TransX That little cross in the Encounter display

Planitia

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In David Courtney's very helpful video on using TransX to do an Earth-Moon transfer (Part 31, at 23:19), the right-hand Encounter display has a small cross at the center. I am trying to recreate this, but on a Mars-Phobos transfer. For me, the Encounter display does not have that little cross, which makes me think I have some setup mode incorrect.

Then when I add delta-V and advance the Manoeuvre date so that a solution should be possible, the encounter details do not appear on the right hand screen.

This is the "TransX-20 14.04.26-Auto-Center-fix" MFD. What am I missing here?
 

dgatsoulis

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It's a bit difficult to understand what you are talking about. I don't recall any "cross" in the Encounter View of TransX. There is an "x" in the Target view of the maneuver mode though. Also what's your starting point? In orbit? Landed on Mars?

Please do the following:

1. Provide a link to the video you mention.
David has a lot of videos, so someone that doesn't know which vid you are talking about, will have to spend a lot of time trying to find it.

2. Post a screenshot of your TransX MFDs with the problem.

3. Post the scenario and clear instructions on how to recreate the problem.
(Example: 1.Load scenario→2.Press VW on right MFD→3.Problem:The "cross" doesn't show).
 

Planitia

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The video is https://www.youtube.com/watch?v=M0nMa1jz0RY

My craft (DGIV-3) is in orbit around Mars, just after the P906S90 launch
procedure has terminated, starting from Olympus Base.

I have attached a screenshot of what I see, as well as a grab from the video
at a corresponding time. I have drawn an orange circle around the part
of the right-hand display I am talking about.

f0OEc4H.jpg


I seem to be using a different version of TransX. I downloaded what I thought was the most recent.
 
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statickid

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Well... I haven't watched the video but here's what I see when I look at that.

TOP: You are planning to transfer to Phobos. In the RIGHT screen, there is no encounter yet, so transx is just showing the outline of the target very close (no encounter)

BOTTOM: Similar situation... however, I see the LEFT screen is showing that the planned trajectory is not very far along in planning, but planning has been started. on the RIGHT screen, the cross represents a very very zoomed out view of the target (no encounter)

These are similar because neither is displaying a proper encounter. They are different because as you are planning TransX will show the disc of the target automatically zoomed with the encounter trajectory, however, if there is no encounter the encounter view will just show nothing but the disc very large(top screen) and if the encounter kind of exists but is really far away, the disc will convert into a small cross to show where the body is (bottom screen)
 

Planitia

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I have taken this scenario all the way to Phobos orbit, but without the benefit of the precise encounter guidance I end up missing Phobos by about 230 km. But at no point along the way does the TransX Encounter window show anything but that big circle. So I do not think it has anything to do with how far along the plan has progressed.

I wonder it if could be that Phobos has a small gravity, 0.0057 m/s^2, that TransX does not "see" it's Sphere of Influence?

To do it without TransX Encounter stage, I figure out when Phobos will cross a node, then work calculate from that in time to get the required launch time. No plane change required. But timing is critical.
 

statickid

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picture.php


Looks like your plan isn't good enough to draw the trajectory. You are correct it does seem to need to be within the sphere of influence to draw the second view. However, if you look at the Cl.App. on your plan it says 8.502megameters. Not too great on the accuracy. Now if you look at my plan, my trajectory puts my craft within 176 meters of hitting the center of the disc and TransX does indeed draw a green line. In fact it will draw the line up until about 7.3km away from smack dab in the middle. Then on my third screen you can see that missing the center by more than 7.4km or so causes the line to disappear.

So in conclusion it is not "without the benefit of the precise encounter guidance" that you are missing Phobos

~~ it is without the benefit of precise encounter PLANNING that you are missing Phobos.

---------- Post added at 03:46 PM ---------- Previous post was at 03:32 PM ----------

It is interesting to note that the orbit of Phobos around mars is between approximately 9.2-9.5Mm. Mars radius is approximately 3.4Mm. If you stood on the surface of mars, and Phobos passed over head, it would only be about 5.98Mm away from you, so having a closest approach of 8.5Mm means that you are probably starting the maneouvre too early, and heading in the wrong direction.
 

Planitia

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Aha. I did do one run with more careful micro tweaking of dV and ManDate and got the Cl App to 8.3km. If I had kept fussing it would have worked. Thanks! Now that I know how close I need to get - under half a diameter, I should be able to complete my challenge.

This was much easier with a plane change! :)
 
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