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Google Loon balloon crashes near Yakima

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Re: Google Loon balloon crashes near Yakima

#41

Post by jacquesm »

mscuwa wrote: post #30
jacquesm wrote: post #3

Earlier quoted context omitted.

The chances of hitting a jet are remote, the balloon would have to loiter at the right altitude for that chance to increase appreciably. Most will go higher, pop and then fall. The barrage balloons of WW-II had to be anchored very carefully to avoid having them go into the stratosphere. As the balloon expands (which it does when it goes higher) it will become more buoyant, not less so there is a positive feedback loo…

Are you sure about positive feedback? Balloon does expand, but air outside becomes thinner, so buoyancy will actually stay constant until the walls are completely unfold, and then drop as gas inside will expand less than necessary to maintain buoyancy.

The gas inside will want to expand further, but it will be restrained by the envelope. Imagine the outside air pressing inward until there is an equilibrium. If the balloon then rises again (for instance, because it warms up) then it can get to a point where the outward force on the envelope exceeds the capacity of the envelop material to restrain that force.

For flexible envelopes this is more or less inevitable (balloon rises->atmospheric pressure drops->balloon expands->density decreases->balloon rise etc), for more rigid envelopes it is a balance that may work out in favor of the balloon staying in one piece (oscillating in altitude as it cools down/heats up again with the day/night cycle), or it may burst depending on the pressure differential. Most of them are pretty flimsy.

From: http://www.stratostar.net/faq.html

"When a balloon is filled on the ground with lift gas (helium or hydrogen), it can range in size from 2.5 ft to 8 ft in diameter. During the balloon's flight it will grow more than 4 times the diameter and upto 83 times the volume measured at launch, until it can't strech any more and will burst! A high-altitude weather balloon filled with 268 cu/ft of helium will have a diameter of about 8 ft at sea level, but as the balloon climbs through the atmosphere it will expand to 35ft in diameter and will have a volume of 22,449 cu/ft before it pops."

Re: Google Loon balloon crashes near Yakima

#42

Post by jacquesm »

plantain wrote: post #29
plantain wrote: post #19

Earlier quoted context omitted.

They have ADS-B transponders. You see them sometimes on flightradar24 floating around at FL650.

http://theaviationist.com/2014/03/01/google-project-loon/

> The helium balloons are all “floating” around 1,000 feet to the southeast of New Zealand

I can't make soup of that.

Re: Google Loon balloon crashes near Yakima

#44

Post by stilldavid »

gregholmberg wrote: post #16
kordless wrote: post #15

The word 'crashes' could easily be substituted with 'drifted into'.

Dropping at 2000 feet per minute is not quite free fall, but it's a long way from a drifting dandelion seed. I wonder if the balloon payload left a crater.

I've launched a handful of latex weather balloons to near-space. They all descend on a parachute and have a target impact velocity of ~2000 feet per minute. None have made so much as a dent in the earth so far.

Re: Google Loon balloon crashes near Yakima

#45

Post by gregholmberg »

stilldavid wrote: post #44
gregholmberg wrote: post #16

Earlier quoted context omitted.

Dropping at 2000 feet per minute is not quite free fall, but it's a long way from a drifting dandelion seed. I wonder if the balloon payload left a crater.

I've launched a handful of latex weather balloons to near-space. They all descend on a parachute and have a target impact velocity of ~2000 feet per minute. None have made so much as a dent in the earth so far.

I believe you. :)

I have no experience with balloons at all, but even a plowed field feels like a sidewalk to me when I run into it at the same speed under canopy. I leave a sizable mark, and I have seen friends break femurs, pelvises, etc at the end of a similar descent.

Re: Google Loon balloon crashes near Yakima

#46

Post by sk5t »

robin_reala wrote: post #31
jgrahamc wrote: post #28

Earlier quoted context omitted.

:-) I used to work for Madge. Why were you running without MAUs?

Possibly the more important question is ‘Why were you running a token ring network in 1999?’! I have no idea why our network was structured like that, this was my first job in the industry and I was a lowly PC tech at the time. If I had to guess, the word that springs to mind is ‘legacy’.

Eh, I was a user on a token ring university network almost that late, and it was superior to the congestion-crippled ethernet networks at more 'advanced' institutions. That said, I definitely didn't enjoy all the practice I got in building token ring-enabled Linux kernels.

Re: Google Loon balloon crashes near Yakima

#47

Post by partomniscient »

gregholmberg wrote: post #6

In the 90s, I would sometimes trip over ethernet cables that had been strung between server racks, across an aisle. Will this be the decade where I get to experience being struck by falling routers and switches, far from any data center? (EDIT: Simply remarking on novelty of problem and upward growth of network. No criticism of any firm implied or intended.)

The children's story will have to be revised.

Chicken little decided to go for a walk outside and was killed when the internet fell on him. The sky continued unabated.

Re: Google Loon balloon crashes near Yakima

#48

Post by mscuwa »

jacquesm wrote: post #41
mscuwa wrote: post #30

Earlier quoted context omitted.

Are you sure about positive feedback? Balloon does expand, but air outside becomes thinner, so buoyancy will actually stay constant until the walls are completely unfold, and then drop as gas inside will expand less than necessary to maintain buoyancy.

The gas inside will want to expand further, but it will be restrained by the envelope. Imagine the outside air pressing inward until there is an equilibrium. If the balloon then rises again (for instance, because it warms up) then it can get to a point where the outward force on the envelope exceeds the capacity of the envelop material to restrain that force. For flexible envelopes this is more or less inevitable (ba…

My point was it's not becoming more buoyant, i.e. lift can only drop when it ascends. I wouldn't argue that it can burst, but it depends on material. As an edge case it won't go to the Moon as lift will be 0 in the vacuum. So unless there is a limit on balloon size the lift will be constant, otherwise it will drop during ascend.

Re: Google Loon balloon crashes near Yakima

#49

Post by jacquesm »

mscuwa wrote: post #48
jacquesm wrote: post #41

Earlier quoted context omitted.

The gas inside will want to expand further, but it will be restrained by the envelope. Imagine the outside air pressing inward until there is an equilibrium. If the balloon then rises again (for instance, because it warms up) then it can get to a point where the outward force on the envelope exceeds the capacity of the envelop material to restrain that force. For flexible envelopes this is more or less inevitable (ba…

My point was it's not becoming more buoyant, i.e. lift can only drop when it ascends. I wouldn't argue that it can burst, but it depends on material. As an edge case it won't go to the Moon as lift will be 0 in the vacuum. So unless there is a limit on balloon size the lift will be constant, otherwise it will drop during ascend.

It won't go to the moon because it does not have sufficient velocity to escape the gravity well. Not because there is no lift in a vacuum (it will never reach a vacuum).

It will simply float to the top of the atmosphere (if it stays in one piece) to the point where the weight of the baloon is balanced by the buoyancy. Just like a rubber ball will not float 'on top' of the water that supports it but slightly inside it.

It's Archimedes' law applied to balloons.

Re: Google Loon balloon crashes near Yakima

#50

Post by utopkara »

jacquesm wrote: post #10
utopkara wrote: post #7

Earlier quoted context omitted.

Indeed they are launched all the time. But, we are talking about the case that the practice becomes popular and the skies become a dense minefield.

That's an interesting back of the envelope question to work out. Something with volume occupied by all aircraft aloft at any given moment, volume of all balloons at any given moment, the total volume of the shell in which commercial air traffic takes place. I think we can safely forget about the chances of spyplanes hitting balloons, the volume of space versus the number of spyplanes would make that a non-issue, even…

Keep in mind that balloons are much cheaper than planes to build and operate. Worse yet, the populated areas on earth are only a fraction of the whole surface area. Expect balloons to make dense clusters rather than evenly distributed over the sky. Needless to say, there will be more flights to more populated areas as well. Increasing the likelihood of collision to a level that the pilots will need to constantly monitor the skies will increase fatigue and cause indirect problems. The cost of all this will be felt by the aviation industry, and will be passed on to us.
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