Cannot reach ISS

[tekinozbek]

Hi,

I've done multiple tutorials etc. and I've read the manuals too.

Here is my problem:

- I take off with DGIV from KSC rwy 33.
- My autotilot automatically orbits.
- I use the "Align plane" MFD to succesfully reduce inclination to 0 degrees (+/- 0.1 degrees).
- I switch to the SYNC ORBIT MFD and set target to ISS.
- I turn to prograde direction and burn main engines until the Sh-ToR(0) and Tg-ToR(1) are equal to each other.

Relative Inclination at 0 degrees, exact alignment and sync orbit successful, I am SUPPOSED to be on top of ISS.

However, My altitude starts increasing from 300 km to 2000, 3000 km which makes me impossible to reach ISS.

How can I maintain the altitude at 300 km?

 

[Fizyk]

You can't. It has to increase, because you made a prograde burn, but unless you exceeded about 11 km/s, it will start to decrease after you reach apogee, and you will be right near the ISS when you reach the perigee once more.

 

[tekinozbek]

You can't. It has to increase, because you made a prograde burn, but unless you exceeded about 11 km/s, it will start to decrease after you reach apogee, and you will be right near the ISS when you reach the perigee once more.

It didn't exceed 11km but I orbited like 50 times, and I was NEVER close to ISS.

By the way, it does start to decrease but never comes close to 300 km.

 

[TMac3000]

That's close enough. At that distance you can set the docking MFD and HUD, put the -V[ISS] Symbol over the target box, and burn straight out to the ISS.

 

[tekinozbek]

That's close enough. At that distance you can set the docking MFD and HUD, put the -V[ISS] Symbol over the target box, and burn straight out to the ISS.

When I said "not even close to 300" I meant I was somewhere around 2000km:lol:


-----Post Added-----


WAIT! I got -V[ISS] and I am flying towards that target. Thats means I'm gonna meet ISS right?


-----Post Added-----


Hmm. I followed the ISS box, came close by 300 km, then the distance increased and I fell down to earth

 

[Fizyk]

Center on your -V indicator (or +V, I never remeber which one, just center on the one that will decrease your relative velocity when burning), and burn until it shows 0 velocity, then center on ISS and burn towards it. Use your attitude thrusters in translational mode to keep your velocity vector centered on the ISS. Once again decrease your velocity when you are close enough (let's say, 1-2 km) and use attitude thrusters to approach the docking port (you might need to change the nav frequency to tune to one of the docking ports).

 

[TSPenguin]

- I turn to prograde direction and burn main engines until the Sh-ToR(0) and Tg-ToR(1) are equal to each other.

to the forum!

Whilst every advice here is true, I believe the core element that is causing the confusion has been left out so far.

First of all, the DTmin value in the MFD always gives you the time difference of you and your target at the specified point. So unless you really need to dock within one orbit, you can just look at that and don't have to compare the values directly.

That beeing said, the mfd only compares position and... errr... strike that.
Imagine you are the MFD, you looking straight up along a wall. You see the ISS directly along the wall. You also see a DGIV in the same position, and you will report the DT(min) to be zero.
Long story short, you can be 1000km over the ISS and the MFD will still show you the same as if you were right next to it within 5m.

It is wise to have the MFD displaying either Intersect 1 or 2 as it will use the actual point where your orbits meet as reference.

I highly recommend reading Orbital Operations by Jared Smith. IMO the best tutorial for, well, orbital operations
(You might want to do some research along the lines of "What is an orbit" before proceeding...)

Happy Orbiting

 

[tekinozbek]

No, that is not my problem. I did what that guy said, two times!

I need to know what to do when I see V[ISS] and -V[ISS].

The document doesn't explain that explicitly. I want to know it like this:

-When you see V[ISS], fly towards it. etc...
-When you see -V[ISS] do that
- do this
-do that.

I full burn towards V[ISS] to reduce my relative speed but once it decreases below 15, it moves next to the ISS (the station itself) and -V[ISS] disappears for some time.

Then when I head for ISS itself, I get closer then move far away and hit earth. Why is that?

 

[TSPenguin]

The tutorial I linked to, explains exactly what you are asking for.

Keep in mind, that there are only two situations where your distance remains constant over time. Directly ahead and behind the ISS when you are in exactly the same orbit.

Once you reduced your relative velocity (15 is totaly fine!), point towards the ISS and do a short burn.

Then when I head for ISS itself, I get closer then move far away and hit earth. Why is that?

If you hit earth, you went way too fast. Watch your relative speed as you approach the station, you have to be able to stop by the time you get to it. Just follow the tutorial I posted and you will dock just fine.

 

[Fizyk]

When you head for ISS, you are probably ahead of it, then burning towards it decreases your velocity relative to Earth and you are not in orbit anymore. Keep your velocity relative to ISS low (I would say max. 150 m/s) when heading for it, or you will change your orbit too much and eventually go far away from the station.

 

[tekinozbek]

I did follow the tutorial.

I am at altitude 1427.5 km and the ISS is around 350.

I burn my engines and fly TOWARDS V[ISS] and the circled cross keeps changing direction. I follow up with the cross. Once I cut down my engines, the relative speed starts to increase therefore I can never keep the ships relative speed around 150 m/s.

Each time I cutoff engines the relative speed starts to incrase.

NONE of the tutorials worked for me. I tried everything on the tutorial you gave me.

My RInc is 0.00 degrees and my DTmin is 0.00 EXACT. I see the ISS, but can go close to it.

 

[Fizyk]

You are doing something wrong, you shouldn't get to over 1400 km when being closest to the ISS.
What is your orbit when you start synchronization? (PeA, ApA)
What is your orbit when two times in sync orbit MFD are equal?
And as TSPenguin said, use intersect points for syncing. When there is no intersection, it means, that your orbit went bad.

 

[tekinozbek]

After takeoff and orbit, I align my orbit to the ISS orbit. That is fine, RINC=0.00. Then, I set my PeA to the RAD of ISS (in Orbit MFD) just as that guy says in his tutorial.

Then I move on to Sync Orbit MFD and execute a prograde/retrograde burn to bring DTmin to 0.00.

After that I switch to Docking MFD and set ISS frequencies and I see the V[ISS]. I burn towards it but it never reaches ZERO, after about 15.00 it starts increasing again and I never get it to be stable.

 

[Fizyk]

Your velocity relative to ISS is not stable, because you are too far away from it.
Are you sure that what you set to the Rad of the ISS is your PeA, not PeD? If it's like that, then you are trying to catch the ISS at the altitude of 6700 km instead of 350 km.

 

[tekinozbek]

Yes it was PeA :rofl:

How do I get that to be PeD???

I clicked on PRJ, FRM, etc. none of them made it PeD?

 

[Fizyk]

It's on the right, the button labeled DST.

 

[Artlav]

<showoff mode>
KSC to ISS in 33 minutes playback:
http://orbides.1gb.ru/orbf/ksc2iss_fast.zip
</showoff mode>

 

[tekinozbek]

It's on the right, the button labeled DST.

Wait... I did press that button, I remember, but it didn't change anything.

And whilst writing that, I confirm that it didn't change anything. This is my 6th flight today


-----Post Added-----


It changes PeA to PeR, NOT PeD.

 

[Artlav]

For example, that will be a proper-looking orbit sync for ISS:
What difference do you have?

Sync MFD:

Orbit MFD:

 

[Fizyk]

Funny, I was pretty sure it was PeD, but I guess PeR makes more sense.