1g Ships and Size:7 worlds...

[Grav_Moped]

I suspect it's a case of "Ships must be able to land, so the rules are wrong".

Wouldn't be the first time.

Actually, it might have been. XBoats came later.

 

[Captain_Ahab]

I borrowed a friend's copy of LBB

For what it's worth, LBB (77' I believe) rules for vector movement with the planetary gravity templates makes it clear that a 1g ship cannot really take off from a world size 8 or greater
But that's okay, because all of the small craft in the book have more than one g acceleration except the life boat
aka, Interface craft

ships may be streamlined to allow entering an atmosphere for landing

any ship may do aero-braking by vectoring close enough to a planet

any ship can do wilderness refueling

A foamed atmospheric reentry ablation shield will burn up if atmosphere is entered with a vector exceeding 12,000 mph (2" game scale) or ~5,400m/s -- Mach 15

everything after this was someone's houserule, but with some of those houserules being made official by getting published by GDW

 

[Spinward Flow]

A key point in my proposal is that the upper constraint is that it's never enough to affect LBB2 space combat maneuvering around planets (otherwise, it would be reflected in the rules -- and it isn't). So, it wouldn't affect operations in very high gravity fields, because doing so would require enough effect to affect movement in those conditions.

So ... rather than being a CONSISTENT problem to deal with, planetary gravity is more like a "bookkeeping nuisance" that can be handwaved away as inconsequential whenever the Players and/or Referee just feel like ignoring planetary gravity wells, eh?

Um ...
Have fun in Your Traveller Universe, I guess?



"Alright, who left the gravitational constant of the universe ON again?"
{ flicks switch }
"Ah. Much better!"

 

[Grav_Moped]

So ... rather than being a CONSISTENT problem to deal with, planetary gravity is more like a "bookkeeping nuisance" that can be handwaved away as inconsequential whenever the Players and/or Referee just feel like ignoring planetary gravity wells, eh?

Honestly, yeah.

The antigrav that 1G ships have, is enough to get them off the ground and flying, because that's how most Traveller ships are drawn. Even those that have more than 1G acceleration (or only 1G when landing on planets of Size 7 or less) are usually shown landing at right angles to their nominal thrust lines ("belly-lander" orientation), which should be impossible given aerodynamics and the typical pad/skid landing gear depicted.

However, whatever antigrav they have is also not enough to affect maneuver under LBB2, or it would do so and the rules would reflect that.

This is science fiction, and concessions get made for artistic purposes.

 

[atpollard]

CT LBB2:77 Horizontal Takeoff using STARSHIP COMBAT rules and Vector Movement.

Ship = 1G
TIME: 1 turn = 10 minutes; 6 turns = 1 hour
DISTANCE: 1” = 1000 miles
1G x 1 turn = +2” vector
PLANETARY TEMPLATE (World = size 9):

• Diameter (D) = 9000 miles = 9”
• Radius (R) = 4500 miles = 4.5”
• Density (K) = 1
• Gravity (G) = K x R/4 = 1.125
• Mass (M) = G^3 = 1.424
• 1.125G Band (L1.125) = 4 x sqrt (M/1.125) = 4.5” radius
• 1.1G Band (L1.1) = 4 x sqrt (M/1.1) = 4.551” radius
• 1G Band (L1) = 4 x sqrt (M/1) = 4.774” radius
• 0.9G Band (L0.9) = 4 x sqrt (M/0.9) = 5.031” radius
• Circumference (C) = 3.14 x D = 28.26”

• TURN 0: vector = 0” (x), position: x=0, y=4.5” … ship at rest at top of world template.
• Turn 1: vector = 2” (x), gravity= -2.25” , x=+2”, y=4.5” … ship travels horizontally 2000 miles along the surface of the planet with gravity (y vector) preventing it from taking off and the surface of the planet preventing it from moving lower than radius 4.5” as it accelerates to a velocity of 2” with a vector tangential to the surface of the world.
• Turn 2: vector = 4” (x), gravity= -2.25” , x=+6”, y=4.59” … ship travels horizontally 6000 miles and breaks free of the planetary surface as the planet with gravity (y vector) draws it back to a radius of 4.59” (falling between the 1.1 G band and the 1.0G band).
• Turn 3: vector = 6” (x), gravity = -2.2” , x=+12”, y=6.44” … ship travels horizontally 12000 miles and breaks free of the planetary gravity (y vector) draws it back to a radius of 6.44” (falling outside the 0.6 G band. The ship has made orbit under the LBB2:77 Vector Movement rules.

One may argue that the “runway” is impossibly long, to which I would respond that this is a simplification and even a modicum of atmospheric lift generated by the body at hypersonic speeds (speed per the Vector Rules) would shorten the takeoff distance … or perhaps they do skip a fifth of the way around the world on the ocean. These are issues ignored by the Vector Movement rules. What the Vector movement RAW do show is that a 1G ship cannot employ a vertical takeoff and it can employ a horizontal takeoff to reach ORBIT from the surface of a size 9 world.

[I drew it graphically but merely presented the results in distance from start point (x) and radius from center of world.]

 

[Condottiere]

Taken to its logical conclusion, you can use a 1G ship to maneuver inside the gravity well of a Large Gas Giant (such as Jupiter) with impunity ... or within "contact range" of stellar photospheres ... because the 1G is "proportional" to the gravity well, rather than any kind of absolute value, regardless of local conditions.

You can make such an argument ... but it passes neither the laugh test nor the roll on the floor screaming and howling test for intellectual rigor.



I'll just leave this little reminder here in case anyone is unclear on the concept (still) ...

https://imgur.com/9ZqAQFJ

1. I'm thinking slingshots.

2. Regardless of velocity, moving through a gravity well is going to influence your trajectory.

3. Brute force will beat gravity.

 

[AnotherDilbert]

CT LBB2:77 Horizontal Takeoff using STARSHIP COMBAT rules and Vector Movement.

Ship = 1G
TIME: 1 turn = 10 minutes; 6 turns = 1 hour
DISTANCE: 1” = 1000 miles
1G x 1 turn = +2” vector
PLANETARY TEMPLATE (World = size 9):

So your solution is to accelerate to orbital speed on the ground, ignoring friction, and even passing through the planet?

What you described is:

Diving straight into the planet.

Gravity affects you even on turn 1.
Friction ("Atmospheric Braking") exists.

I would call that a fail to take off.

 

[AnotherDilbert]

Let's assume the planet is a perfectly smooth billiard-ball and you can roll on it without friction (leaving RAW and physics far behind):

The length of a line tangential to the planet surface to the 1 G line is about 7½", so you would need a velocity vector of 15" parallel to the surface for the midpoint of the vector to fall outside the 1 G band, freeing you from the shackles of the gravity well (according to LBB2).

You can accelerate at 2" every turn, braked ¼" (⅛ G) by the atmosphere, so resulting 1¾" added velocity per turn. Gravity isn't a factor, as we are supported by the ground (without any friction).

You would need 15" / 1¾" ≈ 9 turns ≈ 1.5 h to achieve that speed.

1.5 h at ⅞ G is... Sorry, I can't be bothered with Imperial units, and as I am not a subject of His Britannic Majesty I have freedom not to.
1.5 h at 0.875 G is a velocity of 1.5 h × 3600 s × 8.75 m/s ≈ 47 250 m/s ≈ 170 000 km/h (~106 000 mph for subjects), travelling a distance of d = at²/2 = 8.75 m/s × 5400² / 2 ≈ 127 500 km.

With a 7000 km world radius, that is a circumference of about 44 000 km.

So, we would need a runway all around the world, and go around it almost three times.


I would call that a slightly problematical approach...

 

[Condottiere]

Ground effect might eliminate the need for an overstretched runway.

 

[kilemall]

I’ve been in previous 1G threads before asking about this. I will re present one idea I had to partially handle the lift issue.

The idea is that ships have fusion plants anyway, meaning some manner of maintaining a ball of compressed plasma economically, and need to be able to handle hot landings/takeoffs and space microdebris.

So they have a built in ability to project a grav deflection or fusion plant field for both purposes, and in the case of atmospheres create a conformal wing for lift.

 

[atpollard]

Sorry, I can't be bothered with Imperial units, and as I am not a subject of His Britannic Majesty I have freedom not to.

… and as your House Rules, you are free to use any units you want. I was just attempting to follow LBB2:77 RAW.

(sorry, I couldn’t resist)

 

[atpollard]

So your solution is to accelerate to orbital speed on the ground, ignoring friction, and even passing through the planet?

What you described is:

Diving straight into the planet.

Gravity affects you even on turn 1.
Friction ("Atmospheric Braking") exists.

I would call that a fail to take off.

You have just PROVEN that Grav cars cannot drive forward.
(I am not sure if congratulations are in order, or if you should re-examine your conclusions.)

In the thrust vector diagram, the vertical vector is the weight of the vehicle supported by its landing gear and wheels (A small increase over its weight on Earth and identical to its weight when parked).
So now show your SECOND turn of thrust and see what happens.

 

[atpollard]

You can accelerate at 2" every turn, braked ¼" (⅛ G) by the atmosphere, so resulting 1¾" added velocity per turn. Gravity isn't a factor, as we are supported by the ground (without any friction).

Where are the rules for Atmospheric Breaking in the LBBs?
House Rule or RAW?

 

[Baroun Tardis]

Not necessarily.

A key point in my proposal is that the upper constraint is that it's never enough to affect LBB2 space combat maneuvering around planets (otherwise, it would be reflected in the rules -- and it isn't). So, it wouldn't affect operations in very high gravity fields, because doing so would require enough effect to affect movement in those conditions.

I'm reading that as sort of like BTRC's VDS's grav vehicles: there's a square of the distance thing such that they work great when being a Luke Skywalker land speeder, but lose lots of efficency as you go higher.

Do we all accept that M-Drives need to be in a gravity well to work? Is that just an MT thing or a CT thing too?

If so, can we say that at less than 0.1D M-drives work really well ?

LBB2 space combat is going to be outside the 0.1D limit, isn't it?

 

[Grav_Moped]

I'm reading that as sort of like BTRC's VDS's grav vehicles: there's a square of the distance thing such that they work great when being a Luke Skywalker land speeder, but lose lots of efficency as you go higher.

Do we all accept that M-Drives need to be in a gravity well to work? Is that just an MT thing or a CT thing too?

If so, can we say that at less than 0.1D M-drives work really well ?

LBB2 space combat is going to be outside the 0.1D limit, isn't it?

Might work as a concept.

I'm just trying to come up with something that fits into the gaps in the rules that lets things work the way they appear to work without outright breaking things.

And in fairness, on my part it's mostly argumentation for its own sake.

 

[atpollard]

You have made the first order mistake of assuming that all distances everywhere are exactly the same because GRAVITY DOESN'T EXIST nearby to planets. Why do I say that is the inevitable thrust of the argument you are making? Well, because ...

According to LBB2:77 page 11 what is the distance from Surface to Orbit according to the RAW?
According to LBB2:77 page 10 what is the time required for a 1G ship to travel 10,000 km according to the RAW?
In what universe is following the rules printed in the Rule Book a “first order mistake”?

 

[AnotherDilbert]

Where are the rules for Atmospheric Breaking in the LBBs?
House Rule or RAW?

I would say RAW:

LBB2'77, p35:
_ _ Atmospheric Braking: Ships passing very close to the surface of a world with a standard or dense atmosphere may slow their speed through atmospheric braking. lf any portion of a ship’s vector passes within 1/4 inch of a world’s surface, that vector is reduced by 1/4 inch in length.

 

[AnotherDilbert]

You have just PROVEN that Grav cars cannot drive forward.
(I am not sure if congratulations are in order, or if you should re-examine your conclusions.)

Grav vehicles, just like spacecraft or helicopters need thrust greater than local gravity to fly. As the rules (and physics) say. As I have quoted a few times in this thread.

In the thrust vector diagram, the vertical vector is the weight of the vehicle supported by its landing gear and wheels (A small increase over its weight on Earth and identical to its weight when parked).
So now show your SECOND turn of thrust and see what happens.

By RAW, the picture is what happens.

In reality, gravity will force you down as soon as you try to leave the ground, leading to:

Let's assume the planet is a perfectly smooth billiard-ball and you can roll on it without friction (leaving RAW and physics far behind):

The length of a line tangential to the planet surface to the 1 G line is about 7½", so you would need a velocity vector of 15" parallel to the surface for the midpoint of the vector to fall outside the 1 G band, freeing you from the shackles of the gravity well (according to LBB2).

You can accelerate at 2" every turn, braked ¼" (⅛ G) by the atmosphere, so resulting 1¾" added velocity per turn. Gravity isn't a factor, as we are supported by the ground (without any friction).

You would need 15" / 1¾" ≈ 9 turns ≈ 1.5 h to achieve that speed.

1.5 h at ⅞ G is... Sorry, I can't be bothered with Imperial units, and as I am not a subject of His Britannic Majesty I have freedom not to.
1.5 h at 0.875 G is a velocity of 1.5 h × 3600 s × 8.75 m/s ≈ 47 250 m/s ≈ 170 000 km/h (~106 000 mph for subjects), travelling a distance of d = at²/2 = 8.75 m/s × 5400² / 2 ≈ 127 500 km.

With a 7000 km world radius, that is a circumference of about 44 000 km.

So, we would need a runway all around the world, and go around it almost three times.


I would call that a slightly problematical approach...

 

[AnotherDilbert]

Do we all accept that M-Drives need to be in a gravity well to work? Is that just an MT thing or a CT thing too?

No such limitations in CT or MT. MT introduced limitations for grav drives.

If so, can we say that at less than 0.1D M-drives work really well ?

You can say whatever you want, in YTU. By default there is no such mechanism.

LBB2 space combat is going to be outside the 0.1D limit, isn't it?

Very probably, yes.

 

[whartung]

Grav vehicles, just like spacecraft or helicopters need thrust greater than local gravity to fly.

But, again, an Air Raft can reach orbit in <UPP Size Code> hours. There's no mention of different air rafts for different worlds of different gravities.

The antigrav that 1G ships have, is enough to get them off the ground and flying, because that's how most Traveller ships are drawn. Even those that have more than 1G acceleration (or only 1G when landing on planets of Size 7 or less) are usually shown landing at right angles to their nominal thrust lines ("belly-lander" orientation), which should be impossible given aerodynamics and the typical pad/skid landing gear depicted.

However, whatever antigrav they have is also not enough to affect maneuver under LBB2, or it would do so and the rules would reflect that.

Exactly. This is the "fantasy" element of the Traveller universe.

Ships, air rafts, grav vehicles, etc. land and take off with a hum or even a roar, but not with planet incinerating fire. It's family and friends waving goodbye on the tarmac next to the vehicle as it alights into the sky and then engages its main motors to accelerate into a tiny little dot in the distance.

Even the HEPLaR equipped air rafts of TNE are somehow not a significant threat to life, limb, and communities as they flit hither and yon from A to B carrying everything from school children, groceries, and the highest forms of dignitaries.

There's no mention of "Hey, make sure when you're landing on the plain on the wilderness planet you don't cause a range fire." No "Keep back 500ft" stickers on the air rafts. "We have to buy Timmy another hook, he touched the back of the air raft again after school and melted his first one. You'd think he'd have learned when he lost his hand the first time trying to pull the gum off his shoe." No stories of terrorists incinerating starports or landing terminals by lighting off the drives.

Somehow, the fine details of the final aspects of interface (i.e. touching down and taking off) are not utterly fraught with danger and pending disaster. It's a day to day occurrence, happening everywhere, every minute of every day with few headlines to report.

Fusion powerplants don't (and apparently can't) spontaneously explode, leveling large swaths of towns and cities, irradiating hectares of wreckage for centuries. If they did, they simply wouldn't be allowed. But they are allowed, they're everywhere, they're ubiquitous, seemingly available at the local Home Depot.

Similarly with starship interface. It's drama free. A solved problem.

The world of Traveller can indeed be a dangerous place, but apparently not in the limited realm of taking off and landing ships or flying grav vehicles around.