A couple of questions regarding Grav Decks.

[R.Tempest]

 1: How does the station keeping drive on a Jumpship affect the Grav Deck. In the artwork the deck is oriented at a right angle to the direction of thrust. I realize thrust here is very low but would it be felt on the Grav deck. Clearly the Grav decks on Warships are there for use when the ship is not using the Interplanetary drive. I may have asked this on the old board.
2: On a small Grav deck, or any ship mounted one I suppose, would there be enough of a difference in generated G-force between a persons feet and their head to cause dizziness or nausea or pooling of blood in the feet.

[Weirdo]

1: If a unit is intended to use the grav deck and station-keeping drive at the same time(such as a JumpShip or station), then the deck's walking surface can always be built at a slight angle, calculated so that the offset force from the angled rotation is cancelled out by the force from the station-keeping drive.

Given how little thrust a station-keeping drive puts out(in Battletech terms), the angle needed is probably extremely slight.

2: It can, which is why smaller decks rarely rotate fast enough to produce a full 1G. I believe this is addressed in StratOps somewhere. Long story short, you get enough Gs that regular exercise will keep you healthy, or at least, healthy enough to do your job until you can have some R&R on a planet or a larger grav deck.

[Frabby]

The design concept has been called "carousel mounting" on this forum. Basically, the "floor" of the grav deck isn't installed at a fixed angle, it can tilt to accomodate a perpendicular thrust vector from the station keeping drive.

Also, I doubt that BT grav decks look like in the 2001 - A Space Odyssey movie on the inside. I'd rather expect them to be a number of separate cabins, used primarily for sleeping/downtime.

[Weirdo]

Downtime, yes, but probably not sleep. From what I understand, if you're only going to spend part of your day under gravity, to maintain health you need to spend that time working your bones and muscles. You'll want stuff where people are active, such as gyms, maybe a jogging track on larger decks, lounges, bars, stuff like that. Actual unconsciousness time does nothing for you in this regard, so you might as well do that in zero G. I suspect only the largest stations actually put people's quarters on the grav deck.

[Daryk]

Depending how "tall" the ring is, the sleeping quarters could be in the lightest gravity section simply for comfort, with the gyms and such in the "lowest" part.

[Weirdo]

If you've got multiple floors on your grav deck, I'm fairly certain you're already in the realm of largest stations. Remember, most grav decks aren't bicycle wheel structures like we often visualize, more like subway cars on a loop-shaped track. After all, the middle area has to be kept available for structural members and various systems to pass through.

[Daryk]

If it's an Argo style deck, it could have more than one level even though the square footage meter-age is relatively modest.

[Weirdo]

As in the ship from HBS Battletech? I could see that, yeah. There are probably very good reasons why 99% of all space units in Battletech use wholly internal grav decks, though.

[Daryk]

Totally with you on that... moving parts where they can be shot tend not to stay moving for long...

[cray]

Totally with you on that... moving parts where they can be shot tend not to stay moving for long...

The Argo gets away with it because it was specified as an utterly civilian vessel built at the peak of the Star League.

[Kovax]

If you've got multiple floors on your grav deck, I'm fairly certain you're already in the realm of largest stations. Remember, most grav decks aren't bicycle wheel structures like we often visualize, more like subway cars on a loop-shaped track. After all, the middle area has to be kept available for structural members and various systems to pass through.

More likely, PAIRS of subway cars, spaced 180 degrees apart to preserve balance, and probably with some sort of fluid pumping system to equalize their masses as people/objects enter and leave the cars.  Spinning a single heavy object around the central axis would tend to introduce a lot of wobble.

[Weirdo]

I was thinking of a single continuous circle of cars honestly. That way you can still have a 2001-style jogging track, but safety doors can close when needed to preserve pressure.

[cray]

More likely, PAIRS of subway cars, spaced 180 degrees apart to preserve balance, and probably with some sort of fluid pumping system to equalize their masses as people/objects enter and leave the cars.  Spinning a single heavy object around the central axis would tend to introduce a lot of wobble.

I wouldn't worry about the transfer cars' mass versus the tonnage of a grav deck, which includes the gravdeck mechanism and any quarters, SI tonnage, and other facilities included in it. The balancing system would be able to handle much more than the cars.

[Kovax]

Most importantly, if you start work on a gravitational deck in your campaign, finish the job.  You don't want people to accuse you of not playing with a full deck.

[marcussmythe]

Silly question:

How does one enter and exit the grav deck?  Do you stop it?  Are there long doors on the deck and the adjoining, non-rotating parts of the ship that open when they match up (dont get caught by the rotation!), holes in the grav deck ‘ceiling’?  Something else?

My best mental picture had the grav deck laid out below (+’s are ship ‘normal hull’, —————— represents the transfer car track, >>>>>>>> is the transfer car,  and ===== as the grav deck)

++++++++++++++++++++++++++
——->>>>——->>>>>>———>>>>>
==========================


The transfer cars would be at rest relative to the hull, doors open to the hull.  Doors close, transfer cars all accelerate to the speed of the grav deck, and match up with doors on the other side while people come up to 1G.  Doors open, and people in car climb down ladders/stairs onto grav deck.  Doors close, transfer car slows to match hull.  Repeat.

[Alsadius]

I sort of imagine it like The Martian - there's a ring with spokes leading to the centreline of the ship, and at the axis of the ship there's a doorway where you can go from the spinny bit to the non-spinny bit. You're not spinning all that fast in RPM terms (a 100m grav deck producing 1g spins at 3 RPM, and they tend to produce much less than 1g in practice, so you're probably dealing with ~1 RPM), so you can easily just move in and out.

[Weirdo]

Per StratOps page 139, transfer cars is exactly right, though I don't think ladders would be necessary. Easier to just put the transfer car track alongside the grav deck track at the same radius. A full description of what you can put on grav decks and other tidbits is on page 140.

Long story short: The classic grav deck from 2001? That wouldn't provide jack squat in the way of useful gravity. For a deck that small to be useful, it'd have to spin so fast that you'd be horking every time you moved your head because of coriolis effects, not to mention the weird wind effects you'd get between the stationary air in the middle and the air moving many tens of kph at the rim. On top of that, Discovery must have been very weak structurally, since a grav deck that goes all the way to the middle like that leaves no room for a keel or spine.

[idea weenie]

Per StratOps page 139, transfer cars is exactly right, though I don't think ladders would be necessary. Easier to just put the transfer car track alongside the grav deck track at the same radius. A full description of what you can put on grav decks and other tidbits is on page 140.

Long story short: The classic grav deck from 2001? That wouldn't provide jack squat in the way of useful gravity. For a deck that small to be useful, it'd have to spin so fast that you'd be horking every time you moved your head because of coriolis effects, not to mention the weird wind effects you'd get between the stationary air in the middle and the air moving many tens of kph at the rim. On top of that, Discovery must have been very weak structurally, since a grav deck that goes all the way to the middle like that leaves no room for a keel or spine.

I thought the grav deck like that was contained in the 'ball' at the front of Discovery?

Most importantly, if you start work on a gravitational deck in your campaign, finish the job.  You don't want people to accuse you of not playing with a full deck.

That was horrible.  Wish I had thought of it

[Weirdo]

I thought the grav deck like that was contained in the 'ball' at the front of Discovery?

It was, but given that the ball also contains most/all the 'people live here' bits, it's preferable for that area to survive some damage.

[Arkansas Warrior]

IIRC, some of Kevin Killainy’s Chaos Irregulars stories include sections taking place on a grav deck.  The Engadine two-parter, I think.  It’s been a while though, I’d have to read it again to remember much detail.

[marcussmythe]

Per StratOps page 139, transfer cars is exactly right, though I don't think ladders would be necessary. Easier to just put the transfer car track alongside the grav deck track at the same radius. A full description of what you can put on grav decks and other tidbits is on page 140.

Long story short: The classic grav deck from 2001? That wouldn't provide jack squat in the way of useful gravity. For a deck that small to be useful, it'd have to spin so fast that you'd be horking every time you moved your head because of coriolis effects, not to mention the weird wind effects you'd get between the stationary air in the middle and the air moving many tens of kph at the rim. On top of that, Discovery must have been very weak structurally, since a grav deck that goes all the way to the middle like that leaves no room for a keel or spine.

Teach me to RTM first...  thank you, sir.

[Warship]

I seem to remember in one of the earlier novels where Phelan was climbing down onto a grav deck in a Clan ship and not into cars on a track.  Not owning StratOps, have things been retconned?  Is there any new data on the width and height of a deck based on the tonnage?  If not, I would redesign just about every Jumpship with additional decks used as crew quarters.  Although I agree exercising under gravity helps your skeletal and muscular systems, sleeping under gravity must provide a bonus of some sort.  With their relatively low cost in tons and C-Bills, I would redesign every Jumpship to have several.

[Weirdo]

More like people have put more thought into stuff since older things were written. What was written in the past can't be unwritten(and I'm pretty sure they're never going to issue errata), but that doesn't mean the newer stuff can't be more accurate.

My advice? When reading the older stuff, just fix it in your brain, or gloss over it.

[Daryk]

I'd take it as there simply being more than one way to skin this particular cat...

[Warship]

More like people have put more thought into stuff since older things were written. What was written in the past can't be unwritten(and I'm pretty sure they're never going to issue errata), but that doesn't mean the newer stuff can't be more accurate.

My advice? When reading the older stuff, just fix it in your brain, or gloss over it.

I just edited, but it has been about twenty years since I read the novel in question.

[Weirdo]

As I understand, sleeping in gravity does nothing at all for bone/muscle loss. It's activity or nothing.

[Warship]

I am thinking mental health-wise.

[Weirdo]

No idea if sleeping in gravity feels better than sleeping in zero-g, so I don't know if we can assume there's any mental health benefit.

[Warship]

Gameplay-wise, it probably does not matter.  I just keep thinking of a family-owned jumpship traveling around the Inner Sphere just making their way, Firefly-ish.  Maybe they have a couple of Small Craft for the occasional planetary landfall.  But, for the most part, they live aboard ship.  As such, I am thinking they need a more constant exposure to gravity.

[Weirdo]

Children, yes. I think there was a bit in one of the Camacho's Caballeros novels that said when in space, children of the unit spent most of their time on the JumpShip's grav deck.

I imagine that spacer families avail themselves of station grav decks whenever they're available.

[Frabby]

No idea if sleeping in gravity feels better than sleeping in zero-g, so I don't know if we can assume there's any mental health benefit.

There's the danger of suffocating in your own CO2 bubble when sleeping in vacuum. But you don't quite need to throw a grav deck at this particular problem.

[Weirdo]

I keep hoping to find an environment where my wife won't insist on running some kind of fan at all times, but nooooo...you have to dash my dreams. :'(

I imagine any amount of air movement at all would prevent that. Would the movement caused by breathing itself do that, or should we just thank standard ventilation systems?

[Frabby]

I imagine any amount of air movement at all would prevent that. Would the movement caused by breathing itself do that, or should we just thank standard ventilation systems?

I don't recall where I heard about CO2 bubbles, sorry. But they were mentioned as a non-obvious space travel hazard, so I suppose this means breathing alone (at least slow breathing while asleep) may not be enough.

[cray]

No idea if sleeping in gravity feels better than sleeping in zero-g, so I don't know if we can assume there's any mental health benefit.

Sleep is annoying on primitive, zero-G space stations. Even eliminating the noisiness of the ISS, zero-G conditions tend to come with nausea, a falling sensation, and assorted aches and pains that disrupt sleep. Astronauts are estimated to get an hour less sleep than people on similar gravity-based schedules.

I imagine any amount of air movement at all would prevent that. Would the movement caused by breathing itself do that, or should we just thank standard ventilation systems?

The "cabins" in the US section of the ISS are "well ventilated". "The catch is that they need to tether themselves to something to avoid floating away in the air currents."

I don't recall where I heard about CO2 bubbles, sorry. But they were mentioned as a non-obvious space travel hazard, so I suppose this means breathing alone (at least slow breathing while asleep) may not be enough.

Generally, air is pretty well stirred in real spacecraft for multiple reasons. Besides CO2 control, moving air is the only way to control cabin temperature - otherwise, stationary cold plates or heaters will have the same sort of "bubble" problem as CO2 build-up. Moving air also tends to be key to dust, dirt, and lost item control - Skylab astronauts learned to check air intakes anytime small items disappeared, and there are now filtered air intakes in common eating areas and the toilets. (Crappers are one big wet-dry shop vac. After the Assteroid problem on Apollo 10 and loud astronaut objection to using plastic baggies throughout Gemini and Apollo, Skylab and subsequent US spacecraft have included proper toilets. Defecation is handled by what is basically a large-bore vacuum cleaner. Zero-G toilets in BT also suck, so to speak, hence the popularity of grav deck-based toilets.)

[R.Tempest]

 What about showers/baths/sinks to brush your teeth at? Would you need to offset the drain slightly in a sink in the direction opposite the spin of the deck?

[cray]

What about showers/baths/sinks to brush your teeth at? Would you need to offset the drain slightly in a sink in the direction opposite the spin of the deck?

Nope. The little bit of curve to dropped items is negligible at a scale of 1-2 meters.

Also, does moving the drain around every help your average slob get everything in the sink or toilet? :)

[R.Tempest]

 Point. Definitely a point.

[Von Jankmon]

Thankfully this is a part of Battletech canon taken neatly from real physics and space architecture concepts.

http://www.artificial-gravity.com/JBIS-52-7-Hall.pdf

The above is an excellent introduction to the design involvement and doesnt get in the way of jumpship design.

[R.Tempest]

 Very interesting. I will have to read it a few more times.

[Daryk]

Interesting indeed!  Just reading the list of physiological issues makes me want to add a grav deck to the Scout.  It's not like there isn't room (or even tonnage).

[R.Tempest]

 My impression is that thrust induced G-force has little or no ill effects. Spin induced G however has some problems. I expect the disorientation from moving left or right would be directly related to the diameter of the deck (bigger is better). Having a running track might also problematic.
 These are all issue's that probably won't be resolved until something is built either in orbit or as part of long voyage spacecraft.

[cray]

I expect the disorientation from moving left or right would be directly related to the diameter of the deck (bigger is better).

Yep. Strategic Operations captures some of the diameter-spin speed-puke factor details. The rules of thumb I pulled from NASA studies for StratOps were:

3-4rpm+: No one ever quite adapts fully, and the inner ear will always note weirdness when the head is turned
1-3rpm: People can adapt and not be overly bothered by spin effects
<1rpm: The inner ear might not really notice the spin

At 1rpm, 1G requires an 1800m diameter (approximately). All canon, rules-legal, 1G gravdecks will be noticeable to human inner ears.

Having a running track might also problematic.

Actually, less than you'd expect. If you're keeping your inner ears oriented fairly constantly in one direction (e.g., running around the circumference of a gravdeck), then they're fine. Skylab astronauts managed to run around the tiny interior of that station without horking. Meanwhile, sitting still in one spot of a narrow-diameter, high speed gravdeck (e.g., Disney's Mission: Space) and turning your head can be disorienting (personal experience - had to hold my head still).

[Daryk]

*snip*
At 1rpm, 1G requires an 1800m diameter (approximately). All canon, rules-legal, 1G gravdecks will be noticeable to human inner ears.
*snip*

Oh?  ???

Were the construction rules errata'd, or does it still say "250+ meter" grav decks are 100 tons?

[cray]

Were the construction rules errata'd, or does it still say "250+ meter" grav decks are 100 tons?

My 3rd printing of TacOps, p. 407 (c2013), lists:

*Under 100m diameter: 50 tons
*100-250m diameter: 100 tons
*Over 250m diameter: 500 tons

[Daryk]

Ah, so there has been an errata.  There's still that pesky "Over 250m" bit though, implying that even an 1,800m diameter grav deck would only be 500 tons.

While I have you here Cray, since the rules no longer support the Scout JumpShip having a double sized station keeping drive (for gravity maneuvering), will a grav deck be added to its official stats?  I'm pretty sure the 50 tons are there to support that...

[Daryk]

Nope, just checked my books, and I was mis-remembering the break points.  It's been 50/100/250+ for quite some time now.  Thanks for straightening me out Cray!

As far as a grav deck on the Scout, the largest diameter the deck plans I was working on has 82 meters internal, with a one meter thick hull that could mean 84 meters is what to use for the construction rules (both are under 100m, so no worries, really).

Using that extremely useful "Comfort Zone" chart in the paper Von Jankmon linked, it looks like a ~40m radius can't quite get to 1G at 4 rpm.  The good news is that it looks like 0.5G is possible in the 2-3 rpm range, and the AToW rules don't inflict major penalties until you're below 0.2G.  Of course, the rules are silent on what percentage of your day you have to spend in less than 0.2G to receive those penalties (they were written assuming low planetary gravity).

Construction-wise, this actually could cause a problem with the KF core.  I took the "door" looking part of the nose (that's off centerline) as the core replacement/maintenance hatch.  If the core doesn't have to be the entire length of the ship, this could be essentially ignored by just leaving a "tube" that could be aligned with the core when the grav deck isn't spinning.  If it DOES have to be the length of the ship, then I need to start over (which I basically have to do anyway since I lost the thumb drive that had the most recent Visio file) to put the core on the exact centerline.  That would still leave a bit of a trick for getting to and from the grav deck, but it's not insurmountable.

At the very least, a grav deck will help soak up some of the HUGE volume available inside even a "small" JumpShip like a Scout.

[Robroy]

I use this.

http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm

It uses grav deck radius vs. BTs diameter. Basically from what I have seen using it is it does not like going over 2 rpm before becoming uncomfortable.

[Daryk]

That's a handy calculator, thanks!  :thumbsup:

Using it, it looks like 0.4G will get under Cray's 3 rpm figure a the rim, but of course requires a period of adaptation.  0.4G is also twice the AToW 0.2G limit, so I think it works for a JumpShip crew.

Walking the radius in at 3 rpm makes it look like you can get about 5 4 useful decks of space before the Tangential Velocity gets uncomfortable.  On the deck plans I'm working on, the "strip" of hull at maximum radius is 11 meters wide (or tall, if you look at the ship lengthwise), so that would be ~260 2,800 square meters at the rim.  Going with 2.5 meter "tall" decks (to include headroom, thickness of the decking, and necessary cabling and piping), the total usable comfortable deck space would be ~1160 10,300 square meters.  Another ~770 square meters are on the five decks above that before the Tangential Velocity gets really uncomfortable.  The last five decks (leaving a 9 meter diameter "tube" in the center to move cargo) yield about 375 square meters of quite disorienting space (probably for storage).

EDIT: Various corrections to calculations I did while distracted by my wife and children.

[Robroy]

One thing is, according to the spin calculator, the Merchants 40 meter grav deck is all kinds of uncomfortable. In order to get any benefits the rpm gets to high.

It seems that to be comfortable and get any benefit you need a 100m diameter deck, min.

[Daryk]

At a full 1G, certainly... that's why I mentioned 0.4G above (to keep it in the comfort zone).

[Robroy]

Sorry. Was not commenting on your plans. Just what I was seeing from spin calculator.

Your 82m deck will at worse need a little time to get use to, but that can probably be said for most grav decks.

[Robroy]

While we are talking grav decks, is it said anywhere how wide they are?

[Daryk]

Nope... I think Cray deliberately left that vague in the rules.  I'm only using 11 meters because I'm trying to stick to the art from the original DropShips and JumpShips book.

[R.Tempest]

 The description for the Star Lord says its deck is 20 meters wide.

[Daryk]

Since the rules are vague, you could technically rotate the whole ship...

[Von Jankmon]

Small grav decks make more sense than it first appears, you can have a small deck with fairly minimal gravity, it just has some gravity.  It would include sleep couches, wash units and toilets.  All of which benefit from not being in microgravity.

Even better are spindles, basically line the edge of a 'giant spin dryer' with contoured sleep couches.  Split your watches into sleep as well as work shifts.  Send in a sleep shift strap them in and then turn it on for a couple of hours.

With high rotation spin one of the problems will be gravitational differences between head and foot level, spinning sleep couches eliminate most of those problems.

Spindles could also be built very small fitted with contoured seated couches and spun for higher G, say 2-3G for 20 minutes at a time as a health/exercise/spa treatment for space crews.  Independent motion is what causes nausea, people can take a high spin in a single seated position easily.

Spindles would take up negligible mass and volume and could be calculated according to mass allocation for crew.  A spindle with intermittent high spin/strong G will be of more use to a crew health than a weakly but constantly spinning low G grav deck.  Though you need both.  A grav deck with a lounge and toilet facilities makes sense.

[Daryk]

I'm finding an 82 meter diameter isn't all that small.  Even with a strip only 11 meters wide, there appears to be enough room for medical, exercise, messing and berthing with plenty to spare.  2,800 square meters is actually quite roomy, and that's just the highest G deck out at the rim (granted, it's only 0.4G at 3 rpm).  Three more decks remain squarely in the comfort zone, and they're all over 2,000 square meters each, though with slightly less "gravity".

[cray]

Nope... I think Cray deliberately left that vague in the rules.

Yep.

Since the rules are vague, you could technically rotate the whole ship...

Yep. I was sketching out a non-canon WarShip/troop transport that does just that, giving vast 'Mech bays and troop quarters at ~0.5G.

[BirdofPrey]

Considering ships have to be laid out with decks perpendicular to the path of travel for anything that moves at a significant fraction of Gs, wouldn't it be more efficient to hang a counterwieght off the front of the ship and spin around that center of mass rather than trying to spin the ship about its own axis?

[cray]

Considering ships have to be laid out with decks perpendicular to the path of travel for anything that moves at a significant fraction of Gs, wouldn't it be more efficient to hang a counterwieght off the front of the ship and spin around that center of mass rather than trying to spin the ship about its own axis?

Doing that would inhibit the use of the ship's drive. Spinning along the thrust axis presents a gyroscopic complication while under thrust, but isn't impossible. On the other hand, spinning end over end means the drive is pointing the wrong way for half of the ship's rotation.

[R.Tempest]

Doing that would inhibit the use of the ship's drive. Spinning along the thrust axis presents a gyroscopic complication while under thrust, but isn't impossible.

This would be why the rotation has to be stopped before jumping I would think.

[BirdofPrey]

Doing that would inhibit the use of the ship's drive. Spinning along the thrust axis presents a gyroscopic complication while under thrust, but isn't impossible. On the other hand, spinning end over end means the drive is pointing the wrong way for half of the ship's rotation.

Yes, but if you're under thrust, you don't need the grav deck.

[cray]

Yes, but if you're under thrust, you don't need the grav deck.

Stationkeeping at standard jump points is a perfect time for applying both thrust and spin.

This would be why the rotation has to be stopped before jumping I would think.

Is rotation stopped before jumping? Ships can even be moving when they jump.

[Robroy]

Wouldn't you also be spinning the sail if your spinning the hole ship. Wouldn't that be problematic given how fragile they are?

[cray]

Wouldn't you also be spinning the sail if your spinning the hole ship. Wouldn't that be problematic given how fragile they are?

Oops, good point. De-spinning the sail would be quite a mechanical complication for the design.

[Daryk]

*snip*
Is rotation stopped before jumping? Ships can even be moving when they jump.

Ships are by definition moving when they jump, right?

I think it would be easy enough to mount the sail rigging to not spin with the rest of the ship.  Certainly no harder than installing a 50 ton grav deck...

[Robroy]

There are detachable sails.

Or is that just for war ships?

[Weirdo]

Oops, good point. De-spinning the sail would be quite a mechanical complication for the design.

I imagine complications like this are why even stations appear to have internal(or mostly internal) grav decks as opposed to simply rotating large parts(or even the majority) of the station. :)

[R.Tempest]

 Would the sail spinning make that much of a difference? I can see it might be tricky to deploy or fold, but once its out the spin shouldn't make a big difference in its ability to absorb energy. There would be stress at the connecting points for the shrouds, but it's not like there aren't other wonder materials in use.

[Daryk]

Sails have a huge diameter, so the stresses at the rim would be pretty high if you're spinning the ship fast enough for comfortable gravity at the comparably miniscule radius of the hull.

[Von Jankmon]

Oops, good point. De-spinning the sail would be quite a mechanical complication for the design.

Actually a very gentle spin would be a good way to unfurl a sail, then you only need to tension the draw wires to furl the sail not to deploy it to begin with.  As canon sails are depicted with tension cables but not booms this is a plausible explanation as to how sails are unfurled to begin with.

This spin would be very gentle to deploy the sail at the correct speed, so the sail itself might be deployed from a ring  which is spun slowly to fling weighted end sections and draw out the sail, the connecting booms we do see guide the sail with guide wires, they also help with furling the sail, but as the sail extends far beyond them they are not functional as a mast for the sail itself.

[idea weenie]

There are detachable sails.

Or is that just for war ships?

I'd see that being a method of 'cheating'.  You detach the sail and have a small engine and microwave transmitter on it (and maybe a small battery).  The ship itself has a microwave receiver and a larger battery.  The ship spins, and a microwave receiver array is always kept illuminated by the microwave transmitter from the sail.

Think of it as a strip of receiver array around one section of the ship, like a belt.  If the ship needs to repair part of the microwave receiver array, it transmits to the solar sail to charge its onboard battery instead of transmitting the power.  At the same time, the ship switches over to using the onboard battery to charge the KF core.  The maintenance team goes out to repair, and after they are all back inside, the detached sail is instructed to begin retransmitting power at a slightly higher rate so the sail's onboard battery is drained.  The KF core begins charging again from solar power, and the ship's battery is filled with any excess power.

After the ship jumps, it can start charging the KF core off the internal battery, while the detachable sail is deployed and extended.  The battery is large enough to last until the sail array is transmitting power.

[Daryk]

If the sail is detached, how does it keep station?  ???

[cray]

If the sail is detached, how does it keep station?  ???

Well, let's face it, it's not exactly a rapid, screaming plunge into the star. You only need micro-gravity thrust. If you've got, like, a sail attached to a lithium fusion battery adequate to promptly charge a WarShip's drive, then it won't be hard to strap a small fusion motor on to it so it stays put.

[Robroy]

And if it did drift how far would it go in a week. The jump points can be tens to hundreds of millions of kilometres from the star.

[Daryk]

Which then begs the question as to why JumpShips have station keeping drives at all...

[Weirdo]

I figure the sail just has a beacon, and you let it fall, and then pick it up on the way out. As long as you remember to get it before it falls too far, you've got no problems.

JumpShips need drives because they still need maneuvering ability, such as either staying near the jump limit, or climbing back out to the limit after spending a week falling.

[BirdofPrey]

Oops, good point. De-spinning the sail would be quite a mechanical complication for the design.

Certainly MUCH less complicated than trying to make a workable external grav deck, though.  The sail doesn't have to be sealed and power is easy to transmit through a rotary transformer where a grav deck has to handle holding an atmosphere of pressure in a rotating coupling where many lubricants don't work due to vacuum and extreme temperatures, and has to transfer water and life support gases along with power and data.

Well, let's face it, it's not exactly a rapid, screaming plunge into the star. You only need micro-gravity thrust. If you've got, like, a sail attached to a lithium fusion battery adequate to promptly charge a WarShip's drive, then it won't be hard to strap a small fusion motor on to it so it stays put.

Honestly, that's why I was wondering about just spinning th ship on a counterweight.  Station keeping thrust seems fairly pointless, for a ship that will be moving on after a week or two due to how low acceleration the star would be imparting.  It only makes sense to me for actual stations (and ships trying to keep near it) that will be there long enough for people to have noticed it's moved.

[cray]

And if it did drift how far would it go in a week. The jump points can be tens to hundreds of millions of kilometres from the star.

It depends on the stellar type. The actual gravity at the jump points vary. But for anything K-type or brighter the answer is, "not much."

Which then begs the question as to why JumpShips have station keeping drives at all...

SHH! BattleTech starships have station keeping drives! Don't look too closely at canon, dangit! ;)

[Daryk]

Heh... always a good answer, Cray!  ;D

[Robroy]

It depends on the stellar type. The actual gravity at the jump points vary. But for anything K-type or brighter the answer is, "not much."

SHH! BattleTech starships have station keeping drives! Don't look too closely at canon, dangit! ;)

I was under the impression that the reason the distance varied with the star was to insure the gravity from its mass did not interfere with the drive during jumps. So at the jump points there should be practically no gravity.

[Von Jankmon]

Which then begs the question as to why JumpShips have station keeping drives at all...

SHH! BattleTech starships have station keeping drives! Don't look too closely at canon, dangit! ;)

Actually cray you miss out on opportunities to explain canon. Many of the problems in Battletech, though not all, have a plausible explanation that you can add to canon that explains prior unexplained canon tech.

You need station keeping because you actually need to remain in one spot, or at least to fall at a known rate.  Jump drives are not random, they are very precise, and while most jumps are made at zenith and nadir zones (I cant really call them points) it is a good idea to know where you are so you can jump accurately.

Jumps need to be made towards set target coordinates, these themselves can be very precise and can allow for jumps into pirate points if your star charts are accurate.  But your jump is only as accurate as your fix on your current position. If you can moderate your position relative to absolute point of zenith of nadir, or your pirate legrange point, you can jump accurately.

We can take this further and answer yet unasked questions. 
Normally this doesn't matter too much but it still does.  We must assume that jump zones at even zenith and nadir points are coordinated to minimise chances of misjumps into another vessel.  While this can happen anyway, and is admittedly unlikely because of the vastness of space, its is a viable concern if jumps are as accurate as they are made out to be.  It would be a suicidal thing to do to jump directly onto the absolute zenith or nadir coordinates, in case another incautious jump navigator did the same.  So how do you make sure your jump is to a safe location.  You ship has a registration code right?  It probably has a code for the jump engine too, a unique serial number at at least unique to your factions registry.  Say your ships KF drive is Lyran registered and is given a number of #51023, that or a set factor of that is the number of km you dial in as jump-exit coordinates from absolute zenith/nadir for your jump.  You can randomise the direction for the ship or coordinate them for a convoy so that your jump arrival coordinates can't be intercepted, and remain together, but so long as that unique distance is kept you are guaranteed never to jump into another vessel.  This way you can plot jumps based on a set unique numerical variable that doesn't require prior knowledge of other traffic.

Station keeping then becomes important again to guarantee you never drift off into the path of another jumpship.  While the vastness of space makes KF navigation accidents unlikely they do happen and are horrific when they do, so it would pay for jumpship captains to keep station keeping and obey navigation safety protocols.

[Von Jankmon]

I'm finding an 82 meter diameter isn't all that small.  Even with a strip only 11 meters wide, there appears to be enough room for medical, exercise, messing and berthing with plenty to spare.  2,800 square meters is actually quite roomy, and that's just the highest G deck out at the rim (granted, it's only 0.4G at 3 rpm).  Three more decks remain squarely in the comfort zone, and they're all over 2,000 square meters each, though with slightly less "gravity".

The way I see it the 50 tons for the grav deck is specific allocation for deck components, notably spinning mechanism and the hub.  A lot of the mass is taken up by structure mass as its a not insignificant portion of the volume of the ship.  Also it can account for a portion of the mass allocated to crew quarters.

[cray]

Normally this doesn't matter too much but it still does.  We must assume that jump zones at even zenith and nadir points are coordinated to minimise chances of misjumps into another vessel.

No, you don't need to assume. It's stated in Strategic Operations.

Station keeping then becomes important again to guarantee you never drift off into the path of another jumpship.

Post-arrival maneuvers with stationkeeping drives performed to avoid collisions are also in StratOps.

[Von Jankmon]

No, you don't need to assume. It's stated in Strategic Operations.

Post-arrival maneuvers with stationkeeping drives performed to avoid collisions are also in StratOps.

True, but it is not explained how or why in Strat Ops.

A jumpship can come in from anywhere.  You can move your ship and find yourself in the path of a Capellan frieghter with a cargo of beans.  It doesn't know you are there and you dont know its coming.  A mechanic that keeps ships separate yet allows flexibility of movement would be needed.

[cray]

A jumpship can come in from anywhere.

Yes. And that's why StratOps (p. 131) indicates recharge stations and JumpShips park just inside the proximity limit so a JumpShip can't arrive on them.

  You can move your ship and find yourself in the path of a Capellan frieghter with a cargo of beans.  It doesn't know you are there and you dont know its coming.

Since JumpShips park inside the proximity limit to recharge, an arriving JumpShip can't land on them. Therefore, the only way for JumpShips to collide is for them to move by their stationkeeping engines on a collision course. Sensors like drive plume detectors would give days of warning for collision avoidance.

A mechanic that keeps ships separate yet allows flexibility of movement would be needed.

I'd recommend reading up on the "big sky theory." JumpShips are much less numerous than airplanes, operate in volumes billions of times bigger than the entirety of Earth's atmosphere, and have lines of sight that gives them days of advance warning before a collision.

[Kovax]

I'd recommend reading up on the "big sky theory." JumpShips are much less numerous than airplanes, operate in volumes billions of times bigger than the entirety of Earth's atmosphere, and have lines of sight that gives them days of advance warning before a collision.

...except while jumping into a system.  In that case, there is no line of sight in advance of a possible collision.  Then again, jump "points" are more like line segments with a certain amount of "slop" providing thickness, so you have a cylinder of "usable" space extending out from some distance above and below a star.  It could use a ship registration code or some pre-approved value unique to that vessel to determine the target distance from the axis of that line, as a way of reducing (not absolutely preventing) collisions, but ships moving toward or from stations would regularly cross any chosen point along or extremely close to that axis.

Given the massive areas involved, it wouldn't be a common thing to have one ship jump in too close to another, but a few relatively simple and cheap precautions could reduce the already tiny risk by an order of magnitude or more.

[cray]

...except while jumping into a system.  In that case, there is no line of sight in advance of a possible collision.

Which is why StratOps indicates ships usually move inside the proximity limit upon arrival.

[Von Jankmon]

Which is why StratOps indicates ships usually move inside the proximity limit upon arrival.

They are vulnerable during that transition period.
Yes a jump accident is uncommon, but catastrophic when it happens.

It also takes time for a jumpship to get anywhere adding to recharge times.  Coordinate coding fixes all those problems.