Thermal Vacuum Chamber for CubeSat Qualification

Abstract

The spacecraft design process has a key, unignorable element: the qualification process. Since it is difficult, risky, and expensive to send hardware into orbit, spacecraft need to be qualified to survive the space environments. To this end, testing hardware needs to be designed and manufactured that can replicate those environments. A Thermal Vacuum Chamber, commonly referred to as a TVAC, is one of these testing articles. In space, the spacecraft will be in vacuum and will experience the extreme temperatures that exist in that environment. Sunlight pours energy into the spacecraft in the form of light, which can only be removed from the spacecraft via radiation. The dark side of the spacecraft can be exceptionally cold, since it would have no energy input. When in the shadow of Earth with no heat input, the spacecraft reaches its coldest. Thus, there is a high temperature and a low temperature that the spacecraft must be able to withstand while in vacuum. The scope of this project is to adapt an existing vacuum chamber to have the heating and cooling capabilities to reach a portion of those temperature limits (-20⁰C through 100⁰C). To save cost, an existing vacuum capable chamber will be modified to have the thermal capabilities required for a TVAC. This chamber is a simple vacuum bell jar and baseplate with the ability to feed power into chamber. Within the chamber, the idea is to have a heating and cooling element with an internal heatsink. Heating and cooling will be done using a Peltier module. In addition, temperature sensors with a microcontroller will be used to control heating and cooling such that thermal cycling can be done automatically. Because there will be very little heat transfer between the exterior and interior of the vacuum chamber (only conduction through the baseplate and radiation), these thermal cycles will require the thermal energy of the system to be carefully managed between the heatsink, CubeSat, and Peltier module. 6 Introduction The design process for this TVAC began with the decision to use adapt a commercially available vacuum chamber into a TVAC. There are two reasons for this, and the first is cost. Bell jar vacuum chamber and pump systems can be purchased for under $300, while the design and manufacturing of a custom chamber would cost thousands and take a great deal of time. In addition to the cost, the designer would have to comply with safety regulations when testing and qualifying a custom chamber. For a student working for a single semester, the scope of work to be done to design such a chamber and give it the thermal capabilities it requires is too great. The second major decision to make was how to implement the heat pumping capabilities required in a TVAC. For ease of use and maintenance, the mechanism chosen was a peltier module, which creates a temperature gradient when an electric current is applied to it. The module is solid-state, meaning it has no moving parts to maintain. It also has a useful feature that the direction of the temperature gradient is generates can be reversed by reversing the current flowing through it, giving it the ability to both cool and heat a mass. With these design decisions made, the remainder of the design works to optimize and enable the capabilities of the peltier module and the vacuum chamber. Electric power management and thermal management become the major drivers of how electronics and mechanical components come together.