Beyond all the theoretical implementation complexities of space elevators, we don't even know of a single material with the required tensile strength. Graphene was thought to be strong enough, but recent research found practical graphene had defects that significantly reduces its strength below that required for a space elevator.
Space elevators aren't scrapped, just on the shelf until we even have a material that let's us think they might be feasible. That said, Lunar space elevators could be done with lower-strength materials, like Kevlar, and there are some people working on them.
For Earth orbit, I think the centrifuge concept (e.g. SpinLaunch) has some promise. Still some huge implementation hurdles, but could be a huge step forward to put all of the energy for the first stage on the ground.
Space elevators don't work on the moon. While gravity is weaker, the moon's rotation period is also much lower. To build a space elevator, its center of mass must be in a stationary orbit over the body. A geostationary orbit around the moon (selenostationary) would be about 88,000 km. The moon's Hill sphere, the region where its gravity dominates and thus things can stay in stable orbit around it, is only about 58,000 km. Basically a lunar space elevator would be so tall that Earth's gravity would yoink it off the moon.
You could potentially build a skyhook on the moon, which a space elevator is merely a special case of, but you lose a lot of the advantages of a space elevator - namely you still need something to blast off the surface to reach the skyhook, and you have to carefully time it because everything's moving at extremely high speed. Saves a lot of fuel though.
The most likely place for a space elevator is clearly Mars. At the Mars Society conference there was a talk where somebody went deep into space elevators and Mars is the most likely place to make one anytime soon.
Its far easier then on earth.
One the moon you might just use a mass driver instead, at least for bulk materials. And if not that a reusable rocket works just fine.
What if you position the counterweight of the space elevator at the L1 lagrange point of Earth/Moon? Since the moon is tidally locked, it should always stay about the same spot relative to the lunar surface.
But why not just build a mass driver, then? It's a somewhat large horizontal structure, compared to a space elevator which is an absolutely humongous vertical structure. If you can reach 2 km/s on magnetic rails, you don't need anything else to launch from the Moon -- or even land on it.
Because unless you reach escape velocity, you still need to adjust your trajectory to insert into orbit, or else you're just going to crash back on the surface.
If you use a rocket that's fine you just point in a different direction and burn, but if you're trying to launch, say, a few trillion tons of stuff, you need something a tad more efficient
It's not like you need no maneuvering when you use a space elevator. At some point you have to detach from it. You'll always need course corrections afterwards.
Spinlaunch is potentially okay for cargo, assuming they can overcome limitations imposed by atmospheric drag, and scale up sufficiently to make it practical; but the G forces involved make it impossible to use for human spaceflight.
Is something like spinlaunch (centrifugal force) even better than a hydrogen gun (linear acceleration) from the perspective of g forces? For example Quicklaunch (6 km/s speed, 1100 m barrel) would require ~1700g of acceleration. Spinlaunch appears to be significantly more demanding while providing even smaller initial velocity. Even if it's just cargo applications, surely there's still a difference between 1000g and 10000g.
The main advantages of spin launch's approach over a more conventional mass driver are that it takes up less space (Quicklaunch's proposed driver is over 1km long), and that it requires less peak power to get up to speed (Spinlaunch accelerates over a period of one and half hours).
One could argue that Quicklaunch doesn't practically require much peak power either since you have means to store hydrogen and oxygen in tanks over time if you generate them in trickles. The fact that firing it generates high peak power is no more relevant for practicality than the fact that firing a handgun generates high peak power. It's just combustion.
As for size, honestly, that doesn't seem to be much of a problem. You still have exclusion zones, and I'd argue that the exclusion zone around a spinning device like Spinlaunch proposes would have to be fairly large in all directions. Quicklaunch doesn't have a failure mode where the payload goes sideways at its full speed. Even if Quicklaunch were on land (which it wasn't planned to be), it would still probably require a smaller exclusion area.
> The fact that firing it generates high peak power is no more relevant for practicality than the fact that firing a handgun generates high peak power. It's just combustion.
This is not a trivial engineering problem. And in the case of a light gas gun, not only do you need to dump all this energy into a driver to compress the light gas extremely quickly, you also then must bring that driver to a halt extremely quickly without destroying everything.
I'm not saying that a space gun is simple. But I'm not convinced that it's that much more complicated than a hypersonic centrifuge that provides smaller benefits to begin with.
BTW did Quicklaunch even have a driver/piston? I'm not quite sure that it had.
Yeah, quicklaunch actually uses methane combustion to drive the piston, the hydrogen is just the working gas. The whole advantage of light gas guns is that since you don't need your working fluid to do the combustion, you can use gasses with much higher speeds of sound which can thus produce much higher velocities, such as superheated pure hydrogen.
I am in total agreement though that spinlaunch is a much worse system though.
I checked on the Quicklaunch design (https://vimeo.com/29822477) and the only solid moving mass in the gun is the projectile. So apparently you don't need to "bring [...] driver/piston to a halt extremely quickly" since there is none. They did propose to recover most of the gas by closing the muzzle just after the projectile exit, though. That might be complicated.
There is a piston. At 2:07 they show a close up of the first stage which they are referring to as the "pump tube", that larger diameter section, where the piston is driven up to speed, pumping the hydrogen into the second stage barrel at high pressure.
There is no piston. Where do you see one? Did you even watch the video? The whole launch sequence is shown there. There's a pressurized hot hydrogen tank that empties into the barrel. There's no "piston [...] driven up to speed, pumping the hydrogen". The hydrogen flows into the barrel on its own because it has high static pressure at the moment of firing. The presenter literally explains it in detail.
SpinLaunch is easily the dumbest thing I've seen this year, and I got to become aware of NFTs this year. It's going to end up in the long list of grifts designed to bleed investors.
Curious about your reasoning. I immediately wondered what type of cargo would be suitable for this sort of launch system. I came up with a fairly short list. Fuel/water/perhaps food for interplanetary spacecraft destined for Luna or Mars. I imagine one could design some types of cubesats to withstand the tremendous acceleration forces. That was about it.
Is your skepticism based on cargo suitability or other factors.
I don't think that even Rh(null) blood, unicorn tears or HP color ink liquids are commercially viable to launch at prices around 10-50k$ per liter. And that if that whole assembly will work at all at prices they are advertising today (1/20 of comparable commercial rockets, but it will have very small payload).
PS: I don't have numbers, but I'm guessing that F9 hitchhike Transporter missions cost less per kilogram, compared to the imaginary numbers for non-existing full scale Spinlauch.
Who the fuck cares about cargo before trying to figure out if any second stage rocket that isn't a rock can reasonably survive the extended application of high G-forces
They have some data that indicates most off the shelf electronics survive or need very minor modifications to withstand the G forces. That's better than no data at all but they do have a ways to go.
Some classification considers 3 types of cargo - bulk materials (metals, fuel); complex electronics; humans. The majority of weight is in the 1st type. Unless first two types have complex mechanical structure, where loads can't be distributed into supports - which is an important issue - the first two groups are candidates.
IT make no sense to build a dedicated launch system and non-reusable rocket to deliver a few 100kg max into orbit.
A Starship launches 150 tons reusable. That far cheaper and less work then building 500 Upper-Stages and shoot 500 of those rockets with a SpinLaunch system.
There is really no comparison in cost.
Maybe they could make the upper stage reusable but that would reduce the payload to and even more pathetic amount.
This system simply can not compete against reusable rockets.
But this launch system still needs the projectile itself to be a fairly complex rocket capable of delivering several km/s of delta V and of steering the payload onto a desired orbit. That still implies electronics and mechanical systems onboard even if you're carrying only bulk cargo.
Electronic chips themselves are rather good to withstand acceleration - can be packaged well. Mechanical systems for simple rockets could also be, well, simple - e.g. first orbital launcher of France used pressure-fed engine.
First, you're making a giant spinning thing that contains a ridiculous amount of energy. If the release of the projectile is off by a millisecond, instead of flying through the outlet it's instead flying into the wall of the launcher where it will deliver all of its kinetic energy in the form of an explosion with the energy of about a half ton of TNT, which sounds bad but really isn't compared to the arm its exploding next to that would release the energy of a small nuke if it gets damaged. This isn't a failure mode that can be monitored and avoided; eventually you're going to have a component fail or a software glitch and before the system can even register that something is wrong the launcher will be a crater.
You're launching bulk material into orbit where no one cares if the occasional launch fails so long as it's cheap, and you're wasting that on a launch system where the most minor failure results in not just the loss of the launch vehicle but the entire infrastructure for launching.
But even if everything works exactly as intended there are still issues. Your giant centrifuge spins up in a vacuum because at those speeds air resistance would be extremely damaging. Unfortunately, after you release the payload, it breaches the seal on the outlet and now you have a giant inrush of air into your vacuum chamber. Unfortunately, the giant arm is still spinning at 8000 kph. The surface of the arm is going to ablate as it moves through sea level air at hypersonic speeds, and its going to generate massive shock waves which are going to reverberate in the chamber. All those precision components for releasing your payload with extreme precision are going to be exposed to these hellish conditions. You're going to need extensive repairs or replacements after every launch.
You're doing all this and you still need a launch vehicle with its own rocket engine and propellant, flight control surfaces and surface protection for its own hypersonic journey through the lower atmosphere. Everything needs to survive ridiculous g forces. All this to deliver a few kilograms of low value cargo?
These problems don't go away as you refine the technology, they are fundamental. You will always need precision release mechanisms to avoid catastrophic failure, you will always be exposed to hypersonic conditions, you will always experience ridiculous g forces, you will always need rockets for orbital insertion, you will always be restricted to low value cargo.
It's an interesting engineering problem; they might learn some cool lessons along the way, maybe some valuable patents will come out of it, but there is no hope for developing a practical space launch method competitive with existing methods.
> that would release the energy of a small nuke if it gets damaged
All we need to do now is containerise it for easy transportation across borders! Err..
My first thought on seeing the prototype was whether they've taken a map and drawn an arc in line with the rotation to see the areas that might be impacted when this thing RUDs. Perhaps they'll put it on a turntable?
Nonetheless I'd suggest it's probably safest to build this thing in a concrete pit such that failure results in a big hole, and not hot and spicy hypersonic plasma flung across the continental USA.
Skepticism? I'm not "skeptical" about SpinLaunch. I'm incredulous about SpinLaunch. Skeptical implies that I think there might be a chance, if certain criticisms are addressed. No, I am certain there is no chance SpinLaunch will end up being a thing.
First of all, putting aside the several red-flags for why this looks like a scam, and assuming it's actually do-able, it's still not going to happen. The global space industry is built on rockets. At best, stuff like this--even if it does work--gets a "cute project, kid" pat on the back and then ignored. When was the last time any fundamental redesign of an existing technology take over an industry? It just doesn't happen.
And I think everyone involved probably knows that. You're not going to compete against Google as a scrappy startup trying to make a search engine. You're not going to compete against SpaceX as a scrappy startup trying to make alternative launch systems. Somebody, somewhere, has to understand that. So they have to be in on the scam.
Now, as for the actual idea, there are several problems. First and foremost is: energy is energy. If this thing fails, it blows up just as bad as a chemical rocket on the platform.
At least chemical rockets are based on decades-old materials science. This spinning arm malarky expects us to believe that they can support 10,000x their payload on the arm and be able to release it on a hair trigger? I suppose next they're going to tell us the arm is made of carbon nanotubes or some other unobtanium.
So they want to spin the object in a vacuum. How are they going to seal the spin chamber in such a way that they can generate a significant vacuum while also allowing the payload to escape? They show a paper or some other thin membrane door over the escape hatch that the payload punches through. OK, that means that door needs to be able to support 13.75 pounds per square inch of atmosphere. A 2m x 2m door needs to be able to hold up over 40 tons of atmosphere. The payload needs to punch through a door that is holding up over 40 tons of atmosphere. That payload needs to punch into a 40 ton column of atmosphere. At ~5,000 mph?!
So what I expect to happen is that the payload hits the column of air, creates a mach shockwave that destroys all of the windows in a 5 mile radius, while the rush of air into the chamber and clapping back around the tunnel of vaccum the payload creates blinding spike of plasma (not unlike lightning), that ends up destroying the launch chamber.
Oh, yes, there are "challenges" to "figure out". From their launch command center that was clearly designed for aesthetics more than functionality. Lots of problem solving gonna happen there.
You may or may not have a point, but your entire "argument" is the "argument from incredulity" fallacy and not any actual reasoning.
For example: arguing about "paper" strength to resist air pressure vs vacuum and throwing around numbers like "40 tons" isn't based on any actual materials science. The burst pressure strength for pretty standard office paper is 250 - 300 kPa. Atmospheric pressure at sea level is 101 kPa. So right off the bat, you've multiplied a bunch of numbers together and come up with the wrong answer: the paper I buy from the stationary store is 2-3 times strong enough to resist atmospheric pressure against a vacuum.
Now of course, at a suitably large dimensionality, we have to worry about fiber strength loading etc. but this has so many solutions it's absurd - i.e. 2 sheets of paper with fibers perpendicular for strength, a plastic backer for air permeability, and then weaving strengthening fibers into a grid - remembering that the burst strength is quite different to the resistance to piercing forces (i.e. kevlar will stop a bullet but not a knife).
A similar but somewhat more physicaly sound idea is the Slingatron: a launch track several kilometers long in a spiral shape, on stilts that rotate in synchronization. The g-forces are much more reasonable because of the increasing track diameter.
At about 10,000Gs of acceleration (as per their claims¹ ~2200m/s in a 100m vacuum chamber, e.g. a=v²/r ≈ 97,000m/s² or roughly 10,000Gs) any human passenger would be liquified and form a nice smooth film on the inner surfaces of the vehicle.
Space elevators aren't scrapped, just on the shelf until we even have a material that let's us think they might be feasible. That said, Lunar space elevators could be done with lower-strength materials, like Kevlar, and there are some people working on them.
For Earth orbit, I think the centrifuge concept (e.g. SpinLaunch) has some promise. Still some huge implementation hurdles, but could be a huge step forward to put all of the energy for the first stage on the ground.