Also, having +/- the correct mass would help, as without payload the burn is faster, which makes the vehicle fall earlier into the atmosphere (even with the correct burn dV).
Used ScenarioEditorTLE to load the last STS-131 TLE to Orbiter and surprise surprise: it puts the vehicle 117 to 227Km* ahead of Wolf's scenario.
It's not the full 1000NM difference, but adding the deorbit burn and half a lap around the Earth and it might just be the problem.
*) It depends when on the time the TLE is loaded.
For the scenario you posted (starting at 12:00UTC), everything should be the same except this:Thanks GLS!
So it should work with your editing using the same official DVs and TIG?
Could you please post the scenario you've edited with the TLE loaded?
I am not very familiar with feeding the scenario with the TLEs..
STATUS Orbiting Earth
RPOS -151118.148 -6464691.404 1848625.199
RVEL -7554.6160 544.1731 1317.2668
AROT 16.389 -41.070 14.841
VROT -0.0800 0.0000 0.0000
For the scenario you posted (starting at 12:00UTC), everything should be the same except this:
Go to O-H and grab ScnEditorTLE, it allows TLEs to be loaded into Orbiter.Code:STATUS Orbiting Earth RPOS -151118.148 -6464691.404 1848625.199 RVEL -7554.6160 544.1731 1317.2668 AROT 16.389 -41.070 14.841 VROT -0.0800 0.0000 0.0000
---------- Post added at 11:50 AM ---------- Previous post was at 11:37 AM ----------
Also, don't forget to add mass to the vehicle with the PAYLOAD_MASS parameter (or the real payload), so it +/- matches the real thing. Wikipedia has the landing weight at 102,039 kilograms (224,957 lb), so with the OMS prop for the burn you would need to start the scenario with a mass of about 231klbs.
Thanks a lot for the help
As far as importing the TLE in oObiter I tried with this (seems to be more updated/accurate than ScnEditorTLE) but got problems running it
https://www.orbithangar.com/searchid.php?ID=6850
Have you tried it yourself?
Not sure if it does correctly, but it does. The implementation just looks different to the reference documents.
Where do I get the data to input in PEG 4? (C1, C2, hp etc.)
Where do I get the data to input in PEG 4? (C1, C2, hp etc.)
Those are essentially standard parameters of a generic orbit, you can find the names of those in the DPS dictionary. Its actually easier to describe an Orbit with those than with the PEG7 inputs, because you can literally punch in your target orbit there, if you know how to translate the parameters.
But yes, I must guess sometimes as well there, I can't remember their definition all the time. :facepalm:
So what values are supposed to be used for a specific deorbit burn targeting?
Look here for example for STS-135 on page 18:
https://www.nasa.gov/pdf/573049main_fd14_expk.pdf
Seriously: Those execute packages are one nice thing I REALLY want to have in SSU soon....
A lot of very useful info. Thanks!
---------- Post added at 01:07 PM ---------- Previous post was at 01:11 AM ----------
Now I am disappointed :thumbsdown:
The only Execute package containing the MNVR PAD with PEG-4 data seems to be the STS-135 one (nothing for previous missions)
Is there any other source you are aware of where we can get the MNVR PADS filled in?
Not sure, but I know where I would try to ask...
:rofl:
(Except my external HDD, where I have saved some packages in the past)
Your external HDD could be our saviour here
Or simply asking NASA about them. I think I just have the packages for 5-6 missions around.
---------- Post added at 14:50 ---------- Previous post was at 14:45 ----------
BTW, google is also your friend:
https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts131/news/execute_packages.html
https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts128/news/execute_packages.html
https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts121/mission_docs/execute_packages.html
https://www.jsc.nasa.gov/news/columbia/107_onboard_archive/web/index.html
Those are essentially standard parameters of a generic orbit, you can find the names of those in the DPS dictionary. Its actually easier to describe an Orbit with those than with the PEG7 inputs, because you can literally punch in your target orbit there, if you know how to translate the parameters.
Except the most important non-trivial one to make it all work is the ignition time - and there's no easy way to get it.
Anyway - HT is the height of the entry interface (400.000 ft) - that one is easy. Unless you pose the question whether that's for a geoid earth or a spherical earth...
C1 and C2 describe the descent angle at EI in the most non-intuitive way imaginable - via the implicit relation
v_vert = c2 * v_horiz + c1
Usually these are fairly constant from mission to mission and you might get something like c1= 15,430 and c2 = -0.62 for a de-orbit solution.
theta-T is the angle from TIG to EI how large that ought to be selected depends on how high your orbit initially is.
You can easily eye-ball a de-orbiting solution just based on looking at targeted periapsis (or just by doing rules of thumb with PEG-7) and it's going to be well within cross-range - but the one thing that's always difficult to get is TIG, and messing this up carries you out of cross range pretty quickly.
If you want to guesstimate PEG-4, the problem is that a good theta-T depends on TIG and how high your current orbit is, so to get good non-wasteful parameters, you want to run an optimizer over the possible trajectories - but of course once you run such an offline tool, you might as well use the PEG-7 targets it spits out.
All of this makes a lot more sense if you have weak on-board computing capability and strong on-ground computers - today your smartphone can give you an optimixed PEG-7 target before the Shuttle has done a single guidance cycle...
but that will not guarantee a correct deorbit and reentry due to TIG uncertainty...
So that could be done with an "external tool": is there any available that I can use on my PC?