IMFD Course Enroute iV

[orbekler]

Hello,
I'd like to know the meaning of the iV component in IMFD Course Enroute info. This because it's always there as a non zero value, even if I finished the burn (Burn Vector Total dV=0). In the full manual, is described as inward component, but this should be already included in BV.

 

[mjanicki]

It is possible that iV reads non-zero, even after a successful burn, due to the fact that oV and iV do not take gravity effects into account while overall dV does.

From page 3 of the IMFD v5.3 documentation:

Outward and Invard (sic) velocities oV and iV excludes the effect of the gravity.
Therefore the actual dV that is required is a little different than the oV or iV.

No doubt someone else will have a better explanation, but this would explain the apparent discrepancy in the displayed values.

 

[jarmonik]

The iV is the velocity difference between your ship and the target planet at your arrival in destination. That should allow you to estimate the total dV costs of your mission. You can compute the magnitude of the orbit capture burn from the iV.

 

[Tommy]

iV has different meanings, depending on where it is being used.

When used in trajectory calculations, such as on the main page of Target Intercept, I like to think of it as "Inherent Velocity", and means exactly what Jarmonik said (of course!). If you know the velocity of the desired orbit around your target, you can subtract that from iV and get a pretty good idea of the delta-V that will be required for the orbit insertion.

When iV is used as part of a Burn Vector (as in the lower left corner of Burn View, or in Delta Velocity program) you can think of it as "Inward Velocity".

The difference is in whether it's being used to describe a trajectory (course), or a specific individual burn.

At least, that's how I've come to understand it - ALWAYS take Jarmonik's answers as being the absolute truth if someone else provides a different answer.

 

[orbekler]

...ALWAYS take Jarmonik's answers as being the absolute truth if someone else provides a different answer.

That's what I did!
The question arose because of a discussion, as many people think that IMFD "consumes" more than Trans-X or Transfer MFD. But of course doing different tries with IMFD and Trans-X paired, fed with same parameters for both, the energy spent is the same, as it must be.
But usually Enroute Tot dV gets the focus and is misenterpreted as the transfer energy required.

 

[Tommy]

I see what you mean. The dV values shown in Target Intercept kind of represent the dV needed to get the "Source" to the "Target" - which isn't the same as the dV needed to get from the "Source" to the "Target". Since the source is the planet you are leaving, it doesn't take the vessel's current energy into consideration.

The values you need to compare IMFD to TransX is the Tot dV shown in Orbit Eject. That and the dV for any anticipated plane change made enroute (for two plane transfers, shown in Target Intercept) together show you a very good idea of how much dV you will actually need to get to the target.

 

[orbekler]

I see what you mean. The dV values shown in Target Intercept kind of represent the dV needed to get the "Source" to the "Target" - which isn't the same as the dV needed to get from the "Source" to the "Target". Since the source is the planet you are leaving, it doesn't take the vessel's current energy into consideration.

The values you need to compare IMFD to TransX is the Tot dV shown in Orbit Eject. That and the dV for any anticipated plane change made enroute (for two plane transfers, shown in Target Intercept) together show you a very good idea of how much dV you will actually need to get to the target.

Yes, IMFD takes into account the "whole bunch", but for the Moon I use straightly Course Intercept, Orbit Eject only for planets. in the following image, I first set a launch window in Trans-X (aligned planes), then in IMFD with same parameters, and as you can see the Enroute dV (not Total) is almost equal to Trans-X Delta V (3.107k vs. 3.105k) :thumbup: