[1.1.3] Spaceplane reentry with RSS+RO (FAR & deadly reentry)

[CorvusCorax]

Problem

1. RSS & Realism Overhaul (at least FAR+ deadly reentry) installed - game version 1.0+ (tested in 1.1.3)

2. You got an airplane (anything landing horizontally) into low earth orbit

3. You want to get it back down without burning up.

Usual outcome:

Let's assume, you finally got a craft flying in FAR at both subsonic and high Mach speeds and even have thing not spinning out of control during reentry attempt.
As soon as you try to reenter at LEO entry speeds (~8000m/s ish) stuff simply overheats and explodes :-(

Howto do it anyway:

a) Procedure:

You can't use ablative heat shields, so you'll want a very shallow lifted reentry with as low an initial speed as possible, so the heat load can dissipate. You really need to fly the craft all the way down from orbit using a steep AoA to get a detached bow shock and limit overheating.

1. Get Apogee of your orbit to under 200 km above earth (propulsively or with very careful >100 km perigee atmospheric breaking if you dare) Otherwise your reentry speed will be too high and you will overheat before you even get enough lift to fly.

2. Get your perigee at 70 km or below (very shallow reentry)

3. Make sure the reentry shock front is detached. If your plane is pointy in flight direction (MK2 cockpit - good for supersonic performance on ascent but too pointy for nose first reentry) then you need to fly with high angle of attack to form the shock front on the bottom of your plane (20°-30° AoA or even more!)

4. At 80-90 km altitude you will start to get significant lift (at speeds exceeding Mach 20) keep pitched up to control vertical speed. Try to sink as slowly as possible, don't exceed 100 m/s vertical.

5. Keep flying with high AoA (blunt shockfront, high drag, lots of lift) and low vertical speed. If you can force a shallow climb, do it. It will bleed speed even faster. You will likely end up between 60km and 70km for seemingly ever. The reentry corridor might span 1/3 of a whole orbit from initial reentry until you are slow enough to fly circles or change direction.

6. Once you are below 3000 m/s you basically made it. You can trim down the AoA and descent more aggressively and maneuver around.

b) Craft Design:

1. All "exposed" components should be able to sustain 2500K surface heating. WARNING: Most RCS thruster pods are not, might have to be placed in the back of the craft, above wings or similar to be shielded from reentry bowshock. Most engines also can't survive that much heat and need shielding from front and bottom (like the Shuttle's SSME) -- Hint: Small Landing gear pods can only sustain 1500 K, you'l likely need medium or large unless you reenter bottom up to shield them.

2. The plane must be aerodynamically stable at subsonic (for landing), supersonic, and hypersonic speeds in rarified atmosphere. You can test that with suborbital flights not exceeding 3000 m/s going up to 60-80 km. Many MK-2 fuselage planes tend to enter a flat-spin in thin upper atmosphere even though they are stable further down. I solved that with "SpaceShip 1" style tail-booms, with SR-71 style tail fins on them ... even though they aren't foldable, they gave me both enough tail stability and enough control authority for #3:

3. You need to find a way to trim the plane for extreme AoA flight aerodynamically, so you need quite a lot of control authority. If the airstream at Mach 20 wants to bring the nose down, you can't fight it with RCS for long. Even in this configuration the plane needs to be semi stable (stable enough that SAS can keep it from spinning out of control) - in a nutshell that means you need forgiving stall behaviour (since you basically reenter high-speed-stalled)

 

Example:

Flight with large AoA (22°) and level flight - at this point already descended to 65km and 6100 m/s:  (At this point also my bow and mid section RCS thrusters had all but vaporised, only the three at the tail remained.  FAR and deadly reentry have a habit of overriding your decision where to place RCS thrusters in a very convincing way )

This shuttle can sustain flight at +20° AoA thanks to setting of max control deflection (40°) and AoA setting -200 on the tail boom rudders.

SAS is only used to keep roll and yaw centered.

Tail rudder trim reset to zero AoA and 15° max deflection once speed below 2000 m/s, SAS no longer needed (self stable)

In this flight I overshot my landing site by more than half a continent and ended up in the middle of the Indian ocean. I managed to ditch the craft with onlyminor damage (ripped one of the tail fins off, but the fuselage and wings held, Jeb was fine )

Edited August 12, 2016 by CorvusCorax
spell corrections, more fun details