# Could it be possible to launch a rocket from a balloon?

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.

• Good question. My first thought is; while it might be possible; overcoming the logistical issues would cancel any benefits. Obviously you can not launch from the top of a balloon, and from that issue the logistical issues flow. – James Jenkins Aug 28 '13 at 10:05
• Well, you could use a donut shaped baloon right? The platform could be below the baloon and the rocket could be launched from a tube that passes through the baloon (a bit like a rocket launcher or torpedo tube). – Nallath Aug 28 '13 at 10:09
• You could launch from below, with the balloon filled with hydrogen, self-destructing as soon as the rocket's engines are ignited, or just tether to the rocket long enough that the balloon wouldn't get in the way and the rocket would have time and room to fly around it. More of a problem is the sheer economy of scale. You'd need enormous balloon to lift any considerable payload with sufficient amount of fuel to place it in the orbit. – SF. Aug 28 '13 at 11:52
• @Everyone: The balloon hydrogen is unpressurized, otherwise it would be heavier than air. Air pressure hydrogen is a very low energy density fuel. There's probably more energy involved in compressing it than could be recovered by burning it. – SF. Aug 28 '13 at 17:42
• Ok, which one of you is behind this? – user29 Aug 28 '13 at 22:19

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:

• Increases altitude of the rocket
• Gives the rocket some initial vertical speed (order of 1 km/s)

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.

• isn't it called a rockoons ? – Sujay sreedhar Jan 8 '14 at 10:08
• Am I understanding right that this is a proposal for a cable and pulley system hung from balloons that's going to accelerate the rocket to supersonic speeds? – Russell Borogove Jan 11 '17 at 21:09
• @RussellBorogove Yes for the most part. I don't know if it ever actually gave an upward speed of the mini-rocket at the point of detachment, so it would be premature to assume it's over Mach 1, or that such speeds would be practical. One thing I previously seemed to miss is that the rail tracks aren't actually to exert force, but only to adjust for slack in the tether, like that spring thing on the back of bicycle wheels that allow you to shift to different sized gears. – AlanSE Jan 12 '17 at 2:46
• You said "on the order of 1 km/s" and the paper appeared to say 0.45 km/s. – Russell Borogove Jan 12 '17 at 3:16

There are good reasons why balloons have not been used for launch systems.

1. Fragility of the balloons
2. The highly energetic nature of rocket launches
3. Limited control over balloon trajectory
4. Expense of Helium
5. Flammability of Hydrogen.

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.

• Baumgartner's balloon was not 30 MCF of He at STP. It was 30 MCF at altitude. On the ground the same amount of He was 0.18 MCF. So your dollar figure is high by about two orders of magnitude. More like \$3.5M in He. Though only if the ballon structure scales linearly, which it doesn't. Also I think your He cost per unit volume is about a factor of two low. – Mark Adler Oct 26 '14 at 3:48 • The helium cost was looked up on the day posted. – aramis Sep 18 '15 at 11:29 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. • Actually, that's not entirely true. Because of the rocket equation (you have to launch all of your fuel with you in a normal rocket,) launching from a higher altitude and/or with a significant initial velocity can considerably reduce the amount of fuel required. The space shuttle stack, for instance, burned through nearly half its mass in the first 90 seconds after launch, at which point it's still going quite slow compared to its eventual orbital velocity and it's not even 100,000 ft up yet, IIRC. – reirab Mar 26 '14 at 19:01 • After 90 seconds the space shuttle is traveling at more than 1 kilometer per second, more than one eighth of its orbital speed. – Matthew Piziak Mar 26 '14 at 20:12 • That is an old truth, but in this business everything is challenged. The enthusiasts at JPaerospace intend to have their airship accelerate by an ion engine during many hours or days in the thin air at high altitude. Until it reaches orbital speed. And they do more than photoshopping, they actually build stuff which are full of hot air :-) jpaerospace.com/atohandout.pdf – LocalFluff Sep 13 '14 at 7:56 • The role of the Falcon 9 booster is mostly to achieve altitude. When it's high enough, the upper stage will do the major burn to achieve orbital velocity. Is the Falcon 9 booster trivial? Certainly not. Getting the needed altitude isn't a minor obstacle. I wish people would stop using that XKCD cartoon. That said, balloon launch isn't practical. – HopDavid Jan 25 '17 at 17:02 • "After 90 seconds the space shuttle is traveling at more than 1 kilometer per second," Most of that 1 km/s is vertical. The vertical velocity component shrinks as the shuttle ascends. So that 1 km/s contributes very little to the 7.7 horizontal velocity the shuttle needs to accomplish. – HopDavid Feb 2 '17 at 6:44 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). • That's displacement by Helium gas, right? Would heated Hydrogen change this by much? Also, how much did LDSD test vehicle weigh? I realize it ultimately wasn't space-bound but it was a rocket of sorts and deployed from a high-altitude balloon. – TildalWave Sep 13 '14 at 6:13 • Hydrogen gas would not change the buoyancy by much.$29-4$vs.$29-2$, so maybe another 600 lbm. However the 8000 lbm limit is not from the buoyancy, but rather due to the structural load capacity of the balloon envelope. I tried to get them to give me a little more suspended weight, which in theory they could with a little more helium, but they would not budge due to the load limit of the balloon envelope. The final suspended mass was close to the 8000 lbm limit. That included the balloon train, gondola, and test vehicle. The test vehicle itself was about 6800 lbm. – Mark Adler Sep 13 '14 at 6:49 • I have no idea how you would heat hydrogen, or helium for that matter, and keep it hot up there. – Mark Adler Sep 13 '14 at 6:52 • Yeah that would be a challenge to say the least. Don't know, a rather farfetched idea would be beamed microwave, say high power MASERs at Hydrogen excitation frequency, but yeah ... Sci-Fi :) – TildalWave Sep 13 '14 at 6:57 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. Yes, some people are trying to do it: http://www.bloostar.com/ 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. • This answer should be at least 20km higher than the other's, which seem to me mostly uninformed. – Octopus Mar 31 '15 at 19:39 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. See: Coilgun, Space gun And look at this picture: • ** air friction vs gravity force correlate like 1 vs 100.** is there any proof or reference for this ? – Hash Aug 28 '13 at 15:27 • No, it is just by guess – innocent-world Aug 28 '13 at 15:35 • The 1 vs 100 could be close (although maybe 1 to 20 is better) if you refer to the delta v from air resistance compared to the total delta v to reach orbit. But that's not gravity drag, that's the impulse needed to get to orbital speed. You answer can be taken to be compatible with this, but it's not very explicit. – AlanSE Aug 28 '13 at 15:57 • The photo shows condensation forming in low-pressure areas: the pressure has dropped below the dew point. The plane does not have to pass the speed of sound for this to happen, depending on the weather this phenomenon is visible at lower speeds. – Hobbes Oct 26 '14 at 16:03 • "This two forces, to down and to forward, are equal." Actually, for ISS, they are decidedly not equal all things considered. That's why they have to boost the orbit regularly. Left to its fate, the ISS would fairly quickly re-enter the upper atmosphere due to atmospheric drag costing forward velocity. (Wikipedia gives the orbital decay at 2 km/month.) Given that the station weighs 450,000 kg, I recommend wearing a helmet. – user Oct 29 '14 at 19:33 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 ) 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. • those links are unfortunately dead – nu everest Feb 5 '16 at 14:22 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. • Jeremy welcome to Space Exploration! While this is interesting it doesn't really answer the question as asked and displayed at the top of the page. The gist of it is Could a balloon be used as a launch platform for space-bound rockets? so if you could please edit your answer to also address those concerns, that would be great. Note that we're not a discussion forum but a Q&A. More is explained in our Help center. Thanks! – TildalWave Sep 13 '14 at 6:04 • this is off topic – nu everest Feb 5 '16 at 14:39 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).

• You're not taking into account the tremendous quantities of fuel that are carried and burned in the first 20km (ie. more than half of it's initial mass). What if you could climb those first 20km without that need? – Octopus Mar 31 '15 at 19:31
• That fuel isn't burned just to gain altitude, it's burned to get up to speed. At 20 km, you're looking at 500-1000 m/s. – Hobbes Jan 11 '17 at 16:29