Reentry with Delta Glider IV - when to burn Retrograde?

[Joey]

Hi folks,

so this is my very first post.
First of all: I really like this forum and it already helped me alot, BUT there is one tiny thing (among a bunch of others) that I don't get.

I start a scenario with Delta Glider IV, lets say "Docked to the ISS". I start the normal procedure:
1. Undock
2. Close Nosecone
3. Map MFD -> TGT "Cape Caneveral" (Oh boy... is this the right way to write it? )
4. Burn Normal or Antinormal to get my orbit right above (attention!) KSC ;-)
5. Turn retrograde
6. Program autopilot for reentry (I think Pro104Spec40)

Now the problems normaly start. When do I have to burn retrograde? I know that the correct angle for the reentry is about 1° to 1,5°. BUT what about the distance to KSC?
Is the point of burning somehow connected to my height?

I don't get it and I hope you understand what I mean.

Cheers

Joey

P.S.: I'm german. Please excuse the mistakes

Edit: Forgot to mention: Of course I would like to land exactly on the runway at KSC!

 

[Tommy]

Where you perform your de-orbit burn is related to your orbit altitude. From a 200k orbit, you can de-orbit as close as 12.40M from your base if you manage the descent expertly, although doing it over 14.20m away will let you have a shallower re-entry with less risk of burning up.

Form an orbit of 350k or higher (like when you come from ISS) de-orbit while 17.20M from your target, or more, and burn until you have a re-entry angle of 1.2 degrees.

I recommend using AerobrakeMFD for re-entries, it will help you get spot-on re-entries that allow unpowered landings. With AerobrakeMFD, from a higher LEO (350k) you can de-orbit while directly opposite the target, and Aerobrake will let you manage the braking so you will reach the base and not overshoot.

The main thing is that it's better to de-orbit too soon, than too late. You can use a shallower AOA and extend a re-entry quite a long way, but trying to shorten a re-entry usually results in a fireball.

 

[Joey]

Hey Tommy,

thank you for your reply. I'll try it today as soon as possible.
One question though: How do you know these distances? Try and error? Or is there a chance to calculate them?

Greetings

Joey

 

[Tommy]

Mostly trial and error. The 17.20M comes from the DGIV's manual, in the section covering the Re-Entry AutoPilot (PRO 105 SPEC 50)

 

[WombatControl]

The Map MFD will show you the distance you are from the surface base.

I recommend the BaseSync MFD, that lets you get a precise course to the base and also lets you know how much burn you need to get into the right reentry angle.

 

[Interceptor]

I just wish they explained Base sync in the manual a little better.

 

[Tommy]

Check the bottom of this thread for a mini-tutorial on BaseSyncMFD:

http://orbiter-forum.com/showthread.php?t=5900

 

[Interceptor]

Thanks tommy