Able to skim, but can't land in atmosphere - how is that possible?

[Murphy]

The Broadsword and many other semi-streamlined vessels are able to skim fuel but can only land on airless worlds. The latter assumes they have landing gear, so it must be concluded that atmospheric flight over a terrestrial planet is somehow more straining on the hull than fuel skimming.

Isn't that a bit odd? I imagine that even at skimming depth most gas giant atmospheres would be far denser and more turbulent than nearly any terrestrial planet, barring Venus-like ones...

 

[Whipsnade]

The Broadsword and many other semi-streamlined vessels are able to skim fuel but can only land on airless worlds.

Broadsword is a bad example because it does land in the classic adventure of the same name.

The latter assumes they have landing gear, so it must be concluded that atmospheric flight over a terrestrial planet is somehow more straining on the hull than fuel skimming.

That 'conclusion" is nothing of the sort.

Landing involves more than simply slapping gear on whatever vessel suits your fancy. The structure of the vessel, it's internal organization, and the strength of the landing pad among other things all play a role. Look at the AHL-class for example.

That cruiser's decks happen to run perpendicular to it's thrust. If AHL landed on it's belly, it would have to continually run a gravity field within the vessel otherwise the decks would be walls. If the AHL lands on it's tail, you've just parked a 75+ story skyscraper on the planet's surface. Ever see what sort of foundations a skyscraper requires? In the real world, certain planes cannot use certain runways not because the runway isn't long enough but because the runway isn't strong enough. An AHL wouldn't be able to land on an airless world despite it's hull configuration.

You need to remember that landing is much more than just setting down.

Isn't that a bit odd?

No it isn't when you remember to take into account all the details involved in landing.

I imagine that even at skimming depth most gas giant atmospheres would be far denser and more turbulent than nearly any terrestrial planet, barring Venus-like ones...

Denser at skimming depth? No. More turbulent at skimming depth? Perhaps, but it would depend on the local "weather", wind speeds, etc. Ships would avoid the boundaries between jet streams and cloud layers while also keeping an eye on the sunrise line.

 

[Carlobrand]

Confusing indeed. In the same book:

"The Situation ... After the Broadsword has grounded under cover of the planetary defenses, a single Zhodani Strike Cruiser will arrive in system ... Consensus is that the Broadsword will be safe enough if it stays on the surface, or in orbit with the planet between it and the cruiser. ..."

And yet:

"The ship itself is unstreamlined, although it has sufficient lack of projections to allow it to skim hydrogen from gas giants in order to refuel. It may land on vacuum worlds, but generally interacts with the surfaces of worlds through its complement of 50-ton cutters ..."

The ship is unstreamlined by Book-2 rules - shouldn't be able to skim fuel - but Book-5 rules retroactively set the hull as partially streamlined, therefore able to skim but not land. However, I'll be danged if I can find one word in canon that speaks to "grounding" a partially streamlined ship or how it differs from a garden-variety landing.

 

[sabredog]

Maybe "grounded" means an emergency landing and some damage was sustained. She might still fly - once - but not well, and maybe some bits will fall off.

It is again one of those little bits of errata and gray that floats around all the scattered info in CT. I have always just ignored it since it always made more sense to me that the thing should be able to land. It allows it to act as a sort of base for operations. Besides, it looks like it should be able to land, and I modded HG to allow spheres to land (dunno why they couldn't - Vostoks always could and they don't even have reactionless drives) so IMTU they land.

I would recommend the same solution.

 

[Murphy]

I still can't rationalize a ship that can fly in a gas giant's atmosphere but not in a terrestrial atmosphere.

Landing involves more than simply slapping gear on whatever vessel suits your fancy. The structure of the vessel, it's internal organization, and the strength of the landing pad among other things all play a role.

Yes, that's right. By saying landing gear I meant ability to land.

I.e. let's take a ship able to skim, and able to land on airless worlds only. Ability to skim means it can behave in atmosphere. Ability to land means it has the gear and whatever internal structure is needed.

Now, why would such a ship be unable to land on terrestrial worlds?

P.S. I was under impression there were many ships like that, not just Broadsword.
Looks like this is not the case, at least in MgT ship design rules there's no such kind of streamlining.

 

[Carlobrand]

I still can't rationalize a ship that can fly in a gas giant's atmosphere but not in a terrestrial atmosphere. ...

I'm perplexed too, but I'm not ready to say A = B. There's nothing in canon that says how deep a craft goes when skimming. If they're only hitting, say, a quarter atmosphere pressure, then they're not dealing with the forces they'd face close to ground in a terrestrial atmosphere.

However, the factors that would make a large multi-G ship able to land or not have very little to do with streamlining. Hypothetically, if a ship can do better than 1-G, then it doesn't need any more streamlining than the average helicopter - it should be able to "zero-out" its movement with respect to the local planetary surface while in orbit (essentially "hovering" over a given spot), then slowly descend straight down tail first. It has more velocity in orbit than the local planetary surface/atmosphere, but it can dump that gradually during the descent - just takes a bit longer than your everyday meteoric descent.

At the point where you hit atmosphere, it's more a question of where the thing's center of gravity is and whether it can maintain that tail-first drive-down alignment in a stiff wind or goes toppling over. I don't see a Broadsword having much trouble in that department.

Assuming it doesn't have that "topple over" problem, a ship should be able to land, and support itself, so long as its axis of thrust is in line with the planet's gravitational axis - and has the necessary landing pads and a place that can support its weight. Kinda awkward landing and then toppling over because the ground was too soft or uneven (but I don't see that being a Broadsword problem either).

Now, if it has to land OFF its axis, all bets are off - something like an Azhanti High Lightning might break in half if forced to endure 1-G sideways for a long period. Or it might not - strikes me that something as well-armored as even a regular starship should have quite a lot of structural strength, but I'm know very little about structural engineering matters.

Let's do math:
Earth: 6400 km radius, atmosphere extends up another 500-1000 km but the bulk of it's down below 200 km.
Earth circumference: 40213 km. Day = 24 hours. Spins ~1676 kph
Up at 200 km altitude: 41470 km. To match a point on the surface from that height: 1728 kph. Now, at that point you're way, way below orbital velocity for that altitude (which is ~28 thousand kph) - you're depending almost entirely on your drives to maintain altitude, and you'd drop like the proverbial rock without them. However, WITH them, you can descend at whatever speed you choose, and your lateral speed with respect to the atmosphere is basically zero, plus or minus the wind speed of course. Ought to be able to handle a safe landing in 3-5 hours.

So, really, the only issue is whether you can keep your engines below you or are likely to get pushed over in a stiff wind - which shouldn't be an issue for a Broadsword. And, of course, whether you've actually got landing feet and whether the spot you land can actually bear your weight or leaves you to topple like a building built on marshland - which, for a short squat structure like a Broadsword, also shouldn't be an issue.

 

[far-trader]

...at least in MgT ship design rules there's no such kind of streamlining.

Actually, there is, exactly the same kind as CT HG in fact. MgT has three configuartions:

Standard : equal to CT Partially Streamlined although they used the wrong (imo) descriptive shapes, or failed to fully describe the intent

Streamlined : equal to CT Streamlined

Distributed : equal to CT Unstreamlined

Note that MgT Standard hulls may land BUT require extensive support to lift off again, atmosphere or no, and they are poor handling when entering atmosphere (a world OR gas giant)

 

[Carlobrand]

Actually, there is, exactly the same kind as CT HG in fact. MgT has three configuartions:

Standard : equal to CT Partially Streamlined although they used the wrong (imo) descriptive shapes, or failed to fully describe the intent

Streamlined : equal to CT Streamlined

Distributed : equal to CT Unstreamlined

Note that MgT Standard hulls may land BUT require extensive support to lift off again, atmosphere or no, and they are poor handling when entering atmosphere (a world OR gas giant)

Wha...?? Oh! MgT = Mongoose Traveller? I don't have any Mongoose stuff. Interesting difference.

From MegaTraveller Referee's Manual:

"Unstreamlined: No attempt has been made to streamline the hull. Many protrusions and irregularities exist which significantly increase the vessel's drag, making it difficult or impossible to operate the craft in an atmosphere at a high rate of speed."

"Streamlined: Various cowlings and farings have been added to the hull to streamline it for operation in an atmosphere, although the streamlining is less than that provided by an airframe." Streamlined craft can fly through atmosphere and land, but get no "lift" from its shape. "Without power, a streamlined craft drops like a rock." (Errata)

"Airframe: The hull has been designed for high performance in an atmosphere In order to achieve such performance, exterior design has been a priority." Airframe is optimized for atmosphere. It can achieve higher speeds for the same power, and if the drives cut out, it can try to glide to a landing. (Player's Manual p. 71)

Per MT, streamlining is required for ANY ship of configuration 1-6 to land on a world with atmosphere code greater than one (Referee Manual p58). Further, "If a spacecraft is unsteamlined, it is incapable of travelling in an atmosphere." (Referee Manual p 87).

However, it is possible to build unstreamlined surface craft (think of those brick-shaped postal service vans); they just have a top speed of 300 kph, which is adequate for most ground craft. Seems to be possible to build unstreamlined flying craft as well (the enclosed air/raft is unstreamlined, and Errata 2.2 seems to have decided the open-top air/raft is also unstreamlined).

Is all verrrrry confusing.

 

[Peter Newman]

From MegaTraveller Referee's Manual:

"Unstreamlined: No attempt has been made to streamline the hull.

"Streamlined: Various cowlings and farings have been added to the hull to streamline it for operation in an atmosphere,

"Airframe: The hull has been designed for high performance in an atmosphere

Per MT, streamlining is required for ANY ship of configuration 1-6 to land on a world with atmosphere code greater than one (Referee Manual p58). Further, "If a spacecraft is unsteamlined, it is incapable of travelling in an atmosphere." (Referee Manual p 87).

However, it is possible to build unstreamlined surface craft (think of those brick-shaped postal service vans); they just have a top speed of 300 kph, which is adequate for most ground craft. Seems to be possible to build unstreamlined flying craft as well (the enclosed air/raft is unstreamlined, and Errata 2.2 seems to have decided the open-top air/raft is also unstreamlined).

They seem to assuming that a spaceship descending from orbit will be going faster than 300 kph and/or will encounter winds with a relative speed greater than 300 kph at some
point in the process. It seems to me that if your sensors and your pilot were good enough to avoid weather and you had contra-gravity and went slowly enough that your relative speed stayed below 300 kph that you ought to be able to land an unstreamlined ship on an planet with atmosphere.

It would be risky and I wouldn't be surprised if the terms of a standard mortgage and Imperial regulations both forbade it except in emergency circumstances. A character of mine landed an unstreamlined ship on a planet with an atmosphere once. I believe that the Ref [Aramis] characterized it as a Formidable Task in MT terms. It may have been Fatefull and/or Hazardous as well. Disclaimer - I was playing the pilot, this was all the Captains idea. My character tried to talk his character out of it and I tried to talk him out of it....

 

[aramis]

Winds aloft exceed 300 KPH at certain altitudes almost as a matter of course... Keep in mind - that's about 187MPH... jet stream speeds can reach 400 KPH.

 

[Peter Newman]

Winds aloft exceed 300 KPH at certain altitudes almost as a matter of course... Keep in mind - that's about 187MPH... jet stream speeds can reach 400 KPH.

Right but its the net speed that matters. If you're flying with and at about the same speed as the winds then the net speed will be low. Also high altitude winds are made of thinner air so they produce less pressure for a given speed.

 

[aramis]

Right but its the net speed that matters. If you're flying with and at about the same speed as the winds then the net speed will be low. Also high altitude winds are made of thinner air so they produce less pressure for a given speed.

True enough - but if you're aiming to land, the winds aloft are retrograde to aiming for the surface.

And for the rest of you, Peter's been in several of my games, and seen me allow players to land USL ships... very slowly and carefully.

 

[Carlobrand]

True enough - but if you're aiming to land, the winds aloft are retrograde to aiming for the surface.

And for the rest of you, Peter's been in several of my games, and seen me allow players to land USL ships... very slowly and carefully.

I'm thinking this is going to require quite a bit of original thinking on the part of the game master (gasp!), since there's great variation on the details of the various USL ships and how they might interact with such a wind. Broadsword shouldn't be troubled by it, but a Gazelle isn't going to manage it unless you apply those MT rules about being able to apply thrust lateral to the direction of the drives - and that only by overdriving.

 

[77topaz]

You're talking about the spherical Broadsword, right? Such an aircraft would be very hard to handle in an atmosphere, unless it has very powerful engines, but that still won't help it land. Unless it has grav plates or some other Imperial technology.

 

[aramis]

You're talking about the spherical Broadsword, right? Such an aircraft would be very hard to handle in an atmosphere, unless it has very powerful engines, but that still won't help it land. Unless it has grav plates or some other Imperial technology.

Landing on thrust is a proven technology - it is doable NOW. It's high risk, tho'. Actually, it was done in the 1960's...

 

[Carlobrand]

You're talking about the spherical Broadsword, right? Such an aircraft would be very hard to handle in an atmosphere, unless it has very powerful engines, but that still won't help it land. Unless it has grav plates or some other Imperial technology.

The basic process for landing an unstreamlined craft is to handle them like a helicopter, not an airplane. In other words, you use the drives to counter gravity and back down on that thrust, rather than gliding in - in pretty much the way the lunar module handled the moon.

Broadsword is, to my knowledge, almost unique among unstreamlined/partially-streamlined ships for being spherical. In every other case, you're dealing with a set of engines at one end of a long thin thing that's supposed to be unable to fly longitudinally through atmosphere. Thus, in every other case, you've got a serious center-of-gravity problem if you try to back down on drives. It's like trying to balance a broom upright on the palm of your hand: let the center of gravity slip too much, and that puppy's falling over on its side, which is very, very bad if that ship doesn't have a way of offering 1g thrust in that direction. Makes big craters. And, 300 mph high altitude winds are very good at pushing "brooms" around - the ship "wants" to present the lowest cross-sectional surface to the wind, which unfortunately puts the drives at right angles to the pull of gravity. I'm not sure if the attitude control system of a ship that's not designed to be in atmosphere is going to be strong enough to keep a ship upright when something outside is pushing hard against it.

Broadsword, on the other hand, is a ball: low center of gravity. Easier to balance a ball than a broom. Still not a slam-dunk - I think the winds are pushing harder against those landing legs, tending to push them out from under. However, I would bet on the attitude control of a sphere to keep those legs under her before I'd bet on attitude control keeping something like a Gazelle from tipping over like a tree in a high wind.

 

[77topaz]

Landing on thrust is a proven technology - it is doable NOW. It's high risk, tho'. Actually, it was done in the 1960's...

The Moon doesn't have an atmosphere, though, if that's what you're referring to.

 

[aramis]

The Moon doesn't have an atmosphere, though, if that's what you're referring to.

All the testing was done in atmosphere.

Plus, The Vikings in the 70's on Mars.

Plus, the landing last month.

 

[BlackBat242]

http://www.youtube.com/watch?v=AH0VYi1G6jo

Note that the 2 Lunar Landing Research Vehicles (LLRVs) [and the 3 follow-on Lunar Landing Training Vehicles (LLTVs)] aimed the entire turbofan main thrust engine to maneuver:

sorry about the image size...

 

[Khan Trav]

Lunar Lander:

Note the large indention in the seat cusion to accomodate the pilot's massive cajones. Now that is a brave fellow...