A small probe

[Kerbart]

This started as a simple project for a tutorial. Put a simple sputnik-like probe into space, but give it orbital maneuvering capacity. Small probe, small launch vehicle, two FLT-800's and two small SRB's. There! Orbit! Well... Maybe one FLT-800 and a FLT-400. Maybe less? From there I got carried away with shaving off weight. The fun thing is, that every time you think "I can't take away more weight" it turns out you can. Less fuel = less weight = faster acceleration = making it into orbit anyway. That's a good lesson, because it works in reverse as well of course.

So here's the question: can you get to the Mün on a single FLT-800?

I learned that you can actually get to the Mün with a launch weight equal to that of a single FLT-800. Well, ok, a little bit more, but not much more!

Probe

Stayputnik [1] - 50 kg

Communotron [4] - 20 kg

Z-200 Battery [2] - 10 kg

Xenon Tank [1] - 70 kg (it turned out that using the disc batteries and the radial tank gave better performance than the other way around)

OX-4L Solar Panels [4] - 17.5 kg

RTG [1] - 80 kg

Ion Engine [1] - 250 kg

Total: 560 kg

The Xenon tank and the RTG are mounted opposite from each other. The 10 kg difference is negligible or so I thought. You'll have to baby the probe in flight, but not to the extend that it's hard to control.

2nd stage

TR2 Decoupler - 15 kg

RC001S Remote Guidance - 100 kg - I want some torque for control and the ability to de-orbit the stage after use

Z1K Battery - 50 kg

FL-T200 -1125 kg - this is where the magic happens! An FL-T200 to take you to space! Yay!

LV909 - 500 kg - stay away from an FL-T800 and suddenly an LV909 has enough thrust!

Total: 1790 kg

Total with space craft: 2350 kg, giving us a TWR of 2.17 - this combo will take off like a bat out of hell, but lacks stamina. Give it, say, 800 m/s at 20km for starters and you'll get in orbit. So...

1st stage

TR18A decoupler - 50 kg

Mk I Jet Fuselage - 1100 kg

Turbo Jet engine - 1200 kg

Raidal Air intakes [6] - 600 kg

Total: 2950 kg

Total with space craft and 1st stage: 5300 kg (a bit more than an FL-T800 but not that much more!)

The turbojet produces about 100 kN at take off, enoug for a comfortable lift-off. With four air intakes the flame-out is a smidgen too early and makes for a very tight orbiting run, but six intakes are just enough to get you to 20 km at over 800 m/s, and hardly any fuel used.

Ermged showing off the small size of this Mün-going combination

One of the probes in a 25km orbit above Mün. The sepratrons where an experiment to see if I could add a little boost on my Mün-burn (as opposed to a dozen rotations & burns with the ion engine) but that did not work as expected (probably due to the asymmetric mass distribution). It was fun to see the probe flying around like a balloon, but it didn't really add any relevant delta v. Oh well, we learn

[CaptainArchmage]

You can attach the RTG in series with the xenon tank and ion engine at one end, and the Z-200 battery at the other. That would deal with your center of mass.

[TheWanderer]

dont know why this is not more popular, works really well and looks cool too