skool'd - Orbital Transfer.

[Tachyon]

ok - some help here from the astronauts if you please.....

I can get myself into a perfect (Ecc=0.00000) orbit in minutes .... 1-2 time warps to chase the apsis. However this is
where I get fuzzy about all the lines in the transfer MFD.... of which I'm sure there is a perfectly good sequence to.

Green solid line and circle = me at my current orbit
Yellow solid line and circle = target orbit and the target body.
dashed green or yellow line = projected positions of bodies in the future.
single grey line = eject point ??

Now say I'm in orbit around Mars ... and I want to transfer to a earth orbit. (retrograde burn necessary) Here is what
I know so far.
1) position craft retrograde
2) transfer MFD
3) ref set to sun
4) target set to earth
5) play with the deltaV to create a "intersection" between green and yellow orbits.
6) play with eject point to align the orbital intercepts so that earth will actually be where I'll end up.

Now .. I'm sure there is a easy method. Like, move the eject point until the dotted lines line up with each other. OR
that single grey line, line it up with the dotted yellow line. But I can't seem to quantify these steps..... I've been thru
the tut showing a lunar orbit transfer but there the text says to "do this" (move eject point to x degrees) but doesn't
explain why and x degrees doesn't seem to line any of the lines with any of the other lines..... I need the preverbal
light bulb turned on here guys ..... does some one see what I'm missing?

[tjohns]

Tachyon wrote:
...
Now say I'm in orbit around Mars ... and I want to transfer to a earth orbit. (retrograde burn necessary) Here is what
I know so far.
1) position craft retrograde
....

Wrong at step 1! Forget about you own orbit, and consider that MARS itself doing the transfer. Obviously Mars has to perform
a RETROGRADE burn to decrease it's orbital speed (relative to the Sun) for it's new orbit to reach Earth. You need to time
your ships burn so that a PROGRADE burn sends you off in the same direction that MARS would need to go...it's somewhere
around the time when the Earth appears over your horizon while orbiting.

Also, change the SRC on the Transfer MFD to Mars ... you can then use it to determine what velocity (relative to the Sun) Mars would need to lose to do the transfer - this is the DeltaV you need left over as you leave Mars SOI range.

Trevor



Post Edited ( 01-15-07 10:11 )

[Tachyon]

ok, I think ... but
 
Mars and I *are* the same solar orbit. I just happen to be orbiting Mars. My retrograde was not in reference to Mars
but in reference to SOL. So are you proposing "prograde" (ref Mars) out of Mars orbit in the direction of earth ....
which ends up in the greater scheme of things turns out to be a retro burn with reference to SOL. Thanks .. but
you've not told me anything I didn't already know (or state in my original assertions)

How to use the lines in the transfer MFD to wind up in the general vicinity of my target body, whether in a higher or
lower orbital plane? That is my quandry.

[Voyager]

The big disadvangate of the Transfer MFD is that is has no real support for in transit course corrections. Or at least i
think it didnt have it (been a while since i used it). I do recall that when i tried to get to mars from earth using the
Transfer MFD, the closest i got was serveral million km, not even close enough to see a red spot...

I heard that after you made your orbital burn and left earth's gravity *that is what throws you off course*, you need to make
a course correction to get close to Mars again, but i could never figure it out with the Transfer MFD.

I know its alot more complicated, but my advice would be to forget about the Transfer MFD for interplanetary flight, and only
use it to get to moons of a planet. And use a tool like TransX for interplanetary flight. It has alot more functions,
including course corrections. You can even *while on route to mars* start planning which kind of orbit you want to have to
land yourself instantly at Olympus without having to make alignment burns while in orbit.

Here is a totorial about the basics of interplanetary flight (also features flying to mars using transx)
http://www.orbithangar.com/addons/IPF.pdf

And here is a website with alot of TransX tutorials.
http://www.flytandem.com/orbiter/tutorials/index.htm

Btw, TransX comes standard with Orbiter, all you need do is activate it in the modules tab of the launchpad.

It might look like alot of hassle with TransX, but you'll think its all worth it when you see that big red marble show up out
of nowhere

Voyager

[Tachyon]

Thank you ... I have briefly looked at TransX and you're right - a lot more complicated looking than transfer. But I will
avail my self of the tut's you provided the linkage to  ... The one autoplay demo I saw was really exciting to watch as
the moon showed up out of no where and grew and grew ... THAT'S NO MOON ! IT'S A SPACE STATION .... sry ....
couldn't resist.