Spaceship design - a hypothetical excercise

[bobdude11]

Please note the following:
I am not:

• an engineer
• physicist
• astrophysicist (that is a separate discipline from physicist, yes?)
• mathematician

What I am:

• Sci-fi fan
• cyber-security engineer (I use that term loosely - not sure I really classify as an engineer more than a practitioner of cyber-security principles)
• Basic math
• High school science level
• Rabid curiosity
• Desire to learn

That said, here is my question:
 Assuming we have all of the requisite technologies (warp drive, impulse drive, gravity plating (still not sure how that would work ...), phasers, photon torpedoes, transporters, etc.) and could build a Constitution class starship (for those not familiar: U.S.S. Enterprise - NCC-1701) and based on what I assume to be a huge size (to house all the technologies and the 400+ crew with fairly roomy accommodations), wouldn't the sheer mass prevent the ship from traveling beyond a certain speed or possibly not even able to move at all?
I am not fully clear how the impulse engines would work, but it seems that they would have to put out quite a bit of energy to move the ship with any significant speed much less how big the warp core would have to be or at least how much output it would have to provide to create the warp bubble necessary to get the ship travelling.


Any thoughts from the experts? 

[bknight]

The operative word is ASSUMING and since we have none of those skills/technologies it would be up to the Sci. Fi writers to answer your questions.

[bobdude11]

Point taken. I realized this might just be a pointless question after I posted it.

[Allan F]

In Star Trek, they have control over inertia, and therefore it's not really how fast they CAN accelerate, but how fast they WANT to accelerate. According to DS9 S01E01, the warp field can lower the inertial mass of the object inside it.

[Jason Thompson]

A handy mcguffin that always bugged me, because the thrusters they used to move the station were inside the field but somehow immune to the 'inertial mass lowering' and still generating the same thrust. Shouldn't it have been the same in relative terms and offer no advantage? On the other hand, if they'd lowered the inertial mass of the station it could have been pulled by the two remaining runabouts with a tractor beam. The applied force would then be outside the field and hence comparatively stronger.

[bobdude11]

In Star Trek, they have control over inertia, and therefore it's not really how fast they CAN accelerate, but how fast they WANT to accelerate. According to DS9 S01E01, the warp field can lower the inertial mass of the object inside it.

I remember that and thought it was an interesting take on warp drive. Until that explanation, I always thought the warp "bubble" was meant to move space instead of the ship, hence the idea of "folding space" around the ship.

[Allan F]

Lower mass with same force equals higher exhaust velocity. So the speed the exhaust leaves the rest behind is proportional to the force applied. So lowering the mass to half, will INCREASE the thrust enormously.

[bobdude11]

Lower mass with same force equals higher exhaust velocity. So the speed the exhaust leaves the rest behind is proportional to the force applied. So lowering the mass to half, will INCREASE the thrust enormously.

Thank you, I wasn't aware of this.

[jfb]

wouldn't the sheer mass prevent the ship from traveling beyond a certain speed or possibly not even able to move at all?

Even an itty-bitty ion thruster imparting a fraction of a Newton will eventually get it moving to relativistic speeds, it's just a matter of how long you're willing to wait and how much propellant you have available.  Munging the Tsiolkovsky equation a bit, you can compute the propellant mass as



So if the Enterprise masses, say, 1.9 x 10^8 kg per one online estimate (m_dry), and we want it to go 0.5 c (delta v), and our itty-bitty ion thruster has an exhaust velocity of 50,000 m/s (v_e), then we'd need on the order of e²⁹⁹⁸ kg of propellant. 

That's ... a lot (my calculator overflows on it). So, yeah, practically speaking, getting something as big as the Enterprise moving would be a challenge. 

I am not fully clear how the impulse engines would work, but it seems that they would have to put out quite a bit of energy to move the ship with any significant speed

It's never really explained exactly how impulse engines work.  Given the name, it's strongly implied it's some kind of reaction drive, but God knows what the actual mechanism is.  It could be a fusion drive sort of like what's used in The Expanse (at least the TV version); a pellet of deuterium wrapped in a lithium (I think) shell, blasted by lasers to induce fusion, reaction products are directed out of the engine at near light speed.  Low mass, but super-high velocity, providing a pretty good push.   

But again, it's never really explained, and like with the itty-bitty ion thruster the fuel necessary would likely out-mass the rest of the ship by a lot.   

The genius of warp drive (at least as commonly envisioned) is that you aren't moving very fast at all relative to local space; you're warping spacetime to bring your destination closer to you and push your departure point away from you.  The mass of your vessel is almost irrelevant.  And, what many people seem to miss is that if you can warp spacetime, then you get artificial gravity and inertial damping for free¹. 

It's a big "if", though.  The math works, sure, but the energy requirements are on the far side of feasible.  I know people have been refining Alcubierre's work to bring that energy requirement down, but it's still more than we can realistically generate or harness with any near-term technology.  There's a reason Trek hand-waved it away with anti-matter. 

• Although the Enterprise wouldn't be shaped like that; the images I've seen from Alcubierre's work shows something that looks like an elongated football with a ring around it, and I imagine the force of gravity would be oriented in the direction of travel; IOW, you'd be flying feet-first.

[smartcooky]

In Star Trek, they have control over inertia, and therefore it's not really how fast they CAN accelerate, but how fast they WANT to accelerate. According to DS9 S01E01, the warp field can lower the inertial mass of the object inside it.

I remember that and thought it was an interesting take on warp drive. Until that explanation, I always thought the warp "bubble" was meant to move space instead of the ship, hence the idea of "folding space" around the ship.

Its not original to the writers of Star Trek. EE Doc Smith used this concept in his "Lensman" series, published in the late 1930's and early 1940's.

It was called the "Bergenholm Inertialess Drive", which allowed his spaceships to achieve FTL travel by nullifying, or almost nullifying, inertia (essentially, reducing mass to near zero) so that effectively any thrust would result in the spaceship's near-instant acceleration to near or beyond light speed. Because mass was so dramatically reduced this would result in two things
1. The crew would feel little or no acceleration.
2. A workaround for the problem of relativistic increase in mass to infinity as you approach light speed.

It did have a drawback though.

If a ship were to approach a planet, its lack of mass would mean it could not go into orbit. It would have to power down its "Bergenholm Inertialess Drive" and upon regaining it is mass, it would also regain the original velocity AND vector it had before the drive was turned on (which could be any velocity in any direction) a figure that would almost certainly be significantly different from that that of the planet. This could result in the spaceship instantly tearing away (or towards) the planet at velocities measured in tens of thousands of km/sec, possible colliding with the planets, and certainly turning all the ship's occupants into pink paste. Therefore, prior to shutting down the drive, ship was required to match its natural "intrinsic velocity"[/i] to that of the planet (it is never explained how this was done)

[bobdude11]

Its not original to the writers of Star Trek. EE Doc Smith used this concept in his "Lensman" series, published in the late 1930's and early 1940's.

I am not familiar with this series - looks like I need to expand my Sci-Fi collection!

[bobdude11]

... the images I've seen from Alcubierre's work shows something that looks like an elongated football with a ring around it, and I imagine the force of gravity would be oriented in the direction of travel; IOW, you'd be flying feet-first.

Thank you for the detailed explanation - admittedly, I have only a VERY basic understanding of the math, it still makes sense how you describe it! Also to your note, in the series Enterprise, the Vulcan ships are elongated with a warp ring instead of two nacelles. Perhaps a nod to Alcubierre?

[Peter B]

Its not original to the writers of Star Trek. EE Doc Smith used this concept in his "Lensman" series, published in the late 1930's and early 1940's.

I am not familiar with this series - looks like I need to expand my Sci-Fi collection!

I read the Lensman series in high school back in the 1980s, and I remember enjoying it at the time (and then being surprised to find out when they were written).

Then, a couple of years ago, I bought the entire set at a second hand book sale. I was interested to read them again with 40 more years of reading experience. On the one hand it was fascinating to find out how much I remembered (not much, but a couple of scenes had stuck in my memory). On the other hand, it was clear how much the books were a product of the culture of the time they were written.

I lent them to 17YOS, who loves SF, and he only made it part way through the second book before he gave up.

[bobdude11]

Its not original to the writers of Star Trek. EE Doc Smith used this concept in his "Lensman" series, published in the late 1930's and early 1940's.

I'm going to see if I can add them to my Kindle library ...

I am not familiar with this series - looks like I need to expand my Sci-Fi collection!

I read the Lensman series in high school back in the 1980s, and I remember enjoying it at the time (and then being surprised to find out when they were written).

Then, a couple of years ago, I bought the entire set at a second hand book sale. I was interested to read them again with 40 more years of reading experience. On the one hand it was fascinating to find out how much I remembered (not much, but a couple of scenes had stuck in my memory). On the other hand, it was clear how much the books were a product of the culture of the time they were written.

I lent them to 17YOS, who loves SF, and he only made it part way through the second book before he gave up.

I'm going to see if I can add them to my Kindle library.

[jfb]

... the images I've seen from Alcubierre's work shows something that looks like an elongated football with a ring around it, and I imagine the force of gravity would be oriented in the direction of travel; IOW, you'd be flying feet-first.

Thank you for the detailed explanation - admittedly, I have only a VERY basic understanding of the math, it still makes sense how you describe it! Also to your note, in the series Enterprise, the Vulcan ships are elongated with a warp ring instead of two nacelles. Perhaps a nod to Alcubierre?

Be aware I'm just a moderately enthusiastic code monkey, not an expert in theoretical physics, or aerospace engineering, or much of anything else, really.  I got through one semester of Differential Equations with a D for Done, so I'm going off of a layman's understanding of all of this.  Don't take any of this as more than poorly informed opinion.  I think I'm right in the large, but I couldn't math my way out of a paper bag so I wouldn't be able to back any of it up.