Question IMFD and CalculationMFD - direct re-entry

[MeeexC]

Hi Guys,

I once some questions about two MFDs in combination with the DG IV.

1. The question has been asked before so similar, but is there a step by step guide on how you can do with the IMFD from the moon, for example, with one single burn a direct re-entry with then landing? I know the video from David C. but, he does it with the standard DG and I think there is more room for high ReA. My problems are the values: ReA, Alt and Ant. What should I take for DG IV in the Base App. program?

2. My idea was now another MFD to use for this task and I chose the CalculationMFD. First, I have an automatic re-entry of DG IV from the ISS to Cape Canaveral and recorded flight data. (Attached File)

Now I'm just thinking what point on this trajectory an ideal introduction for the DG IV's reentry program would be. (Perhaps a height of 150 km)
I then know the characteristics of the trajectory that I want to achieve. So I would now have the CalculationMFD write a program that performs a burn to convert the current trajectory in the desired one. Has anyone ever had experience with it? I imagine it like this, that I only have the Lat. and Long. of the base that I want to fly and the program calculates the burn and runs it through. In a first version you should not be able to exert any influence on flight time, etc. the program optimized according to the lowest dV.

Regards Max

 

[dgatsoulis]

Regarding question #1, the only thing different from David's vid, when you are flying the DGIV, is the periapsis altitude. In the video we went as low as 60 km; with the DGIV you don't want to go lower than ~67-66 km. You'll also want the ship to be light, so it's good to dump most of the main fuel before reentry.
ReA (~1.5°) and Ant (~45°) are fine, no need to change them.

The whole method (single burn from the Moon for a direct reentry at the target base of your choice), presupposes that you already know how to perform a direct (inverted) reentry.
If you don't know how to perform one with the DGIV, say so and I or someone else on the forum will provide some more help.

 

[Siliconaut]

Regarding question #1, the only thing different from David's vid, when you are flying the DGIV, is the periapsis altitude. In the video we went as low as 60 km; with the DGIV you don't want to go lower than ~67-66 km. You'll also want the ship to be light, so it's good to dump most of the main fuel before reentry.
ReA (~1.5°) and Ant (~45°) are fine, no need to change them.

The whole method (single burn from the Moon for a direct reentry at the target base of your choice), presupposes that you already know how to perform a direct (inverted) reentry.
If you don't know how to perform one with the DGIV, say so and I or someone else on the forum will provide some more help.

Wait a minute.. There are trajectories that will allow a direct reentry at trans lunar velocities in a DG IV ? I never really thought of that. Just a standard reentry from the ISS is difficult enough for me lol

 

[MeeexC]

Okay, i will try it with these settings later. Is there a possibility to find a trajectory for a regular reentry?

So far i never made an inverted one, but i thinks its like you go upside down and use the drag of the ship to stay inside the atmosphere. Before overheating you rotate until you are in higher atmosphere, then go back up side down. But i dont know the details like pitching etc. It would be nice if you or someone else could explain it in details for me.

 

[dgatsoulis]

Wait a minute.. There are trajectories that will allow a direct reentry at trans lunar velocities in a DG IV ? I never really thought of that. Just a standard reentry from the ISS is difficult enough for me lol

Yes. If you go for a direct normal reentry, you will skip out into space again. To prevent that, you can do two things: Either dive deeper in the atmosphere, which means that you will get a very high dynamic pressure and burn up, or go inverted and use the lift from the wings to keep you inside the atmosphere during the time it takes you to decelerate to suborbital speeds. It's not that difficult once you get the hang of it.

Okay, i will try it with these settings later. Is there a possibility to find a trajectory for a regular reentry?

No. You will either skip out, or burn up.

But i dont know the details like pitching etc. It would be nice if you or someone else could explain it in details for me.

Set your PeA at ~67 km. Once you are close to Earth dump all the main fuel while crossfeeding to the RCS tank. You will end up with a full RCS tank and no main fuel. (You need the ship to be light).

At ~100 km alt, bank 180° and pitch "up" (towards the Earth) to an AoA of ~48°. Set your trim fully up. Set your RCS to ROT.

Use the KillRot AP and the RCS "up" to maintain that AoA, until you reach periapsis. Watch your vertical speed and acceleration in surface MFD.

When the dynamic pressure reaches ~ 8 kpa, you find it difficult to control the ship with RCS. Switch to elevon-auto. Switch on and off the Killrot AP until you can steady the vessel.

When the vertical speed gets close to -50 m/s, pitch slightly "down" (towards space), so that your vertical acceleration is slightly positive. don't pitch down an AoA of less than 27°, because you will lose control and burn up.

Try to hold that altitude (by adjusting your AoA, to keep the vertical velocity close to zero) until your velocity in the surface HUD reaches ~ 8 km/s.

At that point, release the killrot AP and roll the spacecraft upright (holding the "up" button, try to do it in one smooth move). Apply KillRot again once you are close to being upright.

That's it, you can now perform the rest of the aerobrake maneuver the same way you always do.

I'll try to post a vid, sometime during the weekend.