There are several (commercial) organisations looking into alternative means to launch space-bound rockets. One commonly proposed method is to use a large airplane as the launch platform. This method should, theoretically, reduce the cost of sending rockets into space.
Weather balloons can reach an altitude of 20 KM, or more. Could a balloon be used as a launch platform for space-bound rockets? I imagine skipping the first 20km of flight could significantly defray the cost of a launch.
In order to stay within the scope of this question, I will reference one idea that I believe fits the criteria, although that might be disputable.
I'll call the idea balloon-tether LAS, and it was published in a journal paper in 2012. The reason this idea is notable is that it started from a study of previously proposed LAS (Launch Assistance Systems), and formalized the requirements for a realistic system. Because of this, I would say it's one of the "most possible" proposals.
Description
High altitude balloons would suspend large pulleys that are basically pulled by trains. The system would be at a remote location and high altitude. The value of the LAS itself is that it:
From the release point on, the rocket fires and attains orbit for a payload of around 7 kg. This all sounds a little trite. After all, it only accelerates the rocket to a fraction of orbital velocity, to an altitude only a fraction of LEO altitude, the payload is paltry, and the launch rate is only once per day. But this is rocket science, by the rocket equation, these reductions make a bigger difference than you would think.
Here's a picture, with the pink being the balloons, the blue is the rocket, and brown is the tether.
Feasibility
Clearly you can launch something to orbit from balloons, but if there's no economic case for doing it, it won't ever happen. The balloon-tether LAS shows mastery of a couple of the issues that will come with the territory. Mainly, there is a problem that balloons are very limited in their lifting capacity. For more lift you need a larger balloon, and you quickly start to push the limit of what's possible. That puts a lot of downward pressure on the payload sizes.
Because of that size constraint, it's unlikely that any balloon system could compete with heavy lifting capacity or for manned flights. Even for micro-satellites, you can't justify the production chain cost because the launch frequency demand isn't high enough. That's why the balloon-tether LAS proposes a propellant depot model.
There are still some dubious parts to this proposal. There are a couple of fields where exploratory engineering has been proposed using high-altitude tethered balloons. Notably, solar energy, wind energy, and communication balloons. There have been some historical precedents for tethered balloons flying at around 3 km. Military technology bumps up on 7 km or so. To get to the desirable weatherless regions you'll have to go much further, and we're also talking about using really large balloons. There's still the option of not tethering the balloon, and just flying it up and launching a rocket. But where's the re-usability in that? That makes it a difficult equation to make a competitive launch system, although, that depends on the technology status for high altitude tethered systems.
There are good reasons why balloons have not been used for launch systems.
Balloons are inherently fragile. You have to have very thin, very light materials to make an effective high altitude balloon system. Baumgartener launched in a ballon that was 550 feet (168 metre) tall at launch, with 30 million cubic feet (850,000 m³) of helium at STP, to carry about 3150 pounds (1430 kg) of payload. The balloon itself could be easily punctured by a person intent on pushing a finger through it.
For comparison, the Falcon 9 launch mass is about 735,000 pounds (333,000 kg) - about 233 times the weight, before accounting for it's up to 14,000 pound (6350 kg) payload capacity. Plus, since the balloons are so fragile, one would need to use at least three and a gondola system that keeps them well separated, and so one is looking at about 7.2 billion (7.2e9) cubic feet (204 million m³) of lift helium to save on about 10% of launch fuel.
Helium isn't cheap. At 84 dollars per 1000 cubic feet (\$ 2.97/m³), that's \$6.048e8 (just over half a billion dollars) just in helium. The cost savings is not present for large launchers.
Hydrogen, a better lift gas, can be manufactured, but is still going to be about 4 billion cubic feet (113 million m³). But, if it catches fire, it will be a major flame issue. This will then drop any gondola and structure.
Keep in mind that a rocket launch produces up to a half-kilometer long plume of highly energetic gasses. Even tho' combustion has ended, those gasses may still be hot enough to damage the fragile balloon envelope. If that envelope is ignited, the balloon suffers a sudden (and probably catastrophic) loss of lift; if it's filled with hydrogen, it is almost guaranteed to suffer a catastrophic loss of lift.
A Balloon light enough to launch a significant payload will experience a sudden and massive lift as the rocket clears it. Provided that the envelope isn't compromised, loss of 95% of the mass will result in sudden and rapid ascent; not as fast as the rocket, but fast enough that recovery will be an issue. The lack of trajectory control also means having to carefully monitor airflow aloft. In order to recover, either the balloon must be able to compress the envelope, vent the envelope, or detach from the envelope; any of these options adds mass, and two of them render the lift gas a loss. Given the low-thicknesses needed to get efficient lift, compression is unlikely. Therefore most of the lift gas will be unrecoverable.
In the long run, it's simply too expensive and risky to use balloons to overcome the initial liftoff.
http://www.redbullstratos.com/technology/high-altitude-balloon/
http://en.wikipedia.org/wiki/Falcon_9
http://www.weldingandgasestoday.org/index.php/2012/04/a-look-at-rising-helium-prices/
Yes. However the largest high-altitude balloons in operation can only lift 8,000 pounds (3600 kg). Plot from NASA's Columbia Scientific Balloon Facility:
So it would be a pretty small rocket. For comparison, the airplane-launched Pegasus XL weighs about 50,000 pounds (23000 kg).
You probably could, but it wouldn't help very much.
The reason it's hard to get to orbit isn't that space is high up.
It's hard to get to orbit because you have to go so fast.
from XKCD What If? #58
Yes, some people are trying to do it:
There are advantages to this solution, such as less drag during ascent (which is especially important for small launchers due to the square/cube law), and a better Isp due to lower pressure at launch. You might also reduce payload fairing mass. However, the mass of the launcher is severely constrained and you have much less control over your launch procedure. Aborting and getting the launcher and payload back will be very hard.
It has never been attempted, but there have been a few people to consider it. There actually was an extensive section on balloon launches in the Ansari X-Prize competition a decade ago. The most notable rocket to be designed was the da Vinci Project
While this could work for suborbital, it is rather unlikely to work well for an orbital flight. The speed is the key factor for an orbital flight, and you get more from a plane. Plus planes are more flexible in general than a balloon. Overall, they are just easier to work with.
Let me give you a little of calculations:
20 km is only a 5 percents of IIS's Perigee 412 km.
The main resistance is not air, the main resistance is gravitation.
Even on IIS gravity exerts tremendous force, orbital period is 92.87 minutes across the Earth. By 1.5 hours!!! The same force attract IIS to the Earth. This two forces, to down and to forward, are equal. Let propose, i'm going from one of the Earth's point, and after 1.5 hours, i'm crossing the Earth and coming back. It is a mad speed.
To fly rocket must go by diagonal to get orbit, rockets lurches sideways after start.
By 20km may be saved only friction of air, because it is Troposphere (80% of the atmosphere's mass), but the speed of the rocket not so big to feel the air friction.
I'm risky to propose that air friction vs gravity force correlate like 1 vs 100 in this case.
20km(5 percents), cheaply overcome by fuel than keep spaceport on the dirigible.
From the other side, if there will be discovered newest fuel or method to get speed, this spaceport would appear to save from air friction.
Today - it is unnecessary.
And look at this picture:
The ARCA team competing in the Google Lunar Xprize has its mission based on precisely this idea: launching the Helen 2 rocket from a helium balloon raised at 14.000m. They made only one successful launch and the rocket reached 40.000 m altitude. I don't know if they'll participate in the race with the same idea, but I mentioned it as an example that this was tried before.
Yes it is possible to launch rockets from balloon as Reckon. But there are many disadvantages in launching from an balloon
balloons are very hard to steer hence precision in launch is almost impossible
the balloons required to take the rocket to high altitudes must have a very large surface
{
According to this reference
Helium has a lifting force of 1 gram per liter.
So you will require very large balloon to lift the rocket (You need 1000 liters of helium to lift just 1 KG of load)
}
it is almost impossible to launch a rocket over a balloon (launching straight out of earth)
For orbiter its all about the velocity so the more the altitude you go the more acceleration you need to attain the required orbital velocity
launching from earth provides initial velocity but in air its simply not
But still launching from a balloon (If possible) can save your cost on fuel (but not for orbiter) . launch a rocket with a payload is impossible (since there are many technical difficulty )
Ballon talk has me thinking about the alternative to rockets that carbon nanotubes suggest may be available in the hopefully near future. The space elevator.
From a practical standpoint I have thought there is no way they will be able to directly launch a 66,000 mile tow cable into orbit, but assuming we come up with a way to weave together long lengths of nanotubes into a cable or strap and we can fly out, and move a sizeable near earth asteroid to a geosynchronous earth orbit, without precipitating a dinosaurs having a bad day kind of celestial collision, it seems to me that the slow steady climb of a tethered balloon and a crew equipped with space suits will be involved in the final knitting together of the tether. I assume the cable will start being woven together from the asteroid geosynchonously stationed somewhere over Jarvis, Baker, or Howland Islands along the equator in the middle of the Pacific.
I picked those because they are US territories and uninhabited and would seem to make pretty good potential space ports. If private enterprise were to build it, I assume they would want their airspace protected by the world's strongest military to avoid calamities and repairs. Hence those islands.
The question is would the tether being lowered into the atmosphere burn up as gravity tugged it towards the ground?
I also assume a balloon would be needed because a rocket would be moving to fast to work on capturing the descending tether and you would need a relatively stable platform for the crew to work on knitting the final pieces together in a similar way to the joining of the intercontinental railroad in Utah.
It may be possible, but won't help much if you want to reach an orbit. This is easily seen considering the energy budget. The specific orbital energy for a satellite orbiting Earth at mean altidude (orbital semimajor axis minus Earth radius to be precise) $H$ above Earth's surface is $$ E_{sat} = -\frac{GM}{2(R+H)} \approx -\frac{GM}{2R} + \frac{gH}{2} $$ with $M$ and $R$ the Earth mass and radius, respectively, and $g=GM/R^2$ as usual. The specific energy reached by a ballon at altitude $h$ is $$ E_{bal} = -\frac{GM}{R+h} \approx -\frac{GM}{R} + gh $$ (ignoring the small effect from Earth's rotation, i.e. assuming launch at a pole). Thus, when launching a rocket from the altitude $h$, it must still provide the difference $$ \Delta E =E_{sat}-E_{bal} \approx \frac{GM}{2R} + g(H/2-h). $$ Thus, the main contribution $GM/2R$ is not helped by increasing $h$ from $h=0$ (launch at zero altitude).
