Arc Recharge Station

[Lagrange]

As per this thread, it seems that a recharge station can be made extraordinarily cheap enabling their broad use. 

Code: [Select]

Arc Recharge Station
Mass: 107,000 tons
Technology Base: Inner Sphere (Advanced)
Introduced: 3025
Mass: 107,000
Battle Value: 1,064
Tech Rating/Availability: D/X-E-D-D
Cost: 28,220,000 C-bills

Fuel: 500 tons (5,000)
Safe Thrust: 0
Maximum Thrust: 0
Sail Integrity: 4
Heat Sinks: 95
Structural Integrity: 1

Armor
    Nose: 10
    Fore Sides: 10/10
    Aft Sides: 10/10
    Aft: 10

Cargo
    Bay 1:  Small Craft (1)         1 Door   
    Bay 2:  Cargo (2120.0 tons)     1 Door   

Ammunition:
None

Dropship Capacity: 1
Grav Decks: 0
Escape Pods: 6
Life Boats: 6
Crew:  12 officers, 55 enlisted/non-rated, 5 bay personnel

Notes: Equipped with
    1 Energy Storage Battery
75 tons of standard aerospace armor.

Weapons:     Capital Attack Values (Standard)
Arc (Heat) Heat  SRV     MRV     LRV      ERV    Class       
None

The "trick" here is not having a grav deck.  Normally, this would leave necessarily long deployment crews unhealthy.  But if there is no jumpship to worry about you can just spin the entire Arc to give a half-g near the exterior.  And if there is a jumpship then the Arc crew can additionally rotate on and off the jumpship in order to experience a full g regularly.   I'm particularly thinking about deploying these on a jump circuit so there is highly regular access to a jumpship with a grav deck like the Voyager.

[Red Pins]

Yep.  Love these things.  Nothing says it has to be a quarter-million tons, after all.  Of course, I cheated and made mine drones to make them smaller. Now JS only need a control system for them, and repair crews are sent out by the planet on a long-duration small craft.   

[Dragon Cat]

I'd have thought the additional maintenance of using the engines to spin, the stress on the superstructure and the crew not having a stable place for gravity during times you do have JumpShips present would be outweighed just adding a deck or two

If you are at a staging area the space station should be somewhere you could send the crew of your JS for some R&R, see 4 different walls, maybe spend some cash

That's why I'd have a station to bring in trade from those who won't be going in system

[Lagrange]

Yep.  Love these things.  Nothing says it has to be a quarter-million tons, after all.  Of course, I cheated and made mine drones to make them smaller. Now JS only need a control system for them, and repair crews are sent out by the planet on a long-duration small craft.   

The drone options seem to be much more expensive?  I'd love to make that work but I couldn't figure out how to do so.

I'd have thought the additional maintenance of using the engines to spin, the stress on the superstructure and the crew not having a stable place for gravity during times you do have JumpShips present would be outweighed just adding a deck or two

Well, the engine stress seems minimal since you fire the engines for just a few minutes to develop a half-g spin in my understanding.  This is presumably a small fraction of station-keeping engine use. 

If a half-g is to much for fluff reasons you could go with 1/3 g--it's still enough to be better than nothing and my understanding is that people survive fine on Mars in universe which has 1/3 g.  According to the rules at least, space stations can take 1/2 g. 

W.r.t. jumpships not present, I'm intending this for use on a jump circuit so a jumpship will not be present <8 hours per week.

W.r.t. cost, the arc is dirt cheap.  If you add even a minimal grav deck, it doubles the price.   

If you are at a staging area the space station should be somewhere you could send the crew of your JS for some R&R, see 4 different walls, maybe spend some cash

That's why I'd have a station to bring in trade from those who won't be going in system

The other constraint here is that I want it to be transportable by a a https://bg.battletech.com/forums/aerospace/voyager-jumpship/Voyager Yardship which can only go up to 107k tons so you can construct or alter the jump circuit relatively easily.  Given the energy storage batteries are 100k tons and the overhead of a station, this leaves very little room for additional stuff. 

The kind of station you are thinking about is closer to the Way Station design (at the bottom of the first post).  That costs 150M.  Given the costs are so disparate, it seems fine to just have two stations at a jump station stop if both opportunities are desired.

[monbvol]

The part I'm not entirely following is how the engines that are rules limited to 0.1g are able to generate 0.5g.

[Daryk]

Grav decks are so light, I can only wonder why you wouldn't spring for them over a system that burns fuel... 

[Lagrange]

The part I'm not entirely following is how the engines that are rules limited to 0.1g are able to generate 0.5g.

The engines impart a spinning motion for 5 minutes and then shut off leaving the station in a 0.5g spin.  It takes another 5 minutes of thrust in the other direction to cancel the spin when that's needed.

[Daryk]

Five turns of fuel is still more than a grav deck burns...

[monbvol]

Fuel is pretty cheap too.

I'll have to wait until I get home to do the break even calculations but my quick eyeballing says that it'll take a rather long time before a gravdeck wins out.

The engines impart a spinning motion for 5 minutes and then shut off leaving the station in a 0.5g spin.  It takes another 5 minutes of thrust in the other direction to cancel the spin when that's needed.

Still kind of dubious about that working.  At only 107,000 tons I can't see it being that big.  Too fast of rotation with too small a radius will leave people non-functional.

[Daryk]

A small grav deck is only 50 tons.  I can't imagine the pay back being that long...

[wolfgar]

The OP says that they did this so that a Yardship could transfer the station,

If thats the case then why not make it modular so that it can be assembled from 50kton sections, this allows you to have your grav deck as well as everything else, and not have to spend fuel mass, (and internal stress of the frame) by spinning up and down the station.

[Lagrange]

Five turns of fuel is still more than a grav deck burns...

Let's think about a more precise calculation.

The 'small habitat' in TR3057 has a width of 500 meters and so a radius of 250 meters at 120K tons, which is in the ballpark of what we are looking at.  To reach a half g, you want the velocity on the outer shell to satisfy v²/r ~= 4.9 m/s².  Calculating, v = (4.9*250)^0.5=35 m/s.  So for a 1/10th g drive, could spin this up in ~36 seconds.

Logically you could use the main drive if it was arranged in a Mammoth style and you could spin the drive axis 90 degrees, but perhaps we should just use attitude adjustment thrusters.  Attitude adjustment thrusters give a rotational vector in SO at the rate of 60 degree rotation per minute per thrust point.  We're looking for a rotation velocity of 480 degrees per minute, so that takes 8 thrust points which requires 40 minutes with a 1/10th g drive.

So, depending on the rules, the fuel usage varies between .8 tons in the worst case (tactical thrust with standard attitude adjustment thrusters), 0.027 tons (strategic thrust with standard attitude adjustment thrusters), .012 tons (swivel mount main drive with tactical thrust), or even .00072 tons (swivel mount main drive with strategic thrust). 

If you want to go with the worst case, that costs 1.6 tons to spin up and spin down which costs a worst case of 24K c-bills according to CO.  The _smallest_ grav deck (<100M radius) adds 25M to the cost of a station which suggests a breakeven after 1042 weeks if you spin up and spin down once per week.  That's about 20 years and the fuel cost is a negligible additional to the stationkeeping fuel costs.

Personally, I believe the 'strategic thrust with standard attitude thrusters' fits the situation better.  That would have a buyback time of 577 years.

Still kind of dubious about that working.  At only 107,000 tons I can't see it being that big.  Too fast of rotation with too small a radius will leave people non-functional.

The question seems to be "what is the radius"?  Published figures are fairly large: 250meters for the small habitat, 100 meters for a Behemoth, 138 meters for a Mammoth.  These are certainly in the ballpark of grav deck radiuses.

If thats the case then why not make it modular so that it can be assembled from 50kton sections, this allows you to have your grav deck as well as everything else, and not have to spend fuel mass, (and internal stress of the frame) by spinning up and down the station.

Modular stations have a multiplier of 50 instead of 5, so the space station cost balloons to 280M c-bills.   It's definitely cheaper to just use a grav deck.

[monbvol]

Let's think about a more precise calculation.

The 'small habitat' in TR3057 has a width of 500 meters and so a radius of 250 meters at 120K tons, which is in the ballpark of what we are looking at.  To reach a half g, you want the velocity on the outer shell to satisfy v²/r ~= 4.9 m/s².  Calculating, v = (4.9*250)^0.5=35 m/s.  So for a 1/10th g drive, could spin this up in ~36 seconds.

Logically you could use the main drive if it was arranged in a Mammoth style and you could spin the drive axis 90 degrees, but perhaps we should just use attitude adjustment thrusters.  Attitude adjustment thrusters give a rotational vector in SO at the rate of 60 degree rotation per minute per thrust point.  We're looking for a rotation velocity of 480 degrees per minute, so that takes 8 thrust points which requires 40 minutes with a 1/10th g drive.

So, depending on the rules, the fuel usage varies between .8 tons in the worst case (tactical thrust with standard attitude adjustment thrusters), 0.027 tons (strategic thrust with standard attitude adjustment thrusters), .012 tons (swivel mount main drive with tactical thrust), or even .00072 tons (swivel mount main drive with strategic thrust). 

If you want to go with the worst case, that costs 1.6 tons to spin up and spin down which costs a worst case of 24K c-bills according to CO.  The _smallest_ grav deck (<100M radius) adds 25M to the cost of a station which suggests a breakeven after 1042 weeks if you spin up and spin down once per week.  That's about 20 years and the fuel cost is a negligible additional to the stationkeeping fuel costs.

Personally, I believe the 'strategic thrust with standard attitude thrusters' fits the situation better.  That would have a buyback time of 577 years.

The question seems to be "what is the radius"?  Published figures are fairly large: 250meters for the small habitat, 100 meters for a Behemoth, 138 meters for a Mammoth.  These are certainly in the ballpark of grav deck radiuses.

I think the size problem for me comes down to perhaps a poor representation of the issue from the O'Niell Cylander stations that need an 8km diameter to achieve 1g at 2.8 degrees per minute.

But there is another case for using a gravdeck instead of spinning the station.  You need to charge the battery on the station somehow.  I know 500 tons of fuel provides quite a few burn days but without a sail(unusable if you spin the whole station) that does put a bit of a bottleneck on the one docking collar and one small craft bay to keep it topped up.

[Lagrange]

But there is another case for using a gravdeck instead of spinning the station.  You need to charge the battery on the station somehow.  I know 500 tons of fuel provides quite a few burn days but without a sail(unusable if you spin the whole station) that does put a bit of a bottleneck on the one docking collar and one small craft bay to keep it topped up.

Is there anything canonical saying battery charges from fuel or sail?  I agree a sail cannot be up if you are spinning. 

[AlphaMirage]

You could possibly do it if the sail is coming out the narrow ends of a station rather than from the long portion.

I believe canonically Jumpsails are deployed end on in that fashion already. I fluffed it as fuel for my Free Trader's guide but there could just be a complex clipper rig of solar sails linked to each battery or just a massive monosail with distributed power inside the station itself.

[Retry]

Recharge stations can use sails (technically solar collectors but they're fundamentally the same thing) to charge their batteries, that's in Strat Ops & Battlespace.  They probably can use fuel too (probably also Strat Ops but I'm feeling a bit lazy), but that would reduce one of the main draws of recharge stations.

[Red Pins]

Recharge stations can use sails (technically solar collectors but they're fundamentally the same thing) to charge their batteries, that's in Strat Ops & Battlespace.  They probably can use fuel too (probably also Strat Ops but I'm feeling a bit lazy), but that would reduce one of the main draws of recharge stations.

Do we know how many sails they can collect power from at once? 

[Retry]

If you mean how many batteries the sail/solar collector can charge concurrently, it's all of them.

[Red Pins]

Sorry, how many can be installed, I mean.

[Retry]

You install 1 Sail, and that sail services all the batteries.  Presumably the 100 MT weight of the battery also includes any expansion of the sail required to get enough energy to service those batteries.

[Daryk]

I'd be more inclined to believe attitude thrusters use tactical thrust vice strategic.  Also, spinning the whole ship complicates docking.

[Lagrange]

I'd be more inclined to believe attitude thrusters use tactical thrust vice strategic. 

Maybe.  It's still a rounding error on the overall fuel budget so the exact details don't seem relevant.

Note though that in the intended usage, the Arc doesn't need to spin since a jump circuit jumpship with a grav deck is docked almost all the time. 

The Sloth station would spin if it's doing a Zenith/Nadir<->planet transit.

Also, spinning the whole ship complicates docking.

Definitely.  You could only dock on the spin axis and anyone wanting to dock would need to match spin first.

Recharge stations can use sails (technically solar collectors but they're fundamentally the same thing) to charge their batteries, that's in Strat Ops & Battlespace.  They probably can use fuel too (probably also Strat Ops but I'm feeling a bit lazy), but that would reduce one of the main draws of recharge stations.

I agree they can use sails---I'm just any explicit connections to energy storage batteries.  Anyways, I overlooked the solar sail in the Arc design---fixed now.

[monbvol]

Is there anything canonical saying battery charges from fuel or sail?  I agree a sail cannot be up if you are spinning.

Not entirely sure where it is now with all the book splits and re-organizations but in StratOps beore the splits yes if not using jumpsails it burns 10 days worth of fuel to charge from onboard reactors.

You could possibly do it if the sail is coming out the narrow ends of a station rather than from the long portion.

I believe canonically Jumpsails are deployed end on in that fashion already. I fluffed it as fuel for my Free Trader's guide but there could just be a complex clipper rig of solar sails linked to each battery or just a massive monosail with distributed power inside the station itself.

The laws of conservation of energy and momentum mean there is no good way to deploy a sail while the entire station itself is spinning.  Jump sails are described as being kilometer+ in diameter.  So if the station spins it is a matter of when not if the sail's larger diameter creating a rotational offset causes it to fold in on itself and become useless until untangled.

[Lagrange]

Not entirely sure where it is now with all the book splits and re-organizations but in StratOps beore the splits yes if not using jumpsails it burns 10 days worth of fuel to charge from onboard reactors.

Found it---it's in my SO on page 138.

The laws of conservation of energy and momentum mean there is no good way to deploy a sail while the entire station itself is spinning.  Jump sails are described as being kilometer+ in diameter.  So if the station spins it is a matter of when not if the sail's larger diameter creating a rotational offset causes it to fold in on itself and become useless until untangled.

An extremely gentle spin might be helpful in unfurling the sail but anything like the spin we are talking about here would shred it.  My understanding is that sails are made to handle at most station keeping drives (i.e. .1g).

[Daryk]

And that axially...

[Retry]

I agree they can use sails---I'm just any explicit connections to energy storage batteries.

The direct cable connections?  That's mentioned in Strat Ops pg88

[idea weenie]

I think the size problem for me comes down to perhaps a poor representation of the issue from the O'Niell Cylander stations that need an 8km diameter to achieve 1g at 2.8 degrees per minute.

But there is another case for using a gravdeck instead of spinning the station.  You need to charge the battery on the station somehow.  I know 500 tons of fuel provides quite a few burn days but without a sail(unusable if you spin the whole station) that does put a bit of a bottleneck on the one docking collar and one small craft bay to keep it topped up.

From TO:AU&E p118 (corrected 6th printing):

Energy Storage Batteries include massive power plants that can recharge their storage systems about as fast as they can be safely discharged into a
JumpShip. An Energy Storage Battery can thus prepare a new charge for a JumpShip in 100 hours (which can occur concurrently while recharging a K-F
drive). Full rules on constructing space stations are covered in Strategic Operations.

So based on this Energy Storage Batteries use negligible fuel demands to keep the batteries topped up.  The fun part is that the same Energy Storage Battery uses its full charge no matter if it is charging a 90 kTon Scout Jumpship as it would for a 2.4 MTon Leviathan Warship.

You install 1 Sail, and that sail services all the batteries.  Presumably the 100 MT weight of the battery also includes any expansion of the sail required to get enough energy to service those batteries.

100 MT or 100 kT for an Energy Storage Battery?   

Found it---it's in my SO on page 138.
An extremely gentle spin might be helpful in unfurling the sail but anything like the spin we are talking about here would shred it.  My understanding is that sails are made to handle at most station keeping drives (i.e. .1g).

At this point a smart station designer might have the sail separate from the station and a microwave power relay to transfer energy.  As far as I know, it doesn't matter if the microwave emitter turns 360 degrees every few minutes relative to the receiver.

[Retry]

100 MT or 100 kT for an Energy Storage Battery?

Some day I'll get the units right without hiccuping and missing by three orders of magnitude.  But today is not that day...

[Daryk]

It happens to us all now and then... no worries!