The Hinterworlds Rambler
SOC-14 5K
Did I remember seeing this somewhere? Anyone got the data for this?
M-Drive G Rating to Mph/Kph Conversion Data?
- Thread starter The Hinterworlds Rambler
- Start date
Andrew Boulton
The Adminator
It's usually defined as 10m/s^2.
I've got a handy-dandy little tool for that...
http://eaglestone.pocketempires.com/scripts/uwptools.html
http://eaglestone.pocketempires.com/scripts/uwptools.html
Andrew Boulton
The Adminator
Handy.
The most useful thing I learned at school was the equation s=ut+.5at^2
The most useful thing I learned at school was the equation s=ut+.5at^2
The Hinterworlds Rambler
SOC-14 5K
That's the one! Thanks!
selunatic2397
SOC-12
And to think that ages ago when I first started Traveller my answer to that question was a fast and dirty bluff of "1G equals 1000mph". That lasted over 3 years of gaming before the math class wunderkinder realized the referee {me} was bad at math and good at bluffing.....uh guys...how off was I anyway???
Fritz_Brown
Super Moderator
You didn't even have the right units....
(BTW, 1G for 47 seconds will result in 1000mph, and you will have traveled 6.7 miles.)
(BTW, 1G for 47 seconds will result in 1000mph, and you will have traveled 6.7 miles.)
Scott Martin
SOC-13
In a vaccum...
Top speed in atmosphere will be a trade-off of brute power and drag, strongly affected by streamlining. Drag is a Velocity squared function, so to double your speed you need to quadruple your power, or decrease your drag.
Most military aircraft have ~ 1G of thrust (that's Military boyos, commercial jets have much less) and the wide range of top speeds tells you a lot about streamlining issues...
The table is a "guideline" and on my "to do" list for MTU is updating it for different atmospheres. YVMV (Your Velocity May Vary)
Scott Martin
Top speed in atmosphere will be a trade-off of brute power and drag, strongly affected by streamlining. Drag is a Velocity squared function, so to double your speed you need to quadruple your power, or decrease your drag.
Most military aircraft have ~ 1G of thrust (that's Military boyos, commercial jets have much less) and the wide range of top speeds tells you a lot about streamlining issues...
The table is a "guideline" and on my "to do" list for MTU is updating it for different atmospheres. YVMV (Your Velocity May Vary)
Scott Martin
Plankowner
SOC-13
Interestingly, if you take the formula and convert the units to something that is more intuitive than meters and seconds, for space travel you get:
Constant Accell to midpoint, turn and Decell at same rate (initial and final Velocity the same):
T = 2*SQRT(D/A)
Where D is in AU
A is in G's of accelleration
T is in Days.
The unit conversions all basically cancel each other out! It's not exact, but it is pretty close, something like 1.98 instead of 2, but I figure for a game, close enough.
BTW, if you are accellerating straight through, with no turn around, the formula becomes:
T = SQRT(2*D/A)
So half-turn trips are 141% longer than a staight accelleration, at Newtonian speeds anyway.
Constant Accell to midpoint, turn and Decell at same rate (initial and final Velocity the same):
T = 2*SQRT(D/A)
Where D is in AU
A is in G's of accelleration
T is in Days.
The unit conversions all basically cancel each other out! It's not exact, but it is pretty close, something like 1.98 instead of 2, but I figure for a game, close enough.
BTW, if you are accellerating straight through, with no turn around, the formula becomes:
T = SQRT(2*D/A)
So half-turn trips are 141% longer than a staight accelleration, at Newtonian speeds anyway.
princelian
SOC-12
Plankowner's equations are close enough for government work. There are also some good tables for travel times in the magazine-sized CT books (one book was entirely devoted to tables). I'm not sure if that stuff was in the LBBs....
I'll just point out that if you don't perform turnaround, you'll have a velocity at destination of (173,000 seconds x 9.81 m/s^2 =) 1.7 million m/s.
1.7E6 m/s is 6.1 million km/h, or 1/2% of the speed of light. You won't be able to stop until you've (a) arrested all of your velocity, which will take another 2 days, and (b) returned to the destination using turnaround, which will take another 2.8 days.
Plankowner's little equation is very nice because it's in AU (150,000,000 km or thereabouts), which gives you a good idea of how far a ship with fusion drives can go. The space shuttle has about a 3G takeoff, but can't sustain that thrust for longer than a few paltry minutes.
(Altitude at main engine cutoff (MECO) is 113 km, and assuming atmospheric resistance quadruples the acceleration time, that's like 6 minutes. I think that in real life, it's about 8-1/2 minutes to MECO because they cut the main engine thrust back to 25% while they're in deep atmosphere so atmospheric heating doesn't burn up the shuttle...)
I'll just point out that if you don't perform turnaround, you'll have a velocity at destination of (173,000 seconds x 9.81 m/s^2 =) 1.7 million m/s.
1.7E6 m/s is 6.1 million km/h, or 1/2% of the speed of light. You won't be able to stop until you've (a) arrested all of your velocity, which will take another 2 days, and (b) returned to the destination using turnaround, which will take another 2.8 days.
Plankowner's little equation is very nice because it's in AU (150,000,000 km or thereabouts), which gives you a good idea of how far a ship with fusion drives can go. The space shuttle has about a 3G takeoff, but can't sustain that thrust for longer than a few paltry minutes.
(Altitude at main engine cutoff (MECO) is 113 km, and assuming atmospheric resistance quadruples the acceleration time, that's like 6 minutes. I think that in real life, it's about 8-1/2 minutes to MECO because they cut the main engine thrust back to 25% while they're in deep atmosphere so atmospheric heating doesn't burn up the shuttle...)
Plankowner
SOC-13
Back in the Day (TM) when I figured out the equation, I was really surprised how good of an approximation it all came out. Sure, it not exact, but is within about 10%-20% of the real number. Makes for a quick calculation. I think I used 150MKM for an AU and 9.8m/s^2 for a G, just approximations, but it came out pretty close. It's the type of equation that any calculator can do and it doesn't involve a lot of numbers.
The only real issue is to have your distances in AU. Works well on an interplanetary level, but is probably too big for just a jaunt to the 100D limit (about 1.2Mkm or about 0.008 AU) for a size 8 world like Terra.
The only real issue is to have your distances in AU. Works well on an interplanetary level, but is probably too big for just a jaunt to the 100D limit (about 1.2Mkm or about 0.008 AU) for a size 8 world like Terra.
Fritz_Brown
Super Moderator
Oh yeah, they're faster - you decelerate much more quickly on the destination end - on the order of a couple of seconds. They can spread you on
Plankowner
SOC-13
Well Fritz, that depends on what you are trying to do with all that accelleration.
A 1,000,000 dtn ship moving at a small fraction of the speed of light jumping 100d from a planet would make a nice little WMD. "Dagger at Efate" is the scenario, but at MUCH higher speeds. I'm sure the Imperium would NEVER do something like that though...
A 1,000,000 dtn ship moving at a small fraction of the speed of light jumping 100d from a planet would make a nice little WMD. "Dagger at Efate" is the scenario, but at MUCH higher speeds. I'm sure the Imperium would NEVER do something like that though...
Fritz_Brown
Super Moderator
Oh, jiminy, don't even go there, Plankowner....
Plankowner
SOC-13
Well, I guess it's too late.
That's what happens when you store up all these ideas for almost 30 years and finally have an outlet. OF COURSE others have thought of them and they have probably been discussed (and flamed) to death in the intervening years, but they are new to me.
I was NOT trying to start a new war (or resurrect an old one).
As you can tell from some of my other posts, I have an issue with ACCURACY and Interstellar Jumps. I don't think Marc really thought about what it takes to be accurate to within 3000km over 6 parsecs (or even 1 parsec). Maybe this is a beaten to death issue, but I don't know the answer. Marc says that the Jump Drive/Navigation is that accurate and I will accept it, but now, as an engineer, I feel the need to try to explain/understand it.
Oh well, back to the thread...
That's what happens when you store up all these ideas for almost 30 years and finally have an outlet. OF COURSE others have thought of them and they have probably been discussed (and flamed) to death in the intervening years, but they are new to me.
I was NOT trying to start a new war (or resurrect an old one).
As you can tell from some of my other posts, I have an issue with ACCURACY and Interstellar Jumps. I don't think Marc really thought about what it takes to be accurate to within 3000km over 6 parsecs (or even 1 parsec). Maybe this is a beaten to death issue, but I don't know the answer. Marc says that the Jump Drive/Navigation is that accurate and I will accept it, but now, as an engineer, I feel the need to try to explain/understand it.
Oh well, back to the thread...
daryen
SOC-14 1K
Plankowner,
The issue you have raised has nothing to do with ships, per se, but with the logical conclusion of using reactionless thrusters.
Namely, attach the thrusters to as big an asteroid/comet/whatever you can get to move. (Using a ship is wasteful; just use a "free" hunk of rock/ice.) Get it going at some speed aproaching the speed of light. Aim it at the enemy planet. Wash. Rinse. Repeat.
The issue is called "Near-C Rocks" and usually starts a flamefest when mentioned.
The usual solution is to pretend the problem doesn't exist or can't happen for some technobabble reason, and ignore the possibility of near-C rocks.
"Near-C Rocks" and "The Feasability of Piracy" are probably two of the biggest flamefest igniters that I can think of. Now you know. Please move on.
The issue you have raised has nothing to do with ships, per se, but with the logical conclusion of using reactionless thrusters.
Namely, attach the thrusters to as big an asteroid/comet/whatever you can get to move. (Using a ship is wasteful; just use a "free" hunk of rock/ice.) Get it going at some speed aproaching the speed of light. Aim it at the enemy planet. Wash. Rinse. Repeat.
The issue is called "Near-C Rocks" and usually starts a flamefest when mentioned.
The usual solution is to pretend the problem doesn't exist or can't happen for some technobabble reason, and ignore the possibility of near-C rocks.
"Near-C Rocks" and "The Feasability of Piracy" are probably two of the biggest flamefest igniters that I can think of. Now you know. Please move on.
daryen
SOC-14 1K
To help, here is the Traveller Mailing List FAQ. While old, and geared to the TML rather than these forums, it pretty clearly shows what items are old hat to on-line Traveller fandom and what topics will cause people to roll their eyes at the newbie.
In particular, read section 4 'Done To Death'. It won't take you very long.
In particular, read section 4 'Done To Death'. It won't take you very long.
Plankowner
SOC-13
Thanks Daryen, I will have to check it out. I have seen info on the TML, but I have not wanted to wade into to many areas at once. I lurked here for about 3 months before I decided to jump in.
I really don't want to ignite new/old flamefests, I just have questions.....
Now, to issue one more parting shot on this subject: Reactionless drives go back a long way in SciFi. I think one of the best uses of this topic was probably the Lensmen Series. In the end they used entire planets as weapons. Of course Doc Smith also discussed the whole power requirements issue. My take would be that if you want to trash a planet there are plenty of ways to do it: nuclear weapons, Near-C Rocks, the Star Trigger. The GM should decide what if/any he/she wants to employ in a given situation.
The truth is it all comes down to one simple statement:
IT'S A GAME
I really don't want to ignite new/old flamefests, I just have questions.....
Now, to issue one more parting shot on this subject: Reactionless drives go back a long way in SciFi. I think one of the best uses of this topic was probably the Lensmen Series. In the end they used entire planets as weapons. Of course Doc Smith also discussed the whole power requirements issue. My take would be that if you want to trash a planet there are plenty of ways to do it: nuclear weapons, Near-C Rocks, the Star Trigger. The GM should decide what if/any he/she wants to employ in a given situation.
The truth is it all comes down to one simple statement:
IT'S A GAME
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