Lifters: The Other Landing Gear?

[Terry Mixon]

So, the Starship Operator’s Manual talks about them not only being used to move the ship about but also allowing it to hover above the ground. It makes no mention of a time limit. Could a ship choose not to land, say because of poor ground conditions, and hover for a week?

 

[rinku]

Yes. You'd have to keep the power plant running, and high winds might make it unwise or need someone to keep an eye on the flight controls, but for the most part it should work. Maybe use up a little fuel, if it has to be done for a long time and fuel use is a critical issue in the situation?

Some ships may have difficulty unloading their cargo and passengers while hovering, too. (Others won't care, or could use small craft and vehicles).

*Potentially* running the M-Drive or Lifters for an extended time deep in a gravity well might put strain on the hull, or at least be a reason to call for a few extra maintenance rolls.

 

[Condottiere]

 

[Terry Mixon]

The SOM does say they can move a ship around at up to about 25 kph so it could possibly act as its own mooring. Maybe?

 

[rinku]

There would be a threshold, dictated by the physics and greatly affected by the ship's cross sectional area and aerodynamics. At some point the wind speed would be more than the Lifters (and maybe even the M-Drive) could cope with. Plus wind has a nasty habit of changing direction...

Note that even exceeding the threshold by a small amount would cause the ship to drift. Securing the ship to the ground with lines is probably a good idea.

You might benefit from pointing the nose towards the prevailing wings. On the other hand, a lifting body might... lift.

 

[Condottiere]

I was kicking around the idea of gravitating airships, and ran into the wall of their rather large gasbags.

Streamlined or not, that's a large sail equivalent.

 

[rinku]

Yep. The big reason they fell out of use once aeroplanes got going. Too prone to being pushed around by wind, let alone worse weather.

You could avoid the dangers of hydrogen combustion by using helium, but that meant an even bigger envelope per unit payload.

However, if you do have antigravity tech, potentially you might get some kind of advantage - possibly a cost one - from a hybrid that has gas cells enough to help with lift but aren't big enough to provide all of it.

Or the idea of near vacuum airships, but that's basically a materials problem. Potentially gravitics could be part of the solution, but you then run into why bother, when gravitics alone can do the job?

Unless in a particular non-gravitics TU, that's actually how it works - materials so strong that they make vacuum airships possible.

 

[Condottiere]

Okay, we're in a gravity field, so you'd have volume tempered by actual mass.

Which means if levitating, it depends on how much wind force is exerted per square metre.

The other side of that equation, would be that the cable holding the levitating spacecraft, would need to be strong enough to withstand that, plus whatever is anchoring it to the ground.

If it's small enough, tractor beam playing magnetic poles.

 

[Terry Mixon]

Okay, we're in a gravity field, so you'd have volume tempered by actual mass.

Which means if levitating, it depends on how much wind force is exerted per square metre.

The other side of that equation, would be that the cable holding the levitating spacecraft, would need to be strong enough to withstand that, plus whatever is anchoring it to the ground.

If it's small enough, tractor beam playing magnetic poles.

So I wonder how prone to movement in wind that a, say, 50,000 dton ship levitating would be? It’s big but massive. Maybe that’s a @Geir question because maths.

 

[Arkathan]

If there is an atmosphere, you'd need a pilot on duty constantly. Probably have to decrease the hours of each watch duration, because that kind of fiddly adjustments wears on a person quickly.

 

[Terry Mixon]

If there is an atmosphere, you'd need a pilot on duty constantly. Probably have to decrease the hours of each watch duration, because that kind of fiddly adjustments wears on a person quickly.

Or a robot pilot or competent autopilot. Station keeping should be more straightforward than other piloting.

 

[Arkathan]

Still want a competent pilot in the pilot's chair. It's a long way from a bunk/charging station to the chair during an Oscar Sierra event.

 

[NOLATrav]

Large passenger airliners today can fly their routes without human intervention. Or so I’m told.

Ship’s computer can handle floating in winds in the 57th century - if you want it to.

 

[rinku]

Yeah, I'd say at stellar TLs, the provided autopilot would be competent, but definitely need a pilot on watch.

A bit depends on the weather.

As far as the wind force goes, for a spherical hull of 100 dtons the cross sectional area works out to be around 300 square metres. A breeze of 10 kph - 2.77 metres per second - would exert about 1417 Newtons of force (1 Newton is required to accelerate 1kg at 1metre per second squared).

If you assume ships mass around 1000 kg per dTon, that would be enough force to accelerate the ship (100,000 kg) at 0.014 metres per second per second. Well within the gravitics capacity... but even if the wind got up to gale force - let's say 100 kph - the wind load would be about 141,000 Newtons, which would be an acceleration of only 1.41 m/s2. Atmopsheric density affects this, but i think it's going to be still within the ability of Thrust 1 to cope with in most reasonable cases, as long as the ship is pointing in the right direction. A strong wind from aft or abeam may be too much for 10% or 25% thrust to cope with. There's also some suggestion that switching M-Drive thrust direction takes a certain amout of time.

Rapidly gusting high winds might be a problem. Even with a good pilot or autopilot, you can't detect those well, only react to them. If those are expected or happening, you might want to risk physically landing.

(Numbers obtained mostly from: https://www.calctool.org/machines-and-mechanisms/wind-load )

 

[Arkathan]

Winds near the ground tend to be less predictable and give little room for error...
If you trust the machines constantly without supervision, there will eventually be some Oscar Sierra going on.

 

[NOLATrav]

And a M-Drive factor 1 generates 1.21 gigawatts if the winds are 88mph…

 

[rinku]

TLDR... avoid hovering in high wind situations.

In anything.

 

[Endie]

I have very strong doubts as to whether a pilot, sitting at the controls but not doing anything for hours on end, will prevent any wind-related shenanigans that an autopilot would not.

In driving through major (western) cities, humans are about 12 times more likely to kill or injure a pedestrian than a 2025-tech driverless car, and seven times more likely to cause property damage (these are related, because the driverless car is told to hit things if it has to in order to avoid hitting people, and it does so unflinchingly and without delay).

I suspect that, in thousands of years' time with accompanying improvements in software, sensors* etc the simpler problem of "using your sensors to locate yourself, remain exactly where you are, reacting in microsecond timescales to react to wind pressure changes" would have a strong "don't interfere as a human: that's how we get crashes" rule.

*Sensors are a main cause of the remaining fraction of injuries caused by driverless cars, especially at dusk, although they are still better than humans at noticing detail even at that time, in contrast to the position in 2024.

Edit: You can already use doppler radar to detect wind speed (using dust etc suspended in the air) so stellar TL tech will have no problem knowing that in two tenths of a second the wind will suffer an additional 920 newtons of force from a given direction due to a slight change in wind direction and strength.

 

[Condottiere]

 

[Terry Mixon]

Still want a competent pilot in the pilot's chair. It's a long way from a bunk/charging station to the chair during an Oscar Sierra event.

That’s why I build robotic pilot brains. Runs on ships power, has battery backups, and is always on station.