Drives in a 10 ton Fighter

[agorski]

Drives don't scale down for small craft. Here's the note at the bottom of the Starship Drives table 11 in Book 2, page 77, of T5.10.

No drive may be smaller than the Drive-A of the class, even after modifications like Stage Effects.

On page 131, the Power System Rule states:

When installed in a starship, the Drive Potential for an installed Power System must at least equal the greater of the Drive Potential for any of its installed interstellar and interplanetary drives.

So if this does apply to small craft, in a 10 ton design you end up with:

Maneuver 7 Model A TL10 Experimental
EP: 50 Cost: MCr120 Tons: 6

Fusion 7 Model A TL15 Early
EP: 90 Cost: MCr8 Tons: 4

Which is unacceptable. This is the best power plant you can install in a 10 ton hull, and you really have to detune the maneuver drive to get it down to match the power plant potential.

Even if you just need to keep the EP of the maneuver drive less than the power plant, you still end up with a Maneuver 9 Prototype drive, which also sucks.

Things aren't quite so bad for larger small craft, as I've seen in a 30 ton craft design here in one of the threads.

Thoughts?

 

[Timerover51]

Drives don't scale down for small craft. Here's the note at the bottom of the Starship Drives table 11 in Book 2, page 77, of T5.10.

On page 131, the Power System Rule states:

So if this does apply to small craft, in a 10 ton design you end up with:

Maneuver 7 Model A TL10 Experimental
EP: 50 Cost: MCr120 Tons: 6

Fusion 7 Model A TL15 Early
EP: 90 Cost: MCr8 Tons: 4

Which is unacceptable. This is the best power plant you can install in a 10 ton hull, and you really have to detune the maneuver drive to get it down to match the power plant potential.

Even if you just need to keep the EP of the maneuver drive less than the power plant, you still end up with a Maneuver 9 Prototype drive, which also sucks.

Things aren't quite so bad for larger small craft, as I've seen in a 30 ton craft design here in one of the threads.

Thoughts?

Handwave it from an earlier edition, or homerule it, or extrapolate from an earlier edition (maybe High Guard or Robject's Small Craft Book).

 

[Redcap]

I've hit this problem designing a 10 ton assault gig under MT and CT; it just can't happen within the rules. I had to compromise heavily, and make is an assault g-carrier for at maximum orbit to ground and in-planetary-grav-field use only, with a set of 3G thrusters. However, I have NO idea how they devised the stats for the FIFTEEN ton Rampart light fighter :O

 

[Spartan159]

Totally house ruled

What I've been using, yes, it breaks the no smaller drive than A rule.

Small Craft Drives:
DR Drive Rating (Potential) 2 x EP / H

SC Drives - EP - Maneuver - Power plant

s1	10	0.2	1.3
s2	20	0.4	1.6
s3	30	0.6	1.9
s4	40	0.8	2.2
s5	50	1	2.5
s6	60	1.2	2.8
s7	70	1.4	3.1
s8	80	1.6	3.4
s9	90	1.8	3.7
A	100	2	4
B	200	3	7
C	300	5	10
D	400	7	13
E	500	9	16

 

[AnotherDilbert]

We are outside the rules whatever we do...

We have implicitly two limitations on performance:
a) EPs. The drive must produce enough thrust or power to get the needed potential.
b) TL. The drive must must be manufactured at high enough TL to get the needed potential.

We have to use EPs for calculations, since we have no drive potential table for small craft. We only need 45 EP for any possible potential, so TL alone determines max potential in such a small ship.

With CT HG I would say that we get as much acceleration as we have power, so the crafts effective manoeuvre rating becomes the minimum of ( drive rating, power rating ). (Or as you say, just detune the M-drive as desired.)

Since the fusion plant requires higher TL than the M-drive, for the same potential, that basically means that drive potential is only limited by the TL of the fusion plant.

In effect, the fighter gets the acceleration rating from the TL of the power plant, so a Standard set of M-drive A and P Plant A would give a performance of M-5 at TL=12, limited by the TL of the P plant. With an Early P plant we would get 6 G.

Maneuver 7 Model A TL10 Experimental
EP: 50 Cost: MCr120 Tons: 6

M-7 is base TL=12. Experimental is TL -3. An Exp M-7 is then TL (12-3)=9.

Fusion 7 Model A TL15 Early
EP: 90 Cost: MCr8 Tons: 4

P-7 is base TL=14. Early is TL -1. An Early P-7 is then TL (14-1)=13.

 

[Sebastion Russ]

G-drives Exist For A Reason!

G-drives can operate on Fusion+, therefore not requiring a dedicated power plant. With a sufficiently large vessel, they can even operate in space range 1 or 2 (10Xdiameter of nearest object) around their carrier. Modified G-drives are dirt cheap and no larger than an equivalent M-drive and P-plant. I had a player once design what he called a 'hive', which was a detachable "100 ton" chunk of metal with a dozen fighters fitted with gravitics and short range quad fusion guns, held on brackets. They were pretty cheap (~3MCR), wicked fast (7G) and made an excellent screening force against missiles, boarders, and other fightercraft. They could also sacrifice themselves if they ran into a weapon that the player's craft had no defenses for (Meson Gun!).

I required the player to use the smallest (100EP) G-drive, which at TL11, allowed them to get a modified 7G drive for a 14ton fighter, if desired. They went down to a 7 ton hull to fit more in the hanger, but if you wanted a 9G at TL12 your max tonnage calcs out to 11. In all cases, the modified G-drive was 4.5 tons. Assuming .5 tons for the cockpit, That leaves you 6 tons to play around with.

This also makes creating custom shuttlecraft and boarding craft much cheaper and easier. I highly recommend.

 

[AnotherDilbert]

In all cases, the modified G-drive was 4.5 tons.

Stage effects can't make the drive smaller than a base A drive, so minimum 9 Dton for the G drive.

Minimum M + P drives are 2 + 4 = 6 Dton.


Grav drives are cheap though.


Note: The characteristic length of a ship is something like 10-20 m, so a G-drive craft would only work within 100-200 m (Space Range 0) from the mother-craft. Technically possible, but...

 

[Sebastion Russ]

Fair enough on the G-drive weight. I guess then the 11 ton fighter is 9tons of engine, half a ton of gun, half a ton of cockpit, with 1 ton to spare. Feels like a Babylon 5 fightercraft. Although you could argue those were M-drive and P-plant craft, given the MASSIVE fusion reactor right behind the cockpit.

Where do you get 10-20m? That sounds like a 100 ton craft. Displacement tons are 13.5 m^3. a 100ton would be 1350m3, with a cube root of 11m. A 1000 ton craft, more like a small military craft with a wing or two of fighters, would be 24m. 10000 ton, closer to a proper carrier, 51m. And all of this is assuming that you are fighting far enough away from another gravitational body. Most conflicts do not take place in dead space.

Although for an ACS, I do see your point. You would be concerned about pirates or rivals that would attempt to hit you when you are weakest, such as just before or after a jump when you are 100D from your target, or just as you entered/left the 1000D limit for interplanetary travel. And a smaller 100-200 ton free trader is going to have a hell of a time defending itself with a 100-150m fighter screen. Might as well have detachable armored turrets with integrated computers.

I guess the G-drive is better for station based fighter/bombers, especially if they are constructed inside an asteroid. Could also be good for smaller defense carriers near to a planet, for a cheaper intermediary between full spacecraft and ground based aircraft. Like a middle defense sphere supporting orbital platforms.

Edit: We may all be thinking too conventionally. HEPlaR engines are 1 ton and 1 MCR for 100EP, and with 5 tons of fuel tanks could perform 50 burns for a 10 ton fighter. This leaves 4 tons for everything else and you still have a 9-drive equivalent at TL12. Although the rules are unclear if you need a separate fusion P-plant to make this work, or if the superheating is part of the drive. I would err on the side of not needing a P-plant, as it is intended to be a vastly improved rocket engine.

Edit 2: G-drive is back on the menu! Book 2 PG. 111. Diameter is defined as the longest dimension of the object not longer than 5 times any other dimension. As most ships are not spheres, we are now looking at 2-5 times the dimensions above. For the proper carrier, that is now 1-2.5Km, or range 5 - 5.6ish (my logarithms are rusty). Ideal? still no, but workable for a close defensive fighter screen while larger M-drive or HEPlaR fighter/bomber strike craft assault the opposing vessels.

 

[AnotherDilbert]

Yes, sorry, I calculated the radius of a sphere, not the diameter. I used a 1000 Dton ship since that is roughly what we can officially build.

2.5 km is still less than S=1. Note that a 5 second burst of 7 G acceleration will move you 1 km, leaving you outside the gravity well of the carrier without drive power. Not practical.

HEPlaR still needs a power plant to heat the propellant, so does not save much.
HEPlaR-A is 1 Dt, Propellant ~5 Dt, Power plant A 4 Dt, and fuel ~0.5 Dt ≈ 10.5 Dt. Still not very practical.


M-drives are just very, very convenient...

 

[Sebastion Russ]

No argument about convenience. I am pretty focused on cost and practicality. I still think HEPlaR with a generic/basic P-plant and say 3 tons of propellant is reasonable (you shouldn't need constant 9G burns to keep up with the fleet and dogfight). Fightercraft would need to dock and refuel if they get too low, similar to contemporary air superiority craft. This bring down our cost to 2.5-3MCR for the drive system. Although if you do the same to the M-drive setup, that becomes 4-6MCr. The range is based on whether or not you apply generic/basic to the drive itself. You probably want that to be standard or improved to avoid performance hits in critical situations.

As soon as we pull away from 10 tons, the P-plant and M-drive setup starts looking much better. Once we can apply modified to the minimum size to still get a 9-drive (so about 20 tons), you have a ridiculously fast craft that can easily carry a 13ton payload. that is a boarding range KK Missle barbette with a 9 tons of ammunition, with room for sleeping quarters for the pilot and gunner and a month's supply life support and fusion fuel.

This is all pretty high tech though. You could have the same setup for 5G at TL11, which would probably be a better time for cheap, close range kinetic damage, when the main focus is those fancy new radiation beams and all them close range fusion guns. Would be much cheaper too...if you were willing to cut corners.

Question: are you limited to 1 firmpoint for a craft this size? I think I remember reading that if you are smaller than 100 tons, you get 1 firmpoint per 35 tons, minimum 1. If you get up to 3...well then I do like the sound of 3 boarding range KK barbettes on a 20ton craft. Or 2 with a defensive laser turret, more akin to a B-52 superfortress.

Edit: Whoops. KK is bay, not barbette. Guess you end up with a quad missile turret instead, which is a bit underwhelming. This setup could make a comeback at TL 15-16 as a way to deliver AM missile payloads...but my god would that be a suicide mission. I can already see a core of hotshot pilots flying in 20ton crotch rockets armored to hell and back with a 9G drive and a boarding range AM missile rack. High casualty rate, super effective.

Edit 2: Did the math. An experimental boarding range AM barbette is 0.75 tons and 7.5 MCR at TL14. You could also have 10 armor layers on this thing and still have room for everything else. That is...definitely going in my next game.

 

[AnotherDilbert]

HEPlaR isn't very cheap:
MCr 0.5 for the HEPlaR + MCr 8 for the power plant. Same problem for M-drive, of course.
Only 3 turns of propellant. You won't get far...

TL-15  F-1S90                        Ergo 1   Comfort 0    Demand 0        Agility 0
       Fighter                       Total:         0          10,5        Stability 1
SYSTEM                                    #       DTON         COST      
Hull                                               10                    
Config: Streamlined                                             0,8      
Structure: Plate SuperDense    AV=30 ( 300 vs Blast, 165 vs Pen, 4500 vs Heat/Beam, 300 vs Pres, 1500 vs Rad, 0 vs EMP )      
Coating: Reflec                AV= 0 ( 1500 vs Heat/Beam  )      
Armour Std Anti-Kinetic                   1                          AV=15 ( 150 vs Blast, 150 vs Pen, 1500 vs H/B,    0 vs Rad, 0 vs EMP )      
Armour Std Anti-Rad                       1         0,4              AV=15 ( 150 vs Blast,  15 vs Pen, 1500 vs H/B, 1500 vs Rad, 0 vs EMP )      
Landing Skids Tarmac                                                     
Lifters Installed                                               0,1      
                                                                         
Gen HE Drive A  9 G, 90 EP                1         1           0,5      
Ear P Plant A  P 9, 90 EP                 1         4           8        
                                                                         
Fuel, Reaction                                      3,0                  
Fuel, Power  0,5 weeks                              0,1                  
                                                                         
Console, Control Gen C+S=14               1         0,5         0,1        Brain: INT=4, EDU=2
Computer Gen m/0                          1         0,5         0,1      
                                                                         
Sensors                                                                  
Vd  Commu-8 +8A+2 PA(Elec)                1                              
Vd  Radar-9 +9A+2 PA(Elec)                1                              
D  Porth-5 +5A-- P(Phot)                  1                              
                                                                         
Weapons                                                                  
Mod D T3 SLM -15 +17 H:1 Def+1            1         0,5         1        
 Mod D T1 Sand-15 +15 H:1 Def+1           1                              
 Mod D T1 Beam-15 +17 H:1 Def+1           1                              
 Mod SR T1 Miss-15 +15 H:M                1

An M-drive is only marginally more expensive, but have unlimited mission range and leaves 2 Dton free.

TL-15  F-1S90                        Ergo 1   Comfort 0    Demand 0        Agility 0
       Fighter                       Total:         0          12,0        Stability 1
SYSTEM                                    #       DTON         COST      
Hull                                               10                    
Config: Streamlined                                             0,8      
Structure: Plate SuperDense    AV=30 ( 300 vs Blast, 165 vs Pen, 4500 vs Heat/Beam, 300 vs Pres, 1500 vs Rad, 0 vs EMP )      
Coating: Reflec                AV= 0 ( 1500 vs Heat/Beam  )      
Armour Std Anti-Kinetic                   1                          AV=15 ( 150 vs Blast, 150 vs Pen, 1500 vs H/B,    0 vs Rad, 0 vs EMP )      
Armour Std Anti-Rad                       1         0,4              AV=15 ( 150 vs Blast,  15 vs Pen, 1500 vs H/B, 1500 vs Rad, 0 vs EMP )      
Landing Skids Tarmac                                                     
Lifters Installed                                               0,1      
                                                                         
Gen M Drive A  9 G, 90 EP                 1         2           2        
Ear P Plant A  P 9, 90 EP                 1         4           8        
                                                                         
Fuel, Power  0,5 weeks                              0,1                  
                                                                         
Console, Control Gen C+S=14               1         0,5         0,1        Brain: INT=4, EDU=2
Computer Gen m/0                          1         0,5         0,1      
                                                                         
Sensors                                                                  
Vd  Commu-8 +8A+2 PA(Elec)                1                              
Vd  Radar-9 +9A+2 PA(Elec)                1                              
D  Porth-5 +5A-- P(Phot)                  1                              
                                                                         
Cargo                                               2,0                  
                                                                         
Weapons                                                                  
Mod D T3 SLM -15 +17 H:1 Def+1            1         0,5         1        
 Mod D T1 Sand-15 +15 H:1 Def+1           1                              
 Mod D T1 Beam-15 +17 H:1 Def+1           1                              
 Mod SR T1 Miss-15 +15 H:M                1

Yes, 1 firmpoint per 35 Dton.

 

[AnotherDilbert]

At mid tech (TL-12) and cheap drives we are down to 5 G (limited by the power plant):

TL-12  F-1S50                        Ergo 1   Comfort 0    Demand 0        Agility 0
       Fighter                       Total:         0           6,0        Stability 1
SYSTEM                                    #       DTON         COST      
Hull                                               10                    
Config: Streamlined                                             0,8      
Structure: Plate Kinetic       AV=24 ( 240 vs Blast, 132 vs Pen, 3600 vs Heat/Beam, 240 vs Pres, 1200 vs Rad, 0 vs EMP )      
Coating: Reflec                AV= 0 ( 1200 vs Heat/Beam  )      
Armour Std Anti-Kinetic                   1                          AV=12 ( 120 vs Blast, 120 vs Pen, 1200 vs H/B,    0 vs Rad, 0 vs EMP )      
Armour Std Anti-Rad                       1         0,4              AV=12 ( 120 vs Blast,  12 vs Pen, 1200 vs H/B, 1200 vs Rad, 0 vs EMP )      
Landing Skids Tarmac                                                     
Lifters Installed                                               0,1      
                                                                         
Gen M Drive A  5 G, 90 EP                 1         2           2        
Bas P Plant A  P 5, 90 EP                 1         4           2        
                                                                         
Fuel, Power  0,5 weeks                              0,1                  
                                                                         
Console, Control Gen C+S=11               1         0,5         0,1        Brain: INT=4, EDU=2
Computer Gen m/0                          1         0,5         0,1      
                                                                         
Sensors                                                                  
Vd  Commu-8 +8A+2 PA(Elec)                1                              
Vd  Radar-9 +9A+2 PA(Elec)                1                              
D  Porth-5 +5A-- P(Phot)                  1                              
                                                                         
Cargo                                               2,0                  
                                                                         
Weapons                                                                  
Mod D T3 SLM -12 +14 H:1 Def+1            1         0,5         1        
 Mod D T1 Sand-12 +12 H:1 Def+1           1                              
 Mod D T1 Beam-12 +14 H:1 Def+1           1                              
 Mod SR T1 Miss-12 +12 H:M                1

 

[AnotherDilbert]

Edit 2: Did the math. An experimental boarding range AM barbette is 0.75 tons and 7.5 MCR at TL14. You could also have 10 armor layers on this thing and still have room for everything else. That is...definitely going in my next game.

Weapon: AM Missile is MCr 5. Experimental is Cost ×10. Weapon Cost = MCr 50.
Mount: Barbette MCr 3. Range BR Cost /4. Mount Cost = MCr 0,75
Total Cost MCr 50.75

TL Stage Effects apply to the Weapon but not the Mount. It affects cost of the Weapon, but not to the tonnage.
Range Effects apply to the Mount but not the Weapon.

 

[Grav_Moped]

Yes, sorry, I calculated the radius of a sphere, not the diameter. I used a 1000 Dton ship since that is roughly what we can officially build.

2.5 km is still less than S=1. Note that a 5 second burst of 7 G acceleration will move you 1 km, leaving you outside the gravity well of the carrier without drive power. Not practical.

HEPlaR still needs a power plant to heat the propellant, so does not save much.
HEPlaR-A is 1 Dt, Propellant ~5 Dt, Power plant A 4 Dt, and fuel ~0.5 Dt ≈ 10.5 Dt. Still not very practical.


M-drives are just very, very convenient...

Don't think of it as a separate spacecraft, think of it as a self-propelled detached turret... it doesn't need to go far from the carrier, it just has to be able to evade incoming fire. Use for point defense or close-quarters combat.

 

[AnotherDilbert]

Even deployable turrets can roam R=7 (S=2) from the ship.

S=0 is too close to be practical, it leaves next to no room for manoeuvre. Even a few seconds of acceleration in the wrong direction would leave the fighter with no drive power. It would have to be slaved to the mother-ship with a tractor.

If we want extra PD mounts, just make 10 Dt pods permanently attached to the ship. Much cheaper since no drives needed.

 

[dalthor]

Minimum M + P drives are 2 + 4 = 6 Dton.

I like the High Guard rules for small craft -- 1 dTon minimum for the plant and drive.

Tech Level Stage Effects can drop sizes down, but I do still keep the 1 dTon minimum. Then again, I also allow "decimal" sizes, i.e. a 2.5 dTon drive assembly. [EDIT: This is what makes DEPLOYABLE mounts possible!]

For any spacecraft (i.e. any ship that cannot jump) I reduce the P-Plant size by 2 dTons. They don't need to "super pump" LH2, so the attendant large feed pipes, safety systems and pumps are not present. That P-Plant cannot be "upgraded" to jump-capable support - it is a "compact" version.

Yes, that is a personal preference. Then again, (miss you, Hanse) it does make sense.

YMMV, and all that...

 

[Sebastion Russ]

Weapon: AM Missile is MCr 5. Experimental is Cost ×10. Weapon Cost = MCr 50.
Mount: Barbette MCr 3. Range BR Cost /4. Mount Cost = MCr 0,75
Total Cost MCr 50.75

Thanks for the clarification, I missed that note before.

So...much more expensive than I thought. Still, 60MCR for the weapon and ship is not bad for an AM delivery device at TL14, Even if it risks a one-way trip. A weapon like that can decimate an opposing fleet orders of magnitude more valuable., even after the cost of training, life insurance, and hazard pay.

Also, what is the point of a HEPlaR drive if it is limited by P-plant tech level? Can it be used with a fission plant or other power source instead? fuel cells? If it is limited to fusion only, then I do not understand why the tech levels are so different for the different outputs.

 

[agorski]

Question: are you limited to 1 firmpoint for a craft this size? I think I remember reading that if you are smaller than 100 tons, you get 1 firmpoint per 35 tons, minimum 1.

Yes. A single beam laser turret will fit, but it's gonna be a short range model. 1/2 ton max for a firmpoint.

 

[Sebastion Russ]

Yes. A single beam laser turret will fit, but it's gonna be a short range model. 1/2 ton max for a firmpoint.

Book 2 pg. 53: A Firmpoint will accept any mount that is less than one ton.

This is how you end up with boarding range barbettes on space bombers, Or how I intend to put an experimental AM missile launcher on a 20 ton deathball at TL14 where there is few reasonable defenses against such an attack.

 

[AnotherDilbert]

Also, what is the point of a HEPlaR drive if it is limited by P-plant tech level? Can it be used with a fission plant or other power source instead?

HEPlaR is an alternative tech.

For societies which have not discovered the gravity-oriented Maneuver, Gravitic, or Z Drives, alternative insystem drives exist: traditional Rockets, enhanced HEPlaR High Efficiency Plasma Rockets, or Orion Drives.

HEPlaR works with Fusion and Fission, see "How Fuel Works", B2p191.