Optimal shape for massive SSTO scifi spaceships

[Spacescifi]

2 hours ago, Bill Phil said:

1g at 1rpm?

That entails a 1790 meter diameter. 

Or a ship about a mile wide.

I don’t think it’s practical to land anything of that size except on an ocean, and even then... the lightest shape for that diameter will be a torus...

 

Well... this is scifi but theoretically sound.

Ever heard of diamagnetic lithobraking?

Would'nt work on mars (rusty surface would pull you in harder).

With a superpowerful diamagnetic hull belly, you could hover a massive ship over the surface as air friction slows forward momentum down. Eventually the ship could use wheels to land.

Granted the ship would need enough forward momentum to glide over the surface so as not too fall straight down.

Edited June 8, 2019 by Spacescifi

[DDE]

16 hours ago, Spacescifi said:

Ever heard of diamagnetic lithobraking?

Something tells me magnetic hovering doesn’t work as well as you think.

Which is why it doesn’t seem anyone’s heard of it.

[Spacescifi]

21 minutes ago, DDE said:

Something tells me magnetic hovering doesn’t work as well as you think.

Which is why it doesn’t seem anyone’s heard of it.

 

You have not heard of it, but you will be able to google diamagnetic levitation.

The power requirements are ridiculous though, even for the frog levitation.

But with sufficient power.... something a massive scifi spaceship could have, it could do it. Everything is repelled by a strong magnetic field, with the exception of ferromagnetic materials we are more familiar with (metals that are magnetic).

 

Edited June 8, 2019 by Spacescifi

[DDE]

1 minute ago, Spacescifi said:

But with sufficient power.... something a massive scifi spaceship could have, it could do it.

Clearly you haven’t heard of electromagnetic interference, which is not a factor for frogs... but is a factor for complex machinery. During the Nedelin Disaster, outside magnetic interference caused a poorly-designed solenoid to fire, causing second stage engine activation while the R-16 ICBM was on the launchpad and fully fueled. Warships already spend weeks verifying the behavior of their various systems after each major refit, and their radars aren’t even in megawatt territory yet! It’s the same reason many are very cautious about artificial magnetospheres for ships.

The cruel irony is that technological advancements make your systems more vulnerable to interference.

[Spacescifi]

5 minutes ago, DDE said:

Clearly you haven’t heard of electromagnetic interference, which is not a factor for frogs... but is a factor for complex machinery. During the Nedelin Disaster, outside magnetic interference caused a poorly-designed solenoid to fire, causing second stage engine activation while the R-16 ICBM was on the launchpad and fully fueled. Warships already spend weeks verifying the behavior of their various systems after each major refit, and their radars aren’t even in megawatt territory yet! It’s the same reason many are very cautious about artificial magnetospheres for ships.

 

I have personal experience messing up electronics with magnets. I know this all too well.

That said, the fiction part of scifi could easily allow for a magnetic insulator.

Barring any real life ones in dense enough quantity that might work.

Edited June 8, 2019 by Spacescifi

[wumpus]

2 hours ago, DDE said:

Clearly you haven’t heard of electromagnetic interference, which is not a factor for frogs... but is a factor for complex machinery. During the Nedelin Disaster, outside magnetic interference caused a poorly-designed solenoid to fire, causing second stage engine activation while the R-16 ICBM was on the launchpad and fully fueled. Warships already spend weeks verifying the behavior of their various systems after each major refit, and their radars aren’t even in megawatt territory yet! It’s the same reason many are very cautious about artificial magnetospheres for ships.

The cruel irony is that technological advancements make your systems more vulnerable to interference.

Back in the 1990s I was running some equipment through tests before it could be put on board (military) submarines.  One of the tests involved susceptibility to magnetic fields: the device in question was placed inside a 2m circle of highly wrapped wire (enough to drop 150VDC without too much of a short circuit).  When they ran the test, the wrapped wire instantly aligned itself with the Earth's magnetic field, but my device kept on chugging.

The device was primarily a video display, and fortunately used the "fancy new [for the time]" LCD displays.  I knew when I saw that test I couldn't have passed with a CRT (without a lot more work and a ton of research).

[Cunjo Carl]

I think I'll muddy up the works and suggest the saucer. If the ship's really 'super massive' it would need a lot of surface area for landing legs when landing on a planet (which could be full of soft squishy things like forests or cities). The area needed for landing legs feels like it's one of those things that should go with square-cube, and there's no way to make the ground less squishy so I'd base my design on that and worry about the space stuff second. Next, it would be nice if the downwards direction of gravity (when landed) matched the direction of centrifugal artificial gravity (in space) and also direction of force from acceleration when the engines burn (when going between the two). Otherwise you'd need to move all your furniture from the floor to the walls every time you move or land! We could line up these 3 things by having the engines in a separate pod set into in the center of the saucer pointing 'downwards'. This would works well for takeoff and landing, and when you get to space, you can send the engine pod 'up' away from the saucer on a tether and when it reaches the end have it turn 90 degrees and give a bit of thrust to start the whole thing spinning. It's a similar idea to the tether used on Zubrin's Mars Direct. With this approach, we'd need to slam our way out of the atmosphere broadside first, but if fuel really isn't an issue then we could just burn slowly straight up 'till in space, then turn and burn until orbit achieved!

(I really do like @kerbiloid's hamster ball idea though!)

[Spacescifi]

40 minutes ago, Cunjo Carl said:

I think I'll muddy up the works and suggest the saucer. If the ship's really 'super massive' it would need a lot of surface area for landing legs when landing on a planet (which could be full of soft squishy things like forests or cities). The area needed for landing legs feels like it's one of those things that should go with square-cube, and there's no way to make the ground less squishy so I'd base my design on that and worry about the space stuff second. Next, it would be nice if the downwards direction of gravity (when landed) matched the direction of centrifugal artificial gravity (in space) and also direction of force from acceleration when the engines burn (when going between the two). Otherwise you'd need to move all your furniture from the floor to the walls every time you move or land! We could line up these 3 things by having the engines in a separate pod set into in the center of the saucer pointing 'downwards'. This would works well for takeoff and landing, and when you get to space, you can send the engine pod 'up' away from the saucer on a tether and when it reaches the end have it turn 90 degrees and give a bit of thrust to start the whole thing spinning. It's a similar idea to the tether used on Zubrin's Mars Direct. With this approach, we'd need to slam our way out of the atmosphere broadside first, but if fuel really isn't an issue then we could just burn slowly straight up 'till in space, then turn and burn until orbit achieved!

(I really do like @kerbiloid's hamster ball idea though!)

 

A good design if fuel is not an issue. However I do not see a way around reaaranging the furniture on the saucer. Unless you just make it simple with tents and portables.

"Hey everyone! We are going camping on the inner rim! Let's get our tents and portable toilets. And be sure to put away your poo when it fills all your bags."

If I understand Zubrin's idea correctly, it involves letting the engine out with a tether, and then using lateral thrusters on the engines to rotate the ENTIRE ship?

Ingenious! I never had thought of this. I had always thought that putting thrusters near the rim for thrust would be problematic. What with the crew needing that area for rotational gravity.

But it is not necessary, given your ingenious idea.

Although the ship will need some thrusters along the rim for pitch and lateral roll, just not horizontal roll along the rim.

 

By the way: I too like kerboloids hamster wheel approach, but I am not sure how to do it without fictional technologies.

Given the crew won't be in a safe position due to every action requiring an equal and opposite reaction.

The crew sphere would just roll backward, unless they could somehow dump that momentum elsewhere.

Edited June 9, 2019 by Spacescifi

[Cunjo Carl]

18 minutes ago, Spacescifi said:

A good design if fuel is not an issue. However I do not see a way around reaaranging the furniture on the saucer. Unless you just make it simple with tents and portables.

...

Although the ship will need some thrusters along the rim for pitch and lateral roll, just not horizontal roll along the rim.

Glad you like it!

I don't think the people would ever need to move. In this idea, the saucer would probably be several stories tall, 100s of meters wide, and would house people on the inside. People would only live in the outer 75% of the saucer shape, and would never need to enter the central engine section except for the engineers on their work shifts. Because of the way it's set up, the forces would always 'push' people down in the same direction on the saucer, so I don't think they'd ever need to move. Though, in most setups, they would need to go 0g for a time while the system spins up to make artificial gravity. Still, that's an easier problem to deal with than accelerations in all kinds of directions!

I think we could get away with engines all in the central pod. If the central engine pod took up 25% of the total area (and volume), it would take up 50% of the radius, so RCS thrusters put at the sides of the central pod would have about 50% the efficiency of engines out at the rim of the ship. We should then subtract a bit of that for the horizontal roll thrust due to cosine losses of angling the thrusters slightly outwards from the saucer, maybe 40% efficient total? Still, if fuel's not a big deal, we could get away with having all the thrust equipment in the central area, so it could be some really cool and fringe-science like UDH fusion that you may not want too close to the habs. 

 

46 minutes ago, Spacescifi said:

By the way: I too like kerboloids hamster wheel approach, but I am not sure how to do it without fictional technologies.

Given the crew won't be in a safe position due to every action requiring an equal and opposite reaction.

The crew sphere would just roll backward, unless they could somehow dump that momentum elsewhere.

The crew would just have to run along the inside of the ship to keep up!

[Spacescifi]

32 minutes ago, Cunjo Carl said:

Glad you like it!

I don't think the people would ever need to move. In this idea, the saucer would probably be several stories tall, 100s of meters wide, and would house people on the inside. People would only live in the outer 75% of the saucer shape, and would never need to enter the central engine section except for the engineers on their work shifts. Because of the way it's set up, the forces would always 'push' people down in the same direction on the saucer, so I don't think they'd ever need to move. Though, in most setups, they would need to go 0g for a time while the system spins up to make artificial gravity. Still, that's an easier problem to deal with than accelerations in all kinds of directions!

I think we could get away with engines all in the central pod. If the central engine pod took up 25% of the total area (and volume), it would take up 50% of the radius, so RCS thrusters put at the sides of the central pod would have about 50% the efficiency of engines out at the rim of the ship. We should then subtract a bit of that for the horizontal roll thrust due to cosine losses of angling the thrusters slightly outwards from the saucer, maybe 40% efficient total? Still, if fuel's not a big deal, we could get away with having all the thrust equipment in the central area, so it could be some really cool and fringe-science like UDH fusion that you may not want too close to the habs. 

 

The crew would just have to run along the inside of the ship to keep up!

 

Excellent ideas. What is UDH fusion?

 I do think your solution to kerboloids hamster wheel inner sphere to be hilarious though.

Interestingly, a saucer can also have other reasonable configurations still more practical than anything seen on popular scifi.

Like a massive pancake with four smaller pancakes. One for each corner, each about 25% the radius of the big saucer in the middle. The four lateral saucers would be the engines, while you could get away with no engines whatsoever on the main saucer. The flat belly would be great for landing, as the spots for landing gear are numerous.

The irony is that spin gravity is most useful for spaceships that have to worry about running out of fuel.

Another irony is that not aligning a spaceship's crew decks with the engine thrust actually can make plenty of sense for a scifi SSTO. If the spaceship has limited fuel.

Since getting stuff out is easier that way onto the planet, and you're going to spend waay more time coasting than thrusting in space anyway. So such a vessel would not reap the gravitational benefits of thrust g-force anyway.

If anything, a saucer with limited fuel rockets only makes practical sense if it can shield itself from gravity somehoe while launching. Even then, to save fuel the saucer would be wise to fly like a frisbee upward rather than hitting all the air like a shield.

Edited June 9, 2019 by Spacescifi

[Cunjo Carl]

I like it!

14 hours ago, Spacescifi said:

What is UDH fusion?

If it pans out, it's a source of free energy that runs on Hydrogen, which I've also seen being discussed for near-future scifi. It could be used to make a rocket engine in one of a few ways: by heating a working fluid with a heat exchanger (like an NTR), by catalyzing deuterium cold fusion with muons to make a _very_ high velocity exhaust, or directly by some mechanism no one understands to make _very_very_ high velocity exhaust... probably of exotic particles. To put it short, you flow Hydrogen (or deuterium) gas onto a certain common iron-oxide surface, zap it with a low power (few hundred mJ) pulsed laser for a few minutes and suddenly relativistic exotic particles and molecules start zinging out. That's what they're seeing anyways!

This kind of fringe science is normal, and most things that look like this peter into nothing. I happen to have a real soft spot for this one though; experimentally too many things line up for this for it to be easily dismissed as a fluke. Something interesting is going on, there's no doubt. Whether it's exactly as the lead proponent says though is another story entirely; I don't believe it is. Still, it should make for an excellent fringe science rocket engine for a scifi novel, and have seen it discussed as such. If confirmed, developed and scaled, the technology would make for very high thrust and Isp, at the expense of being very radioactive while running!

Just because I'm on a roll and starting to ramble, I put more in the spoiler.
 

Spoiler

 

UDH fusion is a modern update on cold fusion, and has actually been reproduced. Only by 2 labs so far... If I wasn't so dang sick, I'd make sure I was number 3 . Either to confirm or kill it. It's undoubtedly fringe science, and no one besides the lead proponents strongly believe in it, but I consider one of the results from a reproducing lab to be concrete enough that I wanna try! I used the term UDH fusion  because it's the google-able term, but the lead proponent now believes it's not fusion but another nuclear reaction more akin to annihilation.

The idea is a little something like how an eximer laser works. We take our atoms (in this case Hydrogen or Deuterium adsorbed on a surface), and pump them with energy (in this case some laser light) so they form molecules specifically with all the molecular bonds in high energy states (they tend to be extra big, and depending on context will be called eximers, exiplexes or Rydberg matter. It's a form of the 'population inversion' necessary for lasers). This kind of molecule is a bit like a mouse trap, it has a lot of stored energy and wants to decay to a smaller size, if only something sets it off. So we hit the stretched out molecule with light at the right frequency, and the whole thing suddenly loses its extra energy (either to laser light or kinetic energy) and collapses to the ground state where it summarily explodes! This is all normal stuff, used in modern technology like ArF lasers.

At least it was all normal until this guy tries it on Hydrogen adsorbed on a certain metal-oxide surface and inexplicably finds particles flying out at relativistic speeds, among other things. That's not normal. In fact, it's impossible. The thing is, his experimental science looks good, from what can be seen in his papers anyways. I can't stand how he writes, and I'm not sold on any of his theory. I'm an experimentalist though, and the results of one of the collaborating labs is what really has me hooked. When they turned on their system (which they suspect produces muons that can catalyze Deuterium fusion), they're getting something like 1000 neutrons/s (42 counts per second on the detector) out of a nearby bottle of D₂! Detector calibrations wander, but something like that is a smoking gun. Something interesting is going on, and no one really knows what. As a scientist that drives me nuts.

Anyways. I want to believe! But even more so, I want to experiment and verify. And if it works out, add my own techniques to the mix! I don't think it can happen though

Here's the collaborating lab doing a experiment to reproduce results with a few of their own twists. And, this is the part that really sticks out to me!

 

 

Edited June 9, 2019 by Cunjo Carl

[Rakaydos]

Muon catalized fusion works, but a steady supply of muons to keep up with catalist degradation is harder than just building a normal fusion tokamak.

There has been one SSTO superrichet that really didn't have to worry about running out of fuel, actually designed. I'm sure you've heard of it. The Project Orion manned Saturn explorer was shaped like a squat bullet.

[kerbiloid]

51 minutes ago, Rakaydos said:

There has been one SSTO superrichet that really didn't have to worry about running out of fuel, actually designed. I'm sure you've heard of it. The Project Orion manned Saturn explorer was shaped like a squat bullet.

But it required a lot of plutonium. There is no plutonium in wild nature.

Edited June 11, 2019 by kerbiloid

[Rakaydos]

4 minutes ago, kerbiloid said:

But it required a lot of plutonium. There is no plutonium in wild nature.

Why is this a problem?

[kerbiloid]

1 minute ago, Rakaydos said:

Why is this a problem?

Probably because you need to process a lot of uranum, fluorine, and other raw materials to produce  it.

[Rakaydos]

2 minutes ago, kerbiloid said:

Probably because you need to process a lot of uranum, fluorine, and other raw materials to produce  it.

This is a theoretical SSTO. I pointed out one which was designed.  difficulty of construction is irrelevant.