AttitudeMFD Entry interface not defined, why?

[diegorodriguez]

I keep getting this message when the counter hits 0 and the altitude is somewhat 99 km, no matter if I press HLD or REF, so I basically have not a chance to use it so far for re entry.

Why can that be? Am I missing something?

Thank you,

Diego

 

[Rtyh-12]

Could you give us a some more details please?

 

[diegorodriguez]

Yes.

I undock DGS from ISS, make a retrograde burn to de-orbit and start getting time and angle from the Entry Interface mode. So I press Hold in order to keep attitude during entry, but when counter hits 0, at an altitude of about 99 km, 'Entry Interface Undefined' message appears and nothing else can be got from the Entry Interface screen. Vessel keeps plunging into atmosphere without any rection from the Attitude MFD.

 

[Tommy]

At 99km, you are below the re-entry interface. You have passed the Entry Interface, and it's no longer relevant. Attitude should be relative to the velocity vector (ie, Angle of Attack) during re-entry.

 

[diegorodriguez]

I got 99 km as entry interface altitude from the Attitude MFD manual. What do you mean by that?

At 99km, you are below the re-entry interface. You have passed the Entry Interface, and it's no longer relevant. Attitude should be relative to the velocity vector (ie, Angle of Attack) during re-entry.

 

[garyw]

Entry interface is at 120km. It's an arbitrary number based on 'roughly' where the serious atmosphere starts.

What vehicle is this? I'm still at a loss as to exactly what the problem is. Attitude MFD isn't (as far as I know) usable for re-entry. You are better of trying aerobrake MFD.

 

[diegorodriguez]

Using Delta Glider and Attitude MFD in Entry Interface mode to 'keep attitude defined by the velocity vector and local horizon at entry interface. Currently, this feature is only supported for elliptical orbits reentering the Earth's atmosphere (defined as an altitude of
approximately 99 km above the Earth's surface)', from the manual.

I get an elliptical orbit when undocking and de-orbiting from ISS via retrograde burn.

 

[diegorodriguez]

Ok, now I understand how MFD Attitude works in mode Entry Interface:

Whenever your are heading for an atmosphere entry at the defined 99 km height, MFD Attitude calculates the entry angle and the time to get there. Once the vessel reaches that point, it stops calculating and holding desired entry attitude unless another entry interface can be calculated, for instance when the vessel starts to bounce after a too low entry angle.

This feature is nice when you need to find a proper entry angle between bouncing and smashing onto the ground by means of try and error. You don't need to bother about pitch offset. Few seconds into the entry phase and the vessel gets its natural attitude. For DG, I have found this right angle to be between 5 (bounce) and 10 (smash) degrees.

 

[Poscik]

During deorbit, just lower your perigee to about ~50km. Entry interface display should become active. If data satisfy you, just turn it off. It gives some useful parameters, but when time to Ei hits 0, it is no longer needed for the rest of your flight. Simply - after Ei it will not give you any data that may help you in rest of flight.

 

[Tommy]

I got 99 km as entry interface altitude from the Attitude MFD manual. What do you mean by that?

Entry Interface is set at different altitudes in different MFD's. Most use 120k as default for Earth - but 99k works just as well (if not better). It is the altitude at which the atmosphere begins to have a significant effect on your vessel.

Once you are BELOW the EI, it is no longer very useful as a reference for attitude control.

Below EI, you want to reference the attitude (pitch especially) to your velocity vector - to maintain a constant Angle of Attack.

I don't remember how to adjust AttitudeMFD to do this, but I know it's possible. Check through the manual for details.