Propulsion Cold Gas Jets The cold gas jet system was built following a bet with James Macfarlane. The system is heavily, heavily experimental, and I would hardly recommend it for general use. Using a small, steel gas cylinder (A CO2 cylinder, in fact), a solenoid valve releases gas through a simple 4-way circulator, thus altering the trajectory of the rocket. The circulator port is determined by an onboard guidance system coupled to the cold gas jet control system. On a small rocket it is quite heavy, especially when you take into account the control and guidance system and power system as well, but on larger rockets it is ideal since it forms only a small fraction of the total mass.