Welcome to the second week of the new Miles Team Weekly Topic round table! To reiterate, going forward, we here at Team Miles would like to bring a weekly, in-depth look at a rotating variety of topics that are essential to our Mission and the NASA Cube Quest in general. These topics focus on the very foundation of our decision-making and variations in any of these areas have the potential to drastically alter the team, the craft design, and the mission.

This week we will be looking at the topic of propulsion, in particular cold gas propulsion. Last week, the round table focused on the NASA challenge in general, the next week will focus on satellite communications, and the last week will be on the Cube Quest competitive landscape before returning to the start of the round table list of topics.
One of Team Miles’s greatest competitive advantages is our ion propulsion engines, which will be covered in depth in later posts, but it is hardly the only way to get from A to B in space. As revealed in the NASA CubeQuest Summit II, Lunar CubeQuestadors announced their decision to use cold gas propulsion using refrigerant as the reaction mass.

If the reader is unfamiliar with propulsion in space, satellite engines operate using the physics law of the conservation of momentum. Simply put, objects in motion stay in motion, objects at rest stay at rest unless acted upon by an outside force, and momentum is neither gained nor lost, it is only transferred. This applies to cold gas and satellite engines in general by that the engine ejects mass in one direction, and via the principle of the law of conservation of momentum, is propelled in the opposite. This same principle is the reason why firearms have recoil after firing their bullets.

Cold gas thrusters are able to move satellites by expelling a (typically inert) gas as the reaction mass. Cold gas thrusters usually consist of a pressurized tank containing gas, a valve to control its release, a nozzle to control the direction and focus of the mass ejected, and plumbing connecting the three parts. A cold gas thruster is the simplest example of a thermal rocket. The thermal source is the thermal energy in the form of the heat capacity of the gas. Cold gas thrusters usually do not heat the gas and thus the performance of the engine is at its lowest potential. A simple approximation would be to say that the specific impulse or performance of the engine is modeled as proportional to the square root of the gas (absolute) gas temperature. Performance of the engine rises as the gas temperature is increased. Cold gas thrusters are mostly useful for vernier engines (as pictured on the top of this article), and employed chiefly for simplicity and reliability and are mainly used for attitude control on larger spacecraft such as the lunar lander in the article picture. Lunar CubeQuestadors will use two balloons to focus solar rays to heat their gas (refrigerant) and thus increase their engine’s performance.

We here at Miles Space are very excited to see how this propulsion performs in the course of the NASA CubeQuest to help the other contestants achieve their in space goals!


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