Clockwise or Counterclockwise Orbits?

[Astrotropie]

What kind of orbits do you establish around moons and other planets than Kerbin? In reality some Apollo missions used clockwise orbits around the moon, to gain a 'free return' to earth, but I can't find out what kind of orbits other real life satellites use.

Somehow all my orbits apart from those around Kerbin become clockwise, but which approach would you think to be the most efficient or practical?

Edited September 26, 2013 by Astrotropie

[Nexustrimean]

The most efficient follow the orbit of the body, to maximize the Oberth effect for takeoff/departure.

[fatfluffycat]

How does this work? Tell me smart people!

[Josh Harris]

Just play with the maneuver nodes. Mechjeb tends to put ships in a 90 degree heading (Counter-Clockwise). Moving the Node earlier or later, seeing where the Mun will be when the encounter occurs is the key. Later departures tend to lead to 270 degree (Clockwise, Free Return, Apollo-style) orbit.

In the real world passing in front of an orbiting body will slow you down while passing behind the body increases speed (Gravity Assist, or "Slingshot").

[Jodo42]

How does this work? Tell me smart people!

The Oberth effect? I'm no physicist but I believe it's based around the principle of the rocket having more energy at periapsis, when it's falling and at maximum speed, so you get the most bang for your buck when you fire the engines. Someone who actually knows their stuff feel free to correct me/expand upon this.

As to the OP, I really haven't done much inter-planetary stuff, so I can't tell you. I suspect I'd take whatever I could get, however.

[SargeRho]

Engines are apparently able to use part of the kinetic energy of the fuel for propulsion.

[Hav0c13]

Because of the distance that you are covering in inter-planetary travel, whatever direction the planet you are trying orbit is moving is the direction you want your ship to go. If you go for a counter orbit around that planet, you will end up using more fuel.

I got into an intercept trajectory with Jool but I ended up on the side of Jool that was facing me so I wasted alot of fuel trying to slow down to stay in it's SOI, I got into orbit moving the opposite direction of Jool's moons so it set up a nice route for me to moon hop but I had to say bye to that ship cause it wasn't coming home.

[FITorion]

What ever I can get.

In general I'm just happy with "an orbit".

However I do try for counterclockwise orbits. I usually get them around the Mun and other simple targets. Where things get messed up and I'll just be happy for any orbit is when I'm headed for Jool and its moons.

[Matt56]

Ya, it you're planning to land on the body you're orbiting then being in a prograde (usually counter-clockwize when looking down on the north pole) orbit will help you. During decent you'll notice that your velocity drops as you switch from orbital to surface relative velocity. This saves you fuel because you don't have to slow yourself down as much. In the same way, as you ascend, the body's rotation slings you forward and gives you an extra boost on the way up. In a retrograde orbit, that same velocity works against you, so your delta-v requirements go up by twice the body's rotational velocity.

If you were going into Jool orbit, Retrograde might be the way to go, like HavOc13 did, because then you can slingshot your way down using the various moons. I did that once. Came in retrograde, go an encounter with Tylo, dropped a probe as I did a slingshot, aerobraked in Jool and ended up in orbit around Val.

[dragoncannon]

The only satellites moving clockwise (retrograde) in Earth orbit are the surveillance satellites operated by the Israeli Air Force. This is not due to any mission-specific reason, rather, the geopolitical realities of the Middle East. Israeli space launches head west over the Mediterranean so as not to accidentally provoke a war with the hostile neighbors to the East who could misconstrue a rocket launch as an attack.

[EtherDragon]

There are many factors to consider, here is a summary of what has been discussed so far:

On Launch:

The rotation of the body you are launching from adds some velocity to help you get into orbit. For planets, like Kerbal, this means the best way is to go Counter Clock-wise, as seen from above, because the planet is already rotating in that direction. If you choose to go Clockwise, you need to burn extra fuel to overcome the momentum imparted from the planet's rotation.

On Establishing an orbit with Moons:

This one really depends on your ultimate goal. If you are planning orbiting a moon (such as Mun) and want to go interplanetary, then it's best to capture an orbit that is counter-clockwise. This is because when you want to reach escape velocity (for the moon and planet) you get to use a lot of existing momentum - the orbital speed of the moon and your orbital speed around the moon. Note - doing this it's best to leave when the moon is between the planet and the sun if you are headed to an inner planet, or when the planet is between the moon and the sun when you are heading to an outer planet.

On the other hand, if you simply want to establish orbit on a moon and return to it's host planet later, it's more energy efficient to go clockwise - as at Apoapsis you are going very slow. When a moon passes you (because it is going faster) your craft will have an easier time reaching an orbit by burning just enough to let gravity pull you along the clockwise side. Otherwise you have to use more thrust to overtake the moon and get a counter-clockwise orbit.

What about landing on a Moon? Well, again it depends on the particular moon. Most moons rotate so slowly that it doesn't matter - so you actually save fuel by choosing the best insertion orbit (in most cases, clockwise). But if the moon has a decent rotation period, then it's definitely best to orbit in the same direction as the rotation because the energy spent overcoming rotation (as in planetary take-off from before) is more than what would be used correcting a free return trajectory into a counter-clockwise orbit.

For interplanetary insertion - always go for Counter-Clockwise. Yes it's true that you save a bit of fuel by allowing the planet to pass, and go clock-wise - but the distances are so great that you can make any reasonable correction burn to get the orbit insertion point you want in less than 20delta-v. Also, going counter-clockwise on a planet allows for one of the coolest orbital insertion maneuvers - Aero-braking.