IMFD is actually very simple to use... once you got the hang of it. For some reason this process took me a lot of
time
OK, where do we start? First, ignore for the moment offsets and 8-shaped Apollo-style Moon trajectories. These are
nice capabilities of IMFD but unrelated to the interplanetary travel. Also I don't know about you but I can learn very
little if I am presented with a procedure which I should follow without understanding why I am doing this or that. For
that reason I would rather try to explain what various parts of IMFD do.
IMFD consists of a number of programs, which help you solve different problems.
First, a very important principle: All programs, except Map work with a single body affecting your trajectory. This
means that you should select a proper
REF (this is often done automatically by the IMFD). For travel from Earth
to another planet, Sun will be the reference. For a travel between two moons of Jupiter, Jupiter is the reference body.
In other words, the reference should be the body, which influences the trajectories of bodies between you are
travelling most. Next, the source (
Src) and target (
TGT) must be bodies orbiting the reference body. If
you are not orbiting the Sun independently of the Earth (e.g., if you are landed or in Earth's orbit), do not select
yourself ( "x" ) as a source. Select the Earth instead. If you want to travel from another planet to a moon of Jupiter,
do not select the moon as TGT as it travels around the Sun together with Jupiter. Select Jupiter.
As you are programming, you probably know what a tree data structure is. If we build a tree with the Sun as a root
node and parent-child relation is "child orbits around or is landed on parent", then planets will be children of the Sun
(sounds poetic, doesn't it
), and moons will be children of their respective planet. Your spaceship may be in a
different position in this tree - you may be orbiting the Sun far from any planet (child of the Sun node), or
orbiting/landed on a planet (child of the planet node), or orbiting/landed on a moon (child of the moon node). Now if
you want to travel to node B, find the nearest node up the tree (I am assuming the root is at the top), which is an
ancestor of both your ship and your target. This will be your reference. The two nodes immediately below it - the one
on the route from your ship up to the reference and the other on the route from the target up to the reference - will
be Src and TGT.
Now about IMFD programs.
* Surface Launch - helps you launch in the right direction (and in the right time if you want to wait and save fuel). For
trips from a planet to one of its moons, this is the first program you would use. For interplanetary travel or travel
between two moons ( "Rescue Mission on Io" ) first a course must be set up. If we remember the tree discussed
above, the launch program solves the problem how to change from "landed on A" mode to "orbiting A" mode.
* Map - all other IMFD programs assume the influence of a single body, so their solutions are approximate. The Map
program shows a much more precise estimation of your actual trajectory under the influence of multiple bodies. The
Map program itself does not calculate a manoeuvre, but it has a what-if mode (
Plan), which allows you to see
how your trajectory will look after a manoeuvre performed by one of the other IMFD programs. Often it is convenient
to run the Map program on a separate MFD screen. This requires
OpMode of the MFD where Map will be running
to be set to shared with the ID of the other MFD. For example, open IMFD on both left and right MFD screens of DGIV.
Press the upper-left
MNU button if IMFD shows its boot screen. Then note the ID of each MFD in the upper-right
corner of the screen. They should be 0 for the left and 1 for the right MFD. Then in the left MFD select
OpMode and enter MFD ID to be 1. This will make both IMFD share their data.
* Orbit-Eject - this program is usually used for interplanetary travel (or travel between moons) as a next step after
Surface Launch. Again, first a course must be set up. Related to the tree, orbit-eject solves the problem how to
change your mode from "orbiting A" to "orbiting A's parent" (go up the tree).
* Course consists of the following sub-programs:
- Target Intercept - allows you to find a trajectory from body A to body B at any time (at the expense of fuel usage, if
the time of ejection is not appropriate or requested arrival time is too close to the ejection time). Related to the tree,
calculates a travel between two nodes with the same parent.
- Tangential Transfer - solves the same problem as Target Intercept, only in the most fuel-efficient way. Unlike the
standard Transfer MFD, delta-V is computed automatically, you only vary the time of ejection (TEj) to find a target
intercept.
- Planet Approach - helps you adjust your flyby trajectory (the periapsis altitude and the inclination of your orbit)
when you are approaching a planet.
- Orbit Insert - calculates a burn near the periapsis that will turn your flyby trajectory into a circular one (or elliptical
with the specified eccentricity, but this would be rarely needed). Related to the tree, orbit insert solves the problem
how to change your mode from "orbiting B's parent" to "orbiting B" (go down the tree).
- Delta Velocity - allows to perform a custom burn. The source must be some external data, for example calculated by
another MFD or historical data for a mission you are recreating in Orbiter.
* Base Approach - although a separate program, it is very similar to Course / Planet Approach. Allows you to target a
base on the surface of the reference body.
* Orbital - contains three simple tools:
- Circularize - allows to convert your current orbit to circular. The radius of the circular orbit will be close (not exactly
equal due to the burn taking some time) to your radius at the time of the burn.
- Velocity Match - same as DGIV "zero relative speed" autopilot.
- Find Target - helps you orient your ship to point at the specified target. Similar to using DGIV antenna and D9
display mode.
* Sling-shot - the weakest part of IMFD, unless I am missing something. Calculates a sling-shot based on
your
current trajectory relative to the reference body, which means it cannot be used for planning a trip. And when you
are already near, say, Jupiter, it may turn out no slingshot to the course you want to continue with is possible.
More later.Post Edited ( 12-27-07 09:02 )