ProfGrizzlyJon
Cosmic Mongoose
That was the way that I read it. The intent was to use .1G, based on the rest of the context about primitive spacecraft in that Supplement.
Ship Design Philosophy
- Thread starter Condottiere
- Start date
Condottiere
Emperor Mongoose
Upto this point (in time), plasma drive is the most efficient (direct) converter of fuel into thrust, by electrifying it, in Traveller.
But even two and a half times efficiency still ensures it's a gas guzzler, which the stereotype of ye turboprop somewhat contradicts, for a regional airliner, or military transporter.
Also, it takes up a larger percentage of the spacecraft.
Now, reactionary rocket powered spacecraft tend to work out for intraplanetary, orbital, and lunar, transportation, since there is sufficient gas in the tank, and the cost of that is balanced by lower maintenance ones, and capital outlay.
Being within or near orbit, doesn't really make chucking out atomic warheads out the rear cargo hatch, to act as propulsion, appealing to the local electorate.
And, I suspect, atomic warheads aren't cheap.
Lightships might qualify, on the basis that if powered by an active fusion reactor, it's use it or lose it; but, I don't think it's been given the Mongoose treatment.
But even two and a half times efficiency still ensures it's a gas guzzler, which the stereotype of ye turboprop somewhat contradicts, for a regional airliner, or military transporter.
Also, it takes up a larger percentage of the spacecraft.
Now, reactionary rocket powered spacecraft tend to work out for intraplanetary, orbital, and lunar, transportation, since there is sufficient gas in the tank, and the cost of that is balanced by lower maintenance ones, and capital outlay.
Being within or near orbit, doesn't really make chucking out atomic warheads out the rear cargo hatch, to act as propulsion, appealing to the local electorate.
And, I suspect, atomic warheads aren't cheap.
Lightships might qualify, on the basis that if powered by an active fusion reactor, it's use it or lose it; but, I don't think it's been given the Mongoose treatment.
Condottiere
Emperor Mongoose
And speaking of orbital activities.
At some point or another, you would generally come to the conclusion that, in the long run, a gravitationally based manoeuvre drive is the most pragmatic, and that means overall cost of ownership.
Without one, you have to install heat shielding for your spacecraft, to effect atmospheric reentry, and those things aren't cheap, if you compare prices, followed by overall practicality.
Hundred tonne spacecraft, heat shielded, zero tonnes, plus ten megastarbux to the bill of materials.
Hundred tonne spacecraft, factor/one manoeuvre drive, default, one tonne at two megastarbux, and ten power points (early fusion one tonne reactor, half a megastarbux); two tonnes, two and half megastarbux.
At some point or another, you would generally come to the conclusion that, in the long run, a gravitationally based manoeuvre drive is the most pragmatic, and that means overall cost of ownership.
Without one, you have to install heat shielding for your spacecraft, to effect atmospheric reentry, and those things aren't cheap, if you compare prices, followed by overall practicality.
Hundred tonne spacecraft, heat shielded, zero tonnes, plus ten megastarbux to the bill of materials.
Hundred tonne spacecraft, factor/one manoeuvre drive, default, one tonne at two megastarbux, and ten power points (early fusion one tonne reactor, half a megastarbux); two tonnes, two and half megastarbux.
Sigtrygg
Emperor Mongoose
There is more to it than just fuel to thrust.
A plasma drive has to include the power plant and power plant fuel that is required, as well as the fuel it uses for reaction mass.
A standard reaction engine plus "fuel" with no power plant requirement actually uses less tonnage over all than a plasma drive plus power plant plus fuel.
At TL8
plasma drive 20% of hull per thrust, for a 100t ship that's 20t
each ton requires 1 power point so for a 100t ship that's 20 EPs, which requires an additional 2 tons of fission power plant and 1 ton of power plant fuel
fuel is 1% (of hull?) per thrust per hour, so for the 1 hour that's 1t of fuel. Total 24 tons.
For a 100t ship, a 2t reaction drive requires only 2t of fuel for 1 hour. Total 4 tons
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ProfGrizzlyJon
Cosmic Mongoose
You should be able to refine the detonators from liquid hydrogen fuel.
ProfGrizzlyJon
Cosmic Mongoose
Not a valid representation for sustained use.
<21 hours total acceleration/deceleration is where they balance out. Plasma becomes more efficient afterwards.
By comparison, with fuel for only 20 hours of 1G thrust, split into 10 hours of acceleration and 10 hours of deceleration, you can travel from Earth to Mars at closest approach (55 million km) in approximately 2.2 days (53.3 hours)
Alternatively, you only need 3.5 hrs of 1G thrust to travel between Earth orbit and Lunar orbit.
Sigtrygg
Emperor Mongoose
By which time 40% plus of your ship is drives and fuel. Not much chance of building a 2g plasma drive ship is there.
Where the plasma drive would be useful is is using fractional g thrust for long duration. A 0.5g plasma drive is going to achive parity with a reaction engine at a lower tonnage, so of you stick with that 40% payload being drives and fuel you would get the drive down to 10t, the power plant and fuel down to 2 t so 12t with 36 hours of 0.5g thrust available. But MgT doesn't like playing with less thrust than 1g...
Where the plasma drive would be useful is is using fractional g thrust for long duration. A 0.5g plasma drive is going to achive parity with a reaction engine at a lower tonnage, so of you stick with that 40% payload being drives and fuel you would get the drive down to 10t, the power plant and fuel down to 2 t so 12t with 36 hours of 0.5g thrust available. But MgT doesn't like playing with less thrust than 1g...
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ProfGrizzlyJon
Cosmic Mongoose
Same problem as jump drives; plasma drives have the chance for reduced size and reduced fuel as they progress.
.5G still gets you between the Earth and the Moon in 5 hrs (with accel-flip-decel)
Condottiere
Emperor Mongoose
First, you look at the options available.
Then, you figure out their pros and cons, especially in relation to your needs.
Finally, figure out if you can tweak them to more conform with said needs.
If you assume you will have to undertake atmospheric reentry, your path divides to either gravitational derived drive, and/or heat shielding.
You could, of course, acquire a subsidiary spacecraft for that role.
You end up trying to balance availability, acceleration, range, endurance, cost, power, and volume.
In the long run, in terms of endurance, the plasma drive beats the reactionary rockets, but requires tens times more volume.
Then, you figure out their pros and cons, especially in relation to your needs.
Finally, figure out if you can tweak them to more conform with said needs.
If you assume you will have to undertake atmospheric reentry, your path divides to either gravitational derived drive, and/or heat shielding.
You could, of course, acquire a subsidiary spacecraft for that role.
You end up trying to balance availability, acceleration, range, endurance, cost, power, and volume.
In the long run, in terms of endurance, the plasma drive beats the reactionary rockets, but requires tens times more volume.
