How do I send satellites to Mun/Minmus?

[Neil Kermstrong]

I`ve landed on Mun alot of times and just landed on Minmus, but now I want to launch a satellite/probe to both but I don`t know how to.
Until now I only could launch a satellite to Kerbin (and it`s a simple one) because when I try to launch a satellite to another moon it always run out of fuel

[VoidSquid]

16 minutes ago, Neil Kermstrong said:

because when I try to launch a satellite to another moon it always run out of fuel

How can that be when you already have landed on Mun and Minmus? I don't think I understand your problem here.

[Neil Kermstrong]

8 minutes ago, VoidSquid said:

How can that be when you already have landed on Mun and Minmus? I don't think I understand your problem here.

I can never put the satellite in their orbit, it always run out of fuel, is it because of weight? Because I don`t understand the weight system completely

[Superfluous J]

You're asking a very general question here. It's like asking if you can fix your car. We can't answer that without knowing what's wrong with it.

A picture of what you're building can help us help you. Also a description of how you're launching would be beneficial.

[VoidSquid]

Weight, fuel, engine efficiency - how far can I go? The answer to that question is the so called delta v (delta for difference, v for velocity), or short dV. Are you familiar with the terms TWR, ISP, dv?

Edited November 2, 2019 by VoidSquid

[scottadges]

So same process applies to putting a satellite in orbit as landing on a moon.

1. Launch, then circularize at Apopapsis (AP) in Kerbin orbit

2. Create Maneuver Node to transfer to moon at Periapsis (PE) and adjust prograde/normal/radial until you get the encounter

3. Burn prograde to get AP out to moon orbit, then wait until orbit intersects

4. Once in the Sphere of Influence (SOI) of the moon, circularize your orbit at PE

4A. If you want to change your inclination plane (different angles) then create a maneuver node and adjust to the angle you want.

4B. Burn at the node and adjust as needed (Remember: burning to change inclination can be very "expensive", i.e. cost a lot of fuel, to make a big change in inclination angle)

 

If you're doing all those things to land on the moon, you can do the same to put a satellite in orbit. It's exactly the same thing. As for fuel amounts, it's always better to go with more fuel than less. Don't try to get it to an exact amount. Just add more fuel.

 

If you're on PC, it's worth downloading the mod Kerbal Engineer Redux. The latest versions of KSP have some of these tools, but it's useful to see the Thrust-to-Weight (TWR) ratio in KER based on different bodies in the Kerbol system.

You probably know this, but here's a good video (a little old) about orbits:

 

Edited November 2, 2019 by scottadges

[Neil Kermstrong]

2 minutes ago, 5thHorseman said:

You're asking a very general question here. It's like asking if you can fix your car. We can't answer that without knowing what's wrong with it.

A picture of what you're building can help us help you. Also a description of how you're launching would be beneficial.

First I`ve tried with a SSTO, but it didn`t even go off the runway, then I`ve tried with a big rocket that was like the one I`ve flied to mun but I didn`t have enough fuel to burn retrograde when I was at mun`s orbit. (I didn`t try in Minmus yet) Wait a bit and i`ll send the picture

1 minute ago, VoidSquid said:

Weight, fuel, engine efficiency - how far can I go? The answer to that question is thew so called delta v (delta for difference, v for velocity), or short dV. Are you familiar with the terms TWR, ISP, dv?

Nope, what they mean?

[Neil Kermstrong]

25 minutes ago, 5thHorseman said:

You're asking a very general question here. It's like asking if you can fix your car. We can't answer that without knowing what's wrong with it.

A picture of what you're building can help us help you. Also a description of how you're launching would be beneficial.

https://pasteboard.co/IERgr9x.png

Here`s it

Edit: That's only the spaceship I've used to launch it, the satellite isn't inside

Edited November 2, 2019 by Neil Kermstrong
I forgot to point out something

[VoidSquid]

That rocket, even if the displayed dV is vacuum dV (I don't think so) will easily reach orbit around Mun or Minmus, the staging looks ok too (tough not optimal), so it probably is the way you try to achieve your goal.

Do you reach Kerbin orbit and go for Mun/Minmus after that, in a separate step? How much dV you have left after you reach low Kerbin orbit (i.e. approx 100x100km)?

Edited November 2, 2019 by VoidSquid

[Neil Kermstrong]

1 minute ago, VoidSquid said:

That rocket, even if the displayed dV is vacuum dV (I don't think so) will easily reach orbit around Mun or Minmus, the staging looks ok too, so it probably is the way you try to achieve your goal.

Do you reach Kerbin orbit and go for Mun/Minmus after that, in a separate step? How much dV you have left after you reach low Kerbin orbit (i.e. approx 100x100km)?

Well, I always look for 100k meters apoapsis and periapsis, so then I burn until my orbit pass through Mun's, then I just wait until there's a Mun encounter and start burning retrograde, but with this rocket when I try I can't start orbiting it because of low fuel.
About the dV I don't know, I gotta test it

[VoidSquid]

9 minutes ago, Neil Kermstrong said:

then I burn until my orbit pass through Mun's

Do you wait until Mun/Minmus is in a good position for your transfer burn? For Mun, for example, your after-transfer burn-AP should be around 12GM, not more, to have an encounter.

The correct moment to start the transfer burn is about when Mun is a quarter of it's orbit away from your intended encounter, then you simply burn prograde about 860 m/s dV, that should give you an encounter.

If you burn way more than said 860 m/s, then you're burning at the wrong time.

Again, I'm curious how much dV you've left after reaching LKO, please switch the display to vacuum dV for a proper readout. 

Edited November 2, 2019 by VoidSquid

[Neil Kermstrong]

 

7 minutes ago, VoidSquid said:

Do you wait until Mun/Minmus is in a good position for your transfer burn? For Mun, for example, your after-transfer burn-AP should be around 12GM, not more, to have an encounter.

The correct moment to start the transfer burn is about when Mun is a quarter of it's orbit away from your intended encounter, then you simply burn prograde about 860 m/s dV, that should give you an encounter.

If you burn way more than said 860 m/s, then you're burning at the wrong time.

I mostly go to the apoapsis or periapsis and just start burning, I never wait to burn

[VoidSquid]

18 minutes ago, Neil Kermstrong said:

mostly go to the apoapsis or periapsis and just start burning, I never wait to burn

Then we've found the cause of your dV problem.

You might want to check out this video