Escape Velocity Problem Returns in T5!

[esampson]

. . .So, a ship with 0.01G thrust but standard lifters is limited to worlds under 0.5G. A 1G drive is limited to 50G's... making skimming easy. . .

CG lifters are pretty much unnecessary for skimming. All a ship needs to do to skim is have a stable orbit then dip it down into the upper atmosphere. The gravitational field of the planet will largely be irrelevant as the concern of the pilot will be to make sure he remains high enough up that the thrust of his engines can offset the atmospheric drag.

That isn't to say you couldn't use CG lifters while skimming. You could just hover in place while sucking up atmosphere or use them in place of the maneuver drive to regain altitude (by suddenly lowering the gravitational attraction on the ship the lateral motion of the skim should push it up into a higher altitude). Just saying that they aren't at all necessary for skimming.

 

[mike wightman]

You do not need contra grav lifters, all you need is a streamlined hull that generates lift.

Vey few modern planes generate anywhere near 1g thrust, but they can take off just fine, and reach a pretty decent altitude.

Now the laws of physics kick in yet again, gravitational force from the planet falls off with distance (squared), the air thins so that you have less air resistance - net effect you get faster and climb yet higher.

As you climb higher you achieve an orbital velocity, then enough to break orbit. That's what constant acceleration at 1g can do.

An airframe hull will get even more lift than a streamline hull an thus will be able to achieve a higher air speed, reach high altitude faster, reach orbital velocity sooner and achieve escape velocity.

 

[esampson]

Before anyone asks the obvious question, the reason you cannot simply fly a jet aircraft into space is related to the engines. Jet engines need a certain amount of air to function and as they move further away from whatever their optimal altitude is towards their operational ceiling their output decreases. You can plot out the output over altitude as a graph and what happens is that near the end of the curve the output drops off faster than the air resistance drops. At some point in there the plane reaches equilibrium and it can't appreciably gain any more altitude.

As altitude is gained and air thins a plane will lose lift and will need to fly faster to maintain the lift. However, both the formula for lift and for aerodynamic drag use the square of the velocity which means that they essentially will cancel out. If a plane can generate enough lift to ascend at 80% of its maximum optimal output it will always be able to generate enough lift to ascend at 80% of its maximum optimal output. Whether the plane is at 500 feet or 50,000 feet is irrelevant as the plane will simply travel a great deal faster at 50,000 feet, which it will do since there is far less air resistance.

Eventually the speed of the plane will become great enough that centripetal force rather than lift is causing it to gain altitude (this occurs at the Karman line). At that point the plane will still not be in a stable orbit since if it cuts off the engines the air resistance will slow it back down, but stable orbit isn't terribly far off.

 

[Supplement Four]

Those four* worlds in the entire sector, and none of them are on a major X-Boat route (as the X-Boat routes are used as major trade lanes).

No they're not. Or at least, they shouldn't be. X-boat routes are mainly four-parsec jumps; major trade routes are mainly two-parsec jumps (and three-parsec jumps if you're in a High Guard ship design paradign universe). Trade networks and the X-boat network will overlap, of course, since the X-boats touch on important worlds and many important worlds are big trade worlds too. But you'll be getting practically no trade along the X-boat route through Lanth/Lanth, for example.

X-Boat routes do form the basis for major trade routes. See page 150 of TTB--

XBoat Routes: The heavy line connecting several worlds are express boat routes providing communications between worlds of the Imperium. These routes are also common trade and transport routes with regular commercial transportation provided by one or more transport megacorporations.



Also see page 81 of TTB under Communication Routes.

See page 136 of TTA, where the major trade routes of the Aramis subsector are discussed (they follow the xboat routes).

 

[Vladika]

Anybody remembering this guy named Bernoulli? His law has just a wee bit to do with airfoil lifting principles.

 

[esampson]

Anybody remembering this guy named Bernoulli? His law has just a wee bit to do with airfoil lifting principles.

Sure, but it doesn't change the physics that the maximum velocity of the aircraft goes up at the same rate as the minimum airspeed (assuming the efficiency of the engine doesn't change).

 

[Vladika]

Sure, but it doesn't change the physics that the maximum velocity of the aircraft goes up at the same rate as the minimum airspeed (assuming the efficiency of the engine doesn't change).

Until it get's to the point where there is no more lift to be had. Atmosphere thins out and that's all she wrote. Otherwise we'd have had no need for those big Saturn 5s and we'd just fly to the moon. All jet aircraft have a maximum ceiling. Let's just leave prop plans out of this for obvious reasons.

 

[rancke]

X-Boat routes do form the basis for major trade routes. See page 150 of TTB--

XBoat Routes: The heavy line connecting several worlds are express boat routes providing communications between worlds of the Imperium. These routes are also common trade and transport routes with regular commercial transportation provided by one or more transport megacorporations.

That's what it says all right. The problem is, what it says makes no sense for the reason I gave. X-boats are jump-4 routes. Trade routes are J2/J3 routes. So while the twain will sometimes meet, they won't ever follow each other deliberately.

See page 136 of TTA, where the major trade routes of the Aramis subsector are discussed (they follow the xboat routes).

No they don't. For one thing, the X-boat routes in Aramis subsector are few, incongruous, and does not cross the subsector at all. So most of the trade routes have no X-boat routes to follow in Aramis subsector.


Hans

 

[Vladika]

X-Boat routes do form the basis for major trade routes.

Trade routes run from market to market (no matter where Marc decided to draw a line). X-Bout runs attempt to maximize information flow among government and military establishments. "Topography" of space does require lower than J4 runs (Something about those nonexistent roads, hills and trees from another thread...)

Co-existing runs are simply coincidental and a matter of "topographic" convenience.

Hans is correct.

 

[Supplement Four]

Hans is correct.

Only in his TU. I've reported canon for the OTU.

 

[rancke]

Only in his TU. I've reported canon for the OTU.

The thing is, I have also reported canon for the OTU. Ship design canon. X-boat canon. Trade route canon. The statement you've reported is in conflict with these other parts of canon. And with a canon conflict where one part doesn't make sense, that's the part that is wrong[*].

[*] As opposed to canon conflicts where both parts could be true, just not in the same universe. Those are trickier to resolve.​

Hans

 

[Supplement Four]

The thing is, I have also reported canon for the OTU. Ship design canon. X-boat canon. Trade route canon. The statement you've reported is in conflict with these other parts of canon. And with a canon conflict where one part doesn't make sense, that's the part that is wrong
[*].

[*] As opposed to canon conflicts where both parts could be true, just not in the same universe. Those are trickier to resolve.
​

Hans

Point me to where you cite canon. Page number?

 

[rancke]

Point me to where you cite canon. Page number?

No. You know perfectly well where these things are described. I can't be bothered to spend the time telling you what you already know.

Tell you what, though, I'll provide the references to refute your claim about the X-boat routes and the trade routes in TTA because I have it right at hand:

X-boat routes in Aramis subsector: p. 17.
Trade routes in Aramis subsector: p. 136.

EDIT: It turns out that the X-net is actually composed of jump-6 trunk lines between major hubs and lesser jump ships distributing news out from each hub.

I quote from BoJTAS#2, p. 13:

"The xboat network was established to provide the fastest possible transmission of information..." (emphasis mine)

"The operation [...] provides the fastest possible facsimile information transfer between worlds." (emphasis mine)​

It is trivially easy to map out a network that will provide the fastest possible information transfer. It involves jump-6 ships for most of the journey, of course.

Q.E.D.


Hans

 

[Supplement Four]

No. You know perfectly well where these things are described. I can't be bothered to spend the time telling you what you already know.

And, Hans, you know perfectly well that if I said that time in Jump Space equals a number of weeks equal to the number of parsecs traveled--so that J-1 is one week, J-2 is two weeks, J-3 is three weeks--that it's not canon just because I said it is and because it makes sense to me.

You are refuting that canon says major trade routes generally follow the X-Boat lanes. I've provided proof that they do, indeed, mark major trade lines.

It's not something I'm saying just because it makes sense to me.

 

[rancke]

You are refuting that canon says major trade routes generally follow the X-Boat lanes.

Not so. I'm claiming that the canonical statement that major trade routes generally follow the X-boat lanes is flawed.

I've provided proof that they do, indeed, mark major trade lines.

No, you've provided evidence that they mark major trade lines. Just as I've provided evidence that the X-boats involve jump-6. It says so in black and white in the canon statement that I quoted. Fastest possible. Not fastest practical or fastest possible with jump-4[*]. Only, the evidence is flawed. Just as your evidence is flawed. Hence neither statement constitute proof of anything.

[*] Indeed, many of the X-boat routes marked on canon maps aren't even the fastest possible with jump-4.​

I can provide you with canon evidence that the Magihz took place in -927. I can also provide you with canon evidence that it took place in -925. I can also provide you with evidence that it took place in -924. Two of those statements must be wrong, however canonical.[**]

[**] There are a lot more statements that says -924 than there are statements about -925 and -927, so personally I go with -924.​

I can provide you with canon evidence that the four worlds the Darrians and the Sword Worlds fought over were Terant 340, Torment, Trifuge, and Cunnonic. I can also provide you with canon evidence that the four worlds the Darrians and the Sword Worlds fought over were Entrope, Winston, Anselhome and Torment. Multiplke reference for both versions, actually. One of those two statements must be wrong, however canonical.[***]

[***] Both versions have multiple statements supporting them, but personally I think the Entropic worlds win on points. ​

It's not something I'm saying just because it makes sense to me.

Canon that doesn't make sense is not good canon.


Hans

 

[Supplement Four]

Canon that doesn't make sense is not good canon.

We're down to opinion, here. It makes enough sense to me. I buy what it says.

 

[rancke]

We're down to opinion, here. It makes enough sense to me. I buy what it says.

Actually, we're down to logic. It makes sense to you that trade follows routes involving jumps that the ships can't perform? Because it makes sense to me that trade won't follow routes involving jumps the ships can't perform.


Hans

 

[Supplement Four]

It makes sense to you that trade follows routes involving jumps that the ships can't perform?

It makes sense to me because the major trade routes are used mainly by the big MegaCorp ships that can perform the jumps. And, canon doesn't say that the major trade routes are exactly the X-Boat routes. Canon says that X-Boat bases are on major trade routes, and it says that major trade routes generally follow the X-Boat lanes.

The tramps and ships with lower jump capabilities service what they can--major trade routes when possible, off the major lanes as necessary.

And, the major trade routes aren't the only trade routes that exist. The major trade routes are those with high traffic from the big MegaCorp ships. Plenty of minor trade routes exist--off the X-Boat lanes--as shown in TTA.

 

[rancke]

It makes sense to me because the major trade routes are used mainly by the big MegaCorp ships that can perform the jumps.

I'm sorry, I see that I skipped a couple of steps in the chain of logic:

* J2 and J3 ships carry cargo at a cost per parsec that's lower than J4 ships. (Ship design rules).

* Most long-distance cargo carriers, whether owned by megacorps or by fledgeling lines or any size company in between, are not going to be J4 because J4 ships carry cargo at higher cost per parsec than J2 and J3 ships. It has nothing to do with how big and wealthy a company is, it is still not going to spend money it doesn't have to spend. (Simple logic).

* Most long-distance cargo carriers will therefore be J2 or J3 and hence will not be following X-boat routes deliberately. There will be some correlation because many X-boat nodes are also major trade worlds, but the correlation will not be the result of following the X-boat routes. As evidence we have the trade routes in Aramis that does not follow the X-boat routes and the trade routes in Lanth that would not follow the X-boat routes there either.

And, canon doesn't say that the major trade routes are exactly the X-Boat routes. Canon says that X-Boat bases are on major trade routes, and it says that major trade routes generally follow the X-Boat lanes.

Yes, follow the X-boat lanes. As in cause and effect. But the trade routes do not follow the X-boat lanes from Ivendo to D'Ganzio to Lanth to Ghandi to Dinomn, so they? At least, I hope you're going to claim that they do. Or from Aramis to Teh to Pretoria to Ash to Marz to Junidy?

The tramps and ships with lower jump capabilities service what they can--major trade routes when possible, off the major lanes as necessary.

Major trade routes isn't about the size of the jumps. It's about the volume of shipping. Which makes them J2 and J3 routes, because most long-distance trade will go by J2 and J3 ships. Because J2 and J3 shipping is cheaper than J4 shipping.


Hans

 

[esampson]

Until it get's to the point where there is no more lift to be had. Atmosphere thins out and that's all she wrote. Otherwise we'd have had no need for those big Saturn 5s and we'd just fly to the moon. All jet aircraft have a maximum ceiling. Let's just leave prop plans out of this for obvious reasons.

No. That's the point that you are missing. Technically you never completely leave the atmosphere, you just drop down to a point where the atmosphere is so low that for all practical purposes we treat it as 0. Even in interstellar space there is a weak 'atmospheric' pressure caused by those 20-50 atoms per cm³. Those scattered atoms will provide lift just like they will at more normal atmospheric pressures, the only thing is that the lift they provide is incredibly minute.

Fortunately the air resistance is also incredibly minute so a ship that maintains the same amount of thrust as what it needs to ascend in the normal atmosphere will end up travelling so mindbogglingly fast that that minute amount will turn into real lift.

The formula for lift is F_L = (1/2) d v² s C_L with d being the density of the medium, s being the surface area of the wing and C_L being the coefficient of lift.

The formula for drag (using the same symbology and similar sequence) is F_D = (1/2) d v² a C_D where a is the area of the object and C_D is the coefficient of drag.

This means that as d decreases v will increase in order to keep F_D the same (since the thrust of the engine remains constant), and because of how the math works it increases at exactly the rate it has to in order to maintain F_L.

The reason jet aircraft have maximum ceilings is because they are still air-breathing engines. Take one out to the interplanetary medium and it won't even ignite. As the plane moves higher and higher above the engine's optimal altitude (I presume that most jet engines are probably not tuned to be at their most optimal at sea level) their output decreases. This means that F_D also decreases as they gain altitude and so while v might increase for a while as the plane goes higher it won't increase fast enough to maintain F_L. Long before the engine simply cuts out from lack of atmosphere the plane will reach an equilibrium where it will be unable to gain altitude. (This is in reference to a powered ascent. It is entirely possible that some jets may be able to make ballistic ascents that allow their momentum to carry them past the equilibrium point to the point where their engines cut out, but that's not what is being talked about).

Long before you reach interplanetary medium, however, you will cross the Karman line. This is the point in which the velocity of the plane must be so high to maintain lift that the plane is already travelling at orbital velocity and so no longer needs any lift to continue to ascend. It simply needs to increase velocity like any other orbital body.

The primary reason we need the big Saturn V rockets in the real world is because of what is known as specific impulse and the ideal rocket equation. Basically it says that because the amount of thrust produced in relation to the amount of mass expelled (the specific impulse) is relatively low (in relation to theoretical propulsion sources, not in relation to something like a modern car or jet) you have to carry enormous amounts of fuel in order to reach escape velocity. Ships in Traveller have either effectively infinity specific impulse or extremely high specific impulse depending on how you view it (you could arguably create a specific impulse from the amount of fuel required to run the powerplant and maneuver drive of the ship). If you could effectively put an engine with a similar specific impulse and that did not lose efficiency as it gained altitude on a jet then it could simply fly into space, even if the engine's power output was no greater than that produced by the conventional jet engine (i.e. it only has to be a fraction of a G since these don't have to be the jet engines on a fighter. They could be the jet engines on a 747).