Guide: Interstellar Travel

Interstellar Travel is one of the corner stones of Far Lands, so I'd thought i'd make a guide-ish page on Interstellar travel.

Easy Tips
Use gravity assists. Jool is perfect for escaping Kerbol, and from there you are either Extrasolar or Interstellar, depending on what modules you are using. If you can't get to Jool that easily, use Eve or Kerbin gravity assists.

Time your exit burn so that you are going prograde from Kerbin, to retrograde exit from Kerbol. This means that your orbit will be less than Kerbols from escaping.

ISP is your best friend. If you haven't already, install a mod such as TimeControl to deal with low TWRs from high ISP engines.

Solar power has little to no effect when travelling Interstellar, so either pack some Isotopes or hibernate/freeze your probe/pilots. Fuel cells are an option, but should only be used in an eccess of fuel

Ship Design
Crewed ships will have to be large if you want to maximise science points gathered.

Engines
Ion and Fission are cool, but it would ultimately make the vessel too big to get interstellar. You probably want to use either some form of high end fission (like Molten Salt, fission fragment), fusion or antimatter, roughly in order of delta v provided. Molten Salt engines are highly efficient, and fuction similar to vanilla NERVs, allowing for easy ship design. Fusion engines are a bit different. First of all, there are multiple types depending on the reactor type. Secondly, they use different fuel types, and sometimes multiple ones. Finally, they require a large amount of energy to power up to start generating. This could be supplied via large solar panels close to a star or a nuclear reactor. Either way, you need an initial power source. The final propulation method is antimatter. Antimatter uses multiple propellents again, but mainly familiar ones apart from Antihydrogen. It combines these to make a big bang.

Tanks
Your fuel section must be well designed to accomodate the right ratios of fuel. For example, if your engine runs on Antihydrogen and LH2 you will have to balance the LH2 count to make it match the antihydrogen so they run out at the same time and you aren't wasting Delta V.

Recommended mods
Near/Far Future Technologies. Really useful in power, especially Far Future for it's Fusion and Antimatter engines.

DeepFreeze (if playing with life support). Allows your Kerbals to hibernate through extended periods, reducing need for supplies.

PhotonSailor. Allows production of short journey interstellar voyages with laser propelled solar sails, or an effective propellentless travel method

Orion Drive: Efficient propusion method for probes. The G Force would kill Kerbals!

Interstellar Extended. Advanced version of NFT/FFT.

Time Control and BetterTimeWarp. Both useful for long ion burns. I've had never done a mission before using Ion before I got Time Control due to ion's low TWR. Makes it sooo much easier. BetterTimeWarp just means you don't have to leave your game timewarping for hours doing 1y+ journeys.

Mechjeb 2. Makes a lot of things less tedious.

FTL Beacons: Allows you to use beacons to contruct a gateway system between systems, Very Overpowered.

Alcubierre Drive: Very OP warp drive. Even retains velocity.