Alternate Satellite Launch Technique

[Christine Wheelwright]

I do not believe that a rocket is needed. There is no need for a long tube containing propellant; there is only need for a little aerodynamics to reduce air resistance, perhaps some heat shielding, and a tail for stabilization. There is also likely a need for some maneuvering jets to place the satellite in its final orbiting position. By not having a force at the bottom of a long tube pushing it upward, simple, passive techniques for maintaining orientation can be used -- simple drag on the tail perhaps coupled with rifling to provide spin on the vertical axis.

The rocket could dispense with a first stage, but not subsequent stages. it would still need to be long and narrow. The rocket has to be rocket-shaped in other words.
The membrane that the projectile bursts through is also a potential problem. If the window is, say, 2m x 3m, and atmospheric pressure is 15lbs per square inch (and they say inside the spinner is a vacuum?), then the force on the membrane is 144,000lbs. So 'membrane' isn't exactly the right word. And the rocket has to smash through this thing (whatever it is). I would tend to call 'bulls**t and say that their test system did not use a vacuum. That looks almost like paper that it rips through. Also, irrespective of the barrier across the opening, the sudden contact with air is going to be quite an impact. I note that they never show what happens after release in their video. They show the projectile coming through the membrane (clearly tumbling in my opinion) and then cut to a graphic of a nice shiny rocket zooming perfectly upwards.
I don't understand why nobody is pursuing the 'supergun' method of launch. Seems more promising, surely. (Gerald Bull - Wikipedia)

 

[Christine Wheelwright]

Probably the G force would make it unworkable. I just ran a calculation. At 5,000 mph with a radius of 1 mile (2 mile total diameter), the centripetal acceleration is 317 Gs. Reference: SpinCalc

I think they are looking at something with a much smaller radius. The resulting G force would then be several thousand. Even so, I think it could be possible to design a satellite (which is basically a canister full of electronics) that would survive.

 

[Swank]

Probably the G force would make it unworkable. I just ran a calculation. At 5,000 mph with a radius of 1 mile (2 mile total diameter), the centripetal acceleration is 317 Gs. Reference: SpinCalc

Surviving the G load is the other part of the engineering that they are doing.

Though I'm wondering if we are all understanding this correctly. Is it the tangential velocity that creates the initial launch velocity, or the energy measured as G force? If you spin a short arm at 5000 mph, the G is much higher than a very long arm. When you release the device that much higher G is going to act on it differently than a lower G from a longer arm, producing more initial acceleration.

So I'm unsure if the article got it right saying that it is spinning at 5000mph or whether that number is the initial release velocity from whatever G load they build up. (Or I'm just very confused, but I can't see how you could have more potential energy with a short arm at the same velocity and not have it do more work.)

 

[Christine Wheelwright]

Surviving the G load is the other part of the engineering that they are doing.

Though I'm wondering if we are all understanding this correctly. Is it the tangential velocity that creates the initial launch velocity, or the energy measured as G force? If you spin a short arm at 5000 mph, the G is much higher than a very long arm. When you release the device that much higher G is going to act on it differently than a lower G from a longer arm, producing more initial acceleration.

So I'm unsure if the article got it right saying that it is spinning at 5000mph or whether that number is the initial release velocity from whatever G load they build up. (Or I'm just very confused, but I can't see how you could have more potential energy with a short arm at the same velocity and not have it do more work.)

The key number is the speed of the projectile on release. This is the speed at which it will emerge.

Now, that speed (say 5,000mph) can be achieved with a short arm rotating quickly or with a long arm rotating less quickly (in terms of rpm). You are quite right that the g force experienced by the projectile while it rotates in the machine will be higher for the shorter arm. But once released, that g force is no longer relevant. The kinetic energy of the projectile is a function of its speed.....not the g force that was used while spinning it up. Once released there are other problems to worry about (the impact of hitting the 'membrane'....the impact of going from vacuum to dense atmosphere at that speed while also tumbling....etc..etc).

The shorter arm creates more 'tumbling' (a result of the nose and tail of the rocket having different trajectories at the moment of release).

The longer arm is hard to engineer because it will be a big machine. The short arm has its own issues, because of speed. I think people also don't understand how tricky it is to maintain a vacuum in a very large enclosed area (also a reason why Musk's hyperloop concept is fundamentally flawed).

 

[THX1138]

The key number is the speed of the projectile on release. This is the speed at which it will emerge.

Now, that speed (say 5,000mph) can be achieved with a short arm rotating quickly or with a long arm rotating less quickly (in terms of rpm). You are quite right that the g force experienced by the projectile while it rotates in the machine will be higher for the shorter arm. But once released, that g force is no longer relevant. The kinetic energy of the projectile is a function of its speed.....not the g force that was used while spinning it up. Once released there are other problems to worry about (the impact of hitting the 'membrane'....the impact of going from vacuum to dense atmosphere at that speed while also tumbling....etc..etc).

The shorter arm creates more 'tumbling' (a result of the nose and tail of the rocket having different trajectories at the moment of release).

The longer arm is hard to engineer because it will be a big machine. The short arm has its own issues, because of speed. I think people also don't understand how tricky it is to maintain a vacuum in a very large enclosed area (also a reason why Musk's hyperloop concept is fundamentally flawed).

Hitting the membrane and then the atmosphere at that speed are good points of concern.

 

[THX1138]

So, they have two systems. Orbital and suborbital. Looks like the projectiles are ballistic tipped so that answers the atmosphere question.
That 'tumbling' that Christine saw was from the suborbital system, and it does look like it is either tumbling or rotational spinning. Hard to say.
Still looks like a big DLG design in my view. Just a large bullet shape projectile instead of a glider. Still cool!

 

[Swank]

The key number is the speed of the projectile on release. This is the speed at which it will emerge.

Now, that speed (say 5,000mph) can be achieved with a short arm rotating quickly or with a long arm rotating less quickly (in terms of rpm). You are quite right that the g force experienced by the projectile while it rotates in the machine will be higher for the shorter arm. But once released, that g force is no longer relevant. The kinetic energy of the projectile is a function of its speed.....not the g force that was used while spinning it up. Once released there are other problems to worry about (the impact of hitting the 'membrane'....the impact of going from vacuum to dense atmosphere at that speed while also tumbling....etc..etc).

The shorter arm creates more 'tumbling' (a result of the nose and tail of the rocket having different trajectories at the moment of release).

The longer arm is hard to engineer because it will be a big machine. The short arm has its own issues, because of speed. I think people also don't understand how tricky it is to maintain a vacuum in a very large enclosed area (also a reason why Musk's hyperloop concept is fundamentally flawed).

Thanks for sorting that out - I'm sure you're right.

I don't really understand the requirement for vacuum in either case - why not just get the air up to the speed of the projectile, then open a top and bottom hatch simultaneously and launch the projectile in an accelerated air mass, like a jet engine spitting out a rock? Same thing with a hyperloop - make it pneumatic. (I realize that there's drag and compression involved, but it's a thought.)

I wonder if the bladder and wall of air could be breached by a sacrificial block of dry ice or something that would poke through and push the air in a helpful direction while it explosively sublimes?

The tumbling factor is the same reason that small diameter rotating space stations would feel much weirder to occupants than large ones.

Pre-WWI there were competing designs for centrifugal machineguns. But those probably topped out at 500mph.

 

[Christine Wheelwright]

I don't really understand the requirement for vacuum in either case - why not just get the air up to the speed of the projectile, then open a top and bottom hatch simultaneously and launch the projectile in an accelerated air mass, like a jet engine spitting out a rock? Same thing with a hyperloop - make it pneumatic

Well, I'm not defending it. In fact I think both ideas (the spinny thing and the hyperloop) are full of holes (figuratively and literally). I actually think the linear method of satellite launch has way more promise. Basically a gun. A straight tube, quite long, and possibly resting against a mountainside. Accelerate the projectile using explosions or electromagnetics. Modern electronics is easily able to perform the timing required.
The important thing is to:
1) Get a website with no real info but some really cool CGI videos to show the concept
2) Get a charismatic leader who everyone thinks is a genius (but who really understands very little)
3) Hype, hype, bullsh*t, hype
4) Hope an investor (who also understands very little) gives you $$ before someone with a O level in physics points out why it wont work

 

[Swank]

Well, I'm not defending it. In fact I think both ideas (the spinny thing and the hyperloop) are full of holes (figuratively and literally). I actually think the linear method of satellite launch has way more promise. Basically a gun. A straight tube, quite long, and possibly resting against a mountainside. Accelerate the projectile using explosions or electromagnetics. Modern electronics is easily able to perform the timing required.
The important thing is to:
1) Get a website with no real info but some really cool CGI videos to show the concept
2) Get a charismatic leader who everyone thinks is a genius (but who really understands very little)
3) Hype, hype, bullsh*t, hype
4) Hope an investor (who also understands very little) gives you $$ before someone with a O level in physics points out why it wont work.

They are probably afraid the Israelis will bomb the site if they make another cannon.

 

[THX1138]

Posted 4hs ago on NASA. Spinlaunch plan is for their system to take the place of the 1st stage. Their payload vehicle has a booster rocket in it that acts as the 2nd stage.

Found on YouTube.

GIANT CENTRIFUGE! NASA to Test SpinLaunch, a Giant Slingshot for Launching Satellites Into Space

 

[Christine Wheelwright]

Posted 4hs ago on NASA. Spinlaunch plan is for their system to take the place of the 1st stage. Their payload vehicle has a booster rocket in it that acts as the 2nd stage.

Found on YouTube.

GIANT CENTRIFUGE! NASA to Test SpinLaunch, a Giant Slingshot for Launching Satellites Into Space

I'm sure NASA would be interested in checking it out. The 'payload' would be fitted with some kind of accelerometer I would think. I doubt they would put an actual rocket in there! Note that link is not a NASA video.

 

[THX1138]

I'm sure NASA would be interested in checking it out. The 'payload' would be fitted with some kind of accelerometer I would think. I doubt they would put an actual rocket in there! Note that link is not a NASA video.

Thanks for the correction! Nasa Space News.