TL7 Spaceship Design

[scc]

So the thread about how many habitable planets you could cram into a star system by using moons of gas giants to cheat the system inspired me to dust of my steampunk/space fusion idea, and upon looking at my spacecraft designs I know I needed to seek guidance from the rest of the community for what was and wasn't possible and what is and isn't a good idea.

Before I get into the designs I need to talk about the setting a bit. Physically it only consists of moons of a gas giant, three habitable, 4 not, and the whole thing is right on the edge of the life zone which results in Koblillon, my Earth replacement, being rather Cold. Technologically it's TL7 or TL5+2 but is lacking anything that would break a late steampunk vibe, notably anything dieselpunk or electronic, so no cars and computers are Babbage machines. Culturally spaceflight is seen as much more important/sexy, because when you look up in the sky you see unclaimed lands and the potential riches contained therein, also no recent conflicts like the world wars to shake things up (This is important!)

First thing is surface-to-orbit craft, would things like SABRE (An air breathing mode for rocket engines), full-flow staged combustion, and aerospike engines be possible and how would they affect the stock chemical rocket? For SABRE would a single tank of fuel at 3g be able to get the craft up to full speed? I'm asking because I want an SSTO spaceplane that could carry a reasonable number of troops.

Secondary is the subject of trans-lunar transport. My preferred main drive here is magnetic sail, I know supposed to be TL9, but intra-Jovian orbits so maybe possible (And cool, which Steampunk seems to run to) question is should a merchantman that needs to power said sail once a month have to dedicate an entire system to a power-plant when said power plant will be once a month to kickstart the sail, or should I hand wave it?

Would such merchantman need minimally armored hulls or should they just be naked?

I want a troop transport in the setting, for the steampunk era how big would a desired fast reaction force be? My gut says a regiment (1 thousand men), but that makes the transport awfully expensive.

At present I'm using a X10 cost multiplier on base cost and my currant largest merchantman is ~$1B with a total setting GDP of ~$16T, is it realistic that these ships could be built as private ventures?

[Fred Brackin]

Originally Posted by scc

S

First thing is surface-to-orbit craft, would things like SABRE (An air breathing mode for rocket engines), full-flow staged combustion, and aerospike engines be possible

in drive here is magnetic sail, I know supposed to be TL9, but intra-Jovian orbits so maybe possible (And cool, which Steampunk seems to run to) question is should a merchantman that needs to power said sail once a month have to dedicate an entire system to a power-plant when said power plant will be once a month to kickstart the sail, or should I hand wave it?


Would such merchantman need minimally armored hulls or should they just be naked?

?

First question and the answer is "no Sabres" unless the setting is _highly_ Cinematic with high CP Gadgeteers. In realistic terms the best you can do at TL7 is a Saturn-5 and this will put 330,000 lbs into low earth orbit. The Shuttle didn't really come that close to getting off the ground at TL7.

Magsail at TL7 is a little cinematic but probably okay. Handwaving the start-up power is cheating a little. A single fuel cell should be enough and you can get by with the low endurance.

You need hull armor for radiation shielding. You might not have to worry about cosmic rays due to the GG magnetosphere but a big one of those like Jupiter's is its' own radiation hazard. Transhuman Space makes the worst of Jupiter's rad belt 18,000 rads per hour and even multiplying the values from Spaceships 5 by 20 for the low energy radiation there's no way you can build a ship that can handle that.

That's the max though. The minimum is only .01 rads/hour but without at least some shielding that woulds till leave you rolling on the radiation damage table more than once per week and you're probably lsign large portions of your crew to hemopoetetic syndrome before they can sail back home.

You could get your troops down at their target in expendable capsules but SSTO spaceplanes to get them back are a TL7-8 no-go. Maybe TL9.

I recommend superscience. Hard science Steampunk is perverse. :)

[malloyd]

Originally Posted by Fred Brackin

I recommend superscience. Hard science Steampunk is perverse. :)

Hard science spaceflight at TL7 (and possibly ever, though there is still some hope for the future) is basically a plot device - not something you need design rules for. We're closing on TL9 and far it has cost nearly a billion dollars per person put into space, and something like $16 million/person-day.

This simply too expensive to support a setting where spaceflight is a regular enough thing to need detailed spacecraft rules. In a world that has never been able to afford to be flying more than three manned spaceships at a time, and has yet to manufacture more than a few dozen of any one design (yeah, Soyuz reuses the name, but the capsules themselves have seen 7 major redesigns/"generations"), there is not much use for a generic design system.

[Michael Thayne]

Originally Posted by scc

First thing is surface-to-orbit craft, would things like SABRE (An air breathing mode for rocket engines), full-flow staged combustion, and aerospike engines be possible and how would they affect the stock chemical rocket? For SABRE would a single tank of fuel at 3g be able to get the craft up to full speed?

No. Proposals for spaceplanes based on SABRE still require a large majority of their takeoff weight to be fuel. Even with that I don't actually understand how it's supposed to grant SSTO capability. Nuclear thermal rockets might theoretically allow SSTO capability at TL7, and Orion engines certainly would if you don't mind the expense and radiation, but I agree with Fred that you want to go for superscience here.

[Anaraxes]

Jupiters are likely to have radiation belts that would be hazardous to inhabitants of some of their moons. That might make for an adventurous hazard, as well as a reason to choose the "minimally armored" ships over the "naked" ones. The steampunk magnetic fluid geniuses might even figure out their own magnetic shielding to protect the ships, though that will get you back to the power question. There's no novel science involved in that idea -- just quite a lot of engineering and tool development.

As long as I'm ignoring historical development paths, the photovoltaic effect was known in the first half of the 19th century. They had wet solar cells made with precious metal foil (which probably explains why they stuck to burning coal).

I wouldn't ignore the power source for the magsail. Even if you only need it once a month, you still need it when you need it. Whether it's an actual power plant or a super Leyden jar, it's mass, space, and cost that are part of the whole system. You need someplace with big ceramic insulators and sparks crawling up a Jacob's Ladder anyway, right?

[AlexanderHowl]

Even a disposable system can get an upper stage to LEO for relatively cheap ($10,000,000 for a SM+8 three-stage assembly to get a SM+6 reuseable third stage to LEO). If we assume that the third stage is 50% cargo, that ends up being $200,000 per ton at TL7 (which is much better than right now). Even so, current costs are $50 million per person/$1 million per person-day, not $1 billion per person/$50 million per person-day.

[Ulzgoroth]

If the habitable moons are smaller than Earth, getting into orbit might be easier there.

[johndallman]

Originally Posted by Michael Thayne

SABRE still require a large majority of their takeoff weight to be fuel. Even with that I don't actually understand how it's supposed to grant SSTO capability.

SABRE gets you to about Mach 5.1 and 90,000 feet as an airbreathing engine, which is a lot better than you can get with conventional jet engines, and is similar to what you get from the first stage of a 3-stage rocket. Then you get to use the same engine as a rocket for the rest of the way to orbit.

It saves weight over having two engines, and saves a lot of fuel mass by being air-breathing part of the way. It pays a weight penalty for having wings, and it needs to be liquid-hydrogen fuelled because it uses the cold of that fuel to cool incoming air, which is vital for the air-breathing efficiency. However, liquid hydrogen is very bulky, needing large tanks, and requires insulation, which adds weight. The Skylon spaceplane design claims to be able to orbit 17 tons of payload from a 325 ton takeoff mass, about 5%.

It demands good liquid hydrogen handling capability, which is at least TL7, and the heat exchanger is definitely TL8.

[AlexanderHowl]

A three-stage disposable system will get 5% of its mass to LEO as well, and I really doubt that a SABRE is good enough to make it worthwhile. In Spaceships, it would just be subtracting the air speed of 3g from the delta-v, which would result in a required delta-v of 5 mps to reach LEO if you are being realistic. Assuming a control room, one chemical rocket, one armor, and two cargo holds, that leaves only fifteen tanks for fuel, one of which are needed for the hydrogen of the atmospheric portion. That only leaves 3.36 mps of delta-v for the chemical rocket, which is insufficient by 1.64 mps.

[scc]

Responses in order of seaming importance:

Originally Posted by Ulzgoroth

If the habitable moons are smaller than Earth, getting into orbit might be easier there.

I think some people are missing this trick, surface gravity is 0.9 and velocities, escape and orbital, are 86% of Earth.

Originally Posted by Anaraxes

I wouldn't ignore the power source for the magsail. Even if you only need it once a month, you still need it when you need it. Whether it's an actual power plant or a super Leyden jar, it's mass, space, and cost that are part of the whole system. You need someplace with big ceramic insulators and sparks crawling up a Jacob's Ladder anyway, right?

I should clarify that I'm using the Spaceships rules, so a adding a power system consumes 5% of a ships mass, which is separate from the 5% you must spend on the sails them selves.

Originally Posted by Fred Brackin

First question and the answer is "no Sabres" unless the setting is _highly_ Cinematic with high CP Gadgeteers. In realistic terms the best you can do at TL7 is a Saturn-5 and this will put 330,000 lbs into low earth orbit. The Shuttle didn't really come that close to getting off the ground at TL7.

I'm pretty sure that Steampunk as a genre runs on Cinematic Gadgeteers.

Originally Posted by malloyd

Hard science spaceflight at TL7 (and possibly ever, though there is still some hope for the future) is basically a plot device - not something you need design rules for. We're closing on TL9 and far it has cost nearly a billion dollars per person put into space, and something like $16 million/person-day.

This simply too expensive to support a setting where spaceflight is a regular enough thing to need detailed spacecraft rules. In a world that has never been able to afford to be flying more than three manned spaceships at a time, and has yet to manufacture more than a few dozen of any one design (yeah, Soyuz reuses the name, but the capsules themselves have seen 7 major redesigns/"generations"), there is not much use for a generic design system.

Lack of funding and a political has hampered spaceflight in the real world, not really a problem in my setting.

Originally Posted by Michael Thayne

No. Proposals for spaceplanes based on SABRE still require a large majority of their takeoff weight to be fuel. Even with that I don't actually understand how it's supposed to grant SSTO capability. Nuclear thermal rockets might theoretically allow SSTO capability at TL7, and Orion engines certainly would if you don't mind the expense and radiation, but I agree with Fred that you want to go for superscience here.

Nuclear thermal rockets would be an environmental disaster, spewing radiation everywhere.

Originally Posted by AlexanderHowl

Even a disposable system can get an upper stage to LEO for relatively cheap ($10,000,000 for a SM+8 three-stage assembly to get a SM+6 reuseable third stage to LEO). If we assume that the third stage is 50% cargo, that ends up being $200,000 per ton at TL7 (which is much better than right now). Even so, current costs are $50 million per person/$1 million per person-day, not $1 billion per person/$50 million per person-day.

My $1B figure is for a reusable, SM+10 deep space freighter.

Originally Posted by johndallman

SABRE gets you to about Mach 5.1 and 90,000 feet as an airbreathing engine, which is a lot better than you can get with conventional jet engines, and is similar to what you get from the first stage of a 3-stage rocket. Then you get to use the same engine as a rocket for the rest of the way to orbit.

It saves weight over having two engines, and saves a lot of fuel mass by being air-breathing part of the way. It pays a weight penalty for having wings, and it needs to be liquid-hydrogen fuelled because it uses the cold of that fuel to cool incoming air, which is vital for the air-breathing efficiency. However, liquid hydrogen is very bulky, needing large tanks, and requires insulation, which adds weight. The Skylon spaceplane design claims to be able to orbit 17 tons of payload from a 325 ton takeoff mass, about 5%.

It demands good liquid hydrogen handling capability, which is at least TL7, and the heat exchanger is definitely TL8.

So not completely impossible, just highly implausible then.

Originally Posted by AlexanderHowl

A three-stage disposable system will get 5% of its mass to LEO as well, and I really doubt that a SABRE is good enough to make it worthwhile. In Spaceships, it would just be subtracting the air speed of 3g from the delta-v, which would result in a required delta-v of 5 mps to reach LEO if you are being realistic. Assuming a control room, one chemical rocket, one armor, and two cargo holds, that leaves only fifteen tanks for fuel, one of which are needed for the hydrogen of the atmospheric portion. That only leaves 3.36 mps of delta-v for the chemical rocket, which is insufficient by 1.64 mps.

Using Spaceships rules a SABRE engine allows you to get something like 1.19 mps from a single fuel tank, over the 0.15 you'd normally get.