PeA Drops below 150 all the time

[Joepvermaak]

Hi Everyone,

Great stuff this Orbiter, I have managed to get trough the tutorials and I thought I started to get the hang of things....Until:

I have been trying this for a while now and the same problem keeps comming up..What am I doing wrong here?

I depart with the DGIV from KSC succesfully to an orbit with the Pro904spec90 (to MIR) and I succesfully align and sync with MIR. I also get the altitute right at ApA.

Now I only have to get the DTmin to zero and this is where the problem comes up..

Every time I try to adjust this to zero, my PeA drops below 150 km.
If i try to get the PeA up before i start sycronizing, the DTmin is even further off the chart and i have to adjust again (under 150 km PeA)

It is probably something simple and not rocket science...:lol: However; help will be much appreciated..

 

[Urwumpe]

Well, it is rocket science, but different than you expect: By burning to keep dtMin zero (which means changing semi-major axis SMa so T changes), you lower the periapsis (since you plan to keep ApA constant). To avoid this, use a more careful approach of doing the approach in smaller steps, instead of a single large one.

And maybe read this about the relative navigation around a space station:

http://www.orbiterwiki.org/wiki/Rendezvous

 

[TSPenguin]

Orbital Operations is a fantastic tutorial!
Like Urwumpe said, try small adjustments. If it does not work within the specified number of orbits, you'll have to raise your PeA instead of lowering it.

 

[insanity]

When you want to accelerate your orbital velocity, you lower PeAl. With the DGIV you can just thrust prograde at an intersection point (if you are in a circular orbit with a point of intersection) and burn until you have the transfer you want. Because the orbit was circular, the intersection you've burned at has now become the perapsis. Now I usually take two orbits (0,1) to get it 'right'. Check what the altitude of the ISS is at your perapasis for confirmation, slightly adjust PeA and RInc to make docking easier, and enjoy the view from up-high.

 

[halcyon]

I'm guessing that you're using the rendezvous method that was shown in the stock Orbiter training videos, in which you're told to place your PeA or ApA inside the target's PeA/ApA range?
From what you're describing, it also sounds like you're doing a retrograde burn at your ApA to lower your PeA within the targets altitude range and achieve a near zero DTmin?

When syncing your ship to another target in orbit, one of the most important things to note is that making your insertion burn is only efficient when you and your target are close enough.
If you ever watch the DTmin while accelerating time, you'll notice that with every orbit you make around the earth, you get closer to the target and the DTmin starts decreasing on it's own.
Waiting until DTmin is low enough before making your insertion burn will reduce your burn time and prevent you from lowering your orbit into the atmosphere.

When I first started in Orbiter I used to use the same method that's shown in those stock tutorial videos. Then I started playing around with the MFD sync tool, using the other modes such as target's PeA/ApA, or even choosing the manual modes and rotating the line myself to find the lowest DTmin point.
Eventually I learned how to use the newest version of TransX which allows you to pass as close to or as far to the target as you want during rendezvous.
The old method I was using was crude and sometimes I'd come within 800 distance and sometimes I'd only come within 2,000.

There's a great tutorial on using TransX for syncing your orbit with another target, which is at http://www.flytandem.com/orbiter/tutorials/video/index.htm .

 

[Joepvermaak]

Thank you all for the explainations! Things are much easier once you know on which path you can walk. ApA is not the only possible intersection with MIR! Realizing that makes it much easier.

I'll play a bit with the different options in the Sync MFD and let you guys know if i am more succesfull reaching ISS/MIR

 

[n122vu]

The tutorial "Dancing in the Dark" in the Go Play in Space manual has a good tutorial for rendezvous also. You can find it at Migman's site, www.orbiter.migman.com.

 

[Joepvermaak]

It is done!

Hi Guy's,

I made it! Both MIR and ISS are easy accessable once one got the hang of it.

Thanks for the help and now i'll aim for reentry... and then the moon.

" I love it when a plan comes together! " :speakcool: