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Originally posted by Shambolic
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How'd I go??

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Sadly the lighter than air portion of the vehicle may have to be disposable. It may interest you to know the following. Assuming the following:
Mass of the space shuttle orbiter = 250,000 lbs. (no payload)

Lift capacity of 100L He (liq) = 170 lbs (@ STP sea level)

Volume of 100L He (liq) as He (gas) in STP atmosphere
= 2668 cu feet

Amount of 100L He (liq) balloons needed for neutral buoyancy in air for space shuttle orbiter.
= 1470.588235

Volume of Liq He needed (L)
= 147058.8235

Volume of Inflated He balloon (cu Feet)
= 3,923,529.41

Diameter of single spherical balloon needed (feet)
= 195.6858531

This assumes many things are constant when in fact reality can be a bit more complicated. However, a balloon this size should be able to lift a fueled space shuttle to around 100,000 feet, release and allow powered flight from that point.

As a side note, Hydrogen would be about 1.6 - 2 times as efficient, and could substantially reduce the balloon size. Re-using the Hydrogen for fuel would not be practical. Helium is produced on earth only from alpha partials emitted from other radioactive materials, then slowly regaining 2 electrons over time, creating He one atom at a time. This He is then captured in mining operations usually mixed with Methane (about 4%) by volume. Therefore the drawbacks of Hydrogen may outweigh the safety of Helium because of it's relative rarity and expense.

All the above difficulties aside, it might save allot of weight on the first stage or two of launch. Also, releasing the shuttle before apogee would allow the second stage conventional propulsion to begin at a V. velocity above zero; this would also assist in accomplishing nice fuel savings.

Just some thoughts...
Erik

...that a helium baloon was used to lift a conventional rocket to the upper stratosphere and then the rocket took over; firing its engine straight up through the balloon, having a pointed nose cone to affect this achievement.

Even though this was been done before, once launched, one is limited in controlling where the balloon goes as it's carried by winds.

It does work for sounding rockets that just go straight up, however.
Hot air balloons wouldn't work for this application, since the hot air heater would get in the way of the rocket.

Hot air trapped in the balloon displaces colder air of equal volume out side of the balloon. At sea level the air density is relatively high at 1. At 10 km above earth surface the density is 0.239. Higher you go lower the density. It gets to a point where the cold air you are displacing with hot air won't provide enough lift to support the balloon as the wieght of the volume you displace is higher than the weight of the balloon. Helium balloons will go higher. Below is a small article of the worlds record altitude for a manned balloon.

In May, 1961, the current official altitude record was set. Commander Malcolm Ross and Lieutenant Victor A. Prather, Jr. of the US Navy rose 113,740 feet (34,668 m). The name of the balloon was USN Strato-Lab V. This flight was part of a program called Strato-Lab which used experimental high-altitude manned plastic balloons. Prather drowned and died after his Strato-Lab V flight. His pressure suit filled with water as he landed at sea after his record breaking flight.

Why not make a powered lifting body balloon? This could get you to 100,000 feet and then turn on your rockets. A balloon space craft.

Imagine an airframe as had Zepplin but as a lifting body shape. Now imagine you use polyimide cross-linked areogel (X-aerogel) spars and struts which would be strong but lightweight. You fill this with slightly pressurized hydrogen in Tedlar (Dupont) thin film H2 tanks. You could use any gas mixture for power that is nearly equal to the weight of air, as they did to power Zepplin, so you lose nor gain lift as you use fuel. To return to the ground you could burn the H2 as fuel. Very light and very large this would have very low wing loading on re-entry. Besides fuel who says space ships have to be heavy?

[Edited by klreed on 10/26/05 at 14:39]

Lifting Space Shuttle seems a little optimistic
Net lift per liter of helium at STP = 1.03 gr/l
100L would lift 103 grams. It takes about 22 billion liters of He to lift 50,000.

>Lifting Space Shuttle
>Lifting Space Shuttle seems a little optimistic
>Net lift per liter of helium at STP = 1.03 gr/l
>100L would lift 103 grams. It takes about 22 billion >liters of He to lift 50,000

I think we roughly agree; my values for lift are in Liquid Helium. I then converted at 22.4L/mole for volume at STP.

(If I skipped some steps, I apologize)

So I concluded that 3,923,529.41 cubic Feet of Helium may achieve NEUTRAL buoyancy in air on the ground at sea level.

As altitude is increased lift efficiency decreases as the amount of air pushing per unit volume of balloon drops.

I also did not take into account the mass of the balloon(s) or substructures.

I only forwarded those figures to demonstrate the futility of the attempt. Please note I also left information about the creation of He and the incredible difficulty and expense of attaining this substance in large quantities.

I in no way meant to suggest that this was a feasible form of propulsion for the space shuttle orbiter.

Erik