Variable Emissivity Materials For Spacecraft

Technology Roadmap Sections and Deliverables

• 4VEM - Variable Emissivity Materials for Spacecraft

Thermochromic variable emissivity materials (VEMs) can be used for a wide range of applications, from spacecraft radiators to windows used on Earth. For this technology roadmap, the use of VEMs for spacecraft radiators will be the focus.

Roadmap Overview

The only way that orbiting spacecraft can reject heat is through radiation. Because of this, the thermo-optical properties of spacecraft radiators are important. The thermo-optical properties of radiators, such as emissivity, determine how much heat is radiated away.

There is a way to calculate how much heat is radiated from a surface, and it is shown in the equation below. Q is heat being radiated away from a surface, A is the area of the radiating surface, σ is the Stefan-Boltzmann constant, ε is the emissivity of the surface material, and T is the temperature of the surface.

Q=A\sigma\varepsilon T^4

The emissivity of

Figure 1: Diagram of how VEMs affect spacecraft, from [1]

Satellite-based internet/voice access is enabled by satellites, which provide relay to extend communication beyond traditional (terrestrial) line of site of the network and users. Data encoded in radio waves is sent from the ground station, relayed via the satellite, to the user’s location. Advances in technology include High Throughput Satellites (HTS) and some next-generation satellite systems may follow low-earth orbit rather than geosynchronous orbits, which would reduce latency dramatically.

Design Structure Matrix (DSM) Allocation

The 2-SDC tree that we can extract from the DSM above shows us that Satellite Data Communication (2SDC) is part of a larger abstraction of wireless duplex communication (1WDC), and that it requires the following key enabling technologies at the system level:

• 3SCP Satellite Communication Payload
• 3SGT Satellite Gateway Terminal
• 3USM User Satellite Modem
• 3UST User Satellite Terminal

In turn these require enabling technologies at level 4, the technology subsystem level:

• 4SRA Satellite Receive Antenna
• 4STA Satellite Transmit Antenna
• 4SCE Satellite Communication Electronics
• 4SGA Satellite Gateway Aperture
• 4GTE Gateway Transmit Electronics
• 4GRE Gateway Receive Electronics
• 4UMM User Modem Modulator
• 4UMD User Modem Demodulator
• 4USA User Satellite Aperture
• 4TSC Transmit Signal Conditioners
• 4RSC Receive Signal Conditioners

Note the DSM identifies the launch vehicle interface as a critical external dependency. While this is not in the scope of this roadmap, the availability and ultimately cost ($/kg) to launch the satellite to orbit is critical to the 2SDC roadmap and its profitability. Please reference Orbital Launch Vehicle Roadmap for more on that roadmap.

Sources

[1] I. Foster, "Variable Emissivity Materials for Thermal Radiators: Introduction to Characterizing Thermochromic Infrared Surfaces in Space," in AIAA SciTech 2024 Forum, 2024. https://arc-aiaa-org.libproxy.mit.edu/doi/abs/10.2514/6.2024-1295