Shuttle re-entry basics

[george7378]

Hi all,

I have established that the shuttle needs something a little more than a high-angle, nose first entry. I tried this, but an AoA of about 0 was required to keep me on track on the AeroBrakeMFD.

I don't think this would be a problem if I could bank 90 degrees and angle my nose perpendicular to my direction of motion, but surely this would cause heat problems.

 

[agentgonzo]

With the shuttle, you want an AoA of about 40°. You will find that this gives you too much lift and will bounce you back out of the atmosphere, so you will need to perform roll-reversals: bank over to about 60° for a bit, then bank the other way. This will bleed off your speed without chucking you out of the atmosphere.

 

[ex-orbinaut]

Similar question. Something that works for me? See this post. All the best...

http://www.orbiter-forum.com/showpost.php?p=116152&postcount=6

 

[george7378]

Thanks.

Back to the S-turns - do I just need to bank 60 degrees left, then right, without trying to turn (not adding back pressure apart from that required to maintain the 40 degrees AoA).

 

[Urwumpe]

Thanks.

Back to the S-turns - do I just need to bank 60 degrees left, then right, without trying to turn (not adding back pressure apart from that required to maintain the 40 degrees AoA).

Don't aim for an angle - open Surface MFD. Look at the acceleration reading - you want 15 m/s² (16 is a good one for all DG class vessels, most capsules fly at 40 m/s²). Now, let me shorten the physical explanations with:
You change the descend rate, and something magical happens, and then your deceleration changes.

You control the descent rate by banking - if your deceleration is too low, you bank slowly more (increasing your descent rate), if your deceleration is too high, you reduce the bank angle (lowering the descent rate by more vertical lift).

If your ground track is getting too far away from the target base (reentry MFD is very recommended for seeing that), you memorize your current bank angle and bank at the same angle to the other side.

If you have done this a few times, you can use the more accurate guidance data of reentry MFD for doing really pinpoint reentries by setting your deceleration to the recommended value of reentry MFD.

 

[george7378]

OK, so all I need to do, is maintain 40 degrees AoA, and change amounts of bank to control speed?

 

[Urwumpe]

OK, so all I need to do, is maintain 40 degrees AoA, and change amounts of bank to control speed?

Yes, that is the key trick - shuttle fleet does even have an autopilot to do the holding of AOA for you, similar features are in the DG-IV, and DG-XR series. For vessels without such an autopilot, you can have good enough flight control by selecting full up trim.

 

[george7378]

I am finding myself at bank angles of up to 120 degrees (in the stock Atlantis scenario "Re-entry 1"). Is this normal?

 

[V8Li]

Yes, that is the key trick - shuttle fleet does even have an autopilot to do the holding of AOA for you, similar features are in the DG-IV, and DG-XR series.

I'd suggest the XR1 since it (not sure if all the XRx do, haven't used them) also has an option to control the center of gravity which can give impossible AOAs and rock-solid attitudes. A fully manual reentry is EXTREMLY cool and easy with it.

 

[Urwumpe]

I am finding myself at bank angles of up to 120 degrees (in the stock Atlantis scenario "Re-entry 1"). Is this normal?

Not normal, but not extremely far away from normal reentry values - the real Shuttle does not exceed 100°, but you have different aerodynamics on the Orbiter Atlantis (only subsonic aerodynamics, with more L/D).

 

[george7378]

Thanks.

Just to let you know, I have already mastered re-entry in the Delta Glider 4, and the other fictional ships in Orbiter, which just require a level-winged entry, with deceleration controlled using AoA. I use them for regular trips to the moon and back. It is just the stock Atlantis I am having problems with.

Also, a DGIV question - can the weight of the vessel on entry affect the max. temperatures?

---------- Post added at 12:58 ---------- Previous post was at 12:50 ----------

Still no luck. Angles of 130-140 degrees don't work, and it is impossible to maintain 40 degrees AoA.

 

[DaveS]

The stock Atlantis do not have a proper atmospheric flight model. I suggest that you use either SSU or the Shuttle Fleet.

 

[Urwumpe]

Also, a DGIV question - can the weight of the vessel on entry affect the max. temperatures?

Yes, because it affects the gravity force on the vessel, while the lift function is not changing.

More weight => you need a higher speed at the same altitude for just countering gravity => you have a higher heat flux

Still no luck. Angles of 130-140 degrees don't work, and it is impossible to maintain 40 degrees AoA.

Do you start at full lift (wings level)? If not, do it and wait until you reached level flight (vertical velocity = 0) before you start to bank. And use trim, it makes things easier.

 

[george7378]

Thanks - I'll try it.

 

[Tommy]

Also, a DGIV question - can the weight of the vessel on entry affect the max. temperatures?

In and of itself, no. The DGIV can easily generate enough lift to keep itself high enough. You will need to lower the AoA to maintain a slow descent. Since a heavier ship won't slow down as quick, you'll need a slower descent rate than in a lighter DGIV. The same 1 to 1.2 degree reentry angle can be used - a fully loaded DGIV can survive a 5.75 degree ReA from 375k orbit. Empty (just enough fuel to keep the alarm from sounding, no cargo) you can reenter at 6 degrees, 6M from the base!

The main thing is to control the descent rate. This has to be don indirectly - by using changes in AoA or bank to control VACC. Never let your VACC get to big or you will have a lot of VS before you get it under control.