Flight Question TransX Burn Accuracy

[Tniffoc]

When I watch tutorials on TransX, the people doing the burns seem to be able to center the green x much better than I can. When they time accelerate, the x will stay pretty much centered until the very end of the burn. In the end, their dVel will be < 0.0001. For the life of me, I cannot get my dVel below about 0.3. This is obviously causing problems with me totally missing my target.

Any tips on how to make my burns more accurate are greatly appreciated!

Cheers,
Tniffoc

EDIT: Sorry, if an admin stumbles across this, it would be great if it was moved to the MFD section, where it belongs, I'm brand new and messed it up. My bad

 

[Pyromaniac605]

I don't use TransX, personally I prefer IMFD, but are you certain that you have completely killed rotation? Even the slightest movement can make a big difference in time accel.

Edit: Also, if actually centering is the problem, try holding Control, it gives you finer control of RCS. (1/10 IIRC)

 

[Tniffoc]

I'm learning TransX before IMFD as it seems to me to be teaching more about the mechanics of interplanetary travel. While IMFD sounds convenient, I would rather know WHY IMFD is doing what it is doing before I start using it. I began using it and I felt like I was inputting random values, so I went with TransX, and I'm able to derive everything that I put in to it (at least for Earth->Moon and Earth->Mars missions).

I'm sure I completely killed rotation because I'm using the K Rot autopilot and I knew of the control keys, but I can't seem to quite get the x completely centered, much less keep it there.

EDIT: This is what my TransX looks like when I've the the x as centered as I really can. If it matters, I'm using a keyboard to control Orbiter.

 

[Mister Mxyzptlk]

If you can get it to 0.3 k/s then switch to prograde autopilot and finish your burn with translation in fine tune mode (hold CTRL). To finish off in translation mode you activate whichever translation controls are required to get all of your readings to zero.

 

[Tniffoc]

Alright, now that I've managed to seem to get the burn correct, the display of my orbit relative to my target orbit is still WAY off. Screenshot below. Any ideas?

 

[Ripley]

What's in your Launchpad->Parameters->MFD refresh (sec)?

 

[Tniffoc]

Its currently set to 0.20

 

[Bonanza123d]

When I watch tutorials on TransX, the people doing the burns seem to be able to center the green x much better than I can. When they time accelerate, the x will stay pretty much centered until the very end of the burn. In the end, their dVel will be < 0.0001. For the life of me, I cannot get my dVel below about 0.3. This is obviously causing problems with me totally missing my target.

Any tips on how to make my burns more accurate are greatly appreciated!

Cheers,
Tniffoc

EDIT: Sorry, if an admin stumbles across this, it would be great if it was moved to the MFD section, where it belongs, I'm brand new and messed it up. My bad

Welcome to the forum!

I use IMFD. I would start with that.

 

[Ripley]

Its currently set to 0.20

Mine is at 0.01.

I "only" have a Core2 Duo E6600, and no problem for fps.
Try to lower it if you can afford some fps loss, maybe it's because of that (could be).

 

[Wishbone]

The small dV difference doesn't really matter as long as you undertake mid-course corrections. This is the same in RL.

 

[Mister Mxyzptlk]

I don't know. My eject burns are never that far off of hypothetical plan. It isn't MFD refresh rate, mine is still set at 1.0 second and have accurate burns.

Do you "feather"(turn it down) the engine throttle (deltaV) to very low km/s for the end of the burn? Do you reduce your Rel inc. to zero? Try a burn without time acceleration one time and see if it is more accurate.

Also post a finalized scenario about 1000 seconds before the burn, and let some of take a look at it and try to duplicate the problem.

 

[Tniffoc]

I'll post the scenario as soon as I get home. I've used the Align MFD to get my rInc to 0.05 (this wasn't the best flight) and I use the forward translation thrusters towards the end of the burn instead of "feathering" the main engine throttle.

EDIT: Scenario attached.

 

[Tex]

I use IMFD. I would start with that.

And how does that contribute to this discussion? He already explained why he wants to learn TransX. :dry:

I'll post the scenario as soon as I get home. I've used the Align MFD to get my rInc to 0.05 (this wasn't the best flight) and I use the forward translation thrusters towards the end of the burn instead of "feathering" the main engine throttle.

EDIT: Scenario attached.

I noticed you said you only got your Rinc to 0.5. That's still a ways off, I'll take a look at your scenario and post my results in a bit. :thumbup:

 

[Tniffoc]

And how does that contribute to this discussion? He already explained why he wants to learn TransX. :dry:




I noticed you said you only got your Rinc to 0.5. That's still a ways off, I'll take a look at your scenario and post my results in a bit. :thumbup:

IIRC I got the Rinc down to 0.05, and I don't think I've warped from the time when I made the plane alignment burn and the time of the posted scenario. Again, I'll take a look at it when I get home, I was able to get at the scenario over a file share, but I cannot run orbiter from where I am right now.

EDIT: ... and thanks for the help as well.

 

[Tex]

Well, I looked at your scenario. Your plane was indeed off with Rinc at 0.05. You really wanna try and get that on 0 if you can. I fixed the plane for you in the (pre-eject) scenario below. If you load that and pull up the plane MFD, then you will see Rinc is on true 0. After that, I adjusted the prograde variable for your eject plan moving the closest approach a little closer and then burned it. You can see from my screen shot below that the burn was pretty accurate, even with the rush job I did accelerating time.

I provided a pre-eject and post eject scenarios for you below. :tiphat:

 

[Tniffoc]

Thanks a bunch! I'll make sure to pay more attention to the Rinc value next time. I'm still having the same problem with burning in the plan though. Even when I slow time down to 1/10th of normal to make sure I get the x almost perfectly centered, and use the kill rotation autopilot, the green x drifts very far from the original position. When I watched flytandem's video of this (and other) transfer(s), the green x stayed almost dead-center.

Are there any special tricks to this that I'm missing? At first i though that I might have had too low a parking orbit, but your completion of the scenario disproved that idea fairly quickly.

Even at 1x time, I have to perform a correction in the craft's rotation to keep the green x centered. The image attached to this post shows about where my green x is on average.

Just based on the tutorial video(s) that I've watched, I must be doing something horribly wrong.

 

[Mister Mxyzptlk]

I can't emphasize enough how important it is for you people learning transx to:

1. Circularize your orbit.
2. Reduce relative inclintaion to 0, not .05 or .02 but ZERO! (.0001 is OK).
3. Setup your eject plans as finely as possible.
4. Do your burns as precisely as possible.
5. MCC's at the halfway point then at each halfway point after that til you are on course.

If you set up transx imprecisely you wil get imprecise results.

Remember: This IS rocket science, so behave accordingly.

 

[Tex]

Thanks a bunch! I'll make sure to pay more attention to the Rinc value next time. I'm still having the same problem with burning in the plan though. Even when I slow time down to 1/10th of normal to make sure I get the x almost perfectly centered, and use the kill rotation autopilot, the green x drifts very far from the original position. When I watched flytandem's video of this (and other) transfer(s), the green x stayed almost dead-center.

Are there any special tricks to this that I'm missing? At first i though that I might have had too low a parking orbit, but your completion of the scenario disproved that idea fairly quickly.

Even at 1x time, I have to perform a correction in the craft's rotation to keep the green x centered. The image attached to this post shows about where my green x is on average.

Just based on the tutorial video(s) that I've watched, I must be doing something horribly wrong.

What are your realism settings? Gravity-gradient torque can cause the X to move some on you and I know if you have 'Nonspherical gravity sources' activated you will see deviations in your trajectory. I bet the Gravity-gradient torque is what's causing the problem for you. Although I normally play with that option activated, it was not activated in my video tutorials.

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

 

[Tniffoc]

What are your realism settings? Gravity-gradient torque can cause the X to move some on you and I know if you have 'Nonspherical gravity sources' activated you will see deviations in your trajectory. I bet the Gravity-gradient torque is what's causing the problem for you. Although I normally play with that option activated, it was not activated in my video tutorials.

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

I had a similar thought process, I was originally playing with nonsperical gravity sources and Gravity-gradient torque on, but I disabled them when my x seemed to be moving in ways unlike the tutorial. It still seems to drift majorly for me.

I can't emphasize enough how important it is for you people learning transx to:

1. Circularize your orbit.
2. Reduce relative inclintaion to 0, not .05 or .02 but ZERO! (.0001 is OK).
3. Setup your eject plans as finely as possible.
4. Do your burns as precisely as possible.
5. MCC's at the halfway point then at each halfway point after that til you are on course.

If you set up transx imprecisely you wil get imprecise results.

Remember: This IS rocket science, so behave accordingly.

1. IIRC, my Ecc was pretty darn low.
2. Originally, my Rinc was 0.05, but I've tried the same burn using Tex's scenario, where the Rinc had already been adjusted to 0, and had the same problems. My problems are with the execution of the burn, not using TransX, I actually find it quite intuitive.
3. ^ ...
4. This is what I'm trying to do, and, for some reason, failing miserably.
5. I'll do MCCs once I get the initial eject burn done properly.

EDIT: So, I guess my real question is, how do you guys get your burns to execute so nicely and why does my green x drift wheras others don't?

 

[Mister Mxyzptlk]

Oh my god! I just realized that you are using 1/10 time slowdown. That is not good because there is a lag time involved in processing the inputs. It is not necessary to go to 1/10th time, in fact I never use it for burns. It is really important the you FEATHER the acceleration with the throttle, not slow time down!