# [Tutorial] Interplanetary How-To Guide

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On 8/27/2014 at 3:20 PM, SergeantFritz232 said:

This was pretty useful as it stands but I haven't unlocked the nuclear engines in career mode yet so what engine would you recommend for a dres transfer stage. I currently have a Skipper attached with drop tanks.

I suggest Poodle or Terrier. With a lot of fuel.

Use KER to check Dv, for Dres you need about 1533.66 m/s for the ejection from a 100km parking orbit (LKO) and then a bit more for mid-transfer corrections and to capture into orbit (no way of using gravity wells or atmos, no moons or atmosphere at Dres).

The return, if you're doing one, uses about 1285.73 m/s for the ejection from a 30 km orbit, and a bit more for mid-transfer corrections, then you can use Mun, Minmus or Kerbin's atmo to capture into orbit.

You don't need to drop any tanks, the maximum possible Dv for a single 909 powered stage is 8,406m/s, and the mission only needs just over 1533.66m/s+1285.73m/s+200m/s margin=3019.39m/s

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• 1 month later...

@Kosmo-not could you please update the OP as the equations are not displaying. Thanks

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Guys what is t(subH)? I'm confused, also what is the ejection angle equation? The formula is in gibberish.

Thank you!

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2 hours ago, william2002730 said:

Guys what is t(subH)?

I think this is the Time for Hohmann transfer, and some of the equations I can't see, can you Quote it please?

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On 8/9/2012 at 10:20 AM, Kosmo-not said:

Ejection Angle = 180° - ÃŽÂ¸

This one, I can't get the equation to show up.

Also, how do you calculate the time for Hohmann transfer again?

Edited by william2002730
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3 hours ago, william2002730 said:

Also, how do you calculate the time for Hohmann transfer again?

With this Excel formula: -

=(2*PI())*(SQRT((r^3)/μ))

r = semiMajorAxis of the Orbit you want the Period for.

μ = GM = the Gravitational Parameter of the parent body (e.g. the Sun (Kerbol) for Kerbin)

The above will give you the orbital period of the full orbit, for a Hohmann transfer just divide it in half for the transfer time.

I am having the same problem with the Equations in the OP, I have posted in the thread for an update but might have to PM.

Edited by Pretorian28715
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Thank you!

Really dumb question: you said r is the semi major axis of the orbit I want the period for, but what do you mean by the orbit I want the period for?

I have trouble seeing all the png files on this page, and some of the equations as well, so is it possible that someone have a PDF version of this awesome guide?

13 minutes ago, Pretorian28715 said:

With this Excel formula: -

=(2*PI())*(SQRT((r^3)/μ))

r = semiMajorAxis of the Orbit you want the Period for.

μ = GM = the Gravitational Parameter of the parent body (e.g. the Sun (Kerbol) for Kerbin)

The above will give you the orbital period of the full orbit, for a Hohmann transfer just divide it in half for the transfer time.

I am having the same problem with the Equations in the OP, I have posted in the thread for an update but might have to PM.

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1 hour ago, william2002730 said:

but what do you mean by the orbit I want the period for?

The Orbit is a Bodies path around it's Parent Body, e.g. Kerbin around it's Sun, or the Mun around Kerbin.

1 hour ago, william2002730 said:

so is it possible that someone have a PDF version of this awesome guide?

No idea, there is a post mentioning a PDF but it does not seem to be available to all, and I have not found one myself.

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1 minute ago, Pretorian28715 said:

No idea, there is a post mentioning a PDF but it does not seem to be available to all, and I have not found one myself.

But can you see the png files, and this equation: Ejection Angle = 180° - ÃŽÂ¸? If so, you can download this page as a PDF file, by simply going to the print window and on the left bottom corner, there should be an "open PDF", and make sure to only open page 1-5 only. I'll be forever grateful!

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11 minutes ago, william2002730 said:

But can you see the png files

1 hour ago, Pretorian28715 said:

I am having the same problem with the Equations

Edited by Pretorian28715
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Just now, Pretorian28715 said:

I see, thanks anyways. I hope Kosmo-not can fix this up soon!

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1 minute ago, william2002730 said:

I hope Kosmo-not can fix this up soon!

I've PM'd him so hopefully.

This is handy

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17 minutes ago, Nexus24680 said:

Thank you so much!

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3 hours ago, Nexus24680 said:

Here you go

Thank you very much.

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You're welcome.

I'm interested on KSP Math too. If you find more articles or things that use math on KSP, be sure to tell me.

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• 1 year later...

Necropost...

What are the necessary stuff for the calculations, i mean what those symbols stand for, i'm going to make a planet pack and i want to get the Phase Angles using my very own calculations, my very own effort.

Edited by GRS
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• 3 weeks later...

I checked all the equations in the Interplanetary How-to-guide and found an error in section 2.

The formula  v1 = SQRT((r1*(r2*v22 - 2*μ)+2*r2*μ)/(r1*r2))  has an error.

It should read v1 = SQRT((r1*(r2*v22 - μ)+2*r2*μ)/(r1*r2))

This can be verified by using the deriving formula:   v12 = v22 + vesc2  = v22 + (2*μ/r1 - μ/r2) and then reducing to

v1 = SQRT(  v22 + 2*μ/r1 - μ/r2 )

Using the same variables names as the guide:

• r1 = parking orbit radius
• v1 = ejection velocity
• v2 = SOI exit velocity (absolute value)
• vesc = escape velocity taking SOI into consideration

This turns out to be a very small correction because r2 is such a large number.  Only about 6 m/s in the sample problems.

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