Reply To: General thought on old coal mines.

[vansig]

I might not want to do mach 24 in the stratosphere, but it is a conversation point.

The engine needs to have enough air intake to give net forward thrust and lift, after overcoming drag, at any given altitude and velocity. Flying higher reduces drag by reducing density of air, but thrust also declines, requiring faster flight to feed the engine. There is a cross-over point from air-breathing to on-board propellant, as the min and max altitudes for hypothetical top speed converge.

At speeds much lower than mach-24, the craft cannot rely on centripetal motion, so engines and surfaces must provide for both drag and lift. it is interesting that there is a point where these are in the same magnitude. my hope is that the discussion will lead to a proper formula for a flight curve for both suborbital trans-continental transport and orbital insertion.

neglecting drag, perigee at 8 km/s and 36 km altitude would entail apogee near 400 km, and delta-v of ~70 m/s to complete the maneuver. finding the point along this curve where we must switch to on-board propellant will yield knowledge of how much propellant we need to carry.