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#196 |
Beta Tester
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What was your favorite Orbiter ?
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#198 |
Beta Tester
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Never heard her referred to as Disco before. ![]() |
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#199 |
Donator
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So I finally had some time to practice some Rendezvous with SSU and FDO MFD. So far I have succesfully completed STS-114, STS-121 and STS-115. I am still very far from mastering FDO MFD but Indy's walkthrough was very helpful. In all 3 cases I made it to the ISS though the Ti TIGs were not exactly the same as in real life (and in the original FDO MFD plan). In order to keep the Lighting and the vertical velocity within the desired constraints I had to modify the Terminal Initiation TIGs. Long way to go but I am very happy so far.
This tool has been in my wish list since ages and IMHO it brings SSU realism to different level. Some pics from STS-121 RBar arrival just prior to orbital sunset on July 6th 2006 Discovery 600 feet below the ISS View of the PB and the Docking Camera in the monitor A bit of sci-fi with the ISS clearly visible against the darkness of space with the camera switched in Night Vision mode Last edited by Wolf; 03-19-2019 at 06:32 PM. |
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#200 |
Addon Developer
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There has been another release: https://github.com/indy91/Shuttle-FD...ag/0.1.9-alpha A few more things can now take non-spherical gravity into account: -Circularization (CIRC) maneuvers -Height adjustment (HA) maneuvers -apogee and perigee altitude on the evaluation table From the FDO Handbook it seems that the HA and HP on the evaluation table should at least somewhat take non-spherical gravity into account, although the accuracy is not super high (in one example the targeted height is 88.0 NM and the evaluation table says 88.92 NM). So I chose the most simple calculation method for this, just doing a simple J2 approximation. Found a nice subroutine for that in one of the Apollo RTCC documents. OMS-2 is actually interesting as a height adjustment burn. The onboard PEG-4 targeting is not taking non-spherical gravity into account, so the HT value you input would have to be biased. For the standard 51.6° inclination, ascending node ascent and orbit that bias is almost a constant, about 6.2 NM (as per FDO Handbook). Minimum HP after OMS-2 is 105 NM (85 NM with special approval) and the 105 NM biased by the 6.2 NM is about 111 NM. So that is probably why the ascent checklists have 111 NM by default. |
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#201 |
Beta Tester
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Nice to see the ISS in the correct config. ![]() Show more. |
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#203 |
Addon Developer
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There also is the case of a low beta angle, in which case TI isn't set at SS - 36 minutes, but SS - 38.5 minutes. I had that with STS-129 but noticed too late that I should have used 38.5min, only when I checked the Execute Packages. The result is the sun right in the face during the TORVA. Definitely was undesirable in reality. So a few missions (not that many probably) will have the lighting at TI moved to 38.5 minutes to avoid that. |
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#204 |
Addon Developer
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Last edited by DaveS; 03-19-2019 at 07:37 PM. |
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#205 |
Donator
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#207 |
Donator
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Is it ok to use FDO MFD (0.1.9) with Non Spherical Gravity enabled?
I am asking since I am checking it with STS-114 and I get an extremely high DV in the plan for the NPC burn. I am using the actual launch date/time with the ISS state vectors uploaded via the closest time available from Celestrak. With Gravity disebled I end up at MECO with a 0.1° RInc and with Gravity enabled I have 0.05°. I guess this does not work well in the latter case since my mis-alignment will likely get bigger and bigger as I proceed with the mission (I guess due to the nodal regression effect) and that is probably why I have such a huge DV for the NPC burn. Could it be my ISS state vectors are off? Here is the plan before OMS-2 where NPC DV is 171 fps! |
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#208 |
Addon Developer
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Yes, the MFD should give good results with non-spherical gravity enabled in the most recent versions.
The differential nodal regression can cause as much as 0.5° in two days and I've seen NPC DVs of 200 ft/s and more. I've only really had one case where I got a small DV after the ascent. It could be the ISS state vector, but the SSU ascent guidance might also be the problem. I used the "Scenario Editor TLE" for the target vectors, I wonder if it has a problem with propagating a TLE backwards, because in those cases I had bad results. But that is just a theory, it could just be a SSU issue. The trajectory calculation in the MFD is always reliable, so if the TI and MC4 DVY are small, then you know that the NPC targeting worked right. Last edited by indy91; 03-21-2019 at 08:35 PM. |
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#209 |
Addon Developer
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Scenario Editor TLE definitely has issues with historical TLEs. I experienced this first hand when I was setting up the STS-109 launch scenario, that the HST wasn't where it was supposed to at T0. I knew exactly where it was supposed to be at T0 (directly over Tampa, FL) so I checked when it overflew Tampa and adjusted the epoch accordingly. IIRC, it was to make the epoch earlier by about 83 seconds.
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#210 |
Addon Developer
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---------- Post added at 08:59 PM ---------- Previous post was at 08:50 PM ---------- Quote:
Plus, for 28.45º orbits, launching on time almost certainly will not work perfectly as the pad isn't where it should, so the vehicle does a dog leg to correct the inclination, and doing this with no control over LAN... how knows exactly what happens. ![]() What we can do is get a way to convert "our time" to "Orbiter time", and if the TLEs also need a time conversion, figure that out as well, and that should fix the on-orbit issues. For the launch issues, currently it's all about timing, as we lack LAN target capability. Maybe for SSU 6.0... |
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