TL7 Spaceship Design

[AlexanderHowl]

The speed of sounds increases with stiffness of the material. For example, the speed of sound in diamond is 12 km/s. When it comes to air though, the speed of sound is greatest at ground level.

[Rupert]

Originally Posted by AlexanderHowl

The speed of sounds increases with stiffness of the material. For example, the speed of sound in diamond is 12 km/s. When it comes to air though, the speed of sound is greatest at ground level.

That doesn't tell us that it's because of pressure, though - the atmosphere is also quite warm at ground level, and get colder with altitude until it's also very thin.

It's always seemed to me to be one of those annoying things that doesn't follow nice simple rules, but rather involves multiple variables and maths that's past that which I am comfortable with.

[malloyd]

Originally Posted by Rupert

It's always seemed to me to be one of those annoying things that doesn't follow nice simple rules, but rather involves multiple variables and maths that's past that which I am comfortable with.

For pure gases it's actually pretty simple Vsound = sqrt (gamma * R * T/mu) where R is the universal gas constant, T is the temperature, mu is the molar mass and gamma is adiabatic constant for the gas (Cp/Ct), which is equal to f+2/f where f is the number of degrees of freedom of motion of the gas molecules (i.e. 7/5 for diatomic molecules like nitrogen or oxygen, and hence pretty close to that for air).

And yeah, it's pressure independent, which if you think about it is almost required, since sound is a pressure change wave, so if it were pressure dependent the speed of sounds would vary along its path, and depend on things like how loud the sound was.

[Johnny1A.2]

Originally Posted by 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?

Do they have nuclear fission?

[Verjigorm]

Gonna be brutally honest: I don't see any way to reconcile what you want: a mature space faring civilization that can transfer large numbers of people rapidly to different planets, AND TL7.

The best performer at TL7 is the Orion Drive Nuclear Pulse: for 1 engine system and 3 fuel tanks, you can reach Orbit or escape velocity. Of course, this comes along with the provision that that each launch consists of detonating hundreds of atomic bombs. But, it'll let you get a LOT of payload into orbit. Sadly, Orion's are not very good at landing, and you'll need some other sort system to land.

Chemical Rockets are up next: for 16 fuel tanks and an engine, you can get into orbit(but not escape velocity), but that will only leave you with a total of 3 systems to handle armor, flight control, and crew quarters.

Nuclear Thermal Rockets are pretty much a non starter: at TL7 they have an anemic .1G thrust, and only twice the dV of a chemical rocket. The most thrust you can get is .6G, which will require you to take off and land like a plane, and you're still going to need a lot of fuel tanks(atleast 8) to match a chemical rocket. You can make them fission ram-rockets and eke out a minor bit of extra dV that way, but not that much.

TL7 just isn't the way to go. TL8 offers marginal improvements, but not really enough. TL9 on the other hand opens up new options:

HEDM: 8 tanks will get you into Orbit.
NTR: You only need 2-3 engines to get enough thrust to take off like a rocket, and you only need around 8.5-9 tanks to get into orbit.
Orion Drive: 1 tank of fuel is enough to get into orbit

[thrash]

Sean Barrett's article in Roleplayer #29, "Stellar Windjammers," noted that "[m]agsails that can accelerate at greater than 60 milligees in the Solar wind at 1 AU can land on or take off from Earth's magnetic poles."

If you posit that your habitable worlds have equally strong magnetic fields (probably necessary for life to survive on world surfaces near a large gas giant) and allow superconductors with 10x the standard current density as your steampunk departure point, you could have ships with 6 magsail systems (now 0.01g each) take off and land from your habitable moons. Starting at the surface should allow the magsail to be charged by an external power plant on the ground, with top-ups from solar boiler power (SS7, p. 15) in flight.

Perhaps it would be easier to frame the campaign as TL5+2, with limited TL5+4 elements based on high capacity, high temperature superconductors. That would also allow for steampunkish energy weapons: heat rays, ball lightning projectors, etc.

[Johnny1A.2]

Originally Posted by Verjigorm

Gonna be brutally honest: I don't see any way to reconcile what you want: a mature space faring civilization that can transfer large numbers of people rapidly to different planets, AND TL7.

The best performer at TL7 is the Orion Drive Nuclear Pulse: for 1 engine system and 3 fuel tanks, you can reach Orbit or escape velocity. Of course, this comes along with the provision that that each launch consists of detonating hundreds of atomic bombs. But, it'll let you get a LOT of payload into orbit. Sadly, Orion's are not very good at landing, and you'll need some other sort system to land.

Yeah, that's why I asked if the setting had fission. Orion is probably the only viable option at TL7 for regular large-scale space flight. If it could be made practical, it could actually do some pretty amazing stuff at early TL7, if you're prepared to accept the fallout (literally).

[scc]

Originally Posted by Verjigorm

Gonna be brutally honest: I don't see any way to reconcile what you want: a mature space faring civilization that can transfer large numbers of people rapidly to different planets, AND TL7.

The best performer at TL7 is the Orion Drive Nuclear Pulse: for 1 engine system and 3 fuel tanks, you can reach Orbit or escape velocity. Of course, this comes along with the provision that that each launch consists of detonating hundreds of atomic bombs. But, it'll let you get a LOT of payload into orbit. Sadly, Orion's are not very good at landing, and you'll need some other sort system to land.

No society/civilization would ever sign off on Orion Drives for civilian use, especially in atmosphere. First there's the whole problem of mass produce nuclear ordinance for civilian use, sooner or later a terrorist WILL get their hands on one, but more importantly there's no way you can avoid releasing radioactive material.

Originally Posted by thrash

Sean Barrett's article in Roleplayer #29, "Stellar Windjammers," noted that "[m]agsails that can accelerate at greater than 60 milligees in the Solar wind at 1 AU can land on or take off from Earth's magnetic poles."

If you posit that your habitable worlds have equally strong magnetic fields (probably necessary for life to survive on world surfaces near a large gas giant) and allow superconductors with 10x the standard current density as your steampunk departure point, you could have ships with 6 magsail systems (now 0.01g each) take off and land from your habitable moons. Starting at the surface should allow the magsail to be charged by an external power plant on the ground, with top-ups from solar boiler power (SS7, p. 15) in flight.

Perhaps it would be easier to frame the campaign as TL5+2, with limited TL5+4 elements based on high capacity, high temperature superconductors. That would also allow for steampunkish energy weapons: heat rays, ball lightning projectors, etc.

1G or more is need to achieve no matter what.

[thrash]

Originally Posted by scc

1G or more is need to achieve [orbit?] no matter what.

A magsail that can generate 0.06g against the solar wind will generate more than 1.0g against Earth's (much denser) magnetic field, if only directly over the magnetic poles.

[Johnny1A.2]

Originally Posted by scc

No society/civilization would ever sign off on Orion Drives for civilian use, especially in atmosphere. First there's the whole problem of mass produce nuclear ordinance for civilian use, sooner or later a terrorist WILL get their hands on one, but more importantly there's no way you can avoid releasing radioactive material.

Which doesn't mean no civilization would ever use them in atmosphere. It stops our society, but other civilizations have other levels of risk tolerance. It's a mistake to assume that our current standards are some kind of universal law.