KSP Orbital Calculator [V0.10.1] - Now with selectable Celestrial Bodies

[Warringer]

I figured out the experimental launch orbit tool after decompiling your jar.

Velocity vector is (currently) pi/2 radians - velocity vector's angle over the horizon (the yellow circle) in radians.

Both periapsis and apoapsis are radii from the center of the planet, not altitude (altitude displayed in-game + 600,000m)

Other than that, the launch orbit tool does appear to spit out sensible data.

Also, LaunchOrbit.doVels() needs to be called after LaunchOrbit.doAlts(), which must be called before 'a' is calculated.

1. calculate c

2. doAlts()

3. calculate a

4. doVels()

Also also, you'll need a special case for escape trajectories, because it will probably output nonsensical answers.

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Also also also, the bi-elliptic transfer orbit tool should probably show the total as (|dv1| + |dv2| + |dv3|) rather than the somewhat less useful (dv1 + dv2 + dv3).

Also x4, yes, the bi-elliptic transfer orbit tool is buggy... the first burn should be positive dv for sure.

No need to decompile it. You could have just grabbed a clone from the KSP GitHub repo I set up and liked to in the OP...

Also fixed the Bi-Elliptic Orbit bugs now. But I'm note sure if my fix for the Launch Orbit is working correctly.

[Ferrit]

Thank you for this brilliant calculator. Thanks to it I've just managed a 109km orbit with an eccentricity of 0 (more luck than pilot skill but hey) and completed a Hohmann transfer from that orbit to 60km which is being neatened right now.

So again cheers for the awesome! 8)

[Tychonaut]

This is really a fantastic tool. The orbit MFD every Kerbonaut needs! Now if only it was integrated directly into the game UI...

Any chance of a calculator for plane changes, or for de-orbiting with a specific landing target?

[Warringer]

This is really a fantastic tool. The orbit MFD every Kerbonaut needs! Now if only it was integrated directly into the game UI...

Any chance of a calculator for plane changes, or for de-orbiting with a specific landing target?

For that we'd need useful angle displays for the orbit pane and the point over the surface. So until further notice not.

[mixinghoney]

Uhm ok...

[DoctorEvo]

Bi-Ellipstic Transfer

[Warringer]

Oh, you found a typo.

Now you can keep it and put it into a frame for your wall.

[DoctorEvo]

Oh, you found a typo.

Now you can keep it and put it into a frame for your wall.

No thanks... I'd have a lot of explaining to do if I put lipstick on my wall.

[ohadqumpo]

If it was only in the game... Maybe that could be proven and given to the developers ;]

[Warringer]

What do you mean?

[Guest LoSboccacc]

I think I got some overflow in calculations: I was wondering if I could take on the speed challenges by ascending orbits on hohmann trajectories and then flying straight down to the planet (it turns out it doesn't really give you that edge)

long story short, if you get on wildly elongated orbits, the calculator churns out some weird numbers; using a perigee of 40000m and velocity of 3600m/s on the elliptic orbit calculator results in the apogee at about minus 5 million meters.

[DoctorEvo]

I think I got some overflow in calculations: I was wondering if I could take on the speed challenges by ascending orbits on hohmann trajectories and then flying straight down to the planet (it turns out it doesn't really give you that edge)

long story short, if you get on wildly elongated orbits, the calculator churns out some weird numbers; using a perigee of 40000m and velocity of 3600m/s on the elliptic orbit calculator results in the apogee at about minus 5 million meters.

3600 m/s at 40 km is a hyperbolic orbit. That's why you're getting the odd value.

[foamyesque]

What that means is that you've achieved escape v and no longer have an apogee; it's at infinity.

The calc should probably catch that and tell you so, though.

[Warringer]

Hmmm...

Okay, I think that would be a good idea to implement...

[Warringer]

And done.

[Guest LoSboccacc]

hehe I feel so stupid and guilty now ;D

[Warringer]

hehe I feel so stupid and guilty now ;D

No need to.

You pointed me at something I had previously not realized.

[plazmaXIII]

can someone explain how to use the bi elliptic transfer calculator? what is the turnover altitude? i understand how these orbit changes work but cant figure out how to use it :|. it also seems really inefficient.

[Warringer]

The Bi-Elliptic Transfer Orbit someones takes even less Delta-v then the Hohmann Transfer.

For getting it, you transfer into an Elliptic Orbit, not unlike a Hohmann Transfer, but you got further out then to the target Orbit, At the Turnover Point, the new Perikee of the Elliptic Orbit you either do a prograde or retrogade burn to raise/lower the apokee. Followed by a retrograde burn to make sure that you remain in the target orbit.

Essentially its two Hohmann Orbits chained together.

The Turnover Orbit/Altitude is the Altitude where you do the correction burn to get to the target orbit.

Just enter something in the calculator and hit the 'Show Orbits' Button to take a look at the resulting orbits.

[plazmaXIII]

ok, i understand that now. every example ive typed in so far have been more fuel intensive. whats a good example of it being effective to save fuel. also where should the turnover altitude be set for maximum effciency?

[foamyesque]

http://en.wikipedia.org/wiki/Bi-elliptic_transfer

While it requires one more burn than a Hohmann transfer and generally requires a greater period of time, the bi-elliptic transfer may require a lower amount of total delta-v than a Hohmann transfer in situations where the ratio of final to the initial semi-major axis is greater than 11.94 [1].

So basically, it's best reserved for really long Hohmann transfers. Remember your starting radius is 600km, and a low orbit is, say 50km; so transferring from that to an orbit with an ASL altitude of 7200km is where you could start to see the efficiency gains.

[plazmaXIII]

Ok that makes sense thank you. A good but slow technique for future moon landings then.

[MaxSchram]

I have a question how you calculate the delta-v values in your stage calculator, because my calculation lead to different values and i want to know where i'm wrong.

For a single solid booster your delta-v is 3704.029m/s.

My calculations are:

Fthrust = 130kN

m0 = 1.8t

m1 = 0.36t

tBurn = 25s

The mass is linear in t: m(t) = m0 - t * (m0 - m1) / tBurn

The acceleration is: a(t) = Fthrust / m(t)

Integrating this from 0s to tBurn leads to the velocity change: vChange = 3632.41m/s, which is significantly lower than your result.

Where am i wrong?

[Warringer]

I'm doing the calculation over the Specific Impulse of the Engine.

Where I need to have a correction factor of 10 to the Specific Impulse to match the observed Delta-v in KSP.

For example the Specific Impulse of a booster SHOULD be ~230 seconds, but that would only get you a Delta-v of only ~370 m/s. The actual result is ~3700 m/s so the SI of the booster is corrected to be ~2300 seconds.

Going over the Specific Impulse is a little easier as I don't need to Integrate the whole thing.

Through looking at your result, I'm currently looking for a way to get rid of the correction factor and might works with that instead.

[DoctorEvo]

For example the Specific Impulse of a booster SHOULD be ~230 seconds, but that would only get you a Delta-v of only ~370 m/s. The actual result is ~3700 m/s so the SI of the booster is corrected to be ~2300 seconds.

Tsiolkovsky's Rocket Equation uses effective exhaust velocity, not specific impulse (though they amount to the same thing). Apply a conversion factor of g (9.807 m/s²) and you should be good to go.