General How does maneuver drive propel?

[Leitz]

Okay, I may be overthinking this, but I don't understand how multiple turns of maenuver acceleration make the ship go faster than the M rating. If an M1 ship accelerates to max, it's going M1. That's the level of its acceleration; there's no more energy to push out or push against. So a second "turn" of M1 would see it going M1. If you're flying a plane that goes 100 MPH, after three hours, it's still just going 100 MPH. A bigger engine can take a different plane to a different speed, but it still doesn't accelerate past its max.

What am I missing?

 

[AnotherDilbert]

Acceleration is not speed.
Acceleration is change in speed.

Let's say you have a ship with M-1 = 1 G ≈ 1 Gturn / turn (Gturn the speed you get by accelerate by 1 G for one turn).
You start at rest, speed 0.
First turn you accelerate 1 G to speed 1 Gturn.
Second turn you accelerate 1 G to speed 2 Gturns.
Third turn you accelerate 1 G to speed 3 Gturns.
Fourth turn you accelerate 1 G to speed 4 Gturns.
And so on...

There is no speed limit in space, you can go as fast as you like (almost), it just takes a while to get there.

Does that make any sort of sense?

 

[Leitz]

I know that's the book math, but it hasn't ever made sense to me. Consider planetary defense against a long term ship acceleration. The ship could approach the speed of light, and nothing but guesses in math say that it can't go faster. Sensors operate at the speed of radio waves, which are almost the speed of light. That means the sensor could detect the incoming ship before it hit the planet, but it could not relay the threat data any faster than the threat itself. Given machine processing time the sensor data would lag well behind the threat in terms of fractions of a second. What's the effect of a 1000 dT merchant ship hitting a planet? Or even disentigrating the hull in atmo, releasing heavy core inert weapons and nuclear warheads for a high altitude EMP?

 

[Spinward Flow]

If you're flying a plane that goes 100 MPH, after three hours, it's still just going 100 MPH.

Planes flying in air encounter a drag force that limits their top speed.
That drag force "isn't there" in vacuum.

It's a common conceit in movies and anime to show craft in space "flying like airplanes" (Star Wars does this to an almost ridiculous degree, because it's basically WW2 fighter/bombers in space). This leads to the assumption that "constant thrust equals constant velocity equals constant speed" ... because that's how things work IN AIR (see: aerodynamic drag force). But in a vacuum ... you don't have that drag force.

As soon as you get away from the notion that spacecraft in the vacuum of space "behave, move and maneuver" EXACTLY the same way as aircraft do in an atmosphere, you move away from movement dynamics like Star Wars X-Wings (airplanes in space) and get into the realm of Babylon 5 Starfuries (spacecraft in space).

Of course, special effects for spacecraft couldn't even DO proper all aspect 3D viewing of spacecraft using physical models (the model stand gets in the way, limiting camera angles to film with), so if you want to see proper newtonian physics 3D all axes movement of space fighters in space, you HAVE TO move to CGI ... which Babylon 5 did.

I know that's the book math, but it hasn't ever made sense to me.

The vacuum of space CHANGES a LOT of assumptions for "how stuff works" (and moves).

What's the effect of a 1000 dT merchant ship hitting a planet?

Same as a 1000 dT planetoid hitting a planet.
Not necessarily good.

 

[Bartleby]

Back in the 90s the TML would have discussions on what would stop a ship driving an asteroid at near-c speed towards a planet.

I don't know if this comes up in editions beyond CT, but in CT you have to handwave a reason why this never or rarely happens.

 

[Spinward Flow]

what would stop a ship driving an asteroid at near-c speed towards a planet.

The primary answer to the question is NOT one of physics or engineering, because those are "solvable problems" within Traveller.

The real answer to the question of "what can stop it" from happening is less a matter of response (after it has happened) and more a matter of prevention (why it usually isn't done).

Number one reason being that anything "large enough to hurt" moving at near-c speed on impact with a planet will yield an extinction level event ... possibly even turning the planet into a planetoid belt (see: Final War). You don't do that kind of thing to achieve a CAPTURE, you do it to (utterly) DESTROY.

The number two reason being ... it's EXPENSIVE.
You're going to need a "significant maneuver tug" capability (which is specialized and doesn't come for free) to set something like that up ... and A LOT OF TIME.

The speed of light is 299,792,458 m/s.
At a 1G maneuver acceleration of +10m/s², it will require 29,000,000 seconds (8055.55 hours or 335.65 days) to add +299,000,000m/s of velocity to an object ... which should still be NAFAL speed.

Nothing accelerates to near-c speeds "quickly" ... meaning that there is going to be a huge amount of lag time between giving the "Go Order" and when an impact can occur (meaning the "no turning back now" point happens incredibly early in the process). You're also going to need to account for all kinds of "near relativistic" navigational error tolerances that could easily result in a "near miss" rather than an impact (see: SPACE IS BIG).

A MUCH CHEAPER ... FASTER ... and more PRCISE option is ... Mass Drivers from orbit.

Ortillery / orbital bombardment is a MUCH more effective (and quicker!) way to "level" a planetary surface ... in a "bomb them back to the stone age" kind of way ... than trying to deliberately accelerate a rock to near-c speed towards a planet.

 

[mike wightman]

Okay, I may be overthinking this, but I don't understand how multiple turns of maenuver acceleration make the ship go faster than the M rating. If an M1 ship accelerates to max, it's going M1. That's the level of its acceleration; there's no more energy to push out or push against. So a second "turn" of M1 would see it going M1. If you're flying a plane that goes 100 MPH, after three hours, it's still just going 100 MPH. A bigger engine can take a different plane to a different speed, but it still doesn't accelerate past its max.

What am I missing?

Newton's laws of movement.

Law 2

force=mass x acceleration or F=ma

Law1

an object continues in its state of motion unless acted upon by a (resultant) force

a bit of further explanation here, an object often has more than one force acting on them, the resultant force is the overall force that is the result of considering these forces.

So a spaceship is in orbit. For the sake of simplicity we will ignore its circular movement around the planet and assume it has just assumed escape velocity.

It fires its 1g drive, or rather its 1g drive provides a force that accelerates the mass of the ship to 9.8m/s in 1 second.

If the drive shuts off the ship continues on its merry way with a velocity of 9.8m/s - for ever

If the drive continues to apply the same force the ship continues to accelerate, so after 2 seconds the ship now has a velocity of 19.6m/s

For the magic reactionless m-drive provided the maneuver drive can be supplied with energy then the drive will continue to apply a force which will continue to accelerate the ship, once you start to hit relativistic speeds things change.

For a reaction engine there is a top speed which is limited to the speed at which you can throw your exhaust products out the back of an engine (this is a gross simplification).

So can an m-drive get close to c?

According to CT, it's up to you, but there are examples of ships travelling at fractions of c all the way up to 0.9c in the boardgames.

Other iterations of the games have different physics - for example in T5 and MgT the m-drive is only efficient out to 1000D, the TNE HEPlaR drive has to obey the rocket equation so couldn't carry enough fuel to get anywhere near c, that sort of thing.

 

[whartung]

I don't know if this comes up in editions beyond CT, but in CT you have to handwave a reason why this never or rarely happens.

As I understand it, it's "routine" practice in Agent of the Imperium. They seem to routinely drop rocks on planets to great affect. Not necessarily "near C" rocks, but big, accelerated rocks, doing not necessarily extinction level event destruction, but certainly "you may certainly want to reconsider your life choices" destruction.

for example in T5 and MgT the m-drive is only efficient out to 1000D, the TNE HEPlaR drive has to obey the rocket equation so couldn't carry enough fuel to get anywhere near c, that sort of thing.

Potentially a pyrrhic detail.

A TNE scout ship masses 477 tons (empty), and carries 80 GTurns of fuel, with a 2G drive. 40 hours at 2G, with that mass is, ~188 MegaTons of energy.

Mind, it would likely fireball in the atmosphere.

And the 1000D of acceleration (at 2G) bumps it up to ~273 Megatons.

But, the fundamental point being, even with these limitations, ships can still be dangerous.

 

[Enoki]

The limits to a ship's speed isn't acceleration but rather--in space--potential damage from particles and such hitting it at that speed, the speed of light if the speed is relativistic, and most importantly slowing back down to end up stopped where you wanted to go.

 

[AnotherDilbert]

I know that's the book math, but it hasn't ever made sense to me. Consider planetary defense against a long term ship acceleration. The ship could approach the speed of light, and nothing but guesses in math say that it can't go faster. Sensors operate at the speed of radio waves, which are almost the speed of light. That means the sensor could detect the incoming ship before it hit the planet, but it could not relay the threat data any faster than the threat itself. Given machine processing time the sensor data would lag well behind the threat in terms of fractions of a second.

Normally ships are nowhere near light-speed. Even at 1 G continuous acceleration it would take a year or so to get there. By limiting the range of M-drive the rules are trying to limit that.

What's the effect of a 1000 dT merchant ship hitting a planet? Or even disentigrating the hull in atmo, releasing heavy core inert weapons and nuclear warheads for a high altitude EMP?

Close to light-speed? At a guess you now have a new asteroid belt. Perhaps Grandfather did that?

Civilised people don't that to each other, say the Zho and Impies, possibly for fear of retaliation.

 

[infojunky]

Back in the 90s the TML would have discussions on what would stop a ship driving an asteroid at near-c speed towards a planet.

I don't know if this comes up in editions beyond CT, but in CT you have to handwave a reason why this never or rarely happens.

Note this aspect is also one of the Traditional TML/Traveller Flamewar Topics...

 

[Bartleby]

> Note this aspect is also one of the Traditional TML/Traveller Flamewar Topics...

Yes it was. I was trying to remember the others. Piracy certainly. Those were the big two I recall.

 

[whartung]

Pirates with C Rocks is the créme de la créme.

 

[infojunky]

> Note this aspect is also one of the Traditional TML/Traveller Flamewar Topics...

Yes it was. I was trying to remember the others. Piracy certainly. Those were the big two I recall.

Aslan in comfortable shoes...

 

[Marcatlas]

In my CT and now Cepheus games I limit top speed to .15c via M Drives. But I also use real world physics in that there is no stealth in space. See the section with that title on the Atomic Rockets website for the full ramifications of that aspect of physics. One of the main ramifications is that you are not going to be able to accelerate something towards a planet with a space faring civilization without being spotted LONG before it is a threat. Therefore, allowing the "rock" to be intercepted and destroyed.

 

[Marcatlas]

A really neat way for new players to grasp this is with Mayday and the 3 chit spaceship movement system on the space hex grid.

 

[Timerover51]

I just assume that the Dean Drive works and go from there.

 

[Marcatlas]

I just assume that the Dean Drive works and go from there.

I just use a Grav drive. Make a grav well in front of the ship and away you go.

 

[Condottiere]

1. In theory, if you use reactionary rockets or a manoeuvre drive with a fusion reactor, you run out of fuel, in the vast expanse of space between the stars.

2. In practice, you use a ramscoop to collect hydrogen atoms.

3. The effectiveness of solar panelling varies in relation to the distance of a star.

4. Current rules collapses a default manoeuvre drive at a thousand diameters.

5. At which point, you need deep space drives to massage your way across interstellar gaps.

 

[whulorigan]

The ship could approach the speed of light, and nothing but guesses in math say that it can't go faster.

It's not a guess in math. Mass=Energy, and this fact can be demonstrated in the laboratory with subatomic particles in an accelerator. The faster a particle goes, the more kinetic energy it has, and by consequence, its mass is measurably increased by the exact amount predicted by E=mc².

This means that Newton's Law of Motion (F=ma) must be modified, as mass is no longer a constant: a constant force upon an object produces a constantly decreasing acceleration as velocity increases (which can be and has been measured under laboratory conditions). This means that an object under constant force will asymptotical approach a maximum limiting velocity as the mass approaches infinity and the acceleration in turn approaches zero with increasing velocity.

If the ship cannot accelerate to the maximum limiting speed without either an infinite force or an infinite amount of time, then it cannot accelerate past this limiting speed either.

And yes, light having zero rest mass can effectively "accelerate" instantaneously to this speed and cannot alter its speed.