61–70 of 111 posts
Earlier quoted context omitted.
thats what the railgun is for. Altitude is to reduce friction and energy needed.
> thats what the railgun is for A railgun that can provide a delta-v of 8 kilometers per second?
Earlier quoted context omitted.
thats what the railgun is for. Altitude is to reduce friction and energy needed.
> thats what the railgun is for A railgun that can provide a delta-v of 8 kilometers per second?
Existing ship mounted railguns already shoot projectiles around 3km/s. It is generally thought that they could be scaled up to 8 km/s and larger size. The main problem is that if you fire human sized objects that fast at sea level you end up with a plasma ball due to air friction. This isn't an issue with chemical rockets because they start at 0 and accelerate to Vmax, whereas the railgun projectiles start at Vmax and decelerate.
Higher altitude would remove much of the friction problem.
How is the elevator car in a space elevator accelerated horizontally? That's what reaching orbit is, right? Horizontal acceleration? The car starts out on the ground at 465m/s. It has to accelerate to 11,068 km/h. What makes it accelerate? The cable, without any force applied to it anywhere? Or is there a rocket on that car? To put mass into orbit, you have to accelerate that mass. And do it without decelerating the…
Earlier quoted context omitted.
thats what the railgun is for. Altitude is to reduce friction and energy needed.
> thats what the railgun is for A railgun that can provide a delta-v of 8 kilometers per second?
If the railgun is sloped at a 1% grade, it has ~2,000km of length. On that track, a comfy 1.6 Gs of acceleration for 500 seconds gets you up to 8 km/s.
Earlier quoted context omitted.
The anchor would need to be beyond geostationary orbit to keep the center of mass geostationary, so a broken tether would result in the anchor departing "outward". The reason to use an anchor is to avoid creating a tether that's twice as long as it needs to be.
But if you break the tether halfway down the bottom half falls at 16,000 mph right? And then it’s burning and then it cracks like a whip. I don’t know about extinction, but not a fun time for anyone.
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Problem is "some of the momentum" isn't nearly enough to reach orbit (climbing the tower only gains you 3% of orbital speed, or 0.1% the kinetic energy), and there's no hint of a mechanism that's supposed to accelerate a payload the rest of the way to orbital speed.
> Problem is "some of the momentum" isn't nearly enough to reach orbit (climbing the tower only gains you 3% of orbital speed, or 0.1% the kinetic energy) Where is your math? The top of the elevator is travelling at orbital velocity. This is trivial to show in designs with a counterweight. (Here, the magnetic coupling makes it less intuitive.) If you are on an orbiting object, i.e. the top of a space elevator, you’ve…
>The top of the elevator is travelling at orbital velocity. This is trivial to show in designs with a counterweight.
Per the paper this design only reaches 200 km in altitude, therefore it has no counterweight (a counterweight would need to be somewhere above 35,786 km altitude). Speed at the top is far below orbital velocity, so it requires a method of acceleration.
The paper acknowledges this. From the abstract:
"At the top of the loop, vehicles may be accelerated to orbital velocity or higher by rocket motors, electromagnetic propulsion, or hybrid methods."
Earlier quoted context omitted.
The anchor would need to be beyond geostationary orbit to keep the center of mass geostationary, so a broken tether would result in the anchor departing "outward". The reason to use an anchor is to avoid creating a tether that's twice as long as it needs to be.
But if you break the tether halfway down the bottom half falls at 16,000 mph right? And then it’s burning and then it cracks like a whip. I don’t know about extinction, but not a fun time for anyone.
Earlier quoted context omitted.
> thats what the railgun is for A railgun that can provide a delta-v of 8 kilometers per second?
Yes, that would be the proposal. Existing ship mounted railguns already shoot projectiles around 3km/s. It is generally thought that they could be scaled up to 8 km/s and larger size. The main problem is that if you fire human sized objects that fast at sea level you end up with a plasma ball due to air friction. This isn't an issue with chemical rockets because they start at 0 and accelerate to Vmax, whereas the rai…
The biggest advantage of very high altitude reducing the friction problem isn't just that it stops your projectile from turning into plasma, it is that the size of the minimum viable projectile is reduced. People keep focusing on getting people or vehicles into orbit, but the main advantage of a gun-to-orbit system is that the packet size can be made very small. Think machine gun instead of cannon. This means a smaller gun and thus smaller capital investment.
Instead of the balloon-supported long gun that mikewarot suggested, imagine a balloon at 30 km altitude supporting a 5 meter long gun and a few tons of both propellant and This could be a cheap way to get a bunch of metal into orbit, or possibly even fuel and oxidizer.
Earlier quoted context omitted.
Yes, that would be the proposal. Existing ship mounted railguns already shoot projectiles around 3km/s. It is generally thought that they could be scaled up to 8 km/s and larger size. The main problem is that if you fire human sized objects that fast at sea level you end up with a plasma ball due to air friction. This isn't an issue with chemical rockets because they start at 0 and accelerate to Vmax, whereas the rai…
Existing light gas guns can already hit 8 km/s: https://en.wikipedia.org/wiki/Light-gas_gun The biggest advantage of very high altitude reducing the friction problem isn't just that it stops your projectile from turning into plasma, it is that the size of the minimum viable projectile is reduced. People keep focusing on getting people or vehicles into orbit, but the main advantage of a gun-to-orbit system is that the…
There's a simple point about space elevators that most people ignore. We would only build a space elevator if it made economic sense. Given the reality of construction costs, even if we had the materials, it would like cost many trillions of dollars (at least) so whatever we used it for would have to produce much more value than that. Even more importantly, if we had access to the materials necessary to build space e…
Many technologies are developed long before they are viable because they have military value. Access to space is currently a major national security issue, so a space elevator could be a manhattan project. Some technologies are developed by the free market before they are economically viable too. LEO constellations for instance (both the original - iridium, and starlink).
>iridium
For some reason I was skeptical of this (suspiciously tidy) myth-making, and the more I look into it the more I'm convinced I was right to be skeptical.
Turns out the relevant engineers -- Ken Peterson and Ray Leopold -- both worked on military and government communications systems immediately prior to being hired at Motorola and starting the Iridium project. Peterson's bio is rather vague on timelines[0], but available information on Leopold indicates he joined Motorola in 1987[1] (directly from the Air Force Electronic Systems Division,[2] which develops communication systems), which is the same year he and Peterson started work on Iridium.[3]
This has all the hallmarks of one of those nice neat (and of course plausibly deniable) tech transfers from military/taxpayer dollars, complete with the cute official origin story featuring a C-suite executive's wife.
[0] https://www.tributearchive.com/obituaries/25954530/ken-peter...
[1] https://ocw.mit.edu/courses/16-886-air-transportation-system...
[2] https://en.wikipedia.org/wiki/Electronic_Systems_Center
[3] https://www.laits.utexas.edu/~anorman/long.extra/Student.F98...