More Frequently Asked Questions:

Q: How high will it go?

A: The virtual beanstalk platform's average altitude will be between 10 kilometers and 20 kilometers high, depending on its latitude. This is in the lower stratosphere, just a few kilometers over the tropopause.

Q: How high can it go?

A: The platform's lift cells are sized to vent and level out at 25.2 kilometers high, just 200 meters higher than the tether is long. It will never see this altitude, however.

Q: How much payload will it carry?

A: The theoretical maximum limit for payload for a single tether design is 80 tons before the increasing bulk of the platform and tether begin to eat into the virtual beanstalk's performance. More advanced designs could exceed this limit by incorporating multiple tethers and platforms. However, I'm suggesting that we start relatively small, expecting a payload of less than 10 tons for our first prototype.

Q: How long will it stay aloft?

A: With proper maintenance, we can expect the platform to remain on station indefinitely. Throughout the year, and especially during the winter, there will be periods as long as thirty days when atmospheric conditions are too fierce to risk bringing the platform back down through them. So, the rule of thumb is, if a virtual beanstalk can't stay airborne for at least sixty days, don't send it up! Fortunately, we can achieve mission durations as long as a year or more. More advanced designs, employing guy lines and other tricks, could be permanent in the same way as any other building is. During that time, we can shuttle payloads up and down the tether any time we want, keep them on station, and recover them all with 100% success. Nothing comes down until we want it to, and then it comes down exactly where we want it.

Q: How can you keep the platform up for such a long time when other balloons can only stay aloft for a few days?

A: Most weather balloons reach a stable altitude by expanding as big as they can get during the ascent, then venting off their extra gas to get rid of the extra lift. Afterward, they no longer have that extra lift when they need it. A virtual beanstalk, on the other hand, reaches a stable altitude because it's held there at the end of a tether. It retains all that extra lift, and doesn't have to be fully expanded at maximum altitude any more than it has to be fully expanded on the ground. So it can have enough extra gas to offset months of normal losses. In addition, we can send people and supplies up and down the tether for regular maintenance, so not even normal wear limits us as strictly as it limits the flight of a free balloon.

Q: What kinds of loads will be placed on the tether?

A: The wind on the platform alone can create peak loads of up to 30 tons of tension in the tether during ascent. On top of that, we need to maintain another ton of tension in the line to keep it at the proper angle and allow the elevator to ascend. Average tension in the tether will be just under 10 tons. That's a lot of load, and it takes a good rope. The tether load can be changed by paying out or reeling in the tether at the ground station, which adds or subtracts tether weight.

Q: Will the wind blow it down?

A: It always does. With no wind, the platform's balloons would pull it straight up to the top of its tether. However, the average wind forces will blow it over so that the platform rides between 18 and 23 kilometers, depending on the weather. Fortunately, there will always be sufficient lift that the tether will never drag the ground, even in gale force winds.

Q: How will you deal with the twenty-fold expansion of lift gas during the ascent?

A: That's complicated. The simple answer is: Properly folded and with a little reinforcement from the platform keel, the platform lift cells can take care of themselves with a minimum of intervention. A better answer can be found here.

Q: What happens if the tether breaks?

A: All sorts of hair raising adventures could occur if the tether breaks. This is the last thing we want to happen, but we will need to be prepared. The events following a tether break are primarily determined by what point along its length the rope fails at. The two most likely points for the rope to break are the tether mounts at the platform and ground station, since those are the places the tether gets the most wear. Each has its own set of potential problems which contingency plans must account for. Any break will involve some recoil, but it will quickly damp out after the initial shock because the rope is so light and inelastic. The rope is quite lightweight and won't have the momentum to do much damage from the fall alone -- if it hit you, you'd live. If you're interested in the worst case scenario, that's a break in the exact middle of the tether, because then both the platform and the ground station would experience trouble at the same time.

Q: What about airplanes?

A: The future position of the tether cannot be predicted more than a few minutes in advance. The only safe solution for air traffic is to stay out, so we will have to establish a zone of controlled airspace around the virtual beanstalk, within which air traffic may not enter without special permission. The zone of operation for the virtual beanstalk is a cylindrical volume approximately twelve miles in diameter and extending to an altitude of approximately fifteen miles. It's big, but we can get it.

Q: Where would you put a virtual beanstalk?

A: The requirement for controlled airspace is problematic, but not insurmountable. The horizon at the platform is 500 kilometers away. Having to search 100 kilometers for a suitable site would still leave the virtual beanstalk well within this area. We can even deploy one at sea if we have a moored platform or a big enough ship for our "ground station". Climate is a bigger limitation. Midlevel winds vary with latitude and location. There are only certain times of the year when a virtual beanstalk could be deployed or retrieved in areas with strong jet streams. Tropical islands are among the best sites because they can be used year-round and lack violent upper level winds. The polar regions are also potentially useful because their tropopause begins as low as 8 kilometers high, allowing the platform to carry a much greater payload by not lifting all the extra rope it would require at the tropics.

Q: What happens if the tether is struck by lightning?

A: The tether is very non-conductive, but it extends through several layers of atmosphere and is porous enough to retain liquid water. Thus, though rare even in a storm, lightning strikes are an eventuality. The tether is strong enough and non-conductive enough that we expect it to survive a single strike, but every strike degrades it and eventually we would have to replace the tether if we deployed it some place it kept getting zapped.

Q: How can you replace the tether?

A: With my prototype design, we can reel it back down and replace it once we have the platform back on the ground. The winch required to do this will need special features, but the only components not commercially available are a fixed tensioner rated for 20 tons -- basically a pair of come-along winches on shock absorbers placed ahead of the main ground station winch to maintain line tension and allow the main winch to work without binding -- and a custom-made drum large enough to hold 25 kilometers of rope. Even these two items are little different from common industrial products. Only slight modifications to off-the shelf equipment will be required to suit our needs.

More advanced designs can use more ambitious techniques, not requiring them to ever descend at all.

Q: What if something fell off of the platform?

A: Forget broken tethers, lightning strikes and airplane collisions. They may be morbidly fascinating, but dropped tools are the single greatest safety issue posed by a virtual beanstalk. Anything dropped would obviously no longer be available to the crew, but that's the least of our worries. The terminal velocity of a ratchet wrench is hundreds of kilometers per hour. There is no question that it would do damage if it hit something, and it could fall like a bomb anywhere within the beanstalk's airspace. The platform is going to rock like the deck of ship at sea, and just as sailors must take precautions to avoid losing items overboard, so must we. We can't make tools that float, but we can attach streamers designed to break open and slow their descent as they approached the speed of sound. Larger items will have to be lashed to the deck. Everything that moves, whether it's equipment or crew, will need a safety line or some other measure to keep it from accidentally falling overboard. With proper precaution, we can completely avoid inadvertently bombing the populace below, but we can't afford to be lax about it.

Q: What would happen to someone who fell off of the platform?

A: No one can go outside on the platform without a pressure suit. That's not some special safety precaution; it's just the way things are. At 20 kilometers high, the air is so thin that you could suffocate breathing pure oxygen. So, we include a reserve parachute on every pressure suit. Mind you, this alone is not sufficient for safety. Anyone expressly intending to sky-dive from the platform would have to be much better equipped. However, if you didn't panic, the chute opened, and God smiled upon you, a single parachute would be sufficient for you to survive a fall from the platform without injury.

It would take between ten and thirty minutes for a successful skydiver to complete their descent from the platform, depending on their descent profile, or about three minutes for an unsuccessful one.

Q: Can you use balloons partway up the tether to relieve some of the load?

A: No. It sounds like a good idea when you first hear it, but it's not. The reason that the virtual beanstalk only cares about midlevel winds when its going up or coming down is that there is almost nothing for them to push against when it's fully extended. The tether just doesn't catch much wind. Fully extended through the middle of a storm, the wind force on the whole tether compares poorly to the drag on the platform when it's partially inflated on the ground in a breeze. Not having anything hooked to the tether halfway up means we never have to worry about getting the elevator up and down, and we save a lot of maintenance, too. Putting extra balloons in the mid level winds takes away all of that. We don't need them and don't want them.

Q: Can you use an inflatable tether that will support itself?

A: No. In addition to having all of the same problems as adding midlevel balloons, inflatable tethers add two more problems of their own. They have poor shock absorption characteristics (they're stiff), and they have horrendous problems with circumferential tension (they pop). We don't need those either.

Q: Can you use guy lines?

A: Yes, and no. Guy lines are too heavy for single platform designs like my prototype design. We can keep it on station without them, so I recommend we don't use any. However, more advanced designs with multiple platforms and tethers could benefit greatly from guy lines. Guy lines would allow us to reduce the amount of controlled airspace required and dramatically raise the virtual beanstalk's payload at the same time. They also multiply the complexity. So for now, they remain a dream for the future. I expect they'll be a wonderful addition to the VBP Mark 2, but our first prototype won't have any.

Q: What will it be used for?

The prototype will be used as a proving ground. In addition to using it for testing anything we can think of, we will also rent out space for research projects. We've seriously considered selling rides, too.

Q: What can it be used for?

A: Imagine you could always go to roughly the same spot in the sky, over the same town, 20 kilometers high, on any day you wanted. It's a place that has only been visited for a combined total of a few weeks in all of human history. You can see the stars all the time. Thunderstorms can't touch you unless you want to slide down and sit in the middle of them -- and you can. Anything you left in the shade would freeze solid in minutes, but you can boil water just by sticking it out in the sun, and Saran Wrap(tm) has an R-value of 2. You can see anything you want below you, take any luggage you wanted, and your cell phone has a range of a hundred and fifty miles without roaming. Oh yeah, and there's internet access.

Now, what would you like to do once you get there? Perhaps you would like to listen to your local FM station from two hundred miles away? Would you prefer to add a repeater station and make it four hundred miles for the folks on the ground? Maybe you would like to make year-round astronomical photographs of a single stellar object? Does skydiving appeal to you? Or maybe there's some tricky industrial process that's eluded you because you can't fit your entire shop floor in a vacuum chamber for six months at a time? With proper platform design, almost anything could be adequately supported by the virtual beanstalk.

Q: What will it look like?

A: Standing on the ground, it will look like the ground station, with an off-white rope antenna sticking out into the sky at about a 40 degree angle. The rope will disappear from view around half a kilometer away. If you ignore that and look up another twenty to thirty degrees, and you have good eyes, you will see the ground station. It will appear smaller than a passenger jet at cruising altitude. It won't move and won't have a contrail, so look carefully or you'll miss it.

Or, you can catch a ride up the elevator to see the platform close up, in which case it will look about like this.

The rope will point straight down at the platform, and you couldn't see the ground station with the naked eye at the platform even if you knew where to look.

Q: Can you use a virtual beanstalk to reach orbit?

A: Yes and no. The platform can't go high enough to take you there directly, but a virtual beanstalk platform could conceivably be made large enough to lift a manned rocket, allowing it to launch with considerable potential energy of position and only a quarter of the atmospheric drag it would face taking off from the ground. The biggest problem with launching rockets from free-floating "rockoons" is that balloons tend to drift out of their designated launch zones. There'll be none of that with a virtual beanstalk as your launch pad. The virtual beanstalk could also be used in conjunction with a space tether, providing a relatively stable rondevous point above the densest parts of the atmosphere. That saves a lot of mass for a space tether. It would also extend the life of the space tether by essentially giving it a foundation that could be repaired separately and/or changed out without a space mission. A lot of space tether ideas begin with "First, you build a tower fifteen miles high..." Well, we can do that.

Q: How much will it cost?

A: That depends. The simplest, bare minimum design is expected to cost at least three million US dollars. Virtual beanstalks with dedicated crew cabins -- manned platforms -- would start at six to ten million. Those figures don't include payloads. This is much more expensive than weather balloons. However, a weather balloon can't put its payload wherever you want it, whenever you want it and keep it there as long as you want it, nor can it return your expensive instrument packages to you every single time. The virtual beanstalk's added capabilities are worth additional expenses. These figures are premature, of course, and represent final totals for construction costs of our very first beanstalk, assuming no infrastructure initially in place. It's also important to note that we have yet to complete our final feasibility study. Restrictions on viable mission profiles are still a possibility, which would also place restrictions on the price range.

Q: Will the virtual beanstalk oscillate?

A: Yes. The tether is sufficiently viscous to damp out any smaller oscillations before they travel through 25 kilometers of rope. Since the wind drag on the platform is the largest single force on the virtual beanstalk, that will cause most of the observed oscillations. Thus, the most prevalent oscillations will be: a) pendular motion, as the platform bobs up and down at the end of the tether; b) slewing and long period "skip-rope" rotational motion as the wind blows the platform over to new positions, and c) compression "shock" waves up and down the tether as the platform pulls it taught. These waves will require shock absorbers at both the platform and ground station. The ground station can be built with enough steel and concrete to take anything the tether can dish out. The platform is free to move in response to wave forces, spreading out the impulses. The platform shock absorber is also aided by the fact that the tether is long enough to act as its own shock absorber, and the use of a lot of stretchier polyester rope in the platform itself to absorb whatever shocks get through.

Q: Is the Spectra rope of the tether really stronger than steel cable?

A: No. There are a few fibers with a tensile modulus greater than that of steel wire, but not many, and the Kevlar and Spectra used in our tether are not among them. However, sheer tensile strength is not the only quality we need from our tether. The Spectra blend we intend to use gives us the best tradeoff of high strength, light weight and great durability.

Steel cable, for example, is more than twice as strong as Spectra. However, it is also ten times as dense. So even if you have to twine together twice as many Spectra fibers to get the same strength as a given number of steel fibers, the Spectra rope still weighs five times less than the steel. A Spectra rope can stretch all the way to the stratosphere and still be light enough to carry a substantial load. A steel cable of the same size would break under its own weight if you tried to run it the same distance.

Carbon fibers, like those used in carbon composite construction, are both as strong as steel and almost as light as Spectra. If they had any durability at all, they would be superior to Spectra for this application. However, they do not. Carbon fibers are so brittle that a carbon fiber rope would fray and wear out in just a few months or even weeks. They only hold together respectably in composite construction because they are embedded in an epoxy matrix. Spectra fibers are the most plyable and durable of any available currently available fiber with the same tensile strength, enduring for months or years under conditions that would fray steel, carbon fiber, or even pure Kevlar ropes in a matter of hours.

We don't just use Spectra blend rope because it's strong. We use it because it's tough.