Jules Verne Cannon Payload To Orbit.... Feasible?

[Lisias]

50 minutes ago, sevenperforce said:

If you use a counterweight that is heavier than the payload, but closer to the center, then you can reduce the energy you have to absorb from the weight, although I believe the momentum remains the same. 

I was wandering about something similar.  But the closest to the center of the arm the weight is, the longest it will travel until it hits the collector, and in the mean time the arm will rotate and perhaps hit him. The weight must clear the arm's path in less than half a revolution, otherwise we will have a collision.

Damn. Time for some math.

It was stated that the arm will have about 100 meters long (let's settle with 100, it will make calcs easier), and the speed at launch will be ~5.000 MPH, or 8046.72 KM/H or 2.235.2 M/s.

So how many revolutions per second an 100 meters long arm will need to rotate in order to its tip reach 2.200 M/s (another rounding, please..  )?

r = 100m
v = 2200m/s
v = rad/s * r
rad/s = v / r
rad/s = 2200 / 100
rad/s = 22

So the arm will be rotating at 22 radians per second, or 1260.51 degrees/sec or 3.5 revolutions per second! 0.28571429 seconds per revolution. Since the weight needs to clear the arm's path in half of a revolution, it have ~0.14285715 secs to do it.

Or 100m/0.14285715s = ~700 m/s.

In order to reach 700 m/s, the weight must be be at

rads/s = 22
v = 700m/s
v = rad/s * r
r = v / rad/s
r = 700 / 22
r == 31,81818182

But by then you need less time to clear the arm's path, as you have "only"  ~70 meters to go - obviously, assuming that my math is working at this time of the night.  

So, yeah, I think your idea can fly.

Edited November 11, 2021 by Lisias
Fixed a miscalculation

[monophonic]

9 hours ago, Lisias said:

I was wandering about something similar.  But the closest to the center of the arm the weight is, the longest it will travel until it hits the collector, and in the mean time the arm will rotate and perhaps hit him. The weight must clear the arm's path in less than half a revolution, otherwise we will have a collision.

Alternatively the arm and weight could be shaped so that the arm will clear the weight regardless of timing. As we have all three dimensions to work with this should be possible. I think the practical solution could be to split the counterweight into two, one on each side of the counterarm, and placed far enough from the arm itself that distance between the weights will remain more than the payload end mechanisms can safely pass between.

For the gun system, I have a vague idea that I just cannot refine, so I'll just drop it here in case someone more knowledgeable might take interest and break apart. I am thinking of a single chamber gun, but not loaded with a truly explosive charge. Instead the grain in the chamber would be not entirely unlike the grain in a solid fuel rocket. Burning slow enough to keep the acceleration on the payload manageable but providing enough gas to keep the pressure up long enough for the payload to reach the maximum velocity attainable. I wonder if such a system might work even on a theoretical basis.

[tomf]

I think a counterweight could be fired into a long coil, bringing it gently to a halt and recapturing it's energy as electricity. You might need to get that pesky air out of the way.

[kerbiloid]

An underground vacuum spiral hyperloop, 4 000 km in diameter.

Softly accelerates a capsule to 8 km/s in magnetic field, then lets it escape through the tilted escape pipe laying on a 7 km high mountain.

[Lisias]

14 hours ago, monophonic said:

Alternatively the arm and weight could be shaped so that the arm will clear the weight regardless of timing. As we have all three dimensions to work with this should be possible. I think the practical solution could be to split the counterweight into two, one on each side of the counterarm, and placed far enough from the arm itself that distance between the weights will remain more than the payload end mechanisms can safely pass between.

You would need two release mechanisms, that should be triggered in the exact nanosecond. The construction should also be slightly wider to accommodate the extra thick arm, that would be also slightly heavier. On the other hand, having two collectors able to withhold half the energy instead of just a big one is something to be considered, perhaps the total size (and cost) would be smaller.

I'm not exactly inclined to this approach due the extra complexity (but having two smaller collectors for the weight may compensate it!), since I had calculated that there's time to spare for the weight to clear the arm's path - but it's a good idea nevertheless. I didn't considered it myself.

For the sake of completude, I wondered if we could not use a liquid as counterweight - splashing water in a wider area would be easier to cope. But then I realised that the whole mass of water would be released at once and will hit the same spot the same, and then all the energy would make the water to ricochet and splash the whole chamber, that so would need to be cleaned before the next launch. So, terribly idea.  

In time, I just found a picture of the whole building:

And I'm not seeing a place that would allow a "collector" to catch the counterweigh on release (that entry turned to the bottom looks like where they insert the projectile).

So now I'm really curious about how they are rebalancing the arm after launch!

[FleshJeb]

1 hour ago, Lisias said:

that so would need to be cleaned before the next launch.

It's a vacuum chamber--Drain most of it, and the rest will boil when the chamber gets pumped down again.

1 hour ago, Lisias said:

So now I'm really curious about how they are rebalancing the arm after launch!

I had the halfway stupid-idea that maybe they don't. The whole assembly might be robust enough to just take the beating. The mass of the projectile is pretty miniscule compared to the whole rotor.

I screen-capped a few images from renders of the design. (Which they list as 450 RPM = 47 rad/s) https://www.spinlaunch.com/orbital

I did some research, and those types of bearings are typically instrumented, so they can keep an eye on the health and replace it before a critical failure. As it happens:

 

 

[Lisias]

3 hours ago, FleshJeb said:

It's a vacuum chamber--Drain most of it, and the rest will boil when the chamber gets pumped down again.

Exactly. Without air to help to decelerate the water particles, the splashes will go everywhere including bearings (what probably would happen even with air inside, anyway), and then draining into the electrical stuff. Since it's pretty hard to keep airtight seals on moving shafts, it's usually easier to seal the whole machinery together the chamber, so probably the whole shebang would need to be water proof.

And on pumping air out, that moisture would be pulled into the pumping mechanism, that so would need to be water proof too.

None of this is a too difficult problem to solve, but adds cost to the system. The big question is if the costs with dealing with water would worth the eventual savings. I don't have a clue, to tell  you the true…  

 

3 hours ago, FleshJeb said:

I had the halfway stupid-idea that maybe they don't. The whole assembly might be robust enough to just take the beating. The mass of the projectile is pretty miniscule compared to the whole rotor.

I screen-capped a few images from renders of the design. (Which they list as 450 RPM = 47 rad/s) https://www.spinlaunch.com/orbital

Yep, but this one is a prototype. It's smaller, way smaller and it's not intended to endure many launches - it will be used for some test and then dismantled/retired and that's it.

The real deal will be way bigger, will launch way heavier payloads - so  an assembly robust enough to allow this without balancing may not be feasible, or too costly. We are talking about a 100 M arm (weighting probably more than a ton only itself) rotating a 3.5 revolutions per second - this is really something.

Additionally, the whole structure would be subjected to the vibration, not only the bearings - on the other hand, I think the structure should be able to contain a catastrophic failure of the system so this may not be an issue at all.

 

21 hours ago, monophonic said:

For the gun system, I have a vague idea that I just cannot refine, so I'll just drop it here in case someone more knowledgeable might take interest and break apart. I am thinking of a single chamber gun, but not loaded with a truly explosive charge. Instead the grain in the chamber would be not entirely unlike the grain in a solid fuel rocket. Burning slow enough to keep the acceleration on the payload manageable but providing enough gas to keep the pressure up long enough for the payload to reach the maximum velocity attainable. I wonder if such a system might work even on a theoretical basis.

Ingenius! Pretty out-of-the-box thinking, I like it.

There's a problem on it, however - you can't accelerate the capsule faster than the gases you are getting on the burn, so a slow burn is not useful. If you want the capsule to reach 11KM/s at the end of the barrel, you will need something burning in a way that the resulting gases would reach that (and something more, to tell you the true).

Another problem is that burning solid fuel creates a hell of heat, that need to be dissipated by the barrel otherwise it would melt - it's different from detonating explosives, where a significant fraction of the heat created is rapidly absorbed by the gases being expanded. On your solution, the heat would be constantly created during the whole launch.

But so would happen too with a series of chambers detonating their charges sequentially, so your idea is as valid as mine .

But the problem of slow burning still persists. You need something that creates really high speed gases inside the barrel. 

So I thought to myself… What about coating the barrel with the solid fuel? The barrel would be some inches wider than the projectile, and the gaps filled with solid fuel , with firewalls preventing the whole barrel to ignite at once, we want the ignition to be sequential - it's a derivative from my series of chambers idea.

We ignite the first section, the projectile is propelled ahead exposing the next section that would so be ignited, adding impulse to the projectile that would expose the next section, and so it goes until the end of the barrel...

 

21 hours ago, tomf said:

I think a counterweight could be fired into a long coil, bringing it gently to a halt and recapturing it's energy as electricity. You might need to get that pesky air out of the way.

The air will be already out of the way, the whole chamber will be in a vacuum, so this is not a problem. Neat! 

The problem would be enough capacitors to store this energy, not to mention the heat generated by such electricity transfer in so small timeframe you would get - I think you would need some superconductors here. There's also the machinery to recover the counterweight from the deepness of the coil well (it must be somewhat deep, no?).

But if the energy you get from the stunt is enough, you would get some energy back to inject back to the system on the next launch or perhaps on the pre-launch procedures! Neat²!