Author Topic: Mess with your minds: A wind powered craft going faster than a tail wind speed.  (Read 147599 times)

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Offline bdunham7

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Think about this way. You have a large wind turbine generator in low wind speed supplying a much smaller fan that creates even hurricane level winds but since the diameter of the fan is much smaller much less wind is actually moved so is like a gear box.
So say you will want to use the fan to supply the wind turbine then that will not work as power output is much smaller from the fan than what the wind turbine will need to supply the fan.
The propeller is like a diode it can leave air molecules travel from upwind to down wind but not the other way around so it acts as a one way sail while spinning.

But here you only have one fan, the propeller, and it obviously the same size as itself and is pushing directly back at the same wind that is powering it.  So first, I don't see how your 'gearbox' analogy works and second, you didn't respond to the question of how the wind and the 'artificial wind', which you claim can be stronger, can coexist in the same space.
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Offline electrodacus

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But here you only have one fan, the propeller, and it obviously the same size as itself and is pushing directly back at the same wind that is powering it.  So first, I don't see how your 'gearbox' analogy works and second, you didn't respond to the question of how the wind and the 'artificial wind', which you claim can be stronger, can coexist in the same space.

On blackbird the vehicle is like a sail at initial start so wind pushes against the vehicle body and the propeller blades (much smaller area then when the propeller rotates).  This power is split between accelerating the vehicle and powering the propeller by taking energy from the wheel.
So if you disconnect the propeller from the wheel then vehicle in same wind condition can accelerate much faster and get much faster to some speed below wind speed.
But instead of using all wind energy to accelerate fast you divert large part of the energy to power the propeller that creates a sort of artificial wind eventually at multiple times the wind speed.
So wind energy will be stored in vehicle kinetic energy then in propeller kinetic energy (spinning mass flywheel) and finally in pressure differential energy storage.
As you start to put more and more energy in the pressure differential energy storage that starts to also get used by the vehicle but even this is put back in all this 3 forms of energy storage the vehicle kinetic energy the propeller kinetic energy and also very important propeller pressure differential.
But when this pressure differential is the main or even only energy source it is put back in to kinetic energy of the vehicle and propeller kinetic energy so propeller spins faster but because vehicle also move faster the pressure differential drops.
When pressure differential gets so low that it can no longer power the vehicle and max speed is reached the vehicle starts to decelerate and now it is powered both by the vehicle kinetic energy and propeller kinetic energy that at this max speed point are at max charge and as they get used up the vehicle gets to the point where is again below wind speed.     

Offline IanB

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It will be 4800Ws. But there are quite a few seconds during the acceleration phase when the propeller at maybe 70% can compress the air behind in a huge volume of tens of thousand of liters (20m^2 propeller area times the length behind the propeller where pressure drops in a gradient to ambient pressure).

Except for the huge problem that propellers do not compress air. As has been shown by more than one experiment in this thread, the air behind a propeller is actually a vacuum.

The facts are simple: no walls, no containment, no compression, no pressure differential.
 

Offline electrodacus

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Except for the huge problem that propellers do not compress air. As has been shown by more than one experiment in this thread, the air behind a propeller is actually a vacuum.

The facts are simple: no walls, no containment, no compression, no pressure differential.

There is a low level vacuum on one side so lower than ambient pressure and on the other side there is a higher than ambient pressure.
As I mentioned before Wikipedia is not always a source of reliable information but it is sure way better for this than the youtube video performed by someone with no knowledge about the subject.
Link to articlehttps://en.wikipedia.org/wiki/Axial_fan_design
And diagram I posted before showing clearly the pressure differential


Offline IanB

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As I mentioned before Wikipedia is not always a source of reliable information but it is sure way better for this than the youtube video performed by someone with no knowledge about the subject.

You have a problem here in that experiments show what happens in real life. The observations from an experiment are a hard, solid, fact, independent of the knowledge of the person performing the experiment. You could have a two year old perform an experiment, and without them knowing anything, the experiment would still display the factual behavior of the universe.

On the other hand, a written document is simply what someone wrote. It may or may not be accurate, and conveys no factual weight in and of itself.

In this case, there is an obvious flaw. The diagram shows an abrupt change in pressure between P1 and P2, but it shows no simultaneous change in velocity. Since the mass flow between 1 and 2 must be equal by continuity, and since a change in pressure requires a change in density, it follows that the velocity must change abruptly if the pressure changes abruptly. Therefore, the diagram cannot be accepted at face value and must be rejected as an accurate description.
 

Offline bdunham7

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But instead of using all wind energy to accelerate fast you divert large part of the energy to power the propeller that creates a sort of artificial wind eventually at multiple times the wind speed.

So lets focus on just that for now.  How can there be two winds in opposite directions in the same space?  After all, the original wind has to continue to reach the prop to power it, right? 
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Offline electrodacus

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You have a problem here in that experiments show what happens in real life. The observations from an experiment are a hard, solid, fact, independent of the knowledge of the person performing the experiment. You could have a two year old perform an experiment, and without them knowing anything, the experiment would still display the factual behavior of the universe.

On the other hand, a written document is simply what someone wrote. It may or may not be accurate, and conveys no factual weight in and of itself.

In this case, there is an obvious flaw. The diagram shows an abrupt change in pressure between P1 and P2, but it shows no simultaneous change in velocity. Since the mass flow between 1 and 2 must be equal by continuity, and since a change in pressure requires a change in density, it follows that the velocity must change abruptly if the pressure changes abruptly. Therefore, the diagram cannot be accepted at face value and must be rejected as an accurate description.

Is clear you do not know how a fan works or/and what air is.
There is a fairly sudden change in pressure, density and speed of air molecules from one side to the other of the blades.
What happens is that any air molecule that will want to escape from the high density high pressure side will be hit by the propeller blade and sent back in the same direction with quite some speed and the molecules of air that will get to the propeller from the low pressure low density side will also be pushed in to the high density side to maintain the pressure differential.
Have you ever seen a fan in real life ? Was that working like a black hole attracting air molecules from both side and make them disappear ?
Or is your vacuum cleaner sucking air from both sides. Are you even a real human or a decently clever AI ?     :)

Offline electrodacus

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So lets focus on just that for now.  How can there be two winds in opposite directions in the same space?  After all, the original wind has to continue to reach the prop to power it, right?

No the "original wind" does not need to get to propeller to push the vehicle.  Some of the molecules moved by original wind if lucky may get to propeller but most of them will hit another air molecule from the high density side that moves in opposite direction and so same things happens as if you have two marbles hitting each-other.
It is a very fast game of baseball where air particles are the balls almost floating and pushing against each-other as small opposite magnets but doing so from all sides. The propeller blades are like the bat (maybe more like a cricket bat) and they hit the air molecules downwind against the wind keeping much higher density of balls on the downwind side due to the angle of the blades.
I will like to find an animation but with a simple google search I can not find anything to properly show this.
This seems a good explanation of air but nothing about a propeller

Offline bdunham7

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I do understand air and molecules, thanks.  But this misses the point.  In air, the molecules are always moving about and something like wind represents a net movement of all of them as an average.  What you seem to be proposing is that a wind that hits a propeller or fan will somehow generate a counterwind as or more powerful than the original wind, yet still get power from the original wind.  If so, what wind would an observer standing behind the vehicle see?
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Offline electrodacus

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I do understand air and molecules, thanks.  But this misses the point.  In air, the molecules are always moving about and something like wind represents a net movement of all of them as an average.  What you seem to be proposing is that a wind that hits a propeller or fan will somehow generate a counterwind as or more powerful than the original wind, yet still get power from the original wind.  If so, what wind would an observer standing behind the vehicle see?

Air molecules are hit by the propeller blades and sent at high speed in the opposite direction from the air molecules moved by natural wind.
Over time the propeller rotates faster and faster so it will push the air molecules that it will hit at quite a bit higher speed.
So this adds up over time it is not violate the conservation of energy. Both the kinetic energy of the rotating blade but also that of the vehicle will maintain the propeller ever increasing speed.
So at the start propeller hits air molecules but it will not push them faster in average than those coming from opposite direction from natural wind. All this time energy from wind increases the kinetic energy of both vehicle and propeller and that allows the propeller to increase the speed of that artificial wind.

That is also why I can say that pushing the vehicle without any natural wind will make the vehicle work the same way meaning at some point that pressure differential will be large enough that vehicle will accelerate past the speed you pushed the vehicle at.
So that is a good test that should convince anyone about pressure differential energy storage.
« Last Edit: September 02, 2021, 03:13:19 am by electrodacus »
 

Offline IanB

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Is clear you do not know how a fan works or/and what air is.
There is a fairly sudden change in pressure, density and speed of air molecules from one side to the other of the blades.

In the diagram, the curve of "C" shows the velocity (speed) of the air flow. Since you say there should be a sudden change in speed, and yet the diagram shows no such change in speed, you agree that the diagram is bogus?
 

Offline electrodacus

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Is clear you do not know how a fan works or/and what air is.
There is a fairly sudden change in pressure, density and speed of air molecules from one side to the other of the blades.

In the diagram, the curve of "C" shows the velocity (speed) of the air flow. Since you say there should be a sudden change in speed, and yet the diagram shows no such change in speed, you agree that the diagram is bogus?

That is average speed of air molecules but all air particle hit by the propeller will change speed quite dramatically. Imagine a molecule at relatively low speed coming from upstream hit by a propeller at multiple time that speed will have a very serious change in speed from one moment to the other.
But I'm glad you look closer at that diagram.

Offline bdunham7

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So that is a good test that should convince anyone about pressure differential energy storage.

I'm not persuaded one bit by any of that....and you didn't answer the question about what an observer behind the vehicle would feel.

Here's one last thought.  If your theory about pressure accumulation behind the vehicle is true, then that pressure would dissipate equally in all directions, right?  If so, the least area that the pressure could be confined to would be a cylinder the diameter of the propeller and as long as the distance travelled during the storage phase.  Since the pressure is dissipating equally in all directions and only the part that represents the vehicles propeller can actually get any benefit from it, it seems that this would be very, very inefficient.  You'd have to calculate how far the vehicle would travel during the time it takes your pressure balloon to accumulate the needed energy (reduced by this inefficiency) but it seems to me you would only recover a tiny fraction of the total and the rest would just go off into space.
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Offline electrodacus

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I'm not persuaded one bit by any of that....and you didn't answer the question about what an observer behind the vehicle would feel.

Here's one last thought.  If your theory about pressure accumulation behind the vehicle is true, then that pressure would dissipate equally in all directions, right?  If so, the least area that the pressure could be confined to would be a cylinder the diameter of the propeller and as long as the distance travelled during the storage phase.  Since the pressure is dissipating equally in all directions and only the part that represents the vehicles propeller can actually get any benefit from it, it seems that this would be very, very inefficient.  You'd have to calculate how far the vehicle would travel during the time it takes your pressure balloon to accumulate the needed energy (reduced by this inefficiency) but it seems to me you would only recover a tiny fraction of the total and the rest would just go off into space.

You mean that you will not be convinced by a test showing blackbird or small scale model of that pushed to say 12mph and then released and results showing vehicle accelerating to say 24mph then slow down until it stops.
How then will you explain without energy storage that vehicle got from 12mph pushed speed to double that at 24mph ?
Most other people are saying that vehicle will not accelerate past 12mph and just slow down and stop. So if they will see vehicle accelerate past pushed speed they will know my theory is right.

No it will not dissipate equally in all directions as it can not do that where the propeller sweep area is that large 20m^2 disc created by the moving propeller and so air molecules hitting that will just give their energy to the vehicle.
It is relatively an inefficient energy storage device but there is enough energy to power the vehicle for as much as 2 or 3 minutes depending on design and amount of initial energy stored.
Keep in mind that most of that energy vehicle takes from the pressure differential (energy is stored in both sides of the propeller) will be put back in to increase the propeller speed and only a smaller fraction is used for accelerating the vehicle that is why it takes so long a few minutes instead of just a few seconds before the pressure differential drops to low.
Also losses from stored energy are higher at peak when you have the energy storage full and the losses will drop as the pressure differential drops so you will observe a decrease in acceleration rate as you get close to peak speed.

Offline bdunham7

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No it will not dissipate equally in all directions as it can not do that where the propeller sweep area is that large 20m^2 disc created by the moving propeller and so air molecules hitting that will just give their energy to the vehicle.

OK, please describe the area or whatever that stores the energy--the physical dimensions, the method of energy storage (pressure?), etc.  I'm not getting that part.
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Online Kleinstein

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If working at all, energy storage in the pressure field around the vehicle is only short time. This is a bit like tryoing to store energy in a rather leaky capacitor. The pressure will not only push the vehicle, but just dissipare as sound to all other directions. The time constant for the "discharge" of the hypotetical energy storrage is on the order of dimensions divided by the speed of sound. So for the balckbird this are some 5 m divided by 330 m/s, some thing like 2/100 seconds.  So any energy stored would vanish fast, even if the order of magnitude estimate is off by a factor of 2 or Pi it is just a faktor of 1000 to short to keep significant energy.

The argument is about the time scale, so no need to calculate the energy - after some 100 time constants there is essentially nothing left, no matter how much was there to start with.
 

Offline electrodacus

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OK, please describe the area or whatever that stores the energy--the physical dimensions, the method of energy storage (pressure?), etc.  I'm not getting that part.

There is a volume containing that stored energy about half of it in front and the other half on the back of the propeller. See the shape of that in that propeller graph on Wikipedia. And yes pressure differential is what the energy is stored in to.

I'm not a mechanical engineer and I barely passed my fluid dynamics exam at university so sure not the most qualified to precisely calculate the exact amount of energy stored here and the efficiency of this energy storage device.
I'm sure there are simulation tools that can based on correct input data provide fairly accurate results sort of analog to a spice based analog simulation for electronic circuits.
I'm sort of surprised that I sis not see such a simulation for this types of vehicles after all the discussion. I guess some have tried and since they did not see the expected results they did not made the result known as there where thinking that do not know how to properly simulate that.

But not sure how we got to discus energy storage when the treadmill vs paper discussion is not solved. I think explaining pressure differential energy storage is more complex than the wheel only vehicle diagram solution and nobody confirmed that they agree with my claim that vehicle can not move from left to right.  That when understood will demonstrate that exceeding wind speed without energy storage is not possible and then we can discus about more seriously about the pressure differential energy storage.

Offline electrodacus

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If working at all, energy storage in the pressure field around the vehicle is only short time. This is a bit like tryoing to store energy in a rather leaky capacitor. The pressure will not only push the vehicle, but just dissipare as sound to all other directions. The time constant for the "discharge" of the hypotetical energy storrage is on the order of dimensions divided by the speed of sound. So for the balckbird this are some 5 m divided by 330 m/s, some thing like 2/100 seconds.  So any energy stored would vanish fast, even if the order of magnitude estimate is off by a factor of 2 or Pi it is just a faktor of 1000 to short to keep significant energy.

The argument is about the time scale, so no need to calculate the energy - after some 100 time constants there is essentially nothing left, no matter how much was there to start with.

The pressure differential energy storage is equivalent to an inductor while the flywheel kinetic energy storage and vehicle kinetic energy is equivalent with a capacitor.
So while the inductor (pressure differential) is discharging the capacitor (kinetic energy) is charging.

Offline IanB

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But not sure how we got to discus energy storage when the treadmill vs paper discussion is not solved.
It is solved for everyone except you.

Quote
I think explaining pressure differential energy storage is more complex than the wheel only vehicle diagram solution and nobody confirmed that they agree with my claim that vehicle can not move from left to right.
Everybody, without exception, disagrees with your claim.

Quote
That when understood will demonstrate that exceeding wind speed without energy storage is not possible and then we can discus about more seriously about the pressure differential energy storage.
You are doing this backwards. Once understood that the vehicle can move from left to right, it then becomes possible to understand that exceeding wind speed without energy storage is also possible.

If you start by assuming something is impossible, rather than trying to understand how it works, you become stuck in a hole you cannot get out of.
 

Offline electrodacus

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You are doing this backwards. Once understood that the vehicle can move from left to right, it then becomes possible to understand that exceeding wind speed without energy storage is also possible.

If you start by assuming something is impossible, rather than trying to understand how it works, you become stuck in a hole you cannot get out of.

I get your perspective.
The problem is that you did not proved either with a formula or with a test that what I say about vehicle in my diagram being unable to move from left to right is incorrect.
My formula is super simple power at motor wheel is smaller always than power power at generator wheel since generator wheel is what powers the motor wheel thus easy conclusion that vehicle can not advance from left to right.
And what it was showed in tests is completely different from my diagram as there was no treadmill involved. And yes I'm aware you think a piece of paper dragged is the same as a treadmill but it is not (not even close) and you will see that if you will do the experiment.
And the flipped vehicle is the exact same thing as the dragged paper.
I do not want to order some toy wheel vehicle and build a simple treadmill just to demonstrate this simple point.  It will take probably a few weeks to get the parts at my remote location and then I'm left with some useless stuff.  But any of you that already has the wheel vehicle and maybe even a treadmill or can build a simple manual treadmill even out of paper can do the test and prove me wrong. I even offered to provide compensation if I'm wrong and you prove that.     

Online Kleinstein

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The point is not capacitor vs inductor, the point is that it there is any energy stored in the pressure field is dissipates quite fast to the environment, not to the vehicle. The time scale is so short, that even 1/10 of a second is a long time. So the experiments shown are well long enough to be in essentially steady state.

Aerodynamics is a bit difficult, so I avoided going in the details there. The intuition says that if all the energy would rise when the vehicle would go faster, so the ernergy storrage would be more like adding a small part to the energy when moving and thus would work in the other direction. So the energy in the air would be available only when the vehicle slows down and can thus not increase the speed of the vehicle. So I doubt the air pressure could "help" (explain the higher speed) even at the bery short time scale.

The problem with the mis-understanding of paper vs treadmill could be solved if you tell us why the two should be different or how the vehicle could notice the difference. Most of us have a problem spotting the difference.
 

Offline electrodacus

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The point is not capacitor vs inductor, the point is that it there is any energy stored in the pressure field is dissipates quite fast to the environment, not to the vehicle. The time scale is so short, that even 1/10 of a second is a long time. So the experiments shown are well long enough to be in essentially steady state.

Aerodynamics is a bit difficult, so I avoided going in the details there. The intuition says that if all the energy would rise when the vehicle would go faster, so the ernergy storrage would be more like adding a small part to the energy when moving and thus would work in the other direction. So the energy in the air would be available only when the vehicle slows down and can thus not increase the speed of the vehicle. So I doubt the air pressure could "help" (explain the higher speed) even at the bery short time scale.

The problem with the mis-understanding of paper vs treadmill could be solved if you tell us why the two should be different or how the vehicle could notice the difference. Most of us have a problem spotting the difference.

You asked for the electrical analog so I was assuming you understand how an inductor stores energy and that is an almost perfect analog of the pressure differential energy storage works.
The magnetic field around the inductor can also collapse in a fraction of a second depending on the inductor inductance and current but it can also last for many seconds.
The propeller analog equivalent is an inductor parallel with a capacitor and the vehicle is another capacitor. While the inductor discharges it can charge this two capacitors than then continue to push some current trough the inductor maintaining the magnetic field around the inductor for a bit longer.
In any case it is demonstrated in both Blackbird and on treadmill model that there is enough energy stored to power the vehicle for at least about a minute in the case of blackbird and at least a few seconds for the treadmill model.
You will have no choice but to agree with that we can agree that the vehicle in my diagram can not advance from left to right without energy storage equivalent of pressure differential. It seems my power equation is not convincing you while there is nothing wrong with that so best bet is for you to test what is shown in my diagram and see for yourself that vehicle can not travel from left to right.   

Online Kleinstein

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My formula is super simple power at motor wheel is smaller always than power power at generator wheel since generator wheel is what powers the motor wheel thus easy conclusion that vehicle can not advance from left to right.
That simple "fomula" (it is more like an agumant in words) is simple, but simply wrong.

If you argue like this, it could also no more rigth to left and nothing would move at all.

If you really want to argue with power and not force, you have to add the relative movement of the platforms as a 3rd power - and it is a powerfull one. It adds to the power of the generator. Than the formulas suddenly no longer are so simple and the result is that the vehicle does move to the right.

The picture is much easier to understand with only looking at the speeds and use a fixed gear ratio. This formula(s) are really simple (and they are actual formulas) and give a definitive answer: with the right gear ratio you can go left.

The prop will not slow down the collaps (desappears as sound) of the pressure field very much - we don't care about a factor of 10, it is still way faster than the experiment.
 

Offline cbutlera

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You did not took energy from the aeroplane.

You seem to have changed your mind.  In your previous message you not only agreed that I did take energy from the aeroplane, you also correctly calculated how much energy I took.

I may not have been very clear. In your tough experiment there are two sources of energy both contributing to your increase in kinetic energy.
Out of that 14035J you contributed 35J and the plane contributed with 14000J.

You then go on to say.

If the aeroplane did not had a constant speed controller say maybe even engines turned off then you will have slowed down the aeroplane while you where traveling at 1m/s.

Yes, that's right, you've got it!  You have identified the source of the additional energy that I took, and the reason why conservation of energy is not being broken.  When I started walking at 1 m/s, I gained 14,035 joules of kinetic energy (in the frame of reference of the ground). The aeroplane provided 14,000 of those joules, and in doing so lost 14,000 joules of its own kinetic energy, by slowing down very slightly.  The entire system of me plus the aeroplane only gained the 35 joules of kinetic energy that my muscles produced.

So you do agree that I have taken energy from the aeroplane after all, and that I did it while moving slightly faster than the aeroplane.

 

Offline Brumby

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... power at motor wheel ... ... power at generator wheel ...

Still with the wheels.   :palm:



It is pointless to try and explain what is actually going on when you consistently present flawed logic and dismiss any explanation which disagrees with your preconceptions.


For this discussion to have been through so many iterations without you having conceded a single point of any argument that even looks like it challenges your stubbornly held position, then your objectivity is - quite simply - non-existent and your understanding of physics is both narrow and flawed.


So, I'm wondering ... did you try for a job at SpaceX without luck - and now you're working for Blue Origin?

Edit: Amended the above.  Blue Origin have actually got something off the ground.
 


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