ravikr wrote:Noob Question. Why L110 shoots it to 205Kms altitude when required is 170 Kms and when C25 kicks in it starts loosing altitude while gaining RV. Please can any Gurus explain.
Becoz with the relatively underpowered cryo stage, the ISP loss due to gravity is minimized by lofting the upper stage higher then targeted perigee, the C25 is angled for imparting more of tangential velocity (that result in greater centrifugal force, thus minimising need for radial lifting force that is responsible for effective ISP Loss due to gravity) while its radial thrust component is less than gravitational force, so the craft slowly sinks back to earth, giving enough time to Cryo stage to sum up needed delta -V to enter orbital velocity (when effective gravity is zero, the falling back to Earth stops). This will happen when rocket has fallen down to 170 km altitude (still away from effect of atmosphere, which typically is around 105km altitude).
This lofted trajectory is similar in purpose to launching aircrafts from an angled deck of aircraft carrier.