"Impossible" Feats (Jool SSTO)

[Lt_Duckweed]

As the game has evolved, there have been many things that are commonly considered, or were once considered, impossible, until someone (often Brad Whistance or stratzenblitz75) proved them possible.

Examples would be "no SSTO from EVE", "no SSTO from EVE sea level", "no orbit on only ions", "no SSTO to Tylo and back".

What are some other once though "impossible" feats, and what are examples of them being beaten?

 

I'll go first:

"SSTO from Jool is not possible"

This is a stock+dlc SSTO from Jool's lower atmosphere.  (Admittedly a ton of part clipping)  It has 17 RTG's powering 2 medium rotors with 24 of the largest fan blade each, giving it a top speed in Jool's atmosphere of 440m/s at 115km.  Fuel is provided by 32 mk1 liquid fuel tanks clipped into the fairing, 14 big-s wings, and 4 big-s strakes.

It has infinite range  in atmo thanks to the RTG's, and can fly all the way down to 0 elevation, then fly back up to 115km.  At the time of ignition it has an ISP of approximately 558s, with a local TWR of 0.294, but by the time it reaches local mach 1 it has reached a hefty 0.389 local TWR and ISP of 636s.  After that point it's smooth sailing all the way to orbit, the low drag of the craft coupled with the high lift and the low heating of the Joolian atmosphere means that burning up is never a real danger, and it reaches a stable orbit with 452m/s of fuel remaining, 35 min and 1 sec after lighting the nukes.

 

There is still obviously a lot that could be done to refine this craft, for example, we have 17 perfectly good RTG's lying around, why not use them to power a couple of ion engines?  Likewise for the EC being provided by the nukes during the burn.  More wing + more fan blades might possibly allow a higher prop flight ceiling and top speed, potentially saving more fuel/dv on the early stages of the accent than it hurts you due to the extra dry mass, or even enabling dropping an engine (saving a lot of dry mass).

 

So the next question,  with further improvements is Jool sea level -> Kerbin possible?  1880m/s or so gets you a Laythe encounter, from which you can setup a good Tylo encounter for a minimal dv transfer to Kerbin, then perform a gravity assist to lower entry velocity enough to survive on the next pass, or setup a KKE if you want to be extra cautious.

[Lt_Duckweed]

Another possibility for improving this setup, offsetting the blades as far out as they can be while still shielded once the bay is closed could trade away low altitude performance (blade force, both thrust and drag, is farther from center of rotation, thus worse torque to thrust ratio, low altitude is almost always torque limited) for better high altitude performance (blade speed is higher farther from center of rotation giving more thrust per blade, and allowing lower angle of attack, meaning more of the produced thrust is prograde, drag is very low that high so we don't care so much about torque to thrust ratio).