Question: Ships leaving atmosphere

[DFW]

To me there seems to be a major contradiction between these
two chapters.

Yep. The editor thought he/she could make random changes without thinking.

 

[GamerDude]

Without atmosphere everything pretty much gets into orbit the same way... point its nose to the sky and have strong enough engines.

Even an air/raft, or a prospector's buggy on a planet without atmosphe-
re, can reach orbit, and I have never imagined it to point its nose to the
sky or to have unusually strong engines. And I have yet to see any offi-
cial description that a ship's maneuver drive is fundamentally different.

Those use anti-gravity (called contra-grav by some) and not propulsion/thrust.

Again read.

 

[DFW]

Again read.

The modular cutter. It can take off from planets with an at-
mosphere although it has no lift surfaces of any kind, and it has the same
kind of maneuver drive as a ship.

Also: "TL 9: (Pre-Stellar) The defi ning element of TL 9 is the development
of gravity manipulation, which makes space travel vastly safer
and faster."

 

[rust]

Those use anti-gravity (called contra-grav by some) and not propulsion/thrust.

If this were true, and Traveller ships would have to rely on horizontal
thrust only, the chance to get a free trader back into the air after a wa-
ter landing in the wild would be very close to zero, atmosphere or not.
It does not have a configuration that would enable it to skim the water
like a hydrofoil, so it must have some vertical take off capability to get
out of the water, and the only system of the ship which can do that is
the maneuver drive, which happens to be defined as a gravitic drive.

If you think this is wrong, what is your explanation for a starship's abi-
lity to take off from water ?

 

[simonh]

The modular cutter. It can take off from planets with an at-
mosphere although it has no lift surfaces of any kind, and it has the same
kind of maneuver drive as a ship.

According to HG the modular cutter is streamlined, so arguably it has landing gear etc. I don't buy that though, I think you're right on this.

My take is that streamlining just gives enhanced manoeuverability in an atmosphere, and allows the vehicle to go supersonic if it's thrust is 2G or higher. All vessels that aren't distributed hulls have landing gear and can take off ok, atmosphere or no.

I just don't get the controversy over grav vehicles. Gravitic propulsion systems clearly generate thrust, otherwise all grav vehicles would need another propultion system to actualy move.

I'm not exactly sure what 'Contragrav' is supposed to mean - a zero-g field? That would be fine as a variant, cool, I once ran a game in a homegrown setting that had that kidn of gravitic technology, but it ain't the way things are in Traveller as written. I seem to remember this comign up on this forum a while back anyway though, so I'm probably flogging a dead horse on this one.

Simon Hibbs

 

[atpollard]

The real world offers three basic paradigms for spaceships:

1. Horizontal Takeoff/Landing – uses wings and/or lifting body to accelerate horizontally or glide in for a landing – like Virgin Galactic or the StarClipper project.

2. Vertical Takeoff/Landing – uses brute force propulsion to accelerate vertically or slow descent for a vertical landing – like the Lunar Eagle or Phoenix VTOL SSTO project.

3. Crash Landing – there ain’t no way this ship is going to land in one piece – like adding a tug to the ISS and trying to land it on the moon or the Discovery One (HAL) from 2001: A Space Odyssey.

At first I was happy to see that the Core Book seemed to reflect this reality with Streamlined (lifting body shapes), Standard (simple cones and cylinders requiring thrusters to land) and Distributed, but then that one annoying comment about a Cone (like the Phoenix) not being able to take-off on its own dumps a fly in my soup.

Note that Small Craft and Capital Ships do not have this restriction in High Guard – only ‘adventure class’ ships seem so affected.

I choose to view it as yet unpublished errata – of course a Standard Hull can land and take-off in an atmosphere – it just can’t land unpowered (without crashing) like a Streamlined Hull can.

[As an aside, I believe that both cannon-ball manufacturers and Cosmonauts would be surprised to learn that a sphere cannot travel through the atmosphere. Ok, it is not a lifting body like a flattened sphere, but it is capable of atmospheric flight – reality says so.]

 

[DFW]

I'm not exactly sure what 'Contragrav' is supposed to mean - a zero-g field? That would be fine as a variant, cool, I once ran a game in a homegrown setting that had that kidn of gravitic technology, but it ain't the way things are in Traveller as written. I seem to remember this comign up on this forum a while back anyway though, so I'm probably flogging a dead horse on this one.

Simon Hibbs

I think the term is from an earlier version. However, any grav drive is going to be some form of contra (against) gravity. Some people seem to think (incorrectly) that MGT space ships (>TL 8) are using reaction mass propulsion). They aren't. They are using anti-grav drives. There is no need to land "tail" down. They aren't using rockets.

 

[atpollard]

However, any grav drive is going to be some form of contra (against) gravity. Some people seem to think (incorrectly) that MGT space ships (>TL 8 ) are using reaction mass propulsion). They aren't. They are using anti-grav drives. There is no need to land "tail" down. They aren't using rockets.

Yeah, so what is one more handwave about a thruster plate pushing at 90 degrees to itself (plate at back 'lifts' ship vertically).

 

[Egil Skallagrimsson]

I had my "pulling out hair" moment over these rules as written a few months ago, oddly enough over a corsair landing on a planet, like the OP. Ended up scrubbing the "Getting it back into space requires an elaborate lauch sequence and considerable expense" bit, just didn't make sense when the same vessels can refuel at gas giants. The space craft operations section on page 137 makes clear that standard config ships are harder to manourve in atmos, with negative DMs and more skill checks, but by no means impossible to control, so have gone with that, and it works, you just have to be more careful and slower to be safe.

Egil

 

[GamerDude]

I had my "pulling out hair" moment over these rules as written a few months ago, oddly enough over a corsair landing on a planet, like the OP. Ended up scrubbing the "Getting it back into space requires an elaborate lauch sequence and considerable expense" bit, just didn't make sense when the same vessels can refuel at gas giants. The space craft operations section on page 137 makes clear that standard config ships are harder to manourve in atmos, with negative DMs and more skill checks, but by no means impossible to control, so have gone with that, and it works, you just have to be more careful and slower to be safe.

Egil

Actually, the refueling differences of slipstreamed and standard do make a great deal of sense, if it makes sense for YTU to do it differently that's ok too.

As I've said many times before over the past, and every time gotten shouted down: the rules, and canon, establish your baseline for how things were imagined to work by the writers. When you deviate on something for YTU, at least you know what you are deviating from and why.

Let me add, since these forums started I've seen here (and on others) people who have an idea in their head... how they were told it was/works, or they just started doing something a certain way in their TU... and now they will twist the wording and meaning of anything in the rules to make themselves "right", when it's not a matter of right or wrong for their TU but only for when you are discussing what's written in the official books.

Want your ships to fly sideways but when reentering they go tail first? fine in your TU that's how it works just understand how you are being different than the books. That's all. Nothing personal, nothing saying you're smart dumb or just a jerk, etc.

 

[atpollard]

Actually, the refueling differences of slipstreamed and standard do make a great deal of sense, if it makes sense for YTU to do it differently that's ok too.

How does it make sense that a ship can dive deep into the atmosphere of Jupiter, but cannot fly through the atmosphere of Earth?

As I've said many times before over the past, and every time gotten shouted down: the rules, and canon, establish your baseline for how things were imagined to work by the writers. When you deviate on something for YTU, at least you know what you are deviating from and why.

While generally true, how does this apply to the rules that a wedge shaped Standard Hull Small Craft can take off and land in atmosphere, and a wedge shaped Standard Hull Capital Ship can take off and land in atmosphere, but a wedge shaped Standard Hull 200 dTon Starship can NOT take off and land in atmosphere?

 

[rust]

... but a wedge shaped Standard Hull 200 dTon Starship can NOT take off and land in atmosphere?

And since there is a scale from very thin to very dense atmospheres, at
which density of the atmosphere does it become impossible for the ship
to land and take off - it can do so on a vacuum world, will it fail to do so
on one with a very thin atmosphere ?

 

[far-trader]

Actually, the refueling differences of slipstreamed and standard do make a great deal of sense, if it makes sense for YTU to do it differently that's ok too.

How does it make sense that a ship can dive deep into the atmosphere of Jupiter, but cannot fly through the atmosphere of Earth?

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?

 

[atpollard]

So who said you had to "dive deep" and where?

From Classic Traveller: The Traveller Book: Pg 51.
"Gas Giants: Most star systems include in their family of planets one or more gas giants - large worlds with hydrogen or methane atmospheres. These gas giants are a valuable source of fuel for starships.
In order to refuel from a gas giant, a ship must move into orbit around it, and then dive deep into its atmosphere with open fuel scoops. The procedure (called skimming) takes approximately eight hours, and results in fuel tanks filled with unrefined fuel."

From MegaTraveller: Imperial Encyclopedia: Pg 64.
"Gas Giant: A large planet with an extensive atmosphere of hydrogen and hydrogen compounds. Starships fuel themselves by diving into this atmosphere and skimming hydrogen from this atmosphere. Jupiter, in the Sol system, is an example of a gas giant."

From Traveller TNE: Traveller The New Era: Pg 220.
"Gas Glants: Most star systems include in their family of planets one or more gas giants - large worlds with hydrogen or methane atmospheres. These gas giants are a valuable source of fuel for starships.
In order to refuel from a gas giant, a ship must move into orbit around it and then dive deep into its atmosphere with open fuel scoops. The procedure (called skimming) takes approximately 10 hours and results in fuel tanks filled with unrefined fuel. Skimming is an Average task using Pilot (Interface/Grav) ."

From Mongoose Traveller: Core Rulebook: Pg 167.
"Gas Giants: A star system may have one or more gas giant planets (similar to Jupiter or Saturn). The presence of a gas giant allows starships equipped with fuel scoops to refuel by skimming; this eliminates fuel cost for the vessel and increases profit. It also allows refuelling at systems that do not have starports. Refuelling in this fashion requires 1–6 hours. Fuel gained by skimming is unrefined."

Where isn’t it mentioned?

Before anyone comments that Mongoose Traveller does not explicitly state that the ship dives deep, let me point out that the ship collects roughly 10% of its total volume per hour in Liquefied Atmosphere! How large do you think those scoops are? That will not be achievable at Mars-like trace atmosphere densities.

 

[GamerDude]

Actually, the refueling differences of slipstreamed and standard do make a great deal of sense, if it makes sense for YTU to do it differently that's ok too.

How does it make sense that a ship can dive deep into the atmosphere of Jupiter, but cannot fly through the atmosphere of Earth?

I know longer know how to take apart this oversimpflication and properly explain it in a way to prevent any twisting of my words to fit whatever rational the reader has. Things like are you FLYING or just so freaking high up from the gravity well yet the atmosphere is dense enough that you can scoop. Shit, several times in the various Star Trek series they would hide in a gas giant or similar yet it took Voyager being specifically designed to land before any starship would even think of entering a 'class m' planet's atmosphere.

As I've said many times before over the past, and every time gotten shouted down: the rules, and canon, establish your baseline for how things were imagined to work by the writers. When you deviate on something for YTU, at least you know what you are deviating from and why.

While generally true, how does this apply to the rules that a wedge shaped Standard Hull Small Craft can take off and land in atmosphere, and a wedge shaped Standard Hull Capital Ship can take off and land in atmosphere, but a wedge shaped Standard Hull 200 dTon Starship can NOT take off and land in atmosphere?

I am not going to, nor have I ever attempted to be an apologist for a company paying an artist for a drawing of a ship, scene from a book, etc without any quality control over how well that drawing matches the supposed specs, mechanics etc. You're right why can't this one vs that one.

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.

In fact, this is why I understand that anti-grav (by the MGT Core Rulebook) is only listed on vehicles like the air/raft and smaller down to the grav belt. The power it takes to generate a field of a certain size is on a logarithmic scale (like the Richter scale, powers of 10). Say you want to put anti-grav on a space yacht... say it is '8 times bigger' than a standard air raft. It's not 8 times the power you need, but maybe 64 times (8 squared) or worse. Move into the sizes of space ships and it only grows worse.

Here is how I am seeing what the MGT books say about gravitic devices, anti-gravity, contra-gravity, and vehicles/ships having it.
1) No where in any of the books have I found the term 'contra-grav'. It doesn't exist. Only the term 'anti-gravity' is ever used. (NOTE: Just found it ONCE, in the description of 'hovercart' but the drive system is 'lifer')
2) Gravitics is the 'study of gravity' which does not automatically mean a gravitic device generates anti-gravity, otherwise the densitometer in the equipment section would generate an anti-gravity field when it is on (it's application of gravitic science is like x-rays or MRI's or ground echo imaging).
3) Devices that have/use anti-gravity have this expressly listed... Air Raft, Grav Belt, etc.
4) Going through the Core Rule Book, Civilian Vehicles, Military Vehicles, CSC, High guard... ONLY vehicles (Hover/Grav tank and under) have a drive system of "grav" meaning anti-gravity. I can't find any aircraft, not even a helicopter that has any kind of grav life/anti-grav in it. The same with space ships and star ships.
5) Most Space/Starships have grav plates for artificial gravity. What would that do if the ship itself had anti-gravity for lift/propulsion? Shut down the plates while the engines/anti-grav was on? ugh.
6. Space Combat: "2. Manoeuvre Phase: The position of ships is changed based on their thrust."

Personally, I can only read how 'anti-grav/grav' is used in all the books one of two ways... either nothing above a tank in size has anti-gravity/grav drive in it, OR the writers really screwed the pooch on how space/star ships are described. Anti-gravity has always been depicted as more of an 'inertia-less' idea, the Star Trek/Star Wars images of ships turning almost on a dime... as opposed to like in the Honor Harrington novels where ships have to change the direction of their thrust to change their direction and the faster you go the wider your turn will be.

Again, I will agree that some of the drawings are screwed up compared to the descriptions.. still 1970's thinking of the universe created by too much Star Trek & Star Wars. Shuttles totally a flying box that can safely fly inside a planet's atmosphere but isn't supposed to have any gravitic lift systems. The Millenium Falcon had to have some kind of anti-gravity lift system because it had zero lift/control surfaces. Yet these are the things that too many drawings and concepts were (and still are) based on.

I don't expect many (if any) people to agree with my evaluation of the material, or actually to give it serious and sincere consideration in the face of what they've already decided is 'how it is'. I've done my homework, my due diligence and I'm confident in what I feel the books say (and from there make decisions on what happens in MTU)


Densitometer pg 93, 96.Uses an object’s natural gravity to measure its density, building up a three dimensional image of the inside and outside of an object.

Air/Raftpg 103) An open-topped vehicle supported by anti-gravity technology. Air/rafts can even reach orbit but passengers at that altitude must wear vacc suits. They are ubiquitous, remarkably reliable and flexible vehicles. (supported but not driven by?)

Grav Floater: (104) A grav floater is a forerunner of the grav belt, a platform
upon which a single person can stand and be carried along. It cannot achieve any great speed but can, like an air/raft, achieve any altitude up to orbit.

 

[far-trader]

<thorough reply snippage>

Where isn’t it mentioned?

First off thanks for the extensive reply. I was obviously operating at least partly under those blinders of habit and first exposure someone mentioned.

Where isn't it mentioned? An excellent question I didn't think I'd have to answer I'll give it a shot though...

First there's CT LBB2 (Starships) of course, which only says "skimming" (also used in all of your answers) which "dive deep" is contrary to the definition of. And no mention of "deep dive" in that.

Ditto CT LBB5 (High Guard). Just "skimming" with the same implied by the term minimal surface (cloud top) action, and again not a peep of "deep dive" in it.

And exactly the same again in CT LBB6 (Scouts) under the description of GGs.

But last (for me, for now anway) and probably the most thorough (as little as there is) notes on the procedure in CT (that I have at hand anyway) is Supplement 5 (Lightning Class Cruisers - from the AHL game) where it says "skim through the atmosphere" and "dives into the gas giant's atmosphere". Not expressly "deep" you'll note. And there's also a bit of contradictory (to the later deep for skimming notes) evidence in the description of planetary ocean refueling making a point of having to "penetrate the atmosphere". Note that, "penetrate" as opposed to "skimming". One is into (dive deep) the other is on the surface (skimming). Even the note about "dives into the gas giant's atmosphere" need not, does not to me, imply any considerable depth. More it reads to me breaking high orbit and moving towards the GG.

Before anyone comments that Mongoose Traveller does not explicitly state that the ship dives deep, let me point out that the ship collects roughly 10% of its total volume per hour in Liquefied Atmosphere! How large do you think those scoops are? That will not be achievable at Mars-like trace atmosphere densities.

How big do you think they are? See what I did there I think they are quite large, based on numerous illos and iirc some specific area calculations in MT? TNE? (both). I'm guessing you think they are quite small.

Let me ask, how fast do you think the ship is going when it is skimming? Or should I say how slow? I think the speed more than makes the difference for the amount of thin atmo sucked through the scoops and compressed into a usable amount of unrefined fuel. In fact I think the speed is required to provide the compression. I suspect to achieve the compression by diving deep you'll be beyond the crush depth of all but the strongest armoured hulls.

I think our views differ too much to be reconciled And I've probably ignored (blinders) all the silly (imo) "deep dive" notes post CT LBBs or I would have remembered them and not wondered where it actually said it

 

[GamerDude]

First there's CT LBB2 (Starships) of course, which only says "skimming" (also used in all of your answers) which "dive deep" is contrary to the definition of. And no mention of "deep dive" in that.

Ok, let me stop you a moment... While I am quite familiar with CT (and have slight familiarity with the others, and ran Gurps:T for a year), I have been specific I'm only talking about the MGT books. Not that I don't respect the older book (oh but I do) it's just keeping the discussion simple (and these are the Mongoose forums).

I think our views differ too much to be reconciled And I've probably ignored (blinders) all the silly (imo) "deep dive" notes post CT LBBs or I would have remembered them and not wondered where it actually said it

I'm not sure if this is meant for me or atpollard, but we can have a discussion without either of us changing our minds... it's the exchange of ideas and the acknowledgment at least of the other person's right to have a differing viewpoint. It is not a "I must be right, I must win, because I'm too immature to do otherwise" situation.

 

[atpollard]

Where isn’t it mentioned?

First off thanks for the extensive reply. I was obviously operating at least partly under those blinders of habit and first exposure someone mentioned.

Actually, those "blinders of habit and first exposure" apply to me as well ...
... I started with CT: The Traveller Book so for me, Starships have always dived deep to skim.

I also recognize that when dealing with Jupiter, there is deep and there is DEEP! While unspecified, I viewed 'deep' as 'Thin Atmosphere' to 'Standard Atmosphere' in pressure and density. I never imagined skimming the surface where the pressure causes the atmosphere to liquify on its own. I viewed SDB as capable of enduring 'bottom of the ocean' pressures. There is a lot of room between 'Thin Atmosphere' and 'Bottom of the Ocean' pressures.

IMO, scooping trace atmospheres in bulk would require ships with Bussard Ramjet type scoops at the front to collect tons of hydrogen gas per hour. I imagine Traveller ships with scoops more like the Beowulf - 10-20% of the frontage area of the ship.

Cutting through a trace atmosphere at high hypersonic speeds or travelling through Standard Atmosphere at sub-sonic speeds would seem to create similar stresses on the ship. That suggests that any ship that can skim fuel should be able to land and take off from Earth.

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

 

[atpollard]

I am not going to, nor have I ever attempted to be an apologist for a company paying an artist for a drawing of a ship, scene from a book, etc without any quality control over how well that drawing matches the supposed specs, mechanics etc. You're right why can't this one vs that one.

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?

 

[rust]

6. Space Combat: "2. Manoeuvre Phase: The position of ships is changed based on their thrust."

It does say nothing about how that thrust is generated. A grav drive ob-
viously has to generate thrust, too, because otherwise grav belts, grav
platforms and grav vehicles would just float, but would be unable to mo-
ve without an additional drive or an outside force.