How do I deorbit at a lower angle?

[Gonzxor]

Been trying to undock my space shutte from my ISS Replica.

So far, I turn the opposite way im flying around the earth and fire the two rockets on the top part of the rocket (near the tail fin)...That deorbits me, the only problem is that I come in way to fast and burn up.

Do I need to fire the rockets out a different angle or something? Also, im at a 400km orbit around kerbin.

Thank you alot

[Arkalius]

Well the 400km orbit is part of the issue. This will create a higher angle of reentry, and a higher speed at periapsis. What kind of periapsis are you using for reentry? You may want to go for 30-40 km. Also, be sure to try and hold a fairly decent angle of attack with your space plane. This will create more drag early on, bleeding more speed before you get into the deeper, thick parts of the atmosphere.

[kahlzun]

As he said, lower apoapsis or higher periapsis. You can also try burning 'up' as you start to enter the atmosphere.

Edited June 21, 2015 by kahlzun

[Old Foxboy]

If you don't have the Delta-V to lower your orbit first (to a 100x100 orbit for instance), you might as well perform a mini-aerobrake reentry. This is done by setting the periapsis to about 40.000 metres instead of 25.000. The lower density upper atmosphere will break you just a little bit without the whole barbecue effect

Your mileage may vary, depending on your craft and angle of attack. If you have a high AOA like the real space shuttle, you are braking much more than you would if you fly perfectly prograde (streamlined) through the atmosphere.

The missing tilt (AOA) might as well be the problem with your reentry, because your craft won't brake enough in the upper atmosphere and will roar down into the lower, burning up. Try to pull the nose up (with reaction wheels and/or RCS and SAS) to use as much aerobrake in the upper atmopsphere as you can.

If you want to see how the real thing flies, take a look at the "Orbiter" space sim by Martin Schweiger. It's Kerbal Space Program without Kerbal.

[Fearless Son]

I would echo Old Foxboy, you should try aerobreaking first. It does not have to be very deep, just lower your periapsis into the upper atmosphere, and go a few orbits like that to bring your overall speed down. Once you are low enough, you should have shed enough speed that your "full" reentry will not be going to fast as to encounter terminal levels of atmospheric friction.

Also, airbrakes are your new best friend, whether on spaceplane or rocket. Deploy those in the upper atmosphere to shed speed much more quickly, possibly avoiding even getting hot.

[ajburges]

Woha, what's with these low reentry Pe?!

From a 70² to 100² orbits, I use a 45 km Pe for a nice shallow reentry. 50 km would give a prolonged glide.

If you can't lower orbit to that level, do a "skip" reentry. Aim for 50-55 km Pe so that the first pass has you pass through the atmo on an even slower reentry.

[Old Foxboy]

Woha, what's with these low reentry Pe?!

From a 70² to 100² orbits, I use a 45 km Pe for a nice shallow reentry. 50 km would give a prolonged glide.

If you can't lower orbit to that level, do a "skip" reentry. Aim for 50-55 km Pe so that the first pass has you pass through the atmo on an even slower reentry.

It totally depends on the type of craft you fly. With a real Spaceplane, you might get better results coasting in the upper parts of the atmosphere. With a Spaceshuttle type of craft this isn't possible because it is designed to perform a controlled "stall" at high AOA through these layers and only transition to a real glide when all the braking and heating has subsided. If your craft can't hold this high AOA to brake in a way like this, you must of course follow a much shallower flight path because you are actually gliding it down all the way. However, you'll encounter much more heating this way, because you spend much more time in the heating airstream, because you don't brake enough.

Remember:

A) Gliding in the upper parts of the atmosphere = longer braking phase, less heating, but a longer duration of the heating phase.

Stalling into "lower" parts of the upper atmosphere (~25-30km) = shorter braking phase with higher intensity of heat but a shorter heating phase.

You have to find the equilibrium between those two solutions according to the design of your craft.

However, i prefer the low periapsis reentries for precision purposes. I can almost always nail a landing at KSC with my Spaceplanes, and the capsules come down just west of the coast of it. If you have a longer aerobraking phase, it's very difficult to predict the landing site.

[Juicy]

With a non-SSTO, I try to get in a circular orbit at around 100km. Next, when as my apoapsis, I lower my periapsis far enough, that I'd go under ~40 km altitude a bit before I pass my planned landingsite. It gives a pretty shallow re-entry, and with some practice, allows me to land not-too-far from where I want to land (like, less than 25km, which is close enough for me to grab a rover and pick up the data from a probe)

[Snark]

If you're in a fairly high orbit (like 400x400), and you want to go home with minimal dV requirements and minimal "barbecue factor", the most efficient and safe thing to do is this:

1. Do a single retrograde burn (i.e. directly opposite the direction of your orbit, like you're doing already), to lower your periapsis into atmosphere.

2. However, don't lower it very far into the atmosphere. That's your problem, 25 km is too low.

As for "what altitude is best": You have a couple of choices, multi-pass or aerobrake-to-land.

The multi-pass (a.k.a. "super cautious") approach is to keep it really really high, like in the 45-50 km range. That won't take you to the ground, it'll just lower your apoapsis a bit. You can then do multiple aerobraking passes until you're down around a low, nearly-circular orbit. In practice, I find that I never need to do this, Kerbin reentry is fairly gentle.

The brake-to-land approach is to just hit atmosphere and go all the way down. Really, you should be fine with this, just don't aim too low. A periapsis of around 35 km should do it. As you enter atmosphere, make sure you point retrograde during reentry (i.e. with your engines pointing forward), since those have a lot of heat tolerance and are the least likely to blow up (and, if they do, they're the most expendable).

[Bosun]

My first Space Plane design in Mk 2 parts just burned the whole way to the ground. Didn't break up or blow up, just burned a nice, even, 2400 m/s all the way into the hills. Had a nice, shallow AoA and pitch, coming from about a Pe of 109k

Hmm....

[Prepper-Jack]

If you have the extra fuel to spare, you can burn somewhere between retrograde and radial to lower velocity while keeping periapsis at a reasonable level.

[Nich]

if you come in too shallow you should pitch down this way your lift keeps you from going back up and bleeds off speed at the same time. This method can also be used to sling shot off planets with atmospheres however getting the maneuver right is VERY difficult.