Why don't we go to space in one of these babies?

SpaceBull · 2005-09-27 19:21:18

Airships can take us 21 kilometers above ground, and even small ones can lift twice that of a commercial airliner. Why don't we use airships to get into space?

John Creighton · 2005-09-27 19:28:18

see:
http://www.newmars.com/forums/viewtopic.php?t=1851

GCNRevenger · 2005-09-27 20:14:36

You can't use a pure airship because:

-The fly because air supports them. Space has no air, so an airship can't fly there

-To stay in a stable orbit, you need speed. LOTS of speed. 18,000mph speed.

SpaceBull · 2005-09-28 04:13:34

I was actually thinking about the possibility of using an airship to lift a rocket above most the atmosphere, just like SpaceShipOne is using an airplane. An airship have two obvious advantages over an airplane:
1. It can go higher
2. It can lift a lot more
On the downside:
1. more expensive
2. slower

I believe the most efficient shape of such an airship is a sphere, because this is how you would get the most volume out of each square meter of surface area.

An spheric airship with a radius of 10 meter will have a volume of (4/3)pi*r³ = 4188 m³. The surface area will be 4*pi*r² = 1256 m². Volume / Area = 3.33. It will probably not be able to fly. But what happens if we make the radius 1 km? Volume/Area is now 333,33. This is significant because the weight of the materials in your ship will depend mostly on the surface area, not the volume. A huge spheric airship would be able to lift almost anything, and probably enough equipment to get far far out to space. Size clearly matters! (but I hope you understand that a 1 km radius was a theoretical example).

SpaceBull · 2005-09-28 04:32:42

I would like to expand on my example:

Weight of air per liter = 1.2 grams
Weight of helium per liter = 0.18 grams.
Net lift per liter = 1.03 grams
(assuming standard pressure and temperature)

1m³ = 1000 liter
Uplift per m³ = 1.03 kg

A sphere with radius of 1 km will have a volume of 4 188 790 200 m³. Total uplift from helium inside = 4 314 453 906 kg, which is 4.3 million metric tons.

GCNRevenger · 2005-09-28 07:21:02

The problem is all about energy and orbital mechanics...

http://en.wikipedia.org/wiki/Orbit#Understanding_orbits

Here is a good example of what orbital mechanics is, at its heart: that for an object to be "in orbit" it must be moving very, very fast roughly parallel to the surface of the Earth. Your space ship is the "cannon ball," which has to be going so fast that its path curves around the entire Earth without touching it (or the atmosphere). This speed is very high, aproximatly 18,000mph for a stable minimum altitude orbit.

Altitude, simply getting to a tall height above the Earth's surface, is actually very easy compared to reaching this superhigh speed. In fact, a rocket only burns about 5-10% of its fuel to reach a high enough altitude, where the other 90-95% is used to gain this 18,000mph.

A balloon launch would have essentially zero velocity parallel to Earth, and so launching a conventional rocket from a balloon only saves you small fraction of the fuel you need to reach orbit. This is just not worth the trouble of lifting the rocket to such a high altitude for orbital launch.

SpaceBull · 2005-09-28 07:44:42

I am not an expert within this field at all, but wouldn't the air resistance be almost nothing 20-25 kilometers above ground? If there is no air resistance then wouldn't accelerating a space ship to an almost infinity speed require very little energy? Here is a graph I found on air pressure:

GCNRevenger · 2005-09-28 08:03:36

No, air resistance is actually a very small portion (a few percent at most) of the total amount of energy needed to reach orbit. Very little of the rocket fuel in an orbital launch vehicle is used to defeat air resistance.

Rockets are well described by Newtonian mechanics, one of the most important equations is this one:

Kinetic Energy = (1/2) x Mass x (Velocity)^2

This equation is true in even a vacuum, and the rocket fuel is the source of kinetic energy. Notice that if you need to increase your velocity alot, then you need a MASSIVE amount of energy. Therefore, you likewise need a massive amount of rocket fuel, even if your rocket is launched in a perfect vacuum.

SpaceBull · 2005-09-28 09:00:34

Well, you are probably right, but I still want to play around with some numbers to be absolutely sure:

Let's start with your formula. To reach orbit you will need a speed of around 8 kilometers per second. For comparison, a bullet on earth has a speed of around 1.5 kilometers per second. Let's assume that our space ship weighs 20 tons.

Ek = (1/2)*20,000*(8000²)
Ek = 640,000,000,000 J

I found a conversion table, and this energy equals 17,779 Kilowatt-hours. A liter of gasoline have energy equal to 1,200 watt-hrs/liter, meaning that the energy you need to bring our space ship to a speed of 8 km per second is 14 815 liters of gasoline, or around 14 tons. This energy can for instance be used in an electromagnetic catapult on board the airship, although I bet the g-forces will not be pleasant unless you make this catapult very long.

Please let me know if there are any mistakes here.

ftlwright · 2005-09-28 13:15:54

The only reason I can think of for launching from a lighter-than-air airship would be to use a single stage rocket better match to the atmospheric pressure; even then I don't think this is very suitable for orbital space flight. Having an over expanded flow from the nozzle is one of the greatest losses inflicted upon a rocket.

I know the military is interested in using airships in combat zone for providing low-cost arena communications and logistics operations. DoD is having a hard time rationalizing positioning 100M dollar satellites over Afghanistan and Iraq when the adversary doesn't have the means to strike high altitude aircraft. I wouldn't be surprised to see the telecoms do something similar, especially after the destruction of Katrina/Rita. For suborbital tourism, I would much rather launch from a rocket strapped under a balloon rather than ride on Scaled Composites' DeathTrapOne *shutters*.

GCNRevenger · 2005-09-28 13:48:05

Well, you are probably right, but I still want to play around with some numbers to be absolutely sure:
Let's start with your formula. To reach orbit you will need a speed of around 8 kilometers per second. For comparison, a bullet on earth has a speed of around 1.5 kilometers per second. Let's assume that our space ship weighs 20 tons.
Ek = (1/2)*20,000*(8000²)
Ek = 640,000,000,000 J
I found a conversion table, and this energy equals 17,779 Kilowatt-hours. A liter of gasoline have energy equal to 1,200 watt-hrs/liter, meaning that the energy you need to bring our space ship to a speed of 8 km per second is 14 815 liters of gasoline, or around 14 tons. This energy can for instance be used in an electromagnetic catapult on board the airship, although I bet the g-forces will not be pleasant unless you make this catapult very long.
Please let me know if there are any mistakes here.

You forgot one item SpaceBull, the mass of the liquid oxygen needed to burn that gasoline.

The moral of the story though, launching from a balloon isn't going to reduce the total amount you have to accelerate to reach orbit much since it doesn't contribute to your initial velocity, so it doesn't save you much rocket fuel.

RobS · 2005-09-30 18:04:33

Don't forget that even if your little airship could have an electric catapult to hurl things to orbital velocity--which it couldn't--but if if could, the equal and opposite forces on the airship would push it backward at a pretty high speed as well, at a pretty high acceleration, and that would probably destroy the air ship.

-- RobS

Austin Stanley · 2005-09-30 23:00:37

I read a story about a similar concept, suspending a gigantic railgun in the upper atmosphere and using it to deliver cargo into orbit. Far-fetched I know, but presumably if you did build such a gigantic device it's own mass would probably be enough to dampen the majority of the recoil. All the air-friction from the massive ballons would also help out. To me the biggest conceptual problem (if you accept actually building something so large so high in the sky) would be keeping the gun stable for firing.

That and practical transportation of people, things, and (most importantly) power up to it as well.

SpaceBull · 2005-10-01 09:20:25

Don't worry too much about transportation up to such a structure, because this could easily be taken care of by smaller air ships - or maybe even an elevator. Having a cable from the ground up to the structure would also make it possible to power it with electricity from a terrestrial power plant.

Edit: Before people start objecting regarding the weight of such a cable: You don't have to use a single 30 kilometer cable at all, because it could easily be divided into 3 cables of 10 kilometers each suspended between air ships at different heights.

Martian Republic · 2005-10-01 15:33:17

Actually, there is someone trying to use a Balloon to get into space. He ran into two problems that he is currently working on to make that happen.
(':D')

The first problem is that you can't use the same balloon all the way into orbit, because it too heavy. You can't use the same balloon that your orbiting and bringing to the upper atmosphere down and land it on the surface, because the air pressure around it would crush it.

The second problem he has to deal with it to be able have low thrust, but continuous thrust for one week or more to attain orbit or leave orbit.

To solve his problems he wants to do these things.

Build a station that 100,000 feet up called the Dark Star as a transfer station between though to two balloons that he needs to make this two way trip possible.

To deal with his second problem, he want to use something like ion drive that has low thrust and not much mass for fuel to excellerate his over a weeks period of time to excellerate it until it reaches orbit and reverse that process for coming back down. He also won't need a heat shield either because it being done over a one week period of time.

At least he thinks it can be done and he is still working on this project too.

Larry,

SpaceNut · 2005-10-03 20:30:32

While the technology for use here on Earth is still yet to come about it may be mature enough for another location of use. NASA Study Recommends Airship For Exploring Titan

A recent study performed by Langley Research Center for NASA's science mission directorate recommends an airship as the best vehicle for the future exploration of Saturn's moon Titan.
The purpose of the study was to determine "what's the next logical thing to do" after Cassini, according to Henry Wright, a member of the study panel as well as chief engineer for Langley's proposed ARES Mars aircraft. The study team was asked to formulate a "flagship-class" mission that would launch after 2015. The team finished the study in June.

So what size would this ship need to be:

The highly autonomous, helium-filled airship would be 18 meters (59 feet) long and 3.5 meters (11.5 feet) in diameter, carrying a science payload of 26 kilograms (57 pounds). Its normal operating altitude would be one to five kilometers (.62 to 3.1 miles), although it would also have the capability to land periodically and take direct measurements of Titan's surface, Wright said. The study team picked a baseline mission duration of 90 days, the same as the original baseline for the Mars Exploration Rovers.

So what's stopping a mission of this type:

One potential obstacle to the mounting of such a mission is its estimated price tag of $2 billion to $2.5 billion. However, "there's a big mission pull," Wright said. "There are a lot of people who are very interested in an aerial exploration of Titan, so there are a lot of these outer planets road maps that show an aerial-type vehicle exploring Titan."

Yup the almighty Dollar seems to stop almost everything these days.

publiusr · 2005-10-07 09:29:53

JP Aerospace thinks they can get a very lightweight airship up to speed (ATO)

I don't think so.

pete · 2005-10-07 11:42:19

Well I think GNCRevenger is generally right on this issue. This is why airlaunch is a rather rare launch method. But think about the American Pegasus. The Russian MAKS shuttle was supposed to be airlaunched from a Ukrainian AN 225 and think about the Vinci Project (X-Prize participant).

For smaller rockets airlaunch can make sense because smaller rockets suffer most from air drag. Apart from drag and kinetic energy there are a host of lesser advantages like acoustic insulation etc... that work better in 40 km altitude.

But when rockets get bigger fuel increases by the power of 3 (with increasing volume) whereas drag only increases with the power of two. For big rockets drag is not an important factor.

Peter

publiusr · 2005-10-13 10:31:31

The biggest thing I run into is the growing prejudice against rockets.

"Rockets are primative, etc."
"Aren't we past that..."

And the result is a lot of NASA bashing from crack-pots

Stay with what works, people.

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Re: Why don't we go to space in one of these babies?

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