A Morphing Radiator for High-Turndown Thermal Control of Crewed Space Exploration Vehicles

Abstract

Spacecraft designed for missions beyond low earth orbit (LEO) face a difficult thermal control challenge, particularly in the case of crewed vehicles where the thermal control system (TCS) must maintain a relatively constant internal environment temperature despite a vastly varying external thermal environment and despite heat rejection needs that are contrary to the potential of the environment. A thermal control system may be required to reject a higher heat load to warm environments and a lower heat load to cold environments, necessitating a relatively high turndown ratio. A modern thermal control system is capable of a turndown ratio of on the order of 12:1, but crew safety and environment compatibility have constrained these solutions to massive multi-loop fluid systems. This paper discusses the analysis of a unique radiator design that employs the behavior of shape memory alloys (SMAs) to vary the turndown of, and thus enable, a single-loop vehicle thermal control system for space exploration vehicles. This design, a morphing radiator, varies its shape in response to facesheet temperature to control view of space and primary surface emissivity. Because temperature dependence is inherent to SMA behavior, the design requires no accommodation for control, instrumentation, or power supply in order to operate. Thermal and radiation modeling of the morphing radiator predict a turndown ranging from 11.9:1 to 35:1 independent of TCS configuration. Coupled thermal-stress analyses predict that the desired morphing behavior of the concept is attainable. A system level mass analysis shows that by enabling a single loop architecture this design could reduce the TCS mass by between 139 kg and 225 kg. The concept has been demonstrated in proof-of-concept benchtop tests.

An experimentally-fitted thermodynamical constitutive model for polycrystalline shape memory alloys

“…3. Analysis of the system (17)- (19). In this section, we show that the model devised in Section 2 is mathematically well-posed in the sense that it possesses weak solutions and simultaneously we devise a stable and convergent approximation.When scrutinizing a suitable notion of weak solutions, we have to deal with doubly-nonlinear structure of the balance equations for the mechanic variables; cf.…”

“…We will prove existence of weak solutions in the sense of Definition 1 to the system (17)- (19) in two steps. First, using a small parameter η > 0, we regularize the right-hand side of the heat equation to make it uniformly bounded.…”

“…with the boundary/initial conditions (18)- (19) written now for (u η , π η , ξ η , θ η ) instead of (u, π, ξ, θ), where the dissipation rate r is from (14) and where ζ • is a difference quotient approximating ∂ ξ ζ, defined as…”

“…and every such (u, π, ξ, θ, w) is a weak solution to the initial-boundary value problem (17)- (19) due to Definition 1.…”

“…[57,17,18] for overviews. Nevertheless, from the point of view of applications, in particular in medical devices [30], automotive industry [37] or in space exploration [19], models for polycrystalline materials that allow for numerically stable and convergent discretization schemes, efficient computer implementation, and for usage of fast algorithms, as well as for easy adaptation of material parameters are particularly desired. Hence, a large number of such models has been proposed to date, e.g.…”