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Spacescifi

Optimal shapes for limited and constant acceleration starships

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When effectiveness is more important a factor than what looks nice, interesting spaceship shapes result. These are the conclusions I have reached.

Limited thrust starships: When you have to watch your propellant or risk running out. Virtually any shape you want can work, since you will spend more time coasting than under thrust anyway. Even near illogical Star Trek designs can kind of work.

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Constant thrust acceleration: Forget the saucer shape, it's not optimal. Use a cross beam shaped rocket. The mid-beam rocket has an engine at the rear and has the deck oriented for horizontal landings. Thus that is what the mid-beam rocket is for. The cross beam is actually two beams attached to the sides of the mid-beam rocket. These beams rotate so that the floor is oriented with the forward acceleration so any crew in them can have 1g gravity.

So when about to do long periods of constant acceleration, crew go to the side beams and rotate them to have gravity under thrust.

When the ship is about to land, crew leave side beam areas to go to the mid-beam rocket, and the side beams also rotate to match the ground too. Thus all is oriented with 'down' when the vessel lands.

 

EDIT: Realistically constant acceleration of 1g for several days or even months is a dream right now, but if we had it, a shape similar to the one I described would be optimal.

 

What other designs can you think of? Did I overlook anything? What I learned is that spaceships are better off having moveable parts rather than being the static bricks so often seen in scifi that are based more on ocean navies.

Edited by Spacescifi

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If you have the ability to accelerate at 1g for several days you don't need to worry about shape or moving parts. Engine is under the "floor" accelerating toward the ceiling. Whatever shape you want works fine. You don't even need to worry about shape in respect to landing on bodies with atmosphere with such an engine. Just match ground speed and make a powered descent at any velocity you are comfortable with. Why even bother with horizontal landing?

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45 minutes ago, AngrybobH said:

If you have the ability to accelerate at 1g for several days you don't need to worry about shape or moving parts. Engine is under the "floor" accelerating toward the ceiling. Whatever shape you want works fine. You don't even need to worry about shape in respect to landing on bodies with atmosphere with such an engine. Just match ground speed and make a powered descent at any velocity you are comfortable with. Why even bother with horizontal landing?

 

It really depends. See... having been around KSP long enough and read sources too, I know that RCS propellant is a finite resource, I also know that CMG's have limitations that preclude not having any RCS thrusters.

 

So... let's say your engine is below your vessel. Get's to space fine, but flying sideways through an atmosphere means that you will fall forward unless strapped in.

Rear engines solve that, at the expense of needing the setup I offered earlier in the original post.

 

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4 hours ago, kerbiloid said:

The Enterprise shape can not be optimal from any POV

 

It depends really.

What good is a saucer from a functional POV in space anyway?

For forward flight it is hardly an efficient use of space,, but as a rotational space station it is ideal.

 

Conclusion: The Enterprise, with proper modifications, could make a great space station.

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5 hours ago, kerbiloid said:

The Enterprise shape can not be optimal from any pov.

It depends on how warp drive works. If there is some sort of drag-limited warp drive effect, you may well want a shape which maximizes internal volume while minimizing cross-section and sharp angles, in which a saucer with big-ass engines attached is optimal.

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9 minutes ago, sevenperforce said:

It depends on how warp drive works. If there is some sort of drag-limited warp drive effect, you may well want a shape which maximizes internal volume while minimizing cross-section and sharp angles, in which a saucer with big-ass engines attached is optimal.

 

Perhaps...but I was only considering the functional aspects from a realistic POV.

But it is also worth noting that a rod or cylinder could also do the job in Trek physics, unless the warp field is only so big and requires that nothing reach beyond it.

In that case a sphere or saucer would be optimal.

Drag should not matter, as Trek vessels have the power to deflect space dust at warp... FTL warp no less.

 

Edited by Spacescifi

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It really depends on what you want to do with your ship.  For the most part though, I think going "tall" is probably the best choice, since it's easier to account for variations in the center of mass in a "tall" ship than in something spread out wide around the engine.  This can be somewhat mitigated by having multiple engines and using a combination of gimballing and differential throttle to keep your CoM going through your CoT, but in general, it will be easier to keep everything as close to the thrust axis as possible.  The Expanse does a good job of designing believable ships, with the Epstein drive handwave in the mix.

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My guess is that anything going to Mars (or similar) in the next few decades will look a lot like the ISS.  Building along a spine and attaching long tubes that fit inside rocket fairings is simply the best way to build things in space with the current technology.

For technology that includes constant 1g thrust?  You might as well use Jules Verne as a guide: we are at least as far from that as Jules was from Apollo.  Extrapolating from current tech would probably look like building construction: they exist to support structures against a 1g "acceleration".  Just be sure to update your building construction to match the engine tech.

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15 minutes ago, Thor Wotansen said:

It really depends on what you want to do with your ship.  For the most part though, I think going "tall" is probably the best choice, since it's easier to account for variations in the center of mass in a "tall" ship than in something spread out wide around the engine.  This can be somewhat mitigated by having multiple engines and using a combination of gimballing and differential throttle to keep your CoM going through your CoT, but in general, it will be easier to keep everything as close to the thrust axis as possible.  The Expanse does a good job of designing believable ships, with the Epstein drive handwave in the mix.

 

Good point. I had not thought of that, but it does explain why flying saucers fly so wobbly in KSP.

The problem gets worse since RCS requires propellant, and overrime, mass distribution will become unequal on one side of the ship, even if only slightly. When trying to land that could be devastating as the ship may flip towards it's heaviest end on the side when you're only trying to land the belly.

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2 hours ago, sevenperforce said:

It depends on how warp drive works. If there is some sort of drag-limited warp drive effect, you may well want a shape which maximizes internal volume while minimizing cross-section and sharp angles, in which a saucer with big-ass engines attached is optimal.

Then why make the saucer instead of a cylinder?

And why asymmetrical?

Edited by kerbiloid

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3 minutes ago, kerbiloid said:
2 hours ago, sevenperforce said:

If there is some sort of drag-limited warp drive effect, you may well want a shape which maximizes internal volume while minimizing cross-section and sharp angles

Then why make the saucer instead of a cylinder?

Because you may well want a shape which maximizes internal volume while minimizing cross-section. You can make a cylinder as long as you want, of course, but you quickly end up with fineness and bending moment problems. If you have a cylinder, the cross-section grows with the square of increases in diameter; if you have a constant-ratio saucer, the cross-section grows linearly with increases in diameter.

There could be other considerations...for example, if you have antigravity (as in Star Trek), it may only support a single plane within your OML, which would be more convenient if you have a few broad levels than many small levels. Additionally, there may be a polarization component of your warp drive, where "pushing" something in and out of warp is much harder if the object is very long than if it is wide but not high.

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21 minutes ago, sevenperforce said:

Because you may well want a shape which maximizes internal volume while minimizing cross-section.

?
The saucer minimizes the internal volume per same hull mass.

22 minutes ago, sevenperforce said:

fineness and bending moment problems.

Worse bending problem than when two propulsion modules are asymmetrically stripped from one side on long flat pylons?

23 minutes ago, sevenperforce said:

There could be other considerations...for example, if you have antigravity (as in Star Trek), it may only support a single plane within your OML,

A stack of saucers forms a high cylinder and save internal volume and share same structures.
Also probably it's easier to make a small diameter sized gravity.

25 minutes ago, sevenperforce said:

Additionally, there may be a polarization component of your warp drive, where "pushing" something in and out

And as we can see, the Enterprise saucer is tilted from "0°" to "45°" relative to any cylinder.
Also why not attach them from sides?

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37 minutes ago, sevenperforce said:

Because you may well want a shape which maximizes internal volume while minimizing cross-section. You can make a cylinder as long as you want, of course, but you quickly end up with fineness and bending moment problems. If you have a cylinder, the cross-section grows with the square of increases in diameter; if you have a constant-ratio saucer, the cross-section grows linearly with increases in diameter.

There could be other considerations...for example, if you have antigravity (as in Star Trek), it may only support a single plane within your OML, which would be more convenient if you have a few broad levels than many small levels. Additionally, there may be a polarization component of your warp drive, where "pushing" something in and out of warp is much harder if the object is very long than if it is wide but not high.

 

What's OML?

I read a more simple idea that warp fields are toroidal, which still does'nt jive with starfleet's design choices. Unless they just stuck with saucer only designs to fill out the volune of the field.

10 minutes ago, kerbiloid said:

?
The saucer minimizes the internal volume per same hull mass.

Worse bending problem than when two propulsion modules are asymmetrically stripped from one side on long flat pylons?

A stack of saucers forms a high cylinder and save internal volume and share same structures.
Also probably it's easier to make a small diameter sized gravity.

And as we can see, the Enterprise saucer is tilted from "0°" to "45°" relative to any cylinder.
Also why not attach them from sides?

 

Please.

Let us get away from star trek. I well know how absurd their designs are. I just like saucers and am trying to find ways to make them jive with reality in scifi.

 

In fact, I posted the Kelvin class kerbal starfleet ship because it is arguably one of the only ships starfleet has that would fly straight under thrust. The rest of Enterprise ships would spend all their time looping.

Edited by Spacescifi

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1 hour ago, kerbiloid said:

The saucer minimizes the internal volume per same hull mass.

Per hull mass, yes. But not internal volume per cross-section. Enterprise is clearly not mass-limited.

1 hour ago, kerbiloid said:

Worse bending problem than when two propulsion modules are asymmetrically stripped from one side on long flat pylons?

The Enterprise's warp core is in the lower module, while the warp nacelles are up high. Presumably the nacelles need some minimum separation for efficiency or warp field stability. The conventional impulse engines are in the center behind the CoM.

1 hour ago, kerbiloid said:

A stack of saucers forms a high cylinder and save internal volume and share same structures.
Also probably it's easier to make a small diameter sized gravity.

We don't know anything about making artificial gravity, so this could be any sort of solution. If your artificial gravity has a gradient then you want to make your ship as flat as possible.

1 hour ago, kerbiloid said:

And as we can see, the Enterprise saucer is tilted from "0°" to "45°" relative to any cylinder.
Also why not attach them from sides?

Who knows how warp works?

1 hour ago, Spacescifi said:

What's OML?

Outer mold line. Basically the "shape" of the ship.

1 hour ago, Spacescifi said:

I read a more simple idea that warp fields are toroidal, which still does'nt jive with starfleet's design choices. Unless they just stuck with saucer only designs to fill out the volune of the field.

What if warp fields turn out to send conservation of angular momentum haywire, causing roll orientation to go wack? The ship would tend to roll in the warp field and rip itself apart due to the extreme gradient. So you'd want an oblate toroidal field to stabilize.

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