How one is going to get those balloons and helium down afterwards? By sending a bigger plane to weight them down? They apparently have to start it all over again in the next time.
And if those balloons are left up, wouldn’t they burst in the end. Where do they land and what happens then. Could it harm air traffic? If they land on a boat?
I see so much possibilities to extra expenses…
Hundreds of high-altitude helium balloons go up, burst, and come back down a day. No reported incidents of any kind.
Space-launch balloons would be larger but much less frequent than 1600 launches a day.
Perhaps geosynchronous wasn’t the word, but there is an orbit for every speed less than about 15,000 mph, so if you go up high enough eventually you’ll be in orbit where your linear speed matches orbital speed for that elevation. I don’t know how high you’d have to go for that to be 1000mph, but it’s probably well above the atmosphere.
EDIT: According to Wikipedia, you’d have to be further out than the Moon.
That’s because the crews aboard ships the balloons fall on causing a catastrophic disasters are never heard from again.
And let us all not forget the horrors of Balloon Boy.
In addition, the size and complexity of a balloon platform would increase in (roughly) cubic proportion to the weight of the launch vehicle (and therefore the payload). A vehicle the size (and thus, with the payload) of an OSC Pegasus is close to the limit of what one could use for orbital launch with existing commercial aircraft.
The real advantage of air-launched vehicles such as Pegasus or Quick Reach isn’t that they improve performance or allow for a greater payload-to-vehicle mass, but that they allow you to launch at a wide range of azimiuths over broad ocean area, thereby simplifying range hazard analysis and abatement. From [THREAD=“612359”]this[/THREAD] thread:
*Orbital Sciences does this with their commercial Pegasus family of launch vehicles, which are launched from beneath an L-1011. The Pegasus air launch vehicle can be compared directly with a ground launch vehicle, as the OSC Taurus is a Pegasus stack on top of the 92 inch Castor 120 “Stage 0”. For instance, the Taurus 3210 launching from Kwajalein Atoll on the Reagan Test Site can achieve a 200 nmi circular orbit at an 11° inclination with a >1200 kg payload (and larger fairing), while the air launched Pegasus XL launched from RTS can only deliver a payload of about 430 kg to the same orbit. Part of the difference is the level of thrust available from the Castor 120, but the efficiencies gained by air launch from a relatively slow moving aircraft are just not that great. The real advantages are the ability to locate your point of launch to the most efficient azimuth (within the constraints of the range and ground hazards) and increased launch availability (you don’t have to worry about the impact of ground winds and weather conditions on launch constraints, as well as not having to cope with things like ground facility conflicts, environmental impacts (every government-owned space launch range in the continental United States is located in or near a nature preserve or controlled habitat) or protesters.*Air launch also allows you to operate without having to acquire a ground launch facility, which is becoming extremely costly (as SpaceX, launching from commercially leased government facilities at Quaj, the Cape, and Vandenberg, is discovering). Many of the recent crop of space launch hopefuls are actually developing their own complete private launch facilities, but launching from an aircraft reduces (but does not eliminate) the complexity of dealing with appropriate range organization(s). In theory, this should be cheaper (less documentation and bureaucracy); in reality, it requires having enough launches in order to justify maintaining an aircraft specially modified for rocket launches (like OSC’s L-1011 Stargazer) or maintaining a qualified extraction/launch system from a government cargo aircraft (like the C-17). This is done for a number of sounding rocket/target programs, but strictly to achieve the desired trajectory parameters, not to make the vehicle smaller or cheaper than comparable ground launched vehicles.
Launch sites at high altitudes have been proposed for a number of missions to reduce aerodynamic drag and exposure to high wind shear; however, there are few sites that are really suitable (e.g. don’t have populated regions downrange) and none above 10 kft that have sufficient logistics to transport stages, propellant, equipment and personnel, so the cost of developing such sites is much greater than the savings would justify. And, as pointed out earlier in the thread, the vehicle still has to achieve sufficient tangential velocity to achieve and maintain orbit; a few kilometers of height does virtually nothing to reduce that requirement.
Many of the same benefits (to azimuth and reduction of range hazards) can be had by launching from a sea-based platform (as the Boeing-led SeaLaunch) or actually launching a rocket floating in the ocean (Bob Truax’s Sea Bee/See Dragon concept). This environment is far from trivial as well (as anyone familiar with ocean engineering can attest) but does have the benefit that a self-supporting platform or rocket can be made arbitrarily large without the constraint of an aircraft capable of lifting it. The Sea Dragon first stage was actually large enough to contain multiple Saturn V rockets within its envelope, and yet was intended to be built to shipbuilding tolerances and materials that are far less complex than modern ground-launched space launch vehicles like the Atlas V and Delta IV.
Stranger
Hot Air balloons use no helium.
Hot air balloons have much less lift and altitude capability. The altitude record for hot-air balloons is 6.14 km, a far cry from the 39km record for manned helium balloons (and 53km record for unmanned).
OK, then, use hydrogen instead.
Forget all those gases. What we need are rigid nanotube vacuum balloons.
I’m joking… I think. Is there a theoretical material that could be formed into some kind of lattice or honeycomb strong enough to be balloon-sized and be completely devoid of gases without imploding? And could you do it with an overall weight less than that of a current helium balloon, counting the weight of the helium?
Extremely doubtful.
Structures under tension are self-stabilizing: any distortion of the material from the axis of tension tends to result in forces that pull the material back in line with those tensile forces. Example, you take an unopened beer/soda can full of pressurized liquid, poke the side of it, and when you remove your finger the displaced can material is pushed/pulled back to its original position.
Structures under compression have conditional stability. The classic engineering example is a column under compressive load: the required cross-sectional area needs to be much larger than one would expect just based on a simple analysis of compressive stress; this is to prevent the column from bowing out sideways to such an extent that the compressive load tends to bow it out even further, resulting in catastrophic failure. For an easy example, the next time you finish a can of beer or soda, do this:
- place empty can right side up on flat ground.
- carefully stand with one foot on top of the can.
- reach down and tap one side of the can with your finger.
For step 3, you’ll need to retract your finger quickly, because the can will suddenly collapse under your weight.
An analogous situation exists for vacuum vessels. For very large vessels, the wall thickness needs to be very large in order to prevent that sort of unstable failure. Railroad tanker cars are cylindrical, which is a nice stable shape, and they are made of 1/2"-3/4" thick steel - but even that’s not enough to prevent catastrophic buckling failure when a strong vacuum is applied, as this video shows.
A balloon with any significant lifting capacity would need to be far, far larger thank a railroad tanker car; look at the Red Bull Stratos balloon, and see how large it is in comparison. That means the walls would also have to be much, much thicker than those of a railroad tanker car in order to resist buckling failure. Even your proposed carbon nanotube material would have to have substantial thickness to resist buckling failure; where bending/buckling loads are important, the thickness of the structure (or at least its walls) matters. Far better to load the material in tension if possible, and then it only needs to be thick enough to carry those tensile loads. Look again to the Red Bull Stratos balloon, which was described (in terms of thickness) as being something like a giant dry cleaning clothes bag.
The buoyancy of a gas or vacuum is dependent on the difference in density between the gas/vacuum and that of the surrounding medium (in this case, air). Helium and hydrogen already have such low densities that there’s not enough of an increase in buoyancy in switching to a vacuum to offset the extra structural weight. Here:
Lifting capacities in sea-level air (air density, 1.2 kg/m[sup]3[/sup])
*Helium, density 0.1786 kg/m[sup]3[/sup] - lifting capacity = 1.2-0.1786 = 1.02 kg/m[sup]3[/sup]
*Hydrogen, density 0.08988 kg/m[sup]3[/sup] - lifting capacity = 1.2-0.08988 = 1.11 kg/[sup]3[/sup]
*vacuum, density 0 - lifting capacity - 1.2-0 = 1.2kg/[sup]3[/sup]
So switching to vacuum only increases your lifting capacity by about 8 percent. Meh.
You could, perhaps, make a “vacuum balloon” where the envelope itself was all in tension, but with rigid struts supporting it on the inside. In the extreme case, you could fill the entire interior with a foamy rigid material, like an evacuated aerogel. I don’t know if you can make an aerogel that would be lighter than helium if evacuated, though, or how easy it is to evacuate an aerogel.
[THREAD=459843]Can we make a floating metal ball?[/THREAD]
Unless someone is positing a beyond magical technology like Niven’s scrith, it just isn’t possible with structural materials. Now, there are of course ways that you can cause millions of tons of material to float, as evidenced nearly any time you look up in the sky (if it is not a cloudless day). But the material has to be distributed in vapor form, and clouds, of course, don’t form above the mesosphere. Floating a launch vehicle sufficient to lift a large payload to very high altitudes where drag losses are no longer an issue is impractical at best, and is far from the best way to maximize cost-efficiency.
Stranger