SpinLaunch raises $40M to build a machine to catapult objects into space
bloomberg.com
bloomberg.com
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.
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
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/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.
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
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.
[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.
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.
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.
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.
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.
[0] https://www.kickstarter.com/projects/391496725/the-slingatro...
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.
;)
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.
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...
But the physics of getting through the troposphere at 7 to 9 km/sec seem to be really difficult to overcome.
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.
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://www.crunchbase.com/person/ben-einstein
https://www.crunchbase.com/funding_round/spinlaunch-converti...
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.