Reply To: General thought on old coal mines.

[zapkitty]

vansig wrote: ground crews can retreat to safe distance when the craft is in operation. otherwise we’d have to space anodes as close as 3cm apart, tesselating a sphere, to get shielding mass under 100t.

Caps, cooling and aux gear to drive 1400 cores… er… wouldn’t you save time, volume, and lots of money by having a few dozen cores drive the fans until ~mach 6, let straight chemical take you out of the atmosphere and then let the cores take it from there?

vansig wrote: when it comes to space, propellant cost is king.

…me being didactic again :)… constraints on the mass and volume of propellant drive launch vehicle costs… the actual cost of propellant is a negligible factor in current launches.

vansig wrote: it isn’t a fair comparison to say Falcon, etc. is cheaper, as those represent single-use vehicles and a mature technology, whereas the purpose of envisioning this is to have routine, possibly daily, surface-to-orbit and return missions. the facilities cost is amortized over many launches.

Er… The Falcon line is intended to be reusable, or in this context “refurbishable” might be better. And they intend to be able to launch as often as people can pay. A reusable fusion spaceplane only gets you so far if the ballistic launchers are cheaper from the get-go.

But kudos on referring to rockets only as a mature technology. All too many space fans think of it as a perfected technology and it is far from that… there’s still lots of room for improvement.

vansig wrote: let’s see.. 600 kN nominal but maybe 1200 kN max thrust at lift-off;
1200 kN / (100t x 9.8) = 1.2 gee. it’s like an elevator ride

Uh… your bird is carrying propellant, right? If so then gravity and drag losses would eat your lunch, your dinner, your midnight snack, your breakfast and will probably take out options on the Thanksgiving turkey. Spaceplanes actually tend to pull a bit more g’s than ballistic launch vehicles.