Spaceplane reentry

[SingABrightSong]

While I'm sure it varies by design, as a general rule of thumb, how should I go about deorbiting a spaceplane or space shuttle so that I can land it at the KSC runway? Assuming a 100x100 prograde equatorial orbit, at what longitude should I make the burn, and what should my periapsis be before reentry?

[FancyMouse]

My experience is to deorbit so that the blue orbit line is slightly overshoot KSC. I don't look at periapsis. I'm not too picky about the phase angle to initiate deorbit burn - I don't feel difference between 90 degree to 120 degree.

During the hot period I usually watch the vertical speed in KER. Between -100m/s~-200m/s is a reasonable range for this trajectory.

Then down to 20km altitude, I always use the waypoint I create at the runway - I use Waypoint Manager to track my distance to the runway waypoint. I watch for 100km distance @ 1km/s speed. Faster than that at 100km - need to slow down more effectively. Farther than that at 1km/s - might want to stay in upper atmo and reduce drag to glide further, and if necessary start the engine on LF.

This strategy works pretty well for me. I almost never overshoot, and I only once a while need a little bit of LF to reach runway. More than half the time my plane just naturally glides all the way to landing without consuming any of my emergency LF.

Edited November 11, 2016 by FancyMouse

[bewing]

Actually, the design makes a gigantic difference. Also the Ap altitude. Also, your patience and preferred flying style.

Your spaceplane can either be really sleek, or really draggy, or something in between. It can have a lot of wing area, or hardly any at all. It can have a lot of reaction wheel torque, or hardly any at all. You can come in very shallow, and bleed off orbital speed and heat slowly, or you can come in like a rock and hope that the drag will stop you before you blow up. Your spaceplane can be very massive on reentry, or extremely light. You can go with a heat resistant design, or one that is very sensitive to overheating.

I build the lightest sleekest spaceplanes that I can, using MK1 parts -- with as much wing and reaction wheel as I can reasonably do. Many of my spaceplanes are very sensitive to heat. I use a very shallow reentry. I usually put my Pe somewhere between the beginning of the Great Desert, and the Great Bay in the middle of the Great Desert, at about 59km altitude. I hold a radial out orientation as long as the reaction wheels can hold it. I'm looking for a Surface speed of about 1900 m/s at the west edge of the KSC continent, and about 1500 m/s at the mountains just west of KSC. When I can get away with more heat resistance, I put a klaw on the nose. That gives me some more leeway for a lower Pe, at the east edge of the Great Desert.

But really, the only way to find out is to try it once. Take your plane to orbit, pick your favorite Pe straight above KSC, then see how many kilometers you overshoot by. Then subtract.

 

 

[SingABrightSong]

2 hours ago, bewing said:

Actually, the design makes a gigantic difference. Also the Ap altitude. Also, your patience and preferred flying style.

Your spaceplane can either be really sleek, or really draggy, or something in between. It can have a lot of wing area, or hardly any at all. It can have a lot of reaction wheel torque, or hardly any at all. You can come in very shallow, and bleed off orbital speed and heat slowly, or you can come in like a rock and hope that the drag will stop you before you blow up. Your spaceplane can be very massive on reentry, or extremely light. You can go with a heat resistant design, or one that is very sensitive to overheating.

I build the lightest sleekest spaceplanes that I can, using MK1 parts -- with as much wing and reaction wheel as I can reasonably do. Many of my spaceplanes are very sensitive to heat. I use a very shallow reentry. I usually put my Pe somewhere between the beginning of the Great Desert, and the Great Bay in the middle of the Great Desert, at about 59km altitude. I hold a radial out orientation as long as the reaction wheels can hold it. I'm looking for a Surface speed of about 1900 m/s at the west edge of the KSC continent, and about 1500 m/s at the mountains just west of KSC. When I can get away with more heat resistance, I put a klaw on the nose. That gives me some more leeway for a lower Pe, at the east edge of the Great Desert.

But really, the only way to find out is to try it once. Take your plane to orbit, pick your favorite Pe straight above KSC, then see how many kilometers you overshoot by. Then subtract.

 

 

Fair enough. In any case, I've discovered that the Trajectories mod has tools for planning a reentry profile.

[AeroGav]

8 hours ago, SingABrightSong said:

While I'm sure it varies by design, as a general rule of thumb, how should I go about deorbiting a spaceplane or space shuttle so that I can land it at the KSC runway? Assuming a 100x100 prograde equatorial orbit, at what longitude should I make the burn, and what should my periapsis be before reentry?

Heat seems to have been lessened in 1.2.    Bringing a design with a mk1 cockpit back from low kerbin orbit is quite safe now, even if your PE is zero, provided it's an inline cockpit.   The further back you mount it the better it seems, also attaching parts with high heat or radiative capacity direct to the cockpit helps.

ie. wings - attach the largest wing segments you can direct to the cockpit, even if you then offset them elsewhere, the game still sees they are neighbours in the part tree.  Wings have the highest radiative dissipation values.

jet engines - engine nozzles are the next best thing for getting rid of heat.

Intakes - after engines and wings, they also radiate well

fuel tanks - they don't radiate much but they have a high capacity for heat and take a long time to warm up.  Transfer any remaining fuel to tanks attached   to the cockpit before re-entry.

 

Hitting KSC

Like Bewing says, aim for the big desert.   If your PE is high, aim for the furthest end from the space centre, if you retro burned to 0 altitude or something similarly hardcore, you want to aim for the closest end to KSC.

Use your pitch angle to control the glide ratio.

If you are undershooting or concerned you might be,  keep the nose pointing about 7 degrees above prograde (in surface mode) because this is the AoA where your glide ratio is best.  You will find that the blue line starts moving east when you are flying like this, because the blue line predicted trajectory is a ballistic one, it doesn't realise you are flying a glider.

When the blue line starts to overshoot the space centre, pitch UP.   Higher AoA give more lift and initially, your descent rate might decrease , you might even start heading upward again.  But your lift:drag ratio and glide angle will get worse long term and the blue line will start going back west.

Pitching UP is better to DOWN or turning LEFT/RIGHT in my opinion, because unlike the other two it brings you into thinner air where heating is more gradual.    

If you are overheating, also pitch up to like 20-25 degrees above prograde.   This is maximum lift, and will keep you out of the thicker part of the atmosphere until the lowest possible speed.

 

Edited November 11, 2016 by AeroGav