Sky ramp

[wumpus]

51 minutes ago, Rakaydos said:

...I'm not suggesting some kind of absurd Sabatier-thermal rocket. Just a Methane fuel plant for fueling a conventional reusable rocket to carry the same payload instead of the ramp.

In that case the slightly larger rocket with extra methane+liquid oxygen will win for less than 100-1000 reuses.  And getting down to 1000 reuses assumes much cheaper vehicles, and might really take 10,000 launches.  Things get even worse if somebody decides that air-augmented rockets or other airbreathers make sense before you build your skyramp.

Nobody has really built a high-volume means to get into space (although block 5 appears to be getting there), so we really don't know what's most efficient, or even what the requirements are.

[Rakaydos]

1 hour ago, wumpus said:

In that case the slightly larger rocket with extra methane+liquid oxygen will win for less than 100-1000 reuses.  And getting down to 1000 reuses assumes much cheaper vehicles, and might really take 10,000 launches.  Things get even worse if somebody decides that air-augmented rockets or other airbreathers make sense before you build your skyramp.

Nobody has really built a high-volume means to get into space (although block 5 appears to be getting there), so we really don't know what's most efficient, or even what the requirements are.

Again, I think my point was missed. launch for launch, it takes a certian amount of electricity to run the maglev.

How much electricity is that? How much rocket fuel could the Sabatier reactor generate with that much electricity? And how much mass could a first stage with that much fuel (and the same upper stage, minus wings) put into orbit?

[wumpus]

3 hours ago, Rakaydos said:

Again, I think my point was missed. launch for launch, it takes a certian amount of electricity to run the maglev.

How much electricity is that? How much rocket fuel could the Sabatier reactor generate with that much electricity? And how much mass could a first stage with that much fuel (and the same upper stage, minus wings) put into orbit?

Much like the cost of the fuel of the rocket, the cost of the railgun is so high the cost of the electricity will always be in the noise (probably less than maintenance of the railgun).  It is a weird concept to ignore the fuel used in something that is 95+% fuel, but that's how rocket economics work.  But to answer your question I'm sure it is more efficient for higher delta-vs (where the electricity is pushing a constant mass vehicle and the extra-methane rocket has to accelerate the extra methane as well), not sure for values just breaking the transonic area.

If you actually built such a thing there's always the danger that somebody would build a beanstalk and simply take all your business, probably long before you paid off the skyramp and started to worry about the electricity.

- I strongly suspect that any spacecraft that has wings and not using air-breathing engines is doing something wrong (a skyramp might be ideal for a first stage followed by a second stage ramjet.  But I'd assume that such a craft also needs a rocket engine, and why not fire that first as well?):
X-15: most missions didn't go into space
Shuttle: Best way to land in the 1970s, generally the best solution to too many bad specifications, but still didn't produce a good spacecraft for the time
Burran: A very expensive way to learn that the Americans (mostly in Congress) didn't know what they were doing
Space Ship One: just touched space, was an airplane the other 99% of the time.

[dreadanaught]

On 8/10/2018 at 6:13 PM, wumpus said:

The US Navy is trying to replace steam driven catapults with a system called EMALS for electric acceleration.  It will get to 150mph, but is so far unreliable (10% failure rate) and is priced at US carrier volumes but is unlikely to hurt anyone who can meet military pilot health checks (might be a problem with the general public but not astronaut crews for some time).

I'm not saying that they can't go faster, I'm just saying that the amusement park isn't big enough to fit enough track to not render everyone on the ride unconscious by accelerating them to those speeds too quickly. in theory, you could have an amusement park ride that travels that fast, it would just need a much longer distance to get to those speeds. In effect, this would dictate the need to have a rather large (~10km) track, that the rocket would go around a few times, after which it would be diverted to a straight track that gradually becomes sloped to avoid high accelerations and speed decreases from changing the direction of movement to quickly, then once at a sufficient angle, the rocket would leave the track at high velocity, but not having experienced too many Gs of force.