was consistently unsuccessful.

Oscillations of the pressure differential across the pumping menisci were strongly affected by gravity. Significant oscillation amplitudes recorded during ground tests diminished to negligible levels in microgravity. Periodic spikes of the temperature at the liquid inlet-end of the evaporator elements observed on the ground were absent during flight tests.

It is recommended that a reflight be performed with TPF hardware modified to include a dedicated starter pump. The goal is to demonstrate complete reliability of a generic multiple evaporator CPL thermal control system in microgravity.