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 09-07-2018, 04:00 PM #1996 GLS Addon Developer Quote: Originally Posted by DaveS  Well, the angle is very minute and documents with graphics have a very hard time showing very minute details such as sub-degree angles. I just drew a line 0.2° line myself in Paint.NET and it is not even detectable. I can ask someone who should definitely know, a retired NASA-KSC Shuttle Mechanical Systems (group callsign MEQ) engineer who worked alot of orbiter/ET mates (and few demates) right up to the very end. He should know if the the orbiter had an angle when mated. Please ask, as it's much better to hear it from the "horse's mouth" than us here trying to guess. I'm sure there were some tolerances (like 0.0º +/-0.1º), but the "normal" angle is what we need.
 09-07-2018, 10:34 PM #1997 DaveS Addon Developer I have sent the message with the question. I'll relay anything worthwhile. ---------- Post added 09-08-18 at 12:34 AM ---------- Previous post was 09-07-18 at 06:05 PM ---------- Can someone verify the math in this post on the NASASpaceflight.com forum by Fequalsma: https://forum.nasaspaceflight.com/in...722#msg1853722 1.1°s sounds a bit much.
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 09-07-2018, 10:45 PM #1998 GLS Addon Developer Quote: Originally Posted by DaveS  Can someone verify the math in this post on the NASASpaceflight.com forum by Fequalsma: https://forum.nasaspaceflight.com/in...722#msg1853722 1.1°s sounds a bit much. The math is OK. It assumes we want to calculate the angle between the attachments, which is not what we need... We need the angle between the axis of the OV and ET.
 09-07-2018, 11:12 PM #1999 DaveS Addon Developer Quote: Originally Posted by GLS  The math is OK. It assumes we want to calculate the angle between the attachments, which is not what we need... We need the angle between the axis of the OV and ET. Can't that be calculated from the angle between the attachments? They're where they are, that doesn't change. And the orbiter axis doesn't change, it's still level with everything, it's just that the orbiter has a slight positive AoA when mated to the ET. Obviously Enterprise never had any issues with the 6° AoA used for the ALTs. And the shuttle GNC could easily sense the slight AoA as the reference plane never changed.
 09-08-2018, 10:40 AM #2000 GLS Addon Developer Quote: Originally Posted by DaveS  Can't that be calculated from the angle between the attachments? That assumes that the attachment points in the OV are leveled, which they aren't. Quote: Originally Posted by DaveS  And the orbiter axis doesn't change, it's still level with everything, it's just that the orbiter has a slight positive AoA when mated to the ET. These 2 sentences contradict each other. If the axis are leveled, there is no angle. Quote: Originally Posted by DaveS  Obviously Enterprise never had any issues with the 6° AoA used for the ALTs. And the shuttle GNC could easily sense the slight AoA as the reference plane never changed. The Enterprise wasn't controlling the mated flight... I conceed that there may well be an angle in there for aero reasons, but I want to confirm it really exists before I change tons of code. "3D models don't fit" isn't enough evidence for this, especially when there isn't a single bit of info pointing to some angle existing in there, plus there is info saying the axis match, plus it would make GNC harder. ---------- Post added at 11:40 AM ---------- Previous post was at 12:23 AM ---------- I just committed a scenario to run TAEM at Edwards. It should allow all TAEM and A/L trajectory options to be "exercised". FCS is (still) "wonky", so although most guidance references are correct*, they might not be followed perfectly. Tons of things are still missing from the displays, others need fine-tuning. I'll work them after Entry guidance. *) Some parameters are "stock" so the whole thing might not fit perfectly, but it gets to the runway. Also, TAEM has several requirements, so you might see e.g. altitude diverge for a while, but that is to correct Qbar or E/W. PRFNL roll has a small issue... I'll track that down later.
 09-08-2018, 12:57 PM #2001 DaveS Addon Developer Quote: Originally Posted by GLS  That assumes that the attachment points in the OV are leveled, which they aren't. These 2 sentences contradict each other. If the axis are leveled, there is no angle. The Enterprise wasn't controlling the mated flight... But she was active unless you think she was rapidly powered up following separation from the SCA. Only during the Captive-Inert tests was Enterprise powered down, essentially mimicking a ferry flight. Starting with the Captive-Active Tests was she fully powered up and had a crew onboard. So just to clarify here: What we need to know is the orbiter had any AoA when mated to the ET?
 09-08-2018, 02:23 PM #2002 GLS Addon Developer Quote: Originally Posted by DaveS  But she was active unless you think she was rapidly powered up following separation from the SCA. Only during the Captive-Inert tests was Enterprise powered down, essentially mimicking a ferry flight. Starting with the Captive-Active Tests was she fully powered up and had a crew onboard. Yes, the vehicle was "on", but wasn't controlling the flight, i.e., "go up", "turn that way", "more thrust from the jet engines", etc... Quote: Originally Posted by DaveS  So just to clarify here: What we need to know is the orbiter had any AoA when mated to the ET? Pretty much. I'm sure there were tollerances and also things changed as the ET shrunk during tanking, and then expanded again in flight, but in the end we need to know what is the default or standard positioning of the OV in relation to the ET. IMO, all bits of info so far point to them being fully aligned.
 09-12-2018, 06:31 PM #2003 GLS Addon Developer Any "experts" here on M50? I was adding the ECI and ECEF code to UltraMath and noticed this: Code: `const double AXIS_TILT = 23.4458878*RAD;` Decided to cross check with the value Earth.cfg and they don't match... I didn't check where the code is used, but it should be in the OrbitDAP. If nobody knows if changing the value is good or bad, I'll just create a ticket so it doesn't fall thru the cracks.
 09-12-2018, 07:36 PM #2004 Urwumpe Certain Super User Quote: Originally Posted by GLS  Any "experts" here on M50? I was adding the ECI and ECEF code to UltraMath and noticed this: Code: `const double AXIS_TILT = 23.4458878*RAD;` Decided to cross check with the value Earth.cfg and they don't match... I didn't check where the code is used, but it should be in the OrbitDAP. If nobody knows if changing the value is good or bad, I'll just create a ticket so it doesn't fall thru the cracks. Could be correct. W50 uses Epoch B1950 = 1950 January 0.9235 TT, J2000 (Orbiter) uses epoch J2000 = January 1st, 2000 12:00 TT It should be 23.439281° today. Still researching an exact measurement of 1950... ---------- Post added at 21:36 ---------- Previous post was at 21:17 ---------- Here is the source of the axial tilt value, BTW: https://www.orbiter-forum.com/showthread.php?t=981
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 09-12-2018, 08:59 PM #2005 GLS Addon Developer Quote: Originally Posted by Urwumpe  Could be correct. W50 uses Epoch B1950 = 1950 January 0.9235 TT, J2000 (Orbiter) uses epoch J2000 = January 1st, 2000 12:00 TT It should be 23.439281° today. Still researching an exact measurement of 1950... ---------- Post added at 21:36 ---------- Previous post was at 21:17 ---------- Here is the source of the axial tilt value, BTW: https://www.orbiter-forum.com/showthread.php?t=981 Thanks! That's another thing I'd like to see done: a finished/fixed OrbitDAP so we can point whatever part of the vehicle to whatever part of the sky or Earth.

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