Rock, Paper, Shotgun

randomnine says:

Orbiting is not difficult but it does require some care – and a final stage with a liquid fuel booster, if you want a circular orbit. Here’s my rocket’s final stage passing over its launch pad in a stable 150km orbit.

Near Earth, a 150km orbit would be stupid – atmospheric drag would claw down anything that close. But this isn’t Earth.

Here is some FACT SCIENCE derived from a few stable orbits:

- The Kerbal planet has a radius of around 590km, so is roughly 1/11th as wide as Earth

- It has a mass of about 5.2*10^22kg, so around 1/114th Earth’s mass

Because it’s so much smaller, reaching space is much easier! Escape velocity from Earth’s surface is 11.2km/s – on the Kerbal planet, it’s 3.4km/s. Escape velocity from an altitude of 100km is 3.2km/s. If you’re going faster than this when you hit this altitude, you will never come back down.

If you want to get into orbit, you can derive the correct orbital velocities given the numbers above… but here are a few (approximate) orbit velocities:

at 100km: 2246m/s
at 200km: 2100m/s
at 2000km: 1161m/s
at 20000km: 412m/s
at 385000km (equal to Moon orbit): 95m/s

Process for orbital insertion:

1. Launch straight up. You need to escape atmospheric drag as quickly as possible.
2. Once you reach at least 40km or so altitude, accelerate horizontally to around 2500m/s for a low orbit or around 3000m/s for an extremely high one.
3. Climb slowly to required orbital altitude. Once there, thrust downwards until altitude stabilises.
4. Watch altitude. If you are accelerating downwards, accelerate forwards a few m/s and then restabilise altitude. If you are accelerating upwards, accelerate backwards a few m/s and then restabilise altitude. Repeat until altitude is stable.
5. If you wish to deorbit for landing, accelerate backwards, not downwards. Accelerating downwards will speed you up and slingshot you into a higher, more elliptical orbit.

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