i need help with reentering the atmosphere with the space shuttle

[Star explorer]

i know how to select the target landing point and wait until my orbit is over the place im going to land. i need help with when to start the retro grade burn so i reenter over KSC

 

[ar81]

I usually start deorbit wneh I am in the opposite side of Earth.
I try to stay low, between 150-200km for Earth.
I use BaseSyncMFD and AerobrakeMFD.
BaseSyncMFD allows you to align with your base, and AerobrakeMFD makes you to land at the precise spot since it calculates aerobraking trajectory for a given angle of attack.

 

[Star explorer]

i have aerobrake MFD i just dont know how to use it very well

 

[ar81]

If you select your target TGT base, it will tell you where the impact point is.
If you select CNT you can center around the impact point, and if you zoom in Z+, you can see if there is a gap between impact point and your base. You can see your trajectory until it hits surface. Your base is marked by a line coming out from center of the planet to the surface.

 

[V8Li]

Use the ReentryMFD from http://www.orbitermars.co.uk/ . I've used AeroBrake too, it's just gonna confuse you even more since it projects the path live. Example: if you bank 2 deg to the left it will show your path as if you were gonna bank all the way until touchdown, which doesn't help. Again, trust me, I've perfected reentries since it's my favorite maneuver, you will just get confused and frustrated using the Aerobrake MFD especially if you're new to all this.

Here's how I do it:
I use the XR1 but it applies to all ships. I always start from a 150x150Km orbit. When the path crosses the base, I wait until I'm on the other side. Then I watch Reentry MFD (set it for the base first) until it shows a Required Deceleration of 2.2 . That's usually 12k Km from base. I lower the Pe to 20Km altitude. By the time I hit the atmosphere (70Km) the required deceleration would have reached 10m/s and that's easy to keep (let us know if you don't know how to keep a constant deceleration by banking and using diff AOAs and someone will explain it to you). I never got the temperature higher than 800 deg C at the nose.

Again, use Reentry MFD or you'll hate life until you get it. I left Orbitersim for 6 months when I was learning because I was always either burning up or not hitting the base. I've never missed a reentry ever since, it's not some abstract art that seems at first, everything makes sense. Aerobrake is OK for the Moon or something like that but it'll mess things up on Earth and will just confuse you if you don't know what reentries are about. It's not a learning tool.

 

[ar81]

It is curious, I love AerobrakeMFD and I never got to use Reentry MFD properly.
The problem I had with Reentry MFD was that it may show you how much braking you need, but I used to overshoot the target because I did not get to have enough drag, or I had too much lift.
I see Reentry MFD like a more complex MFD in a way, but that's me.

 

[Whatu]

IMHO, Aerobrake projecting the path 'live' is its best feature. You just manouver a bit to see how the path behaves, and when you got the hang of it, it simply the perfect tool to enter atmosphere, because it allows you to see how any slight attitude difference affects your actual path. The only thing you have to be careful is to "aim long" in the first de-orbit burn, because the path will be shrinking constantly, I believe due to your ship being slower everytime it calculates.

I love Aerobrake too :lol:

 

[astrosammy]

Yes, Aerobrake MFD is very nice. But the problem is if you use an Apollo-like ship that it calculates the tajectory of the whole ship before seperation, so after CM separation you will have an completly different trajectory.

 

[V8Li]

Ok, I've made a quick playback (attached) in case you need extra help. I was in an orbit for the Moon so at the retrograde burn the path was not exactly over KSC but if you have the Map MFD on you can see how I change the trajectory during reentry.

I've used the stock DG with deltatweak 2.0 ( [ame="http://www.orbithangar.com/searchid.php?ID=2648"]DeltaTweak 0.2[/ame] ), I don't know if it's a must, however if you get a CTD or it's messed up get it, the playback might need the same aerodynamic properties for the ship.

Turn that option to run at playback speed off and load the Map MFD and Reentry MFD and set Cape as target in both of them. Turn the "run at playback speed" on and wait to see where I burn, check Decel req mainly and position from base. I'll set the Pe to 20Km. Set the Com/Nav and HSI now if you use them.

I've used the HUDdataMFD to get on screen these important values: Vertical Speed, Vertical Acceleration, AOA, G force and Acceleration. You can get all those values from Surface MFD but you'll get a free MFD if you use the HUDdataMFD.

During reentry watch the Vertical Speed value. When you see that I keep it >-30 m/s it means I want to keep the acceleration (deceleration actually) constant. During the innitial phase I'll play with the yaw and bank to see how those affect the Vertical Acceleration (and in turn Vertical Speed).

I wanted to finish the reentry quick so I was too fast at about 300Km from base. No problem, you can always do a bigger S turn and cover some more distance that way (I've pulled 6Gs dough).

So, during reentry watch the Decel values from Reentry MFD and the Vertical Speed. If I want to decelerate I descend into thicker atmosphere by banking (and in trun by decreasing the Vertical Speed). At one point, at about 500Km from base you will see that the actual deceleration is well higher than the required deceleration. It's because I want to decelerate fast, the goal is to get the required deceleration to about 5 at 500Km from base. To hit the base right you should be at about 800-1000m/s velocity at 120Km from runway (25-30 Km altitude). In this mission I will approach at a heading of 150 deg; the VOR at KSC is about 20Km away from the 15/33 runway so if the VOR shows you're 100Km from it, you're at about 80 from the runway. Landing and final approach is about practicing anyway.

If you think it's to chaotic I'll make a cleaner playback with the XR1 since I'm used to it. However, the first part of the reentry demonstrates the concept and should be enough.

Replay it with Aerobrake MFD if you like.