Spinlaunch... Can it succeed?

[thinkfat]

I could see this working on bodies with lower mass so you could throw (for instance) the output of mines into orbit where something could rendezvous with it. I can't see it being practical on Earth

Like, in Robert Heinleins "The moon is a harsh mistress". There they used a "railgun" to catapult containers with local produce towards earth, to have them plunge into the Indian ocean. No need to rendezvous with them when you can just use atmospheric braking.

[fourfathom]

Like, in Robert Heinleins "The moon is a harsh mistress". There they used a "railgun" to catapult containers with local produce towards earth, to have them plunge into the Indian ocean. No need to rendezvous with them when you can just use atmospheric braking.

I'm pretty sure that Heinlein's launcher was a multi-stage magnetic launcher, not a true railgun.  Also the containers had retro-rockets, which were removed when they started "throwing rocks".  Having low gravity and no atmosphere makes it all much easier.

Great book, by the way.

[hli]

The electronics used in guided projectiles have to withstand about a tenth of these levels and it is very challenging.

I just looked up an SSD datasheet (the first one I found was for a 'BarraCuda SSD from Seagate - https://www.seagate.com/www-content/datasheets/pdfs/barracuda-ssd-DS1984-3-1806-WW-en_US.pdf ). It states a shock resistance of 1500G. If a simple SSD can withstand these forces (and I guess these are conservative values because they guarantee them) most likely it should not be that difficult to improve tenfold. Has someone some figures how big the actual shock forces are during a rocket start (the constant acceleration are not the only forces, just simply dropping the PCB on a surface has higher G-forces).
(Actually googling 'electronics g shock resistance' found me this one: https://www.researchgate.net/figure/Survivability-of-various-TV-configurations-10-000g-shock_fig20_304014433 which indicates these forces seem to be no issue at all).

[AndyBeez]

On the subject of G force, what happens to the spin launcher when the projectile/payload is released? Does the launcher experience a recoil effect and destroy itself? How exactly does the the center of gravity stay inside the center of rotation as the payload mass departs?

[PlainName]

In the video they muse over two options:

1. A counterweight that's let go at the same time as the payload. The counterweight exits down its own tunnel into something that can absorb the energy. That is a LOT of energy with a very short deceleration path.

2. The counterweight is let go at the same point as the payload, so it follows the payload out of the normal exit. They reckon it won't be unbalanced enough to cause a problem for that half revolution. I think they may have forgotten that the exit airlock is now pressurised so they can't open the inner doors without a catastrophic vacuum loss.

I will be interested to see either or both of those actually working! A pretty good indication of problems could be wind turbines - we see videos of them overspeeding and then becoming dismantled where all three arms let go at once. My understanding is that it is just one arm that lets go, but the shock causes the others to break and leave in sympathy.

[CatalinaWOW]

The electronics used in guided projectiles have to withstand about a tenth of these levels and it is very challenging.

I just looked up an SSD datasheet (the first one I found was for a 'BarraCuda SSD from Seagate - https://www.seagate.com/www-content/datasheets/pdfs/barracuda-ssd-DS1984-3-1806-WW-en_US.pdf ). It states a shock resistance of 1500G. If a simple SSD can withstand these forces (and I guess these are conservative values because they guarantee them) most likely it should not be that difficult to improve tenfold. Has someone some figures how big the actual shock forces are during a rocket start (the constant acceleration are not the only forces, just simply dropping the PCB on a surface has higher G-forces).
(Actually googling 'electronics g shock resistance' found me this one: https://www.researchgate.net/figure/Survivability-of-various-TV-configurations-10-000g-shock_fig20_304014433 which indicates these forces seem to be no issue at all).

In the early 70s I was involved in some work on guided projectiles.  We found many surprises.  Being able to see the outline of the die inside a hermetic package from the lid crushing down for example.   Bigger surprise, some of these still worked.  There were many other problems.  Modern packaging techniques have alleviated, but not eliminated some of them.

Shock loads have to be understood thoroughly.  Duration matters as much or more than amplitude.  You can see 100kg accelerations dropping a small hard object on a hard surface.  But the durations are measured in milliseconds or less.  Nothing has a chance to move far before the shock is over.  The situation is far different when durations are longer. 

Another example of the difference time makes.  American football players frequently encounter 200g shocks during impact, but with durations measured in fractions of a second.  CED not withstanding, this is not usually a fatal event.  But exposure to 10g steady acceleration makes almost everyone black out.  And 200g of steady acceleration is fatal.

Another example:  Many people are familiar with the famous viscosity experiment in which a specimen of pitch has been allowed to flow for more than a century, with the first drip still to happen.  A short, high g shock to this experiment would have had little effect early in the experiment.  Now that a drip is forming a short shock could cause the drip to separate.  Application of very high g for the duration would have resulted in significant flow.  Many materials cold flow under enough pressure.  Some that we typically think of as solid.  Think of batteries.

As in everything the devil is in the details.  The problem with spin launch is how many of these details there are to work out.   It is an engineering paradise in my view, because as an engineer I am happiest in a problem rich environment.  But the practicality is deeply in question.  Unless the only purpose is to get investors to pay to let engineers play.

[Rick Law]

... ...
I just looked up an SSD datasheet ... ... It states a shock resistance of 1500G. If a simple SSD can withstand these forces (and I guess these are conservative values because they guarantee them) most likely it should not be that difficult to improve tenfold.
... ...

The difficulty level doesn't scale at the same proportion as scaling a goal.  Case and point is the Concorde.  Production Concorde planes travel at Mach 2.  (Around 2.04 is the limit).  One would think, and they did consider, how about scaling up just a bit further to March 3...  Just a 50% scale up, not 5x.  Material limitation that isn't an issue at Mach 2 comes into play at Mach 3.  They will have to switch over from aluminum body to some other material because of temperature.  Okay, say you replace it with titanium, that will work.  But that means they have to create all the body works method and tools.  Tools and experience is wide spread for making plane body/wings/etc with aluminum, but not with titanium which (at the time) was known to be a difficult material to work with.  Doable of course, but financially financial feasibility put that out of consideration.

Another good example is the traditional spinning disc hard drives.  Fast ones are 15k RPM, max I've seen is 20k RPM.  Scale it up more, the glass-disc may shatter and the aluminum-disc may deform.

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Hats off to CatalinaWOW for the reply below!  This is such a good explanation I feel I must quote it, and add an example (of duration vs raw amplitude) that CatalinaWOW brought up in the reply:

Why a bullet mere leave a hole in a (non-laminated) glass window whereas a hammer would shatter it?  Duration.  The millisecond it took the bullet to pass leaves it no time for the shock to spread.  The same doesn't apply with hammer strike.

The electronics used in guided projectiles have to withstand about a tenth of these levels and it is very challenging.

I just looked up an SSD datasheet (the first one I found was for a 'BarraCuda SSD from Seagate - https://www.seagate.com/www-content/datasheets/pdfs/barracuda-ssd-DS1984-3-1806-WW-en_US.pdf ). It states a shock resistance of 1500G. If a simple SSD can withstand these forces (and I guess these are conservative values because they guarantee them) most likely it should not be that difficult to improve tenfold. Has someone some figures how big the actual shock forces are during a rocket start (the constant acceleration are not the only forces, just simply dropping the PCB on a surface has higher G-forces).
(Actually googling 'electronics g shock resistance' found me this one: https://www.researchgate.net/figure/Survivability-of-various-TV-configurations-10-000g-shock_fig20_304014433 which indicates these forces seem to be no issue at all).

In the early 70s I was involved in some work on guided projectiles.  We found many surprises.  Being able to see the outline of the die inside a hermetic package from the lid crushing down for example.   Bigger surprise, some of these still worked.  There were many other problems.  Modern packaging techniques have alleviated, but not eliminated some of them.

Shock loads have to be understood thoroughly.  Duration matters as much or more than amplitude.  You can see 100kg accelerations dropping a small hard object on a hard surface.  But the durations are measured in milliseconds or less.  Nothing has a chance to move far before the shock is over.  The situation is far different when durations are longer. 

Another example of the difference time makes.  American football players frequently encounter 200g shocks during impact, but with durations measured in fractions of a second.  CED not withstanding, this is not usually a fatal event.  But exposure to 10g steady acceleration makes almost everyone black out.  And 200g of steady acceleration is fatal.

Another example:  Many people are familiar with the famous viscosity experiment in which a specimen of pitch has been allowed to flow for more than a century, with the first drip still to happen.  A short, high g shock to this experiment would have had little effect early in the experiment.  Now that a drip is forming a short shock could cause the drip to separate.  Application of very high g for the duration would have resulted in significant flow.  Many materials cold flow under enough pressure.  Some that we typically think of as solid.  Think of batteries.

As in everything the devil is in the details.  The problem with spin launch is how many of these details there are to work out.   It is an engineering paradise in my view, because as an engineer I am happiest in a problem rich environment.  But the practicality is deeply in question.  Unless the only purpose is to get investors to pay to let engineers play.

EDIT:  Corrected a typo, and added an example  of duration issue which CatalinaWOW pointed out.

[DougSpindler]

"Another good example is the traditional spinning disc hard drives.  Fast ones are 15k RPM, max I've seen is 20k RPM.  Scale it up more, the glass-disc may shatter and the aluminum-disc may deform."

The dirty secret with some 15k and 20k disc drives is that they were really standard 7,200 10k RPM drives.  To call them 15k/20k they just used the inside tracks.  This is why there capacity was half that of a 7,200/10k drive.

[SiliconWizard]

Oh yeah, what's an order of magnitude anyway?

[DougSpindler]

@CatalinaWOW  You appear to be the expert in this area.  What do you think Spinlaunch will be successful at?  Launching satellites?  Or burning through VC money without ever launching one?

[AndyBeez]

In the video they muse over two options:

1. A counterweight that's let go at the same time as the payload. The counterweight exits down its own tunnel into something that can absorb the energy. That is a LOT of energy with a very short deceleration path.

2. The counterweight is let go at the same point as the payload, so it follows the payload out of the normal exit. They reckon it won't be unbalanced enough to cause a problem for that half revolution. I think they may have forgotten that the exit airlock is now pressurised so they can't open the inner doors without a catastrophic vacuum loss.

I will be interested to see either or both of those actually working! A pretty good indication of problems could be wind turbines - we see videos of them overspeeding and then becoming dismantled where all three arms let go at once. My understanding is that it is just one arm that lets go, but the shock causes the others to break and leave in sympathy.

And here is a problem; the spin launcher is not just accelerating the payload to a ballistic velocity but, it is also accelerating the counter weight too. So that's double the energy input, double the stress loading? Both 'ends' must detatch symetrically. The payload goes up, which means the counterweight must go down - 180 degrees in phase at the same speed. Otherwise there will be a jolt that's going to break something.

What arrests the "mass ejection"? Hydraulics? As you say, too much energy. Like stopping an anti-tank round. Maybe the counterweight could slam into a layer of explosives? Magnetics? Maybe a mile long linear deccelerator? But that's more energy waisted that could be expended accelerating the payload upwards.

Anyone with a basic electric fan knows a grain of weight difference in the blades results in a rattle. As for wind turbines, the loss of even a bladetip results in a catastrophic failure. The spin launcher will need to be oscillation free and made to tollerances exceeding a jet engine's turbine blades. Or a super fast hard disk drive.

It's an interesting exercise in engineering philosophy though.

[PlainName]

Another good example is the traditional spinning disc hard drives.  Fast ones are 15k RPM, max I've seen is 20k RPM.  Scale it up more, the glass-disc may shatter and the aluminum-disc may deform.

I'm sure there is more to it that plain speed. The forces would depend on diameter, and perversely 7k5rpm was noticeably absent on 2.5" drives where it was reasonably common on 3.5". There would be the rate at which you can read/write the magnetic bits, and once you hit that rate you're not going to cram more into a track regardless of how much faster it goes past.

[DougSpindler]

Another good example is the traditional spinning disc hard drives.  Fast ones are 15k RPM, max I've seen is 20k RPM.  Scale it up more, the glass-disc may shatter and the aluminum-disc may deform.

I'm sure there is more to it that plain speed. The forces would depend on diameter, and perversely 7k5rpm was noticeably absent on 2.5" drives where it was reasonably common on 3.5". There would be the rate at which you can read/write the magnetic bits, and once you hit that rate you're not going to cram more into a track regardless of how much faster it goes past.

The data could be read if they could get the drive to spin faster, that's not the limiting factor.  I think as will Spinlauch will find out the forces involved in spinning a hard drive platter faster than 10K RPM become nearly impossible to solve cost effectively.  But if you use the inner tracks and use the magic of marketing you can call in a 15K or 20k drive    (In performance written in fine print.)

[PlainName]

But if you use the inner tracks and use the magic of marketing you can call in a 15K or 20k drive

How does that work? I can't see that using the inner tracks gets you better performance, just less data per track.

the forces involved in spinning a hard drive platter faster than 10K RPM become nearly impossible to solve cost effectively

I wonder if this is a fake video then:


According to some random Internet place, the real reason is power - it takes significant power to spin it up that speed. Probably why laptop drives were low-speed.

[DougSpindler]

I think the guy is a fool running a drive that fast without some blast shield around it.  If this guy were younger I would think he's trying for a Darwin award.

Drives are divided into sectors and each sector has the same amount of data.   The data on the sectors for the outside tracks are spaced father apart and take longer to read.  Data in the inner track is much closer together and takes less time to read.

In the video I don't see the guy transferring any data, just spinning the drive.  I will give the guy the benefit of the doubt and will agree the drive is spinning at 20ki or 22k for a short period of time.  But that's not the same as running the drive for several years with a flying above.  I suspect the turbulence caused by the head moving across the platter could cause so imbalance causing the disk to vibrate. 

[PlainName]

Drives are divided into sectors and each sector has the same amount of data.   The data on the sectors for the outside tracks are spaced father apart and take longer to read.  Data in the inner track is much closer together and takes less time to read.

I think you are wr incorrect there. For two reasons:

1. Assuming there is the same number of sectors on inner and outer tracks, the read times are identical since the disk is spinning at the same speed for them all. That is, it takes some specific time to do one rotation, and in that time it will read the amount of data in one track. Which, as you point out, will be the same number of sectors and, hence, data.

2. You can improve storage space by having more sectors on the outer tracks. There is a limit as to how close the 'bits' can be, and on the inner tracks that spacing would be, let's say, 'tight'. As you move out, the same data is spread over more disk  so the density is less. If you squash it up to be just as 'tight' as on the inner tracks you now have more sectors on the outer tracks.

Maybe you've just spotted that in case 2 you now have more sectors going under the head per rotation, and that means in the same time. Thus you get a performance increase if you cram more sectors into the outer tracks. So you are kind of right in that the effective performance can be increased, but missed how it's done.


[edit: 'wrong' is a negative word]

[CatalinaWOW]

@CatalinaWOW  You appear to be the expert in this area.  What do you think Spinlaunch will be successful at?  Launching satellites?  Or burning through VC money without ever launching one?

I think it is highly unlikely that they will actually launch a satellite.

And extraordinarily unlikely that they will find a market big enough and lucrative enough to repay the development costs.

Their investors had better hope that they can sell any technologies or plant that is developed.  It isn't obvious to me that there is any value there either, but hope springs eternal.

[DougSpindler]

Drives are divided into sectors and each sector has the same amount of data.   The data on the sectors for the outside tracks are spaced father apart and take longer to read.  Data in the inner track is much closer together and takes less time to read.

I think you are wr incorrect there. For two reasons:

1. Assuming there is the same number of sectors on inner and outer tracks, the read times are identical since the disk is spinning at the same speed for them all. That is, it takes some specific time to do one rotation, and in that time it will read the amount of data in one track. Which, as you point out, will be the same number of sectors and, hence, data.

2. You can improve storage space by having more sectors on the outer tracks. There is a limit as to how close the 'bits' can be, and on the inner tracks that spacing would be, let's say, 'tight'. As you move out, the same data is spread over more disk  so the density is less. If you squash it up to be just as 'tight' as on the inner tracks you now have more sectors on the outer tracks.

Maybe you've just spotted that in case 2 you now have more sectors going under the head per rotation, and that means in the same time. Thus you get a performance increase if you cram more sectors into the outer tracks. So you are kind of right in that the effective performance can be increased, but missed how it's done.


[edit: 'wrong' is a negative word]

Not trying to be negative here either but you should have spent a few minutes Googling/Wikipediaing before posting.
The sector is the minimum storage unit of a hard drive.  Sectors stores a fixed amount of data 512 bytes and was the standard for decades until Advanced Format came along just 11 years ago when 4096 byte became the standard.

With each sector having a fixed amount of data, and sectors being pie or pizza slice shaped the data at the outside edge is spaced further apart if compared to the data stored in the inner tracks.  There is far more latency when reading data from the outside track.  That's why disk defragmenters would allow you to place data used most often on the inner tracks and data least used on the outside tracks.

[PlainName]

I would suggest you do some simple maths, Doug. Take the number of sectors per track and the rpm of the drive. For nice round figures let's say 20 sectors per track and 10krpm and track 1. We are seeing 200k sectors per minute pass under the head. Notice that it's not dependent on track number - all that does is change how squeezed up the data is, but with a fixed number of sectors per track the data rate will be exactly the same.

Don't believe me?

Effect of areal density
HDD data transfer rate depends upon the rotational speed of the disks and the data recording density. Because heat and vibration limit rotational speed, increasing density has become the main method to improve sequential transfer rates.[36] Areal density (the number of bits that can be stored in a certain area of the disk) has been increased over time by increasing both the number of tracks across the disk, and the number of sectors per track. The latter will increase the data transfer rate for a given RPM speed. Improvement of data transfer rate performance is correlated to the areal density only by increasing a track's linear surface bit density (sectors per track). Simply increasing the number of tracks on a disk can affect seek times but not gross transfer rates. According to industry observers and analysts for 2011 to 2016,[37][38] “The current roadmap predicts no more than a 20%/yr improvement in bit density”.[39] Seek times have not kept up with throughput increases, which themselves have not kept up with growth in bit density and storage capacity.

Just in case that wasn't clear: "Simply increasing the number of tracks on a disk can affect seek times but not gross transfer rates."

That's why disk defragmenters would allow you to place data used most often on the inner tracks and data least used on the outside tracks

You're making it up, Doug, or mis-remembering things. You would put often-read data on the inner tracks to reduce the distance the head has to move to get to it. You move everything to one end of the disk (otherwise it would remain fragmented) and it makes sense to have your most accessed data (maybe the OS) all in one place close up together. Thus the head doesn't spend half the access time traversing the tracks. Yes, that's a performance increase but it has nothing whatever to do with data rate UNLESS you have varying number of sectors per track. And then it will be the outer tracks that have the better performance.

[DougSpindler]

I would suggest you do some simple maths, Doug. Take the number of sectors per track and the rpm of the drive. For nice round figures let's say 20 sectors per track and 10krpm and track 1. We are seeing 200k sectors per minute pass under the head. Notice that it's not dependent on track number - all that does is change how squeezed up the data is, but with a fixed number of sectors per track the data rate will be exactly the same.

Don't believe me?

Effect of areal density
HDD data transfer rate depends upon the rotational speed of the disks and the data recording density. Because heat and vibration limit rotational speed, increasing density has become the main method to improve sequential transfer rates.[36] Areal density (the number of bits that can be stored in a certain area of the disk) has been increased over time by increasing both the number of tracks across the disk, and the number of sectors per track. The latter will increase the data transfer rate for a given RPM speed. Improvement of data transfer rate performance is correlated to the areal density only by increasing a track's linear surface bit density (sectors per track). Simply increasing the number of tracks on a disk can affect seek times but not gross transfer rates. According to industry observers and analysts for 2011 to 2016,[37][38] “The current roadmap predicts no more than a 20%/yr improvement in bit density”.[39] Seek times have not kept up with throughput increases, which themselves have not kept up with growth in bit density and storage capacity.

Just in case that wasn't clear: "Simply increasing the number of tracks on a disk can affect seek times but not gross transfer rates."

That's why disk defragmenters would allow you to place data used most often on the inner tracks and data least used on the outside tracks

You're making it up, Doug, or mis-remembering things. You would put often-read data on the inner tracks to reduce the distance the head has to move to get to it. You move everything to one end of the disk (otherwise it would remain fragmented) and it makes sense to have your most accessed data (maybe the OS) all in one place close up together. Thus the head doesn't spend half the access time traversing the tracks. Yes, that's a performance increase but it has nothing whatever to do with data rate UNLESS you have varying number of sectors per track. And then it will be the outer tracks that have the better performance.

You are partially correct   If a pie slice sector has 512 byte doesn't it reason the spacing between the magnetic bits on the platters are closer together for the inner tracks and further apart of the outer tracks?

[fourfathom]

What arrests the "mass ejection"? Hydraulics? As you say, too much energy. Like stopping an anti-tank round. Maybe the counterweight could slam into a layer of explosives? Magnetics? Maybe a mile long linear deccelerator? But that's more energy waisted that could be expended accelerating the payload

Well then, don't waste the energy.  Capture the counterweight energy with the magnetic decelerator, essentially regenerative braking.  Then find somewhere to store that energy for powering the next spin-up.

But no, I'm not really serious, because the whole thing is doomed to be a practical failure.

[DougSpindler]

What arrests the "mass ejection"? Hydraulics? As you say, too much energy. Like stopping an anti-tank round. Maybe the counterweight could slam into a layer of explosives? Magnetics? Maybe a mile long linear deccelerator? But that's more energy waisted that could be expended accelerating the payload

Well then, don't waste the energy.  Capture the counterweight energy with the magnetic decelerator, essentially regenerative braking.  Then find somewhere to store that energy for powering the next spin-up.

But no, I'm not really serious, because the whole thing is doomed to be a practical failure.

I've got the perfect solution.  When I was 8 years old I was given an airplane with rubber band.  All Spinlaunch has to is scale it up and get a giant rubber band. 

[Kleinstein]

With modern hard discs the magnetic surface is limiting the density of the data, not so much the read electronics. So they usually have more sectors per track for the outer tracks and an approximately constant geometric bit spacing. With most floppy discs and some older (e.g. MFM) hard discs they used a constant frequency to keep the electronics simple. AFAIK alread the IDE discs were essentially all with more sectors on the outside.

For the read speed and latency the RPMs for the disc obviously stays constant and thus the same latency to wait for a sector to come around. With the outer tracks the transfer speed for the data is higher as more sectors come in for the same time.  So speed wise the outer tracks are the better ones.

Some of the very high RPM HDs used a smaller plattern than the case suggsted to allow a higher RPM without an excessive speed and centrifugal force. So a disc in 5.25 form factor may internally only have 3 inch discs to run them faster. The higher RPM was also a reason why they increasingly got smaller. This looks like not having the outer tracks - not just not using them, but not having the plattern part too.

[thinkfat]

Like, in Robert Heinleins "The moon is a harsh mistress". There they used a "railgun" to catapult containers with local produce towards earth, to have them plunge into the Indian ocean. No need to rendezvous with them when you can just use atmospheric braking.

I'm pretty sure that Heinlein's launcher was a multi-stage magnetic launcher, not a true railgun.  Also the containers had retro-rockets, which were removed when they started "throwing rocks".  Having low gravity and no atmosphere makes it all much easier.

Great book, by the way.

I'm relatively sure the retro rockets were only used to steer the containers into a trajectory that allowed maximum atmospheric braking. Also, not so sure they were removed for "throwing rocks". Mike steered several containers far off shore into oceans as political tide on earth started turning.

[PlainName]

If a pie slice sector has 512 byte doesn't it reason the spacing between the magnetic bits on the platters are closer together for the inner tracks and further apart of the outer tracks?

Yes, they are closer together. You can look at it one of two ways:

1. The linear speed of the disk under the head is SLOWER on the inner tracks for the same RPM.

2. The time it takes for that pie sector of 512 bytes to rotate is the same for every track.

The data rate does not change - it is the same whichever track the data is on.