Simple but fun; Dessert Airfield Race.

[boriz]

The smaller boosters don't gimbal unfortunately. I had to reduce the fuel and thrust on these.

[Ultimate Steve]

Here's my 7:39 or 7:42 run depending on how you count, in a ship I call the Pluto I as it kind of looks like a Project Pluto missile.

My strategy was to try to get as close as possible to the Rapier speed limit of Mach 5. Mach is higher lower down due to the higher temperatures, so the lower you go, the faster you can go, but then you run into heating issues. I attempted to make a decently thermally resistant craft using creative though not excessive node routing, without going into straight up total thermal/aerodynamic occlusion tech.

There is an additional bonus from flying low, the total distance traveled is shorter because the world is round.

The vehicle in question.

The Vector is responsible for rapidly accelerating the vehicle to about 1000m/s, which makes our time faster, allows the Rapier time to spool up, negates the need for landing gear, and gets the Rapier into the regime it works best at, avoiding the transonic doldrums.

After it is out of fuel, the Vector is jettisoned. The fuel tanks and engine are shielded from aerodynamic and thermal forces due to being in a fairing, and the forward fairing, heat shield, and intake are routed in a way where it is pretty aerodynamic and the heat shield takes the brunt of the heating, while still allowing the intake to work, though this is a little cheesey.

The first challenge is clearing the mountains and not going too high.

The next challenge is heat. If you wanted to, you could probably do the run without the elevons with a redesign, but the elevons are the limiting factor right now because you can't stick them in a fairing. 2-3km seemed to be the sweet spot, but I had to constantly manage throttle to keep the elevons from melting. A few runs were ended because of this.

Due to the adjustments required and the 1 degree resolution of MechJeb, at one point I tried 2 elevons in the middle to act as adjustible wings with the deploy function, but they melted very easily and were removed.

I was able to keep a cruising speed of roughly 1820m/s for the whole thing, up to 1830 at times, with the elevon overheat indicator between 99 and 99.5%, although the average was definitely slower as I frequently cut the throttle in a panic when the heat rose too high, and dipped down to the 1700s for a while, taking some time to recover.

The Pluto I is slowed down by blowing the fairings. I blew them a bit early here, so early I had to go to full throttle and pull all the way up to just barely reach the runway.

The parachutes are deployed in 3 stages. There's a drogue, which allows you some amount of engine control if you over or undershoot (the sideways runway is a very small target in this axis), the first main, which lets you pick your landing site for good (engine control can't do much after this point), and the other 2 mains, which were supposed to be deployed right above the ground to cushion the impact. Unfortunately, I came in too fast and deployed both of them early to slow down, so there were several seconds of falling.

Touchdown at 7:39.

Stable on the ground at 7:42.

This design can be improved perhaps down to 7:10 with better piloting - I did a very conservative approach and slowed down way too early. You can probably pass over the runway at full speed at 7:00 (no slowing down for landing).

There's not much better you can do with the Rapier alone without doing actual thermal exploits and I don't think that's within the spirit.

I suspect that this design is near a local maximum, and that the optimal design for the challenge is a gigantic booster pancake that goes high enough to avoid heating and drag.

Edited April 19 by Ultimate Steve