Satellites and space stations stay aloft by orbiting the earth at escape velocity. They are moving so fast that the curved earth literally falls away beneath them faster than gravity can pull them down. It has nothing to do with helium. (Or were you kidding about that?)
A nitpick (but I did like the helium line, somebody has to fall for it), if they were going that fast, they would escape. They are going fast enough so that the earth falls away (due to curvature) at the same rate the satellite would be falling.
I think the international space station (ISS) orbits at about 17,000 MPH, and escape velocity is about 25,000 MPH.