How can I know my speed in mach?

[goldenpeach]

Hi!

Like the tittle say, I would like to know my speed in mach.

Is there a mod that let me know it?

Sub question: I once read that the speed of sound in KSP was constant(while in real life it depend of the temperature of the air), is that true(and if it is, what is the speed of sound)?

[AlamoVampire]

honestly, I do not think there is a mod for this, but, try this website: http://www.calculateme.com/Speed/MetersperSecond/ToMilesperHour.htm

just convert your m/s into MPH on that site and then convert to mach numbers, but, I think 2000 m/s is about 4473mph give or take which is mach 5.877. gotten from:

http://calculator-converter.com/converter_mph_to_mach_calculator.php

[LameLefty]

Mach number is a function of the speed of sound in the medium. Speed of sound, in turn, is dependent on the density of the medium. For a compressible fluid, density in turn is dependent on pressure and temperature.

[AlamoVampire]

Lamelefty while you are correct, it does not apply to KSP, as Mach is a consistent number no matter temperature, altitude or medium. so, I think its safe to assume it can be considered what mach 1 is at sea level on earth.

[goldenpeach]

Thank you for the fats answers!

Also, I did more research and found that steam gauge plugin give your speed in mach.

I will do a basic experiment to know the speed sound in KSP.

EDIT: the first result(which come from a descending craft that was send high by a SRB): the speed of sound is between 320 m/s and 330 m/s.

[ferram4]

Depends on temperature, which depends on altitude. If you assume that Kerbin's atmosphere is made up of the same stuff as Earth's (reasonable based on a pressure of 1 atm at sea level with a density of 1.225 kg/m^3, taken from the game itself), then using the temperature curve (which is also sort of like Earth's) you get a speed of sound of ~330 m/s at sea level, decreasing to ~290 m/s above ~10 km, where it stays sort of constant until increasing above ~25 km. At least that's what FAR does, since it's consistent with real life.

[LameLefty]

Lamelefty while you are correct, it does not apply to KSP, as Mach is a consistent number no matter temperature, altitude or medium.

Nope, not really. "Mach number" is a defined term in the physics of compressible fluid dynamics. Now, that being said, it IS simpler in KSP than the real world. For instance, atmospheric temperature isn't really modeled realistically so far that I know, and pressure change with altitude is much smoother in the game than it is in real-life. But even though the model is simplified, the speed of sound on Kerbin is, by definition, different at sea level than it is at 30km because the atmospheric pressure - and density - is different.

[AlamoVampire]

look, all of this lame is moot until the devs give us actual numbers for what the speed of sound on KERBIN is. While, this is an invigorating conversation to be sure, we are only speculating on something we cannot know, not because the numbers are not there, but, we do not KNOW where that line is in this game. The ONLY thing we can use as a HINT is watching for the Mach Cone and getting a screen cap the INSTANT it appears with our M/S emblazoned on screen.

I am not trying to insult you Ferram or Lame, but, this is how it is, until Felipe says or one of the Devs state what Mach 1 is in the game, we can only draw on hints and supposition. Even if Ferrams math is about as close as we can get right now, it is STILL only a guess until Squad says its fact. Sorry to sound like a mushed up Kerbal, but, I can only go on what Squad says as fact lol

[Themohawkninja]

look, all of this lame is moot until the devs give us actual numbers for what the speed of sound on KERBIN is. While, this is an invigorating conversation to be sure, we are only speculating on something we cannot know, not because the numbers are not there, but, we do not KNOW where that line is in this game. The ONLY thing we can use as a HINT is watching for the Mach Cone and getting a screen cap the INSTANT it appears with our M/S emblazoned on screen.

I am not trying to insult you Ferram or Lame, but, this is how it is, until Felipe says or one of the Devs state what Mach 1 is in the game, we can only draw on hints and supposition. Even if Ferrams math is about as close as we can get right now, it is STILL only a guess until Squad says its fact. Sorry to sound like a mushed up Kerbal, but, I can only go on what Squad says as fact lol

Actually, I'd argue that the Mach effects at altitude-based velocities IS what the devs have stated as the speed of sound on Kerbin.

That being said, for now you could just do the layman's way of doing it, and divide your velocity (m/s) by 340, as that is the speed of sound on Earth at 1 atm.

[ferram4]

I am not trying to insult you Ferram or Lame, but, this is how it is, until Felipe says or one of the Devs state what Mach 1 is in the game, we can only draw on hints and supposition. Even if Ferrams math is about as close as we can get right now, it is STILL only a guess until Squad says its fact. Sorry to sound like a mushed up Kerbal, but, I can only go on what Squad says as fact lol

Yes, and we can't know that the sun will rise tomorrow. Sure, everything about the universe indicates that the probability of the sun rising tomorrow is a virtual certainty, and all of what we have learned abut the universe indicates that it would take either a severe world-ending event for that to happen or for the laws of physics to be violated, but it's STILL only a guess until [insert your particular all-knowing creator deity here] says it's fact.

Considering that atmospheric pressure at sea level is the same on Earth and on Kerbin, that atmospheric density is the same on Earth and on Kerbin, atmospheric temperature is the same on Earth and on Kerbin, and jet engines burn fuel and intake air at about the same ratio as a stoichiometric mixture of kerosene and air, I think we can logically conclude that we're looking at an atmosphere around Kerbin that's the same composition as the one around Earth.

Honestly, after all the work that's been put into making these things so close to Earth-like I'm going to be severely disappointed if the "canon" atmospheric properties go off on some unrealistic tangent.

[GDJ]

340 m/s is roughly Mach 1 in KSP.

Close enough.

[FITorion]

Mach always confuses me... The speed of sound changes depending on conditions... are the gauges taking into account pressure and temperature when they display the Mach value? or are they just calling the speed of sound at 1 atm at 70 F Mach 1 and then going from there? If so then you could actually break the sound barrier before reaching mach 1 because you're flying at an altitude where the pressure is less and thus the speed of sound is slower. Once you got out of the atmosphere then mach would have no meaning either...

[UmbralRaptor]

With stock aerodynamics, you're always at mach 0; there are no compressibility effects in stock drag. I believe that FAR will show you your current mach number?

[AlamoVampire]

well, far as i can tell, orbital speed at kerbin is what 2000 m/s give or take, and thats barely 4500 miles per hour give or take, so, would not surprise me if 'mach 1' is a lil lower in KSP, but, what ever it is, all i need to concern myself with is: pointy end goes up, fire goes down, and jebediah decorates KSC with more scrap XD

[tavert]

Considering that atmospheric pressure at sea level is the same on Earth and on Kerbin, that atmospheric density is the same on Earth and on Kerbin, atmospheric temperature is the same on Earth and on Kerbin, and jet engines burn fuel and intake air at about the same ratio as a stoichiometric mixture of kerosene and air, I think we can logically conclude that we're looking at an atmosphere around Kerbin that's the same composition as the one around Earth.

Honestly, after all the work that's been put into making these things so close to Earth-like I'm going to be severely disappointed if the "canon" atmospheric properties go off on some unrealistic tangent.

There is the slight hiccup of the stock atmosphere not behaving like an ideal gas. For Mach number to be well-defined you need a well-defined speed of sound, which we don't exactly have in stock KSP. The temperature sensor readings are annoyingly decoupled from the rest of the atmospheric physics, so are mostly useless. If we assume ideal gas behavior then either the temperature readings are wrong or the pressure-density relationship is wrong. If we ignore the temperature readings, Kerbin's atmosphere behaves isothermally which would indicate a constant speed of sound if the molecular composition is also constant.

[FITorion]

There is the slight hiccup of the stock atmosphere not behaving like an ideal gas. For Mach number to be well-defined you need a well-defined speed of sound, which we don't exactly have in stock KSP. The temperature sensor readings are annoyingly decoupled from the rest of the atmospheric physics, so are mostly useless. If we assume ideal gas behavior then either the temperature readings are wrong or the pressure-density relationship is wrong. If we ignore the temperature readings, Kerbin's atmosphere behaves isothermally which would indicate a constant speed of sound if the molecular composition is also constant.

It's been stated several times I believe by the devs that the temperatures are just a stand in and have no meaning yet. They'll redo them at some later date.

[Tripzter]

I'm hoping by the end of my life time Lightspeed be the standard unit of speed in space

[LordOfTheOrbits]

Currently there are no mechanics in KSP that care about the speed of sound, so it doesn't matter at all.

If you would rather like a realistic aerodynamic mechanics go try out FAR: http://forum.kerbalspaceprogram.com/threads/20451

[irongut]

honestly, I do not think there is a mod for this, but, try this website: http://www.calculateme.com/Speed/MetersperSecond/ToMilesperHour.htm

just convert your m/s into MPH on that site and then convert to mach numbers, but, I think 2000 m/s is about 4473mph give or take which is mach 5.877. gotten from:

http://calculator-converter.com/converter_mph_to_mach_calculator.php

Why on Earth (or Kerbin) would you convert lovely m/s to horrible mph? The speed of sound at sea level on Earth is approx 330m/s so just divide your speed in m/s by 330 and that gives you the rough Mach value.

Note: I know that Kerbin is not exactly like Earth and that the speed of sound (and even light!) depends on the density of the medium it is passing through but for a nice Kerbal-like, back of a fag packet calculation dividing by 330 should be good enough.