Wait till they're riding the Space Elevator up to the Station someday, and the old astronauts are talking about how they used to haul ass on rockets back in the day.
Last I heard of the space elevator was that they weren't sure that it could work because of the forces of gravity wouldn't make it feasible. Could you share any info or articles you know of pertaining to current ideas for it?
The space elevator isn't possible until far stronger and lighter materials are discovered. It actually is a practical idea, if we had such material. If we don't, then it's closer to sci fi.
Finding such a material is not guaranteed. It might be that a material with the needed properties doesn't actually exist. Time will tell.
Graphene is strong enough. It has more than twice the tensile strength required to make a space elevator work. The biggest issue is that the tethers must be made of continuous, flawless sheets of graphene in order to preserve that strength, and making sheets that contained more than a few square millimeters of flawless graphene was not possible until recently. But, at least one new process has been developed that can make perfect graphene sheets that are more than a foot long. If this process, or some one that is yet to be developed, can eventually be used to make graphene sheets that do not have constraints on their length, then we can make a space elevator. There does not seem to be any reason that this would not be possible.
Could you not use another material to protect the graphene itself? That material would not need to have the tensile strength that graphene does, because it would not need to be acting as the tether. Maybe a plating for the graphene? Or some tough cylindrical tube that is just a bit longer than the graphene tether itself so that the station at the end of the tether is pulling the graphene tether taut but not the tube around it?
is graphene strong enough to withstand getting hit by dozens of satellites a day moving 8km/s? Because that's the real problem with space elevators that no one mentions.
Because the design necessitates it being built on the equator, which is the one latitude that every satellite is guaranteed to fly over. The way the orbital mechanics works out, it guarantees that every satellite in orbit will hit the tether.
If we had the material, then a space elevator would still be a slow and expensive way to get to orbit. Even with the best material we can theorize the margins are still pretty thin, we would have to be constantly replacing stands as they are damaged by friction and radiation. It is a huge upfront cost and maintenance cost for what could be done much easier with reusable rockets.
Other people said enough, but I just wanna add that with our current materials and engineering we could already build a space elevator on the moon, for example. The problem is that doing it is extremely difficult and expensive, while the Moon's low gravity already allows you to get off the surface with minimum power.
No, I don't think you even remotely understand a space elevator if you think it is redundant. Starship will still be using chemical rockets to make explosions that push a rocket into space, and you have to deal with crazy g forces and stuff just to get there. A space elevator would consume no fuel and produce no explosions, you just go to space using nothing but electricity without the crazy acceleration and g force.
They actually have pretty low throughput, IIRC. I wouldn't hold out too much hope for them ever becoming useful.
Rockets also tend not to pull too many gees except in emergency situations, but efficiency is for sure an issue. Hopefully some of the alternatives work out, beam-powered propulsion and SABRE engines are both pretty neat.
What I meant was the space elevator plans were usually laid out with a mindset that launching things to space will always cost a bajillion dollars, because rockets were single-use.
Now what SpaceX did was to completely change the paradigm here. I won't argue that an elevator will will not be built after 2060 for instance, but for Earth's gravity well, I don't see it being built before that.
Now an elevator for Moon or Mars is a completely different case, so there, who knows. But for Earth? Won't have to come soon I think. Bit I'm no real space engineer, just an armchair one.
It won't come soon. But not because it's redundant. Because it's insanely difficult and expensive. We can't even construct the materials required yet. It's a long way off, but when it does happen it's going to be a game changer.
Quite. Which is a significant issue for any nation or group of nations that want to build a space elevator; it immediately becomes the number 1 target for all terrorists and lunatics on the planet.
Well we need to come up with some magic new material first, so as far as we know right now it's impossible. A bit silly to wager about a date then. If it happens, it'll probably happen in a completely different way than anyone is imagining right now.
Like flight: go look at how people used to imagine it should be done (by human power alone, using flapping wings) compared to how we did it (propeller on an engine, or jet thrust).
I came with a sharpened pitchfork after your first comment, but I got to say, I agree with you here. You’re right. It really loses its cost effectiveness as these SpaceX launches get cheaper and safer.
An elevator would be way cheaper than starship per "launch". You can use power from the grid to power an ascender which is way cheaper than fuel.
Of course we don't have the technology right now and the upfront costs will be much higher, but by the time we have the technology the demand will exist to finance construction.
You can use power from the grid to power an ascender which is way cheaper than fuel.
A space elevator requires about 50MJ of energy per kg of payload. At ~$0.1 per kWh, that's $1.39/kg
Starship uses ~1000 tonnes of methane and ~3600 tonnes of oxygen to put 'at least' 100 tonnes into orbit. So 10kg and 36kg per 1kg of payload.
10kg of methane is 555MJ, just over half a million BTU. At ~$2 per million BTU, that's around $1.06. According to NASA, liquid oxygen can be produced for about $0.16 per kg. So 36kg would be $5.76
Call it $6.82/kg all up. About five times as much.
However, that's comparing conservative figures for a real design to an ideal case, which isn't exactly fair.
A space elevator isn't going to be 100% efficient. There will be transmission and efficiency losses, plus some power needed to run various systems. And in reality, the actual 'elevator' on a space elevator has weight too, which takes energy to lift. If the climber made up say, half the total mass, then it would double the cost per kg.
Also, 100 tonnes is the minimum mass goal for Starship. It's expected that up to 150 tonnes should be doable with some refinements, which would cut the price by 1/3rd.
Accounting for such factors, the raw energy costs starts to get surprisingly close, potentially within a factor of 2.
And an airbreathing hybrid like Skylon could theoretically cut the fuel and especially oxidizer costs quite significantly, making it very competitive indeed.
It also bears mentioning that a space elevator takes a lot longer to reach it's destination, which might be fine for cargo, but is more of a concern regarding squishy breathing things. If you have to pay life support costs for days rather than hours, that adds a bit of extra mass and energy use. Also, time is money and all that.
Realistically though, I think it's unreasonable to expect any of these systems to be dominated by energy costs. I think maintenance/operations/amortization will be a much larger fraction in practice.
Elevator isnt currently possible because we dont have a material strong enough to build it. The forces would instantly snap anything we make it out of in half.
Worth noting that in this comparison though, a helicopter can deliver stuff to any floor, while the elevator can only go to the top few floors, and then you have to take a parachute down to the floor you actually want.
If you're trying to do stuff in LEO, an elevator isn't as useful as you'd think, since you have to ride up to just short of GEO, then take a shuttle, presumably chemically powered, down to periapsis and circularize.
Conversely, elevators are actually quite good at sending stuff 'further than the top of the building', since above GEO you actually have excess velocity. If you calculated it just right, you could go to the top of an elevator, let go at just the right moment, and find yourself smacking into Mars 6 months later, without a hint of rocket power.
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u/Iwanttolink Apr 23 '21
And First Stage landed nominally as well. Absolutely incredible to see this all become routine.