Some Questions on 2300 AD Era Ships

[PFVA63]

Hi,

I have a couple questions about 2300 AD era ship's that have confused me for a while that maybe some one here can help me with.

First off, with spin habitats, if you are rotating them in one direction, what prevents the rest of the ship from rotating in the opposite direction? If I am understanding correctly, on craft like helicopters, many of them use tail rotors, or two separate sets of rotors, or even a single set of contra-rotating blades to conter act the tendancy of the craft to want to spin in the opposite direction of the rotors. Is this an issue with starships in 2300 AD, and if so how do they account for this?

Second, from college physics, if I am understanding correctly things like a two-bladed propeller (and I'm assuming a two arm spin habitat) are concidered dynamically not fully stable because their cross-moments of inertia don't cancel out, but on some aircraft this is compensated for by the use of small balancing weights near the hub. As such, on 2300 era ships are similar things necessary for ships with two arm spin habitats?

Third, if I am understanding correctly the stutterwarp drive is supposed to be a reactionless drive, what are the bright shiny things at the back end of some of the ships like shown on the cover of the "Mission Arcturus" ( http://rpg.drivethrustuff.com/product_info.php?products_id=433&it=1 ) or on alot of the ship's shown on the Etranger website ( http://www.users.globalnet.co.uk/~dheb/2300/Admin/Index5.htm )? Are these some of secondary drives for operating in gravity wells?

If anyone has any thoughts I'd be happy to hear from them. Thanks.

Regards

PF

 

[Mithras]

perhaps gyros could be used?

 

[ElHombre]

Oh-oh. It looks like somebody has discovered the wrench in the works. ;-)

1) Yes, spin habitats need a counter-rotational device of some sort. The easiest way to deal with this is to assume that there's some sort of flywheel gyro included in the mechanics of the habitats (thus there wouldn't be any extra costs involved). Ships with two spin habitats will rotate in opposite directions and won't have that problem.

2) Your idea sounds good and doesn't involve any extra rules. Thus, it's perfect.

3)And you've noted another little wrench in the works. I've always assumed that those were used to make orbital adjustments. It's noted that stuuterwarp drive efficiency drops below that of rockets in gravity fields greater than .1G. They don't provide any additional movement and are included in the cost of the drive systems.

 

[TWILIGHT]

The Bayern's Spin sections counter-spin each other.

 

[shanksow]

Hi,

I have a couple questions about 2300 AD era ship's that have confused me for a while that maybe some one here can help me with.

First off, with spin habitats, if you are rotating them in one direction, what prevents the rest of the ship from rotating in the opposite direction? If I am understanding correctly, on craft like helicopters, many of them use tail rotors, or two separate sets of rotors, or even a single set of contra-rotating blades to conter act the tendancy of the craft to want to spin in the opposite direction of the rotors. Is this an issue with starships in 2300 AD, and if so how do they account for this?

Second, from college physics, if I am understanding correctly things like a two-bladed propeller (and I'm assuming a two arm spin habitat) are concidered dynamically not fully stable because their cross-moments of inertia don't cancel out, but on some aircraft this is compensated for by the use of small balancing weights near the hub. As such, on 2300 era ships are similar things necessary for ships with two arm spin habitats?

If anyone has any thoughts I'd be happy to hear from them. Thanks.

Regards

PF

To offset the P-factor, I've always thought there was some sort of internal counter balance in the hub itself. Like a superdense counter-weight 90 degrees off from each support arm that spins in the opposite direction in some sort of "Jeffereies Tube" using superconducting technology (i.e. the counter weights of prop hubs that you mentioned above). This would still be true for ships that have multiple rotating habs. And in those cases, the habs would spin in opposite direction for better direction stablility. So in this example: Spin ring Alpha rotate clockwise around the ship axis, while spin ring Beta spins counter-clockwise.

 

[shanksow]

Hi,

I have a couple questions about 2300 AD era ship's that have confused me for a while that maybe some one here can help me with.

Third, if I am understanding correctly the stutterwarp drive is supposed to be a reactionless drive, what are the bright shiny things at the back end of some of the ships like shown on the cover of the "Mission Arcturus" Are these some of secondary drives for operating in gravity wells?

PF

In a word - yes. I don't think the Star Cruiser rules really covered this (in hindsight now) like they should have. There was always fuel for control thrusters. But the artists that were drawing ships needed something else to convey speed. A glowing blue thruster bell on the backside of a ship does just that. Like in regular Traveller, one must have a means of getting 1 planetary diameter away from a planet before jumping can take place. I'm just trusting my memory on this since its been years since I had a chance to play Star Cruiser or Traveller.

 

[G. Fieendish]

Re:this thread
As I recall, the Stutterwarp drive is completely useless as a means of propulsion at the 0.1G gravity gradient of a planet....
While a civilian ship may have the equivalent of navigation thrusters for stationkeeping or for heading at low speed for a orbitial facility, military vessels need fairly hefty M-drives, for changing their delta-V in combat situations.....
There's a nice illustration of a spin habitat equipped vessel, (the "Wagon Wheel") at Classic Battletech.com's download section...
(They allow you to down PDF "tasters" of their technical readouts, & the "Wagon Wheel" is one of their tasters....)

 

[GJD]

In Artur C Clarkes 2001 the Discovery had an internal spin hab, a horizontal disc running above the pod bay and below the bridge. In the novel it mentions having a flywheel and a gearing system to counteract the torque, and having to keep supplying power as the bearings induced friction and slowdown.

In 2010 the derelict discovery is found to be rotating end over end, as the angular momentum of the spin hab has been transferred to the ship itself. I can't get my head around the physics in this, but Clarke is suaually pretty sound.

G.

 

[aramis]

I suspect Mr. Clarke forgot he had counterrotatng weights...

It should have simply come to a stop, perhaps with a very slow spin.

Now, if the net spin between the two was for some reason imballanced, gyroscopic precession would take over, and slowly impart a wobble...

 

[AndrewR]

Hi PF!

First off, with spin habitats, if you are rotating them in one direction, what prevents the rest of the ship from rotating in the opposite direction? If I am understanding correctly, on craft like helicopters, many of them use tail rotors, or two separate sets of rotors, or even a single set of contra-rotating blades to conter act the tendancy of the craft to want to spin in the opposite direction of the rotors. Is this an issue with starships in 2300 AD, and if so how do they account for this?

As has already been said: Counterwheels/Flywheels. If there is a counter-flywheel in the hub of the spin habitat, it's have to be both massive and spin fast to counter the longer movement arms of the habitat sections. Some ships, like the American luxury liner that appeared in Ships of the French Arm, don't bother with counterspin: the entire ship spins (there may be a small center section that counterspins, I don't remember). Someone with more Physics-wise can tell me if I'm right on this: Wouldn't counter-spinning spin habitats have to be on the opposite ends of the center of mass, in order to correctly counter the torgue of each other?

Third, if I am understanding correctly the stutterwarp drive is supposed to be a reactionless drive, what are the bright shiny things at the back end of some of the ships like shown on the cover of the "Mission Arcturus" ( http://rpg.drivethrustuff.com/product_info.php?products_id=433&it=1 ) or on alot of the ship's shown on the Etranger website ( http://www.users.globalnet.co.uk/~dheb/2300/Admin/Index5.htm )? Are these some of secondary drives for operating in gravity wells?

It's already been mentioned that they could be maneuver drives, but the vast majority of ship-to-ship combat is at stutterwarp speeds. Instead, I think of them as exhausts for their powerplants. One thing 2300AD (in its original incarnation) didn't address very much was the issue of heat and thermal-radiation. Craft with Fusion powerplants and MHD drives need a way to dump lots of heat, and the original design process didn't detail any kind of radiators or heat sinks. For a very good resource for "Real Physics" check out: http://www.projectrho.com/rocket/index.html

As for the "Tumbling Discovery" discussion: remember she'd been without human or computer control for nearly nine years before the US/USSR team caught up with her in 2010. She was without power most of that time, and thus her spin section (and counterweight) eventually stopped from friction. Finally, consider she was inbetween the gravity wells of IO and Jupiter, so any forces could send her wobbling. Even if she had the gyroscopic stabilizing force of a spin section, the gravitational forces pulling on her could easily have over come that.

Anyway, my 0.02lv...
-Andrew

 

[PFVA63]

Hi

Hi,

All these responses have been very informative, thanks for the input.

Hi PF!
It's already been mentioned that they could be maneuver drives, but the vast majority of ship-to-ship combat is at stutterwarp speeds. Instead, I think of them as exhausts for their powerplants.

I was wondering about that myself. I recall reading something onetime on a 2300AD website that got into the whole waste heat issue and I wasn't sure how the issue is supposed to be handled in the rules.

A few weeks ago, I got my 2300AD stuff out and have been sketching up an idea I had for a Research Ship, but I keep getting distracted by other things. I wanted to try and make it look reasonably realistic per what little I know about physics and the like while still making it reasonably consistant with Star Cruiser.

Anyway, hopefully I'll get around to finishing it sometime.

Regards

PF

 

[HandyCleo]

I came across this thread and i have to add this:
a vessel with a spin-habitat will not allways nead a counter-rotating device.
As these vessels move in zero-g, as well will the habitat. So it will move without contact to the other parts of the vessel.
A counter rotating-device will thus only be needed while the vessel is acellerating.
But when a vessel is accellarating or will perform any kind of manuever, every captain will automatically stop its spin-habitat before doing so.

 

[yatima]

Another glossed over problem with spin habitats in 2300 is the length of the arms. I recall reading that the length of the arms on most designs would require quite a high rate of rotation to get up to any useful fraction of a G in the habitats. The problem with this is that most people wouldn't be able to stomach rates at or above 2 or 3 RPM without losing their lunch. I suppose the shorter arm lengths looked better on the ship artwork.

And if we're we're roasting old chestnuts here, the lack of enough surface area to radiate waste heat on 2300 ships warrants a mention. Though this did make it into the 2320 alternate technologies section, IIRC.

 

[GJD]

Funnily enough the arm length thing came up in another discussion I was having on a Star Frontiers page - a sci-fi game at the extreme opposite end of the realism scale, and I came up with this spiffy graph:

Spin effects can be mostly ignored at 1 or 2 RPM and are tolerable at 3, but are strong enough to cause everyday tasks to be difficult. ABove 3rpm there are noticable nausea and motion sickness effects, although some people are able to function at up to 5 rpm for short periods.

G.

 

[yatima]

Spin effects can be mostly ignored at 1 or 2 RPM and are tolerable at 3, but are strong enough to cause everyday tasks to be difficult. Above 3rpm there are noticeable nausea and motion sickness effects, although some people are able to function at up to 5 rpm for short periods.
G.

Spin Rates aren't the only thing that might cause a problem. At shorter arm lengths the gravity gradient also becomes a factor, as the pseudo gravity experienced at your feet may differ noticeably from that experienced at your head. This can be most disconcerting, I imagine.

I've seen various figures on what's tolerable, I think John Cramer stated that something like 20% or less per meter is an acceptable value. Cramer had a good piece online somewhere that talked about other counterintuitive effects of life in a spinning frame of reference. For example the trajectory of dropped or thrown objects is counter intuitive, as is the variation in your weight if you run spinwwise or counter-spinwise. The Coriolis effect encountered when moving up or down from the hub is also interesting. I must look that article out again, it'd be great to have a bluffer's guide written up to add a bit of realism to shipboard life in 2300.

 

[yatima]

Here are the articles I mentioned in my last post, for those who hadn't seen them before:

Artificial Gravity: Which way is Up? by John G Cramer, with some well-drawn examples of what's different about life in a spin habitat.

Inhabiting Artificial Gravity by Theodore W Hall. All the math you'll ever need to simulate hooping, throwing etc. in a spinning frame of reference. It summarises and analyses all figures from other authorities on what spin rates are deemed comfortable etc. The section on Variation within the Supposed Comfort Zone has the piece I read on Gravituy gradients.

Enjoy.

 

[mbrinkhues]

The official 2300AD material ignores a few points for the sake of a fast construction and game system. These are:

+ Heat issues of any kind
+ Fuel for attitude control thrusters
+ Any details on life support beyond the x kg per manday requirement
+ Spin/Counterspin problems and some effects on the human ear

And according to the game as written space combat happens between the 0.1 and 0.001g Gradients. In that region ships under Stutterwarp are fast and agile yet slower than light making for a nice wargame.

 

[feld]

Spin hab and s/c attitude control misconceptions

A few common misconceptions about S/C design represented in this thread:

1. It is incorrect to say that spacecraft with rotating sections "need" extra gyroscopic devices when accelerating (either linearly or angularly). What they need is enough control force from the thrusters or control moment gyroscopes to overcome the added angular momentum of the spin habitat and some way to make sure the spin habitat keeps spinning at the proper speed as the ship pushes on it. It just so happens that momentum wheels/gyros are a good way to deal with this problem. We've build many spacecraft (Galileo mission to Jupiter being one) that had spun sections and de-spun sections and conducted pointing and tracking operations all the time. They did not stop the spinning section to do it.

2. While we're on the topic of spacecraft attitude control: most s/c that we've built that require precise maneuvering use a combination of momentum wheels or control moment gyroscopes (CMGs) and thrusters. Basically, for a given mass, mechanical gyros are a better way to reliably turn your spacecraft IF you have the power. SC ships certainly have the power. I would expect ships with MW class power plants (by contrast the largest human SC built to date will only have ~150 kW when completed) to make use of CMGs more than attitude thrusters. Attitude thrusters are required to dump the momentum from the wheels when they get "saturated" i.e. they start spinning faster than their bearings can withstand.

3. Waste heat: Don't knock Star Cruiser too much on heat. I study these things professionally and I think that they did reasonably well.
Consider:
The power plants in use in the game, even by the largest ships like the Richelieu, are ridiculously LOW powered compared to the Atomic Rocket websites much more realistic newtonian designs (fusion torches, fission rockets, etc.). Basically, this is because the stutterwarp is a FANTASTIC converter of power into displacement. To give you an idea, one NASA fusion torchship design from a few years back had a 6000 MW exhaust plume for a 240 meter ship that was largely radiator.

Contrast this with a couple of hundred megawatts on a ship like Richelieu of similar dimensions and you realize that the 2300AD ships are getting rid of ~1/10 the heat that a rocket propelled ship would need. They're not perfect: the fusion ship's like the Kennedy and Richelieu do not appear to have the necessary radiator area built in...but 2 things save them:
-You can operate a fusion plant open cycle and dump the exhaust out the back, just like with an MHD plant. Now, that plume could have radio, UV, and x-ray characteristics that make it hard to mask, but any energy in vented fusion plasma "ash" will not need radiators. I like to think that this is the reason that Suffren on the cover of Mission Arcturus has a nice blue glow going on...that's her fusion exhaust.
-Perhaps most of the powerplant output is going to spin the stutterwarp core. The 2320AD book makes it clear that the stutterwarp core is a piece of rotating machinery. Granted, it's a piece of superconducting, magnetically levitated, quantum rotating machinery. We're pretty good at converting the energy in a fluid to rotational energy (modern steam turbines have *mechanical* (not overall or thermal) efficiencies on the order of 98%). So if most of what your power is going to do is spin the stutter core very fast, you might be able to do it very efficiently indeed...

Feld

PS - Google 'Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion" for the paper. It's a must read for any hard SF fan and it's the most fully realized fusion ship I've seen since JBIS Daedalus in the late 70s.

 

[Anders]

The "Realizing 2001" paper looks really yummy. Thanks for the reference!

However, I wonder about the stutterwarp as a good waste heat sink. Nothing is thermodynamically perfect. On the other hand, given that gravitational fields are apparently extremely low entropy (according to Penrose at least), maybe the drive is actually self-cooling by transferring entropy in matter degrees of freedom to gravitational entropy.

But even if the energy used for the drive is converted directly to work, then there will probably be a few percent waste heat from the reactor itself. Getting rid of just a few MW from a mid-sized 50 MW reactor would require about 100 m^2 of radiators (assuming blackbody radiators at 1000K). If, as I think is likely, the drive is not 100% effective and self-cooling, then this scales up a lot. Personally I love ships with radiators, so I have no problems with this.

When I started looking at interstellar speed differences, it became rather clear that we need some more serious thrusters. Without them it becomes very hard to slow down enough to discharge in some systems - going to Barnard's star from the sun is going to impose 140 km/s velocity on the visiting ship! None of the presented designs seem to have engines that could give that kind of delta-v.

 

[Uncle Bob]

PS - Google 'Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion" for the paper. It's a must read for any hard SF fan and it's the most fully realized fusion ship I've seen since JBIS Daedalus in the late 70s.

A terrific reference. Many thanks!!