SWTC: Sublight Propulsion

[Ender]

http://www.theforce.net/swtc/propulsion.html

Discuss

[Hardy]

I really want to respond with a liberal flurry of smilies as I've wanted Dr. Saxton to devote a page to this subject for quite some time. A lot of the content of this page involves stuff that I've never been exposed to before, so I look forward to learning a few new things from this page.

[Surlethe]

I approve. Wholeheartedly. And I will digest the math when I am more awake -- it looks to be rather straightforward.

[Einhander Sn0m4n]

Absolutely wonderful and quite entertaining to read! This will be hella useful for improving my starship design philosophy

[Warspite]

Very interesting, especially the part about sideslip maneuvres.

I find a problem with thrust ejections in atmospheres though. In the SW universe, everyone happily stands and walks around while main engines are being fired. Consider:
AOTC - the final scene with the Acclamators taking off, Padme's ship landing on Tatooine, Dooku's escape from Geonosis,
ROTS - Anakin saying goodbye to Padme and speeding away in his starfighter, at one point the exhaust was pointing straight at Padme, Obi-Wan landing on Utapau, the Venators taking off Coruscant,
ANH - the Millenium Falcon blasting off Tattooine,
ESB - the MF speeding away from the inside of Echo Base.

in all these cases, most starships were on iddle or going to full thrust, unless there are complex shields in place, and this would mean all over the place where mushy organics walk around, there must be another reason why thrust ejections don't carve a glowing trail behind them when operating on worlds.

[Hardy]

in all these cases, most starships were on idle or going to full thrust, unless there are complex shields in place, and this would mean all over the place where mushy organics walk around, there must be another reason why thrust ejections don't carve a glowing trail behind them when operating on worlds.

Repulsorlifts can provide thrust, too. I'm willing to guess that in most of those scenarios, that's the case. The kinetic energy of the exhaust doesn't nescesarily need to be high, also. Good point, though.

And thanks to that page, I finally understand how to calcuate and use Lorentz Factors

[Illuminatus Primus]

Very interesting, especially the part about sideslip maneuvres.

I find a problem with thrust ejections in atmospheres though. In the SW universe, everyone happily stands and walks around while main engines are being fired. Consider:
AOTC - the final scene with the Acclamators taking off, Padme's ship landing on Tatooine, Dooku's escape from Geonosis,
ROTS - Anakin saying goodbye to Padme and speeding away in his starfighter, at one point the exhaust was pointing straight at Padme, Obi-Wan landing on Utapau, the Venators taking off Coruscant,
ANH - the Millenium Falcon blasting off Tattooine,
ESB - the MF speeding away from the inside of Echo Base.

in all these cases, most starships were on iddle or going to full thrust, unless there are complex shields in place, and this would mean all over the place where mushy organics walk around, there must be another reason why thrust ejections don't carve a glowing trail behind them when operating on worlds.

No, its quite simple. The glowing of the engines themselves do not mean relativistic thrust streams are emiting from the back; I doubt SW vessels light their engines at lower altitudes than above the ionosphere, and probably much higher to avoid befouling a planet's magnetosphere or irradiating a planet. Likely the engines glow even when idling; I doubt they cold start them every time. Afterall, ANH tells us repulsorlifts are effective and indeed the preferred means of acceleration up to six planetary diameters from the planet in question (incidentally this explains how the Rebel and Imperial fleets in ROTJ did not flip over for retrothrust; they simply used their repulsorlifts to push against the moon and slow down).

[Warspite]

No, its quite simple. The glowing of the engines themselves do not mean relativistic thrust streams are emiting from the back; I doubt SW vessels light their engines at lower altitudes than above the ionosphere, and probably much higher to avoid befouling a planet's magnetosphere or irradiating a planet. Likely the engines glow even when idling; I doubt they cold start them every time. Afterall, ANH tells us repulsorlifts are effective and indeed the preferred means of acceleration up to six planetary diameters from the planet in question (incidentally this explains how the Rebel and Imperial fleets in ROTJ did not flip over for retrothrust; they simply used their repulsorlifts to push against the moon and slow down).

I fully understand what you're saying, but if we're seeing lit engines then they're expelling something out of them, which by the very nature of SW engines isn't good for your health, after all ions shooting out (even if not at high fractions of c) is like having a plasma torch bigger than a house blowing in your face.

[Illuminatus Primus]

No, its quite simple. The glowing of the engines themselves do not mean relativistic thrust streams are emiting from the back; I doubt SW vessels light their engines at lower altitudes than above the ionosphere, and probably much higher to avoid befouling a planet's magnetosphere or irradiating a planet. Likely the engines glow even when idling; I doubt they cold start them every time. Afterall, ANH tells us repulsorlifts are effective and indeed the preferred means of acceleration up to six planetary diameters from the planet in question (incidentally this explains how the Rebel and Imperial fleets in ROTJ did not flip over for retrothrust; they simply used their repulsorlifts to push against the moon and slow down).

I fully understand what you're saying, but if we're seeing lit engines then they're expelling something out of them, which by the very nature of SW engines isn't good for your health, after all ions shooting out (even if not at high fractions of c) is like having a plasma torch bigger than a house blowing in your face.

Really? Authors intent does not override observed effect. All that is required for the engines to glow is that the metal of the engines is hot. That's it.

[Connor MacLeod]

No, its quite simple. The glowing of the engines themselves do not mean relativistic thrust streams are emiting from the back; I doubt SW vessels light their engines at lower altitudes than above the ionosphere, and probably much higher to avoid befouling a planet's magnetosphere or irradiating a planet. Likely the engines glow even when idling; I doubt they cold start them every time. Afterall, ANH tells us repulsorlifts are effective and indeed the preferred means of acceleration up to six planetary diameters from the planet in question (incidentally this explains how the Rebel and Imperial fleets in ROTJ did not flip over for retrothrust; they simply used their repulsorlifts to push against the moon and slow down).

Well, yes and no. Repulsors can provide thrust after a fashion (so can tractor beams) but only in the direction of the mass they are within range of. For example, if a ship is facing towards a planet, it could use its repuslors/tractor beams to accelerate towards or away from the planet, but repulsors (by themselves at least) are unlikely to provide much manuvering unless they had something else to push against (a station, ,orbital or whatever.)

Most Repulsor-equipped craft (like LAAT gunships) still need another form of "engine" to provide thrust while using repulsors in an atmosphere (gunships for example use a combustion engine/jet engine to propel themselves) Smaller craft (like X-wings) either use somethign similar or they simply use a low velocity/high density thrust (in an atmosphere, its possible they can use the air as supplementary propellant in an atmosphere.)

[Illuminatus Primus]

There are no turbines or engines visible on Snowspeeders. The nodules at the rear are the rear tips of the laser cannon.

[Connor MacLeod]

There are no turbines or engines visible on Snowspeeders. The nodules at the rear are the rear tips of the laser cannon.

According to what? Looking at the SW:ICS, the rearmost "nodules" as you call them are not labeled as part of the laser cannons. In fact they're indicated to be part of the engines (repuslor elements, air intakes, fuel tank, etc.)

Besides, there's also absolutely *nothing* for it to push against to use repulsors, except the ground. And all that would do is to alter the pitch of the ship.

[Illuminatus Primus]

There are no turbines or engines visible on Snowspeeders. The nodules at the rear are the rear tips of the laser cannon.

According to what? Looking at the SW:ICS, the rearmost "nodules" as you call them are not labeled as part of the laser cannons. In fact they're indicated to be part of the engines (repuslor elements, air intakes, fuel tank, etc.)

Besides, there's also absolutely *nothing* for it to push against to use repulsors, except the ground. And all that would do is to alter the pitch of the ship.

Well flying around at thousands of kilometers a hour is probably just a produce of the engine mechanisms being used to accelerate air or low-intensity plasma. But as for the huge G take-offs (reaching orbit in minutes or less) all they need to do is point the nose up and then the repulsorlifts do that, not relativistic thrust streams (such as Dooku's sailer).

[Connor MacLeod]

Well flying around at thousands of kilometers a hour is probably just a produce of the engine mechanisms being used to accelerate air or low-intensity plasma.

Curtis covered that possibility with the "low velocity/high density" exhaust option. The Trade-off being that you expend propellant at a proportionally greater rate.

But as for the huge G take-offs (reaching orbit in minutes or less) all they need to do is point the nose up and then the repulsorlifts do that

Yes, but I already mentioned that now, didn't I?

[Winston Blake]

I fully understand what you're saying, but if we're seeing lit engines then they're expelling something out of them, which by the very nature of SW engines isn't good for your health, after all ions shooting out (even if not at high fractions of c) is like having a plasma torch bigger than a house blowing in your face.

Really? Authors intent does not override observed effect. All that is required for the engines to glow is that the metal of the engines is hot. That's it.

Don't we see the exhaust itself glowing on several occasions? e.g. IIRC in the opening space battle of ROTS the Eta-2's exhaust looks like a blue blowtorch flame, and then when Anakin flies away from Padme on Coruscant the exhaust looks identical. Is it reasonable that atmospheric interaction + low-power idling could produce the exact same exhaust apperance as that in space?

[Ender]

I fully understand what you're saying, but if we're seeing lit engines then they're expelling something out of them, which by the very nature of SW engines isn't good for your health, after all ions shooting out (even if not at high fractions of c) is like having a plasma torch bigger than a house blowing in your face.

Really? Authors intent does not override observed effect. All that is required for the engines to glow is that the metal of the engines is hot. That's it.

Don't we see the exhaust itself glowing on several occasions? e.g. IIRC in the opening space battle of ROTS the Eta-2's exhaust looks like a blue blowtorch flame, and then when Anakin flies away from Padme on Coruscant the exhaust looks identical. Is it reasonable that atmospheric interaction + low-power idling could produce the exact same exhaust apperance as that in space?

the first I think they were technically in space. The second, that's what I've assumed it was, but I've never tested it. We only see a short burst immediately after the engines begin to glow in earnest, and the sudden dumping of several hundred megawatts to gigawatts would couse some impressive thermal bloom. But someday someone needs to make an attempt to calc it out and check.

[Connor MacLeod]

A truly wacky idea is that they're using neutrinos to generate thrust

[Connor MacLeod]

A truly wacky idea is that they're using neutrinos to generate thrust

[Winston Blake]

Regarding repulsorcraft, it seems they can exert forces parallel to the ground they're flying across. MTTs and AATs have no thrusters on them the way speeder bikes, LAATs and Anakin's AOTC speeder do. (Although i don't think it was intended, i agree with the idea that the snowspeeder's rear 'stubs' should be small thrusters.)

The AAT entry in the TPM:ICS says "Heavy duty repulsors (both disc and coils) keep the AAT just off the ground and propel it foward".

[Ender]

Here's something wacky about repulsors- look at the grass under the tanks during the TPM battle scene. No change in it. If you are applying the force to keep a multi ton craft suspended a few feet above the ground, that force shoudl crush light grass to the dirt. But ths is not the case.

I'm trying to decide if that's an important trait, or something like the goofy lightsabres in ANH to be ignored.

[Grandmaster Jogurt]

A truly wacky idea is that they're using neutrinos to generate thrust

If it's thought to be used as the opposing force on an SPHAT's heavy gun, is there any reason that that couldn't be used? I understand that there doesn't appear to be any evidence for it, so it's just pointless speculation, but would it be possible?

[Ender]

A truly wacky idea is that they're using neutrinos to generate thrust

If it's thought to be used as the opposing force on an SPHAT's heavy gun, is there any reason that that couldn't be used? I understand that there doesn't appear to be any evidence for it, so it's just pointless speculation, but would it be possible?

To me, the idea of neutrino counter beams is far worse then counter repulsors, as it doubles the applied stress, and also increases the required energy.

[Hardy]

Here's something wacky about repulsors- look at the grass under the tanks during the TPM battle scene. No change in it. If you are applying the force to keep a multi ton craft suspended a few feet above the ground, that force shoudl crush light grass to the dirt. But ths is not the case.

Unless you increase the area the force is being applied over and therefore reduce pressure. And IIRC, the grass didn't remain completely undisturbed.

The AAT entry in the TPM:ICS says "Heavy duty repulsors (both disc and coils) keep the AAT just off the ground and propel it foward".

I was discussing that with Connor earlier. For example, a large speeder could weigh 20 kN and would require 100 kN thrust to keep it moving at x speed through the air. To maintain velocity and altitude the repulsors could be set to provide 102 kN thrust and then be angled backwards by 79 degrees. At that angle, the speeder's weight would be matched and the nescesary thrust would be provided. It would be sort of like a helicopter. The AAT might work like that.

[Winston Blake]

A truly wacky idea is that they're using neutrinos to generate thrust

If it's thought to be used as the opposing force on an SPHAT's heavy gun, is there any reason that that couldn't be used? I understand that there doesn't appear to be any evidence for it, so it's just pointless speculation, but would it be possible?

It's only proposed to be one possible solution for the recoil, the other being anchoring the SPHA-T to the ground with repulsors/tractor beams and keeping it together with tensor fields. I think that one makes much more sense.

[Winston Blake]

Here's something wacky about repulsors- look at the grass under the tanks during the TPM battle scene. No change in it. If you are applying the force to keep a multi ton craft suspended a few feet above the ground, that force shoudl crush light grass to the dirt. But ths is not the case.

Unless you increase the area the force is being applied over and therefore reduce pressure. And IIRC, the grass didn't remain completely undisturbed.

Didn't Qui-Gon and Jar-Jar fall right under that MTT at the start and there was no effect (aside from being windy)? Also the MTT is supposed to vent its engine/cooling exhaust straight down, so the grass moving could be explained by the AAT being similar.

The AAT entry in the TPM:ICS says "Heavy duty repulsors (both disc and coils) keep the AAT just off the ground and propel it foward".

I was discussing that with Connor earlier. For example, a large speeder could weigh 20 kN and would require 100 kN thrust to keep it moving at x speed through the air. To maintain velocity and altitude the repulsors could be set to provide 102 kN thrust and then be angled backwards by 79 degrees. At that angle, the speeder's weight would be matched and the nescesary thrust would be provided. It would be sort of like a helicopter. The AAT might work like that.

It really depends on how repulsors are supposed to work. I mean, when i think of repulsors, i have a general idea in my head of two like electric charges repelling each other, except it works for all mundane matter. I'm sure it's a common feeling. (This idea is messed up by the MTT scene mentioned above, where i would have expected them to be squished flat). Anyway, even though it doesn't feel intuitive, i don't see any reason why repulsors couldn't somehow angle their force in a direction the way you describe.