Help docking DG to ISS

[startrekmaniac]

Could you show me a picture?

 

[polaris149Tiberius]

You need to wait for the path of the target's orbit to pass over your launch site:
Bring up Map MFD.
Select ISS as target,
the yellow line is the ground track of the ISS's orbit.
the yellow line will slowly move as the Earth rotates.
You should wait until the yellow line passes overhead (or very nearly so).

Based on your earlier posts, you already figured out how to align planes. All waiting until the correct launch time does is make aligning planes easier/less fuel intensive.

Agreed. The path of the ISS's orbit plane moves from Right to Left while the ISS itself orbits counter clockwise. This tells you your Azimuth will be Eastward to match the orbit of the ISS. When the path of the ISS's orbit plane gets near Cape Canaveral from the east, you will want to get ready to launch. If the ISS is downrange then you should go, otherwise fast forward until you have these conditions for the next launch window.
Your orbit should be lower (closer to earth lower altitude) than the ISS so you can catch up to the ISS. If your orbit is circular then you will catch up sooner than if you have an eliptical orbit.

When you get into LEO then circularize. I found that a final orbit altitude or 200 to 250 Km is a good catch-up orbit altitude. When you get close to the ISS (say 300Km) you will want to change your ApA to just above the ISS's current altitude.
This will make your orbit higher aty one point. It will also slow your speed towards the ISS. This is ok. I use rendezvousMFD to do this for me. When you get within 30km your near final approach phase.
I use IMFD's Velocity Match when I start to go away from ISS. Just close in on the ISS using those other tutorials for now, Im still working on my final approach testing.
I hope this helps for now.

 

[startrekmaniac]

How close to the cape. Just show me a picture. I learn by seeing things. It takes me longer to learn something if I just read it. Thats why im having some much trouble with getting to the ISS.

 

[Urwumpe]

How close to the cape. Just show me a picture. I learn by seeing things. It takes me longer to learn something if I just read it. Thats why im having some much trouble with getting to the ISS.

Your problem is not having to read it or see it - your problem is a strong lack of imagination, requiring people to explain you what you see with your own eyes in Orbiter. Can you imagine what a "orbit plane" is?

Close to your launch site on Map MFD is simple: So close that your orbit plane is as equal to the ISS orbit plane as possible. When the ISS orbit runs exactly over your launch site in zoomed Map MFD, it is maybe good enough.

Better is using Align plane MFD - set the target to ISS and watch the time to the next node. When the time left is around 85 seconds, launch a vertical launching rocket. For a horizontal take off, like the DG, use around 120 seconds.

Basically, docking can be quickly solved with imagination and trying it. Most mechanics behind docking are easily visible with the standard tools.

 

[startrekmaniac]

okay ill give it a try.

Did I get it right?


--------------------------------------------------------------------
Moderator Note:

*Posts merged, -10 post count. No double posting. Forum rules HERE.

Regards,
-Tex
--------------------------------------------------------------------

 

[startrekmaniac]

DG to ISS part 2

Okay so Im now trying to sync my orbit. My RInc is 0.01 but my DTMin is 303.8. I cant get it down to 0 to save my life. What im I doing wrong? Yes ive been looking at the video.

 

[Urwumpe]

okay ill give it a try.

Did I get it right?

Still too much distance. When you see only ONE line on map MFD, you are right.

 

[Urwumpe]

I got my DTmin down to 0.03. Close enough?

Do you also have a intersection now by crossing the orbit of the ISS? Otherwise, this should, in a perfect world, bring you as close as 233 m.

 

[startrekmaniac]

My Rinc is 0.01, if thats wht you mean.

 

[Urwumpe]

My Rinc is 0.01, if thats wht you mean.

No, I mean intersection inside the same orbit plane.

Your orbit should cross or touch the orbit of the ISS.

Let's assume you are in a nearly circular orbit (Low ecc) below the ISS. Then you select Tg-Pe as intersection mode in sync orbit. When this display reaches the final orbit until minimum time distance (DT), switch to intersection #1 and burn prograde until it shows a intersection again. Burn longer if this reduces the DT on the top orbit. Otherwise, stop with the intersection.

See this now for getting close:
http://www.orbiterwiki.org/wiki/Rendezvous

 

[startrekmaniac]

When you say intersection are you talking about the sync orbit mfd. I was below the iss by only a few kelamters. The ISS was at 369.7 when it was at my apa. I burned prograde at Pea and brought it up to 369.7. So I should be able to meet up with it. Is that what your talking about?

 

[startrekmaniac]

Still needing help

If was about ten kil below the ISS what would I need to burn Pe or Ap?

 

[skeemo]

Going by the screen shot you posted...assuming your plane is already aligned with ISS you need to do the following:




1. Match one side of your Orbit altitude to ISS - Either PeA or ApA, which ever is on the daylight side I would suggest which from the screen shot looks like PeA.

• Select ISS as a target on your Orbit MFD.
• Look at ISS's altitude just as it crosses your PeA and write it down.
• Coast around till you reach your ApA.
• Burn either prograde or retograde at ApA to match your orbit altitude on the opposite side of the planet to ISS. Percision here will make docking easier. (If ISS is at 360.2K at your PeA, then your altitude should be exactly the same at that location.)

2. Sync Orbit with ISS

• Now that you've matched your orbit altitude to ISS at the point in your orbit where you wish to intercept ISS (your PeA), you can now use the Sync Orbit MFD.
• Target ISS and press MOD until you see Sh periapsis or Sh apopsis (choose the side which is at the same altitude as ISS which in your screen shot is going to be PeA, so choose Sh periapsis.)
• Finally coast around to the spot you selected and do your sync burn.
  • If ISS is behind you, burn prograde allowing ISS to catch you.
  • If ISS is in front, burn retrograde allowing you to catch ISS.
• Do your burn until *DTmin reaches '0'. You may have to use translation thrusters to hit 0 exactly. You want this number right at 0.

*If burning retrograde, watch your orbit altitude on the other side making sure it gets no lower than 150k!

[EDIT]Sorry, I missed a few details I added, if you already read the post you might re-read it.[/EDIT]

Hi there,

this is my first post, so i'd like to say hello

anyway, i am stuck to orbiter now for 2 weeks, its really a great sim.
For myself, as a old sim player, its really what i've been looking for

however i tried the tutorials from "go play in space" but i cannot get to the iss

Here's what i've done and where the problems are :

• i correctly aligned planes (Rinc = 0.00), which is preset by the scenario.
• i watched and wrote down the ISS' altitude (e.g. 360.3 km) at MY ships periapsis.
• due to my PeA isnt the same, i do a correction burn at the apoapsis.
  in the tutorial scenario my PeA is lower so i do prepar to do a prograde burn at the apoapsis.
• i wait (using time compr.) till i reach apoapsis and go prograde and start firing the main thrusters. i then do some fine corrections to tune the PeA to exactly match the ISS value (e.g. 360.3 km).
• But, and this is where it starts to screw up, the new PeA is not stable. it will raise more and more.
• so after syncing orbits via sync mfd (DTmin a.s.o.) i alway end up below or above the ISS.

I have no idea what to do to solve this. I also believe that the ISS changes its altitude over my Periapsis as well as i do.
I tried to start burning earlier (T to periapsis -30 sec) or later.
I watched the playback for the scenario, and the altitude keeps stable there.
I dunno what i am doing wrong here

I hope somebody can help me with this

thx

cu

 

[Tex]

Hi skeemo

May I ask what your lowest altitude was in orbit? If it's below 150.0k then you're experiencing atmospheric drag which will change your orbit altitude on the other side of earth as the atmosphere slows you down slightly it will lower the altitude on the other side.


*Edit - I just noticed you said it was raising... Maybe this could be caused from a realism setting called 'Nonsperical gravity sources'. I'm not positive on that though, could someone clarify for me if I am wrong. Thanks!

 

[Dr Pepper]

Hi there,

this is my first post, so i'd like to say hello

anyway, i am stuck to orbiter now for 2 weeks, its really a great sim.
For myself, as a old sim player, its really what i've been looking for

however i tried the tutorials from "go play in space" but i cannot get to the iss

Here's what i've done and where the problems are :

• i correctly aligned planes (Rinc = 0.00), which is preset by the scenario.
• i watched and wrote down the ISS' altitude (e.g. 360.3 km) at MY ships periapsis.
• due to my PeA isnt the same, i do a correction burn at the apoapsis.
  in the tutorial scenario my PeA is lower so i do prepar to do a prograde burn at the apoapsis.
• i wait (using time compr.) till i reach apoapsis and go prograde and start firing the main thrusters. i then do some fine corrections to tune the PeA to exactly match the ISS value (e.g. 360.3 km).
• But, and this is where it starts to screw up, the new PeA is not stable. it will raise more and more.
• so after syncing orbits via sync mfd (DTmin a.s.o.) i alway end up below or above the ISS.

I have no idea what to do to solve this. I also believe that the ISS changes its altitude over my Periapsis as well as i do.
I tried to start burning earlier (T to periapsis -30 sec) or later.
I watched the playback for the scenario, and the altitude keeps stable there.
I dunno what i am doing wrong here

I hope somebody can help me with this

thx

cu

Hi, on average, just how far above or below are you? If you have Nonspherical Gravity Sources enabled (like Tex mentioned), it's inevitable that this will happen, but you should still be able to make it within at least 20-30km of your intended target.

I have found that, after your initial rendevous burn, at the perapsis of each orbit, make a small correction burn using the RCS in translation mode to bring the DTe on the Rendevous MFD back down (or in some cases up) to zero. You can typically get within +-10km in altitude at the actual Rendevous by doing this. Note that if Nonspherical Gravity Sources is enabled, as soon as you finish the correction burn the DTe will start increasing or decreasing again. Don't try to "chase" the numbers as you will never keep it at zero. Once it reaches zero during the burn, wait until you come around to perapsis again to correct again.

 

[skeemo]

Hi

Thanks for your fast replies. :speakcool:

First things first :

Tex, altitude values in the tutorial scenario are all well above 150 km
(PeA 306, ApA 441, Alt 310).

Anyway, yes i checked the "Nonspherical Gravity Sources" box.
Will try later if unchecking solves the problem and report back

thx again

Re:

ok unchecking "Nonspherical Gravity Sources" solved the problem
PeA now keeps stable
thank you all :speakcool:

 

[startrekmaniac]

Okay in going to try it again. Before I start I need to know one thing, what should my km be?

 

[Dr Pepper]

Okay in going to try it again. Before I start I need to know one thing, what should my km be?

...From what Tex posted:

1. Match one side of your Orbit altitude to ISS - Either PeA or ApA, which ever is on the daylight side I would suggest which from the screen shot looks like PeA.

• Select ISS as a target on your Orbit MFD.
• Look at ISS's altitude just as it crosses your PeA and write it down.
• Coast around till you reach your ApA.
• Burn either prograde or retograde at ApA to match your orbit altitude on the opposite side of the planet to ISS. Percision here will make docking easier. (If ISS is at 360.2K at your PeA, then your altitude should be exactly the same at that location.)

2. Sync Orbit with ISS

• Now that you've matched your orbit altitude to ISS at the point in your orbit where you wish to intercept ISS (your PeA), you can now use the Sync Orbit MFD.
• Target ISS and press MOD until you see Sh periapsis or Sh apopsis (choose the side which is at the same altitude as ISS which in your screen shot is going to be PeA, so choose Sh periapsis.)
• Finally coast around to the spot you selected and do your sync burn.
  • If ISS is behind you, burn prograde allowing ISS to catch you.
  • If ISS is in front, burn retrograde allowing you to catch ISS.
• Do your burn until *DTmin reaches '0'. You may have to use translation thrusters to hit 0 exactly. You want this number right at 0.

*If burning retrograde, watch your orbit altitude on the other side making sure it gets no lower than 150k!

There is no fixed set of values for your Apogee and Perigee that you must reach to achieve a rendevous with your target. Unless you do the scenario exactly the same (which is not practically possible), the numbers will change.

 

[startrekmaniac]

No, Im talking about getting into orbit. How high do I need to be?

 

[Dr Pepper]

That's really up to you. Generally I prefer to be about 50km or so below my target (ApA and PeA are about 50km below target's ApA and PeA). Just experiment and see what comes up easiest for you.