[TransX] Escape Plan launch ... explain what's atually going on?

[dgatsoulis]

I hope this video explains better. At first you see all the ships from the scenario I posted on post #3 after they have performed the TMI burns. At that point their trajectories are shown relative to Earth. Later in the video you see their trajectories relative to the sun.

Test1.avi - YouTube

Test1.avi - YouTube

[Furet]

Quote:

Originally Posted by blixel

 I still can't visualize it. It's just magic.

Perhaps it could be easier to understand if we think it is roughly the same situation when we are in LEO trying to reach the ISS: we are pointing prograde or retrograde in order to synchronize our orbit with the target.

When we try to reach Mars, we have to change the orbit "inherited" from the Earth and make it tangent with destination's orbit.

(Hope this comparison won't drive the specialists mad. )

[blixel]

Quote:

Originally Posted by dgatsoulis

 I hope this video explains better.

Excellent visualization. That explains it very well. Thank you.

[ADSWNJ]

Quote:

Originally Posted by blixel

 Excellent visualization. That explains it very well. Thank you.

Yeah me too - thanks Dimitri.

So ... treat the line of nodes as the sighting mechanism on an Earth-sized railgun. You want to point this railgun to fire the spacecraft onto the trans-Mars orbit (Rollerball-cannon style, to mix analogies!). You are going to burn somewhere between the two nodes (e.g. dead middle I assume), to fire from the circular orbit exactly into the trans-Mars orbit. And back to FlyTandem's analogy, overarm, roundhouse, underarm - they all end up a rounding error of a difference on a near perfect parallel trajectory as Dimitri's video shows.

So back to my question posed to FlyTandem ... if you are in one of these infinite number of parking orbits, with RInc at 0.000 to the TransX eject plan, then is the TMI maneuver going to be nearly pure prograde?

(By the way - awesome thread + big thanks all!!)

[ADSWNJ]

Ok - I think I've got this one figured out now! After several delays due to RL, I've now played with getting a perfect RInc from launch per TransX's eject plan. This puts you into an orbit with ascending and descending nodes on the transfer plane over to Earth at the ideal eject time. The orientation about that axis really doesn't matter at all, because as FlyTandem said, you will fire out of Martian orbit either dead on the plane, or up to an orbit radius high or low of the plane, but the key point is that exactly midway between those nodes you are pointing along the right vector.

Back to TransX, you want to set up a prograde burn maneuver of the required DeltaV for the eject (from the escape plan), aim the exact eject burn time plus or minus some
hyper-fine tuning to get to the right point on the orbit. You need to rotate your meneuver around to overlay right on the plan. You'll see that even in Hyper, the eject date is critical to a single click up or down, because you are looking to hit the dead midpoint of the nodes. If you do it right, you need to add single digit amounts of plane or outward, versus say 2200 of prograde, so it's essentially 100% prograde.

So to recap, your big chunks of plane change and any outwards velocity from the original plan were all taken care of on the climb out, so all you have left is just the prograde element plus or minus some tiny tuning. Neat eh?

If you are left with some RInc on the climb out, despite flying the required heading and rolling left or right to get it to single digit degrees of error, then in the cruise up to your ApA try some normal thrust. If you are still in some atmosphere, then orient prograde and use some hover thrusters (or manually roll 180 deg and hover the other way round). Doing this keeps your clean profile as you climb through the last bits of atmosphere. If you STILL have some left (hopefully 1-2 degrees at most) then you can use Align Planes MFD to set a manual ELS target of the Inc and LAN to get it close, then watch the TransX screen and shift-translate thrusts to get it perfect.

I found visualizing the eject to be the biggest challenge. You are flying eastwards round Mars, with the planet's spin, for least delta V take off to orbit. You are adding prograde to break out of Martian orbit, but doing it on the sunny side, so you are simultaneously thrusting retro with respect to the Sun. Despite breaking out of Martian orbit, you are still flying prograde round the sun, just slow enough to arc inwards to intercept the lower planet. And all that precise work with TransX eject planning was to put you momentarily on the perfect velocity vector to arc down the gravity slope to Earth with the perfect prograde velocity nudge.

It's a beautiful thing this orbital mechanics, and even more when you get that Eureka moment where it snaps into place.

Thanks to all the experts on this thread for the education, especially FlyTandem and Dimitri. Awesome, guys!