MGT Only: duel drive fighter

[Xerxeskingofking]

The Duel drive fighter (sometimes called a "Transit Drive Fighter") is a design paradigm that is the solution to a problem unique to TL 9 civilisations, due to a specific combination of circumstances at that TL. The problem in question is the 1G gravitic M drive.

At TL 9, Gravtic M drives allow, for the first time, space travel free form the tyranny of Tsiolkovsky's Rocket Equation. it became possible to build a ship with a powered endurance of weeks or even months, compared to the hour or two most reaction drives can sustain, and are able to carry much larger payloads over those long duration trips as the fuel required drops to a fraction of what was previously required. This massive increase in capability allows for meaningful space exploration, colonisation.....and warfare.

It is in war that the limits of the 1G drive were most felt, especially by fighter craft. While Gravtic drive ships had the endurance to preform long range missions, traditional reaction drives offered much higher performance, with 6 or even 9G drives being common on some fighters. A fighter equipped with only a 1G grav drive could simply not compete with a reaction drive fighter inside the R-drive fighter’s radius of action.

Thus, the duel drive fighter, carrying both gravtic and reaction drives, able to stay deployed for many hours on patrol, and also had enough thrust to compete with R drive fighters in a dogfight. At TL10 and above, the increasing power of gravtic drives allows them to totally replace the R drive, leading to this concept falling out of favour.

Spoiler:

Dual drive fighter

40 tons, streamlined (2.4 Mcr, 16 hull points)
Armour: 8 points, titanium steel (8 tons, 0.5 MCr)

Drives:
M-Drive: 1G (0.4 tons, 0.8 Mcr, 4PP)
R-Drive: 6G (4.8 tons 0.96 Mcr)
R Drive fuel: 2 hours @6G (12 tons, 120 thrust-turns of fuel)
P-plant: Fusion-8, 20PP (2 tons, 1Mcr)
Basic systems: 8 PP
M Drive: 4 pp
Sensors: 1 PP
Weapons: 1PP
Total: 14 PP
P plant fuel: 1 ton (four weeks/24 weeks?)
Bridge: 3 tons (0.5 MCr)
Computer/10: (0.16 Mcr)
Sensors: civil grade (1 ton, 3Mcr, 1PP )
Weapons:
Pulse laser (1Mcr, 1PP)
Missile Rack (0.75Mcr)
Missile storage: 4 in rack, 24 in mag (2 tons)
Stateroom: 4 tons, 0.5 Mcr)
Cargo: 1.8 tons
Total cost: 11.57 Mcr.

Ammo costs:
28 standard missiles: 7Mcr
28 Nuclear missiles: 12.6 Mcr

I came up with the idea when browsing the MgT2e High Guard rules, and spotted the 1G limit for TL9 M drives. I doubt my design is exactly optimal, but its built for long duration missions, hence the full bridge and stateroom. the idea is that a fleet making a long in system transit can push out these fighters, and then leave them out on sentry duty for two or three days without needing to change the ship or crew out. to better optimise the design, I reckon if I stripped out the staterooms and switched to a cockpit, I could free up enough space to install and fuel a bigger R drive, or maybe replace both weapons with a Torpedo Barbette and some rounds.


The combination of low M-drive thrust and R drives is, I believe, a quirk of the MgT rules, but I am sure a similar thing could be built in other systems (t4 would seem very easy to do this in, given that R drives are standard in that)

 

[kilemall]

IMTU CT/HG I allow for mixed grav/reaction without penalty, as each has different uses, particularly since I have such a vast setting in the Oort Cloud.

 

[Condottiere]

Since it's Mongosian, and ship design, I did research along those lines:

1. The reaction rockets can act as adterburners, which means you can run both drives simultaneously.

2. Pilots shouldn't have longer than twelve hour shifts, sixteen exceptionally, and as I recall, the cockpit's only good for twenty four; I'm not sure for how long the diaper's good for.

3. I tend to use them as point defence interceptors, or short range (ground) attack craft; their usefulness in other roles is really defined by the size of their fuel tanks.

4. Speaking of which, first edition variants were more attractive, since the rocket motors were much smaller; second edition they're twice the size of manoeuvre drives.

 

[whartung]

The important thing to note here is that the addition of the 1G drive is probably not as much of a performance hinderance in space combat as one might think, nor is it particularly more expensive (I don't know exactly how much the drives adds to the cost, but at 11MCr already, the fighter is not particularly expensive).

The only real tangible costs outside of the vehicle itself are any changes necessary to adapt any carriers to handle the new fighter. The question also becomes the value of the fighter in terms of long duration missions in contrast to just being the teeth of a carrier along with it's support elements.

While a fighter can last for weeks in space, is it actually comfortable to do so.

In TNE parlance, the fighter has 24 G Turns of fuel, with a 6G drive. TNE Turns are 1/2 hour. So, as this fighter has fuel to burn 6G for 2 hours, and 4 turns at 6 G, or 24 G Turns total.

The M-Drive gives the fighter significant loiter capability, even for short duration patrols, while using the reaction engine essentially as an "afterburner" of sorts.

Plus it gets to come home after it runs out of reaction mass.

 

[Xerxeskingofking]

The important thing to note here is that the addition of the 1G drive is probably not as much of a performance hinderance in space combat as one might think, nor is it particularly more expensive (I don't know exactly how much the drives adds to the cost, but at 11MCr already, the fighter is not particularly expensive).

The only real tangible costs outside of the vehicle itself are any changes necessary to adapt any carriers to handle the new fighter. The question also becomes the value of the fighter in terms of long duration missions in contrast to just being the teeth of a carrier along with it's support elements.

While a fighter can last for weeks in space, is it actually comfortable to do so.

In TNE parlance, the fighter has 24 G Turns of fuel, with a 6G drive. TNE Turns are 1/2 hour. So, as this fighter has fuel to burn 6G for 2 hours, and 4 turns at 6 G, or 24 G Turns total.

The M-Drive gives the fighter significant loiter capability, even for short duration patrols, while using the reaction engine essentially as an "afterburner" of sorts.

Plus it gets to come home after it runs out of reaction mass.

the M drive itself costs 0.8Mcr (ie 800,000Cr). without it I could just about get by with 1 ton of P plant, saving another 0.5 Mcr. so, at most, 1.3Mcr, or less than the cost of 6 standard missiles.


the point is that a R drive only fighter cannot loiter for very long, as its limited by its fuel (in MgT space combat turns are 6 minutes long, so it has 120 G-turns of fuel by that standard), so a carrier commander would want to keep his R drive fighters in the hanger as long as possible, to preserve fuel, and wont be running any sort of serious patrols, whereas with M drives, you can hold off at long range, launch the fighters and let them get shot up, and also have a significant scouting/screening force out without burning all the fuel up.

1. The reaction rockets can act as adterburners, which means you can run both drives simultaneously.

2. Pilots shouldn't have longer than twelve hour shifts, sixteen exceptionally, and as I recall, the cockpit's only good for twenty four; I'm not sure for how long the diaper's good for.

3. I tend to use them as point defence interceptors, or short range (ground) attack craft; their usefulness in other roles is really defined by the size of their fuel tanks.

indeed, a cockpit alone would be 12ish hours, but as its got a full bridge, and a stateroom, so their is enough room for 2 pilots, a bunk, a toilet, a shower, a microwave, maybe a comfy chair and a flatscreen….. Enough space for 2 crew to function more or less normally for a few days, on a long in-system burn or as a the rear guard of a fleet. With the M drive, they have the ability to loiter like that, which is something that R drive fighters just cant do, and while this sort of ability is standard at higher tech levels, it would be revolutionary at TL9, when it is first introduced.

In combat, the 2nd pilot could take over sensor/EW or maybe gunner, leaving the other guy free to concentrate on just flying.

you have a rules quote or something to back up the add together rule? i've not seen that, just curious if it was a common sense thing or was written down somewhere.

Plus it gets to come home after it runs out of reaction mass

yhea, the separate fuel for the P-plant was a design feature, to ensure it could do just that (and thus spend all its R drive fuel on the attack run)

 

[Condottiere]

This is easily mounted on a ship by adding an additional reaction drive. Ship architects should note that a reaction drive used as a high burn thruster is likely to require far less fuel than a ship that relies on a reaction drive alone for thrust.

The effect of a high-burn thruster is cumulative with that of the ship’s regular drive system.

No one has really explained how this works in Mongoose Second, so by default, normal fuel usage.

 

[AnotherDilbert]

This is a very good concept for fighters in MgT2. It's very useful at all TLs:
http://www.travellerrpg.com/CotI/Discuss/showthread.php?t=36151

 

[AnotherDilbert]

you have a rules quote or something to back up the add together rule? i've not seen that, just curious if it was a common sense thing or was written down somewhere.

HG, p36, High-burn Thrusters

The effect of a high-burn thruster is cumulative with that of the ship’s regular drive system.

 

[AnotherDilbert]

Ammo costs:
28 standard missiles: 7Mcr
28 Nuclear missiles: 12.6 Mcr

The cost of missiles are per Dton (12 missiles). Cf. missile prices in Core.

28 Nuclear missiles are just MCr 1.05.

 

[Straybow]

At TL 9, Gravtic M drives allow, for the first time, space travel free form the tyranny of Tsiolkovsky's Rocket Equation.
...

It is in war that the limits of the 1G drive were most felt, especially by fighter craft. While Gravtic drive ships had the endurance to preform long range missions, traditional reaction drives offered much higher performance, with 6 or even 9G drives being common on some fighters. A fighter equipped with only a 1G grav drive could simply not compete with a reaction drive fighter inside the R-drive fighter’s radius of action.

I think the real problem is the quaint idea that a high-G reaction drive is actually possible. For example, a typical rocket with a human payload (and all the support equipment that must include) can lift off at 2½-3 Gs. However, this requires a gargantuan booster with stupendous fuel consumption. That 2½-3 Gs only lasts a few minutes before exhausting the onboard fuel.

So the real problem is that R drives given in the books ignore Tsiolkovsky to claim multi-G performance that lasts for hours. I haven't really studied it, but I've read posts on this forum saying that HEPlaR probably couldn't produce a fraction of the rated thrust in real world physics. I'm absolutely certain that no rocket could produce 2 hours of 6 G thrust (or similar 24 G-turns) with onboard reaction mass in keeping with Tsiolkovsky.

You'd have to imagine some system capable of highly relativistic exhaust velocity to achieve it, and then it is no longer a reaction drive but rather a handwavium drive. I believe I once calculated a Ve for a 2G CT Scout Courier with 48 hours endurance for the listed fuel at 0.5c or thereabouts. Then again, that might have included all the Courier's fuel, including jump fuel. I'll have to find that calc.

 

[BlackBat242]

So what is the drive fighting?

Or did you mean "dual" drive?

:smirk:

 

[Straybow]

Everybody was Kung-Fu Fighting!
Those cats was fast as lightening!

Here's the link to Exhaust Velocity Calc which comes to 0.72c using 2 Td maneuver fuel or 0.046c using all fuel for two days at 1 G.

I didn't double-check the calc, but I don't think it is off by much.