Using Falcon I booster as a suborbital vehicle

I was looking at the Falcon I flight profile on the SpaceX website and noticed that its second stage ignition didn't occur until it reached 324,000 feet. This means that its first stage has effectively launched the weight of the second stage and payload to 61.4 miles. Assuming that the second stage hasn't lost all its momentum when it fires its engine, this gives the booster the capability of launching a craft into space on a suborbital trajectory.

I have not been able to find the mass of its second stage but you can make a rough guess. If you take the thrust (7000lbs) and ISP (327 sec) of its Kestrel engine together with the burn time of 378 seconds you can come up with the weight of fuel assuming the engine operates at full throttle.

fuel consumption per second = 7000/327 = 21.4lbs Approx

total fuel consumption = 21.4 x 378 = 8091lbs (3678kg)
Quoted payload to LEO = 570kg
Engine Mass = 52kg
Assume 200kg for everything else (Big assumption)

This gives a total of 4500kg, I would have thought more than enough to create a suborbital craft capable of carrying 6 people or so. Since the booster is reusable and the craft could be a simple capsule with a parachute the launch costs should be a lot less than the $6.7m quoted which throws away an upper stage with every launch.

I guess SpaceX can always go into the suborbital tourism business if satellite launch doesn't work out for them.

Fascinating. They didn't try to make this booster man-rated, but presumably they could produce a version of it that is. The engine will already need to be man-rated because they will use it on Falcon 9. What's left is probably mostly the avionics needing more redundancy, I suppose.