The Spin Thruster is a new block that was added in the Galacticraft 184.108.40.206 (BETA) release, for MC 1.7.2 And 1.7.10. Spin Thrusters are primarily for rotating space stations.
It is quite useful for making a moving space station, so you can find say... New biomes. Just make sure that you can get back to the station if you jump off. (The thrusters have no actual use in the game as of now but future use mAy be added. It is important to note that the thrusters do in fact add some noticeable gravity but not enough to justify adding them for the cost of materials unless looking to add a neat effect.)