Maneuver Drives

[Jame]

Can anyone tell me something about the reactionless drives, e.g. a 1-G drive propels a ship at this percent of c, and etcetera?

 

[hemulen]

What sort of details are you after? 1G is an acceleration rather than a speed i.e. 9.81 m/s/s, so if you do it long enough, you'll (theoretically) end up doing c (300,000 km/s), although you migh notice a few funny things happening before then...

cheers,

Mark

 

[Jame]

How fast are you going if you accelerate to 1G and stop accelerating?

 

[Borodin]

Depends on how long you accelerated.

V = A x T + V0

V is your final velocity in meters per second
A is the acceleration of your ship x 9.81
T is the amount of time you accelerated
V0 is your starting velocity (usually 0)

The manuever drive ratings do not tell you a maximum speed, they tell you how fast your ship can accelerate. So if your ship has a 2G drive, and accelerates for 20 minutes (1200 seconds, 1 standard starship combat round, I think) from a dead stop, it will have a velocity of

V = 2 x 9.81 x 1200 + 0 = 23544 m/s, or ~ 24 km/s.

Now, the reason Traveller rates the drive in terms of acceleration rather than speed is that in space the important thing is how fast you can change velocity, not what your final velocity may be. With basically no drag, with any acceleration and enough time you could theoretically achieve any velocity you want, its just a question of how long it takes you to get there.

Or, another way, the big question is not how fast can your Far Trader go compared to that pirate Corsair, but do you stand a chance of outrunning it or is it only a matter of time til you're pirate food.

(Most of the time, your Far Trader will be toast.)

 

[Ben W Bell]

Originally posted by Jame:
How fast are you going if you accelerate to 1G and stop accelerating?

Um I'm not sure I understand you there Jame. 1G is a measuere of acceleration, not velocity. 1G is the measure of acceleration of an object you or I would drop on earth as there is the effect of 1 standard gravity on it (Earths gravity at the surface is taken as 1G for simplicity).

 

[Jame]

So 1G acceleration is 23.5 km/s, or gaining that much per second. Let me put it this way: what percent of the speed of light would a Beowulf achieve normally, and how would I calculate maximum speed for other ships and engines?

 

[Ranger]

Originally posted by Jame:
So 1G acceleration is 23.5 km/s, or gaining that much per second. Let me put it this way: what percent of the speed of light would a Beowulf achieve normally, and how would I calculate maximum speed for other ships and engines?

That depends on how far you are going and how fast you can accelerate. The old Traveller books used to have charts that told you how long it would take to travel a known distance by excelerating half the way there, then decelerating half the way, so you arrived at your destination with 0 V. This issue wasn't how fast you were going, but how long it takes to get there.

Rob

 

[Jame]

How about this: how fast can the average Traveller vessel go as a % of c, assuming 2G drives and taking an average for 2-G accel trip between Earth and Mars, or Earth to Jump and Jump to Alpha Centauri Mainworld?

 

[ninthcouncil]

If a vessel accelerates constantly at 1-G, it will attain 1% of the speed of light in about
3.5 days (c ~ 300,000 km/s). So, during a typical insystem hop, you aren't talking about approaching anything near light speed, even in a 6-G vessel, which would attain 0.01c in a little over half a day. And remember, you spend the second half of the journey accelerating in the opposite direction to slow down, since you probably want to be stationary when you arrive

To attain 100% of light speed it would seem that you could accelerate at 1-G for about a year, but this wouldn't happen, because:
i) you'd run out of fuel
ii) relativity theory tells us that as an object approaches "c", its effective mass increases. It therefore becomes incerasingly difficult to increase its velocity, so that in the extreme case it would require infinite amounts of energy to reach light speed.

In normal play, relativistic effects like that shouldn't come into play - there's no way you're ever going to be going fast enough.

 

[Uncle Bob]

Originally posted by Jame:
How about this: how fast can the average Traveller vessel go as a % of c, assuming 2G drives and taking an average for 2-G accel trip between Earth and Mars, or Earth to Jump and Jump to Alpha Centauri Mainworld?

Well, the jump point is 100 diameters, so for an earth sized world that is about 1.2 million kilometers, or 1.2 billion meters. Assuming you accellerate at 2g (20 m/s/s) you will reach the jump point in about 4 1/2 hours (I refuse to do the calculus to properly account for gravity) you will hit the jump point at about 150 kilometers/second.

Earth to Mars... that could be anything between 50 million and 350 kilometers. I'll assume 200 million kilometers. The ship will accellerate to midway, then decellerate to the destination.
1 G: 78 hours, top speed 1,400 km/sec
2 G: 56 hours, top speed 2,000 km/sec
3 G: 45 hours, top speed 2,450 Km/sec
4 G: 41 hours, top speed 2,800 Km/sec
5 G: 35 hours, top speed 3,160 Km/sec
6 G: 32 hours, top speed 3,460 Km/sec

So it takes a little over 3 days at 1 G. At 5 G it still takes a day-and-a-half and you are going more than twice as fast at turnover

Want to go to Mars when it is close (50 million kilometers)? At 2 G that will take 28 hr with a top speed of 1,000 Km/sec

IIRC, the algebra for all this was in Book 2.

 

[Uncle Bob]

Oh, if you want to go to Alpha Centauri at 2 G you will seem to get there in two years. Actually it would have taken you ten (??? A resonably acurate answer requires integrating the lorentz expression over the trip. I did it once.)

At turnover a year in you will think you are going 4 times the speed of light, but you are actually moving at 0.94 the speed of light with a distorted sense of time.