SpinLaunch: General Company and Development Updates and Discussions

[Robotbeat]

I used to use just a piece of packing tape when shooting stuff out of a vacuum tube into atmosphere ~supersonically. That stuff is super cheap.

[high road]

So what happens when you puncture the packaging tape when it's in vacuum, so without shooting? That's what Spinlaunch does.

As soon as you fire, it's no longer a vacuum, as your projectile rides a pressure wave. Assuming you're not talking about a rail gun, that is.

[edzieba]

So what happens when you puncture the packaging tape when it's in vacuum, so without shooting? That's what Spinlaunch does.

As soon as you fire, it's no longer a vacuum, as your projectile rides a pressure wave. Assuming you're not talking about a rail gun, that is.

The projectile travels forward within an evacuated tube and punctures the barrier film on exit, so no difference between a spin-launched projectile and an LGG-launched projectile there, and therefore demonstrated to be feasible.

Moving the goalposts to the effect of inrushing atmosphere on the launching equipment rather than the projectile: the projectile is relatively small diameter, at the end of a tunnel (i.e. some distance between the spinup chamber and the exit film). That chokes the inflow to a manageable level, and as the entire setup is stationary you can build it to easily withstand the forces on the chamber walls. That leaves the spinning structure itself experiencing a pressure rise from inflowing air. Using a ballpark of 1m diameter projectile (leaving a 1m diameter hole), a 10m long tunnel, and a 100m diameter 5m high chamber, you have 39,000m^3 to fill from a 1 bar (14 PSI) external pressure, which gives a peak of ~64 cubic metres per minute flow, or about 10 hours to refill the chamber back to 1 ATM. Ample time to close a mechanical door within the barrel section after firing and minimise pressure rise. Adding baffles within the exit tunnel (the same concept as a silencer, but in reverse and without contact wipers) the prompt pressure wave can also be damped.

[high road]

So what happens when you puncture the packaging tape when it's in vacuum, so without shooting? That's what Spinlaunch does.

As soon as you fire, it's no longer a vacuum, as your projectile rides a pressure wave. Assuming you're not talking about a rail gun, that is.

The projectile travels forward within an evacuated tube and punctures the barrier film on exit, so no difference between a spin-launched projectile and an LGG-launched projectile there, and therefore demonstrated to be feasible.

Moving the goalposts to the effect of inrushing atmosphere on the launching equipment rather than the projectile: the projectile is relatively small diameter, at the end of a tunnel (i.e. some distance between the spinup chamber and the exit film). That chokes the inflow to a manageable level, and as the entire setup is stationary you can build it to easily withstand the forces on the chamber walls. That leaves the spinning structure itself experiencing a pressure rise from inflowing air. Using a ballpark of 1m diameter projectile (leaving a 1m diameter hole), a 10m long tunnel, and a 100m diameter 5m high chamber, you have 39,000m^3 to fill from a 1 bar (14 PSI) external pressure, which gives a peak of ~64 cubic metres per minute flow, or about 10 hours to refill the chamber back to 1 ATM. Ample time to close a mechanical door within the barrel section after firing and minimise pressure rise. Adding baffles within the exit tunnel (the same concept as a silencer, but in reverse and without contact wipers) the prompt pressure wave can also be damped.

The last part is what I was asking about, no goal posts moved ;-) That leaves plenty of time to potentially open said mechanical door a safe number of seconds before and still release the payload in mostly vacuum.

Any debris (like pieces of the 1m diameter expendable seal) or wayward birds being sucked in and hitting the centrifuge arm at high speed would not be a problem either?

[Robotbeat]

So what happens when you puncture the packaging tape when it's in vacuum, so without shooting? That's what Spinlaunch does.

As soon as you fire, it's no longer a vacuum, as your projectile rides a pressure wave. Assuming you're not talking about a rail gun, that is.

What do you mean, "what happens"? I fail to see the overriding relevance of that. It would just puncture the tape like shooting an arrow through a balloon.

Liquids are far denser than air, but an arrow will shoot right through it:

[Robotbeat]

So what happens when you puncture the packaging tape when it's in vacuum, so without shooting? That's what Spinlaunch does.

As soon as you fire, it's no longer a vacuum, as your projectile rides a pressure wave. Assuming you're not talking about a rail gun, that is.

The projectile travels forward within an evacuated tube and punctures the barrier film on exit, so no difference between a spin-launched projectile and an LGG-launched projectile there, and therefore demonstrated to be feasible.

Moving the goalposts to the effect of inrushing atmosphere on the launching equipment rather than the projectile: the projectile is relatively small diameter, at the end of a tunnel (i.e. some distance between the spinup chamber and the exit film). That chokes the inflow to a manageable level, and as the entire setup is stationary you can build it to easily withstand the forces on the chamber walls. That leaves the spinning structure itself experiencing a pressure rise from inflowing air. Using a ballpark of 1m diameter projectile (leaving a 1m diameter hole), a 10m long tunnel, and a 100m diameter 5m high chamber, you have 39,000m^3 to fill from a 1 bar (14 PSI) external pressure, which gives a peak of ~64 cubic metres per minute flow, or about 10 hours to refill the chamber back to 1 ATM. Ample time to close a mechanical door within the barrel section after firing and minimise pressure rise. Adding baffles within the exit tunnel (the same concept as a silencer, but in reverse and without contact wipers) the prompt pressure wave can also be damped.

The last part is what I was asking about, no goal posts moved ;-) That leaves plenty of time to potentially open said mechanical door a safe number of seconds before and still release the payload in mostly vacuum.

Any debris (like pieces of the 1m diameter expendable seal) or wayward birds being sucked in and hitting the centrifuge arm at high speed would not be a problem either?

I actually don't think it would. Thin plastic stuff would at worst make a mess by collision-melting (and even that probably wouldn't happen) but wouldn't actually damage the extremely solid centrifuge arm, even at Mach 5 or whatever.

For a 1 meter diameter seal, you'd likely use a whole bunch of layers (like 10 or 20) instead of 1, allowing you to use thin plastic, like 10-20 microns thick or something.

[Robotbeat]

You also could intentionally dump air into the centrifuge right as the projectile is released. That'd prevent pieces of plastic from blowing into the centrifuge. (Not that it really matters.) And it'd also slow the centrifuge down.

[Robotbeat]

With enough power, you don't HAVE to use a vacuum.

(I think these guys get to like Mach 0.5, but still.)



That arm doesn't look terribly aerodynamic, either. Scary as heck.

[tpw2]

So what happens when you puncture the packaging tape when it's in vacuum, so without shooting? That's what Spinlaunch does.

As soon as you fire, it's no longer a vacuum, as your projectile rides a pressure wave. Assuming you're not talking about a rail gun, that is.

The projectile travels forward within an evacuated tube and punctures the barrier film on exit, so no difference between a spin-launched projectile and an LGG-launched projectile there, and therefore demonstrated to be feasible.

Moving the goalposts to the effect of inrushing atmosphere on the launching equipment rather than the projectile: the projectile is relatively small diameter, at the end of a tunnel (i.e. some distance between the spinup chamber and the exit film). That chokes the inflow to a manageable level, and as the entire setup is stationary you can build it to easily withstand the forces on the chamber walls. That leaves the spinning structure itself experiencing a pressure rise from inflowing air. Using a ballpark of 1m diameter projectile (leaving a 1m diameter hole), a 10m long tunnel, and a 100m diameter 5m high chamber, you have 39,000m^3 to fill from a 1 bar (14 PSI) external pressure, which gives a peak of ~64 cubic metres per minute flow, or about 10 hours to refill the chamber back to 1 ATM. Ample time to close a mechanical door within the barrel section after firing and minimise pressure rise. Adding baffles within the exit tunnel (the same concept as a silencer, but in reverse and without contact wipers) the prompt pressure wave can also be damped.

Are you sure about the flow rate? It sounds way too low to me...

[cdebuhr]

So what happens when you puncture the packaging tape when it's in vacuum, so without shooting? That's what Spinlaunch does.

As soon as you fire, it's no longer a vacuum, as your projectile rides a pressure wave. Assuming you're not talking about a rail gun, that is.

The projectile travels forward within an evacuated tube and punctures the barrier film on exit, so no difference between a spin-launched projectile and an LGG-launched projectile there, and therefore demonstrated to be feasible.

Moving the goalposts to the effect of inrushing atmosphere on the launching equipment rather than the projectile: the projectile is relatively small diameter, at the end of a tunnel (i.e. some distance between the spinup chamber and the exit film). That chokes the inflow to a manageable level, and as the entire setup is stationary you can build it to easily withstand the forces on the chamber walls. That leaves the spinning structure itself experiencing a pressure rise from inflowing air. Using a ballpark of 1m diameter projectile (leaving a 1m diameter hole), a 10m long tunnel, and a 100m diameter 5m high chamber, you have 39,000m^3 to fill from a 1 bar (14 PSI) external pressure, which gives a peak of ~64 cubic metres per minute flow, or about 10 hours to refill the chamber back to 1 ATM. Ample time to close a mechanical door within the barrel section after firing and minimise pressure rise. Adding baffles within the exit tunnel (the same concept as a silencer, but in reverse and without contact wipers) the prompt pressure wave can also be damped.

Are you sure about the flow rate? It sounds way too low to me...

Yeah - that really doesn't pass the smell test, does it.  If we assume that the air is rushing in at something close to the speed of sound, I get an initial inflow rate that would fill the chamber back up to 1atm in around 2 minutes.  Now, as the chamber pressure comes up, that flow rate may start to drop off somewhat, but its sure not going to take 10 hours. If it took more than ten minutes I'd be surprised.  Even so, I suppose if you had an air shutter that could close within, say, 1 second of launch (should be doable), you might be able to keep most of your vacuum and not wreck the centrifuge.  Still, I'll believe this is a viable launch system once it starts putting things into orbit. 

[Robotbeat]

My main thing is the accelerations involved mean your rocket stages have to be built very heavy and therefore will have crappy mass fractions and much of your advantage is eaten in aero losses which are already high for small vehicles. So you get maybe a 1km/s advantage but you can only launch tiny payloads that can withstand high gees and the stages have to be really sturdy and so have a high dry mass and will be significantly more expensive to make plus expendable.

It’s actually possible to do it. “Viable” in the sense that it may not even be the craziest rocket system anyone has ever built (Sprint missiles or something like it gotta take that prize). But outside of MAYBE munitions tests, I don’t see how it’s competitive.

I mean, maybe if you’re launching up to a Rotovator or something and so don’t need a rocket (other than maneuvering thrusters)? But without a rotovator, you already need an 8km/s rocket, and I doubt a 9.3km/s rocket built to withstand 10gees max (and only getting Mach 1 at about 0.3 atmospheres of pressure) will be more expensive than an 8km/s rocket able to withstand 20,000 gees and Mach 5 at sea level.

[LouScheffer]

That leaves the spinning structure itself experiencing a pressure rise from inflowing air. Using a ballpark of 1m diameter projectile (leaving a 1m diameter hole), a 10m long tunnel, and a 100m diameter 5m high chamber, you have 39,000m^3 to fill from a 1 bar (14 PSI) external pressure, which gives a peak of ~64 cubic metres per minute flow

Are you sure about the flow rate? It sounds way too low to me...

Yes, that can't possibly be right.  A 1 meter diameter hole has an area of 0.785 m^2.  So 64 m^3 per minute implies a speed of 81.5 meters per minute, or 1.35 m/s, or 4.89 km/hr, or a gentle breeze.   The real number has to be orders of magnitude higher.  And if you go to an online calculator Air Flow Through an Orifice and enter 1 ATM in, 0.001 ATM out, 23 degrees C, 1 meter diameter, it gives 7640 m^3/minute.

[ZChris13]

the good news is that the fastest the air can get moving through that hole is roughly mach 1, and the projectile is already moving at mach 6
not a big deal

[high road]

My issue was what a mach 1 airflow, and the potential debris sucked in by it, might do to the bunker and the centrifuge. Not necessarily the projectile. But if it can be beefed up to withstand any impacts, it should be fine apparently.

[Robotbeat]

My issue was what a mach 1 airflow, and the potential debris sucked in by it, might do to the bunker and the centrifuge. Not necessarily the projectile. But if it can be beefed up to withstand any impacts, it should be fine apparently.

The only debris is super thin plastic material. Like an empty potato bag. And before the potato bag entered, the chamber will already have some air in it, so any potato bag impact will be less than Mach 1 except for the motion of the arm (which could be slowed quite a bit before the bag would hit). There’s no real possibility of major damage. Only possibility is a mess. I know because I’ve done this before with a vacuum tube and puncturing a plastic seal.

[ncb1397]

I mean, maybe if you’re launching up to a Rotovator or something and so don’t need a rocket (other than maneuvering thrusters)? But without a rotovator, you already need an 8km/s rocket, and I doubt a 9.3km/s rocket built to withstand 10gees max (and only getting Mach 1 at about 0.3 atmospheres of pressure) will be more expensive than an 8km/s rocket able to withstand 20,000 gees and Mach 5 at sea level.

I don't think 20,000 is the right number. 20,000 gees and mach 5 is a 15 meter arm. The arm appears to be longer than that. (somewhere between 40-50 meters).

image source: https://www.wired.com/story/inside-spinlaunch-the-space-industrys-best-kept-secret/

[Robotbeat]

I mean, maybe if you’re launching up to a Rotovator or something and so don’t need a rocket (other than maneuvering thrusters)? But without a rotovator, you already need an 8km/s rocket, and I doubt a 9.3km/s rocket built to withstand 10gees max (and only getting Mach 1 at about 0.3 atmospheres of pressure) will be more expensive than an 8km/s rocket able to withstand 20,000 gees and Mach 5 at sea level.

I don't think 20,000 is the right number. 20,000 gees and mach 5 is a 15 meter arm. The arm appears to be longer than that. (somewhere between 40-50 meters).

image source: https://www.wired.com/story/inside-spinlaunch-the-space-industrys-best-kept-secret/

Thanks. The 15m arm and Mach 5 is for an earlier model (the one they just announced they're building in New Mexico). Your figure is for a later one.

I'll write radius per second as w. The equation is:
r*w^2 = accel. Since v = r*w, the equation can be written as v^2/r = a. Or just v*w = a, so we don't even need the exact radius of the arm. They explicitly give both velocity v and angular speed (which we need to convert to w). 7500kph and 450rpm gives 10,000 gees.

Thanks for a correction on the number, it makes less than half an order of magnitude difference, but the argument hardly changes as we're still talking 3 orders of magnitude difference, here. That little rocket is going to be way more expensive. And you've just traded a factor of 2 reduction in acceleration for a MUCH larger and more expensive pressure vessel (note the pressure vessel scales roughly as the radius cubed).


To reduce acceleration from 10,000 gees down to 10 gees would require an arm 1000 times as long, so a pressure vessel with a billion times the volume (shape stays the same as it's already pretty optimal). At best, pressure vessel mass scales with volume. This will be worse as it's "negative" relative pressure. A billion times the material. Steel prices alone will kill the concept because we're still talking just a Mach 6 assist.

[ncb1397]

To reduce acceleration from 10,000 gees down to 10 gees would require an arm 1000 times as long, so a pressure vessel with a billion times the volume (shape stays the same as it's already pretty optimal). At best, pressure vessel mass scales with volume. This will be worse as it's "negative" relative pressure. A billion times the material. Steel prices alone will kill the concept because we're still talking just a Mach 6 assist.

If you were to theoretically build a vacuum chamber 1000x bigger, why would you still limit yourself to mach 6? You could increase your speed by 5x and still reduce your g-forces to 40x(10000g -> 250g). And you could largely eliminate your rocket system. At 250 g, humans wouldn't be launchable (live at least), but certain small insects could be.

Anyways, there are tons of variables (g-forces, arm radius, exit speed, payload mass). Not every value you can plug into them or calculate would make sense practically, that doesn't mean there isn't a trade space where it might. The (10 g, 50,000 meter long arm, mach 6,  100 kg) solution probably isn't in the "makes sense category". Neither is a 100 km tall Big falcon rocket.

[Robotbeat]

To reduce acceleration from 10,000 gees down to 10 gees would require an arm 1000 times as long, so a pressure vessel with a billion times the volume (shape stays the same as it's already pretty optimal). At best, pressure vessel mass scales with volume. This will be worse as it's "negative" relative pressure. A billion times the material. Steel prices alone will kill the concept because we're still talking just a Mach 6 assist.

If you were to theoretically build a vacuum chamber 1000x bigger, why would you still limit yourself to mach 6? You could increase your speed by 5x and still reduce your g-forces to 40x(10000g -> 250g). And you could largely eliminate your rocket system. At 250 g, humans wouldn't be launchable (live at least), but certain small insects could be.

Anyways, there are tons of variables (g-forces, arm radius, exit speed, payload mass). Not every value you can plug into them or calculate would make sense practically, that doesn't mean there isn't a trade space where it might. The (10 g, 50,000 meter long arm, mach 6,  100 kg) solution probably isn't in the "makes sense category". Neither is a 100 km tall Big falcon rocket.

Well probably because you'd effectively vaporize whatever it is you're launching (so like half your mass would be ablative shielding). Losses are very nonlinear with speed, so you would need a launch speed much higher than orbital velocity. And, you know, have a pressure vessel weighing approximately a trillion tons (give or take). And still not be able to launch humans without turning them to jelly.

EDIT: Also, there aren't materials strong enough to build a centrifuge arm that spins that fast. Or, rather, there are, but it'd require a payload-to-arm mass of worse than one to a million in order to enable your 10.26km/s launch speed. Since electric motors are at best ~99% efficient and needs to spin up the whole arm, that means you've basically invented the most inefficient launch method ever (chemical rockets being like 1000 times as energy efficient).

EDIT: Math is from this paper, using materials with 4GPa/(g/cc) specific strength (which has some small amount of factor of safety). https://www.researchgate.net/publication/245438136_Design_of_Tether_Sling_for_Human_Transportation_System_Between_Earth_and_Mars (equations 7-9)

[ncb1397]

To reduce acceleration from 10,000 gees down to 10 gees would require an arm 1000 times as long, so a pressure vessel with a billion times the volume (shape stays the same as it's already pretty optimal). At best, pressure vessel mass scales with volume. This will be worse as it's "negative" relative pressure. A billion times the material. Steel prices alone will kill the concept because we're still talking just a Mach 6 assist.

If you were to theoretically build a vacuum chamber 1000x bigger, why would you still limit yourself to mach 6? You could increase your speed by 5x and still reduce your g-forces to 40x(10000g -> 250g). And you could largely eliminate your rocket system. At 250 g, humans wouldn't be launchable (live at least), but certain small insects could be.

Anyways, there are tons of variables (g-forces, arm radius, exit speed, payload mass). Not every value you can plug into them or calculate would make sense practically, that doesn't mean there isn't a trade space where it might. The (10 g, 50,000 meter long arm, mach 6,  100 kg) solution probably isn't in the "makes sense category". Neither is a 100 km tall Big falcon rocket.

Well probably because you'd effectively vaporize whatever it is you're launching (so like half your mass would be ablative shielding). Losses are very nonlinear with speed, so you would need a launch speed much higher than orbital velocity. And, you know, have a pressure vessel weighing approximately a trillion tons (give or take). And still not be able to launch humans without turning them to jelly.

EDIT: Also, there aren't materials strong enough to build a centrifuge arm that spins that fast. Or, rather, there are, but it'd require a payload-to-arm mass of worse than one to a million in order to enable your 10.26km/s launch speed. Since electric motors are at best ~99% efficient and needs to spin up the whole arm, that means you've basically invented the most inefficient launch method ever (chemical rockets being like 1000 times as energy efficient).

EDIT: Math is from this paper, using materials with 4GPa/(g/cc) specific strength (which has some small amount of factor of safety). https://www.researchgate.net/publication/245438136_Design_of_Tether_Sling_for_Human_Transportation_System_Between_Earth_and_Mars (equations 7-9)

It still doesn't explain why you would limit yourself to mach 6. 6 km/s reduces the tether mass (for Zylon) from 4.5 million times the payload mass to under 500 or a factor of ~10,000. If the chemical rocket is 1,000x more energy efficient, then you would have closed your gap. But theoretically, you could have material strong enough for the 10 km/s case (using numbers for boron nitride nanotubes that is lab demonstrated but not commercially available gives a mass for the tether of under 200x).So, sure, 10 km/s wouldn't make sense as a point solution, but mach 6-18 still is technically feasible.

Anyways, let's forget about low-g payloads. Small satellites or raw materials don't necessarily need it. A starlink satellite with 30 satellites stacked on top of it is suspending probably on the order of ~100x times its own weight during launch (without issue so far). Another satellite not built for those loads wouldn't survive, and they haven't really reached some sort of fundamental limit (I'm sure).