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Broadband Blimps
mcabiling writes "SansWire Networks will demonstrate their "Stratellite" technology next week. For those of you who aren't familiar with SansWire, they plan to build a wireless network with balloons or "airships" as they call them.
"A Stratellite(TM) is a high-altitude airship that when in place in the stratosphere will provide a stationary platform for transmitting various types of wireless communications services currently transmitted from cell towers and satellites. It is not a balloon or a blimp. It is a high-altitude airship."
Looks like a blimp to me..."
The things that make the stratellite airship not a balloon or a blimp, based on reading the fine FAQ are:
A communication platform that sits at 65000 feet and stays relatively still sounds like a dream come true. None of the cost of keeping a constellation of LEO satellites moving, none of the latency of geosync. This would also seem a great technology for providing ad hoc coverage to a remote area for a special event. Put a couple of moderately directional (say +23 dBi) antennas, one pointed at Black Rock City, and the other at Civilization, and you have low-cost temporary ludicrous bandwidth at Burning Man. (Feel free to substitute YOUR favorite boondock~based used-to-be-cool-'til-they-sold-out art festival if you are offended by BM)
I for one, welcome our helium filled stationary communication overlords.
How does the Slashdot Effect happen given that no slashdotters ever RTFA?
probably as dumpable ballast to maintain altitude
The difference in pathloss between the SSP (21km slantrange) and the edge of a 75 mile coverage circle (122km slant range) is only 15.3 dB. Not an insurmountable design figure. You might need to use a directional antenna at the edge of coverage, where a more omni antenna would suffice at the center.
How does the Slashdot Effect happen given that no slashdotters ever RTFA?
NH3 is a lifting gas. Some balloonists use it as an alternative to helium (expensive) or hydrogen (safety risks).
Sounds like an attempt to overcome the runaway expenditures of Teledesic's failed LEO project. The problem with these high-altitude sender/receivers is that--while they offer a technology solution--there is a corresponding weakness in application.
For example, latency in these systems make it unattractive for many internet applications (who wants to play FPS's over a spread-slotted Aloha CDMA system?).
As long as you have a relatively nearby ground station to relay to, latency isn't a horrible problem. Right underneath one of these things, round-trip latency is about 0.13 milliseconds. At the edge of a blimp's broadcast range (around 100 km if I'm reading things correctly), it's 1.3 milliseconds round-trip.
Think of these as a much cheaper way of building a very tall relay tower, for something closer to reality than the "satellite" analogy.
By definition, an airship has a rigid framework, blimps and ballons are shaped just by internal gas pressure.
Imagine 802.16 on one of these things.
The difference between a zeppelin and a blimp is a zeppelin has a rigid airframe. That may be what they're talking about when saying it's an airship, not a blimp.
Any aircraft that gets most of its lift from lighter-than air gases and can be propelled against the wind is an airship. It floats in air and it goes where you want it, so it is an air-ship. Ok? Blimps are airships. Or dirigibles--different verbal approach, same idea, because the word emphasizes you can _direct_ the motion.
Several operations have tried this high-altitude business. There are issues with it but if you can make it work, the advantages over satellites should be clear. Why not use an airplane? Because the damn things use a lot of fuel and must move faster than the airship might be forced by shifting winds to move--relative speed matters with high-bandwidth connections.
The high altitude is chosen in part for the coverage range, but also to seek a layer of air where the average wind _force_ is lowest, to minimize the power needed to stay in place. With this design of airship they are going to have to turn to keep drag down if the wind shifts. True of all practical designs yet except spheres which have unacceptably high drag in _every_ direction--flattened disks called "lenticular" layouts might have lower inherent profile drag but have a tendency to pitch sideways to the wind that can only be combatted with fins that break the symmetry. So inevitably they will be blown off their ideal station point from time to time, the question is can they turn into the new wind fast enough to keep the divergence small. It depends on what the system users consider a small deviation at that range.
I would wait and see if their next demo comes off. Their last demo was about a year and a half ago, using Techsphere spherical airships. Just before the scheduled launch date their demo airship blew away! Nowadays Techsphere is persuading the Navy they can reliably operate for surveillance missions--I don't know if they paid attention to suggestions from people like me about how to reduce the drag of a sphere or if they have just had the good luck not to encounter severe winds in their demos yet. But meanwhile Sanswire has clearly washed their hands of Techsphere! Anyway they have been here before. We'll see I hope.
135 _micro_seconds. Times two to get back down to ground-based networks, and you're at a whopping 0.270 milliseconds. I just pinged google and got return times of around 100 milliseconds. So the signal propogation time is essentially totally insignificant.
Dyolf Knip
It's line-of-sight, though. Distance is far less important for QRP microwave than obstructions.
From the Federal Aviation Regulations:
- Airship means an engine-driven lighter-than-air aircraft that can be steered.
- Balloon means a lighter-than-air aircraft that is not engine driven, and that sustains flight through the use of either gas buoyancy or an airborne heater.
Unfortunately, they don't define blimp.
There really isn't much call for using hydrogen these days; helium costs more but it will be only a small part of the total outlay, it's not like in the 1930s.
BTW Hindenburg was _not_ covered in flash powder! That theory is dead wrong. Its main proponent made a complete fool of himself by staging a demonstration where he ignited a piece of the Hindenburg's skin with a blowtorch, and the damn thing just smoldered a little. It was the hydrogen, which was equivalent in heat release potential to 50 tons of gasoline but burned a lot faster, that burned up the ship and there is zero evidence the skin had anything to do with it. Or how come this guy had a piece of it to abuse on camera?
As for hurricanes--how fast does the wind blow 65000 feet _above_ a hurricane? Probalby no faster than winds are already blowing up there is my guess. If not, you can always have extra airships and station then upwind so new ones are being blown in as fast as old ones blown out, and bring the displaced ones down afterward and use them later. For the latter option it helps not to use hydrogen!