[Spaceships] A Few Questions

[scc]

1. What needs armor? I'm working on a series of deep space freighter designs, do they need armor systems or will they be just fine without them?

2. High power systems, if my only high power systems is a magsail, which only requires power on start up, do I still need a power plant?

3. Jet engines, chemical rockets and fuel, if my chemical rockets are burning kerosene instead of hydrogen how do I calculate fuel used for Delta-V Increase?

4. SABRE rocket engines, simply treat the craft as if it also as 3g in jet engines and ignore fuel useage?

[Daigoro]

Originally Posted by scc

1. What needs armor? I'm working on a series of deep space freighter designs, do they need armor systems or will they be just fine without them?

Armour's not obligatory. As per SSp10, unarmoured sections have DR2/dDR0 (DR3 if streamlined).

2. High power systems, if my only high power systems is a magsail, which only requires power on start up, do I still need a power plant?

There's some write-ups for battery systems floating around. They might be useful for your needs.

Q3&4? Dunno, sorry.

[RogerBW]

Originally Posted by scc

3. Jet engines, chemical rockets and fuel, if my chemical rockets are burning kerosene instead of hydrogen how do I calculate fuel used for Delta-V Increase?

This is below the resolution of the Spaceships system. "Rocket fuel" is "rocket fuel".

[Daigoro]

Originally Posted by Daigoro

There's some write-ups for battery systems floating around. They might be useful for your needs.

Eric B. Smith's optional rules, here, have the Energy Bank system. And if you're not using his design spreadsheet, well, you should be.

Originally Posted by RogerBW

This is below the resolution of the Spaceships system. "Rocket fuel" is "rocket fuel".

TL7 Chemical Rockets on p21 give Acc 3G/delta-V 0.15mps, so you could probably just downgrade those numbers by a third or so for TL6-ish numbers.

[Fred Brackin]

Originally Posted by Daigoro

E

TL7 Chemical Rockets on p21 give Acc 3G/delta-V 0.15mps, so you could probably just downgrade those numbers by a third or so for TL6-ish numbers.

Historically, TL6 jet and liquid fuel rocket engines just barely exist as prototypes. It was hard to make any sort of functioning vehicle out of them. They don't really need Spaceships stats. If you learned enough to make a successful one that would push you into TL7.

[ericthered]

Kerosene is not a TL6 only rocket fuel. Its still used today, most often in the lower stages of rockets. Its specific impulse is 75% of hydrogen (when comparing the average of the ranges given on wikipedia) and reportedly quite a bit cheaper than hydrogen in the current economy. It also requires a smaller tank to store, which won't effect spaceships stats (empty fuel tanks weigh nothing) but conceivably you could change the cost of the fuel tanks for being smaller. And for containing a fuel that's a liquid at room temperature and doesn't require extreme pressurization and cooling.

[Humabout]

The RL10 (the most commonly used hydrolox engine currently in use) has an Isp of about 420 s, and typical kerolox engines today have an Isp of around 350. The designers' notes for Spaceships explains how to get performance and dv from this.

Furthermore, modern engines provide up to 3 g of acceleration because any more would crush the structure of the rockets and be rather unpleasanr for the squichy meatsacks riding in them. They could be designed for higher thrust. They just aren't for other reasons.

[scc]

Originally Posted by ericthered

Kerosene is not a TL6 only rocket fuel. Its still used today, most often in the lower stages of rockets. Its specific impulse is 75% of hydrogen (when comparing the average of the ranges given on wikipedia) and reportedly quite a bit cheaper than hydrogen in the current economy. It also requires a smaller tank to store, which won't effect spaceships stats (empty fuel tanks weigh nothing) but conceivably you could change the cost of the fuel tanks for being smaller. And for containing a fuel that's a liquid at room temperature and doesn't require extreme pressurization and cooling.

Kerosene is also a superior deeper in the atmosphere, which is why the Saturn V used it for it's first stage, Atlas 5 does the same thing.

[Humabout]

Originally Posted by scc

Kerosene is also a superior deeper in the atmosphere, which is why the Saturn V used it for it's first stage, Atlas 5 does the same thing.

This has nothing to do with atmosphere. Kerosene is much denser than H2, so you can jam more of it in a smaller rocket. And smaller rocket = less structural mass fraction. It is also heavier, so burning it deeper in the gravity well (which on Earth does equate to deeper in atmosphere, but not necessarily on other worlds) means you boost less mass more quickly. This is so called gravity drag. Decrease your mass as fast as possible so you get more bang for your fuel.

Kerolox isn't currently used in vacuum because vacuum happens away from gravity wells where gravity drag is a concern and hydrolox is more efficient (see the higher Isp I mentioned earlier).

If we are to be complete here, there is talk these days of making methalox rockets. There are a number of technical difficulties here, and it tends to be less efficient. The upside is that there is a lot of methane in the solar system, and that's the generally the driving factor for such designs - ISRU.

[Fred Brackin]

Originally Posted by Humabout

T
Furthermore, modern engines provide up to 3 g of acceleration because any more would crush the structure of the rockets and be rather unpleasanr for the squichy meatsacks riding in them. They could be designed for higher thrust. They just aren't for other reasons.

That 3G limit was true for the Shuttle but that has to do with weight savings. The crew could have taken more and rockets have been designed that gave more. Gemini launches topped out just short of 7 Gs. So did some X-15 flights.

3Gs isn't some magic number for either hardware or wetware.