Three dumb design questions

[jhulse]

I haven't been on the boards in a long while.
I have been playing a combo of Traveller, fantasy based games, Serenity, and LARPS over the last few months.
I have sold my house and I'm in the beginning stages of relocating from Florida to either the Dallas area or to the Atlanta area.
So I am preparing a few modules for future games. These questions came up recently, and I wasn’t sure how to answer them.

1) Fuel Purification Plans:
Hydrogen is used to fuel ships. The rules say that a ship can skim gas giants, or get fuel from any water source, liquid or ice. But since hydrogen is the most common element, can a ship with fuel purification systems skim just about any atmosphere? If a ship were to skim the earth’s atmosphere, could the fuel purification system simply crack and strain the hydrogen? Could this work with any gas or liquid which contains hydrogen?

2) Maneuver drives:
Maneuver ratings are based on earth-gravity. If a ship were at rest on a large planet, say 4 times the mass of earth, would a ship with a 1-G maneuver be able to break orbit? Or would a ships maneuver rating even be brought into consideration when dealing with planetary sizes?

3) Spinal mount weapons:
For spinal mount weapons, sizes are given in tonnage, but is there a rule of thumb for the actual size? If I were to design a deck plan for a module, how large should the weapon be? 3 meters in diameter? 10 meters in diameter? Or can it be any size (even a cube) so long as the displacement tonnage is correct?

Thanks.

 

[JAFARR]

Jak, in order asked, here are my ideas.

1. No just accept that even if it is possible you would use more fuel in a habitable atmosphere than you would accumulate.

2. It is possible (in therory) for a bumble bee to reach escape orbit. (In other therory it is impossible for a bumble bee to fly, but bumblees don't know about that therory so they fly anyway.) Don't worry about it.

3. By the name, they are part of the spine (or structure) of the ship. The drawings of the High Lightning ships show a huge opening for the spinal mount with very small openings for the fighter launch tubes. I guess you could play with the numbers to calculate how much was used to project the energy and how much was the area it projected through, buy I have never seen any specs for that info.

Hope that helps.

 

[DaveShayne]

1) While hydrogen is the most common element in the universe it is only a trace element in the atmosphere of earth (see http://en.wikipedia.org/wiki/Earth's_atmosphere ) probably much easier to fly off to the nearest lake/river/ocean to get some water to crack. Or if that's not possible set out some buckets and wait for a good rainstorm.

2) 4 times the mass equals 4 times the gravity so your 1 g ship will be stuck on the ground. Best to park the Beowulf at the high port in that situation and take the shuttle dirtside.

3) There is no official rule that I'm aware off but it should be long and thin. Almost as long as the longest dimension of the ship and then as far around as necesary for the tonage to work out right is how I would do it.

 

[GypsyComet]

Originally posted by DaveShayne:

2) 4 times the mass equals 4 times the gravity so your 1 g ship will be stuck on the ground. Best to park the Beowulf at the high port in that situation and take the shuttle dirtside.

This does vary with edition.

MT assumed (via the Starship Operators Manual) that manuever drives could be run hot for brief periods, producing up to 4 times their usual thrust. Assuming a world at "not quite 4g" surface gravity, this would allow for a white-knuckle lift with a 1G ship.

TNE splits the drive into two components, comprising lift and drive. The lift component ("Contra-Gravity Lifters") nullifies 99% of the ambient gravity effects on the ship, allowing the drives to push the ship around at near-full rated thrust.

Arguments regarding the application of either solution to other editions of Traveller are pointless, due to one simple question: How do *you* want the drives (and by extension, ship design practice) to work in this situation?

If you assume neither of the above caveats:

In civilized areas, a planet like this that expects service from Sandwich-class free traders and other low-thrust designs *will* have a highport and strong warnings against attempting surface landings. Of course, with 4G on the surface, *everything* meant for humans is going to be under artificial gravity, and surface landing zones will, if at all possible, be at higher elevations where the gravity is a few percent lower. *Lifting* ability will be assumed for any vessel that could make a safe landing in the first place, but why redline your hardware if you don't have to?

If servicing worlds like this is expected to be commonplace in the wilds, ships for that purpose will either have higher thrust ratings or, as noted above, have high-G subcraft.

 

[Chaos]

re 1.) the purification plant should work on any molecule that contains hydrogen; mostly that´s the hydrogen molecules themselves (H2), plus water (H2O). But I guess it would also work with ammonia (NH3, IIRC) as well as natural gasses and oils (CH4, C2H6, C3H8 and so on).

re 2.) (and adding to GypsyComet) I suppose that such worlds could also install launch tubes for smaller starships to help them get to orbit.

 

[tjoneslo]

Answer to question 3: I read in White Dwarf (IIRC) a system where you could buy/rent booster rockets for your 1G merchant ship to take off from a world where the gravity was greater than 1G. So for a few hundred credits, they jack your free trader up on its tail, strap on a set of solid rocket boosters and fire you off into space. Sound like fun yet.

Other option, use a magnetic linear accelerator. This is a giant gauss gun which fires your ship off into orbit. Since your ship can provide most of the thrust needed, the accelerator does not need to use the 100G+ normally associated with these devices. Usually the safety systems prevent the use of full power on crewed ships.

Sould I describe the giant laser launch system? Here they strap a giant piece of plastic on the underside of the ship, and haul it over a spinal mount weapon class laser. The laser fires short bursts at the plastic, which vaporises providing additional thrust for the ship. By the time you reach orbit the plastic is gone and the laser shut off.

 

[far-trader]

Originally posted by tjoneslo:
Answer to question 3: I read in White Dwarf (IIRC) a system where you could buy/rent booster rockets for your 1G merchant ship to take off from a world where the gravity was greater than 1G. So for a few hundred credits, they jack your free trader up on its tail, strap on a set of solid rocket boosters and fire you off into space. Sound like fun yet.

It does sound like fun

I recall a world writeup, in Dragon perhaps (Exonidus Spaceport maybe?) where it was noted that this high-pop high-tech high-traffic world didn't let anybody control their own ship landing or takeoffs, using planetary based repulsor/tractors to launch and land all traffic, even unpowered shipping crates iirc. Now that sounds like fun too, and a solution for some high-g worlds to boot. Kind of like you linac idea.

I really don't want the locals shooting the planetary defense laser at my ship to kick me off the world, even with some plastic ablative

 

[jhulse]

I skipped many years between CT and T20, so most of the TNE and MT tech / explanations are still unknown to me. What is known is GURPS Traveller. I think they also have contra-gravity units, which negate up to 3 G's of force inside a vessel. I’m not sure if it also applies to lift. For my purposes I’m leaning towards that explanation.

The questions for skimming other atmospheres besides gas giants came up in a Serenity Game. Because "The Serenity" has large turbo-fan like engines, we surmised that these could act like Traveller fuel scoops, which could be large enough to process hydrogen out of almost any atmosphere, then use it directly for trust. It sounds like an interesting idea. Free fuel for your M-drives as long as you are in an atmosphere, and then you don’t have to use the fuel from your internal tanks.

The question about hi-G worlds is because I'm working on an adventure where pirates attack refueling ships, then dive deep into the clouds of the Gas Giant to escape. Their base is either a small moon on the opposite side of the planet or a floating "city" or station deep in the atmosphere. Deep enough to escape detection from local orbiting patrol vessels. The floating station would strain hydrogen directly from the atmosphere and feed it directly into the drive holding it in very low orbit. The gravity would be higher than normal and the pressure would also be higher than normal. If I go with a 4G environment, Contra gravity will nullify 3 G's, making "inside the base" 1-G, but a ship at rest outside on a landing platform will be at 4-G's. So a ship would need at least a Maneuver rating of 4, plus an improved hull (for external pressure) to even attempt to land. I might even through it a “mad scientist” scenario who is actually in control of the base, and up to some devious mad scientist plan. Human experiments anyone???

The question about the actual size of a spinal weapon has to do with a "sneak aboard and disable the main gun" scenario I'm working on. I want to draw deck plans so the players can pick places to sabotage, plant timed explosives, etc...
Anyway, that's those are very beginning of ideas I've been kicking around for a while.
Thanks for all the input.

 

[Rover]

The 1G listerd on the manuever drive is a measure of acceleration, the rate of change in speed. While a 4G world, the g is a measure of the gravity. It would have a higher escape velocity, but all that means is it would take a little longer for a 1G ship to reach orbit than a 4g ship.

This of course pre-supposes a world with some atmosphere and a streamlined ship.

Most airplanes don't have 1g acceeration, yet they can still leave the ground. If they could provide constant acceleration, even at 1/10G, they could still build up to escape veocity.

I am not sure how this would work on a 4g vaccume world.

Jim

 

[Piper]

Originally posted by Jak Nazrith:
The question about the actual size of a spinal weapon has to do with a "sneak aboard and disable the main gun" scenario I'm working on. I want to draw deck plans so the players can pick places to sabotage, plant timed explosives, etc...

This web site (although a bit tedious to navigate) has some good info on the innards and workings of a large particle accelerator.

This site is a virtual tour through a meson factory.

Hope this helps.

 

[DaveShayne]

Originally posted by Rover:
The 1G listerd on the manuever drive is a measure of acceleration, the rate of change in speed. While a 4G world, the g is a measure of the gravity.

Gravity is acceleration as well. That 4G world will be pulling down 4 times faster than a 1G ship can push up.

Aircraft cheat as they use thrust not directly against gravity but perpendicular to it to draw air over wings to create lift. Lift is also acceleration and if it doesn't exceed the force of gravity the plane will not lift off (or if already aloft will return to the surface with perhaps painfull consequences.)

So barring lift surfaces (which most Traveller ships don't even pretend to have though that is rule set dependent) a 1G ship isn't making it off a 4G world without some external thrust agent or TNE style contragrav.

 

[aramis]

Take for example White Knight/Space Ship One.

White Knight only gets about 0.5G's acceleration, but that can overcome several hundred miles/hour of drag (about 450, IIGR). That drag, however, converts airflow in to about 11-12m/s/s of vertical acceleration, of which 9.8 is lost to gravity. Net gain,a couple m/s/s of resultant gain, to a max of a hundred or so m/s.

SS1 likewise gets some aerodynamic lift, but quickly loses that as it climbs, due to decreasing density. From surface, the SS1 craft is going to not even make suborbital. But, given 6-10km of altitude, courtesy of WK, it can hit suborbital flight. Given a slightly better propellant kit, it can probably make VLEO.

Now, it pulls several G's, about 5, again If I Guess Correctly. So it accellerates at about 4G's. (I once did the math for an SSTO at modern TL's with CORPS VDS... atmospheric low thrust to max altitude, then 5-6 minutes at 4G put it into a VLEO.)

Now, in T20, you have Airframes available. An Airframe should be able to make orbit on 1G, assuming that the top speeds on the tables go up as atmospheric density drops from altitude. Of course, the specific speed/lift curve changes with density... and while I am aware of the maths, I am not knowledgeable enough to find the maths nor extrapolate them for game purposes.

The idea was that a craft should be able to make 1.25xG rating to escape a planet by using a parabola and airframe.

 

[TheEngineer]

Hi Jak !

Some more answers:

1)
You really might skim anythere. And Traveller fuel scoops canonically seem to get along with either gases or liquids. Its just a matter of efficiency.
E.g. skimming in Earth atmo at sea level, there is just around 6e-7 kg Hydrogen in one m3 air, so it needs to "suck" 1,5 million m³ to get one kg.
Given a collector area of 10 m² the starship has to cross 150 km to put the air thru passivly.
Or it could use something like a compressor to drag the air thru the collectors, which perhaps may take around half an hour per kg.
Guess thats ok to get some bits of fuel in an emergency situation, but its perhaps not very efficient during regular operation.
Anyway, higher concentrations of hydrogen, methan or even water vapour are possible and might reduce athmo skimming considerably. So, in a jungle climate theres around 100 g water in one cubic air and skimming would work pretty fast here...
Ok, thats on sea level. The gas concentrations in the upper areas of regular planets atmossphere are terribly low. Taking earth it drops to 6e-13 kg/m³ at 100 km height. Thats awfully low, so you might need more energy to skim than fuel is given back...

2)
Guess, the basic question is already answered

Well, its a regular topic and the Traveller maneuver drive properties are vague or even contradicting sometimes, depending on the edition.
At least in MT its pretty obvious, that even a humble 1g trader can lift off from a size A world, because of the given travel times and the way atmo velocities for m-drive vehicles are calculated.
If the effective g-rating is calculated IYTU by substracting local gravity, there are several approaches to explain 1g ship mobility:
- assume additonal antigrav units incorporated in the m-drive to provide a bit additional take off thrust (using std grav this usually is just a fraction of overall m-drive cost)
- assume the SOM overdrive method (which I still like the most) to provide a bit accelaration usable for liftoff.
As always there are many ways, just Traveller.

Well, indeed there are airframes in MT or T20, but this might not help with the good old regular Traveller starship types.

As for the deep atmo setting: guess thats pretty cool. IMHO you can simply define an environment, that fits, meaning a gas giant with a proper size.
Guess the atmo pressure is not a problem. You would have to dive into Jupiters atmo quite deep to reach a pressure comrarable to earths sea level. Refering to the Galileo probe date its around 470 km from virtual atmo border (1e-7 bar pressure) down to the 1 bar level. 18 km below is the base of the cloud cover, perhaps a good hiding place. Pressure was 1,6 bar here.

3) Spinal Mounts
As a over the tumb rule I consider a length to diameter proportion of 10:1 up to 20:1, where high TL structures might be bulkier/shorter, while lower tech accelerators need a bit more length.
E.g. a TL 8 factor A gun is perhaps 330 meters long with a spinal diameter of 17 meters, while the high end TL 15 factor T gun is maybe just 157 meters long with a diameter of 18 meters.
Though I would not put it into a simple cube shape I could of course think of a ring design. Might look pretty cool.
But thats just MTU. It helps me to set up the rough design as the spinal mount is the bone of the ship.

Best regards,

TheEngineer
Back from sunny Southern France

 

[Rover]

Originally posted by DaveShayne:
Gravity is acceleration as well. That 4G world will be pulling down 4 times faster than a 1G ship can push up.

Aircraft cheat as they use thrust not directly against gravity but perpendicular to it to draw air over wings to create lift. Lift is also acceleration and if it doesn't exceed the force of gravity the plane will not lift off (or if already aloft will return to the surface with perhaps painfull consequences.)

So barring lift surfaces (which most Traveller ships don't even pretend to have though that is rule set dependent) a 1G ship isn't making it off a 4G world without some external thrust agent or TNE style contragrav.

Acceleration is not a measure of thrust. It is the thrust that moves the ship. Since Traveller has no rules for thrust, or mass for that matter. We all turn a blind eye to the fact that in Traveller the acceleration drives are determined by volume not mass. A ship will accelerate the same if loaded with feathers or depleted uranium. Mass does not matter in Traveller.

If you really need a rule for this you would have to house rule it. Without a quantification of mass and thrust, the measure of acceleration is of little value in this situation.

As you point out, in an atmosphere, a ship with an airframe can build up to escape velocity through lateral travel.

Lift is also not a measure of acceleration. Lift is a force. Acceleration is a measure of the change in velocity. Lift merely has to overcome the force of gravity (weight of the plane),

In a vacuum, or with out an airframe, you could say that on a 4G world a ship would have a effective vertical acceleration of N/4. n=Maneuver rating of the ship.

INHO

 

[DaveShayne]

Originally posted by Rover:
In a vacuum, or with out an airframe, you could say that on a 4G world a ship would have a effective vertical acceleration of N/4. n=Maneuver rating of the ship.

On bizzarro world maybe. In the real world vectors are additive so the ship would have an effective accelleration of N-W. Where N is the ships accelleration in Gs and W is the planetary gravity also in Gs.

Also, a definition for you. Accelleration is change in velocity over time. Wheather that change in velocity is due to thrust, gravity, lift, drag, or some other cause is immaterial.

 

[Rover]

News Flash

Traveller is a bizarro world cuz mass doesn't matter and thrust does not exist.

And yes I know that acceleration is a change over time. Pls excuse my brevity.

Using the formula F=MA where A is 1G pls solve for the other two variables. It can't be done. Sure we could make some assumptions. But in the end, mass does not have an effect in Traveller and there is no quantification of thrust. There for I stand by my formula a=n/g in Traveller, not the real world.

It is possible, with the correct amount of thrust to accelerate vertically with at less than 1G. Next time you ride an elevator be thankful you don't rise upwards at 1g or you would have to support twice your body weight. Vectors are additive remember.

1KG of Mass will have a weight of 4KG on a 4G world. Appling a force 4.000001KG vertically will cause the object to rise and accelerate at a rate far below 1G.

Jim

 

[DaveShayne]

Originally posted by Rover:
1KG of Mass will have a weight of 4KG on a 4G world. Appling a force 4.000001KG vertically will cause the object to rise and accelerate at a rate far below 1G.

Yes and applying that force will require just over 4Gs of acceleration to counteract the 4G constant acceleration of the local gravity.

You are corect enough when you say most versions of Traveller gloss over mass when calculating starship acceleration. Ships are assumed to have a specific weight to volume ratio (I believe TNE used 10 tonnes/Dton) for the G rating calculations. This is to make the process of starship design easier but does not imply a change in the laws of physics as we know them.

To accelerate away from a 4G world you will still need to apply over 4Gs of thrust. Be that direct thrust, aerodynamic lift or what have you.

 

[Anthony]

Originally posted by Rover:
1KG of Mass will have a weight of 4KG on a 4G world.

Technically, it will have a weight of 39.24N. kg is a unit of mass, not force.

 

[Rover]

Dave I really think we are talking past each other here. Acceleration is not a force. It is effect of applying a force to a mass.

For any given mass M, on a 4G world it will have a weight of 4M. In order to accelerate that mass vertically we gave to apply a thrust force greater than 4M, that is all. It is not a matter of acceleration. It is the excess force above 4M that will cause acceleration.

In my example above applying a force of 4.000001 kg on that object would cause it to accelerate upward at very low rate. Much lower than 1G. It is the downward force caused by gravity that must be overcome not the rate at which it is measured. As long as that force is greater than 4kg the object will continue to accelerat upwards.

In a Traveller game B/C we do not know the thrust nor the mass, there is no way to calaculate what if any acceleration there would be. Which is why, for a simple game mechanic, I suggested a=n/g

 

[Rover]

Originally posted by Anthony:
</font><blockquote>quote:</font><hr />Originally posted by Rover:
1KG of Mass will have a weight of 4KG on a 4G world.

Technically, it will have a weight of 39.24N. kg is a unit of mass, not force. </font>[/QUOTE]Tony,
Its been 23 years since I took HS physics. I may not remember all the details, but still have a handle on the comcepts.

Jim