Replacing heavy cranes with airships for alien city building? Pros/cons?

Question

We are doing construction on an alien world with unbreathable air

This creates a very big problem for a growing city which needs to expand. Workers cannot go outside safely for long periods. Goal: Minimizing outside time and staying inside a climate-controlled environment reduces injuries to workers. Anything that makes the job easier makes it faster.

I want to reduce ground crews by simply flying overhead with tethered construction airships.

• Assume no wind hazards. Winds are moderate and manageable, no storms on record.
• Airships can be tethered to the ground for better stability, but the gas bags provide the lift.
• Likely, the hoist can move around on tracks as well rather than maneuvering the whole ship.

The several disadvantage to heavy ground equipment I feel could be addressed this way are:

• Erecting a bridge or tower crane requires a large team working outside.
• Rigging cranes with counterweights, and assembling their masts on the ground.
• Large cranes need smaller crawler cranes to build them; Poor viewing angle to the hook and load make errors more likely.

These are the things I can think of. But a construction airship will likely need to be designed differently than the passenger liners we are familiar with. I don't know what those differences may be, but it seems that in general, airships can provide a much safer work environment at large construction projects in unbreathable air.

What might be the pitfalls, or what should they be prepared for?

Parameters:

• Air density = 15 kg/m$^3$
• Terrain = rocky
• Buildings considered:
  1. Large open space / covered colosseum of 10 acres
  2. 20-story masonry buildings (which will be domed over)
  3. Framed biodome covering 30 acres

Answer 1

Airships are complex and expensive compared to cranes... there are a whole new collection of pitfalls which your construction crew can now suffer from... as if operation in a toxic alien atmosphere weren't enough, now you have to deal with air traffic control, too.

Airships can be tethered to the ground for better stability, but the gas bags provide the lift.

One thing you'll need to bear in mind is the airship's need to maintain neutral buoyancy, something a crane does not really care about. If you load up a floating airship, it will sink. You then need to offload ballast, or compress lifting gas in order to restore equilibrium, and reverse the process when you release the cargo. You might be able to offset this by having massive mobile ballast trucks on the ground below, and a positively buoyant airship tethered to them. Accidents may now involve the airship suddenly shooting skywards at high speeds.

Erecting a bridge or tower crane requires a large team working outside.

Well, does it? I mean, you're operating on an alien world. Unless you got there by magic, there's a whole new arsenal of engineering technologies that are effectively "table stakes" for interstellar colonization.

Consider also that one of the most useful things your airship might do is to position some large tower cranes and then fly away. Ground-mounted stuff can be made arbitrarily strong and tough (up to the limits of your materials technology and the cargo capacity of your airships) and dealing with issues of power and crew access becomes much simpler.

Rigging cranes with counterweights, and assembling their masts on the ground.

Airships need mooring and ballast and fuel and lifting gas and colossal hangars in which to perform maintenance and repairs. If you are using these things, how many can you afford to support? Seems like a good argument for having few of these in order to assemble and tear down larger numbers of big tower cranes.

20-story masonry buildings (which will be domed over)

Why so tall? You get 20 story buildings in cities because land is expensive compared to the cost of constructing 20 story buildings and the value of stuffing a lot of people in that space.

Here construction is necessarily complex and expensive and dangerous, and you need to build pressure-safe buildings which are life support systems for their soft meaty cargo. Build low and wide, dig down if you need more space. Dig deep lightwells, construct around them. Invest in display screen technologies and daylight-balanced lighting systems so you can just have underground construction that seems like its outside.

Living for extended periods of time in 20 atmospheres of pressure is already known to be hazardous on Earth, so you'll need to have some magical new pharmaceuticals, or you'll need to be building pressure hulls that let you have Earth-normal pressure (or at least, a decent reduction from ambient).

Given the cost of building a free-standing 20-story submarine, and the safety implications of issues with your construction, digging or building wide and low seems like a much more sensible thing to do.

Framed biodome covering 30 acres

Don't build such a large structure from the outside. Build it from the inside, and middle, outwards. Pressurise the dome to float it up, makes construction much easier, under the circumstances.

Doesn't work if you want a reduction in pressure inside, of course.

Answer 2

For this answer I am assuming that airships arent based on WWII technological limitations and are a developed, modern design, modern propulsion techniques and with modern materials.

Pros:

• its extremely resiliant to wind. Its limits will be the same as regular cranes. The load will start swaying too much above 30km/h and it becomes too hazardous to load/unload it as the windspeed increases, while a good airship will be able to handle air speeds up to its maximum speed. Unlike a regular crane, an airship could partially solve this problem since it could lower a straight and solid support down with the cables to minimize the swaying of the cables, meaning the airship would be able to work at higher windspeeds than regular cranes.

• an airship is the most stable of aircraft ever designed, even if we talk about WWII style airships. This is the one vehicle where the square cube law is a positive, as the wind can only push the surface area while the larger the airship gets the more mass is inside that needs to be displaced (it doesnt matter if its lighter than air, mass is mass!). This means that it takes a LOT of wind and time to get the airship off position, and gives plenty of time for engines to correct the wind pressure. It also means that individual wind blasts are less influential.

• it doesnt take a lot of space. Cranes require space to set up and a lot of thought in where you set it up, the variable winds at different heights of the crane, counterweights, properly ankered into solid enough ground, the reach of the boom, minimum height the load needs to clear, possible necessity to anker the crane to nearby objects along its length. The airship can get there without impeding traffic and then hang above the target area where it is necessary. Since air traffic wouldnt be flying so low to a construction site it wouldnt impede airtraffic either.

• airships are perfect for construction in hostile environments or environments with low infrastructure where it is harder to get a crane to the location (although you could technically let the airship bring a crane and build it up at the location instead).

Cons:

• the airship needs to go off-station any time the stormwinds are predicted, where a crane can remain assembled (although a surprising amount of cranes fall over during storms, mostly due to human error building the cranes apparently).

• a crane just sways in the wind, an airship, even a tethered one, will need to use fuel or energy to balance itself and stay in position. The only way to avoid this is to build high poles and tether the airship tightly at its own height, or have many tethers in all directions so that the length of the cables limits the amount the airship can move off before several cables go taut.

Answer 3

That's not an airship; that's a blimp

If you tether it to the ground, and use it to lift, it just doesn't have or need the same things as a zeppelin. You might get away with a balloon.

The dimensional settings on this console are a bit iffy, but I'm pulling through a bunch of stories about your development plan:

Robot Balloon Cranes Could Revolutionize World’s Seaports

Skylifter Balloon Can Lift Entire Buildings and Put ‘Em Down Gently

IT'S A BLIMP, IT'S A CRANE, IT'S A HELI-STAT Helicopter pioneer Frank Piasecki hopes his weird-looking new flying machine will give a lift to the logging industry.

In this simulation or yours, I think it's plausible to do this. Blimps use somewhat different building materials than cranes (much less need for compressive strength) so this might pay off well in the right environment.