1991-07-01

Hermes Thermal Control Design and Architecture 911449

The aim of this paper is to present the Hermes Thermal Control Concept which constitutes the reference baseline for the phase 2 of the Hermes program.
The technical solutions based on active and passive means, are dictated by a variety of requirements including temperature and heat flux limits, mass & power minimization, availability of space for accommodation of TCS devices.
Furthermore thecomplex mission profile (including atmospheric flight and several modes of operation o002d;orbit) and the configuration of the space-vehicle, require the adoption of a particularly flexible thermal control.
The ATCS (Active Thermal Control Section) is based on a dual loop concept, using both water and Freon R114 cooling loops for heat collection from the various sources, heat transportation and heat rejection through dedicated devices.
The main heat sources to be considered are those extracted from the cabin air loop, the electronics, the power generation items (fuel cells and lithium batteries) and the environmental loads during ascent and re-entry.
The major heat rejection devices are the Ground Support Equipment Heat Exchangers (on ground, before launch and after landing), the Ammonia Boilers during ascent or re-entry (low altitude), the Hermes Radiators on orbit, the Water Evaporators during ascent and re-entry (high altitudes) and to complement the radiator rejection capability.
The PTCS (Passive Thermal Control Section) relies on different concepts of insulations together with a system of temperature sensors and heaters, to control the thermal excursions of the space-plane components and structural parts, within the specified limits.
Thermal insulation blankets (foams, thermal control coatings, multi layer insulations) involve an extensive material research and testing activity, since they are subjected to quite different conditions: vacuum, atmospheric, internal, external and very different level of temperatures depending on the location.
The present design of the Thermal Control Subsystem is oriented to the minimization of mass and power budgets and to respect the quantitative and qualitative safety and reliability requirements.

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