Question Trip to Venus

[Goth]

It keeps pointing me straight at the Earth and burning me straight into it.

That's just because you have to wait a bit. The graph on Orbit eject shows you pretty well if you're going to hit the Earth or not (if you're in Self PRJ). If you are hitting it, just wait (time warping) and fire the autoburn again. If you're not sure when is the right moment, just point the nose in the direction told by the burn vector and time warp untill your nose point far enough from the Earth.

And do I just ignore Ejection time on the left MFD? It shows zero.

Yes because you already are in the right launch window.

 

[greyrogue715]

Another attempt. It seems to insist on ejecting me on the night side of the planet. It autoburns for about 10 seconds, changes attitude straight at Earth. And refires engines. Idk what's going on, but I thinking I may be better sticking with Earth orbit operations, which is getting boring after 5 years of attempted interplanetary flight.

 

[Goth]

I tried that date and I get weird results as well. I suppose we both have to wait an IMFD expert. ^^

 

[greyrogue715]

I'll try what you said and also another date.

---------- Post added at 08:53 AM ---------- Previous post was at 08:28 AM ----------

Same result. I don;t know if there are IMFD experts on here. Maybe a few ten year olds. lol

 

[Ripley]

You are not in an external view while AB takes place, are you??

 

[Goth]

Ok the PeA was not the thing to watch out.
I've attached a scenario. You will reach Venus close enough and using no midcourse corrections.
I just incremented TIn a bit so that the trajectory became circular enough to save fuel.
Since you're already in a nice launch window there was nothing else to worry about.

Now the question is:
why IMFD shows that the PeA is 0.702AU when I actually encounter Venus at something like 500k and so my plan is actually good?

This is one thing I've never understood about the IMFD.
Especially since I'm used to the "Close approach" variable in TransX.


EDIT
Bad scenario. See the new one:
http://www.orbiter-forum.com/showthread.php?p=360838&postcount=37

 

[greyrogue715]

I made it at least to the orbit of Venus. I applied MCCs and then shot in front of Venus and ended up with a PeA back in the Ms. I kept trying autoburn to correct and it made it worse. I'll make attempt number 904 sometime today and not make any corrections until Planet Approach.

I did notice a major thing with your scenario that obviously is a problem. When I switched to burn view, both MFDs changed to burn view. I wasn't getting that before. Like I said, I don't think the two are syncing up for some reason.

 

[Linguofreak]

Now the question is:
why IMFD shows that the PeA is 0.702AU when I actually encounter Venus at something like 500k and so my plan is actually good?

I'm thinking it's probably a Sun-relative PeA. Venus is 0.72 AU from the Sun.

 

[Goth]

Yeah that's why.

@greyrogue715
For the midcourse corrections you have to be sure you still have the same plan open in the IMFD, and then change the source. If for some reason you lost it, you have to target again Venus and manually adjust TIn to save dV (the starting plan will be too fuel expensive).

When I switched to burn view, both MFDs changed to burn view.

Doesn't happen to me. :idk:
In my scenario they are connected, if for any reason they aren't when you run it, just manually share one of them.
If you meant it happens in your scenario, then yes, you have not correctly shared them. Go to the Menu with both and see what's written in OpMode.

 

[greyrogue715]

Yeah, your scenario they were connected, mine no. OK I will do so.

---------- Post added at 04:38 PM ---------- Previous post was at 04:26 PM ----------

Well I managed to screw up the scenario you sent me. I load it now and go to the burn view page and it tells me 'no burn vector'. I wanted to send the scenario back to you to see if you can see what I did to it, but I don't see any 'attach file' button here.

 

[Goth]

Well, can't you download it again?
Anyway, maybe you get no burn vector because you use the target intercept program. You have to press AB (or using the manual burn vector display) from the MFD which has the Orbit eject program.

Attach file is at the end of the post edit page. Click Go Advanced when you quick reply and look at the bottom of that page.

 

[ADSWNJ]

Launch 90-ish or 270-ish

As you see on this crappy Paint-drawing, perform the prograde ejection-burn from e.g. a 0 inclination circular orbit around the Earth on the Earth's sun-lit site (red circle), and therefore rising you ApA, until you have reached the escape-velocity. Then you have at the same time performed a retrograde-brun Sun-relative, and have lowered your PeA around the Sun (golden circle), and have a perfect rendezvous comming up in a few months with Venus or Mercury!:thumbup:

It's funny - last weekend, I was messing around with TransX to go to Mercury from Earth. Never gone to an inside planet before, but I'm pretty comfortable with TransX, so I thought what the hell ... do it by intuition. (p.s. TransX / IMFD independent ... you could use either for this). SO I was thinking ... I need a launch window with a 270 degree heading, to fly backwards round the Earth, so I can do a "normal" prograde burn (on the dark side), to get out of the Earth gravity well to then track prograde round the Sun and drop in on Mercury.

For some reason, I never thought of launching 90 degrees and burning on the inside of Earth on the sunny side! Doh!

 

[greyrogue715]

OK, I got the scenario back. I don't think I can go any further with this until I find out why the 2 MFD are not syncing up.

 

[Goth]

If you open my scenario and you see that the "Orbit eject" program is displaying something, then the two MFDs ARE correctly syncronized.
Otherwise, the "Orbit eject" program would give you an error (no graph, only a yellow text), since you've selected "Course" but it can't read the course because it's not linked to the other MFD.
I don't know why you think they are not linked, they actually are.

Are you using version 5.5?

Just so you make sure my scenario is working, left MFD should be Target intercept, right one should be Orbit eject program.


EDIT
Another thing. I asked for clarifications in the italian orbiter forum and this is what I got:
- EIn (plane alignment error) must be set as close to zero as possible, changing TIn;
- the IMFD always makes you reach the center of the target planet, so you will always encounter the planet;
- but of course you will need MCCs at some point.

So if you miss Venus:
-bad MCCs;
-bad EIn *;
-or that problem about sharing one MFD with the other.

Other things, like choosing an ejection/intersect time or another, just change the required dV, so that's not a cause of failing the encounter.



* I totally forgot the EIn variable. :facepalm: Here's about it from the manual:

EIn: Escape/Ejection Inclination.
An angle between escape vector and the orbital plane of the ship. In a transfer program, it is also the angle between the orbital plane of the ship and the target position at the time of interception.

 

[greyrogue715]

They are synced then. When I first ran your scenario and changed to the burn screen, the other MFD changed with it. When I tried again later, this didn't happen, making me think I screwed something up with your scenario. Idk why this happened. At any rate, they must be synced.

I did notice your scenario put Orbit Eject on the left and tgt intercept on the right, so I will switch them.

I'll work with the EIn variable and see what I come up with.

I appreciate all the help you been giving me, Goth (and others). I will get this thing figured out once and for all.

 

[Ripley]

...Does the Left MFD have to also be set to shared with the right. I set the right for left, but do they both have to be set?...

No, only one.

From IMFD manual, page 2:

Sharing Flight Plans
a Single flight plan can be "shared" between multible MFDs by seting the IMFD into the remote access mode by pressing [PG] button in main menu. Popup window will ask about an ID code of the MFD being accessed.
...snip...
When using multible instances of IMFD they must not access in each other. For an example when using two instances only one of them can use remote access.

 

[Goth]

Oh, still another thing: having the orbital plane aligned with the Venus' one is also important.

After having jogged my memory and having taken into account all the things I've said in this topic, I tried again and reached Venus hitting it in the center using 4'534 m/s and two small MCCs.
I've made a ZIP file with three scenarios showing my trip.
:tiphat:

My plan encounters Venus in the second intersection point (not the first one). So my trip lasts more then what the launch window schedule suggests. That's because IMFD gave me a nice plan with that date. I don't know if it's possible to change this, but the important things are that I met Venus and that I did it using a decent amount of fuel.
My guess is that since I worried about EIn I made the TIn too high. Maybe I can launch anyway even if EIn is something like 3°? I'll try but I ask for clarification.

I have aligned the orbital plane with Venus (well, then it went up to 2,15° but it's not a big deal) while in orbit (just for simplicity) and then I filled the fuel to the max with the scenario editor so you can easily see the used dV from the DG panel (just do 29'925 - current dV). But just pretend that I launched from the surface with the right inclination to enter an orbit with zero inclination with the Venus' orbital plane. This is of course the right procedure to save fuel.

Of course you are not supposed to crash into Venus ^^, so after the last MCC use the Planet approach program, but be sure that you are near the Venus SOI. If you use that program too early, it will use A LOT of fuel and it might even fail to make you reach the destination.

Even better than what I did should be using the Tangential transfer program, but I miserably failed trying.

Anyway, I prefer TransX because:
-if you have a nice "closest approach" variable it will always make you reach the target [IMFD just fails too many times (but it could be my fault)];
-I almost never need MCCs, so you save fuel;
-TransX is so precise that I don't even need to use the planet approach program (again, saves fuel usage).

 

[greyrogue715]

I always make sure orbital planes are aligned first so that is not a factor.

My plan encounters Venus in the second intersection point (not the first one). So my trip lasts more then what the launch window schedule suggests.

On the Orbit Eject page, is this what the view multiple periapsis selection is or does that refer to being under the influence of multiple bodies (Sun, Moon, Earth etc.)?

Maybe I will blow the dust off Trans X and see if I can't figure her out, as well. I would like to learn both MFDs, as well as the DV Tools MFD eventually. I was reading the manual on that last night and it looks interesting.

As per your earlier question Goth, I have a few different IMFDs but I use v.5.5. What version of TransX are you using?

For now, I'll persist with IMFD until I can get a handle on it, but I will also re-read the TransX manual(s) today.

 

[Goth]

Yep, the best thing is indeed learning both MFDs, so keep trying to understand IMFD before.

What version of TransX are you using?

Click here to download the last TransX version. It has a graphic fix and a useful Enter button to enter values directly.

On the Orbit Eject page, is this what the view multiple periapsis selection is or does that refer to being under the influence of multiple bodies (Sun, Moon, Earth etc.)?

I don't know what you refer to, but you can see that just looking at the graph. The target intercept program graph is just like the sync orbit MFD. Looking at it you can see where the HTO orbit (the planned one) intersects with the target planet orbit, so you can see if you will intersect the planet on the first intersection point or the second one. Tangential transfers have only one intersection point.

 

[greyrogue715]

Thanks for that link. I see it has the fix that I assume was from the white disc graphics error showing up on one of the pages. I quit using it back when I encountered that error, and that is why I began using IMFD. I will try your two scenarios, as well. Thanks again.