The thruster we will see in action on SpaceX’s next launch on March 1st will be the Draco. The Draco thruster is the smallest engine in the SpaceX fleet but don’t let the size fool you, it packs 90 pounds (400 N) of thrust. The Draco is a liquid propellant thruster that uses Monomethyl Hydranzine. There is an oxidizer needed with a liquid rocket engine and SpaceX uses Nitrogen Tetroxide, the combination of orbital propellant and oxidizer that were used for the Space Shuttle.
SpaceX went with a liquid fuel rocket because, while the thruster design is more complex, the advantage is variable thrust meaning the amount of fuel and the fuel burn rate can change during flight. Liquid fuel rocket engines can not only be throttled but are able to shut down and be restarted. Having so many options for throttle and restart are helpful in a redundancy situation. It also aides in maneuvering the precise approach required for to berth with the International Space Station (ISS). The combination of the propellant and the oxidizer keeps the fuel stable allowing the Dragon capsule to be berthed to the ISS for up to a year, providing a life boat of sorts for our cosmonauts.