Interplanetary Travel

[travchao999]

I remember that in CT, it described interplanetary travel (realistically), where the ship has to spend half of the trip accelerating, and then turn around, or otherwise orient its thrusters in the other direction, and spend the second half of the trip decelerating.

Is this principle pretty much unchanged in Mongoose Traveller?

 

[Reynard]

It's a bit confusing though it seems Mongoose vaguely points to travel times involving inertial and accel/decel and don't detail exactly what a 'gravitic maneuver drive' is. Essentially, a ship maneuvers by facing its nose in the new direction and fire the engines to push against gravity wells and achieve a new vector. Most of the time this is a simple straight line between two points with a 180 mid-point slowdown. Combat can get more complex. Thank you they keep maneuvering VERY simple in combat situations otherwise try to find the rules for Mayday and see what detailed vector movement is like. It's not pretty.

The seven versions of Traveller I have all use vector movement in various levels of detail, eight if you include Mayday. Each edition has variations on the thrust mechanics of the drives both reaction and reactionless from rockets to HEPlaR to thruster plate.

 

[Tom Kalbfus]

It's a bit confusing though it seems Mongoose vaguely points to travel times involving inertial and accel/decel and don't detail exactly what a 'gravitic maneuver drive' is. Essentially, a ship maneuvers by facing its nose in the new direction and fire the engines to push against gravity wells and achieve a new vector. Most of the time this is a simple straight line between two points with a 180 mid-point slowdown. Combat can get more complex. Thank you they keep maneuvering VERY simple in combat situations otherwise try to find the rules for Mayday and see what detailed vector movement is like. It's not pretty.

The seven versions of Traveller I have all use vector movement in various levels of detail, eight if you include Mayday. Each edition has variations on the thrust mechanics of the drives both reaction and reactionless from rockets to HEPlaR to thruster plate.

I can understand the Jump Drive, but why exactly a gravitic maneuver Drive? It has a fusion reactor, why not a fusion drive? Fusion drives work by accelerating and decelerating just the same as the gravitic drive, you just have to keep track of your reaction mass that's all Pretty much the jump fuel could be used as reaction mass, the fuel consumption requirements of the maneuver drive would provide fuel for the power plant which is then applied to the Jump Fuel reaction mass, and the Jump Drive itself simply requires charging of its capacitors, once the capacitors are fully charged, you can initiate a jump, that is the way I would do it.

 

[sideranautae]

I remember that in CT, it described interplanetary travel (realistically), where the ship has to spend half of the trip accelerating, and then turn around, or otherwise orient its thrusters in the other direction, and spend the second half of the trip decelerating.

Is this principle pretty much unchanged in Mongoose Traveller?

In MGT you accelerate for half the trip then decelerator the last half. The ships don't use reaction based thrusters so don't need to spin around and point.

 

[sideranautae]

I can understand the Jump Drive, but why exactly a gravitic maneuver Drive? It has a fusion reactor, why not a fusion drive? Fusion drives work by accelerating and decelerating just the same as the gravitic drive,

Because you wouldn't be able to carry enough reaction mass to do multiple G's for days on end.

 

[sideranautae]

Is this principle pretty much unchanged in Mongoose Traveller?

Here's a handy utility for figuring out travel times. It is an html file. Just save to a directory and open it. I found it on these forums a while ago.

https://www.dropbox.com/l/vP7PmrfgI3osLXyQMItfyq?

 

[Tom Kalbfus]

I can understand the Jump Drive, but why exactly a gravitic maneuver Drive? It has a fusion reactor, why not a fusion drive? Fusion drives work by accelerating and decelerating just the same as the gravitic drive,

Because you wouldn't be able to carry enough reaction mass to do multiple G's for days on end.

What's the hurry? You don't need to do that to travel around the Solar System. If you accelerage at 1 g for 3.5 days, you'll be going at 1% of the speed of light, if you do it for 2 weeks, you'll be going at 4% of the speed of light. A fusion drive can probably reach 1% of the speed of light, and 2% of the speed of light is not such a stretch either, no gravitic technology required. The Daedalus star probe can reach 12.5% of the speed of light in two stages, which means each stage can reach 6.25% of the speed of light.

The Daedalus star probe doesn't rely on gravitic technology. A fusion drive could reach 2% of light speed.

 

[sideranautae]

What's the hurry? You don't need to do that to travel around the Solar System.

Maybe you don't but, most others do. Also, your "small craft" would be the size of Oil tankers.

Delta V is your enemy.

 

[GypsyComet]

The one edition to explicitly employ reaction thrusters had to posit outrageously high fuel efficiencies just to get part way to the typical assumption of thrusting to midpoint, etc. Magic tech is just simpler.

 

[dragoner]

Travel times: http://www.transhuman.talktalk.net/iw/TravTime.htm

 

[Tom Kalbfus]

What's the hurry? You don't need to do that to travel around the Solar System.

Maybe you don't but, most others do. Also, your "small craft" would be the size of Oil tankers.

Delta V is your enemy.

You only have to get to 100 diameters to use your jump drive, the gravitic thrusters is an overkill for this purpose, what you could do is reach relativistic velocities using only a fusion power plant try it some time. Lets say you took a Scout/Courier, removed the Jump Drive and devoted the jump fuel plus the space freed up by the Jump Drive for extra maneuver fuel tankage, so how long could the maneuver drive operate with all that extra power plant fuel and what's the ultimate fastest velocity it could reach? You thinking of having a STL campaign using gravitic thrusters to travel between the stars? Low Berths could come in handy right here.

 

[phavoc]

You only have to get to 100 diameters to use your jump drive, the gravitic thrusters is an overkill for this purpose, what you could do is reach relativistic velocities using only a fusion power plant try it some time. Lets say you took a Scout/Courier, removed the Jump Drive and devoted the jump fuel plus the space freed up by the Jump Drive for extra maneuver fuel tankage, so how long could the maneuver drive operate with all that extra power plant fuel and what's the ultimate fastest velocity it could reach? You thinking of having a STL campaign using gravitic thrusters to travel between the stars? Low Berths could come in handy right here.

You won't always be using a jump drive for interplanetary travel. Since most planets and asteroid belts are more or less fall within the systems plane of eliptic, travel from one side of the system to the other involves moving through the 100D limit of the sun. The rules state if you come within that diameter you get yoinked out of jump space. To get there safely you'd have to travel for a period to ensure your jump path did not intersect with the 100D star limit, and then when you emerged, you would have to travel in N-space for a more or less equivalent amount of time to reach your destination. With the angle you couldn't emerge within 100D of your target or else you'd probably hit the star's 100D limit.

Plus an interstellar ship can devote more space to cargo since it does not need additional space for a jump drive and jump fuel. The space saved would allow you to potentially double, or triple your M-drive (along with an uprated power plant), and probably still save space.

For example, a 1,000 ton freighter with an E-class M-drive/PP gives 1G acceleration. To give it Jump-1 takes 22 tons for the J-drive and 100 tons for the fuel. If you bumped the M-drive to 3G and added in the same sized powerplant you are at 50 tons total (23 tons is necessary to get 1G). So for 27 tons (which is just about the size of the J-drive) you triple your normal-space speed (and save 100MCr for the Jump-1 drive).

To put that into travel time perspective, from the Earth to Jupiter, at 1G takes 6.5 days, accelerating at 1G, then doing a turnover to arrive zero-zero at Jupiter's orbit. Which is faster than jumping. If you were going 2G it would be 4.5 days, and at 3G it would be a little less than 4 days. Bumping it all the way up to 6G's takes a total of 100 tons for the drives, 22 tons of fuel for 1 week, but would get you there in 2.5 days. So a ship travelling in N-space would be able to reach Jupiter, unload cargo, reload & refuel, and make it back to Earth before a jump-capable freighter would reach it's destination - essentially doubling the capability of the ship for roughly the same cost.

If you were hoofing it from Earth to Pluto, travel time is 8 days at 6 G's, meaning that a jump ship may or may not get there before you. Travel in N-space is underrated. Then again most games seem to be oriented around jumping from system to system, so NOT having a jump drive means either taking other people's ships, or piggybacking on a freighter to get from system to system.

 

[Reynard]

"I can understand the Jump Drive, but why exactly a gravitic maneuver Drive? It has a fusion reactor, why not a fusion drive? Fusion drives work by accelerating and decelerating just the same as the gravitic drive, you just have to keep track of your reaction mass that's all Pretty much the jump fuel could be used as reaction mass, the fuel consumption requirements of the maneuver drive would provide fuel for the power plant which is then applied to the Jump Fuel reaction mass, and the Jump Drive itself simply requires charging of its capacitors, once the capacitors are fully charged, you can initiate a jump, that is the way I would do it."

The problem with the Reaction drive (which describes a lot like a HEPlaR, a recombustion addition to the fusion power plant from earlier editions) is you need additional fuel to the fuel already accounted for in the power plant. Replace a Maneuver drive with the Reaction drive on a scout (2g) and travel 100D from Earth (1,280,000km) for 4.4 hrs. That would mean an extra 22 tons fuel! You need 44 tons to land on a similar size destination world. The Maneuver drive does this using power from the plant for two weeks at a slightly greater cost.

You can't use the Jump fuel for maneuver if you plan to jump and you can't use the Power plant fuel because you need to run the PP to operate the Reaction drive. Obviously cheap comes with a high price.

 

[sideranautae]

You only have to get to 100 diameters to use your jump drive, the gravitic thrusters is an overkill for this purpose,

Um, nope. Refueling at a GG. TRavelling from Earth to Mars, etc., etc.

what you could do is reach relativistic velocities using only a fusion power plant try it some time.

Not without HUGE reaction mass fuel tanks. Did you calc the Delta V for something like a Type S going a considerable fraction of c? I'll wait until you present the "V" calcs...

 

[Condottiere]

1. I get mixed messages on this issue.

2. I'm told that acceleration is limited by the drive's gee factor, which means that once it hits a certain threshold, your velocity won't increase. Not being a physicist, not quite sure what to make of that.

3. With a normal reaction drive, you either accelerate and drift, or run out of fuel.

4.There are no grav drive design sequences for Adventure or capital class.

 

[sideranautae]

2. I'm told that acceleration is limited by the drive's gee factor, which means that once it hits a certain threshold, your velocity won't increase. Not being a physicist, not quite sure what to make of that.

c (speed of light) is the limit.

4.There are no grav drive design sequences for Adventure or capital class.

MRB & HG use Grav Drives as the default drives for both. You should buy both books.

 

[phavoc]

1. I get mixed messages on this issue.

2. I'm told that acceleration is limited by the drive's gee factor, which means that once it hits a certain threshold, your velocity won't increase. Not being a physicist, not quite sure what to make of that.

3. With a normal reaction drive, you either accelerate and drift, or run out of fuel.

4.There are no grav drive design sequences for Adventure or capital class.

For Traveller drives once you reach your maximum speed you max out your thrust, but you'll continue to accelerate at your G rating. So a 1G maneuver drive will accelerate at 1G for 50% of it's route, then have to decelerate at 1G for the same period to come to a relative stop.

Being able to accelerate continuously at even .5G for days or weeks would give you a huge relative speed in normal space. Today we have to use gravity slingshots because our chemical thrusters don't have the capability to carry that much reaction mass. The magical maneuver drives of the Traveller universe would actually open up the universe to us, albeit we'd have to go the slow way through normal space. But it would allow us to actually reach other stars in our lifetime.

 

[Reynard]

I think the problem is people are used to Star Wars/Star Trek physics which act more like planetary vehicles than ships in a vacuum and have the ability to move, slow and stop at the speed of plot. Traveller simulates real space travel and the laws of motion - When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force. In space, thrust is the external force. Constant thrust accelerates a vessel at a constant rate because there's almost no matter to act as drag. Once thrust stops a vessel continues moving at the velocity of thrust. The reason a car slows and finally comes to a stop is the drag from air and friction from contact with the road. The reason you move at a constant velocity when driving is you are applying power that translates to forward movement to neutralize the drag and friction.

I wish I could think of the names for several video games from the Eighties and Nineties that featured vector thrust; I think Asteroids was one. You moved by spinning the ship in the direction you wanted then pressed the thrust at variable rates. When you didn't apply thrust the ship still kept moving in the last direction and speed even if you spin the ship.

 

[sideranautae]

I wish I could think of the names for several video games from the Eighties and Nineties that featured vector thrust; I think Asteroids was one. You moved by spinning the ship in the direction you wanted then pressed the thrust at variable rates. When you didn't apply thrust the ship still kept moving in the last direction and speed even if you spin the ship.

http://en.wikipedia.org/wiki/Spacewar_%28video_game%29

Spacewar had an arcade version in the 70's. It used vector movement. I had it on a PDP-73 too.

Asteroids had you slow down after ending thrust.

 

[Condottiere]

Dizzying, to be sure.

As for Adventure and Capital class design sequences, I may have missed the relevant tables; if you could be so kind as to mention page and paragraph?