Ship Design Philosophy

[Condottiere]

Happy X Mass Bomber!

 

[Condottiere]

Spaceships: Dogfighting and Reactionary Acceleration

When you're up close and personal, reactionary bunkerage would become fractions of thrust hours, six hundredths I believe.

That six seconds of afterburner could position your vessel in an advantageous position, on regard to a fighter that might not have that extra juice.

Also, what I assume is meant by High Burn Thruster in this edition.

 

[Condottiere]

Spaceships: Engineering, Reaction Drive, and Auxiliary Chemical Rocket

As I read it, whether in Mongoose First or Second, it's implied that Reaction Drives burn hydrogen, while it's stated auxiliary rockets burn chemical fuel.

From Scoundrel:

To determine the effects of the thrusters, choose a Manoeuvre Drive that produces the desired speed. (For example, to get six gee acceleration on a two hundred tonne ship requires a Manoeuvre Drive F.) The high–burn thruster weighs twenty percent and costs twenty percent of that Manoeuvre Drive (2.2 tons and 4.8MCr, in the case of a Manoeuvre Drive F).

Thrusters require fuel depending on the thruster’s drive number. Fuel equal to twenty five percent of the mass of the drive gives enough for one full hour of operation (ten space combat turns). Fuel costs 10,000 Cr./ton. A high–burn thrusters may not operate for more than one hour before requiring a shut–down period equal to the duration of operation.

I don't see any specific definition in Mongoose Second, making it about as useful as your appendix.

 

[baithammer]

Hydrogen is a chemical and rockets require no power in order generate thrust in exchange fuel consumption is greater and can generate more thrust of a comparable m-drive.

 

[Sigtrygg]

If its a chemical rocket your hydrogen is also going to require oxygen. Note a chemical rocket can not be the model for the MgT reaction drive - fuel requirements are way way way too low.

If all you are doing is using the hydrogen as reaction mass having heated it using a nuclear reactor then it is a nuclear powered reaction drive and not a chemical reaction... once again the fuel requirements are ridiculously low for the stated performance.

 

[Condottiere]

I don't think that the original Classic conception conceives of mixing oxygen in the thrust fuel.

 

[Sigtrygg]

The Classic Traveller maneuver drive was a fusion rocket - it said so in first edition High Guard,

 

[baithammer]

Going over my copy of CT HG has no mention of fusion rockets or rockets period.

 

[phavoc]

I've been reading Conway's History of Ships - Eclipse of the Big Gun. It's a pretty detailed book on the many aspects of naval architecture, ship types, even fleet trains. It's a great book if you'd like a reference or just something to give you ideas on historically how warships were designed and deployed from 1906-1945. There are other books covering modern ships.

https://www.librarything.com/work/108617

 

[Sigtrygg]

Going over my copy of CT HG has no mention of fusion rockets or rockets period.

You don't have the original version of High Guard then.
GDW High Guard first edition 1979 page 40:

Fusion Drives as weapons: Any ship may use its maneuver drive as a weapon...

 

[AnotherDilbert]

The Classic Traveller maneuver drive was a fusion rocket - it said so in first edition High Guard,

CT 1st edition in 1977 had reaction drives. CT 2nd edition, from High Guard 1980 (i.e. most material), had reaction-less drives.

 

[Sigtrygg]

Not necessarily.

There is no additional information in 81CT LBB2 or HG80 to overwrite the fusion drive description in HG79.

The descriptive text of the maneuver drive in LBB2 both editions is similar, as is the descriptive text in 79HG and 80HG - in fact the text on page 17 of each book regarding the maneuver drive is identical.

We know two things for certain:

MegaTraveller changed it to a reactionless drive

Frank Chadwick insisted that TNE go back to a reaction drive as it was originally intended to be.

 

[Condottiere]

When is a battlecruiser not a battlecruiser?

When it's too costly to lose.

 

[AnotherDilbert]

There is no additional information in 81CT LBB2 or HG80 to overwrite the fusion drive description in HG79.

The "Fusion Drives As Weapons" attack is only in HG'79, not in LBB2, removed in HG'80.
HG'80 does not extend HG'79, it replaces it. There is no need to countermand any information in HG'79.

Manoeuvre drives are not detailed, but only in LBB2'77 might they use reaction mass. In later books, even HG'79, they do not use reaction mass.


1977:

A fully fuelled power plant will enable a starship an effectively unlimited number of accelerations (at least 288) if necessary to use the maneuver drive during the trip...

So we can accelerate two days (or more), presumably limited by consuming reaction mass.


1979:
It's a strange kind of fusion rocket in HG'79:

Fuel consumption for starships is inconsequential, and assumed to be part of the power plant consumption, regardless of the degree of maneuver undertaken.
...
A power plant uses fuel equal to 1% of the ship's tonnage every four weeks, regardless of actual power drain; this usage is primarily to maintain the fusion bottle and other housekeeping functions. Other fuel requirements are considered inconsequential.

It uses no reaction mass.


1980:

Fuel consumption for maneuver drives is inconsequential, and is assumed to be part of the power plant consumption, regardless of the degree of maneuver undertaken.

Still no reaction mass.


1981:

Power plant fuel under the formula (10Pn) allows routine operations and maneuver for four weeks.

So we can accelerate for the full 4 weeks the PP has fuel, without using reaction mass.

 

[phavoc]

By the example cited, the maneuver drive isn't reaction less. If fuel use is inconsequential that means it IS being used, but at a rate that has little effect to your overall fuel consumption. Which makes sense as all illustrations show ships and small craft with engines in the rear of the ship.

 

[AnotherDilbert]

By the example cited, the maneuver drive isn't reaction less. If fuel use is inconsequential that means it IS being used, but at a rate that has little effect to your overall fuel consumption.

Possibly, but:

A power plant uses fuel equal to 1% of the ship's tonnage every four weeks, regardless of actual power drain; this usage is primarily to maintain the fusion bottle and other housekeeping functions. Other fuel requirements are considered inconsequential.

This might simply mean that using power from the power plant, e.g. to power the manoeuvre drive, consumes inconsequential fuel compared to idling the power plant.


There is a problem: it's certainly too little reaction mass.

E.g. the Free Trader; It uses 10 Dt = 10 tonnes of hydrogen for four weeks, or 4 g/s. If we say that inconsequential is 1%, then we use around 40 mg/s reaction mass to achieve 1 G ≈ 10 m/s² acceleration. So in 1 s 40 mg of reaction mass would increase the ships speed by 10 m/s.

By conservation of momentum MrVr = MsVs, so the velocity of the ejected reaction mass would need to be Vr = MsVs/Mr ≈ 1000000 × 10 / 0.00004 = 2.5 × 10¹¹ m/s = 250 million km/s or about 1000 times the speed of light.

At this energy level we have to consider energy rather than velocity. At close to lightspeed MrVr = MsVs would be Mr = MsVs / Vr ≈ 1000000 × 10 / 300000000 = 33 g of pure energy which by E=mc² is 3 × 10¹⁵ J which in 1 s is 3 PW = 3000000 GW. Obviously this can be produced by neither a fusion rocket nor the power plant.

Even if we could eject the reaction mass at close to lightspeed we would need several thousand times more reaction mass.

I would argue that reaction drives that use no noticeable reaction mass are even more magical than gravitic drives.

 

[Sigtrygg]

Have you run the numbers for the MgT reaction drive?

My solution to the fusion drive/low amount of fuel used was to have the m-drive reduce the inertial mass of the ship (handwave gravitics tech here) so that the fusion gun used for acceleration can produce the performance indicated.

Another solution I have used for a low tech campaign was to use the jump drive fuel % as reaction mass - much like TNE would eventually do. Full tanks provide 1 hour at full thrust - 60% of the ship as fuel can do 6g for one hour, or 1g for 6 hours. It used to be longer duration but then I read Atomic Rockets...

 

[phavoc]

I agree the maneuver drive issue was never really well thought out.

But I'm more comfortable with the idea of it using some fuel as reaction mass than none. Why? Because the game still embraces newtonian movement. And it's easier to stomach using a little reaction mass than none at all.

If it were none then we'd have other parts of the game falling apart. This way at least the crazy is consistent.

 

[AnotherDilbert]

Have you run the numbers for the MgT reaction drive?

No, because I suspect I will not like the result...

Let's see, a 100 Dt ship would use 2.5 Dt to produce 1 G for 1 h. If the fuel is hydrogen that is ~0.7 kg/s.

By conservation of momentum MrVr = MsVs, so the velocity of the ejected reaction mass would need to be Vr = MsVs/Mr ≈ 1000000 × 10 / 0.7 = 14000 km/s or about 5% of the speed of light.

Theoretically, by mass and energy, it would be possible. There are other limitations.

 

[AnotherDilbert]

But I'm more comfortable with the idea of it using some fuel as reaction mass than none. Why? Because the game still embraces newtonian movement. And it's easier to stomach using a little reaction mass than none at all.

I've always assumed the ship interacts with the local gravity field to exchange momentum with the local system, maintaining basic physics. It's obvious that a ship's power plant can't produce enough power to accelerate the ship (which is irrelevant if the M-drive is a fusion rocket that produces its own energy).

I believe Traveller use general relativity, not newtonian physics, hence speed is limited to the speed of light. The difference is negligible at "normal" sizes, low speeds, and low energies.