You are not logged in.
Lets say for example we start by launching a satellite orbit, the satellite contains liquid hydrogen as it boils of, 5000 balloons are inflated with the hydrogen gas boil off, the balloons are very low pressure, about 1 millibar of pressure in hydrogen gas, each balloon if 100 meters in radius. The membrane of each balloon is 1 micrometer thick.
The second thing we do is launch a suborbital craft, say for instance SpaceshipTwo, a capsule is ejected from the spaceship, right in the path of the orbiting balloons. The balloons hit the capsule with astronauts inside. The capsule undergoes 6-g of acceleration as it passes through each balloon for about 2 minute until it reached 8 km/sec. The balloons are spaced far enough apart so that one rupturing doesn't affect the next one until the capsule hit it, the capsule then passes through the hydrogen gas within each balloon before it gets a chance to escape into space. Since the hydrogen gas is moving at orbital velocity, this accelerates the capsule towards orbital velocity. Its density is 0. 08988 grams per cubic centimeter, therefore .088988 kg per cubic meter, at 1 milibar its .000088988 kg per cubic meter volume of a sphere is 4/3*pi*r^3 with r = 50 meters we have 523,599 cubic meters for a mass of each balloon being 47 kg, 5000 of such balloons would weigh 232.97013906 tons. This is about the payload of 2 Saturn V rockets to orbit, perhaps an extraterrestrial source for this gas could be found such as an asteroid for instance. a carbonaceous Chrondite asteroid for example that contains hydrogen compounds, a 1 micrometer thin polymer could be manufactured to fill for the balloons, and a SpaceshipTwo launches a capsule into space for collision with the balloons to accelerate it to orbital velocity in about 2 minutes at 6-g.
Offline
Just doing the tensile calculations, a balloon that is 100 m in radius containing 1 mb (100 Pa) of pressure, and has a skin 1 micrometer thick will have a stress in both the x and y directions of:
sigma=Pr/2t
Or 5 GPa. Using the von mises stress (to combine the two) the polymer would need to have a tensile strength of 7.1 GPa. Pressure vessels usually have a margin of at least 5, but let's say you use 2; You need a material with a tensile strength of 14.2 GPa, which is firmly out of the range of any known polymer.
If you use an anisotropic composite with T1000 fibers (the von mises stress calculation above doesn't apply, you have to do the stress in each direction instead), and assume the composite is 50% sealant/binder, the required thickness would be 10 micrometers. For weaker materials, proportionally less, of course.
-Josh
Offline
Ok so it is 10 micrometers, so what would happen if something like an Apollo capsule were to crash into such a balloon at 8 km per second. Would it survive the impact and go through the balloon being slowed down relative to the balloon by the gas within, or would the capsule disintegrate by the energy of impact. Lets say the capsule is 3 meters wide and hits the balloon with its circular heat shield. So kinetic energy becomes heat energy as it impacts with the balloon membrane and vaporizes it, it then passes through the hydrogen gas as it rushes out of the balloon and then hits the other side of the balloon before passing back into space, then it hits another balloon and repeats the process until it passes through 5000 balloons covering a distance of 500 km. The horizontal velocity is 0 relative to the Earth's surface before it hits the first balloon and 8 km after it passes through the last balloon. I think the internal pressure of each balloon may need to be adjusted to make this happen, the later balloons could have thicker membranes and higher pressures inside as the capsule will be passing through those more slowly. I think the balloons may have to be guided by tiny rockets, say three to a balloon, the rockets home in on a radio signal from the capsule to make sure the balloons hit it, this presumes we have a cheap supply of hydrogen gas originating from space. It might not make sense to lift this gas from the ground, because as I said it would weigh over 200 tons!
Offline
With such a thin skin I would expect the balloons to burst upon impact. You might have trouble with the later balloons in terms of the craft not moving quickly enough to pop them.
The effect of each balloon will decrease aymptomatically towards zero, so some kind of rocket burn will be necessary to actually achieve orbit.
-Josh
Offline
Yes the balloons will burst about impact, but it will take some time for the gas to disperse into space and get out of the way of the space craft which after all will be moving 8 km/s relative to it, that means it moves through 100 meters of balloon in 1/80th of a second!
Offline
Well, I'm just talking about the decreasing relative speeds. After all, as the payload speeds up its relative velocity goes down.
Using the equation:
F_d=Cd*rho*A*V^2
We see that drag force is proportional to speed; but impulse, P=Ft=Fd/V, is inversely proportional to speed; Therefore I would expect that the impulse transfered by each balloon would be inversely proportional to the speed of the payload. I don't know what that point is, though, that's more up to the designer/engineer/businesspeople/you.
-Josh
Offline
Well there are two Solutions the Balloons could be in the lower part of their ellipitical orbit, they get destroyed each time they are used, in this case it could bring the capsule up to orbital velocity, otherwise small rockets will be required. Probably the balloons will need rockets to guide them as well, just make sure the capsules don't hit the rockets!
Actually it might make sense to put the balloons in elliptical orbit, if extraterrestrial resources are used. Here's what you would do.
1) Find a Near Earth Asteroid
2) Alter the asteroid's course to put it on a near flyby of the Moon.
3) The gravitational interaction with the Moon's gravity causes the asteroid to settle into an elliptical orbit around the Earth.
4) Mine the asteroid, process its material to make hydrogen gas from frozen water or hydrates, and the carbon is processed into balloon polymer.
5) Manufacture the balloons in space and inflate them and put them in highly elliptical orbits who's low points are just above the atmosphere. These orbits will rapidly decay, but before they do, you launch your suborbital space capsule
6) The capsule collides with the balloons and are boosted to a low Earth circular orbit.
Last edited by Tom Kalbfus (2013-12-20 07:22:24)
Offline
Why not just have a suborbital craft that's capable of 4km/s, rendezvous with an orbital craft that's slowed itself down to meet it and then boost them back up to orbital velocity?
Even without aerobraking, if the suborbital craft can reach 5km/s, then the rendezvous craft needs a delta-V of 6km/s, so it can slow itself down, meet the craft, and then boost them both back to orbital velocity. In fact, the orbital one will need to be closer to 7km/s, accounting for the extra mass... perhaps if both craft are capable of 6.5km/s...
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
Online
Balloons are easier and simpler to make, they are just gas bags! An actual spaceship is a little more complicated.
Offline
On the other hand, the spaceship is reusable.
Funny thing about balloons made from Carbon fiber, by the way... they're not just gas bags. I'm sorry if I misled you about this, but making the balloon material is nontrivial, insofar as the material you're looking for probably doesn't exist yet.
-Josh
Offline
By the way, I'm only half serious on the spaceship idea - I think TSTO is much easier to achieve and with much less opportunity for failure. That said, staging at 3km/s, boosting up to 6km/s, and rendezvousing with a spaceship that will take it up to orbit *would* allow much more mass to be carried to orbit... total delta-Vs of each part wouldn't be much more than 4km/s, achievable even with storable propellents.
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
Online
On the other hand, the spaceship is reusable.
Funny thing about balloons made from Carbon fiber, by the way... they're not just gas bags. I'm sorry if I misled you about this, but making the balloon material is nontrivial, insofar as the material you're looking for probably doesn't exist yet.
So what balloons were 100 meters in diameter? Have any balloons that big ever been produced? I'll Google it:
http://www.wired.com/playbook/2012/10/r … s-balloon/
The World’s Wildest Skydive Requires the World’s Biggest Balloon
BY CHUCK SQUATRIGLIA10.02.123:30 PMThis balloon, which carried Felix Baumgartner to an altitude of 13 miles in March, is 128 feet tall. Big, yes, but nothing compared to the 334-foot-tall monster that will carry him to the edge of the stratosphere on Monday. Photo: Jörg Mitter/Red Bull Content Pool
Late Sunday night, 15 men will clear every last stick and stone from a runway in the New Mexico desert as 10 more men wearing cotton gloves and protective suits unfurl and inflate the world’s largest helium balloon.The job will take about eight hours, which seems like a long time until you realize the balloon weighs almost two tons and is taller than the Statue of Liberty. Simply filling it will take 45 minutes to an hour, which doesn’t seem long at all when you realize the balloon has a volume of 180,000 cubic feet.
This is no ordinary balloon. But then, this is no ordinary mission.
Crew members gather up the Red Bull Stratos balloon after Felix Baumgartner’s second test flight in July. The balloon that carried him to 97,145 feet in July was just one-quarter the size of the 55-story behemoth that will carry him to 120,000 feet on Monday. Photo: Red Bull Content Pool
MORE ON ‘FEARLESS’ FELIX:What We Can Learn from ‘Fearless’ Felix’s Supersonic Skydive
What Does One Wear on a 23-Mile Skydive
‘Fearless’ Felix Hopes to Break Record, Sound Barrier, In 23-Mile Skydive
The Physics of the Red Bull Stratos Jump
The balloon will carry “Fearless Felix” Baumgartner to the edge of the stratosphere for his record-setting skydive from 120,000 feet. At that altitude, the balloon will have a volume of 30 million cubic feet. Red Bull, his sponsor, calls it the largest balloon ever used for manned flight. Fitting, because everything about Red Bull Stratos is larger than life.Baumgartner hopes to break the unofficial record Joe Kittinger, a retired Air Force colonel from Florida, set in 1960 when he jumped from 102,800 feet during Project Excelsior. If he pulls it off, the 43-year-old Austrian adventurer also will claim records for the highest manned balloon flight and the longest free fall by a skydiver. As if all that weren’t cool enough, Baumgartner also wants to become the first person to exceed the speed of sound — about 700 mph at that altitude — in free fall.
Baumgartner, showing just how flimsy the balloon is. The polyethelene envelope is just 0.0008 inches thick. Photo: Jörg Mitter/Red Bull Content Pool
The former military parachutist has made two successful test jumps, from 13 miles and 18 miles up. During his test in July, Baumgartner’s descent from 18 miles took 10 minutes and 36 seconds, and he reached 536 mph during a freefall that lasted 3 minutes and 48 seconds. His capsule took a beating when it landed in the desert outside Roswell, New Mexico, but checked out during testing last week.After five years of preparation, all systems are go. The launch window opens Monday morning. Now everyone’s watching the weather.
The last report from team meteorologist Don Day has a cold front moving east and southeast through the area. Cold temperatures aren’t the problem — it’ll hit 70 below zero where Baumgartner’s headed. It’s the wind that has people worried. It must be blowing less than 2 mph at take-off because the balloon is made of whisper-thin plastic just 0.0008 inches thick. That’s 10 times thinner than the baggie holding your sandwich.
The balloon stands 55 stories tall and weighs 3,708 pounds out of the box. It was constructed from strips of polyethelene that would cover 40 acres if laid out over a field. The balloon will measure 334 feet tall and 424 feet in diameter when Baumgartner reaches peak altitude.
Monday’s launch is slated for dawn. About eight hours before, a crew will clear the runway as another crew, wearing gloves and protective suits to avoid tearing the envelope, carefully removes the balloon from its box and begins laying it out on a protective layer of Herculite.
An hour before launch, mission control will give crew chief Ed Coca the all clear to begin inflating the balloon. The job will take 45 minutes to an hour.
Then, as the sun breaks over the horizon, Baumgartner will begin his ascent.
"The balloon will measure 334 feet tall and 424 feet in diameter"
I think this qualifies as a balloon about 100 meters in diameter, doesn't it? I believe 424 feet is greater than 100 meters!
Last edited by Tom Kalbfus (2013-12-21 16:43:43)
Offline
There's a big difference between a zero pressure balloon and what you're proposing.
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
Online
Here's a question: Why is this better than the rotating tether skyhook we were talking about in the other thread?
By the way, the "Ask Zubrin" question submission thread is open, I know you wanted to ask something Tom, and the thread is here
-Josh
Offline
Tethers are a different sort of technology, it might be easier to make the balloons in space, that materials for space elevators and tethers. I think we need a lot of options for going into space besides the traditional ones of launching an expendable rocket from a launch pad. We don't really know which ones are going to pan out, so I', just throwing out some ideas.
Offline
Sure. And I suppose it's not a bad idea, not at all. Actually, it seems to be a very good idea for a way to leverage existing orbital infrastructure to make it cheaper to get things into orbit. It's also more failsafe than a skyhook, since it's not dependent on each individual balloon. On the other hand, it represents a significant orbital debris risk. I'd have to imagine that the orbital positioning of each would be rather difficult.
The idea of sending things down to send things up is a good one though. How can we leverage this to make it less failure prone and annoying?
-Josh
Offline