What is the best design for a parachute to deploy after a weather balloon pops?

[guss]

Hey, I am building a weather balloon with a small payload that will ascend to approximately 105,000 feet, pop, and then fall to the ground.

I am having trouble coming up with a design for a parachute that will deploy after the balloon pops. There is obviously less air at that altitude, so if the parachute relies on air resistance to deploy it would probably have to get to an altitude where there is enough resistance to push the parachute out, or whatever. I don't want to use anything electrical or complex in this design, and want it to be as simple as possible. The parachute can't have a chance of deploying while the balloon is ascending.

I thought of the idea of putting the parachute inside the balloon, but this is unreliable because it would be difficult to keep the parachute attached to the payload after the balloon pops, so I do not want to use this idea.

Does anyone have any experience in this or a good idea? The parachute would obviously be pretty small, maybe 5 feet in diameter.

Thanks.

 

[Sakha]

How about using a high center of mass, so when the balloon pops the probe will turn upside down, and use a simple air-drag-deployed parachute?

 

[berkeman]

Hey, I am building a weather balloon with a small payload that will ascend to approximately 105,000 feet, pop, and then fall to the ground.

I am having trouble coming up with a design for a parachute that will deploy after the balloon pops. There is obviously less air at that altitude, so if the parachute relies on air resistance to deploy it would probably have to get to an altitude where there is enough resistance to push the parachute out, or whatever. I don't want to use anything electrical or complex in this design, and want it to be as simple as possible. The parachute can't have a chance of deploying while the balloon is ascending.

I thought of the idea of putting the parachute inside the balloon, but this is unreliable because it would be difficult to keep the parachute attached to the payload after the balloon pops, so I do not want to use this idea.

Does anyone have any experience in this or a good idea? The parachute would obviously be pretty small, maybe 5 feet in diameter.

Thanks.

Does it have to pop? Can you just slowly vent the hydrogen out to have it descend in a fairly controlled way?

 

[guss]

How about using a high center of mass, so when the balloon pops the probe will turn upside down, and use a simple air-drag-deployed parachute?

Not sure exactly what you mean, but I have an idea. I'm not sure how you would get it to balance like that, and then flip when it pops.

Does it have to pop? Can you just slowly vent the hydrogen out to have it descend in a fairly controlled way?

Yeah, it has to pop. I could vent the gas out, but it would be much more complex. I'm also using helium since it's really difficult to get a lot of hydrogen (about 70 cubic feet).

I have an idea, but I'm pretty sure it won't work. Let's say theoretically you have a round wooden pole. You attach a few small weights to one side, and drop it from high up so the pole is parallel to the ground. The weighted side won't always be the side to hit the ground first, correct? I know this is basic physics but I just want to be sure there's not something different that would happen in this scenario.

 

[Sakha]

Thats what I meant with the high center of gravity, so it pops and the center of gravity has to be lower, so it turns around. With some aerodynamics you can maintain it that way without flipping (I think so).

 

[guss]

Thats what I meant with the high center of gravity, so it pops and the center of gravity has to be lower, so it turns around. With some aerodynamics you can maintain it that way without flipping (I think so).

Yeah, it's a good idea, but the problem is that there will be 100mph winds at that altitude, and I want to be 100% sure the parachute doesn't deploy early

I think I have a good idea. Have the payload attached to the balloon with a 20 foot "main" rope. Then, have another rope that has the parachute attached to it. This rope will be tied a few feet from the top of "main" rope. Have the very top of the parachute taped to the balloon with a very small amount of duct tape. The balloon will pop, causing the parachute to be free.

The only problem could be that the expanding latex, or whatever material, of the weather balloon causes the tape to come undone from the balloon. But, this would only happen at high altitudes where the balloon would have expanded a lot, and the extra air resistance the parachute could make, that would slow the ascent, would not be a big deal.

 

[Sakha]

Yeah, it's a good idea, but the problem is that there will be 100mph winds at that altitude, and I want to be 100% sure the parachute doesn't deploy early

The only way it would deploy early is if the system is compeltely upside down (i.e balloon below payload).

Your tape idea sounds goo too but as you said, the stretching of the balloon might deploy it earlier.

 

[Nik_2213]

Don't weather balloons carry their parachute loosely furled between the balloon and sensor payload ? That way, deployment is automatic...

I'd be wary of using tape etc as anything above 10,000 ft is really, really cold and you can't trust either the glue or material. Also, you want the payload to come down fairly quickly, so it doesn't drift dozens of miles down-wind. That means your payload will land *hard*. So, you must cushion it well. That will also help to insulate it against the frigid stratosphere. What terminal velocity can your package tolerate ?? Perhaps you only need a simple streamer or drogue, not a 'chute...

Perhaps model rocketry websites can suggest ways to toughen your package ?

 

[Sakha]

Talking about the temperature in the probe, be sure to have a moderate temp and to test it out. Too much insulation might fry up the electronics.

 

[guss]

Good point about the tape. It gets really cold up there, -50 Centigrade. I'm going to test out the parachute, my goal is to slow it down, but not too much.

I also want to shrink my parachute, or maybe just cut a circular hole in the middle to make it so it doesn't go too slow. I want to try it out first, though.

And yeah, I'm going to use good insulation, as well as put some hand warmers in there for a decent heat source.

 

[berkeman]

A friend just sent me this video of a project very similar to yours. It should give you some feel for how the parachute can work. Very cool pictures!

"Space Balloon" http://www.brooklynspaceprogram.org/BSP/Space_Balloon.html

.
.

 

[JohnnyP]

I've done this a few times now and the parachute within the balloon works, as does the standard having the parachute between the balloon and the payload. I've also used an elastic band to hold the top of the parachute against the payload string which gets pushed off when the decent begins and the parachute opens. The only way that it seems to go wrong is if the parachute is acting as a drag on the way up as this slows your ascent and means that you're going to have to go further to retrieve it.

Don't worry about how the package decends at altitude, work out the parachute size that you need to have the package land at about 12mph (5 meters per second). This means that it will accelerate to about 120mph (50mps) at 100,000 feet (due to the lack of air resistance up there).

Basically, it doesn't matter how it falls, so long as it's stable and has slowed sufficiently when it hits the ground. You can test that with your parachute with the same weight as your payload if you have access to a high building.

For a bit of added protection, I use a loosely crumpled up ball of alluminium foil on the bottom of the package which works as both a radar reflector and absorbs some of the impact.

 

[guss]

I've done this a few times now and the parachute within the balloon works, as does the standard having the parachute between the balloon and the payload. I've also used an elastic band to hold the top of the parachute against the payload string which gets pushed off when the decent begins and the parachute opens. The only way that it seems to go wrong is if the parachute is acting as a drag on the way up as this slows your ascent and means that you're going to have to go further to retrieve it.

Don't worry about how the package decends at altitude, work out the parachute size that you need to have the package land at about 12mph (5 meters per second). This means that it will accelerate to about 120mph (50mps) at 100,000 feet (due to the lack of air resistance up there).

Basically, it doesn't matter how it falls, so long as it's stable and has slowed sufficiently when it hits the ground. You can test that with your parachute with the same weight as your payload if you have access to a high building.

For a bit of added protection, I use a loosely crumpled up ball of alluminium foil on the bottom of the package which works as both a radar reflector and absorbs some of the impact.

Awesome, thanks.

 

[Barnzman]

There are parachutes designed for weather balloon and they can be purchased for about $12.00 in the US. They can be used with payloads of 600g with a 4.m/s descent rate.

Try Kaymont or InterMet Systems

I have used smaller chutes from the model rockets and placed them inside the balloon before inflating but this requires 3 chutes and takes a lot more time.

 

[chemisttree]

http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=ea968eea871ed9ab2380f6d979eaa7a6&rgn=div5&view=text&node=14:2.0.1.3.15&idno=14#14:2.0.1.3.15.4"

If you are going to use radio for telemetry, you need to stay in the amateur band which requires at least a basic license. You can use GPS with cell phone without any special license but you need cell coverage over the landing zone. You probably won't be in cell range above 5000 feet. FAA requires that you have a payload of less than 6lb for unmanned balloons. Here is a http://www.classzone.com/books/earth_science/terc/content/investigations/es1702/es1702page05.cfm" both on ascent and decent. If you are near any airbases, review their "MOA" (good Google term).

How will you know how much helium to add to your balloon? Add too little and it may not pop until it drifts waaaay downrange. Add too much and it comes down too early.
Hmmmm.

 

[LURCH]

Can't you just drape the parachute over the ballon, so that, when the balloon pops, the chute is left empty?

 

[guss]

Thanks a lot for the great help everyone. I can calculate how much helium to use, and also the site I bought the helium from tells me to use 127 cubic feet. As long the balloon gets to 90,000 feet I'm happy.

I thought about using hydrogen, but how much more difficult is that to get helium? I was just going to buy a bunch of 14.9 cubic foot disposable helium tanks from my local hardware store because it will be much easier. I don't care too much about how long it takes for the balloon to fill.

If hydrogen is easily available, it could give me at least 60% more lift for the same amount. I would use less gas (which would save money and time), and the balloon would rise higher and more quickly. The problems with this, though, are getting a regulator for the tank, and finding a place to buy the tank. Or, I suppose I could use disposable ones like I am with helium but I don't think anyone sells those.

The balloon company I bought it from recommends 127 cubic feet of helium, so I figure 100 cubic feet of hydrogen would be about right. They sell helium is 110 cubic foot tanks, and I bet they sell hydrogen in the same amount.

An addition question, if I were to buy an industrial helium tank, how difficult would it be to fill the balloon without the regulator? The guy I was talking to said it was doable but difficult. The balloon I have is large, so even if I let the gas out too quickly at first it shouldn't be too bad. Anyone have experience with filling balloons like this, or any suggestions? Thanks.

 

[rcoert]

Perhaps you attach the pay load under the parachute, and attach the apex of the parachute to the balloon.
When the balloon pops, the heavier payload will fall, the parachute opens. My only concern is the envelope of the balloon falling faster than the payload. The envelope might fall over the parachute and cover it.

 

[guss]

Perhaps you attach the pay load under the parachute, and attach the apex of the parachute to the balloon.
When the balloon pops, the heavier payload will fall, the parachute opens. My only concern is the envelope of the balloon falling faster than the payload. The envelope might fall over the parachute and cover it.

Yeah, that's what I'm planning to do.