# Calculating the glidepath and velocity of a suborbital spacecraft.

1. Apr 25, 2009

### n707jt

Hello guys

Its my first post in the Physics Forum so hello to everyone!

I am actually currently engaged with a team in a suborbital spacecraft design (like the Spaceship2!) in my university for my final year design project.

I am kinda stuck with the calculation of the glidepath and velocity of a suborbital craft upon re-entry. The suborbital craft is supposed to achieve an apogee of 100km (like in the X-plane prize!) and then glide back to its point of origin. After some research, my team in school has found out that most suborbital craft would re-enter at approximately Mach 3.5. (correct me if I'm wrong) After which is is supposed to slow down, do a series of circles and then approach the airport. All those has to be done within the gliding ability of the suborbital craft. As of now, I still have not got a weight, nor do I have a lift or drag coefficient of the craft as the CFD simulation has yet to be done.

I have read various aircraft design books and it turns out that there are various standard formulas used for sailplanes in turning gliding flight which allows me to calculate the vertical velocity (sink rate) but I am not so sure if they are applicable here? Am I right to say those formulas are valid so long as I compensate for density differences? Also, at what altitude does suborbital craft actually starts to circle to slow down for approach back to the airport? Is there some sort of a standard?