Suitable Delta-V for Phoenix lander

[Kemo]

The ejection burn always seems to boggle me. The IMFD notes that came with the phoenix addon suggested that I should have a minimum Delta-V of atleast 4.150k. After the burn, I would not have or barely enough fuel which is needed for landing. What's the most suitable Delta-V for the ejection burn?

 

[Urwumpe]

4150 sounds exactly correct for reaching mars in the needed time.

 

[Kemo]

Yeah.. but then I would not have enough fuel for the correction burn. (DV requirements are around 60 m/s)

 

[Urwumpe]

Yeah.. but then I would not have enough fuel for the correction burn. (DV requirements are around 60 m/s)

Are you sure? Also, you don't need a correction burn, if you are right on track.

You need at least 3800 m/s for a eject burn to mars.

EDIT: Which stage do you use for ejection?

You need both second and third stage for the ejection burn.

 

[Kemo]

I use both stages to perform the ejection burn.

EDIT: IMFD Sure has a habit of overshooting, there a way to correct this?

 

[Urwumpe]

I use both stages to perform the ejection burn.

EDIT: IMFD Sure has a habit of overshooting, there a way to correct this?

IMFD does not overshoot. But maybe the third stage is solid and can't be stopped after ignition.

Did you check this?

 

[Kemo]

Oddly this may sound odd but IMFD does manage to shut down the third stage and attempt to "self correct." (The usual reorient and a quick small correction burn.)

Is that a problem?

 

[Dr Pepper]

Oddly this may sound odd but IMFD does manage to shut down the third stage and attempt to "self correct." (The usual reorient and a quick small correction burn.)

Is that a problem?

The Pheonix add-on uses a multistage.dll vessel for the Delta II launch vehicle, and multistage doesn't recognize the difference between any type of engine (solid, liquid, ect.), so no, it's not really a problem.

I too have trouble getting there with the Pheonix add-on, and I have not pinned down the reason why either. Most likely from something we are doing, though.

 

[BrianJ]

Hi,
assuming you're in a reasonable parking orbit and have ~34% fuel left in the second stage of the DeltaII, you should have enough dV for the job.

A couple of suggestions for getting a more accurate injection burn from IMFD5.1m (latest version I think)

1. Go to the IMFD "Configuration" page and increase the parameter
"AB Throttle down" from 20.0 to 200.0

2. Open up IMFD "Map" display in another MFD and watch your PeA at Mars. Kill the AutoBurn function [AB] when you think the PeA is good.

3. Do the burn manually, without AutoBurn function.

Method 1. usually puts me about 0.3Gm at PeA with Mars (which is coincidentally about the same as the nominal mission offset)

Method 3. I can usually get the PeA down to 0.15Gm at Mars.

The largest PeA with Mars at the end of the injection burn that I can still get an accurate landing from is about 2Gm.

Hope this helps

Brian