This Company Built a Gigantic Centrifuge to Fling Rockets Into Space

Popular Mechanics ^ | 01/30/2020 | Courtney Linder

[Svartalfiar]

I see they plan to spin inside a huge vacuum chamber. That almost eliminates the bird problem, but the release must be timed with incredible precision.

They open the exit port just before releasing the rocket. Air floods in, the spin slows down slightly, then release.

Someone else posted that the ordnance will bed hitting about four revolutions per second (I did no math). If true, the doors have to be timed to fully open in less than a quarter of a second. Doors big enough for the rocket, and heavy duty enough to seal in a vacuum for the entire time it's spinning. That's a lot of movement, fast.

And, as you mentioned, the release timing. At those tangential speeds, you're probably looking at a millisecond window, if not nanoseconds. Combined with the sudden hit of air pressure (that'll be a big punch), plus the friction slow for the half-turn or so, means it's even more variable in timing. Air is going to have different densities/fill rates depending on time of day, temperature, moon/sun position (air has tides just like the ocean), wind velocity, and probably several other environmental factors. I really don't see this turning out well, for several trials at least.

[TChad]

Doors big enough for the rocket, and heavy duty enough to seal in a vacuum for the entire time it's spinning. That's a lot of movement, fast.

Might be possible with a lightweight metal (titanium?) iris door (beware of loud soundtrack):

https://www.youtube.com/watch?time_continue=5&v=wYIm5Hx82Dk&feature=emb_logo

Air is going to have different densities/fill rates depending on time of day, temperature, moon/sun position

Yes, that sounds like an unquantifiable aerodynamic mess, but the rocket is heavy and is moving much faster than the incoming wind, and most of the wind will be blowing directly at the pointed nose, so the effect on the rocket's trajectory might be minimal.

If a counterbalance to the rocket is used during spinup, something has to be done with it on launch. If the launch is parallel to the ground plane, then you might as well balance one rocket with a second rocket, launch both at once in opposite directions, then use fins/steering rockets to change the rockets' trajectories. If you launch at an angle, then the counterbalance must be slammed into the ground. Instant earthquake?

I really don't see this turning out well, for several trials at least.

One nice thing about this idea is that you can work out many of the bugs using small cheap models.

Hmm.

[Brilliant]

1/6 that of earth. It you still need some fuel and more importantly you somehow have to get the lift off vehicle to the moon. An electromagnetic rail would be a multiple use mechanical device that would simply use electricity generated on the moon.

[Svartalfiar]

Might be possible with a lightweight metal (titanium?) iris door (beware of loud soundtrack):

Except those doors are gonna have a lot more cracks that need to be vacuum sealed, and need to be very precision-fit to seal the center when closed. And to open a door that size in that manner, in the time required? Gears and runner tracks are going to be much more problematic at the speeds and pressures required, than a simple one-way full door that can have a track distance to slow down after being forced open.


Yes, that sounds like an unquantifiable aerodynamic mess, but the rocket is heavy and is moving much faster than the incoming wind, and most of the wind will be blowing directly at the pointed nose, so the effect on the rocket's trajectory might be minimal.

True, but in this situation, even minimal uncertainty can be enough to push the rocket release off by just enough nanoseconds to not be correct. And it's not just the rocket, it's the whole arm, counterbalance, and atmosphere inside the pivot point / drive mechanism. Any turbulence generated might have an effect on the sides of the projectile. Also, it's not necessarily just air: that sudden inrush might pull dirt or anything outside the door in. Even if it's well-cleaned, the occasional leaf might be enough to do damage. You ever ridden a motorcycle and hit a tiny bug at 70mph?


If a counterbalance to the rocket is used during spinup, something has to be done with it on launch. If the launch is parallel to the ground plane, then you might as well balance one rocket with a second rocket, launch both at once in opposite directions, then use fins/steering rockets to change the rockets' trajectories. If you launch at an angle, then the counterbalance must be slammed into the ground. Instant earthquake?

Yes, looks like there is a counterbalance, and it is being released simultaneously. The track can't be horizontal, that would shoot the rocket out, not up. So the counterbalance has to be released straight down. Assuming an identical setup (release door, tube, etc) it's gonna need a decently long tunnel to slow and stop without hitting the end hard and destroying itself. Can't really use any kind of buffer pad, as that would do damage just on the initial 'catch'. Not sure how they have this figured out, maybe a long tunnel that's well-lubricated and slopes gently back up to the surface? Let the counterbalance just glide the whole length?


One nice thing about this idea is that you can work out many of the bugs using small cheap models.

Eh, yes and no. Many of the bugs are going to be scale issues that only really present at the full-size. You don't have nearly the same momentum on smaller stuff (mom = mass x velocity), so the counterbalance, the atmosphere hit, are all less of an issue. Tensile and shear strengths don't scale linearly. A rod that's twice the length generally needs to be twice the width AND twice the height to have the same strength. So doubling in size means EIGHT times the mass. Take a foot-long ruler, and try to bend it. not much. But take a yardstick of the same build, and it's much more bendy, even just for the length of a foot-long part of it. Not to mention the release mechanism. How does that work? Any kind of clamp is going to have tons of friction, all that centripetal force is going to push them together. It needs to be strong enough to hold onto the rocket, but be able to let go despite the friction. (Hold that ruler over the edge of your desk, gently. Use your other hand to pull it out. Now try again, but this time use your full wight on your fist to hold the ruler down. MUCH harder to pull it out.)


Really, I think it would be cool if they could make this work, but from an engineering perspective it seems a lot more difficult than they seem to think it will be.