The Compleat LBB2 Ship Design

[whulorigan]

. . . and then the NAFAL-Drive works everywhere (possibly using the gravity of the galaxy as its interaction)

Actually NAFAL works out to about 1/8 light-year, per the T5 text.

T5.10: Book 2, p.104:

NAFAL
The Not As Fast As Light Drive is a gravity-based vector-movement interstellar drive. N-Drive accelerations are expressed in tenth G (0.1G) increments (drive potential 1 for NAFAL = 0.1G). The N-Drive operates on the same general principles as the G-Drive and M-Drive. It has, however, two specific limitations:

• D Limit. NAFAL can only accelerate within about one-eighth light-year (or about 51 weeks of acceleration) of a gravity source. It can similarly decelerate only within the one-eighth light year distance (also about 51 weeks).
• Vector Limit. NAFAL has a vector limit (based on its potential) of about one-tenth light speed per potential. Drive potential 1 has a vector limit of 0.1c; drive potential 9 has a vector limit of 0.9c.

 

[AnotherDilbert]

Fusion rockets also made an appearance in the MT Hard Times design sequence, I would have to go back through decades old notes but if I recall correctly, they were a better way of moving a ship than the thruster/power plant combo (because of the mess they made with converting Striker to ship power plant scale).

In fact, they were not better than thruster plates, but they were better than gravitic M-drive (TL9-11)...

If you look at the errata, the fuel consumption is prohibitive. A Scout would use 1000 m³/h.

The drive itself is tiny.

 

[McPerth]

If you look at the errata, the fuel consumption is prohibitive. A Scout would use 1000 m³/h.

That's not what my numbers give...

HT fusion rockets consume 5 l/hour per 195 tons of thrust (1 kl of drives).

A scout's loaded mass is (according MT:IE) 916 tons, so it needs about 1800 TT. Let's say 10 kl, that would produce 1950 TT. They would use 50 l (so 0.05) kl/hour, not the 1000 kl you say (and, BTW, produce 39 Mw to use for other ship systems, at a total cost of 3.5 MCr)...

 

[AnotherDilbert]

Yes, at that rate it's far superior, but:

MT Consolidated Errata V2.21 (02/23/13):

...


205 m³/h is slightly more...

 

[McPerth]

Oh, OK, somehow I didn't read that you refered to errata.

I don't know where did they take those (or the previous, for what's worth) numbers that are, as you say, enormously increased (they multiply the needs by 41000...

But MT fuel efficiency is always low, to say the least...

 

[kilemall]

So 10kg per 1g per 600 seconds per 100,000kg of ship...

I wonder what the exhaust velocity would have to be...

At one point I assumed the m-drive was mostly a particle accelerator.

Then like a zen acolyte, I was slapped and enlightened.

 

[Condottiere]

I don't think the ion drive is mentioned in Traveller.

Slower, but less energy intensive.

 

[Grav_Moped]

The rules are conflicting:
• The fuel use rules says power plants use 10Pn, or small craft use 10 kg/burn (not both).
• The note on the page describing existing non-starships says 10 kg/burn for all non-starships.

I'll go with the fuel use rules.

Thank you for that direct comparison -- it's exactly what I needed.

The rules do not conflict. (To be clear, I'm discussing LBB2'77).

10Pn (1000kg*Pn, with Pn=G) provides one week of acceleration at 10kg/G, which is "all you need" for starship interstellar flights. Even the worst-case of a gas-giant to gas-giant jump is still technically possible by coasting partway through each of the 100D zones -- and that's all that's necessary to handwave it. Insystem trips longer than 7 days acceleration are accomplished by Jumping.

However, one week of acceleration is not enough for all in-system flights! (For example, Mars is an average of 140 million miles from Earth, and a week's fuel burn at 1g only gets you about 1 million miles...) So, if a non-starship needs to go farther than a week's worth of acceleration provides, it needs more than a week's worth of fuel (at 60kg/g per hour, or 1.44 tons/g per day), not merely the 10Pn that only covers the first million or so miles.

That '77 tracks fuel use at a flat-rate per G/turn (not tons of thrust/turn) is self-evidently absurd, but it shows what they were thinking.

 

[McPerth]

I don't think the ion drive is mentioned in Traveller.

Slower, but less energy intensive.

It is also metioned in MT:HT (also in One Small Steep, so also in Challenge).

It used 0.5 Mw and 0.0001 kl of fuel per Kl, giving .0.05 TT (both, in HT and errata), so giving very low thrust...

 

[Grav_Moped]

The rules do not conflict. (To be clear, I'm discussing LBB2'77).

Crosslinking to my discussion of '77 vs '81 fuel rules.