No new innovation lives up to the hype, and it is good to see that a lot of realistic uses were found for graphene.
this post was submitted on 23 Sep 2024
91 points (97.9% liked)
Futurology
1771 readers
129 users here now
founded 1 year ago
MODERATORS
The main barrier to the Stan Lee stuff is just that we can't really manufacture it with any quality. The author really should have mentioned that. It sounds like they may have some personal stake in graphene, though, and could be going for "actually, it was a success all along".
We don't need no stinking space elevator!
All we need are SKYHOOKS!
Kursgesat forgets to mention the incredible forces that would put on the payload. NASA funded a study that suggested they start with a jet going mach 10, or 3.5 km/s. The fastest a person has ever gone is mach 6.7 or 2.02km/s. For efficiency sake, you'd want to get up to speed in a reasonable amount of time. I doubt humans can effectively use sky hooks. Could be really good for stuff though
NASA funded a study that suggested they start with a jet going mach 10, or 3.5 km/s. The fastest a person has ever gone is mach 6.7 or 2.02km/s.
In a jet. In a rocket, just the ISS is going at >7km/s, so obviously it's routine. A (scram)jet would be nicer from a fuel point of view, but you don't need it. In any case, to get to double the velocity with the same acceleration, you just accelerate twice as long - space is always big enough for a pure rocket-type craft (beamed power or gun-type are a different matter).
When it comes to the skyhooks themselves, the study you're thinking of gave a spread of different accelerations for the designs, from <1 G to quite heavy (but manageable for a trained professional).
The fastest a person has ever gone is mach 6.7 or 2.02km/s.
Astronauts on the ISS are currently zipping along at at 7.67 km/s just fine. The issue is acceleration, not speed. Tethers rotate fairly slowly, so the acceleration should be less than that of a rocket launch.
Astronauts on the ISS are currently zipping along at at 7.67 km/s just fine.
And we've all been zipping around the sun at 29.78 km/s since each of our inceptions.
Our Sun moves around the centre of the Milky Way at a speed of 240 km/s or 864,000 km/h, so do we plus or minus ~30km/s!
I've been reading about graphene going to be changing the world for like 20 years now.
I heard the cold fusion reactors will be made with it.
IF fully reusable spacecraft ever becomes reality, then a space elevator ON EARTH would probably never be needed.
On the moon, probably. On Mars, maybe. But Earth, a fully reusable rocket, combined with in space assembly just makes a lot more sense.
Especially long term when we actually start gathering raw materials in space. We'll eventually only need to send people , and complex things like microprocessors into space, and the rest can just be made up there.
The benefit of a space elevator is that the fuel is supplied by the ground and does not need to be carried as part of the payload. Remember in the rocket equation, most of the fuel is used for carrying just the mass of the fuel itself. A space elevator eliminates the rocket equation for lifting mass into orbit, and would be much more efficient than any rocket, reusable or not
There are major disadvantages as well.
You have a limited number of locations, which limits the rate of payloads. You can deploy them at the equator, so you'd have to transport things to the lifting pad beforehand, which would primarily need to be transported by sea.
We don't have a way to power the lifter, you can use microwaves or lasers, but that generates a lot of heat, which would be difficult to dissipate at high altitudes.
We also don't have a way to actually build one, but we do have a way to build reusable rockets (the details aren't complete, but several companies are well on their way to building them.)
By the time we'd be able to build a real space elevator, we'd probably already have asteroid mining, and in space constructions and manufacturing. So we're really only sending small, highly technical, or human payloads up, at which point a space elevator isn't really needed.
On top of all that, a fully reusable rocket powered by fuel that can be synthetically created, would be just as environmentally sustainable (assuming any ozone or ionosphere issues don't become an issue.)
I'm all for working on it if it becomes possible, but it's likely a technology that would be obsolete by the time it's possible.
Okay
I mean, it's more of an economic question then an engineering one, if we're assuming ahead of time that it's possible. If we could build an Earth space elevator for the volumetric price of water, you bet we'd be sending one up regardless of how cheap SpaceX launches are.
That's probably never going to happen, but energy prices and expected investment returns could all change quite a lot in the indefinite future, and a space elevator with regenerative breaking is always going to use less energy than anything else.
Especially long term when we actually start gathering raw materials in space. We’ll eventually only need to send people , and complex things like microprocessors into space, and the rest can just be made up there.
Actually, microprocessors would be easier to make in a natural hard vacuum, as would things like magnesium or solar cells. In the long term I'd expect the limiting factors will be elements, and general demand to send things to inhospitable places in the first place. Maybe energy if fusion turns out to be way harder than we expected, and we still want to hang out on Pluto or Titan.
Even reusable rockets use a tremendous amount of fuel. Falcon 9 burns 700,000 gallons per second.
Untrue, that's many times over the 25,000 gallons of kerosene they keep on board. That's still a lot of gas, but not 700,000 gallons, not by a long shot. If it burned that much per second it wouldn't even produce enough thrust to carry its own fuel payload
My bad for trusting Google top result.
395,700 kg fuel first stage. Burn time 162 seconds.
25,000 gallons of kerosene they keep on board.
The 39,000 gallons of LOX in the Falcon 9 doesn't make itself.
To inject a source, there's 395,700 kg total propellant on the first stage, and a burn time of 162 seconds. That gives about 2,442.6 kg/second, and assuming it's fuel balanced it comes out to something like 700 liters of RP-1 per second. Could OP have been using thousands of gallons instead, by accident?
It's still a lot, though, while a space elevator is just a really tall elevator, or alternatively an EV that goes up and down.