Orbital velocity

[MaxwellsDemon]

There's a line in the original "Star Wars" where a Death Star flunky reports, "Orbiting the planet at maximum velocity."

For a long time, I decided this meant that they were orbiting Yavin at faster-than-orbital velocity, using constant expenditure of energy to avoid moving into a higher orbit.  This sounds sensible (in a technobabble sort of way).   But is this even possible, even with continuous input of energy?  Wouldn't they simply be boosting their apoYavin of the other side of the planet or otherwise changing their trajectory, without increasing their orbital velocity, no matter what?

Yeah, I know, trying to apply real physics to "Star Wars" is a pretty useless exercise.  But is there in fact *any* possible way to increase orbital velocity while keeping orbital altitude constant?

[Shpaget]

Sure, it's just a matter of finding the right thrust vector.

[p1t1o]

Yes it is, you just have to thrust inwards once you have attained your desired speed (which will be attained with a combination of prograde and inward (anti-radial) thrust).

In this manner one can have any "orbital" (I think technically its not an orbit) velocity you want from zero to <c. 

For slower-than-orbital speeds, you thrust outwards.

Edited October 27, 2017 by p1t1o

[MaxwellsDemon]

28 minutes ago, p1t1o said:

Yes it is, you just have to thrust inwards once you have attained your desired speed (which will be attained with a combination of prograde and inward (anti-radial) thrust).

In this manner one can have any "orbital" (I think technically its not an orbit) velocity you want from zero to <c. 

For slower-than-orbital speeds, you thrust outwards.

So, basically one would be following a hyperbolic trajectory, continuously altering the trajectory to follow a path that looks like an orbit?   OK, I can see that.   I agree, it couldn't really be called an "orbit."

[wumpus]

This is Star Wars we are talking about.  Expect it to mean "over 12 parsecs".

[YNM]

It's a film, no need to be realistic.

 

Though, from realistic viewpoints, basically you just need to simulate higher gravity. So point your engine inwards.

[MaxwellsDemon]

24 minutes ago, wumpus said:

This is Star Wars we are talking about.  Expect it to mean "over 12 parsecs".

I may have mentioned this before, but I learned something interesting not long ago... that infamous "less than 12 parsecs" line was supposed to be a tip-off to the audience that Han Solo was lying (check Kenobi's expression just after the line).  Solo was originally supposed to be a much more slimy and untrustworthy character, but Harrison Ford's portrayal was so heroic that any line the character uttered was taken as read.

13 minutes ago, YNM said:

It's a film, no need to be realistic.

Oh, definitely.  I have more issues with the supposedly-realistic "Gravity" than I do with the obviously-fantastic "Star Wars."

[KSK]

Hmm, it could be that the Death Star was orbiting at the lowest possible altitude where it wasnt' unduly affected by atmospheric drag. Although admittedly, that's overthinking things for Star Wars and would also be super lame if the Empire got it wrong.

"Rebel base in firing range, sir."
"Excellent - you may fire when ready."

Wah, wah, wah, wahhhhhh

"The Rebel base appears to be still intact, lieutnenant?"
"Yessir. Superlaser firing sequence aborted, sir."
"Would you care to elaborate, lieutenant?"
"Uh - unexpected damage to focusing dish, sir. Sensors indicate partial melting due to atmospheric contact, sir. Please don't tell Lord Vader, sir."

[Ten Key]

4 hours ago, p1t1o said:

Yes it is, you just have to thrust inwards once you have attained your desired speed (which will be attained with a combination of prograde and inward (anti-radial) thrust).

In this manner one can have any "orbital" (I think technically its not an orbit) velocity you want from zero to <c. 

For slower-than-orbital speeds, you thrust outwards.

^^ This.

 

 

[wumpus]

There are also claims that Harrison  Ford ad libbed it because George Lucas's writing was so bad (most of the rest were better than the script, but whoever came up with this  botched it).  We are dealing with a universe that:

Has fighter spacecraft using aerodynamics in space
Lasers move slow enough to observe their propagation
Sound travels in space
light sabres exist (don't ask everything that is wrong with them)
[and with the newest movie]
Interstellar distances are next to nothing.

While I'm sure I missed plenty of other howlers, there is no reason to believe that the "parsec" blunder wasn't just Star Wars being Star Wars.  While "maximum orbital velocity" is effectively escape velocity (and initial capture velocity) I don't believe for a second it isn't just thrown in there to sound good.  If you want to geek out about something, I'd recommend something that at least tried to be consistent ("this is your father's light sabre [he killed 30 children with it]").

[MaxwellsDemon]

I believe I've stipulated several times that "Star Wars" and physics have very little to do with each other.    

Edited October 27, 2017 by MaxwellsDemon

[mikegarrison]

 

And then, in the best Star Wars style, they later redid their "HISHE" with a "special edition" version.

 

[Vanamonde]

Star Wars is not the topic of this thread, folks. 

As for the actual subject, yes, it is possible to use thrust to hold an orbital path which would otherwise necessitate a lower speed. In fact, I have done this while arranging orbital rendezvous in KSP.

[MaxwellsDemon]

14 minutes ago, Vanamonde said:

As for the actual subject, yes, it is possible to use thrust to hold an orbital path which would otherwise necessitate a lower speed. In fact, I have done this while arranging orbital rendezvous in KSP.

Hm.  Is there a speed record for Kerbin [forced] orbit?

[DAL59]

Watch "your physics have no power over me by" Manley.

 

 

[PB666]

6 hours ago, Ten Key said:

^^ This.

 

 

He was traveling at escape velocity not orbital velocity, its does not reflect reality.

[LordFerret]

4 hours ago, MaxwellsDemon said:

Hm.  Is there a speed record for Kerbin [forced] orbit?

Yes, it's Ludicrous Speed.

[Ten Key]

42 minutes ago, PB666 said:

He was traveling at escape velocity not orbital velocity, its does not reflect reality.

11 hours ago, MaxwellsDemon said:

For a long time, I decided this meant that they were orbiting Yavin at faster-than-orbital velocity, using constant expenditure of energy to avoid moving into a higher orbit.  This sounds sensible (in a technobabble sort of way).   But is this even possible, even with continuous input of energy?

The vehicle in that video is using aerodynamic down force to keep from exiting the atmosphere. As far as I can see, that down force is more or less the same as a continual "radial in" burn. While the stunt in the video is certainly fiction, I have no reason to think the basic orbital mechanics in Orbiter are wrong. If a continuous down force could be applied (say, through the use of Star Wars Space Magic), I seems perfectly sound for the Death Star to orbit a planet at a rate greater than escape velocity. 

And now, having more than exhausted my knowledge of the subject, I'm going to sit down and shut up.

[PB666]

13 hours ago, Ten Key said:

The vehicle in that video is using aerodynamic down force to keep from exiting the atmosphere. As far as I can see, that down force is more or less the same as a continual "radial in" burn. While the stunt in the video is certainly fiction, I have no reason to think the basic orbital mechanics in Orbiter are wrong. If a continuous down force could be applied (say, through the use of Star Wars Space Magic), I seems perfectly sound for the Death Star to orbit a planet at a rate greater than escape velocity. 

And now, having more than exhausted my knowledge of the subject, I'm going to sit down and shut up.

In the words of K2,  there's no reaction force. He's to far up.

This is the equation looking at specific force. V^2/r = u/r2  V = SQRT(u/r) that is for a velocity of 7866 m/s ~ 9.5m/s

Just guessing  = (11300/7866)^2 ~ 2.2g. Therefore he need the application of 1.25 g of downforce, which means he need a rocket thrusting vectoring  in the negative radial at 1.25*g*mass.

[magnemoe]

23 hours ago, wumpus said:

There are also claims that Harrison  Ford ad libbed it because George Lucas's writing was so bad (most of the rest were better than the script, but whoever came up with this  botched it).  We are dealing with a universe that:

Has fighter spacecraft using aerodynamics in space
Lasers move slow enough to observe their propagation
Sound travels in space
light sabres exist (don't ask everything that is wrong with them)
[and with the newest movie]
Interstellar distances are next to nothing.

While I'm sure I missed plenty of other howlers, there is no reason to believe that the "parsec" blunder wasn't just Star Wars being Star Wars.  While "maximum orbital velocity" is effectively escape velocity (and initial capture velocity) I don't believe for a second it isn't just thrown in there to sound good.  If you want to geek out about something, I'd recommend something that at least tried to be consistent ("this is your father's light sabre [he killed 30 children with it]").

Star wars fighter scenes is WW2 air combat. Watch some WW2 documentaries.
This is intended as its the most visual style of air combat. 
Light sables are also rule of cool, as an added insult an sabre has an curved blade, yes its exceptions. But  Light sable sound cooler than light sword. 

Don't think the death star orbited Yavin at all, it would be pretty pointless it only needed to get in range to fire, it wanted to get in range as fast as possible to prevent escape primarily 
Probably another sound cool thing 

Edited October 28, 2017 by magnemoe

[wumpus]

18 minutes ago, magnemoe said:

Star wars fighter scenes is WW2 air combat. Watch some WW2 documentaries.

It is specifically based on the WW2 movie The Dam Busters (1955).  They never bothered to come up with their own "air" combat.

22 hours ago, Vanamonde said:

Star Wars is not the topic of this thread, folks. 

As for the actual subject, yes, it is possible to use thrust to hold an orbital path which would otherwise necessitate a lower speed. In fact, I have done this while arranging orbital rendezvous in KSP.

While Star Wars might not be appropriate for "Science and Spaceflight", it certainly follows from the OP's question.  "Maximum Orbital Speed" (unboosted) will asymptotically approach escape velocity (for m/s, but the slowest orbital period) or skim the planet at minimum distance (for angular velocity, but minimum m/s).  Since the quote is from Star Wars and the rest of the movie gets *everything* wrong related to space, it doesn't make a whole lot of sense to extract significant meaning from the  quote.  You can learn "maximum orbital speed" from KSP.  Don't expect much from SF movie technobable, and even less from Star Wars.

It is of course possible to reach a higher boosted speed (and since the Death Star could exceed the speed of light [presumably, more recently it appears that the stars were packed remarkably close "a long time ago in [that] galaxy far, far away"]).

Edited October 28, 2017 by wumpus

[MaxwellsDemon]

Well, as p1t1o pointed out ^ it's not really an orbit of Yavin.  The moment Tarkin or one of his flunkies orders the engines turned off, the Death Star starts flying off in the hyperbolic trajectory that the engines were keeping it from.  (Although, as numerous posters have pointed out, it would then be a rather startlingly rare example of real physics in the movie.)

No, I didn't intend for the thread to become a rehash of all the physics problems involved in "Star Wars," which are legion; merely that specific line and problem.

[FleshJeb]

@Ten Key That's a fantastic video.

 

I used to do cicumnavigations like that in the old aero. My record is a little under 23 minutes. IIRC my velocity was somewhere between 3300 and 3600 m/s, altitude 55km, with a continuous downward thrust of 1.2g. The rocket had 21 to 23 km/s of dV.

[PB666]

Why stop at 1.2, give yourself infinite fuel and use 4 g of thrust.

At 70 km v =2295.  where v = SQRT(u/r). V²/r =  u/r² that is derived from the equation w²r = u/r²   Since u/r2 provides ~.8 g (kerbin unlike earth is so compact that the atmosphere height significantly decreases g from ground level) of pull and TWR = 4 gives you 4.8 or approximately 48 a downward force. 48 = V²/r   V² = 48 * 675000 [altitude = 75000, altitude management will be difficult with such a downward force] V = SQRT(48*670000) = 5670 m/s

 

[PakledHostage]

On 27/10/2017 at 10:12 AM, MaxwellsDemon said:

Oh, definitely.  I have more issues with the supposedly-realistic "Gravity" than I do with the obviously-fantastic "Star Wars."

I couldn't agree more. Star Wars is an entertaining "space Western" who's sins against real world physics can be forgiven. Gravity, on the other hand, is cliche ridden schlok that is going to burn for all eternity.

Edited October 30, 2017 by PakledHostage