Question: Ships leaving atmosphere

[phavoc]

Just a minor point of clarification, my concern is not with artwork but with the actual rules:

Mongoose Traveller: Core Rulebook: Pg 106
“A ship may have any of three configurations – standard (a wedge, cone, sphere or cylinder), streamlined (a wing, disc or other lifting body allowing it to enter the atmosphere easily) or distributed (made up of several sections, and incapable of entering an atmosphere or maintaining its shape under gravity).”

Mongoose Traveller: Core Rulebook: Pg 106
“A standard-hull ship may still enter atmosphere but is very ungainly and ponderous, capable only of making a controlled glide to the surface. Getting it back into space requires an elaborate launch setup and considerable expense. A standard-hull ship may have scoops for gathering fuel from a gas giant but the process will be much more difficult and less efficient. Larger ships of this type will often carry a specialized sub-craft (such as a modular cutter, see page 135) to perform the actual atmospheric skimming. See Atmospheric Operations on page 137.”

Per the rules, on the same page in the core rulebook, a “wedge, cone, sphere or cylinder” hull cannot land and re-launch without “an elaborate launch setup and considerable expense.”

In general, scale/size has a great deal to do with this... as in going from 100t to 200t doesn't mean a simple doubling in volume mass etc. Things like stresses, torque, etc grow exponentially. Look at a square, 1"x1"... "double it" which to most people means now it is 2"x2"... yet the area just quadrupled.

I agree, and this is why is bothers me that a Standard (a wedge, cone, sphere or cylinder) Hull Small Craft and a needle, wedge and cone shaped Capital Ship Hull can both explicitly land and take-off from a world with an atmosphere, but a Standard Hull ship larger than a Small Craft and smaller than a Capital Ship cannot. It is capricious, illogical and adds nothing to the game. It appears to be a simple errata rather than a grand design that is part of how the creators envisioned the game.

Grav, Contra-grav and Anti-gravity Drives actually have nothing to do with the hull configuration and streamlining issue. The same rules and arguments would apply to a TL 7 (pre-Grav tech) Reaction Thruster Small Craft and 200 ton Interplanetary spacecraft.

Per page 106, the Phoenix SSTO VTOL spacecraft would not be able to land, except via a controlled crash landing, and could not lift-off without an elaborate launch setup and considerable expense (whatever that means in game terms). [Unless it was less than 100 tons or more than 2000 tons.]

Does that pass YOUR smell test?

Just to stir the discussion pot some, I think the rules (or at least they appear to) contradict themselves. First off, the venerable Type S Scout class vessel is a wedge. It doesn't, as far as I can tell, have any lifiting surfaces, control veins or anything else that would be considered streamlining. One could argue that its a lifting body... but then again many things are lifting bodies if you have enough thrust.

Now look at the Free Trader, Far Trader, even the Fat Trader. These don't seem to be the aerodynamic designs as defined by the book.. Yet they land on planets, as well as are copiously illustrated and used as examples for ships that have landed.

My personal take on all this is that pretty much any ship should be able to land on any planet... but with caveats. If the ship has anti-gravity lifting capablities then it should be able to simply lower itself into the gravit well and land at its designated spot. It would basically be akin to a dirigible or even a helicopter. The antigravity works to counteract the ungainliness of the ship. It won't do it fast, it won't do it prettily, but so long as you can counteract gravity, then its really a matter of structural integrity of the vessel entering the gravity well. And, I suppose, the speed at which it enters and the density of the atmosphere. So I don't see a spindly ship diving through a gas giant, as the shear stresses would probably tear it apart. But it could probably survive a slow entry into an atmosphere, and a very extended period of time there sucking in gases. It might also be able to land on an ocean, but again it would have to be slow, and the design would have to be able to at least support itself in a gravity well.

Rather than imposing hard-and-fast rules, I've always taken the idea with a grain of salt. Sure, its nice to zip around the atmosphere and leave in a hurry. But not all ships are going to go to the expense of being designed that way. And of course sometimes you are not going to bother with the expense of designing a ship to do that. Plus, well, who wants to try and land a 500,000 ton warship in an atmosphere? First you probably can't land anywhere but the ocean, or a large field far away from cities (in case of a grav drive failure and you fall to the planet and go boom). But also you don't want to have such a valuable asset stuck at the bottom of a gravity well if the enemy shows up unexpectedly.

 

[rust]

Plus, well, who wants to try and land a 500,000 ton warship in an atmosphere? First you probably can't land anywhere but the ocean, or a large field far away from cities (in case of a grav drive failure and you fall to the planet and go boom). But also you don't want to have such a valuable asset stuck at the bottom of a gravity well if the enemy shows up unexpectedly.

Besides, unless the crew keeps the drive running all the time, the mass
of such a ship would be too much for almost any kind of ground except
bedrock, otherwise there would be a real risk that the ship would sink
deep enough into the ground to make it difficult to take off again - and
a capital ship that is stuck in the mud is not very impressive anymore.

 

[simonh]

All of that aside, claiming that the Atlas/Delta rocket cannot take off from Earth because its "standard" (cylinder/cone) shape is not "streamlined" (like a flying saucer) doesn't pass my laugh test.
YMMV

Nobody has claimed that though, even the rules don't claim it. They just say it needs an expensive and elaborate launch setup, like perhaps a huge tractor vehicle to carry it out to a specially designed launch pad equipped with a supply tower.

Like the one shown in the link above being used by a Delta II rocket, for example.

I think the intent of the rule is kind of understandable, it's just too generalised.

Simon Hibbs

 

[Rikki Tikki Traveller]

Maybe I haven't read the rules thoroughly enough, but here is how I have always defined the three basic hull types (not shapes, TYPE).

Standard: Partially streamlined. Nothing sticks out, so it can take off and land through a standard atmosphere. These hull types can skim fuel from Gas Giants (I figure 0.5 Atmos for skimming, THIN atmospheres). They are NOT very maneuverable, no real control or lifting surfaces, they get knocked about by wind etc, but CAN take off and land. Standard M-Drive provides the gravitic thrust for operations. Lift-to-Drag Ratios of 1 or less.

Streamlined: Lifting bodies that provide additional lift and control. Nothing sticks out and you have wings and control surfaces (even if they are small). Lift-to-Drag Ratios up to 20 or so.

Unstreamlined: ANY shape that has things sticking off of the hull (like radar dishes etc). Cannot skim GG and cannot takeoff or land through an atmosphere thicker than Trace (Mars is at the limit).

Aerofins: These are EXTRA control surfaces that can be added to a streamlined hull to give it aircraft-like performance.

Modern aircraft are Streamlined with Aerofins. The Space Shuttle is Streamlined (although it has a very low Lift-to-Drag ratio for other reasons).

A Standard Hull can takeoff and land, but it is ungainly and not very maneuverable. Perfectly acceptable for a small tramp freighter (or a scout ship), but not for a shuttle specifically designed for interface operations.

 

[GamerDude]

All of that aside, claiming that the Atlas/Delta rocket cannot take off from Earth because its "standard" (cylinder/cone) shape is not "streamlined" (like a flying saucer) doesn't pass my laugh test.
YMMV

Actually, I am going to declare a small 'foul on the play' here. Why? An Atlas/Delta rocket does not "can not" reenter the atmosphere except to crash. It is the 'expensive means' by which objects like satellites are tossed into space. It is not streamlined nor standard, by the intent of the definitions.

This is actually more of a corroded-iron argument, come up with something totally bogus and clearly outside the intent of the rules.

Actually the 'standard' type hull would use maybe an Atlas/Delta rocket-like way to get back into space.

 

[DFW]

So who said you had to "dive deep" and where? It's always been called "skimming" as far as I recall. It's always been presumably cloud top level very thin atmo by that usage of terminology. Diving deep into a GG is going to require a lot more than a simple hull has enough of to survive. SDBs lurk deep in GG. Heavily armoured, powerfully engined, expertly crewed, SDBs. Perhaps you have conflated the two?

Not really relevant to planetary landings. With grav equal or greater to the planets gravity, you can enter and set down at 10 kph if you want. Otherwise, ships without lifting surfaces (standard hulls) couldn't do it at all.

Therefore, any ship with enough M-drive can enter any density of atmosphere and land. Of course, certain large ships that aren't designed to set down (distributed, no landing gear, etc. might be damaged). Otherwise there are no tech issues.

 

[GamerDude]

phavoc, atpollard, simonh, Rikki Tikki Traveller, far-trader

First, thank you for understanding of what I've been trying to say and participating in an intelligent discussion of the MGT rules as written, of setting the base-line there.

Now that we are at this point, let me toss out where I disagree with how the rules are presented, the conflicts. Basically you five have hit it on the head.

I feel the definitions for the three hull types (shape descriptions not included) are perfect. Again 'standard hull' is like our space shuttle... some maneuverability but the tanks for enough fuel and the engines for it to lift off on it's own (either vertically by being pointed nose up, or like an aircraft) aren't included in the design and the 'air frame' doesn't generate enough lift for it to do so.

The 'shape descriptions' of cone, wedge, etc. are very much (to me) bad 70's mentality still carried forth today. Period.

I grew up hearing quite often hearing the latest announcement by Boeing or Pan-Am about new a "space plane" concept, plans for regular scheduled 'Earth-to-Orbit' flights, etc. Their designs were much closer to an aircraft than our current shuttle... but still they were mired in the 60's and 70's understanding of space flight.

The GURPS Traveller books had a good explanation of the difference between standard and streamlined... because of the streamlining they lost 20% of the internal volume/capacity compared to the same dTon standard hull... the price for being able to "fly" up and down through an atmosphere. GENIUS!

NOTE: Please add the move "2001: A Space Odyssey" to my list of movies influencing this time.

On Anti-Gravity/Contra-Gravity... my only point is that (to me at least) it is NOT in the rules/materials for anything over a tank... by the rules space ships and star ships don't have anything for countering gravity as an aid to flight.

That is BY THE RULES. Do I have a problem with 'adding it' to space/starships so things make more sense? No... but to be reasonable the simple acknowledgment that "I know it's not in the rules but I don't see things working any otherway, so I've included..." is all one needs.

Hell, I don't care if you put ice cream dispensers on the OUTSIDE of every ship hull in YTU, as long as you don't try to rationalize to others this is something found in the rules.

So, my personal TU?
-Distributed like Lab Ships, spheres, blocks, etc... shapes that just don't do well in atmo at all are all 'orbit and farther out'. They don't get closer than a certain point (based on the planet's gravity).

-Standard hull ships are like the shuttle... those are the pictures of the ship "blasting off" in a vertical position or on a big tank like the shuttle. Simple but very costly, too many parts not reusable.

-Streamlined, the old "space plane" concept. Designed to land & take off like an airplane, like the good ol' Millenium Falcon. 20% less volume (thank you GT).


For the pictures we've been talking about... the thinking probably was with contra-gravity/anti-gravity, but some how that concept didn't make it into the MGT books.

 

[atpollard]

All of that aside, claiming that the Atlas/Delta rocket cannot take off from Earth because its "standard" (cylinder/cone) shape is not "streamlined" (like a flying saucer) doesn't pass my laugh test.
YMMV

Actually, I am going to declare a small 'foul on the play' here. Why? An Atlas/Delta rocket does not "can not" reenter the atmosphere except to crash. It is the 'expensive means' by which objects like satellites are tossed into space. It is not streamlined nor standard, by the intent of the definitions.

This is actually more of a corroded-iron argument, come up with something totally bogus and clearly outside the intent of the rules.

Actually the 'standard' type hull would use maybe an Atlas/Delta rocket-like way to get back into space.

Nice job of straining gnats and swallowing camels.

A 200 ton free trader shaped like the Saturn V or Atlas or Delta or "V-2 inspired 1950's sci-fi story" rocket would be a cone or cylinder shape and a Standard hull configration under the rules in the core book on page 106 [the rules on configuration under Starship Design] and would be incapable of unaided liftoff per those same rules.

The Saturn Application SSTO Rocket Design by Bono and the Phoenix SSTO VTOL Rocket by Douglas (IIRC) are two real rocket proposals by two real rocket engineers that are exactly the same cone/cylinder configuration and intended to lift-off, land refuel and lift-off again with minimum fuss and infrastructure.

Please do not confuse the FORM of a vehicle with the technical limitations of 1960's rockets. Even the Shuttle needs months of preparation to launch, does that mean that Streamlined Spacecraft also cannot launch without extensive supporting infrastructure? Of course not.

 

[DFW]

Again 'standard hull' is like our space shuttle... some maneuverability

Not per MGT rules. Streamlined hulls have lifting surfaces. Not standard hulls.

 

[atpollard]

Nobody has claimed that though, even the rules don't claim it. They just say it needs an expensive and elaborate launch setup, like perhaps a huge tractor vehicle to carry it out to a specially designed launch pad equipped with a supply tower.

Like the one shown in the link above being used by a Delta II rocket, for example.

I think the intent of the rule is kind of understandable, it's just too generalised.

Simon Hibbs

A SCUD missile (same basic shape) needs an I-beam welded to a pickup. Is that what was meant by "an expensive and elaborate launch setup"?

 

[DFW]

A SCUD missile (same basic shape) needs an I-beam welded to a pickup. Is that what was meant by "an expensive and elaborate launch setup"?

Good one.

This of course begs the question as to why a streamlined ship doesn't need a similar set up. HUGE contradiction in the rules.

 

[rust]

Well, for me the case is closed.

According to the rules, a ship with a standard hull can land for ocean re-
fuelling. Oceans of liquid water can only exist on planets with atmosphe-
res. After the ocean refuelling the ship can only take off again from a pla-
net with an atmosphere with an elaborate and expensive facility, which
usually is impossible to construct on some ocean in the wilds.

So the majority of all standard hull ships which land for ocean refuelling
on my water world will never take off again, and after a few decades the
oceans will be full of stranded starships. An excellent source of raw ma-
terials on a water world, where seafloor mining would be more expensive
than scavenging those starships.

All that is left to do is to design a Starship Scavenger career for my water
world's colonists, and their economy will boom.

 

[atpollard]

Again 'standard hull' is like our space shuttle... some maneuverability

Not per MGT rules. Streamlined hulls have lifting surfaces. Not standard hulls.

Yup.
And Ironically, the wings on the Shuttle make it much harder to launch since they provide an undesirable lateral force (that must be countered by vectoring the thrust) as the craft rises vertically through the air.

There was a good reason that the original Shuttle concepts wanted to launch 'like an airplane'.

A cone on a cylinder is an ideal shape for vertical launch, that's why it is chosen so often in real life.

 

[DFW]

Yup.
And Ironically, the wings on the Shuttle make it much harder to launch since they provide an undesirable lateral force (that must be countered by vectoring the thrust) as the craft rises vertically through the air.

There was a good reason that the original Shuttle concepts wanted to launch 'like an airplane'.

A cone on a cylinder is an ideal shape for vertical launch, that's why it is chosen so often in real life.

Yes, it is called induced drag. But, since MGT space ships use anti-grav drives (per the rules) and don't use rocket reaction drives that must be pointing in the "right direction" it is moot anyway.

 

[phavoc]

So I guess its settled? Add this to the list of "Things to be Corrected in Starship Design"?

 

[rust]

So I guess its settled? Add this to the list of "Things to be Corrected in Starship Design"?

I would see it this way, although at least one person is very unlikely to
agree.

 

[DFW]

So I guess its settled? Add this to the list of "Things to be Corrected in Starship Design"?

Yes. I think if you remove the one paragraph requiring that standard hulled ships require "launch facilities" most would be handled.

 

[far-trader]

So I guess its settled? Add this to the list of "Things to be Corrected in Starship Design"?

lol :wink: I doubt it will be so easy

I have a word or two yet as a final summation rebuttal, but I'm too short on time at the moment.

 

[rust]

I have a word or two yet as a final summation rebuttal, but I'm too short on time at the moment.

I am highly unlikely to change my mind. In the Classic Traveller adventu-
re Broadsword, written by Marc Miller, a definitely not streamlined merce-
nary cruiser lands on Garda Vilis and takes off again, obviously without
any problems. Frankly, if Marc Miller's unstreamlined starships can do it,
so can mine. :wink:

 

[simonh]

I prefer to assume that spaceship drives are designed to be able to exert enough lateral thrust to allow ships to land and takeoff belly-down under power.

Perhaps they can only do this safely for short periods, with higher G-rated drives being more capable in this regard.

Simon Hibbs