Reaction Drives and the Single-System Campaign

[Mithras]

This has always been something I wanted to do. With High Guard I've realised that I may be able to pull it off using all of MgTs rules as written (a first for me in any system). Ideally a near future campaign set in the Solar System, very much like Transhuman Space.

I created a small transport ship (I imagine most ships will be small): the Procyon, 200 tons, a crew of 5 with 10 tons of cargo and 138 cold sleep capsules for passenger haulage. It includes a lander (a 20 ton launch, not sure of the stats yet). It has a 2G reaction drive and a level 2 fission plant, and 4 thrust-hours of fuel.

I used the 'simple delta-v' formula in THS (V in miles per second = G rating x Thrust hours x11)to come up with a very rough travel time of 34 days to reach Mercury from Earth. This includes a 2 hour burn at either end.

Now, will it make money? As the rules go, no. I had to assume the vessel was subsidized using rules from Traveller LBB 2, then this made money.

On the long run out to Europa the travel time was 128 days (4.3 months), the costs are multipled by 4.3 (all except fuel), and so the cargo and passenger incomes must really reflect that 4.3 multiplier. I decided to use the 1 parsec costs of travel (freight and passenger) multiplied by the months it takes to get to the destination. It made sense considering the quadrupling of the costs based on monthly outgoings like life support, maintenance and wages.

Again, this made money for the ship operator. Subsidized ships are built by colony worlds, corporations and nations, operated by independant merchants and perhaps sold on after 40 years at cut rates to other player character types wanting to make a (slow!) buck.

So I think I might explore the STL single system campaign a little more using the MgTraveller rules.

I've written up a simple rule to include rotating habitats, and I'll need some small reaction drive craft (though I've just downloaded Golden Age Starships 5- Archaic Small Craft that will really help).

My main puzzle is fission powerplants. I see these like submarine reactors, capable of remaining unfuelled for several years at a time. With the 200 ton Procyon I followed the guidelines for fission plants, using stats in the Core book but doubling cost and mass. I have ignored fuel completely. If I wanted to include fuel cells, would these count as chemical powerplants? On the nature of drives, I am colouring the Procyon's reaction drive as a fusion drive, nuclear thermal, using the fission plant for heat.


Hope this all makes sense!

 

[Klaus Kipling]

Looks interesting....

 

[Mithras]

 

[atpollard]

I would suggest moving the rotating section forward and the reaction mass near the engine. The reaction mass will shield you from the drive (if necessary) and it will reduce the length of the 'fuel lines'.

Two pairs of counter rotating arms would balance the torque.

 

[atpollard]

My main puzzle is fission powerplants. I see these like submarine reactors, capable of remaining unfuelled for several years at a time. With the 200 ton Procyon I followed the guidelines for fission plants, using stats in the Core book but doubling cost and mass. I have ignored fuel completely. If I wanted to include fuel cells, would these count as chemical powerplants? On the nature of drives, I am colouring the Procyon's reaction drive as a fusion drive, nuclear thermal, using the fission plant for heat.

see THIS for ideas:
http://www.nuclearspace.com/PWrussview_fin.aspx

 

[rust]

I've written up a simple rule to include rotating habitats ...

While my TL9/10 setting uses gravitics, they are extremely expensive,
so a rotating habitat for a space station might well make sense. Perhaps
you could post your rule for rotating habitats ?

Since most facilities and vehicles in my setting are under water, I also
use the fission reactors exactly like submarine reactors, with the need
to either refuel after one year or to store enough fuel for several years
(making the reactor bigger and more expensive).
I also use additional fuel cells with some designs, and treat them as re-
dundant systems as described in the core rulebook.

 

[Mithras]

Ooh, nice link!

 

[Mithras]

Perhaps
you could post your rule for rotating habitats ?.

Its very quick and simple. Add all staterooms, lowberths and related passenger accomodation up along with cargo space that is preferred to be in gravity; the arms and rotating mechanisms mass x0.2 of that stateroom total.

Each ton of rotating equipment costs Cr100,000.

Any thrust requires the arms to be locked in position, and all passengers/crew to be in acceleration couches.

 

[rust]

Thank you.

 

[BP]

Sweet!

Like atpollard's suggestions... just a quick point - wonder why the cold sleep berths are in the rotating part?

Also, you could sweep the rotating arms forward at the extremities to allow for more distance from reactors...

Since you are being hard sci-fi here - might detail heat dissipation and retention (such as pop-up thermal vanes that extend and retract with rotation and exposure - light versus dark side on arms and extremities)...

Assuming the reaction mass has to come from a station or fueler vessel since the launch seems rather tiny for the job... also the launch, if not gravitic, will be more of a challenge!

If you are doing a single system you might want to add orbital characteristics and gravity assists = so that Mercury to Earth would take 34 days only at one time - at others it will take a substantially different time. Thus the launch windows might dictate waiting for a longer period to head off somewhere in order to get there quicker! (i.e. moving with a planetary body instead of thrusting)...

 

[Mithras]

Regarding low-berths in gravity, if the trip is to Jupiter then the poor saps will arrive after spending 4 months or more in zero G without exercise, they won't be able to walk at the end of it.

Like atpollard's suggestions... just a quick point - wonder why the cold sleep berths are in the rotating part?

I like the ideas for the arms and the radiators, nothing in MGT for those is there. Regarding transit times, I created a system last year I will be using. It was to assume the outer planets were in the same position throughout the campaign, at such vast distances their distance relative to the inner planets make them fairly static (from an RPG sense). For the inner planets I created a 'race-track system' and every game month advanced every planet one square on the race track. To calculate distance the player counts squares along the orbit.

I had made up my own design sequences up and everything, but now HG is out I'd like to go back and recreate the setting using the HG rules as written if at all possible.

 

[BP]

Regarding low-berths in gravity, if the trip is to Jupiter then the poor saps will arrive after spending 4 months or more in zero G without exercise, they won't be able to walk at the end of it.

Uhmmm... thought low-berth meant cryo-sleep (suspended animation/cold sleep)- so they ain't get'n no exercise no how?! :wink:

For the inner planets I created a 'race-track system' and every game month advanced every planet one square on the race track. To calculate distance the player counts squares along the orbit.

Shinny!

Assume each planet has an orbital speed/direction and is moved as the count is made to account for orbital differentials over the time it takes to travel? Also assume the square counting avoids passing through the sun and other bodies...

 

[BillDowns]

That's a cool arrangement, Mithras.

I would offer 1 enhancement for a similar scheme I had years ago. Place any weapons on arms that extend just a little farther than the accomodation arms, so their field of fire isn't blocked. You could even have them rotate under control, so the ship doesn't have to be rotated for combat.

 

[Mithras]

Just what is the High Guard reaction drive trying to mirror, I wonder?

Several hours of acceleration followed by coasting, but with accelerations of 1-6G. I can't find anything like it on the great Atomic Rocket website.

http://www.projectrho.com/rocket/rocket3c.html

 

[BP]

Existing rockets! - they accelerate with high boost reaction mass and then coast till they have to decelerate - typically taking advantage of local gravity wells to accelerate and decelerate further...

Some course adjustments being in order typically to optimally use gravity assists - often involving several fly-bys.

Note that these trajectories always follow a curve as this is the most optimal approach.

(More continuous thrust would use plasma/ion/EM style drives which accelerate a smaller reaction mass but at a much higher velocity)

 

[saundby]

At the low energy end of the spectrum you get from one planet to another by following Hohmann transfer orbits. For these, you do a burn to put yourself into the transfer orbit from your starting orbit. Then you wait. When you get to your new orbit, you do another burn to put yourself in that orbit. The burn will consist of using whatever source of thrust you have on your craft.

This is a slow way to go, but it minimizes the energy required to go from A to B.

An enhancement to this is the gravity-assisted flybys.

An enhancement to the enhancement is the fancy ways of using the topology of the solar system to find lower-energy paths than Hohmann orbits, and to get gravity assists without actually flying by a body.

Then, at the other end of the spectrum there's the "torch ship." In this case you're brute-force powering yourself half the way, then in brute force deceleration the other half. One side effect of more or less constant acceleration is that you don't need a rotating section to provide gravity. Your thrust gives you all the gravity you need (and possibly more, on a ship with more than 1g of thrust.)

Between the low energy extreme and the torch ship there are many possibilities. If propellant costs make torch ships impractical, then perhaps a slower trip with less propellant use will make up the difference. Or there can be a mix. Torch ships for the small, light, high priority stuff. Slower ships for the stuff that doesn't pay its way as well.

As to the HG designs, I think there's mostly an assumption that you've got something like standard 3I tech on hand or importable to your shipyards. If you feel the need to add radiators and such to your ships, I would just do so as window dressing rather than add additional detail to the ship design process, along with any other window dressing that gives the ships a more TL8 feel.

You might also want to look at things like the Mars Cycler. These are slow ships that do what they do by having several craft in more or less continuous transfer between different solar orbits. There's also been some work on using space habitats in this sort of role. In places in your solar system that are considered settled rather than being frontier, this might work for you.

 

[Bygoneyrs]

I must say having a Traveller based campaign limited to one main star system and maybe a few others might be extremely refreshing and fun. The tech could be limited to the tech of like that of Alien's II.

Penn

 

[lastbesthope]

At the low energy end of the spectrum you get from one planet to another by following Hohmann transfer orbits. For these, you do a burn to put yourself into the transfer orbit from your starting orbit. Then you wait. When you get to your new orbit, you do another burn to put yourself in that orbit. The burn will consist of using whatever source of thrust you have on your craft.

This is a slow way to go, but it minimizes the energy required to go from A to B.

Depends, if the new orbit is big enough relative to the starting orbit you'd be better doing a bi-elliptic transfer, similar idea, but one extra burn.

http://en.wikipedia.org/wiki/Bi-elliptic_transfer

LBH

 

[kristof65]

I must say having a Traveller based campaign limited to one main star system and maybe a few others might be extremely refreshing and fun.

Not only that, but the whole idea of a First Contact or FTL Breakthrough being the campaign basis sounds cool, too.

 

[Mithras]

Yes I have something in mind for that.

Something to do with the strange 'bulge' in Iapetus' equator. Now that's not natural is it?? What if its a hyperspace acceleration drive or some kind of gate device.