Spinlaunch... Can it succeed?

[DougSpindler]

Correct me if I'm wrong, but won't the skin of the satellite crumple due to the G force difference between side that's closer to the point of rotation vs the outer side?  What would be the G force difference is the satellite were say 2 feet in diameter. 

[CatalinaWOW]

Correct me if I'm wrong, but won't the skin of the satellite crumple due to the G force difference between side that's closer to the point of rotation vs the outer side?  What would be the G force difference is the satellite were say 2 feet in diameter.

Conventional satellite skins would indeed fail.  Maybe crumble, maybe tear depending on whether the satellite is supported by a cradle or hung from a hook.  A spin launch satellite would not be weight efficient as current satellites are. Structure would be the dominant weight component.  Not sensors, not electronics, not anything useful.

[Marco]

Spin or gun launch satellites would have to be designed like modern mobile electronics, minimum dead space, so potting doesn't increase weight too much. Also perfectly fitted for the hole in the steel sabot.

[DougSpindler]

Spin or gun launch satellites would have to be designed like modern mobile electronics, minimum dead space, so potting doesn't increase weight too much. Also perfectly fitted for the hole in the steel sabot.

Why wouldn’t the walls of the sabot buckle or tear do to the differential in G forces?

[Marco]

From the images they look like solid chunks.

[CatalinaWOW]

Spin or gun launch satellites would have to be designed like modern mobile electronics, minimum dead space, so potting doesn't increase weight too much. Also perfectly fitted for the hole in the steel sabot.

Marco you are on the right track, but now think about chips fracturing because of stress between solder joints or not having perfect support on ball grids.  Voids in potting matter and even differences in compressive strength.  Once you have this monoblock mechanically sorted think about the difficulty of test and repair.  None of that is impossible, but it isn't free.  Remember this is supposed to be low cost access to space.  Unless a market for chunks of metal develops this will severely impact the economics.

[fourfathom]

Unless a market for chunks of metal develops this will severely impact the economics.

Perhaps this is how we launch Jerry Pournelle's "flying crowbar" weapons.

[DougSpindler]

You know something else I don't think people have mentioned is the sudden temperature change the launch object will experiences as it punctures the membrane holding the vacuum.  I still think the skin of the object being launched will experience structural damage to force differential as it's spinning.  Remember wall of the projectile that's closure to the center of the arm rotating the mass.  Using a centrifugal calculator a mass of 1000 lbs and a tangential velocity of 1,000 feet/s at 100 foot radius would have a force of 1,382,550 N and an effective mass of 141,434 kg.  Assuming the projectile has a width of 5 feet, the force would be 1,316,714 N and the effective mass would be 134,721 kg.

Do we know of any material which could withstand this differential in torque and light enough to toss into space?  I'm thinking not, but could be wrong.



https://www.omnicalculator.com/physics/centrifugal-force

[Rick Law]

Correct me if I'm wrong, but won't the skin of the satellite crumple due to the G force difference between side that's closer to the point of rotation vs the outer side?  What would be the G force difference is the satellite were say 2 feet in diameter.

You are correct.  The outer side of the launch vehicle will experience different G verses the inner side.


Using the numbers in the OP's video which is 450rpm and 100 meter diameter (50 meters radius).  This is for the targeted launch configuration, not the prototype which is smaller and much lower RPM.

450 round per minute = 450/60 round per second = 7.5 round per second
Each round travels the circumference 2*pi*radius
7.5 round per second so total travel in one second = 2*pi*radius*7.5

First, the outer side  (at the edge of the spinning wheel):
Plug the numbers in, you have:
2*3.1416*50meter*7.5/second = 2356 meters per second (this is actually close to mach 7)
centrifugal acceleration = V²/r
centrifugal g force = (V²/r) /9.8
 = (2356*2356/50)/9.8
= 11,328g

Now the inner side of the payload vehicle which you are using 2 feet wide  (0.61 meter), the radius of rotation is thus (50-0.61) = 49.39 meter
The inner-side velocity is:
2*3.1416*49.39meter*7.5/second = 2327 meters per second
centrifugal g force = (V²/r) / 50) /9.8
 = (2327 *2327 /49.3)/9.8
= 11,208g

So, here is your answer to the 2 feet wide satellite payload g delta:
outer exit velocity is 2356m/s and centrifugal g is 11,328g
2 feet width in, inner exit velocity is 2327 m/s, 11,208g


Note 1:
Look at the exit velocity delta, outer side is 2356m/s and inner side is 2327m/s, 29m/s less.  That is why I insisted that the payload will exit with an end-to-end rotating force.  One side is moving 29 m/s faster than the other side, 48x the width of the payload (per second) if the payload is indeed 2 feet wide.  The delta is progressively decreasing as you move from one side to the other but there is a delta none the less.  You can trade speed for steering, but that is yet another problem non the less.

Note 2:
No doubt the spinner and even the booster rocket can be engineer to withstand the 11,000g.  The payload.... that is where the problem lies.  I just visited their website.  I can't find anything about payload hardening.  They just say their launcher (will?) withstands 20,000g.  It is left for the audience to imagine how a satellite will look after it is hardened to withstand 11,000g, how much cost it will add to making that 11,000g proof satellite.  etc.  Seem to me "buyer beware" should apply here.

[DougSpindler]

Thanks you for the confirmation and excellent explanation.  In doing so, you made me realize something else.  If one side of the satellite is traveling faster as a rotates when it gets released and begins traveling linearly it will begin tumbling.  The concept is similar to what is shown in this Veratasium video.


 

[Nusa]

The payload.... that is where the problem lies.  I just visited their website.  I can't find anything about payload hardening.

You could have watched the video posted in this thread about two weeks ago. Here's the interview about payload hardening: https://youtu.be/yrc632oilWo?t=2157

[PlainName]

think about the difficulty of test and repair

I think repair of something heading to space would be tricky enough however you launch it

[twospoons]

I would like to remind everyone that GPS guided artillery shells experience accelerations on the order of 16000g. If thats typical in use, then you can guarantee they can withstand more than that for reliability.
If we can build electronics to withstand being blasted out of a short 155mm artillery barrel, then Spinlaunch doesn't seem like so much of a stretch.

[PlainName]

You know something else I don't think people have mentioned is the sudden temperature change the launch object will experiences as it punctures the membrane holding the vacuum.

They're not puncturing any membrane. Before you sound of any more, perhaps you should review the video posted a little while ago. Many of your questions are either answered or shown to be inappropriate in that, so it's worth watching just to be up to date with the current arguments du jour.

Regarding the (non-)membrance, the video at this time explains how the projectile will exit: https://youtu.be/yrc632oilWo?t=980

[Nusa]

Doug is using details from the simplified 1/3 scale test videos as being final design elements, which in this case we know is not true if you've kept up. But never let the facts get in the way of something you've taken a stand on.

[SiliconWizard]

Nice marketing video though.

[Marco]

Does it matter? It's going from vacuum to mach whatever, however you do it, it's going to be a tad violent.

I think greenlaunch had an estimate how much nose cone they were going to ablate but I can't quickly find it.

[CatalinaWOW]

think about the difficulty of test and repair

I think repair of something heading to space would be tricky enough however you launch it

I am not talking repair after launch.  I am talking about the repair/modification of prototypes when they don't nail the elx design right out of the box.  Because they didn't properly account for the parasitic effects of all of the hardening.  And then the repair of the units that come off the assembly line wrong, since this won't be a high volume line, tweaked over time to get near 100% yield.  Sure you can just discard the failures, but read and think about the previous sentence.

[AnalogueLove1867]

Ah yes, Project Babylon.
A commission ordered by Saddam Hussein with chief scientist Gerald Bull.
Then Mossad assassinated Gerald Bull for obvious reasons haha.

https://en.wikipedia.org/wiki/Project_Babylon
https://en.wikipedia.org/wiki/Gerald_Bull

[AnalogueLove1867]

More to the point, it would be emitting a continuous shock wave.  It would get very hot indeed in there.

https://en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech
Loudest propeller aircraft ever made with continuous shockwave supersonic prop tips.

[DougSpindler]

I think this is like Thorium reactors, there are a number of technical issues which still need to be solved.  I think like Thorium reactors, Theranos, Hyperloop, and Nikola Trucks until they run out of money they will keep saying it can be done.  Then once they’ve burned through all of the money the employees will come clean saying we knew all along it was never going to work.

[PlainName]

I think like Thorium reactors, Theranos,

Careful, Doug. Theranos was a scam (whether knowingly from the off or unwittingly by a non-expert until they got informed), but thorium works. There are many reasons why thorium isn't used commercially, but 'scam' is not one of them. You're not doing yourself any favours by failing to note the differences.

[wraper]

I think this is like Thorium reactors, there are a number of technical issues which still need to be solved.  I think like Thorium reactors, Theranos, Hyperloop, and Nikola Trucks until they run out of money they will keep saying it can be done.  Then once they’ve burned through all of the money the employees will come clean saying we knew all along it was never going to work.

What a mess comparing those things. Theranos and Nikola are companies created by scam artists. Hyperloop is a concept not owned by anyone, anyone is free to try implementing it or use the name. Thorium reactors can be built if there is incentive (and were built) but industry has gone to Uranium direction. Likely in part because they are useless for producing nuclear weapons. USSR and USA were the two major forces doing nuclear research and certainly wanted those weapons. If there was no Uranium to mine, very likely we would have Thorium reactors instead. Too much effort and too much uncertainty for business to pull it off without involvement of government.

[AndyBeez]

Not sure if anyone else has mentioned this before, but what happens when the unleashed payload collides with the self generated sonic boom that it is already travelling outwards from the launch site? Surely there is a sweet spot where the departing shock wave is so dense, it will form a 'brick wall' ahead of the departing launch vehicle? Or are we launching from the Moon to avoid claims for broken windows, 50 miles away?

And even if the launch vehicle has the strength of a bowling ball, the induced spin at "unleash", will turn all but the very center of the payload into mincemeat?

[PlainName]

The have a graph showing the drag tail off a bit as you go over mach1, so exiting pretty sharpish might be less stressful than going slower! Also, the air will get less dense as they progress, and by the time they release they should be going slower in much more rarefied air, so coming apart shouldn't be a big issue. If they are going as fast as a normal first stage when it separates they would be doing well.

the induced spin at "unleash"

I imagine that can be accounted for. They can leave go of the front slightly earlier or later than the rear to induce rotation in either direction, so getting it to balance out is surely just maths. And engineering.