Problem DG4-ISS Orbit sync and TransX problem

[Bluemarble]

Hi all ,

Long term Orbiter, long term in that I first tried Orbiter back in 05 - only recently really getting back into it . Starting from scratch is hard. I have the patched 2010 version and DG4. ProSpec'd my way into orbit - easy, aligned planes too within 0.000 degrees fine, sync orbit...mmmmh

1 ) - Watching Tex's great youtube vid I thought I do exactly what he has done, I would like to see what the ISS Apoapsis alt is at its Ap 'zero' point on the orbit MFD, it never seems to actually get there though with both the Periapsis and Apoapsis points on the MFD moving about a lot - how on earth did Tex have those points steady in his orbit MFD ? My orbit is perfect as is my alignment...

2) Having the above issue I though there has to be a alternative - indeed TransX seemed to fit the bill. Diligently copying the

youtube link from Tex , step by step. I loaded the Tx-ISS scenario and get to the point of changing the MJD date - even with Hyper fidelity I am only able to get the distance down too say 1000 m - but again the constant change is a problem, whilst changing the fidelity from medium to fine etc and ever lowering the distance I notice the constant distance is changing so much - I get it down to 1k and seconds later its 1.2k, 1.3k - Tex's vid shows an enviable 'lock' on any such change as was the case with the Orbit snyc MFD, not too mention that 'hyper' is moving the distance by 1k at a time instead of the very fine adjustments in the vid. Is the matching of the 'blue line' into the 'Yellow line' the point in which the above problem originates ?


Thank you Tex for the vids - I can tell this is the beginning of a real obsession, I just wish I could follow the tutorials without the above issues. Help please !

Thanks...Jon

 

[flytandem]

That video is made with non-spherical gravity unchecked. Maybe that's it?

 

[Tex]

Hi Bluemarble, welcome back!

I must give credit where credit is due... With the exception of my "XR2 Wideawake to Brighton Beach" tutorial, all other TransX video tutorials are by flytandem, I just uploaded them with his permission.

What is your current realism settings? Your problem sounds like normal behavior IF you have 'Nonspherical gravity sources' actived, which it is not so in the videos.


FWIW, I play with the following realism settings:

Complex flight model: ON
Damage & failure simulation: ON
Limited fuel: ON
Auto-refuel on pad: OFF
Nonspherical gravity sources: OFF
Radiation pressure: OFF
Gravity-gradient torque: ON


EDIT - Ninja'd by the man himself. :ninja:

 

[Bluemarble]

Ha, awesome - quick reply - and I do indeed have non spherical ON - .....thanks.

Strange 'game' this , as difficult as certain parts are , it is almost a calming experience to pilot a craft over the planet - the exactness of every move required and the speeds involved to end up docking at <0.02m/s cant be found in any other Sim.

---------- Post added 03-02-11 at 10:58 AM ---------- Previous post was 03-01-11 at 11:11 PM ----------

After sorting out the correct settings it looked like I was all set. Again following the youtube link tutorial - I got my approach in TransX to around 300m - waited till 70 seconds too burn and linked up the 'X' - Rvel down too 0.00xx At burn point I was still 400k away so sped up time until perhaps 10 k away - Rvel was around 50m/s but dropping - but 8k was the closest I got !

I had the second TransX MFD open showing that my approach should have got me within 300 m - It got one thing right - I did indeed reach 0.00xx Rvel - but this figure went up to 5m/s , 30m/s quite quickly and the ISS waved goodbye .....

I have the exact same settings - what could be going on here ?

thanks...

 

[blixel]

Ha, awesome - quick reply - and I do indeed have non spherical ON - .....thanks.

I can relate to this. I had a very difficult time following the instructions to sync with the ISS because my Periapsis and Apoapsis were constantly moving. Once I turned off Nonspherical gravity sources, Radiation pressure, and Gravity-gradient torque, it made my experience a whole heck of a lot easier.

Now, having said that, if you want to see how to compensate for those additional Perturbations, there is an awesome Playback/Tutorial called "Space Shuttle to ISS" in the folder: 2010 Edition/New tutorials

If you like to watch playbacks, that is a great one to watch. (Period.) Plus, it explains "what the heck is up" with the moving Periapsis and Apoapsis, and it explains how to figure it into your rendezvous effort.

Strange 'game' this , as difficult as certain parts are , it is almost a calming experience too pilot a craft over the planet - the exactness of every move required and the speeds involved to end up docking at <0.02m/s cant be found in any other Sim.

Agreed. In the back of my mind, I realize it's just a bunch of numbers being "crunched" in the computer. But even with that realization, there is something extremely fun and, as you said, almost calming about getting into orbit, killing the main engines, and drifting along around the planet.

I like the regular internal cockpit sound. It's good ambient noise. (I don't most of the various random event sounds though, so I disabled those in the sound editor. Some of them are good, but some of them are irritating.)

Regarding the problem you're still having, I'll let someone else answer. I don't use TransX for rendezvousing with the ISS/Mir/etc. I use the same method that the guy uses in that playback I mentioned above.

 

[Bluemarble]

Thanks for the link Blixel - I will watch that. Im not that enamoured with TransX at the mo, just want to dock - otherwise what kind of laughing stock of a orbinaut am I! .


Taking the 'calming' aspect a little further, and transgressing a little...orbiter preceded Google earth by a few years, I noticed since using it - and google earth, that I have a deeper understanding of our insignificance and able to put things into perspective when needed. Perhaps Orbiter should be mandatory for schools - a cliche' perhaps , but the no-country-border-were-all-together-in-this aspect of this software could be a great influence.

 

[blixel]

Thanks for the link Blixel - I will watch that. Im not that enamoured with TransX at the mo, just want to dock - otherwise what kind of laughing stock of a orbinaut am I! .

I'm pretty interested in this docking topic because I only just figured it out within the last week. I'm paranoid about forgetting things I've learned (especially after taking a hiatus), so I have been documenting all my Orbiter experience. I have started my docking "guide" (for my records), but it's not done yet. Otherwise I'd offer to email it to you.

I'm not crazy about TransX. I've learned enough about it to be able to use it instead of the Transfer MFD for getting to the moon, but I prefer the Transfer MFD. I would have to be convinced that TransX is "better" than the standard Orbit MFD and Sync Orbit MFD to even bother trying to use it for rendezvousing with the ISS.

I suppose when I "get bored" with all there is to do on and above Earth, and going to the moon, I may have to learn to like TransX for going to Venus/Mars.

Taking the 'calming' aspect a little further, and transgressing a little...orbiter preceded Google earth by a few years, I noticed since using it - and google earth, that I have a deeper understanding of our insignificance and able to put things into perspective when needed. Perhaps Orbiter should be mandatory for schools - a cliche' perhaps , but the no-country-border-were-all-together-in-this aspect of this software could be a great influence.

This comment reminds me of this documentary I saw, about a year ago.

http://documentaryheaven.com/james-may-at-the-edge-of-space/

After taking a ride up to 72,000+ feet in a U2, and looking back at the earth, he says ‎"If everyone could do that once, it would completely change the face of global politics, religion, everything."

 

[Tex]

I have the exact same settings - what could be going on here ?

Could you post your scenario here in which you're having the problem so I can take a look at it?

I would have to be convinced that TransX is "better" than the standard Orbit MFD and Sync Orbit MFD to even bother trying to use it for rendezvousing with the ISS.

TransX is good for getting to ISS with a single burn. If you want to get there as quickly as possible, then it is a good solution. Otherwise, using the SyncMFD and taking your time by using more orbits and less fuel is the more 'realistic' way of doing it.

 

[Bluemarble]

Tex - I have all Perturbations off - do you mean the 'log' file - where ever I might find that ? - otherwise the situation is as the video shows - getting DeltaV down to less than 0.1 m/s - at that point I am 400k away from ISS.

I simply speed up time until perhaps 10 k away at which time at approx 100m/s Rvel but dropping - at maybe 3/4 km Rvel after reaching 0m/s briefly starts going negative again ...?

 

[blixel]

I simply speed up time until perhaps 10 k away at which time at approx 100m/s Rvel but dropping - at maybe 3/4 km Rvel after reaching 0m/s briefly starts going negative again ...?

If you are getting to that point, you are 99% done.

Make sure you have the Docking HUD up (as opposed to the Orbit HUD), then you need to cancel out your relative velocity by rotating your spacecraft to the velocity indicator. (Which appears as a + sign inside of a circle.)

Using translation thrusters, (and even CTRL+ for tight precision if necessary), keep your spacecraft pointed at that indicator while you cancel out all the relative velocity. (It will never stay at 0 at all times. But as long as you cancel out the majority of it, then you will stay in proximity with the ISS for a very long time. Several orbits I would imagine.)

I would say that is your next logical hurdle. Actually docking with the ISS is a hurdle unto itself. But getting in proximity of the ISS and being able to *stay* there without drifting off sounds like the point you are at.

 

[Bluemarble]

Blixel , unfortunately not - At 10 k or so , Rvel is 100-200m/s , constantly falling all the way down too 0m/s, and then this figure starts climbing into the negatives -1m/s , -20m/s etc while ISS slides by.

 

[Wishbone]

Ticking off the possibilities of gaffes I would have made: have all your engines been turned off?

EDIT: including RCS, retro and hover, especially hover.

 

[blixel]

Blixel , unfortunately not - At 10 k or so , Rvel is 100-200m/s , constantly falling all the way down too 0m/s, and then this figure starts climbing into the negatives -1m/s , -20m/s etc while ISS slides by.

Here's what it sounds like to me. (And I could be wrong mind you.)

When you are at that point where you are going to rendezvous with the ISS, you have to keep in mind that you are still on a completely different orbital path than the ISS. Your Periapsis OR Apoapsis will be completely out of sync with the ISS.

For example, if you chose the Periapsis as your rendezvous point, then your Apoapsis will be completely out of sync with the ISS. And if you chose your Apoapsis as the rendezvous point, then your Periapsis will be completely out of sync with the ISS.

That means, when you are closing in on the ISS, you have a relatively narrow window of opportunity to adjust your orbital path so that it matches the ISS. (This is done by way of canceling the relative velocity between you in the ISS. In so doing, it has the Net Effect of making your orbital path match the ISS.)

For example, if you are rendezvousing with the ISS at Periapsis, that means your Apoapsis is probably 10, 20, 30, or even 50 or 100 kilometers higher or lower than the ISS on the other side of the planet.

Therefore, if you don't "fix" your Apoapsis at rendezvous. The ISS is going to buzz right by on its pre-defined orbital path (remember - it's not changing its path, you are changing your path to match its path.)

But don't focus on changing your Apoapsis. Focus on eliminating the relative velocity between you and the ISS. In so doing, it will automatically "correct" your Apoapsis.

I have attached a playback that I literally just made a minute ago. This uses all default Orbiter 2010 stuff, so it will definitely work.

This playback picks up right at the point where I am about 35 kilometers away from the ISS and closing in on it a hurry.

Notice how far out of alignment my orbit is with the ISS before I cancel the relative velocity. Then notice how my orbit matches the ISS after I bring the relative velocity down to zero.

The point you have to understand is that just because the ISS is closing in on you and the relative velocity is getting smaller does NOT mean that your orbital paths are the same. Therefore, once the ISS catches up to you ... even though it shows a 0 relative velocity for maybe all of 5 seconds, it is going to increase rapidly after that point because it is going on its normal orbital path ... and you are going off on a different orbital path.

I think if you watch this playback, it will "click"

P.S. Ignore my absolutely HORRID dock ... (if you bother to watch it that long). I turned on Gravity-gradient torque and forgot about it. So it made the docking a lot harder than I'm use to. Without Gravity-gradient torque, I can almost dock with my eyes closed now.

 

[Bluemarble]

Thanks Blixel - a lot clearer now - I do know what to do, except I cannot get the velocity vector + in a circle over ISS - how did you manage this ?, I am in docking mode .....

 

[blixel]

Thanks Blixel - a lot clearer now - I do know what to do, except I cannot get the velocity vector + in a circle over ISS - how did you manage this ?, I am in docking mode .....

The velocity vector + in a circle is located at the direction of the velocity difference ... which usually is not in the same direction as the ISS. In my playback, it just happened to be close by, but in most of my rendezvous, the velocity vector + in a circle is off to 90 degrees to my spacecraft's right, off to the left, or slightly above me or slightly below me.

If you follow the V[ISS] indicator using rotation thrusters, you will find it eventually. (Sometimes I feel like I've rotated my Delta-glider 360 degrees in every direction before I finally find the darn thing.)

The thing to understand about that indicator is that it's not just the difference in velocity between you and the ISS, it's the difference in velocity between and the ISS as it relates to your orbital path.

EDIT: A picture is worth a thousand words, so here's a screenshot compilation to illustrate the point. When you rendezvous with the ISS, your Orbit will probably look something like the BEFORE picture. You have only a few precious minutes to hone in on that velocity vector and "zero out" your orbit. Once you have done as much, your Orbit should look like the AFTER picture. (That is, your Orbit and the ISS Orbit should be nearly 1:1. Your orbits will not be perfectly aligned, but they should be so closely aligned that you should have no problem at all keeping yourself in proximity with the ISS for as long as you like. You can stay undocked from the ISS and complete an entire half orbit and only have a difference of maybe 5 kilometers ... which of course can be closed with translation thrusters.)

http://i.imgur.com/9owZE.png

 

[Bluemarble]

thanks for your patience, I'm just not sure when to null my velocity, at say 35 km ISS is showing as 100m/s Rvel, I try and null it then , fine, but the close I get the Rvel starts shooting off again. Chasing this figure down doesnt seem right.

 

[blixel]

thanks for your patience, I'm just not sure when to null my velocity, at say 35 km ISS is showing as 100m/s Rvel, I try and null it then , fine, but the close I get the Rvel starts shooting off again. Chasing this figure down doesnt seem right.

Hmm... that last edit didn't go right. I'll try again with this image tag

I know exactly what you're talking about ... I had all these exact same problems you're having just a week ago. This is all fresh in my head ... that's why I'm really interested in this topic with you.

The first time I closed the gap, it felt dirty to me. (e.g. I felt like I got lucky ... and I couldn't duplicate the result.)

The second time wasn't any better. I caught up to the ISS ... and kind of sort of balanced things out ... but everything I did seemed opposite of what the directions said I was supposed to do. (e.g. I was applying forward thrust to eliminate the velocity difference and that was working ... even though directions I was reading said I would need reverse thrusters.)

It was really frustrating.

There are actually two velocity vectors. (Just like there is PRO GRADE and RETRO GRADE, and Ascending Node and Descending Node.) There is also a + Velocity Vector and a - Velocity Vector. (And they are 180 degrees apart.)

You can use either one. Just like you can go PRO GRADE and use Reverse thrusters (as opposed to going RETRO GRADE and using main engines.) Likewise, you can face the + Velocity Vector and use Retro engines. Which is what I did in that playback. The reason I did that was because I knew the retro engines were more than capable of eliminating the difference in velocity. But if you happen to be closing in on the ISS insanely fast, you very well may need to face the - Velocity Vector (which looks like a Bullseye target) and fire main engines.

As far as when to fire the engines ... that is going to depend on the velocity difference. As Tex pointed out in an earlier message, the "realistic" approach (which I assume means the way NASA does it) ... will have you approaching the ISS with a minimal difference in velocity. That would make sense because the Space Shuttle does not have power Delta-glider engines.

As such, the ISS is approaching so slowly that you don't need to take much action until it's quite close. (e.g. 20 kilometers, even 10km I would imagine.)

But if you are using TransX and warp drive technology to close in on the ISS at some screaming fast speed, then you'll need to act sooner.

 

[Bluemarble]

Blixel - its sorted !


Got up to about 35 km away and forgot too null velocity

IN THE DIRECTION OF THE CROSS SYMBOL THINGY !



Ha, was trying to null looking at the ship proximity distance - other than that , got too within 20 cm of docking and ship was at wrong angle but lots of fun shifting around the ISS in 3D.

Thanks for the explanations - its quite something when you overcome a problem in this game. I like the scn feature of being able to watch someone else's handy work in real time (tiny file size too ) ...Well done me lol



Now too try the 'Grand Tour' ! ................jst kiddin

 

[blixel]

Blixel - its sorted !

Awesome.

 

[Bluemarble]

I could of just PRO300SPEC0'D it ! - great autopilot on the DG4...what do the real Shuttle pilots do ? - manual ?