Airship to Orbit, Airship video.

[cmedwards]

A hydrogen:air mixture will burn at as little as 5mbar pressure, and it may be possible to light it off at less. Only the critical combustion limits change with pressure. If you start with pure hydrogen, a leak will always dilute to some concentration at which it could burn. Adding helium to the mix doesn't help much, either.<br /><br />Hydrogen isn't much of a problem for a Mars balloon though. And it stores so reliably in hydrate form. <br /><br />Hmm...

 

[nacnud]

A Mars aerostat! That would be a great way to study the atmosphere, complete with sampling. A power source might be tricky though.

 

[josh_simonson]

Mar's atmosphere is formed of denser gasses than earth's due to the solar wind stripping away the lighter molecules. Fatal to terraforming, but a boon to balloonists because you get about 50% more lift at a given ambient pressure.

 

[mcbethcg]

Has anyone done the math on the theoretical maximum height of a balloon of a given size?<br /><br />For example, if you had a balloon full of helium at ambient pressure (Its allowed to leak out the bottom as it ascends) that is a mile wide, made of a molecule thin layer of _______(Fill in the blank, I dont know what the strongest light material is), what is the maximum possible altitude?<br /><br />I like the sky station idea- it gets fragile materials out of the wind, and might make insanely thin membranes more possible.<br /><br />Where is the math on this?

 

[josh_simonson]

Pretty straightforeward, just the height where the mass of a volume of air of the same size is 1.38x the mass of the balloon skin and payload.<br /><br />JP will use aerodynamic lift to fly higher than the balloon could float on it's own bouyancy. The military is working on a similar heavier than air airship called the 'walrus' that works at lower altitudes - JP plans to do the same thing, only use an ion engine so the airship won't lose thrust and stall at some altitude.<br /><br />Seems like the biggest potential showstopper is the skin, which will have to remain intact with air molecules bombarding it at mach 26. Due to the thin-ness of the air the skin shouldn't get hot overall, but individual molecules will really get twanged and heated - breaking down organic materials like plastic. This might be solveable by plating the skin with some sort of ablative material like was used by the recent IRDT demonstrator described here http://www.space.com/businesstechnology/technology/051012_irdt.html it's unclear if this material would be light enough for an airship.<br /><br />If the airship doesn't pan out, a mass driver on the DSS may be able to orbit small, rugged payloads since it's beyond most atmospheric resistance.

 

[mcbethcg]

OK, so what are the answers? How high can a balloon go with no payload but the weight of its own skin?

 

[josh_simonson]

Depends on the type of skin and the size of the balloon.

 

[chriscdc]

One thing that has bugged me about this is, how does the skin of the balloon survive impact with gas particles at around mach 21?

 

[tap_sa]

<font color="yellow">"Seems like the biggest potential showstopper is the skin, which will have to remain intact with air molecules bombarding it at mach 26."</font><br /><br />Don't worry, you can probably <i>run</i> faster than the orbital blimp's top speed. Hint: Try calculating the drag force on that behemoth in high altitudes and compare to the power levels of existing and proposed electric thrusters.<br /><br />

 

[mcbethcg]

The best skin material we have, 500 meters wide.

 

[josh_simonson]

>Don't worry, you can probably run faster than the orbital blimp's top speed. Hint: Try calculating the drag force on that behemoth in high altitudes and compare to the power levels of existing and proposed electric thrusters. <br /><br />That makes no sense, if it's orbital, it'll have to go to about mach 26. Where it operates the air is just thin enough that the air resistance is less than the thrust of the ion engine. The air resistance may feel like you're just walking along, but the air particles will strike very hard. An N2 molecule striking at mach 26 is equivalent to a 40000'C molecule hitting you. That's alot of energy packed into a tiny impact zone.

 

[mcbethcg]

OK, so whats the max altitude, with the best skin material we have, 500 meters wide?<br /><br />Any able to do the math?<br /><br />Whats the theoretical limit?<br /><br />

 

[mcbethcg]

I kjust love it when I ask a question, and someone says that its easy to answer... and then does not answer.

 

[josh_simonson]

Here ya go:<br />Your spherical balloon has volume of 65.5 million square meters. Filled with helium, it's got 58 million pounds of lift on the ground, 466 thousand kg lift at 20 miles and 58 thousand kg lift at 30 miles. To get to that height your balloon must have a skin that weighs less than 74g/m^2. Going down to a 100m balloon brings you down to 26g/m^2 because of the increase in surface area to volume. You'll have to research the skin on your own.

 

[mcbethcg]

I dont have the knowledge to solve this problem- I just want to know what the theoretical altitude limit for a balloon is with current materials.<br /><br />The answer to this question would tell us how close to space a balloon with no payload can actually go.<br /><br />Have the guys that make the ballons on the site come up with an answer?<br /><br />Surely someone has.<br />

 

[josh_simonson]

It doesn't matter how high up a balloon can go if it can't get into orbit. The x-prize showed it's relatively easy to go high, it's going high and getting to mach 26 that's hard.

 

[mcbethcg]

If a membrane can get to 100 miles, maybe it can be affected by solar wind, solar radiation, tethers interacting with the magnetosphere, etc.<br /><br />Altitude make a huge difference if it can get high enough.<br /><br />Don't get me wrong- 100 miles seem completely impossible to me.<br /><br />But I don't know it, because no one seems to have done the math.

 

[josh_simonson]

Here's more info. http://spiff.rit.edu/classes/phys317/lectures/multiple_funcs/temp_profile.html Note the temperature also undergoes dramatic changes between -80 and +100'C. Your membrane would have to not become brittle on the low side and not melt on the high side. At 100 miles, your balloon of 500m could only weight 110g. I think it's safe to say 100m won't happen on bouyancy alone.

 

[mcbethcg]

Thanks, thats the kind of answer I was hoping for. You have been very patient and helpful.

 

[jpowell]

Floating to 100 miles up may be tough, but 45 miles may just be doable.<br /><br />JP<br /><br />www.jpaerospace.com

 

[mlorrey]

I just love it when someone says something is impossible, but proudly declares they are too mathematically incompetent to prove it.<br /><br />In fact, metal wire fabric impregnated with silica/silicone rubber can and has reentered the atmosphere at suborbital speeds.<br /><br />Have you ever flown a flight sim at 300,000 feet? At that altitude, your indicated airspeed, when flying mach 25, is about 30 miles per hour. Or less. There is only slightly more than nothing there. There is, however, just enough air to fuel an ion engine. Whether the drag of hundreds of square feet of cross sectional area can be overcome by a mere ion engine is a good question, one which I doubt any of the armchair quarterbacks can honestly give an answer too. I look forward to JP's first real powered flight of one of these things.

 

[klreed]

Hello jpowell,<br /><br />Interesting work with the Airship. Ever thought of adding a Biefeld-Brown Lifter (asymetric capacitor lift)? Graphite paper would make good electrodes for these and they would weigh less than your keel truss beam. You seem to have the exact shape for a Naudin version (triangle lifter) or lifter-cell.<br />http://lifterproject.online.fr/liftercell/index.htm <br /><br /> For instance CP1/a-Si:H solar cells weigh about 1 kg for every 35 m2. Cp1/a-Si:H power density is 4300 Watts/kg and I guess 300 V output is not a problem... A fly-back circuit can boost power from 300 V to 50 kV to power the ion lifter. You would have a nice ion booster for your airship so a lot more payload capacity tha helium alone. Best is that large area of ionized air would make about the best reflecting antenna possible so less on-board transponders would be needed, than on a satellite for instance, to provide telephone, video, broadband, telemetry. CP1/a-Si:H link is here:<br />http://home.earthlink.net/~klreed/recordpowerdensitysolarcell/id1.html

 

[qso1]

Whats the current status of this project? <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[jpowell]

The program is moving along very well. We have two airships under construction, one is nearly complete.<br /><br />We're getting the next Away mission ready. It will be a run to 100,000 feet. It will fly in the next few weeks.<br /><br />This fall we'll be bringing the preliminary electric propulsion system on line.<br /><br />JP <br />www.jpaerospace.com

 

[qso1]

Good luck and looking forward to seeing the results. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>