How to do anything interplanetary?

[SF-1 Raptor]

Ok. The one time I got an interplanetary mission, I could only manage a distant flyby (burnt all m fuel trying to slow down). Any tips on how to reach a planet and how to slow down once I'm there?

[nukeboyt]

After you've left the Kerbin Sphere of Influence (SOI) and while you are still a long way away from the target planet, experiment with very short (momentary) burns in EACH of the 6 main directions (Prograde, Retrograde, Normal, Antinormal, Radial, Antiradial). As you do each burn, watch the periapsys (or closest approach) and how it changes with each burn. (Mouse over in map view, then left-click to keep it up). You will find that each burn will either make the periapsis GROW (get further away) or SHRINK (get closer). Do longer burns on the ones that SHRINK the periapsis (or closest approach) and stop burning when the value quits SHRINKING. Then repeat for the other directions. You will soon learn that one direction will have a much bigger effect than all the others.

When you have an encounter, use the TAB key to focus the view on the planet in question. You should be able to see the periapsis of your upcoming encounter. Continue to use the method above to get the periapsis down to the value you want. I suggest that you learn first on planets or moons with atmospheres. Because these can help you slow down by aerobreaking. For example, at jool, I set my periapsis to about 120K and it will slow me down enough to get into orbit. Setting the periapsis too low, will result in having to land (or crash).

For planets / moons without atmospheres, you will have to just bring more fuel

Edited January 2, 2015 by nukeboyt

[The_Rocketeer]

1. Very best advise is to make course corrections very early, as late corrections cost much fuel.

2. Aim for a really low (but safe!) Periapsis on your flyby as this will maximise the benefit of the planet's gravity to assist matching speed.

3a. If the planet has at atmo you can aero-brake - this means dipping into the atmosphere to use drag to slow you down. It's dangerous because if you slow down too fast you will end up descending to the surface, but it can save a lot of fuel if done right.

3b. If not, you need to get as close to matching orbit during transfer as possible before the encounter starts, which will minimise fuel use during the encounter.

4. I recommend practising making transfers from Mun to Minmus and back. Using an ion engines will help to simulate the speed differences and longer burn times for planetary transfers, but 'hitting the target' (getting an encounter) is easier.

[Perry Apsis]

There are a number of tutorials on YouTube and here on the Forum that can help you get started. The essence is to use what's called a transfer orbit. Your ship is always in an orbit. When you leave Kerbin's sphere of influence, you're in an orbit that touches Kerbin's orbit at one end, with the other end out in space somewhere. If you've done it right, the other end is closer to your target's orbit. As a rule of thumb, if you want to go to a planet farther from the sun, you want to thrust across the dark side of Kerbin so you escape in the direction of Kerbin's orbit. If you want to go to a world closer to the sun, you thrust across the light side. Play with the maneuver node so that your course when you escape is parallel to Kerbin's orbit.

Once in interplanetary space, you want to modify your orbit so that one end touches the orbit of your target. That's your transfer ("Hohmann") orbit. That's easy to do once you've got a handle on how to use maneuver nodes. The trick is to time the burn so that when you get to the far end of the orbit, that's when the target is there, too. If you select the world as your target in map mode, the game will show you where the target will be when you touch its orbit. It could be that you'll have to wait a year or even a few before the target and your ship are in the right place in your orbits so that sliding the maneuver node around will get you a close intercept.

This should give you an intersection that didn't cost too much fuel to create, and where the relative speed when you get there won't be too high. If you're still running out of fuel when you get there, then you may want to built another, much bigger stage onto the bottom of your ship, so that you're essentially launching the existing ship from somewhere above the surface and already moving. You might also consider using the nuclear engine on one of your upper stages, even though the burns can be painfully slow. It's much more fuel-efficient.

Another thing to think of is minimizing the weight of your lander, and particularly the amount of mass you carry back up from the surface. That will have a cascade effect all the way down through the rest of your ship. If you're trying to use the same capsule to get there, land, take off, and come back, consider using a separate lander. You could even launch one ship to go there, land, and take off, and another ship to go out there, retrieve the other astronaut and come back. Once you've got your technique down, you can get fancy, and do an Apollo-style mission where your lander rides along with your main ship.

Post some screen shots of what you come up with and how it works.

Good luck, and fly safe!

One way to get a feel for the maneuvering and burning is to get MechJeb. It can create the maneuvers for you, and even execute them. I learned a lot about orbital mechanics from watching MechJeb.

[DrD]

You need also to launch at the right time. For this you need 2 things:

1. phase angle calculator. There are some really good ones, do a google search. I use http://ksp.olex.biz Basically this tells you the angle you need between Kerbin and your target body when you launch

2. A way to know current phase angle. Some use a protractor on the monitor (a real protractor.) Considering phase angles are given in hundredths of degrees I'm not sure this is accurate enough. I use Kerbal engineer, the rendevous tab give you phase angle from current active ship to any selected body.

Tip: you can select anything on Kerbin or in orbit as the phase angle will not change significantly during an orbit. This is important because if phase angle is off you will need to accelerate time A LOT or wait A LONG TIME. Since time acceleration is limited when you're in orbit the smartest thing is to plant a flag somewhere in the space center and "fly" the flag. Then you can speed up time to the max.

I've found that if phase angle is off even by a degree it's very difficult to get an encounter.

[SF-1 Raptor]

Thanks for the tips guys. I'll should be able to make it now.

[klesh]

One thing I might add is depending on the size of your ship (smaller is better), RCS is a fantastic way to fine tune your trajectories. You can use shift to make smaller bursts of RCS, so you can get really quite exact. You can also just point your ship prograde and use the H,N,I,J,K, and L keys to operate RCS in all the directions, though it is easy to get disoriented this way.

I definitely second the advice to make corrective burns early in your path from one body to the next, as smaller changes in velocity are more efficient early on. A .5m/s corrective RCS burst a few minutes after your big burn to head off to the Mun can alter your eventual destination by hundreds of KM. Doing that same .5m/s corrective RCS burn when you're almost at the Mun will change you very little, maybe a few hundred meters.

[bdito]

Simple. Give yourself WAY more deltaV than necessary. Use nuclear engines as they're the most efficient.

[StrandedonEarth]

An easy way that costs more dV is to get into solar orbit then create a maneuver node. You can then move the node all the way around Kerbol to find the right time to burn. This is less efficient than burning straight out of LKO but doesn't need any fancy tools to find the window. You can even quick load back to when you were in LKO and to the transfer window you found, then set up the node again to save some dv

I use the mod Kerbal Alarm Clock to avoid missing nodes. It also has a tab that lists transfer windows that are somewhat accurate. That's all I use to find transfer windows. Another useful mod is the Trajectories mod, which will show your orbit after passing through an atmosphere. It is extremely useful for aerobraking and precision landings. I'd link the mods but I'm on mobile right now.