i

A satellite orbit's Inclination (i) indicates the angle of the satellite orbit plane measured from the Earth's equatorial plane. Inclination can range anywhere from 0 to 180 degrees. An orbit inclination of between 0 and 90 degrees is called a prograde orbit. An orbit inclination of between 90 and 180 degrees is called a retrograde orbit.

"051.6421" = an orbit inclination of 51^o.6421 above the Earth's equatorial plane.

Therefore, the ISS has a prograde orbit.