Your comment is quite correct as photonic pressure does indeed provide a force applied to all objects in orbit exposed to direct sunlight. The result is the orbital path of such objects changes over time and requires course corrections by firing thrusters. When the thruster fuel (mass) is used up that vehicle will eventually cease to be operational.
The pressure of light photons is very slight and has been postulated as a propellant force for deep space exploration. Such craft would have to deploy light sails made of very thin metalized Mylar and rigged with Kevlar cords after launch.
The sails would probably be configured something like a parachute jib on a water going sail boat. Manipulating the Kevlar rigging would allow course corrections of the vehicle with no consumption of mass. The sails would have to be huge (acres?) to move a photon powered craft in any reasonable time frame. Tracking the craft from earth with a large laser beam would allow additional boost for a push during the initial phase of the journey.
However, the photon pressure is not causing rotation of the radiometer directly. If you look at the pictures you should notice that each vane is twisted slightly with respect to the center support. Also note that each vane is white on one side while the reverse side is black. Light shining on the radiometer heats the black side of the vanes but has a very slight effect on the white sides. The difference in heating creates a slight convection current of the gas contained in the globe. The motion of the gas is enough to spin the rotor, not the result of light directly.
Regards,
GtG
There was a Isaac Asimov short story about such a craft.