Basic Microwave Powered Plasma Spacecraft - sswelm/KSPInterstellar GitHub Wiki

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This guide will help you build a basic microwave power network and a plasma spacecraft that isn't useless using only basic fission reactors and microwave transceivers.

At first glance, the Plasma Engine seems to be rather lackluster when first unlocked. When paired with an un-upgraded 1.25m fission reactor and [generator](Electrical Generators) and fueled with Xenon, it produces equal thrust to the stock Ion Engine, but with less ISP and more weight. Any other combination performs just as bad.

However, that doesn't make the plasma engine useless. Un-upgraded fission reactors are far to heavy to carry around for the power they generate. However, if you use [microwave transmission](Microwave Power Transceiver), you don't have to! In fact, it is perfectly possible to build a plasma-powered spacecraft capable of flying to the Mun and back ten times in a row without refueling using nothing but un-upgraded fission reactors and microwave transceivers.

Here's how.

Building the Microwave Network

First, you have to build a microwave power network. This is actually much simpler than it sounds. Since we're just flying to the Mun, we don't need to worry about long distance transmission losses. If you would like to fly interplanetary missions, there are ways to deal with those. We, however, can ignore them.

Step 1: Figuring out your power requirements

We need 2 gigawatts of power to get roughly 25 kN of thrust with liquid fuel. We will need multiple reactors to give us that much power. We're going to use the 3.75m reactor and generator to power our network. They produce the most power for their weight, and the most power overall, so we will only need three satellites in total. This may seem daunting at first, as they will weigh upwards of 60 tons each. However, using the smaller 2.5m reactors, we would need 19 of them, so it ends up being simpler.

Step 2: Launching the generators

Now we have to get these nuclear power satellites into orbit. This may be somewhat of a challenge, but there are plenty of heavy-lift guides out there to help you do so. The actual orbit does not matter, so long as the inclination is less than 30 degrees and the periapsis is above the atmosphere.

Protip: You can use that giant, 28-ton reactor to your advantage. By strapping a [thermal rocket nozzle](Thermal Rocket Nozzle and Thermal Turbojet) to it and feeding in LFO from the boosters using fuel lines, you get 1600 kN of thrust at 686.25 s, equal to a mainsail in thrust but with double the ISP. You will need additional boosters for the first 20,000 km, as the thermal rocket's thrust decreases rapidly with increased atmospheric pressure.

Step 3: Launching relays

In order to ensure your plasma craft will receive adequate power during your entire trip, you will need to place relays in orbit around Kerbin. A triangle pattern of three relays set 120 degrees apart from each other is enough to ensure you will always have power. The relays require only a transceiver set to relay mode, and so will be very light compared to the power satellites.

For Kerbin, the minimum orbit for these relays is 600 km. However, to give ourselves some margin for error, it's best to make the orbit at least 700 km. This gives us about 5 degrees of leeway in our relay placement. Feel free to increase that height even more if you are unsure about your ability to accurately place the relays. You want the orbits of the satellites to be about equal in height, and you want them all to be as close to circular and equatorial as you can get.

Bonus: If you want to be able to fire your engine at any point in the Mun's SoI, you will need to place at least one relay to give you power when the Mun is between you and Kerbin. The best way to ensure you always have power is to place three relays in the same pattern as you made around Kerbin. The minimum orbit for these relays is 200 km.

Building and piloting the craft

Congratulations! You now have a basic microwave power network. It was a lot of work, but it will provide you with 2 gigawatts of power no matter where you are in Kerbin's orbit. They will run out of fuel eventually, but they can be either reprocessed using a docked [refinery](ISRU refinery) or science lab, or they can be de-orbited and replaced with fresh satellites. You can also upgrade your network by launching more satellites, and thanks to your relay system, it doesn't matter where you put them as long as they're in orbit.

Now that we've finished that, on to our craft.

Step 4: Designing the craft

This part is very simple. We need a plasma engine, some radiators, some liquid fuel, a cockpit, and a few microwave receivers. We'll start with liquid fuel. We can use the MK-I or MK-II fuselage for our fuel. The MK-I looks better, but the MK-II holds slightly more fuel with the same weight of tank. Attached to that, we should add a cockpit on top and a 1.25m plasma engine on the bottom.

Next, we add some radiators. We can get by with only two medium-sized radiators, as we don't have an onboard reactor and we can shut off the receivers when we aren't running the engine.

Finally, we add the receivers. We will need several of them to ensure that we get a good angle. Spread them out so that most sides of the vessel are covered.

Step 5: Flying the craft

Flying a microwave-powered craft is simple. You just have to be mindful of your receiver's angle, as it will affect the amount of power you will be receiving.

Strap your tiny plasma craft to a rocket of your choice and get it into a stable orbit around Kerbin. Once you have reached orbit, activate your microwave receivers and your plasma engine. Set up a maneuver node to intercept the Mun as you would normally. Time warp until you get close to the node.

Now comes the tricky part. First, line up your vessel with the node. Then, roll it until you find the position that gets you the most power from your microwave receivers. If you placed your receivers well, it should be close to 2 gigawatts. Once you have your ship lined up properly, burn as you would with any engine.

That's all there is to it!