7. Thermal Control
7.4 Typical Requirements and Design Considerations
During the spaceflight mission, the thermal control system supports the other subsystem designs and interfaces between thermal connections. As always, the size, weight, and powers are obvious requirements or design drivers. For the thermal subsystem specifically, an orbit is a significant design driver. The internal components of the spacecraft are generally the same but the space environment could vary wildly from being up close and personal with the sun or venturing between stars with little to no external heat source. Regardless of the space environment, here are some typical spacecraft components operational temperature range requirements:
- Maintain batteries between 10-20C
- Maintain computers between 10-50C
- Maintain humans alive (e.g. crew cabin at ~295K)
- Maintain liquid propellant from freezing/boiling
- Maintain instruments cold
- Maintain RTG heat source cool
- Avoid thermal cycling of components that can lead to thermal fatigue and structural failure
Just like the other subsystems, we shall think about sources for requirements outside the space mission. During manufacturing and assembly, thermal engineers need to ensure that the thermal components that require proper contact are integrated as such.
Reference Document
During testing, external requirements from the launch provider commonly include thermal vacuum bakeout. The CubeSat Design Specification Rev. 14 specifies that:
“3.2.1 Thermal vacuum bakeout shall be performed to ensure proper outgassing of components.
3.2.2 The test specification will be defined by the Launch Provider.”
The NanoRacks External CubeSat Deployer IDD states: “The CubeSat shall be capable of withstanding the expected thermal environments for all mission phases, which are enveloped by the on-orbit EVR phase prior to deployment. The expected thermal environments for all phases of the mission leading up to deployment are below in Table 4.3.5-1”:
Although these mission phases reside outside the testing phase, these thermal conditions should be replicated in a finite element analysis and/or in a test chamber to ensure the survivability of these physical components. Another thermal test that should be done during the testing phase simulates the mission’s space environment within a thermal vacuum chamber to validate the results of finite element analysis and/or to observe how the physical behavior differs from a modeled behavior. This test could require specific testing fixtures and mounting holes on the spacecraft.
The transport, handling, and re-deployment requirements were expressed earlier in the launch provider requirements. Outside of these external launch provider requirements (or really, constraints), the thermal control system’s primary responsibility is to enable the other spacecraft subsystems, particularly the payload. The TCS requirements follow the component selection and cannot be finalized until the design freezes to some degree. Here are the initial requirements that drove the Artemis CubeSat kit.
Artemis Kit Specific
The operating and survival temperature for each component lives in a thermal budget, which helps visualize the most thermally sensitive components. The Artemis CubeSat Kit thermal budget lives here.
| 3.2 | The CubeSat thermal system shall verify or regulate that all components are within an acceptable thermally operational range |
| 3.2.1 | All components shall operate between 0 and 50 degrees Celsius |
| 3.2.2 | The CubeSat’s estimated thermal profile shall not exceed the 0 to 50 degree Celsius range for an ISS orbit |
| 3.2.3 | Heaters and thermal straps shall provide thermal control of the sensitive components |
Suggested Activity
“What kind of thermal requirements must you impose on your system to fulfill your science mission?”
Make your own thermal budget to identify the most thermally sensitive component.
