Is it possible to have water vapour at -5°C

Yes, it is possible.

It is called humidity. The quantity is reduced as the temperature go down. That’s why it condenses in a fridge or in a air conditioner unit. To create vapor there is various ways such as heating (evaporation) or fogging of liquid water. It will stop when the vapor pressure is reached and it depends of the temperature. The vapor pressure of water is 101.32 kPa at 100°C, which is the atmospheric pressure at sea level. It means that at that pressure and that temperature and above the water is totally converted in gas in the boiling process.

the device is called “ rocket engine”

we need to know the time interval during which the force acts. impulse of force = momentum change