The speed of space travel

[Sigtrygg]

48 days of constant acceleration at 6g gets you to 0.83c.

Jump into a system a long way out.

Accelerate towards your target for 10 days at 6g then launch your 95t 6g smallcraft fitted with extra fuel as cargo.

These continue on course to the target you want obliterate for 38 days.

950000x250,000,000x250,000,000x0.5 = 3x10^23 J of energy dumped into the atmosphere.

4.2x10^15 J is the energy release by a 1Mt nuke.

 

[locarno24]

I think you were trying to use v²=u²+2as

I am. But since you are only accelerating for half the distance, if you use the full travel distance for the trip (both the 'accelerate' and 'brake' portions), as stated, which is double the 'accelerate' portion, the '2' disappears anyway...

 

[Ishmael]

Discussing relativistic speeds without mentioning Lorentz or frames of reference?

Near c rocks are what you get in a universe with reactionless drives and cheap energy....live with it or use 'realistic' thrusters ( rockets ) instead.
Cold war era MAD policies and reactions should curtail them, mostly.

 

[Monstro44122]

It feels like someone on the ground would have the capability of knocking a ship out of the sky. A 5 ton missile with a 10G thrust ought to do the trick.

The problem here is that, in reality, every combat technology is generally met with its defense. Someone, in the long history of Traveller, would eventually figure out how to prevent any yahoo with a souped-up cutter from destroying their planet.

The trick seems to me to be to set up your description of planetary defenses early on. Include big sensor arrays and big guns. If Traveller is the age of sails, then the space port is the fort you're sailing towards.

 

[locarno24]

It feels like someone on the ground would have the capability of knocking a ship out of the sky. A 5 ton missile with a 10G thrust ought to do the trick.

Planetary guns - as I've heard them described - tend towards the equivalent of spinal-mount meson weapons, which would do the job most satisfactorily.

 

[GypsyComet]

48 days of constant acceleration at 6g gets you to 0.83c.

Jump into a system a long way out.

Accelerate towards your target for 10 days at 6g then launch your 95t 6g smallcraft fitted with extra fuel as cargo.

These continue on course to the target you want obliterate for 38 days.

950000x250,000,000x250,000,000x0.5 = 3x10^23 J of energy dumped into the atmosphere.

4.2x10^15 J is the energy release by a 1Mt nuke.

Factoid not mentioned in Mongoose: Maneuver Drives (which use a variation of gravitics) supposedly drop to a small percentage of their normal output thrust beyond ~10,000 radii of the star (locally, 3x Pluto's orbit). The half a light year you would need for this trick is well beyond that, so you would not be getting all that acceleration time at full, and it would take a lot longer than 48 days.

 

[Wil Mireu]

Factoid not mentioned in Mongoose: Maneuver Drives (which use a variation of gravitics) supposedly drop to a small percentage of their normal output thrust beyond ~10,000 radii of the star (locally, 3x Pluto's orbit). The half a light year you would need for this trick is well beyond that, so you would not be getting all that acceleration time at full, and it would take a lot longer than 48 days.

Source?

As I said in the slingshot thread:

Artificial Gravity is described [in FF&S] (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).

It doesn't mention any dropoff in performance beyond a given distance.

 

[Sigtrygg]

Factoid not mentioned in Mongoose: Maneuver Drives (which use a variation of gravitics) supposedly drop to a small percentage of their normal output thrust beyond ~10,000 radii of the star (locally, 3x Pluto's orbit). The half a light year you would need for this trick is well beyond that, so you would not be getting all that acceleration time at full, and it would take a lot longer than 48 days.

Good try, but that M drive reduction wasn't invented until a Q&A in a MT journal

The fall off is mentioned in T4 and T5 so I'll allow it to be assumed for MgT too - even though it isn't mentioned anywhere

But it doesn't take half a light year - 10,000,000,000km will do

Which is about 0.17 light years

So not very feasible if M rives drop off like that.

 

[GypsyComet]

FF&S wouldn't mention it because Thrusters weren't the default tech for that edition.

"Good try"? You do realize that was nearly 25 years ago, right?

 

[CosmicGamer]

Monstro44122, stay tuned, I address your issues at the end.

You are right, space is friggin vast. But so are the oceans, and the airways. Commercial traffic fly in corridors for a reason. Space traffic would be the same. Granted the corridors might be a bit more 3-D, but the concept remains the same. Because space is so big, if you want a chance of rescue, you are going to have to tell people where and when you are going, what path you are flying, and when you expect to get there. So 'stumbling' upon scheduled traffic is expected.

Except
1) other than near a destination/departure location, I'd think it would be hard to have dedicated flight corridors. For example, going from earth to mars: one ship at 1G constant thrust and deceleration vs 2G vs 3G and so on would have very different travel times, arrival locations (yes mars, but different locations in it's orbit) and thus different flight corridors.
2) with space traffic the flight corridors constantly change with time since destinations move about as they orbit and dance through the cosmos.
3) a ships course is determined based on acceleration and deceleration and if it is somehow disabled during this journey it will quickly go off course and out of the expected flight path

I'm not sure why systems would allow ships to zip around at near light speed near their planets.

The rules can not cover everything. That's why we have these discussions.

One thing I consider is that space is big and I see no reason for a ship to zip around at near light speed near planets. On the rare occasions where three locations are orbiting such that they are lined up you might go from point A to point C and come close to point B. I'm no math or physics or astronomy expert so I don't know the odds of this happening. My guess is that the distance between point A and C are great enough that the much smaller distance for going slightly out of the way around point B wouldn't be too much of a problem in regards to time or fuel waste.

I mean, you're going half the speed of light, someone disables your capacity to decelerate in space combat, aren't you pretty much a giant fusion bomb moving at unheard of velocities, which is, more than likely, on a collision course with the nearest starport?

Even if a ship was somehow disabled while on a course to the starport or other destination, if it does not decelerate it will be very much off it's original flight plan. My first thoughts are that any danger of this type would either be an extremely unlikely needle in a haystack accident or

theoretically there's nothing stopping you from attaching M-Drives to a small asteroid in the outer system and accelerate it to ridiculous speeds so that it hits a planet with enough force to obliterate a hemisphere

something planned.

Any system with the capability would probably be trying to detect what's out there. Location, distance, current speed, thrust, acceleration or deceleration, and so on. As indicated in earlier posts, a typical ship going very fast would have to accelerate for a long time. Hours. Days. Weeks. It would take about as long for the typical travelling ship to decelerate. If a ship (or asteroid with thrusters) is traveling too fast to be able to decelerate and appears to be on a destructive course there should be time to intercept. Again, assuming a system with the resources and not just some science outpost.

Back to Monstro44122's adventure

I'm planning an adventure where a prison ship has had a mutiny while passing a space station.

Although my first thought was that it would be very close, "pass" is a pretty vague term and can probably work. Within range to match course?

The characters come across the prison ship en route to the space station.

Was the premise that the prison ship is in route to the station or is it the characters or both?

The captain comes to a full stop so as to leave the ship hanging in space with red alert klaxons going.

As mentioned before, coming to a full stop is a pretty relative thing. In an emergency I could see the captain altering course to arrive near a source of assistance.
A) Perhaps lucky enough to come close to matching speed and course
B) or maybe just pass by it if there is not time to match speed.

So, how far away is the prison ship from the station? 1,000 km, 10,000 km, 1 million km?

If you go with A) above, then it is whatever the captain set the course to be. If you go with B) above, then it is whatever you want it to be and you will need to determine the rate the distance is changing as the adventure progresses since the prison ship and space station are not in synch with this option.

 

[Wil Mireu]

I'll look it up, but it is late MegaTrav, IIRC. FF&S wouldn't mention it because Thrusters weren't the default tech for that edition.

They weren't, but they were still described in some detail in the alternative tech section.

I have a vague recollection here, but didn't MT actually have two types of thruster? One worked the way you described, the other (more advanced one) didn't have that limitation?

 

[phavoc]

48 days of constant acceleration at 6g gets you to 0.83c.

Jump into a system a long way out.

Accelerate towards your target for 10 days at 6g then launch your 95t 6g smallcraft fitted with extra fuel as cargo.

These continue on course to the target you want obliterate for 38 days.

950000x250,000,000x250,000,000x0.5 = 3x10^23 J of energy dumped into the atmosphere.

4.2x10^15 J is the energy release by a 1Mt nuke.

Of course, if you are worried about near light-speed attacks, you can easily seed your system with sensor satellites that have control over launchers with high-speed missiles that would leave an array/cloud of even ballbearings in the path of the small craft. At that speed dodging would be nearly impossible and striking anything would essentially obliterate the small craft.

The rules really don't go into detail about high-speed collisions with normal space debris. It's a game, so things like that are included.

 

[Sigtrygg]

You' have to intercept the near c object a long way from the planet - you need time for the hugely energetic ball of plasma to dissipate.

A plasma jet hitting a planet with the energy of 10,000 nukes is just as bad as the small craft hitting the atmosphere intact.

 

[GypsyComet]

I'll look it up, but it is late MegaTrav, IIRC. FF&S wouldn't mention it because Thrusters weren't the default tech for that edition.

They weren't, but they were still described in some detail in the alternative tech section.

I have a vague recollection here, but didn't MT actually have two types of thruster? One worked the way you described, the other (more advanced one) didn't have that limitation?

You are remembering mostly correctly, but the earlier type conks out about 10 diameters out while the later type gets out to 10,000. The earlier type is what grav vehicles still use.

 

[Monstro44122]

Hey CosmicGamer,

So, basically the scenario is this. There's a space station out in the big empty and it's being dismantled. The space station is actually a number of smaller science vehicles retrofitted to a very old space station belonging to an unknown alien race. The space station is haunted by the ancient alien race who were experimented on by another unknown alien race (both long dead).

So, as a penal ship (Boat A) passes by the space station, they get possessed by the ghosts with the result that the ship is taken over. Two passengers, having escaped possession, are able to disembark separately. One is the ship's pilot (Boat B) and one is a prisoner who jettisons towards the space station and docks. How close do they pass? Close enough that they could be possessed and not so far out that the station is an enormous problem for the entire system.

The characters (Boat C) are en route to the space station. For the sake of dramatic usefulness, I would like the characters to be able to travel from Boat B and A to the space station without it taken them several days. Basically, I want them all in radar range of each other.

That being said, the penal ship was not going to the satellite. According to Traveller, if the penal ship started decelerating at the point of the mutiny, it would probably be damned far away from the action.

I think my answer is just to ignore all those charts and tables but I have players who may very well bring up this point: why was the penal ship decelerating as if it were going to the space station. I don't want them to ask that question because it leads to a line of inquiry that I don't want.

So, realism is no good, unrealism is no good. My answer may be for me just to say, "yeah, I changed that up so that the adventure wouldn't suck," but I'm not all that happy about breaking the fourth wall.

Or I may say the ship just wasn't moving the way that ship's do in Traveller Universe. In MTU, getting spotted out in the big empty isn't particularly safe and running engines continuously is a good way of getting spotted. There are solutions; they just aren't convivial to that travel time chart.

As for big rocks approaching C, I can think of 10 ways, off the top of my head, to make that not matter using nothing more than half understood jargon and pseudo science. I recommend that you do too. Players don't like it when their plans don't work "just because." If it helps, I'm very fond of using the words "dark matter" incorrectly.

 

[Sigtrygg]

Penal ship is transporting prisoners, right?

To where, from where?

If the penal ship is en-route to a prison satellite or colony on/around a gas giant moon the derelict space station could be within range of the prison ship's deceleration trajectory.

PC's could be passing by for lots of reasons, fuel skimming, trade delivery or whatever you wish.

This puts them in range of the station, the prison ship - and the potential penal colony could be close enough by that if they don't deal with the prison ship in time you could have a whole prison full of hosts for the alien ghosts...

 

[F33D]

It feels like someone on the ground would have the capability of knocking a ship out of the sky. A 5 ton missile with a 10G thrust ought to do the trick.

The problem here is that, in reality, every combat technology is generally met with its defense. Someone, in the long history of Traveller, would eventually figure out how to prevent any yahoo with a souped-up cutter from destroying their planet.

The trick seems to me to be to set up your description of planetary defenses early on. Include big sensor arrays and big guns. If Traveller is the age of sails, then the space port is the fort you're sailing towards.

You are quite correct. Sounds like you are already getting the hang of the game.

 

[dlpulver]

You could put the space station near a gas giant (orbiting it). Then maybe the penal ship was decelerating to skim fuel from the gas giant when the mutiny occurred.