Flight Question How do you use stacks with IMFD?

[Pyromaniac605]

How exactly do you use IMFD with a stack? (For example a few modules docked together with a NERVA 2 at the back.) Because the extra weight at the front when using the NERVA 2 to AB makes it go off target almost immediately. Also what do you do with the long burn times? I mean I set a course for Mars then it starts to burn then if I'm lucky every five minutes it might change the orbit a little, it takes so long, how do you overcome this?

Darren

 

[Lucy]

Don't use AutoBurn, do the burn manually with the burn view and correct for the extra mass (It's not weight when you're weightless) yourself.

 

[Wafel]

Try rotating NERVA with ''angular velocity'' tab (custom>scenario edidor>NERVA>angular velocity). To leave the planet you have to burn prograde in perigee a few times. For the first time wait until time to burn=0, then burn when you are close to perigee. Remember that your stack must be symmetric (NERVA must burn in the center of COG).

 

[Pyromaniac605]

Don't use AutoBurn, do the burn manually with the burn view and correct for the extra mass (It's not weight when you're weightless) yourself.

:facepalm: I guess it shows that is 12:23 AM right now. How do you get to the burn view? Is it BV? if so it says no burn vector, and doesn't show anything.

Darren

 

[Lucy]

Uh, yes, Burn Vector, sorry. When you're in a position to hit AB (i.e when you have a burn all ready to go) the BV display will display an attitude alignment layout. Point towards the cross, wait for the time to burn to hit 0, and burn until the remaining delta-v hits zero.

You can watch AutoBurn do exactly this with the BV view, too.

 

[Pyromaniac605]

I set it all up but it still says no burn vector. :idk:

Darren

 

[Sky Captain]

Are you using an orbit eject function to escape from Earth? You must set up a course first and then use orbit eject function to execute the TMI burn.

 

[Pyromaniac605]

So I have to use AB for a bit before I can view the BV?

Darren

 

[garyw]

No, BV will be there if the burn is valid. If you see "no burn vector" then something is wrong with your burn setup

 

[Pyromaniac605]

Perhaps it is the setup I am using that makes the burns take so long? My setup is Orbit eject > Course, Course, Target Intercept > TGT > Mars > PG > AB. It works but the burns take soooo long. I never got to see if it actually works because it takes far too long.

Darren

 

[Sky Captain]

Have you tried default Deltaglider. Perhaps you have too much stuff docked to NERVA2 and get poor thrust to mass ratio because of that and can't achieve escape velocity in time.

 

[Pyromaniac605]

I've tried with DGIV and XR2, but it still is incredibly slow.

Darren

 

[garyw]

Are you launching during a Mars window?

What's the MJD that you are using?

 

[tblaxland]

Perhaps it is the setup I am using that makes the burns take so long? My setup is Orbit eject > Course, Course, Target Intercept > TGT > Mars > PG > AB. It works but the burns take soooo long. I never got to see if it actually works because it takes far too long.

Are you in the Orbit Eject or Target Intercept screen when you are trying to make the burn? If you are in the Target Intercept screen, my guess is that the source is Earth, which explains why you can't make the burn. If you are still having trouble, post a screenie of your burn setup.

 

[Tommy]

When you dock the modules to the Nerva, you change it's COG. However, the attitude RCS doesn't adapt for this, and that makes IMFD unable to properly orient the vessel. Manual attitude control will be required.

If you get "No burn vector" displayed in burn view, there is something wrong with the set-up, or how you are using IMFD. If tblaxland's advice (ensure you are in Orbit Eject, not Target Intercept) doesn't work, do as he said and post screenshots.

As for the burn time, even a DG (with it's very high thrust to mass ratio) takes almost 10 minutes of burn for an Earth - Jupiter trip. For a more "realistic" vessel, like your stack, burn times will be much longer.

 

[Pyromaniac605]

I am currently using MJD 55872 which, according to Wikipedia, is a Mars launch window.
I can now see the burn vector, I didn't change anything so I don't know how. But it works now so now I just need help with the burn times.

Also I've noticed some problems with saving a scenario and then loading it later if you use IMFD. Firstly the IMFD window doesn't let you Auto Burn no matter what you do, and the orbit changes from a small circle requiring a prograde burn to a straight line requiring a much longer retrograde burn. That gets really annoying.

Is there anyway I can easily keep the ship pointing in one direction rather than having to take it out of time warp every few seconds?

Darren

PS: Took me 5 tries to get this post through. :facepalm:

Edit: Looks like the second IMFD bug I had was a blessing in disguise, my Deltaglider is now visibly changing its orbit with its burns.

Edit2: or not I can't even see Mars when I press F9, I did something really wrong didn't I?

 

[Tommy]

I haven't used IMFD with 2010P1 much yet, but I've never seen anything like what you are describing. Screenshots would be very useful to help me understand whats going on.

IMFD should save it's all of it's settings as long as at least one MFD is open to IMFD when you exit or save.

I'll check that window and see how it looks. Keep in mind that windows vary depending on the type of transfer - an off-plane window may vary from a target plane window - but not by that much. A solution should still be available, if not the most efficient one. I'll get back to you in a bit on the window.



OK, window looks OK. A quick check show optimal ejection for an Off-plane transfer is about MJD 55888.5. A planar transfer usually wants a bit earlier ejection, so 55872 should be fine. What TIn do you have? For my Off-plane transfer, TIn was 56140, for a TOF (Time-Of-Flight, or TIn minus TEj) of about 252 days. If your TOF is significantly different that may cause your problem.

 

[Pyromaniac605]

Maybe thats the problem I'm off plane, I think, how can I tell if I'm in plane with Mars or not?

Darren

Edit: Also am I supposed to do an AB in orbit eject mode first? If so thats probably my problem I haven't been doing that.

 

[tblaxland]

Edit: Also am I supposed to do an AB in orbit eject mode first? If so thats probably my problem I haven't been doing that.

Yes, you need to do the orbit eject burn first (that's what I was on about up there ^). It doesn't have to be an auto-burn, a manual burn will do fine as long as you line up with the burn vector first and achieve the delta-v required in the burn vector view. At the end of the orbit eject burn, your spacecraft should be on a trajectory such that it aligns with the one predicted by the course program once you leave Earth's SOI.

 

[Pyromaniac605]

Ok got it so my basic plan should be Orbit Eject Burn > Course Burn > Orbit Circularise Burn. I get it now, time to go (hopefully) fly something to Mars.

Darren