Need help getting to orbit with OMS burns

[DaveS]

What's the correct mode for this phase?

A/AUTO/PRI.

 

[Urwumpe]

What's the correct mode for this phase?

AUTO mode. A or B. Not INRTL, LVLH oder FREE.

 

[Goth]

As it is by default.
So the problem must be something else.

---------- Post added at 23:10 ---------- Previous post was at 22:23 ----------

I did it, starting from another scenario.
Unless I'm wrong of course, there should be a bug in "STS-107\STS-107 launch scenario", because after MECO the ApA is way too low (~110). And that may be the reason why the DAP failed when I tried to do the OMS burn. Running the "ET Attach test" scenario for example, I've encountered no problems and the OMS burn was successful.

 

[SiameseCat]

I just ran the STS-107 launch scenario, and the OMS burn occurs without any problems. The DAP is in INRTL (not AUTO) by default, so make sure you're in the correct DAP mode.

The STS-107 scenario does have a problem with the ApA; the MECO parameters need to be fixed.

 

[Goth]

So I would now want to know how to calculate the dV correctly.
1) How to do the calculations manually (possibly a link with not too generic formulae)?
2) How to use IMFD (or other MFDs) to calculate the dV for the OMS burn with SSU?

Any link/tutorial, etc.

 

[Urwumpe]

So I would now want to know how to calculate the dV correctly.
1) How to do the calculations manually (possibly a link with not too generic formulae)?
2) How to use IMFD (or other MFDs) to calculate the dV for the OMS burn with SSU?

Any link/tutorial, etc.

With IMFD, you can get the required data directly for input in SSU, it can output the solution in feet/second and X,Y,Z coordinates, as used by Apollo and Shuttle.

Manual calculations are also not that hard, a good pocket calculator can handle this. The Vis Viva formula is a good hint there, it permits calculating the velocity at a point on a orbit. The velocity difference between your current orbit at the maneuver point and the target orbit is what you need to use as DV.

Long-term goal is having a simulated mission control to give you the burn data according your flight plan... but that will take a long while longer at the current pace.

 

[DaveS]

To change and calculate new MECO targets, use the MECOTool.exe utility that can be found in Orbitersdk\Space Shuttle Ultra.

 

[Goth]

With IMFD, you can get the required data directly for input in SSU, it can output the solution in feet/second and X,Y,Z coordinates, as used by Apollo and Shuttle.

Which program should I use? Without an actual target object I feel lost.

 

[Urwumpe]

Which program should I use? Without an actual target object I feel lost.

There are many programs, it depends on the situation. Would need to start orbiter again to know the actual program names properly. The "transfer program" works for example great for rendezvous missions, but there are also others like circularization or planet approach that can be helpful.

But every Burn Solution View of IMFD shows the parameters you need to enter into the DPS, regardless of the program that you have used to calculate that solution.

 

[Goth]

But every Burn Solution View of IMFD shows the parameters you need to enter into the DPS, regardless of the program that you have used to calculate that solution.

Yes, you just press "BV" which stands for burn view.
But I have tried all the programs and it seems to me that without a surrogate ship there's no way to do it.
Only the "circularize" mode of the "Orbital" program looks fine for what I need but it doesn't have the burn view so it's useless. :shrug:

 

[Urwumpe]

Yes, you just press "BV" which stands for burn view.
But I have tried all the programs and it seems to me that without a surrogate ship there's no way to do it.

Tell me what you want to achieve, and I will tell you how to calculate it with IMFD. Looks like I will have a weekend "home alone", should have time for this.

 

[Goth]

Tell me what you want to achieve

We were talking about doing the OMS burn, so I want to achieve a circular orbit and raise the ApA.

---------- Post added at 14:53 ---------- Previous post was at 14:44 ----------

Sorry I meant raising the PeA to obtain a circular orbit.

 

[Urwumpe]

We were talking about doing the OMS burn, so I want to achieve a circular orbit and raise the ApA.

---------- Post added at 14:53 ---------- Previous post was at 14:44 ----------

Sorry I meant raising the PeA to obtain a circular orbit.

Yes. I wanted to post a formula there for you to calculate it with a pocket calculator or a slide rule (no joke), but Orbiter-Forum has a bug in the Latex rendering it seems.

The formula for calculating the X velocity change at OMS-2 is really simple, if you can read Orbit MFD. I will try to get it posted in some way.

In pseudo code it is:

v = SQRT(mu * (1/Sma - 1/ApR))

(I am sure it can be made even simpler, but lack my big black book of black math)

With ApR and Sma being the quantities from Orbit MFD (Apogee Radius and Semimajor axis), Mu is the standard gravitational parameter for Earth (Mu = GM = 398600.4418 for Earth, if you use km as unit of length).

 

[Goth]

---

 

[Urwumpe]

---

-. --- / -. . . -.. / - --- / ... .- -.-- / --- .-.-.- / .. - / ... - ..- ..-. ..-. / -.-- --- ..- / .-.. . .- .-. -. / .. -. / - .... . / ..-. .. .-. ... - / ..--- / -- --- -. - .... ... / --- ..-. / - .... . / ..-. .. .-. ... - / .-.. . -.-. - ..- .-. . / --- ..-. / ... .--. .- -.-. . ..-. .-.. .. --. .... - / - . -.-. .... -. --- .-.. --- --. -.-- .-.-.-

:sos:

 

[Goth]

LOL
I posted writing "ok no hurry" while you were ninjaing me editing your post adding the formula, so I "deleted" my post.

Thanks I'm gonna try it.
Are you sure about 1/ApR?
It gives me something like 1.495886[...]e-4
EDIT
Ah, it's km ok.

 

[Ripley]

LOL
Me thinks Morse isn't very practical as a forum language!!

 

[Goth]

Me thinks Morse isn't very practical as a forum language!!

Agree, it also crashed the forum for a couple of minutes! :lol:

BTW, I got square root of -121.
Variables used:
ApR: 6'685
SMa: 6'567
Mu: 398600.4418

 

[Urwumpe]

Try the corrected version - I had used the wrong order in the Vis Viva equation... had no time to look it up and used the formula, that I remembered... incorrectly.

 

[Goth]

7 doesn't look like a nice result. :lol:
Basing on what wiki says, isn't it 2/r and not 1/r?