[X] My Assistant

[jamescanvin]

Of course the ballon could go a LONG way in 24 hours and could make recovery quite a lot more difficult. I quite like the quick up and down mission profile.

James

[nprev]

Hmm...How many "Bobs" do you think we get if we sent Newhart up, anyhow?...
(Interpretation for our non-US friends: The Bob Newhart Show was a popular sitcom in the 70s, and a drinking game emerged where, while watching the program, everybody had to take a swig when any of the characters said "Bob". You'd usually have quite a buzz by the end of the show...)

I agree with James; balloon station-keeping is problematic at best...unless it was tethered. However, 20 km of cable seems like a pretty significant aviation hazard.

EGD, venting gas to descend sounds reasonable. The only thing that bugs me is that high-alt balloons usually launch fairly empty-looking, isnce the gas expands so much when it reaches its target altitude...think that the venting process would have to be MOST carefully controlled to assure a safe landing (talking a control loop that would regulate the venting with respect to ambient pressure & temp, here), and even then you have the drift problem to deal with.

[ElkGroveDan]

EGD, venting gas to descend sounds reasonable. The only thing that bugs me is that high-alt balloons usually launch fairly empty-looking, isnce the gas expands so much when it reaches its target altitude...think that the venting process would have to be MOST carefully controlled to assure a safe landing (talking a control loop that would regulate the venting with respect to ambient pressure & temp, here), and even then you have the drift problem to deal with.

Actually I meant it more as a delay in the balloon bursting than a descent tool . Maybe a minimal amount of venting that allows you to hang around a bit longer prior to the burst.

[nprev]

Oh, okay; I'm with you now! Yeah, that would be a lot easier to do; basically, you'd just pick a target altitude & hold it by venting until you're out of gas. Could conceivably get several hours of hang-time that way.

[helvick]

The thing is that you want to keep this all very, very simple from a mechanical point of view. Adding control capabilities to the balloon is probably asking for too much automation. If you are going to do that then you probably could add computer control to the image acquisition at no mass cost though by resusing the altitude control hardware. In any case such a capability will require either expensive custom hardware (which could be relatively light) or some cables and a cheap second hand laptop PC or something similar (which would be relatively heavy). Now I've no what the cost of the basic balloon, helium and tracker are going to be but adding that sort of capability to it is going to significantly ramp up the financial cost and payload mass.

I think we'd be better served by making the payload as light as possible (say < 2kg total for the camera, tracker and extra power), and push for altitude at speed rather than hang time - after all it's not as if we're going to waiting for something in particular, we just want something to get up high. The Sable team's site commented that they didn't get very many "good" pictures so the real challenge here would be how to build an imaging component out of cheap digicams that significantly improved on that.

One possible pitfall is that COTS digicams aren't going to work well at 10's of km altitude and the corresponding <<0degC temperatures and low pressure environment. I suspect that some attempt will need to be made to keep the camera warm and it probably wouldn't be a bad idea to try and enclose it in a 1 bar zero humidity atmosphere while you're at it. Ah yes we have scope creep.

[AndyG]

EDITED: This...this is crazy...

...and - interestingly - it's from an altitude where the pressure is virtually identical to that of the Martian surface ...Not that this is a cheap way to test equipment for Mars!

Andy

[ustrax]

I'm seing many of us interested in this theme that I will dare to advance with a proposal...
How about a UMSF communal project? An international team working on several continents sharing its diversified skills to take us to near space, that sounds really great to me...
What's your opinion? Doug, guys?...

[djellison]

I just ebay'd my old Canon S2 IS for about £150 - it's intervalometer was fantastic but its batterylife had reduced to nothing - a real shame. I'm sure some stacked Li-Poly's could fix that in a payload situation. The temperature issue is a challenge though - and really you would want two - one horizon looking - on down looking - OR - do you split the FOV two ways with a mirror either shot-by-shot or splitting the instantanous FOV. The smaller Canon's have Intervalometers as well - perhaps the payload could stretch to two?

Let's keep it casual - but think it through as much as is possible - as well as possible.

[ustrax]

Let's keep it casual - but think it through as much as is possible - as well as possible.

I like the way you put it...

I have one of this that the dog chewed a bit...It might get sacrificed for the good of mankind...And it already made part of the Cynthia-I launch...
It also as good performance regarding an aspect that I would like to see debated, how about filming?
With the card I have I'm able to get 15minutes of good quality video.

Another crazy approach...can't we think about something that would mark the difference? Some kind of testimony?
We could fill the balloon with testimonies of the participants and when it bursts would deliver our thoughts, messages, ugly faces in the near space...

[djellison]

Hmm- was your dog in Milan last year? Helen had one of those - and it got stolen while on holiday in Milan It was a great camera.

I think the way to choose payload elements is to think of items that are as self contained as possible - so any small camera that has the ability to take images every X seconds built in would be suitable. The lightest (size doesn't really matter - a polystyrene housing isn't going to be very 'massive' - it's mass that's the issue I would have thought) camera with a nice wide field of view, and a self-timer facility is the thing to use.

[ustrax]

Hmm- was your dog in Milan last year? Helen had one of those - and it got stolen while on holiday in Milan It was a great camera.

Who knows? I'll have to ask the dog...
And it is indeed a great camera.

I agree with you Doug on keeping things simple but I would love to see it filmed...
I started building a polystyrene shell to house the camera, not difficult to do (don't know really why I abandoned the idea...).
I'll search for it, but my guess is that the lady in the house got rid of it and it is now probably orbiting some dumpyard...

[Ant103]

Hmmm

Interesting proposition Rui. I enjoy if I can join the project you want to start .
And I have a question : about the balloon, which element you want see to use into it? Helium, warm air? I had listenning about some black plastic balloon who inflate themselves with sun illumination, and air temperatures at the interior rise more and more. At the end, the balloon lift-off and can transport payload (mass in relationship to size of the balloon...).

So, I'm very interest into making/design of this project .

[nprev]

Gotta be helium to reach the kind of altitudes desired. Here's a pretty good project summary of one such effort:

http://moo.pl/~tygrys/balloon/

[AndyG]

This is a highly achievable goal in terms of the engineering and cost, compared to, say, a stratospheric amateur rocket.

Playing with Excel, it really boils down to minimising envelope mass. Of course, the envelope mass is not helped by having to be big enough to contain the expanding lifting gas at high altitudes - the volume of the gas increases 70 times at 30km, 130 times at 34km. Obviously the excess envelope required at altitude is just deadweight at pressures nearer the surface.

However, using standard (and cheap) thin poly materials I calculate:

A 13.5 kg envelope (with an inflated size of 13m in diameter) could loft 2kg of payload to an altitude of 30km using less than 3kg of Helium. A more modest 4m-diameter envelope could take 500 grammes of payload to ~22km.

Not bad!

Andy

[Ant103]

I found this page about solar balloons : http://perso.orange.fr/ballonsolaire/en-index.htm
I will try it myself