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

[ADSWNJ]

Can anyone take me through what is actually happening with the launch planning steps with TransX. I can do the steps just fine ... i.e. set up the eject in Step 2, then come back to Step 1, set the date 3 or 4 days before using scenario editor, set the Pe Radius to 6.571M (= 200km alt), swing Ej Orientation to move the grey line onto the green ellipse and seeing it come out to the planet edge, then accelerate time around keeping the grey line on the green ellipse until the heading is close to 90 degrees (flipping it to the other way round if it doesn't want to converge).

BUT...

I'm trying to get my head around what exactly I am doing! Can any TransX experts do a play by play of this explaining what the graphics are actually showing, and what the parameters represent in 3D space? (Maybe explain the projections for different perspectives?)

Some questions in my head...

1. What exactly is the Ej Orientation angle, versus the Heading?
2. What is the grey line, exactly, and what does it run through, ealtive to our current position and to our target parking orbit?
3. Why does the green ellipse an ellipse come the enter of the Earth, when I am on the ground (e.g. at Kennedy or Wideawake)?
4. If I adjust the launch so that TransX calls for a heading of 090, so I take off headed 90 degrees from say Kennedy, then by the time I'm at 200km alt in orbit, have I actually slewed right across to the plane of the equator? I mean I can't orbit on a plane not going through the center of gravity of the Earth, so what actually is going on when I head 90 degrees and keep going, and how can this be on the desired eject plane?
5. Thinking about the various planes ... I assume I want to be in an orbital inclination matching the eject plane, so I'm just doing a prograde burn (and maybe some outward) on the eject. Help me visualize this plane relative to parked on the ground ... I'e how do you transform into this eject plane just by holding the desired heading throughout the launch?
6. During the launch ride to orbit, how do the numbers trend towards the desired zero RInc (i.e. what's happening in 3D space).


I think there comes a time when you graduate from blindly doing a set of steps that you know to work in practice, to trying to make the leap to understand the 3D geometry and physics of what you are actually doing, and how it relates back to the graphics and parameters on a screen like the TransX Eject Plan.

I'm hoping that there are some true TransX rocket scientists out there that can help me on this learning quest!

 

[ADSWNJ]

So I did an experiment with a DG, launching from KSC and heading 90 degrees all the way to orbital velocity, whilst watching the latitude coords on the Surface HUD. As you pick up speed, the southerly trend picks up despite flying 090. When you hit orbit, hey presto, the orbit originates East of KSC, and ground-tracks south across the equator just like a normal orbit! (Who knew?!)

So as a thought-experiment ... if you had unlimited fuel, staying sub-orbital velocity, level flight, 090 degrees, you would track a constant latitude ring around the Earth (eg. at 28.5N). Get to orbital velocity, and you transition into an orbit centered a the center of gravity of the Earth as the centrifugal and centripetal forces balance each other out and "take charge" of the velocity vector of the craft regardless of the 090 heading. Question ... how sharp is the transition from a constant-latitude path to a standard orbit path (eg. is it over 1000 m/s, or 20 m/s of velocity, or what)?

 

[dgatsoulis]

EDIT: Answers to post No1:

Let's start with No.3 first:

Why does the green ellipse an ellipse come the enter of the Earth, when I am on the ground (e.g. at Kennedy or Wideawake)?

That's because even when you are landed, you are in an "orbit" arourd the Earth, with specific characteristics. In this case Earth's surface doesn't allow you to go below your Apoapsis altitude, but if you can imagine a point in space with the Earth's mass, then that would be your orbit around it.

What is the grey line, exactly, and what does it run through, ealtive to our current position and to our target parking orbit?

The grey line is the line of nodes, it connects the ascending node and the descending node of your current-landed-orbit with the orbital plane of the TMI plan. That's why you have to change the eject orientation to an angle that passes above your landing site.

What exactly is the Ej Orientation angle, versus the Heading?

Once you establish a plan for an interplanetary trajectory, there is -in theory- an infinite amount of orbits that can get get you there, all passing over the same LAN. But if you are landed, there is only ONE that coincides with the Great Circle that passes over your launch site and the plane of the ejection plan's trajectory. (ok, there are two actually, but one of them is retrograde). That's why you need to launch at a specific heading.

If I adjust the launch so that TransX calls for a heading of 090, so I take off headed 90 degrees from say Kennedy, then by the time I'm at 200km alt in orbit, have I actually slewed right across to the plane of the equator? I mean I can't orbit on a plane not going through the center of gravity of the Earth, so what actually is going on when I head 90 degrees and keep going, and how can this be on the desired eject plane?

Not sure what you mean there. The lattitude of your launch site is also the minimum equatorial inclination you can achieve, by launching at a heading of 90 (or 270) degrees. Any other heading will take you to a higher inclination. Remember that the most important thing is the Longitude of Ascending (or descending) Node. LDN=LAN-180.

For the rest of the questions, look at the rest of the post.

Here is what I did when I had a similar "visualization" problem.

The first thing to keep in mind is that when you are orbiting a planet your path along space is an "S" pattern. Here is a pic:

You can see that when you apply thrust to your ship on the night-side of the planet, you will raise your apoapsis relative to the sun and when you apply thrust on the day-side you will lower your periapsis.

Now try this experiment.
1.Place a bunch of ships on random places on the planet.
Here I've placed 9 ships

2.Go to ship No1 and setup a transX plan for Mars. Advance the date to 1 day before the ejection burn and swing the eject orientation over your site to get the correct heading.
3.Go to ship No2 "Inherit" the plan from ship No1, adjust the eject orientation to match the new site. Keep doing this for all the ships in your scenario.
You will notice that eventhough the headings and inclinations will be different, all the ships will have the same LAN or LAN-180 degrees.
4.Go ahead and launch all of the ships. Activate Artlav's videnie addon, zoom out and look at the ships' orbits.

5.Make all the TMI burns wait until you are outside of Earth's SOI (weak G<0.50) and watch the ships's orbits relative to the sun.

Here is the scenario with 9 DGs on random landing sites (pic2):

BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 51981.6163532495
END_ENVIRONMENT

BEGIN_FOCUS
  Ship GL-01
END_FOCUS

BEGIN_CAMERA
  TARGET GL-01
  MODE Cockpit
  FOV 60.00
END_CAMERA

BEGIN_MFD Left
  TYPE Map
  REF Earth
  OTARGET 9
  BTARGET Cape Canaveral
  POS 0.00 0.00
END_MFD

BEGIN_MFD Right
  TYPE User
  MODE Radio/mp3 Panel
END_MFD

BEGIN_SHIPS
GL-01:DeltaGlider
  STATUS Landed Earth
  BASE Cape Canaveral:1
  POS -80.6758964 28.5227640
  HEADING 150.00
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 402 94 0 0
  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
2:Deltaglider
  STATUS Landed Earth
  POS -27.4388700 0.1329030
  HEADING 66.56
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0 0 0
  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
3:Deltaglider
  STATUS Landed Earth
  POS 63.3300000 45.9200000
  HEADING 66.57
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0 0 0
  XPDR 0
  AAP 0:0 0:0 0:0
END
4:Deltaglider
  STATUS Landed Earth
  POS 20.3200000 -34.5800000
  HEADING 66.56
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0 0 0
  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
5:Deltaglider
  STATUS Landed Earth
  POS 35.3000000 69.3000000
  HEADING 66.56
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0 0 0
  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
6:Deltaglider
  STATUS Landed Earth
  POS 80.3000000 13.8000000
  HEADING 66.56
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0 0 0
  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
7:Deltaglider
  STATUS Landed Earth
  POS 136.8000000 -31.1000000
  HEADING 66.57
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0 0 0
  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
8:Deltaglider
  STATUS Landed Earth
  POS 138.5000000 51.5000000
  HEADING 66.56
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0 0 0
  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
9:Deltaglider
  STATUS Landed Earth
  POS -52.7300000 5.2000000
  HEADING 66.56
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0 0 0
  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
END_SHIPS

BEGIN_ExtMFD
END

And here is one after they've been launched on their correct orbits to make the TMI burns (pic3):

BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 52022.5091124693
END_ENVIRONMENT

BEGIN_FOCUS
  Ship 9
END_FOCUS

BEGIN_CAMERA
  TARGET 9
  MODE Cockpit
  FOV 60.00
END_CAMERA

BEGIN_HUD
  TYPE Surface
END_HUD

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  TYPE User
  MODE TransX
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  FNumber 2
  Int 1
  Orbit True
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  Vector  1875.0708825 1828.42718618 7334.51266396
  Double  3.98600439969e+014
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  Handle Earth
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  Vector  780.98447387 5496.99637865 -5461.42900459
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  Finish BaseFunction
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  Vector  832.327288582 -2406.71604697 -7359.96341732
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Try it yourself and then have a look at your questions again. Repost the ones that you still don't quite grasp.

Hope this helps

 

[ADSWNJ]

EDIT: Answers to post No1:

Let's start with No.3 first:
{snip}

Hope this helps

Dgatsoulis ... thank you so much. I'll study this over the weekend and let you know what clicks. I *love* that visualization with videnie (sp?). I tried that addon a while ago and never got it to work, but I'll have to retry it.

On the orbit ... I was wondering when you transition from a circular non-great-circle orbit (i.e constant non-equitorial latitude, sub-orbital, vector 090 direction circle), to a true orbit centered through the Earth's COG. That was the question and experiment on the transition from one sub0orbit to the other true orbit.

 

[ADSWNJ]

OK so I've launched all those DeltaGliders to a perfect 200x200 orbit, with 0.000 RInc. (As an aside - it was like driving your first car again ... so raw and simple, just point and blast to orbit ). Due to RL intervening, I haven't done the TMI burns yet.

Looking at the orbits - I see they go through the same node-points. What I find curious about this is that I expected the orbits to all end up coplanar with the Earth-Mars plane, so that the ejects were all just prograde.

Once I get these 9 launched, I'm going to go back and put all 9 back at KSC, and launch them at 0.1 MJD intervals to see the effect. I expect they will end up looking similar to the current "Orange segment" picture, as the Earth rotates around.

Question for you: the Heading on the Escape Plan ... how long do you hold it on your way up? All they way to orbit? What's the procedure for getting RInc down close to zero on the ride up?

 

[dgatsoulis]

Looking at the orbits - I see they go through the same node-points.

Exactly. The important thing here is the node. Here is another example, from a different journey. (Earth-Moon)

Every single one of the 18 orbits you see in the pic above, AND everyone inbetween can get you to your destination (In this example the moon), as long as they pass through that node. When you are landed, anywhere on Earth, there is only ONE [ame="http://en.wikipedia.org/wiki/Great_circle"]Great circle[/ame] that passes from your launch site and that node.

Question for you: the Heading on the Escape Plan ... how long do you hold it on your way up? All they way to orbit? What's the procedure for getting RInc down close to zero on the ride up?

You hold the same direction you had at the time of launch. Not the same heading. When the RInc drops to about ~1 degree you make slight adjustments to your course, to get it as close to zero as you can.

 

[Furet]

Thanks a lot Dimitri. This is very interesting.

I understand that all these orbits can get to destination. This is certainly a matter of neophyte, but I wonder which orbit is the most fuel efficient, if any (presumably the orbit in the same plane as the destination)?
:tiphat:

 

[dgatsoulis]

Thanks a lot Dimitri. This is very interesting.

I understand that all these orbits can get to destination. This is certainly a matter of neophyte, but I wonder which orbit is the most fuel efficient, if any (presumably the orbit in the same plane as the destination)?
:tiphat:

All the orbits are equally efficient in terms of the dV.

 

[flytandem]

I got inspired to try the videnie addon to play with eject orientation as a way to help explain what is happening. I set up a plan to go to Mars and placed 3 deltagliders in a 200 by 200 orbit at Earth. I also set each one up with a different eject orientation the first at zero eject orientation and the second at -120 degrees eject orientation and the third at 120 degrees eject orientation.

A simply way to think of eject orientation is to think of a pitcher throwing a ball. He could throw it overhand (let's call it a 12 o'clock orientation) or right side handed (let's call it 3 o'clock orientation) or underhanded (let's call it a 6 o'clock orientation) or any orientation in a 360 degree clock. The direction of the throw is the same regardless of the orientation of the throw.

Below is am image showing the 3 ships each aligned with the eject plan to go to mars. m1 is in zero eject orientation and m2 is -120 and m3 is =+120 degrees eject orientation.

Then after they have each done their respective eject burns. BTW their burns were all the same amount at about 3730 m/s. Using the pitcher and clock description of orientation, the m1 ship was oriented for a 3 o'clock throw, m2 is a 7o'clock throw and m3 is an 11 o'clock throw.

And now note that they are all heading out into the same direction on their way to Mars. This is a wide view showing the orbit of the moon in brown at left.

And if you want to see the scenario used with the ships in orbit aligned with their individually oriented plans it is below...

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[C3PO]

All the orbits are equally efficient in terms of the dV.

The theoretical difference is probably smaller than the correction burns you have to do anyway. [Edit]The largest difference is probably the arrival time[/Edit]

3-body calculation (like TransX) is an approximation where you "jump" between SOI's. Orbiter models the gradual change in gravitational influence, so you need to "clean up" the error of the TransX plan.

 

[ADSWNJ]

A simple way to think of eject orientation is to think of a pitcher throwing a ball. He could throw it overhand (let's call it a 12 o'clock orientation) or right side handed (let's call it 3 o'clock orientation) or underhanded (let's call it a 6 o'clock orientation) or any orientation in a 360 degree clock. The direction of the throw is the same regardless of the orientation of the throw.

Thanks for the visualization, FT. When you set up the eject burn maneuvers, thus dropping the original plan, did you just add prograde to each parking orbit, or did you need still a whole whack of plane change?

See this for me is still the crux of it: I thought that the whole idea of getting into a precise parking orbit was to get your plane aligned with your Earth-Mars plane, so that the eject was in one dimension (prograde).

What's a bit mind boggling here is that you can be in an infinite number of orbits around the same nodes, and all of them still get you there!

Back to your pitcher analogy ... would you say that the note points are like the pitcher's shoulders at release point? I.e. you can pitch overhand, roundhouse, underarm, but your shoulders have to point to the batter or you'll throw anywhere. If so ... given the infinite number of orbits, WHAT exactly are those node points doing?

 

[blixel]

See this for me is still the crux of it: I thought that the whole idea of getting into a precise parking orbit was to get your plane aligned with your Earth-Mars plane, so that the eject was in one dimension (prograde).

This is what I always thought as well. In my mind, I pictured the "right" path between Earth and Mars as being like a thin sheet of paper stretched across the solar system. I thought the point of getting into a precise parking orbit is so that you can get in the same plane as that thin sheet of paper. If you were not in the same plane as that thin sheet of paper, then you would end up going "above" or "below" Mars. Though, I thought you could still get to Mars if you were a bit off from that thin sheet of paper, so long as you performed the necessary MCC's to get you back in the plane of that thin sheet of paper.

What's a bit mind boggling here is that you can be in an infinite number of orbits around the same nodes, and all of them still get you there!

Back to your pitcher analogy ... would you say that the note points are like the pitcher's shoulders at release point? I.e. you can pitch overhand, roundhouse, underarm, but your shoulders have to point to the batter or you'll throw anywhere. If so ... given the infinite number of orbits, WHAT exactly are those node points doing?

Question for flytandem/dgatsoulis. Do these pictures represent what's going on? (Pardon the crudity of the models, I don't know how to use image editing software very well.)

In this image, we would be missing Mars because the node is not in line with Mars.

In this image, the node lines up with Mars, so it would be right.

Is that what is going on? Or do I still have the wrong picture?

 

[C3PO]

That line shouldn't point at Mars (or where Mars is going to be when we get there). You can think of that line as a tangent to the solar orbit when we leave the Earth's SOI.

The ejection orbits are close enough to parabolic that we can consider them parallel after they've left Earth's SOI. Parallel is probably not the correct word because you will never travel in a straight line, but they will all be traveling in the same direction.

 

[blixel]

That line shouldn't point at Mars

Ah ... of course. It can't point to where Mars is now, because Mars won't be in the same place by the time we get there. But it surprises me that it shouldn't point to where Mars will be.

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

 

[C3PO]

But it surprises me that it shouldn't point to where Mars will be.

Because you are in a solar orbit when you travel from Earth to Mars, and you never travel in a straight line when you're orbiting a celestial body.

BTW that's why I prefer teaching basic orbit maneuvers around Mars. Somehow it's easier to get away from the intuitive knowledge everyone has about physics on the surface of the Earth.
And as a plus Mars has two moons you can use for target practice, and transfers don't take as much time or DV as in LEO.

 

[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.

 

[Furet]

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. :hide

 

[blixel]

I hope this video explains better.

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

 

[ADSWNJ]

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!