Sling-shot Maneuvers

[SSWarlock]

I'm at a loss on how to handle a combat situation so I'd thought I'd submit it to this forum for discussion.

1) How would a GM account for a ship using a planet's gravity well to sling-shot away from incoming missiles if he/she is using range bands to manage ship combat?
2) Can the missiles easily perform the same maneuver to follow? Would such maneuvering be limited to "smart" missiles? If not, what would be the task rolls for both smart and non-smart missiles?

 

[Wil Mireu]

I suspect that slingshot manoeuvres would take place over too long a timescale to be possible in combat (each combat round is 6 minutes, slingshots usually take hours to complete, and would just take the ship out of the combat completely anyway).

See http://en.wikipedia.org/wiki/Gravity_assist for more info.

 

[Galadrion]

Honestly, if an incoming missile is low-tech enough to be defeated by a slingshot maneuver, then it's not going to have any real chance of hitting an M-drive vessel anyway, unless the target's pilot really screws up and ducks right into the missile. When you have targets and ordinance all operating in a constant-boost multiple-G regime, the difference that an orbital acceleration rate would make is negligible. By the time it would become significant, you'd already be so deep inside the atmosphere that drag would be a much bigger factor - and using reentry as a maneuver to spoof an incoming missile sounds like a really effective way to become a crater.

 

[Wil Mireu]

Honestly, if an incoming missile is low-tech enough to be defeated by a slingshot maneuver, then it's not going to have any real chance of hitting an M-drive vessel anyway, unless the target's pilot really screws up and ducks right into the missile. When you have targets and ordinance all operating in a constant-boost multiple-G regime, the difference that an orbital acceleration rate would make is negligible. By the time it would become significant, you'd already be so deep inside the atmosphere that drag would be a much bigger factor - and using reentry as a maneuver to spoof an incoming missile sounds like a really effective way to become a crater.

Um... sorry, but do you actually know what a slingshot manoeuvre is? I would really suggest reading the link I posted.

It's when you use a planet's gravity to increase (or decrease) your velocity. It's not done anywhere near the atmosphere (not unless you want to burn up and die. Or possibly aerobrake).

 

[rust]

How would a GM account for a ship using a planet's gravity well to sling-shot away from incoming missiles if he/she is using range bands to manage ship combat?

This is the kind of player idea where I hand the players paper,
pencil and calculator and ask them to wake me up when they
have found a plausible solution. 8)

 

[locarno24]

Wil Mireu is right.

At a fundamental level, a 'slingshot' is using a planet's gravity-at-current-orbital height.

It's like solar sails - useful in contemporary astrogation because it's significant amounts of 'free' acceleration that doesn't need you to burn fuel, but essentially stationary in traveller space combat terms

With a traveller setting, you've got 1 earth-g-at-planetary-surface acceleration available, indefinitely, on tap. The kind of acceleration you get from a slingshot at orbital altitudes would be unimpressive for a fat trader and a 10G missile really wouldn't give a pair of fetid dingo's kidneys. At best, at absolute best, it gives you a point of thrust for dodging over and above what's available for your engines. But since the acceleration is entirely predictable, I'd hesitate to even offer that.

Can the missiles easily perform the same maneuver to follow?

Depends how smart you think a non-smart missile is. But once again, at the level of acceleration a traveller ship-to-ship missile is capable of, it's like trying to deflect a longbow arrow by blowing on it sideways.

 

[Galadrion]

Wil - I am aware of what a slingshot maneuver is. Apparently, you didn't even read all of your own source; down in the article, in the section about "Limits of", is this:

Another limitation is the atmosphere, if any, of the available planet. The closer the spacecraft can approach, the more boost it gets, because gravity falls off with the square of distance from a planet's center. If a spacecraft gets too far into the atmosphere, the energy lost to drag can exceed that gained from the planet's gravity.

My point is that, by the time the boost of the planet's gravity becomes significant compared to the boosts involved with M-drive platforms (and both starships and missiles qualify), you are already so far into the gravity well that atmospheric drag exceeds any benefit from the slingshot.

 

[Wil Mireu]

Wil - I am aware of what a slingshot maneuver is. Apparently, you didn't even read all of your own source; down in the article, in the section about "Limits of", is this

I did read that. That's why I mentioned aerobraking, which is in the very next sentence that you didn't quote here. Whatever you were describing certainly wasn't anything to do with gravity assists though.

My point is that, by the time the boost of the planet's gravity becomes significant compared to the boosts involved with M-drive platforms (and both starships and missiles qualify), you are already so far into the gravity well that atmospheric drag exceeds any benefit from the slingshot.

And my point is that you don't have to be anywhere near the atmosphere to gain a lot of velocity to do a gravity assist. You're correct in that M-Drives can potentially provide greater accelerations though.

 

[SSWarlock]

It seems the consensus is as a combat maneuver, slingshotting is too slow and weak to be useful. Very good. Thanks, everyone.

 

[phavoc]

I'm at a loss on how to handle a combat situation so I'd thought I'd submit it to this forum for discussion.

1) How would a GM account for a ship using a planet's gravity well to sling-shot away from incoming missiles if he/she is using range bands to manage ship combat?
2) Can the missiles easily perform the same maneuver to follow? Would such maneuvering be limited to "smart" missiles? If not, what would be the task rolls for both smart and non-smart missiles?

1) Depending on your velocity, the maneuver might be incorporated into your turn. But you'd have to already be moving at a pretty fast clip (i.e. you were incoming to the planetary body already, not just sitting in orbit). But for the most part the combat structure of Traveller doesn't take into account orbital mechanics like this, so if you want to do it, I'd say look outside the Traveller ruleset for one that does incorporate it.

2) Again, Traveller combat system doesn't really take this into account. The "smart" missiles get another shot at a target if they miss (which also doesn't take into account orbital mechanics). "Dumb" missiles get one attack run. Could they do something like this? Sure, there's no reason why not. Onboard computing power will be pretty high compared to systems of today, and if it's smart enough to figure out it's way in space, it should be able to continue to follow the target. Then again, maybe the sensor package is too basic for that, and it can't unless the missile has an upgraded targeting/sensor package added. If it was controlled by the launching ship, then probably wouldn't be too much of an issue. But that's more complexity than you probably want to interject.

As far as how far into/does a ship or object go into the atmosphere to do a slingshot, that's really more a question of the structure of the ship and the atmosphere of the planet. A planet like Earth has a much denser atmosphere, so naturally you can't go as deep into it as you could a gas giant's. So that's a "it depends" type of question. Without more detail the answer is a qualified "maybe". And don't forget if you do enter the atmosphere you also run the risk of bouncing off due to your entry angle (or conversely, finding yourself too deep and you go down instead of up...).

And.... don't forget some ship structures take entry into the atmosphere and maneuvers inside of it far better than others.

Yay for complexity!

 

[Infojunky]

I'm at a loss on how to handle a combat situation so I'd thought I'd submit it to this forum for discussion.

1) How would a GM account for a ship using a planet's gravity well to sling-shot away from incoming missiles if he/she is using range bands to manage ship combat?

A pilot roll..... Or what ever is more dramatic in the game.

2) Can the missiles easily perform the same maneuver to follow? Would such maneuvering be limited to "smart" missiles? If not, what would be the task rolls for both smart and non-smart missiles?

Honestly I would say they could, with that standard command guided missiles I would have the shooting ship roll to maintain control of the missiles during the maneuver, "smart" missiles on the other hand I would allow to tag along.

Mostly my answer is what is best for your game. All the debate here is just that, debate.

 

[locarno24]

Of course, there is a different question on this subject where slingshots are more relevant.


This is a question for all you well-read "I've been doing this for 3,456,781 editions since Marc Miller was three years old" Traveller types, who've been through the background with a fine toothed comb, and also have a bit of a practical physics background.

As I understand it, a gravetic M-Drive, when powered up, creates a localised gravity well in front of the ship that the ship then 'falls' towards (but never catches up to, because it drags the projector, and hence the gravity well's locus, with it as it does so).

Since the gravity well is the equivalent of a given 'virtual mass', the gravetic force is directly proportional to the mass of the ship, hence acceleration is the same regardless of its actual mass - which is why the rules don't care if you're stuffed to the gunnels with prefabricated bonded superdense plates or running completely empty.

The question, however, is this: who else sees/experiences the drive effects?

I'm talking about something akin to the Honor Harrington concept of 'wedge interference'; if a ship is a few hundred metres off my port side - because we're both coming in to dock, for example - am I going to start experiencing the acceleration from their gravetic drive? Equally, a localised 3G well sufficient to heft a starship about hanging just off the ship's bow is going to cause some bloody wierd atmospheric turbulence.

The reason I ask, in the context of this thread, is this - is it practical for ships; especially small craft 'skin dancing', to 'slingshot' themselves - and this time a genuinely meaningful 3-6G slingshot - around other ships?

 

[Wil Mireu]

That's the first I've heard of that explanation for how it works. As far as I can recall, gravitic M-Drives have not been very well explained anywhere except in TNE's Fire Fusion and Steel.

Artificial Gravity is described there (pg 73) as being a "force which could either push or pull and which acted on a gravitational field of a mass". Thruster plates are an extension of that, in which "the force generated by the drive pushed on the actual thruster plates of the ship itself". It's a reactionless drive though that just converts energy into thrust, and essentially it's like the ship is "pulling itself along with its bootstraps" (which doesn't really make any physical sense, but the text is honest enough to say that too).

Either way, there's no "mass or gravity well in front of the ship" involved at all, so your question simply doesn't apply.

 

[SSWarlock]

The start of a discussion on the nature of gravitic M-Drives has brought to mind a similar discussion on the Traveller Mailing List 'way back on '98. I'm going to post what I gathered from that discussion in a new thread in the hopes it can add something useful..or at least lead to some fun mental exercise.

 

[alex_greene]

WilMy point is that, by the time the boost of the planet's gravity becomes significant compared to the boosts involved with M-drive platforms (and both starships and missiles qualify), you are already so far into the gravity well that atmospheric drag exceeds any benefit from the slingshot.

Unless it is a vacuum world or moon ...

 

[SSWarlock]

Unless it is a vacuum world or moon ...

"That's no moon."
- Han Solo


(Sorry. Couldn't resist.)