I'm gonna use the reentry MFD (you can find it here:
http://www.orbitermars.co.uk/) to get the right deceleration rate - I'm not sure how the reentryMFD was built, but I think it's pretty simple: it knows my speed, the distance to target and uses the info to tell me the required deceleration, heading to print a simple reprezentation of my landing spot etc. (more later). Obviously, you can do a reentry without it by looking at the map but you need alot of practice and math.
Start a scenario where you are in orbit docked (I've used both docked to ISS / MIR , any scenario will do). Nose cone, get the MapMfd and allign with Cape Canaveral (if necessary) bla bla bla...
Do the deorbit burn on the other side of the planet (if you are at abot 300-320Km altitude). We'll see later that the deorbit point is not that crytical. O, and stop the burn when PeD reaches about 60 Km (the old get into atmosphere to slow you down thing).
Now open the SurfaceMFD and ReentryMFD. At about 105Km turn off prograde and do something to keep an AOA of 18-22 (not that crytical). About "doing something": I'm using the AeroBrakeMFD (
http://www.orbithangar.com/searchauth.php?search=gp) to keep my AOA since it has an autopilot. I could use the DGIII's autopilot but it is not that acurate and I only want to use the AOA autopilot and do the banks myself (you should use the DGIII's autopilot 'till you understand what's going on). I'm gonna use the Kill Rotation to help keep the AOA since the AeroBrake's autopilot is not that efficient (fuel consumption: after landing I had 77.1% RCS left and I started with 100% so the reentry was pruity efficient). You can see your AOA on the lower-right corner of your SurfaceMFD (AOA, deg, 18 on my screenshot). Leave the Bank angle to 85-90 deg.
Important:
- the cross on the ReentryMFD is your ship and the dot is the target (Cape Canaveral). If the dot is on the lower side of the MFD you will overshoot (pass) your target, if it is on the upper side (on top of the +) you will come short (not reach the target). The same for right and left. Take your time and understand this, it is important. Just remember the target is the circle.
- Use the BSE button (ReentryMFD) to select the base. Cape Canaveral is the last one in the list, after Habana.
- Decel Act (screenshot: 5.762, same as ACC, m/s2, lower left corner, surface MFD wich is actually the acceleration but since we're braking is negative) is the actual deceleration. Decel req (5.783) is the required deceleration, stick to it and you'll drop on target (not really, more later).
Now here's what's all about, I didn't found a tutorial to tell me this so it was a "long way home" for me, that is if I got to land and not burn. The vessel looses lift since it's not a plane anymore, but a hevy object without wings. Gravity pulls you down and your wings do not sustain you. So at those speeds you will use the AOA to slow you down and the Bank to loose altitude. Why loose altitude? Whell, you will get a higher deceleration at 50 Km that you would at 80 Km (air is denser at lower altitudes). And by banking you actually increase the distance to your target. So there are 2 choices: use a high AOA (let's say 30 deg) at a high altitude (let's say 75 Km) or a lower AOA (18 deg at 60 Km). The choice is yours, I preffer using the altitude to slow me down.
Back to our tutorial: You are at about 105 Km, an AOA of 20 deg, 85-90 deg bank (left if the circle is on the left side of the ReentryMFD). We're using a high bank because we want to drop fast to about 65 Km to decelerate. AOA of 20 deg to decelerate more effective (you could use 0 deg Aoa and air will still slow you down at 50 Km but not fast enough, that's why we're using a high AOA).
As you drop to about 90-85 Km the Decel Act will get higher (we found some air and decelerating). Our main goal is to get it just above Decel req's value. Do that by going at a lower altitude (to find some more air). Also, check out the VS on the SurfaceMFD (VS, m/s, -6.68 in my screenshot). This value shows you how many metters/second you are droping (loosing altitude). At about 90 Km it should be -100 to -80. Up to about 75 Km it will increase (-75, -60), then start droping again. This value is the one to watch. If it gets too high (-50 or below) the vessel will heat up. The vessel will keep a constant temperature at a value of -20 and start decrease the temperature at higher values (if the value is higher than 0 you will start bouncing back into space).
So let's say you are about 70 Km high. The VS is about -70 (droping fast) and the temperature increasing. By now the deceleration (Decel Act) should be high (let's say 4.01). The deorbit burn was to late and Decel req is high (let's say 8.0 and increasing because our actual deceleration is lower: 4.01 < 8.0). Decrease the Bank angle (from 85 to let's say 60) until the VS starts to get higher but find the bank angle that will kepp it lower than -40. You're still loosing altitude, heating up (but not so fast since VS got higher and friction lower) and in the same time decelerating fast. When the Decel Act is over 8.0 or so decrease the bank angle since you found the optimal altitude for braking. Keep the Decel Act over Decel req until the Decel req decreases to about a safe 5.0 to 4.0. If the Decel req is too high you will need to keep the Decel Act to about 9.0 to get some fast deceleration (that means getting a lower altitude or higher AOA). During the deceleration keep the VS constant at about -20, -10. The temperature will be constant all the way.
At one point you will get something similar to my screenshot: My Decel Act is 5.762, the Decel req is 5.783, 1.728 Km from base (all reentryMFD), the VS is -6.68 and I am at 63.50 Km altitude (surface MFD). The actual deceleration is lower than the required deceleration wich is 5.783 (too much, I want it between 5.0 and 4.0, I will tell you later why). To decelerate some more I will bank some more (current 57 deg left, 58 deg will do) to get a little lower into atmosphere (VS might get to -7.0). When the deceleration is higher than the required deceleration stay at that altitude (banking more or less as required). Because the AOA is pozitive and you are banking you will start to "steer" the ship as you get more lift. Bank the other way when the circle (reentry MFD) stays too long on the lateral side of the mfd (remember the circle is the base displayed relative to your ship, LIVE - not projected, more later). Check out the temperature: 259 deg at max, the ship is "freezing" althought I am decelerating fast. In this reentry the flames never showed.
Let's review:
- 300 - 360 Km alt, deorbit burn on the other side (not that vital but do not exagerate)
- 105 Km high (6000 - 4000 distance from base, map MFD), get an AOA of 15 - 20. The old 40 deg AOA (most tutorials) is way too high. The autopilot can't keep it, at lower altitudes the nose will drop and the surface MFD will show an AOA of 11 at it's best. That's the actual AOA and not 40 deg, the value that the autopilot is trying to achive. Usng my techniques (altitude to brake and a close to 0 VS) I was able to mantain 18 deg AOA all the way.
- As you drop (loose altitude) you will start to decelerate. Stop the "dive" when the Decel Act is higher than Decel req (getting the VS to about -10 to 0) by banking less. If the decel act is too high get some more altitude (VS > 0) to brake less. You found the optimal altitude for braking. Bank the other way if the circel (reentry MFD, the target) reaches the side of the MFD. Tip: before changing the bank check out the current bank angle, lower the VS to about -40, reverse the bank at the same angle. If the VS hasn't got back to the previous value do the necessary adjustments. Keep the VS higher than -20 and the temperature will start to drop.
Now, this is the final aproach. The reentry MFD doesn't really care where you will find thick air to slow you down, so if you decelerate his way you will be on target (I guess the VOR) but not on the runway at a 0 Km/h speed. Not what we want, ha? Plus, as you get to a lower altitude (< 25 Km) the actual deceleration will get so high that you will not even reach the target. So ignore the decel values from about 0.600M from target (Base D, reentry MFD, 1.728 on the screnshot). The idea is to get the speed to about 1000 m/s (GS, surface MFD) at 0.100M from target (100 Km). That's why it is important to get a required deceleration of about 5.0 - 4.0 by 0.800 km from target, so we can brake if necessary (by lowering the altitude). In the same time, if we brake too much we can get to a higher altitude and brake less verry fast. So keep the decel req between 5.0 and 4.0 by 0.800M from target.
If you did everything the right way and you are at 100 Km from target at about 1000 m/s (2 - 3 mach); wait until you reach about 30 Km distance to target. You should be at about 30 Km altitude. Lower the AOA all the way from 100 Km even more if necessary so the deceleration gets to about 2.0, 1.0 and you don't drop too fast (VS < 100). I've reached 100 Km at 0.800 m/s once and I was sure I wasn't gonna get to the runway but I found the best AOA (about 6 deg) to get the best lift and the less deceleration. At 30 Km from the target nose dive pointing the velocity indicator on the middle of the runway and keep it there. As you reach 20 Km or less altitude you will decelerate fast and get to about 250 m/s, a low speed (about 0.7 mach). Don't worry, it will stay there since you are dropping fast and the atmosphere is slowing you down at the same time. The rest is practice, landing without thrusters mainly. You can start by reaching 100 Km distance from target at about 1200 m/s or higher, I used lower speeds to get the most out of the handling. Stay as much as possible at a high altitude (30 Km) to get closer to the target since the air at a lower altitude will slow you down way too fast. Make sure you have the right heading to land on the runway (use the reentry MFD).
So this is it: use a low and manageable AOA (20 deg or less), use the air at different altitudes to slow you down (change altitude by banking more or less) instead of modifying the AOA, keep the VS as close to -5 as possible when you found the best altitude (to slow down in a constant way) and the temperature will drop, bank from right to left to stay on course, ignore the decel values at about 0.700 Km from target (get there at about 4.5 decel req), get at 100 Km from target at 1000 m/s or so and lower the AOA if necessary to stay at 40 Km - 30 Km high, at about 35 - 30 Km from target point the nose to the target. That's it. Remember that the braking itself does not heat up the ship to 1500 deg, but the dropping rate (VS), don't drop too fast (-100 or so) if not necessary!
I know this is a hard to understand, the tutorial might not be the best, I can't explain better. But I hope it helps those who don't want to just use a MFD to do a reentry and want to actually learn something about what's involved. Once you do, you'll do wonders: 600 deg max temp all the way, manage the time you will spend with the reentry, you won't even have to use the reentry MFD once you know what's the speed you should reach at a certain distance from target. That's it, VS and altitude.
. I haven't read it in any great detail but some comments from the brief look I had:
. I'll change all of it. Why I said forty two degrees is because that is ISS heading and most missions are to it. What font should it be?
