Reply To: General thought on old coal mines.

[zapkitty]

Tulse wrote:

mach 8-10, which seems to be an optimal velocity to launch to orbit from…

Perhaps I’m not following, but can you clarify what you mean here? Isn’t orbital velocity ~ Mach 25?

“… optimal velocity to launch to orbit from…”

Spacecraft of all types want to get above the sensible atmosphere first before seriously putting on speed. Chemically-powered spaceplanes scoop air to supplement their fuel while in atmosphere but they have to carry all of the fuel and oxidizer for that final sprint to orbit when the air runs out… as well as the fuel for the air-breathing portion of the flight.

So spaceplanes want to get as high and as fast as is feasible before heading for orbit… but pushing that too far ends up hurting more than it helps as they have to carry and burn up fuel that could be better used on the climb to orbit. Different concepts take off for orbit between mach 8 and mach 12 depending on the design.

I just got carried away with the fuel-free aspect of DPF flight without realizing I was literally poking holes in my “friendly neighbor” paradigm. Shiny objects, y’know 🙂

(for something often compared to an ion drive the FF version of a DPF can actually pack quite a kick for something that can be treated in the short term as an essentially fuelless thruster)