Kind obvious solution when you loop the idea of long gun launch into a fast spinning ferris wheel. Much easy and simpler power delivery. Centripetal acceleration bites though.
The tyranny of Tsiolkovsky's rocket equation [1] results from the need to burn fuel now to accelerate fuel for later. "Catapulting" sidesteps this issue by energizing on the ground.
In selling away the rocket equation you buy yourself drag. Lots of energy up front means lots of drag. Overcoming that drag means more energy and, hence, more drag. The middle child of this solution is tremendous G force.
You can't slingshot complex things into space. Pretty much just fuel and raw materials. That means you need in-space (a) refueling and (b) additive manufacturing capabilities. There are teams working on both problems, though they are presently in the domain of science versus engineering. Perhaps that will now be incentivized to change.
It saves you about 6% of fuel, assuming the launch location is on the equator, is suitable for roads and can handle a lot of noise / avelanches. Getting into space is the easy bit (energy-wise). Getting up to orbital speed takes much more fuel and energy.
The problem is that now you have to transport everything near and up the mountain, which costs a ton in logistics (getting a road up a mountain that can handle a entire assembled rocket isn't cheap, nor easy). Most launches have delta-v to spare because satellites are usually nowhere near the rocket's maximum payload weight.
tl;dr it can save 6% in a ideal situation, but the extra cost and logistical problems aren't worth it.
>tl;dr it can save 6% in a ideal situation, but the extra cost and logistical problems aren't worth it.
Unless you launch by means of a mass driver/rail gun [1] built into the side of Mt Everest with a piggy backed elevator for tourists. Tourists would arrive to a pressurized viewing area at the summit and have the option of donning an oxygen mask, going outside and posing for photos next to a cutout of Sir Hillary. I have never understood why serious rock climbing friends get so upset whenever I have mentioned this idea over the years.
Skip Everest and go with Mt Kenya. It's equatorial location means that you are getting a nice delta-v boost, its shape is more suited to this purpose, and it is far more accessible.
You seem to only be considering the fuel saving of the higher altitude. If we're considering a ground based mass driver launch, rather than a conventional rocket-only launch, then I think there would be a substantial practicality gain from firing into thinner air.
At the proposed 5000mph, air resistance at sea level would be tremendous. Greater atmospheric losses would entail either bringing more fuel to complete the orbit, or larger launch loop / greater acceleration force.
> In selling away the rocket equation you buy yourself drag. Lots of energy up front means lots of drag. Overcoming that drag means more energy and, hence, more drag. The middle child of this solution is tremendous G force.
Would it be possible and useful to do it with a 2 payloads system: one dumb piece of material first which can take lot of G followed closely by your "fragile" payload using its draft?
You have to accelerate both pieces to the same speed, which implies (in a rotational launcher), the same G (acceleration). Maybe there's some configuration where the leading payload pushes air out of the way for the first few km (the 'real' payload drafting behind), but the blocking payload isn't given enough energy to reach orbit and falls short. Seems like the following payload would crash into the leading one though.
> followed closely by your "fragile" payload using its draft?
G-forces [1] are a consequence of acceleration. An accelerating object will experience g-forces in an atmosphere or in a vacuum. ("Drafting" [2] is an aerodynamic process by which a following object exploits a leading object's slipstream to reduce the former's drag.)
With a slingshot, the destructive force is the g-force inflicted by the acceleration. (With a rocket, the destructive forces are mostly vibrations and aerodynamic stress.)
Note that a slingshot doesn't require lots of Gs. One could use a super-long slingshot to achieve the necessary velocity. But super long is super expensive, so high Gs it is.
I can imagine a heavy dead weight accelerated in the slingshot. Once released, it drags a cable, carefully laid out at an angle, with the payload attached. That payload would be accelerated into line behind the weight over a brief period. Taking fewer Gs and only once.
Very long cables are a lot cheaper than very large slingshots?
Of course it would. Like a lever has different forces on the short end and the long end, the cable could be curved and lengthened to control exactly the rate of transfer of momentum between weight and payload.
Assuming that the rocket has moment of inertia similar to a hollow cylinder with radius 1ft, conversion from rotation energy to linear is perfect, and final linear velocity is 5000 mph, the rocket would have to be spinning at
1/2 * I * w^2 = 1/2 * m * v^2
1/2 * (m * r^2) * w^2 = 1/2 * m * v^2
w = v / r = 7333 rad/s ~ 70,000 rpm
Maybe the payload of the rocket could be connected to the body of the rocket with magnetic bearings so that it isn't spinning, i.e. not experiencing the massive accelerations.
1) accelerate fast enough to penetrate the atmosphere at high speeds (and remember, the faster you travel, the air resistance is the square of your velocity).
2) withstand the crazy max-q as soon as you leave the spiral (which I assume is vacuumed).
3) make the centrifugal forces reasonable during the acceleration
The article mentions acceleration to 5000mph, which would be enough if there was no atmosphere, but I highly doubt it will work with.
If it affects rotation, which it will to an immeasurable degree, it'll affect the orbit, though I doubt by less than an amount we could ever measure or simulate.
I wonder what the flight path would have to look like - I assume you wouldn't be able to accelerate in a circle on the ground and then tilt upwards because of the G force of the tilt. So you would either sling horizontally at a fairly slight incline (taking advantage of the curvature of the earth, but imagine keeping that flight path clear), have a slowly increasing ramp that would probably have to be really long to manage the G force, or accelerate in a vertically-oriented loop (which would have to be huge to cope with faster speeds). I'm guessing the slow ramp is most practical.
If the radius of the ramp is the same as the loop wouldn’t it experience the same acceleration once diverted to the ramp? (but in a different direction)
I did the maths and if I'm right (I'm terrible at maths) then a loop would be impractical for any reasonable G force anyway - the radius would have to be over 100km for even 50gs. I'm guessing they'd need some kind of linear acceleration, in which case they can just point upwards anyway.
It shouldn't. A second push is needed up change direction from "away from Earth" to "going around Earth", because the atmosphere creates too much drag to get there in one push.
> the atmosphere creates too much drag to get there in one push
This is not true. Feasibly designs have been worked out. The challenge is the trade off between cheap, short and high-G systems and expensive, long and low-G systems.
The second push has nothing to do with atmosphere. It's because orbits repeat. As soon as the push is done, you are in the initial orbit heading away from the surface. In other words, your initial orbit intersects the ground and it would be unwise to complete a full orbit.
The second push converts the narrow ellipse of the initial orbit into a wider orbit which avoids the ground-penetrating aspect of the first orbit.
The notion of sending volatile fuel sufficient to make the correction and yet somehow not kablooeying at launch seems like a hard problem to me.
Simple. You pitch the idea to the investor, promise big money in the future, you take small money now and use part of it to build some nonviable prototype, what's left is your profit.
The article is very light on details, but I believe what's being proposed is an evacuated tube with maglev propulsion, used to accelerate a rocket up to 5000mph (as stated in the article) while on the ground. The rocket is then released, and travels until some altitude is reached, at which point engine then starts and it continues to orbit. This results in a large fuel saving over a conventional rocket.
The g-forces involved would be very high, well beyond lethal to a human, so this would be for launching robust satellites, raw materials, or fuel cheaply into space. They would still be substantially lower than those of a space gun / intercontinental artillery.
Given that the grandparent is presumably Ben Einstein of Bolt VC, an early investor in SpinLaunch, it sounds safe to say it's not using maglev at all. They say the catapult will be a centrifuge spinning inside a vacuum.
It’s surprising how many ways there are to get things into space. Everyone seems to assume we’ve already considered all alternatives and rockets are all we have.
The amount of raw material in space is utterly ridiculous. The most boring, irrelevant asteroid probably has more usable raw material in it than the largest mines on Earth.
Been a trope in scifi for a long time, I remember reading about automated mining systems in a scifi novel back in the 80's.
It refined pure metals and then blew gas through them (think of a Carbury's wispa), these where then dropped into the pacific and floated until a ship retrieved them.
The idea seemed neat though the line from "We are going to drop a 1000 tonnes of metal into the pacific and that of we are going to drop a 1000 tonnes of metal onto your house" seemed a thin one.
It's hard to defend from the bottom of a gravity well against someone at the top of one.
Dropping metal back on Earth presumes that we'd actually care about Earth at that point. There might be so many resources up there that nobody comes back.
This. I have the idea that folks on the ground will play games with money, and imagine themselves wealthy while developing asteroid resources. But it'll all be for the benefit of space-based industry, which will server space-based populations. Ultimately Earth will realize they have a big pile of imaginary points and no more metal.
So, I worked at Hyperloop One for a time, and that experience made me skeptical of the type of complaint I see in this thread.
Yes, a high school physics student can tell you the accelerations will be huge unless the loop is too, and a smart one can explain you need a circularizing burn.
But, contrary to popular belief investors aren’t total idiots who neglect basic questions. Hard tech companies do face major challenges of course, but they aren’t the ones armchair engineers on HN can point out with 5 minutes thought.
So instead of indulging in the “hurrr it’ll never work” superiority stimulus, I’d Like to point out some rays of hope:
I don’t think “catapult” means “solid arm on an axle spinning at high speed.” I’m guessing it actually means a large-ish diameter magnetically levitated and accelerated loop. That makes much larger radii possible: at 1 mile you’re looking at ~300g acceleration, 150g at 2 mile. We have loops much bigger than this with much more complex magnetics and vacuum components in our particle accelerators, so this wouldn’t be terrifyingly novel tech.
Those accelerations are big but not horribly painful to make a smallsat stand up to. We have guided artillery shells that bear 15,000g launches.
I think it’s somewhat feasible. I also think big fully reusable chemical rockets will beat this thing on cost and ease of use, but i don’t think it’ll fail because of armchair physics.
> We have loops much bigger than this with much more complex magnetics and vacuum components in our particle accelerators, so this wouldn’t be terrifyingly novel tech
Last cost estimate I saw for a reasonably-sized slingshot was $10 billion, which is in the neighbourhood of the LHC's €7.5 billion accelerator + accoutrements cost [1].
Some of the skepticism in this thread, particularly regarding the technology's core viability, is premature. But economic scepticism is warranted. I would be skeptical of a space elevator project without mass-manufactured carbon fibre; I am skeptical of a slingshot proposal without cheap superconductors.
Keith Lofstrom wrote about the electronics costs associated with a mass driver back in the '90s [1]. It's dated so some of the base costs have gone down, but it's still a good primer.
My first thought was that maybe this would lower the cost of particle accelerators like the LHC, due to more mass production of superconducting magnets.
The other consideration is that apparently we now have much more powerful, higher temperature superconductors, at least the talk about MIT's current fusion project says so.
Indeed! Assuming that your centripital accel. numbers are right, I wonder why not even just use linear accel.
Assuming that you want to exit the tube/system at 5000mph, you could keep acceleration to 9g (tolerable for a human)with less than a 9 mile long acclerator and 18 seconds. If you were ok with 40g, you're down under 4miles and 6 seconds.
(I'm not estimating the deceleration Gs from suddenly hitting MaxQ on exiting into the lower atmosphere. So perhaps that shock puts us up into a high G situation anyway, so might as well go for the smaller real-estate circular acceleration option?)
edit: "tolerable for a human" might better read "survivable for trained humans"
I don't see the term "MaxQ" very applicable here. The idea of Max Q is that you start at low aerodynamic forces and then accelerate via rocket thrust, with dynamic pressure increasing until the atmosphere density causes it to fall.
For a projectile from this launcher, MaxQ is the second it opens the airlock of the vacuum chamber and releases it to atmosphere. Then it hits a wall of air, and dynamic pressure spikes to the maximum instantly. It is true that you get rid of the centripetal acceleration upon release, so to a degree you trade the centripetal acceleration for drag acceleration.
Yeah I'm not up on my supersonic aero anywhere near enough to work out max-Q for their very pointy projectile, but I'll point out that 'suddenly hitting MaxQ' is a jerk problem, not an acceleration one. MaxQ is MaxQ, whether you've been cruising at that speed and air density for hours or just hit it out of a near-vacuum.
I think centripetal / launch acceleration dramatically outweighs air drag though, by analogy to the SR-71. The max thrust divided by its dry mass gives a maximum thrust/weight of about 1g, and that thing could cruise at Mach 3+ which is about halfway to Spinlaunch's 5000 mph.
Their little teardrop projectiles have got to be way lower drag than anything with wings and intakes, and it's probably much heavier for its size than the SR-71 as well, so I can't imagine MaxQ on these things gets past 10-15g.
> at 1 mile you’re looking at ~300g acceleration, 150g at 2 mile.
Could you explain? Centripetal acceleration is v^2/r, so naively I'd think something moving at LEO orbital velocity in a radius of 1 mile requires ~4,000g because LEO has a radius ~4k miles under 1g.
That is only about 1/4 of the velocity needed for low earth orbit [1]. The goal here seems to be to replace the first stage of a rocket by flinging it above most of the atmosphere.
Yes — rocket is still needed for circularizing burn (i.e, achieving orbital velocity).
(Which makes sense — if you managed to accelerate something to orbital velocity at sea level, it would (1) shed much of that speed before it actually reached a near-zero-atmosphere altitude and (2) burn up.)
25% the velocity but 1-.75^2 = 43.75% of the energy.
Further the rocket equation is a bitch so your saving even more fuel. The problem is you also end up with a lot of atmospheric drag and heat so the final savings are not as huge.
I don't think you did that right. The energy to get to (1/4)V is (V2)/16. The energy to get to V is (V2)/1. So your payload is only 1/16th of the way there or 6.25%.
Agreed about the rocket equation though - that first 6.25% of payload energy is much harder than the rest
If it makes you feel better picture the same energy accelerating the space shuttle it's solid rocket boosters and that huge fuel tank to some velocity vs just the shuttle to a much higher velocity. Or say to yourself it's all relative. Like tossing a ball between you and your friend on a train does not take more or less energy from you as the train is moving at higher or lower speeds, but it does take different amounts of energy from the train.
Rockets get energy from their fuel directly from burning it, but also from the kinetic energy of their fuel. So in space a rocket that can add 100km per hour of delta V from fuel before running out can do that at 0MPH , 1000 MPH, or -10,000MPH all the way up until relativity becomes an issue.
So, first find out how much speed/energy you need as a baseline it's velocity squared (100% velocity)^2 = (1v)^2 = 1e = 100% energy. Now instead of that we need to go from V1 to V2 you need (V2 - V1)^2 energy. That's (100%v - 25%v)^2 = (1v-0.25v)^2 = (0.75v)^2 = 0.5625e so we still need 56.25% as much energy, and we gained 100%e - 56.25%e = 43.75% energy.
PS: Unfortunately, these things don't start in space so we need to consider air resistance.
Why are you skeptical? HN community always been this negative, or even more! Remember the initial Drew's DropBox idea that majority bashed him that its a stupid idea because... everyone would rather built its own software? Drew Stock in Drop is $1B worth right now.
If anything, I think its opposite - the more HNers are negative the more your idea has a strong standing!
Coincidentally, on the subject of catapults, just recently I was bashed by "always_good" that "I'm sure a bunch of children also wonder the same thing" [1]
>But, contrary to popular belief investors aren’t total idiots who neglect basic questions
Investors, particularly tech investors often do neglect basic (tech DD) questions.
Sometimes it’s because they’re investing in the “team” and neglect DD. Sometimes it’s because the area is hot and they need to make a play... or just because they happen to know or like the people involved.
Whatever the reason, it’s dangerous to assume that the investors must have done their DD (see Theranos for example). Not saying that this is the case here, and often things work out anyway...
Theranos isn't the best example. DFJ invested in their seed, but the vast majority of their funds were less sophisticated non-tech investors. Using them as a poster child for Silicon Valley dysfunction is a bit off to me.
Your broader point is well taken though, there are certainly cases where investors completely skip tech DD. Eg, Juicero's absolutely comical "engineering" that killed them with obscenely high costs.
Theranos had a bunch of larger investors [1] many of them as sophisticated as any tech investor. I’m not saying SV investors are particularly dysfunctional, just that it’s pretty normal for tech DD to not get done, or get done badly. I use the Theranos example because it’s big and public (most disappear without any news).
While the high engineering costs are definitely comical, wasn't Juicero's failure because nobody wanted their revenue-driving product, the juice bags? Seems like a $600 device could still be profitable (and subsidized) if the core revenue driver was viable.
Long ago I heard that the reason why the Jules Verne space cannon was infeasible was not so much the acceleration as the aerodynamics; 5000mph is "hypersonic". I'm not quite clear whether the spinlauncher's rocket is just for circularisation or whether it's needed to clear the atmosphere too?
One question I've never been able to figure out with this concept is what happens when this fast moving launch vehicle hits the stationary air. Would it be like hitting a wall? I'm a bit physics ignorant.
>> To my knowledge, there is no reason to minimize jerk for machinery.
Maybe not for a blob of homogeneous metal parts, but with complex structures that jerk can multiply into bad things. As the nose hits air (the sudden high G-load) a shockwave moves down the vehicle at the speed of sound (sound through metal, not air). Shockwaves can do funny things in complex structures. Imagine that this thing had a solid rocket motor for circulization. As the shockwave moving down the metal walls at one speed, slower through the fuel, the fuel might crack in ways that are not-good for a rocket.
Fluid-filled things like pipes can also be subject to water hammer-like effects when g-loading changes abruptly as opposed to a gradual onset. The fluid gets moving quickly as the pipe stretches at one end, then must stop abruptly as the pipe hits its limit.
Another comment mentioned "hammer-like effects"... I can see it. Mentally, I picture a half-filed milk jug being pushed around the counter. Smooth acceleration changes cause the water level to safely assume the new steady-state, but high jerk values can cause the container to collide with the water hard. If you have hardened electronics, hopefully none of the components are loose.
You'd probably have a stationary launch ramp exit, built up the side of a mountain. If you can put the top of the tube at 10-15k ft that will reduce air drag _substantially_. Even a 5000ft exit would be in substantially thinner air.
I have a hard time believing that the reduction is anywhere near substantial enough. Friction heating was a major issue for high speed aircraft like the SR-71, and they "only" fly at ~3500 km/h at 20+ km altitudes.
Converting everything to metric and working out the centripetal acceleration, a radius of 1 mile yields a centripetal acceleration of 232g, to an arbitrary 3 significant figures. A radius of 2 miles yields 116g. The acceleration would drop linearly along the length of the "arm" as you move toward the center, so you could calculate (with calculus, over which I can't be bothered at the moment) the optimal way to taper the arm from root to tip for a given end load.
Drag losses on the arm at a 1 or 2 mile radius would dominate, and ridiculously so. Frankly, roughly 100-230g is not severe at all for a properly engineered vehicle at the payload ratio you could expect to achieve if you get the first 2.2 km/sec "free", as you would in this scheme. That's the majority of a factor of exhaust velocity for a kerosene/lox engine, and all of a factor of the exhaust velocity for a solid rocket motor. Multiples of exhaust velocities are factors of e, so you're probably better than doubling the payload ratio. Perhaps counterintuitively, going from 3 percent mass fraction to 6 percent brings your vehicle size down by half. You go from ~33 times the payload to ~16 times the payload. And, while others are talking a good game about drag, this saves you loads in gravity losses, as the rocket is spending far less time fighting gravity with this initial boost. (1g for two minutes is 1.2 km/s, give or take centripetal effects from your curved launch trajectory. Not negligible, at all.) The other commenters seem also to be mostly neglecting that the motor/engine will very quickly reach near-vacuum conditions, not immodestly increasing its ISP.
Much better than a mile-long tether would be, in my not-so-humble initial opinion, to reduce the tether length by a factor of 10 or 100 from "a mile", to give a centripetal g load of 2k-20k g. Again, calculus tells you how to taper your (probably carbon fiber, possibly consumable, most definitely streamlined) attachment rod. And don't bother with the complexity of a vacuum. The Nike program launched vehicles at Mach 10 in the lower atmosphere. That's 3.4 km/s, 1.2 km/s faster than SpinLaunch's proposal. Given that heating goes something like the 4th power of velocity, Mach 6 or so is going to be much, much less severe than the Mach 10 environment encountered by Nike. Why, SpinLaunch vehicles won't even get to glow white hot!
As I said above, I highly doubt it’s a literal arm / sling being used. I think it’s a magnetically guided and accelerated loop, so the payload is the only part of the system moving at all. You’re right the drag/tension on an actual arm would be ludicrous, and would certainly force you to a smaller radius.
This doesn't seem impossible. There are some PoCs to be found in old technology.
The shock loads are surmountable. We made an atomic bomb that worked after enduring at least 10KG acceleration. [1]
The aero loads (mechanical and thermal) also seem feasible. We built guided interceptors that launched from sea level and accelerated at 100G to over 7,000 mi/hr. [2] These endured incandescent skin temps within a few seconds of flight.
Aero drag loads can be mitigated mechanically. The aerospike on the Trident missile shows one way of reducing drag by putting a small mechanical probe ahead of the vehicle. [3]
No idea about the economics, but I wish them every success.
There is a lot of published raw science on Electromagnetic Linear Motors, with several feasibility studies on Earth to Orbit and Earth to Moon systems.
There are several challenges with building on that large, such as building large capacitors, building a structure big enough, and dealing with something that high energy. However, I think we are at a critical point where this might become something we understand how to build. We use the fundamental technology everyday in high speed rail, and we've learned a lot from constructing projects like the LHC and Hyperloop. The Navy is planning on implemented these motors for launch assist on the next generation of aircraft carriers.
I’ve wanted to build a Gerald Bull style space cannon (but the more modern UW RAMAC style) for a long time. Prototype would be $2-5mm, something small which could actually put something decent into orbit around $50mm. I’ve heard there is a group in SoCal which finally got funding to build it.
Would love to know more if you have a link about this group. For some reason I'm fascinated by the space gun concept. Even if it were only used to launch raw materials into space cheaply that could still be a huge boost to space exploration.
Years ago I backed the Slingatron [0] on Kickstarter, but sadly it was not funded. At first I thought maybe SpinLaunch was a rebrand of HyperV, but that is not the case and its an entirely different group of people. Either way, I'm glad this is getting actual money behind it since it's a very interesting solution, and I hope it "takes off" (sorry).
I've been exploring large-scale structures built using the "Tensegrity" concepts of Bucky Fuller and Ken Snelson. I'm pretty sure you can build really large structures using modern materials (e.g. kevlar and carbon fiber.) Call it "giga-tech" (like nano-tech but scale up instead of down.)
One thing in particular that seems feasible is a large floating structure, like a mile-high pyramid, placed on an ocean at the equator, and supporting a launch structure.
I think you can make a very large whip-like jointed spaceframe that acts like a catapult to accelerate payloads.
By enclosing the outer surface with a membrane you can use solar energy to evaporate water, then condense it at the top of the structure into holding tanks. The mass of the water powers the whip like a trebuchet. (Or you can extract electricity using the principle of Lord Kelvin's Thunderstorm.)
I'm pretty sure it would work. No advanced technology or concepts used at all. I don't quite have the chops to do the back-of-envelope math though. Right now I'm working on computer simulations (Finite Element Method.) I'm fortunate that NASA has a program working on tensegrity robots for exploring the surfaces of other planets, and they have released a tool that can simulate tensegrity structures.
One other thing, in re: rockets and drag. I can't find a reference right now, but electrifying a rocket with a charge difference from the nose to the tail can significantly reduce drag as the field accelerates the air itself.
This is just total lunacy. Have we reached peak VC yet? If not I have a startup that is building a warp drive even though its totally theoretical and the technology to build one is 100+ years away. Throw money at me please.
I'm very skeptical, of course I'm not as smart or as informed as many other people so what I'm saying might not mean anything.
1) if the idea is to impart all of the kinetic energy needed to get into LEO at once, on the ground, then you are talking ~17,000 MPH worth of KE (though truly, more, because of loss to drag). There's a reason why max-q is an important consideration in the design of space vehicles. The space shuttle reaches max-q at 30K feet, where the density of air is 3x less than at sea level. How do you design your vehicle so that it doesn't turn into dust when it hits 1 ATM at 17,000+ MPH?
2) the centripetal force on the vehicle, prior to launch, will be enormous. So in addition to not deforming and/or burning up the moment the vehicle hits the air, the vehicle also needs to be built sturdily enough to not get crushed while being accelerated.
I read Bad Blood a few weekends ago. Holmes hoodwinked investors who wanted to believe that a fairy tale technology could exist, by never publishing or otherwise allowing outside scrutiny of their technology. How is this company different?
> So in addition to not deforming and/or burning up the moment the vehicle hits the air, the vehicle also needs to be built sturdily enough to not get crushed while being accelerated.
Since launch mass is less of a concern maybe they can just manufature the satellites differently, e.g. filling the voids with a resin or oil which distributes the forces uniformly.
I would love to see these guys succeed both because it would be something truly novel, and because I think low cost access to space is going to be critical moving forward.
But the physics of getting through the troposphere at 7 to 9 km/sec seem to be really difficult to overcome.
110 comments
[ 3.3 ms ] story [ 105 ms ] threadIn selling away the rocket equation you buy yourself drag. Lots of energy up front means lots of drag. Overcoming that drag means more energy and, hence, more drag. The middle child of this solution is tremendous G force.
You can't slingshot complex things into space. Pretty much just fuel and raw materials. That means you need in-space (a) refueling and (b) additive manufacturing capabilities. There are teams working on both problems, though they are presently in the domain of science versus engineering. Perhaps that will now be incentivized to change.
[1] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
The problem is that now you have to transport everything near and up the mountain, which costs a ton in logistics (getting a road up a mountain that can handle a entire assembled rocket isn't cheap, nor easy). Most launches have delta-v to spare because satellites are usually nowhere near the rocket's maximum payload weight.
tl;dr it can save 6% in a ideal situation, but the extra cost and logistical problems aren't worth it.
Unless you launch by means of a mass driver/rail gun [1] built into the side of Mt Everest with a piggy backed elevator for tourists. Tourists would arrive to a pressurized viewing area at the summit and have the option of donning an oxygen mask, going outside and posing for photos next to a cutout of Sir Hillary. I have never understood why serious rock climbing friends get so upset whenever I have mentioned this idea over the years.
1 https://en.wikipedia.org/wiki/Mass_driver
At the proposed 5000mph, air resistance at sea level would be tremendous. Greater atmospheric losses would entail either bringing more fuel to complete the orbit, or larger launch loop / greater acceleration force.
Would it be possible and useful to do it with a 2 payloads system: one dumb piece of material first which can take lot of G followed closely by your "fragile" payload using its draft?
G-forces [1] are a consequence of acceleration. An accelerating object will experience g-forces in an atmosphere or in a vacuum. ("Drafting" [2] is an aerodynamic process by which a following object exploits a leading object's slipstream to reduce the former's drag.)
With a slingshot, the destructive force is the g-force inflicted by the acceleration. (With a rocket, the destructive forces are mostly vibrations and aerodynamic stress.)
Note that a slingshot doesn't require lots of Gs. One could use a super-long slingshot to achieve the necessary velocity. But super long is super expensive, so high Gs it is.
[1] https://en.wikipedia.org/wiki/G-force
[2] https://en.wikipedia.org/wiki/Drafting_(aerodynamics)
Very long cables are a lot cheaper than very large slingshots?
Anyway just thinking out loud.
Unless your cable were elastic, this would not materially change the payload's acceleration. That said, you might find skyhooks [1][2] interesting.
[1] https://en.wikipedia.org/wiki/Skyhook_%28structure%29
[2] http://adventuretime.wikia.com/wiki/Skyhooks
Assuming that the rocket has moment of inertia similar to a hollow cylinder with radius 1ft, conversion from rotation energy to linear is perfect, and final linear velocity is 5000 mph, the rocket would have to be spinning at
1/2 * I * w^2 = 1/2 * m * v^2
1/2 * (m * r^2) * w^2 = 1/2 * m * v^2
w = v / r = 7333 rad/s ~ 70,000 rpm
Maybe the payload of the rocket could be connected to the body of the rocket with magnetic bearings so that it isn't spinning, i.e. not experiencing the massive accelerations.
1) accelerate fast enough to penetrate the atmosphere at high speeds (and remember, the faster you travel, the air resistance is the square of your velocity).
2) withstand the crazy max-q as soon as you leave the spiral (which I assume is vacuumed).
3) make the centrifugal forces reasonable during the acceleration
The article mentions acceleration to 5000mph, which would be enough if there was no atmosphere, but I highly doubt it will work with.
Every time that an object leaves our planet’s atmosphere we (apparently) minutely change the earth’s orbit.
https://space.stackexchange.com/questions/26733/does-launchi...
Either way, there's some interesting info on the concept at https://en.wikipedia.org/wiki/Space_gun and https://en.wikipedia.org/wiki/Mass_driver.
This is not true. Feasibly designs have been worked out. The challenge is the trade off between cheap, short and high-G systems and expensive, long and low-G systems.
The second push converts the narrow ellipse of the initial orbit into a wider orbit which avoids the ground-penetrating aspect of the first orbit.
The notion of sending volatile fuel sufficient to make the correction and yet somehow not kablooeying at launch seems like a hard problem to me.
https://en.wikipedia.org/wiki/Mass_driver
The g-forces involved would be very high, well beyond lethal to a human, so this would be for launching robust satellites, raw materials, or fuel cheaply into space. They would still be substantially lower than those of a space gun / intercontinental artillery.
https://en.wikipedia.org/wiki/Space_gun#Practical_attempts
https://www.crunchbase.com/person/ben-einstein
https://www.crunchbase.com/funding_round/spinlaunch-converti...
https://en.wikipedia.org/wiki/Pumpkin_chucking
Off the top of my head:
Providing laser power from the ground station
Giant rail gun
Launch fountain
Launch loop
Space elevator
Sky hook
This spin machine
It refined pure metals and then blew gas through them (think of a Carbury's wispa), these where then dropped into the pacific and floated until a ship retrieved them.
The idea seemed neat though the line from "We are going to drop a 1000 tonnes of metal into the pacific and that of we are going to drop a 1000 tonnes of metal onto your house" seemed a thin one.
It's hard to defend from the bottom of a gravity well against someone at the top of one.
A giant torus that floats near the edge of the atmosphere. Spin it for more lift, stability, and to throw things.
;)
Yes, a high school physics student can tell you the accelerations will be huge unless the loop is too, and a smart one can explain you need a circularizing burn.
But, contrary to popular belief investors aren’t total idiots who neglect basic questions. Hard tech companies do face major challenges of course, but they aren’t the ones armchair engineers on HN can point out with 5 minutes thought.
So instead of indulging in the “hurrr it’ll never work” superiority stimulus, I’d Like to point out some rays of hope:
I don’t think “catapult” means “solid arm on an axle spinning at high speed.” I’m guessing it actually means a large-ish diameter magnetically levitated and accelerated loop. That makes much larger radii possible: at 1 mile you’re looking at ~300g acceleration, 150g at 2 mile. We have loops much bigger than this with much more complex magnetics and vacuum components in our particle accelerators, so this wouldn’t be terrifyingly novel tech.
Those accelerations are big but not horribly painful to make a smallsat stand up to. We have guided artillery shells that bear 15,000g launches.
I think it’s somewhat feasible. I also think big fully reusable chemical rockets will beat this thing on cost and ease of use, but i don’t think it’ll fail because of armchair physics.
You just lost your credibility.
https://news.ycombinator.com/newsguidelines.html
Last cost estimate I saw for a reasonably-sized slingshot was $10 billion, which is in the neighbourhood of the LHC's €7.5 billion accelerator + accoutrements cost [1].
Some of the skepticism in this thread, particularly regarding the technology's core viability, is premature. But economic scepticism is warranted. I would be skeptical of a space elevator project without mass-manufactured carbon fibre; I am skeptical of a slingshot proposal without cheap superconductors.
[1] https://en.wikipedia.org/wiki/Large_Hadron_Collider#Cost
[1] https://settlement.arc.nasa.gov/Nowicki/SPBI1SI.HTM
The other consideration is that apparently we now have much more powerful, higher temperature superconductors, at least the talk about MIT's current fusion project says so.
https://www.youtube.com/watch?v=L0KuAx1COEk
Not sure if they are cheaper, but since there would be less bulk and no need for liquid helium, that would be my guess.
Assuming that you want to exit the tube/system at 5000mph, you could keep acceleration to 9g (tolerable for a human)with less than a 9 mile long acclerator and 18 seconds. If you were ok with 40g, you're down under 4miles and 6 seconds.
(I'm not estimating the deceleration Gs from suddenly hitting MaxQ on exiting into the lower atmosphere. So perhaps that shock puts us up into a high G situation anyway, so might as well go for the smaller real-estate circular acceleration option?)
edit: "tolerable for a human" might better read "survivable for trained humans"
For a projectile from this launcher, MaxQ is the second it opens the airlock of the vacuum chamber and releases it to atmosphere. Then it hits a wall of air, and dynamic pressure spikes to the maximum instantly. It is true that you get rid of the centripetal acceleration upon release, so to a degree you trade the centripetal acceleration for drag acceleration.
I think centripetal / launch acceleration dramatically outweighs air drag though, by analogy to the SR-71. The max thrust divided by its dry mass gives a maximum thrust/weight of about 1g, and that thing could cruise at Mach 3+ which is about halfway to Spinlaunch's 5000 mph.
Their little teardrop projectiles have got to be way lower drag than anything with wings and intakes, and it's probably much heavier for its size than the SR-71 as well, so I can't imagine MaxQ on these things gets past 10-15g.
Could you explain? Centripetal acceleration is v^2/r, so naively I'd think something moving at LEO orbital velocity in a radius of 1 mile requires ~4,000g because LEO has a radius ~4k miles under 1g.
[1] https://en.wikipedia.org/wiki/Low_Earth_orbit#Orbital_charac...
(Which makes sense — if you managed to accelerate something to orbital velocity at sea level, it would (1) shed much of that speed before it actually reached a near-zero-atmosphere altitude and (2) burn up.)
Further the rocket equation is a bitch so your saving even more fuel. The problem is you also end up with a lot of atmospheric drag and heat so the final savings are not as huge.
Agreed about the rocket equation though - that first 6.25% of payload energy is much harder than the rest
Rockets get energy from their fuel directly from burning it, but also from the kinetic energy of their fuel. So in space a rocket that can add 100km per hour of delta V from fuel before running out can do that at 0MPH , 1000 MPH, or -10,000MPH all the way up until relativity becomes an issue.
So, first find out how much speed/energy you need as a baseline it's velocity squared (100% velocity)^2 = (1v)^2 = 1e = 100% energy. Now instead of that we need to go from V1 to V2 you need (V2 - V1)^2 energy. That's (100%v - 25%v)^2 = (1v-0.25v)^2 = (0.75v)^2 = 0.5625e so we still need 56.25% as much energy, and we gained 100%e - 56.25%e = 43.75% energy.
PS: Unfortunately, these things don't start in space so we need to consider air resistance.
If anything, I think its opposite - the more HNers are negative the more your idea has a strong standing!
Coincidentally, on the subject of catapults, just recently I was bashed by "always_good" that "I'm sure a bunch of children also wonder the same thing" [1]
[1] https://news.ycombinator.com/item?id=17174196
Edit: made it less personal :)
Investors, particularly tech investors often do neglect basic (tech DD) questions.
Sometimes it’s because they’re investing in the “team” and neglect DD. Sometimes it’s because the area is hot and they need to make a play... or just because they happen to know or like the people involved.
Whatever the reason, it’s dangerous to assume that the investors must have done their DD (see Theranos for example). Not saying that this is the case here, and often things work out anyway...
Your broader point is well taken though, there are certainly cases where investors completely skip tech DD. Eg, Juicero's absolutely comical "engineering" that killed them with obscenely high costs.
[1] https://www.crunchbase.com/organization/theranos/investors/i...
https://en.wikipedia.org/wiki/Momentum_exchange_tether
https://techcrunch.com/2018/02/22/spinlaunch-2/
https://en.wikipedia.org/wiki/Jerk_(physics)
To my knowledge, there is no reason to minimize jerk for machinery. Only the maximum acceleration value matters.
Maybe not for a blob of homogeneous metal parts, but with complex structures that jerk can multiply into bad things. As the nose hits air (the sudden high G-load) a shockwave moves down the vehicle at the speed of sound (sound through metal, not air). Shockwaves can do funny things in complex structures. Imagine that this thing had a solid rocket motor for circulization. As the shockwave moving down the metal walls at one speed, slower through the fuel, the fuel might crack in ways that are not-good for a rocket.
Fluid-filled things like pipes can also be subject to water hammer-like effects when g-loading changes abruptly as opposed to a gradual onset. The fluid gets moving quickly as the pipe stretches at one end, then must stop abruptly as the pipe hits its limit.
Thank you.
Ib4 hyperloop EXCALIBUR.
Drag losses on the arm at a 1 or 2 mile radius would dominate, and ridiculously so. Frankly, roughly 100-230g is not severe at all for a properly engineered vehicle at the payload ratio you could expect to achieve if you get the first 2.2 km/sec "free", as you would in this scheme. That's the majority of a factor of exhaust velocity for a kerosene/lox engine, and all of a factor of the exhaust velocity for a solid rocket motor. Multiples of exhaust velocities are factors of e, so you're probably better than doubling the payload ratio. Perhaps counterintuitively, going from 3 percent mass fraction to 6 percent brings your vehicle size down by half. You go from ~33 times the payload to ~16 times the payload. And, while others are talking a good game about drag, this saves you loads in gravity losses, as the rocket is spending far less time fighting gravity with this initial boost. (1g for two minutes is 1.2 km/s, give or take centripetal effects from your curved launch trajectory. Not negligible, at all.) The other commenters seem also to be mostly neglecting that the motor/engine will very quickly reach near-vacuum conditions, not immodestly increasing its ISP.
Much better than a mile-long tether would be, in my not-so-humble initial opinion, to reduce the tether length by a factor of 10 or 100 from "a mile", to give a centripetal g load of 2k-20k g. Again, calculus tells you how to taper your (probably carbon fiber, possibly consumable, most definitely streamlined) attachment rod. And don't bother with the complexity of a vacuum. The Nike program launched vehicles at Mach 10 in the lower atmosphere. That's 3.4 km/s, 1.2 km/s faster than SpinLaunch's proposal. Given that heating goes something like the 4th power of velocity, Mach 6 or so is going to be much, much less severe than the Mach 10 environment encountered by Nike. Why, SpinLaunch vehicles won't even get to glow white hot!
The shock loads are surmountable. We made an atomic bomb that worked after enduring at least 10KG acceleration. [1]
The aero loads (mechanical and thermal) also seem feasible. We built guided interceptors that launched from sea level and accelerated at 100G to over 7,000 mi/hr. [2] These endured incandescent skin temps within a few seconds of flight.
Aero drag loads can be mitigated mechanically. The aerospike on the Trident missile shows one way of reducing drag by putting a small mechanical probe ahead of the vehicle. [3]
No idea about the economics, but I wish them every success.
[1] https://en.wikipedia.org/wiki/M65_atomic_cannon [2] https://en.wikipedia.org/wiki/Sprint_(missile) [3] https://en.wikipedia.org/wiki/Drag-reducing_aerospike
There are several challenges with building on that large, such as building large capacitors, building a structure big enough, and dealing with something that high energy. However, I think we are at a critical point where this might become something we understand how to build. We use the fundamental technology everyday in high speed rail, and we've learned a lot from constructing projects like the LHC and Hyperloop. The Navy is planning on implemented these motors for launch assist on the next generation of aircraft carriers.
[0] https://www.kickstarter.com/projects/391496725/the-slingatro...
One thing in particular that seems feasible is a large floating structure, like a mile-high pyramid, placed on an ocean at the equator, and supporting a launch structure.
I think you can make a very large whip-like jointed spaceframe that acts like a catapult to accelerate payloads.
By enclosing the outer surface with a membrane you can use solar energy to evaporate water, then condense it at the top of the structure into holding tanks. The mass of the water powers the whip like a trebuchet. (Or you can extract electricity using the principle of Lord Kelvin's Thunderstorm.)
I'm pretty sure it would work. No advanced technology or concepts used at all. I don't quite have the chops to do the back-of-envelope math though. Right now I'm working on computer simulations (Finite Element Method.) I'm fortunate that NASA has a program working on tensegrity robots for exploring the surfaces of other planets, and they have released a tool that can simulate tensegrity structures.
One other thing, in re: rockets and drag. I can't find a reference right now, but electrifying a rocket with a charge difference from the nose to the tail can significantly reduce drag as the field accelerates the air itself.
1) if the idea is to impart all of the kinetic energy needed to get into LEO at once, on the ground, then you are talking ~17,000 MPH worth of KE (though truly, more, because of loss to drag). There's a reason why max-q is an important consideration in the design of space vehicles. The space shuttle reaches max-q at 30K feet, where the density of air is 3x less than at sea level. How do you design your vehicle so that it doesn't turn into dust when it hits 1 ATM at 17,000+ MPH?
2) the centripetal force on the vehicle, prior to launch, will be enormous. So in addition to not deforming and/or burning up the moment the vehicle hits the air, the vehicle also needs to be built sturdily enough to not get crushed while being accelerated.
I read Bad Blood a few weekends ago. Holmes hoodwinked investors who wanted to believe that a fairy tale technology could exist, by never publishing or otherwise allowing outside scrutiny of their technology. How is this company different?
Since launch mass is less of a concern maybe they can just manufature the satellites differently, e.g. filling the voids with a resin or oil which distributes the forces uniformly.
But the physics of getting through the troposphere at 7 to 9 km/sec seem to be really difficult to overcome.