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Author Topic: causal discussion: main forward thruster, needed?  (Read 5931 times)

maximilianyuen

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causal discussion: main forward thruster, needed?
« on: June 17, 2013, 09:42:28 AM »

assuming a ship runs on propulsion engine, not those anti gravity stuff, not those standard auxiliary lateral engines for subtle control , is a main forward thruster needed?

for a car, the control all comes from the identical wheels
for a ship, the engine could go reverse and give somehow similar reverse power

but for a spaceship, especially a battleship which tactical maneuver is essential, seeing that the main engine could not give reverse power, is a forward placing reverse engine essential or redundant?

coz recently i start to see a few spaceships incorporate such forward engine and it makes sense to me, while 99% of the spaceship design won't even got a hints of such engine exist.

just wanna know what you guys would think.
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xenoargh

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Re: causal discussion: main forward thruster, needed?
« Reply #1 on: June 17, 2013, 10:00:44 AM »

Usually from an engineering / cost perspective, it would rarely be done in the real world, for the same reasons why real-world battleships can't go very fast using their propellers in reverse (it does "work", but not well).

It's cheaper to simply turn the spacecraft around and change the current vector or alter the magnitude. 

In the real world, the distances involved are so vast and the likely time-tables for space battles are so long that very small changes in current velocity (albeit at pretty high g-forces) would be enough to cause attacks to miss.

At the extremely short ranges of Starfarer battles, however, it might make sense, if the thrust provided by conventional engines was the primary means of changing velocity. 

However, given the fragile nature of engines, would make spacecraft very expensive and give it two major areas of weakness that would have to be shielded.  Even in the Starfarer universe, this probably wouldn't make sense, simply because a successful alpha-strike on the front of the vessel could put your battleship out of control.
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PCCL

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Re: causal discussion: main forward thruster, needed?
« Reply #2 on: June 17, 2013, 10:06:10 AM »

Firstly, i think starsector should keep thrusters as is for stylistic purposes

now, tactically, I think a ship should have the strongest thrusters facing back, second strongest thrusters facing front for rapid deceleration, and small rcs ports pointing every other direction for maneuvering

it would make sense for a main engine to point in one direction for travel, no point building big engines everywhere for that, the front facing decelerators are a tactical consideration, for when you need to slow down or back up in a hurry while facing the enemy, mounted 180° from the main so the ship never have to turn more than 90° to bring a thruster pack to bear. Due to budget and size concern, only rcs ports are used everywhere else
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K-64

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Re: causal discussion: main forward thruster, needed?
« Reply #3 on: June 17, 2013, 11:20:16 AM »

Usually from an engineering / cost perspective, it would rarely be done in the real world, for the same reasons why real-world battleships can't go very fast using their propellers in reverse (it does "work", but not well).

That point is a rather bad comparison, since real-world battleships have an entirely method of propulsion. I think the best comparison should be in current space craft (obviously). How many rockets have you seen that can reverse the direction of its thrust? That's the main issue here
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xenoargh

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Re: causal discussion: main forward thruster, needed?
« Reply #4 on: June 17, 2013, 11:46:40 AM »

Well, not many, for the same reason as on battleships in water.

Engines are big, complicated, need energy sources (fuel, electricity etc.) and put a lot of strain on a vessel's frame when active.  Most vehicles have to be engineered around their motive source and its limitations.  Modern spacecraft are almost entirely built around their propulsion systems.  But modern spacecraft aren't deep-space craft; they're either one-use vehicles or are designed to use passive means (gliding, parachutes) to return to a planetary surface.

There are plenty of jets that can use vectored thrust, and certainly a combat spacecraft could do the same, but there are a lot of practical limitations to that, such as having to mount the engine where it could be turned to different angles of attack, etc., which would introduce all sorts of problems for a combat spacecraft.  However, engines could be mounted on turrets that would allow for direction control and thrust on all axes.  I presume that IRL, the weight / complexity of such systems makes them impractical for today's spacecraft, since they need to get out of planetary gravity wells, but for a deep-space craft, it might make perfect sense.
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K-64

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Re: causal discussion: main forward thruster, needed?
« Reply #5 on: June 17, 2013, 08:38:18 PM »

The thing is, with current thrust vector vehicles, they use air resistance and whatnot to keep the craft balanced. In space all you would be doing is deflecting your direction to elsewhere. Since full directional coverage would be more than a bit difficult without cooking your own ship
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maximilianyuen

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Re: causal discussion: main forward thruster, needed?
« Reply #6 on: June 17, 2013, 11:21:54 PM »

Usually from an engineering / cost perspective, it would rarely be done in the real world, for the same reasons why real-world battleships can't go very fast using their propellers in reverse (it does "work", but not well).

That point is a rather bad comparison, since real-world battleships have an entirely method of propulsion. I think the best comparison should be in current space craft (obviously). How many rockets have you seen that can reverse the direction of its thrust? That's the main issue here

Again, rocket is still not the best comparison. In fact there's no known good comparison i guess.

Current spacecraft are most orbiting in nature, their movement simply involve adjusting the orbit, be it the orbiting height, the change of orbiting pivot from earth to moon, or to use gravitational acceleration (sorry my bad english for special terms, but still should get the meaning i hope) to get to the needed escape velocity....

and for that, speed is almost the only thing current spacecraft got to control, hence it's only need/capable of speed up and slow down for such adjustment , hence forward thrust is never there nor the tech level allow

but in star sector/more ideal spacecraft environment, i still tend to believe forward thrust, need not to be a conventional main engine, can be a charged emergency engine thats compact but high power which can't last long, etc, is somewhat essential.

hope i din't make it too board sense, but a forward mounted engine thats more powerful than the lateral engine is needed in my imagination(and only in mine for now it seems)

having it allow battleship to

1)arrive tactical destination earlier without the need to slow down much earlier for the lack of stoping power, or turning 180' which is not always feasible, and mostly not feasible in battlefield when you got the shield strength, ship weakspot, weapon coverage to keep in mind

2)higher maneuverability obviously, say in asteroid belts. You don't fly in opposite direction, but even if you follow the flow their speeds aren't exactly consisten

3)reliability. while you can very reasonably see that the forward engine could be another giant weakspot, it can however, also see as a backup engine that offer additional mean to control the ship (assuming not conflicting with my earlier suggestion of using short burst engine)



not trying to state i am correct, just want to test are my reasons at least able to stand for a while if i put a forward engine to my current WIP ship which is about 2 km large.

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FloW

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Re: causal discussion: main forward thruster, needed?
« Reply #7 on: June 18, 2013, 12:05:20 AM »

They had them in some versions of Elite. Emergency Reverse Thrusters, that is. They were of limited use (also, limited number of uses), but useful if you started a fight with something that was faster than you (Thargoids. Oh god, so many Thargoids).

So they weren't exactly useful at slowing down a ship, but at legging it.
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maximilianyuen

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Re: causal discussion: main forward thruster, needed?
« Reply #8 on: June 19, 2013, 05:54:08 AM »

They had them in some versions of Elite. Emergency Reverse Thrusters, that is. They were of limited use (also, limited number of uses), but useful if you started a fight with something that was faster than you (Thargoids. Oh god, so many Thargoids).

So they weren't exactly useful at slowing down a ship, but at legging it.

sorry what "Elite" are you referring to?
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Pelly

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Re: causal discussion: main forward thruster, needed?
« Reply #9 on: June 19, 2013, 06:19:51 AM »

I think he means elite variants?
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Upgradecap

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Re: causal discussion: main forward thruster, needed?
« Reply #10 on: June 19, 2013, 06:38:39 AM »

Elite. As in, the game, Elite. I think that's what fits the description.
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FloW

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Re: causal discussion: main forward thruster, needed?
« Reply #11 on: June 19, 2013, 02:50:41 PM »

Holy crap. I didn't think that I was THAT old. Yes, of course I meant the game Elite. THAT GAME. The one game that pretty much founded the space game genre.
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Psygnosis

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Re: causal discussion: main forward thruster, needed?
« Reply #12 on: July 07, 2013, 05:30:21 AM »

Holy crap. I didn't think that I was THAT old. Yes, of course I meant the game Elite. THAT GAME. The one game that pretty much founded the space game genre.
Bah, the line version was better. i had that on DOS.

And im surprised more people didnt get it. ELITE the goddamn grand-daddy of all space 4X / Trading games.

Now; on topic.

ive toyed with several designs of spaceships in other games (where you had to actually think about center of mass vs thrust and all that) and to be honest the most practical designs are often not the best looking. not to mention its always a challenge between agility and Armour.

Consider that in order to have the best agility you want your translation drives the furthest away from your center of mass. which would make a ship roughly + shaped. however such a ship would be a large target, the side arms making it very wide. so we can reduce it to a | but this limits our space for weapons and thrusters, unless we take a broadside design in which case we're strong on the way in, hard to hit, but weak in combat because to bring our guns to bear we have to present our widest flank.

In terms of mounting braking or reverse thrusts you could do that but youre simply using space space that as the hegemony would say "could be used for more guns"

Not to mention anything larger than a destroyer has so much mass. that to produce anykind of desired braking effect you would be much better off rotating the whole craft.

And dont get me started on g-forces involved. even if you artificial gravity the stresses upon the frame would be immense.

lastly: it wouldnt look that good.

TL:DR
Yeah we can add reverse thrusters, but youll be using up valuable weapon space.
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Grug

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Re: causal discussion: main forward thruster, needed?
« Reply #13 on: July 07, 2013, 10:22:58 AM »

I can't really see this as being needed. Vectoring nozzles on the rear engines, and course corrections would be more than adequate, no?
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Psygnosis

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Re: causal discussion: main forward thruster, needed?
« Reply #14 on: July 07, 2013, 11:16:13 PM »

I can't really see this as being needed. Vectoring nozzles on the rear engines, and course corrections would be more than adequate, no?

Very hard to efficiently vector 180*

atleast even today 90* vectors (VTOL) cause the engine efficiency to drop pretty dramatically. 
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