Excellent description of the physics, Joe. I think the really incredible thing is how impermeable these balloon skins must be to circle the earth multiple times and remain aloft for weeks or even months!
73 de Bill, KG5FQX
On Fri, Dec 30, 2016 at 4:21 PM, Joe nss@mwt.net wrote:
Jeff and the others. Both are close but also not totally correct either.
Bob has the correct theory about size and max altitude.
And Jeff is also correct about the home made custom envelope.
BUT......
These are NOT zero pressure balloons.
They are acting as super pressure balloons.
They are sealed tight, And Must be perfectly tight as they say "Bubble" tight. Any leak at all, and the flight will not even last 24 hours.
As Jeff said "they put enough gas into to get it off the ground with a specific amount of lift. "
Very true and that is the key to these flights, they are talking lifts level in the amount of grams, not even a single ounce. In like the big latex flights that we all have done. My group has done 60+ of them some fill lifts is the mounts of pounds even more than the payload weighs. And of course all those flight last 90 to 120 minutes mostly.
Now again as Jeff Said, "they put enough gas into to get it off the ground with a specific amount of lift. "
The amount of lifts are minimal. and as any balloon flight that happens once you have positive lift you WILL have positive lift until something happens. PERIOD!
In ANY balloon the gas expands to equalize the pressures inside vs outside the balloon. Just like ANY and EVERY balloon does.
But once the balloon is as big as it can get the inside volume can not get any greater, One of Three things happens.
1- The internal pressure just like a party balloon or the 30 foot diameter latex balloon, if you put too much inside more volume that the balloon can hold, the envelope ruptures and it's done.
2- The Zero pressure balloon behaves in the exact same way expands as gasses expand. BUT, once it is full and can not expand any more, instead of rupturing, built into the balloon is a special valve that lets some of the gas out, so the internal pressure can not build up high enough to cause the balloon to rupture. Eventually enough gas is released and the balloon does not go any higher and it floats somewhat like these long duration flights have been. BUT not the same. because these zero pressure balloons. Once the sun goes down they loose that energy, gasses shrink and the balloon comes down. The ONLY was a zero pressure balloon can stay aloft is to drop about 10% of it's weight every sundown.
3- Now this is how these flights are happening, they are operating in the world of "Super Pressure Balloons" Just on a tiny tiny scale.
Now how this system works.
In reality the numbers used are incredibly small and stretched out toseveral decimal places. But for explanation purposes here I will use large and rounded off whole numbers just to make it clearer and less number cumbersome.
At sea level or close to it, just enough lifting gas is injected intothe Balloon. Just enough to give the few grams of lift.
But for easier to understand Say In this case say Free lift will be 8 ounces.
So in other words when the lifting balloon is filled to the correct amount and everything is attached in the flight train, there is an excess of 8 ounces of lift. ( like I said these numbers are extremely larger than the real ones.
Say the volume of the balloon when full is 160 cubic feet. Wecalculate that if we put in 16 cubic feet on the ground, once it reaches 60,000 feet it has expanded and filled the balloon fully. Remember these numbers are all wrong and are not even close. It is just to explain how the system works.
Now is when the magic starts. As with any normal balloon as it risesthe atmospheric pressure and density drops. And any regular balloon also expands to equal out the pressure and also overall density. But this is where this system is different and is cool.
Say at 60,000 feet, the density of air is 0.1 ounce per cubic foot.So, In this balloon, it is contains a volume of 160 cubic feet that weighs 16 ounces. I know it is less because it is a lifting gas, but the theory is all the same.
And since it has a volume of 160 cubic feet, it is also displacing 160 cubic feet of air outside the balloon that also weighs 16 ounces.. 0.1 ounce per cubic foot.
OK, we still have positive lift of 8 ounces and the flight traincontinues to rise. It is rising into less dense air of course.
So now say it is at 70,000 feet.
Pressure has dropped, and the air surrounding the balloon is less dense.
BUT, the balloon envelope could not stretch any more and did not allow the 160 cubic feet of "GAS" inside the balloon to equalize the pressure and expand.
The 160 cubic feet of gas inside the balloon, is still having the properties of the gas had at 60,000 feet. I.E.: It still weighs 16 ounces.
But the air at 70,000 feet outside the pumpkin has expanded andbecame less dense.
It is now having a density of 0.05 oz per cubic foot.
So The balloon is still displacing 160 cubic feet of the atmosphere.
But this atmosphere at 70,000 feet weighs less than it did at 60,000 feet. 0.05 oz per cubic foot. So 0.05 X 160 cubic feet = 8 ounces. And now because of this, the whole flight train stops rising because the train has magically become 8 ounces heavier than it was at 60,000 feet!
The gas in the balloon still weighs 16 ounces, but the air it isdisplacing only weighs 8 ounces, so the balloon is 8 ounces heavier now. How cool is that?! And that is it! That's how it works. Pretty cool huh?
And thats how these balloons are staying up there for these incredible times.
Joe WB9SB
Sig The Original Rolling Ball Clock Idle Tyme Idle-Tyme.com http://www.idle-tyme.com
On 12/30/2016 2:50 PM, Jeff Moore wrote:
Interesting concept (mylar party balloons), but no, that is not what they are doing. They're using a custom made mylar envelope that I suspect is using very very thin mylar, this is a rather large envelope that you put enough gas into to get it off the ground with a specific amount of lift. The ones that have been flying are stabilized at around 50 to 60,000 ft. and will hang at that altitude as long as the gas is contained within the envelope eventually slowly lowering in altitude until they can't sustain flight any longer.
AS the balloon rises, the gas expands and fills up more of the envelope, the envelope should never actually get round like a traditional balloon unless the volume of gas at altitude approaches the actual volume of the envelope. At no time should you be able to get a pressure reading from the balloon - hence why it is called a zero pressure envelope. Definitely not a party balloon.
Jeff Moore -- KE7ACY Near Space SIG - High Desert Amateur Radio Group Bend, Oregon
On Fri, Dec 30, 2016 at 9:19 AM, Robert Bruninga bruninga@usna.edu wrote:
We tried zero pressure balloons (Mylar party balloons) but the max
possible height was just 23,000 feet or so due to the weight of the balloon itself. It's a direct calculation. So we paralleled balloons, but still, no matter how many balloons you add, the math still comes out to asymptotically approach the same max altitude due to the mass of the balloon material itself and its volume.
We did learn one other thing. With 5 under filled Mylar balloons to reach a cruise altitude around 23,000 feet (from memory?) we sent the cut-down command and nothing happened. (launching from Maryland is a guaranteed ocean landing unless you can come down in 65 miles or so)...
On recovery, we found one balloon had burst, and so it hung DOWN from the other 4 and got all wrapped around the payload. So when we sent the cut-down command, it worked, but the entangled lines kept everything together.
But now with only 4 of the 5 balloons providing lift, it came down at a very slow rate... about the same as the ascent rate... which means we chased it TWICE as far as intended.
Oh the fun of discovery! The event is shown on our web page (Spycam mission starts about 30% down the page) http://aprs.org/balloons.html
Bob, Wb4APR
-----Original Message----- From: AMSAT-BB [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Richard Tejera Sent: Friday, December 23, 2016 3:08 PM To: Dave Marthouse; 'AMSAT' Subject: Re: [amsat-bb] Questions On Balloons With Amateur Packages
Dave,
Knowing the weight of the payload, they will fill it with enough gas to become neutrally buoyant at the target altitude.
If altitude is the goal, enough gas will be filled to take it to an altitude that will exceed the Burt diameter.
Rick Tejera K7TEJ Saguaro Astronomy Club www.SaguaroAstro.org Thunderbird Amateur Radio Club www.w7tbc.org
On December 23, 2016, at 11:01, Dave Marthouse dmarthouse@gmail.com wrote:
I have seen posts from time to time on the BB about balloons with amateur radio payloads on them.
I've got a question regarding the missions that carry payloads around the world. What stops the balloons from going up until they explode do to the high altitude. How are the packages kept from doing this to achieve such long distance flights?
--
Dave Marthouse N2AAM dmarthouse@gmail.com
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb