General Question Timedifference (Scenario Editor -> Date -> Now)

[BerZerK]

Recently I started to imported actual ISS, HST and Tiangong Orbital-Data from (www.heavens-above.com and http://www.celestrak.com) via conversed "Two Line Elements" (TLE). I do this with the "Scenario Editor TLE"-Addon ([ame="http://www.orbithangar.com/searchid.php?ID=2617"]http://www.orbithangar.com/searchid.php?ID=2617[/ame]).

Today i wondered, why there is a certain difference between the ISS's position shown in orbiters map MFD and online visualisation applets in the internet or my heavens above app on my android tablet. I always thought its a calculation error somehow in the conversion formula from TLE to the orbiter format. Then just by accident i saw, that the UTC time differs by exactly 1 minute and 6 seconds from my internet-synchronised pc clock. When i manually set the time in the scenario editor the position of the ISS is (almost) perfect.

How does this come? Does this difference to the PC-clock has a special background? Somewhere i read orbiter uses a special time (Dynamical Barycentric Time) which is "not the same but similar" to UTC. Before orbiter i never heard of that time before, but after i read about it in wikipedia i understood the necessity. But is that especially this time difference? As i understood this Barycentric Time there must be a difference of about 8 minutes to the barycenter?

 

[Urwumpe]

Then just by accident i saw, that the UTC time differs by exactly 1 minute and 6 seconds from my internet-synchronised pc clock.

Thats strange - we should have 36 leap seconds right now between TAI (and thus, UT1) and UTC.

 

[BerZerK]

Timescales

I found this http://stjarnhimlen.se/comp/time.html : But i still have to figure it out what that all means.
But the 67.something Seconds could fit to 1 minute 6 seconds.

Table of time scales 1972-present, and some predictions

TT = TAI+32.184s ==> UT-UTC = TAI-UTC - (TT-UT) + 32.184s

Starting at    TAI-UTC   GPS-UTC   TT-UT1    UT1-UTC

2001-01-01        "        "       +64.09    +0.09
2001-07-01        "        "       +64.20    -0.02
2002-01-01        "        "       +64.30    -0.12
2002-07-01        "        "       +64.41    -0.23
2003-01-01        "        "       +64.47    -0.29
2003-07-01        "        "       +64.55    -0.37
2004-01-01        "        "       +64.57    -0.39
2004-07-01        "        "       +64.65    -0.47
2005-01-01        "        "       +64.68    -0.50
2005-07-01        "        "       +64.80    -0.62
2006-01-01       +33      14       +64.85    +0.33
2006-07-01        "        "       +64.99    +0.19
2007-01-01        "        "       +65.15    +0.03
2007-07-01        "        "       +65.34    -0.16
2008-01-01        "        "       +65.45    -0.27
2008-07-01        "        "       +65.63    -0.45
2009-01-01       +34      15       +65.78    +0.40
2009-07-01        "        "       +65.95    +0.23
2010-01-01        "        "       +66.07    +0.11
2010-07-01        "        "       +66.24    -0.06
2011-01-01        "        "       +66.32    -0.14
2011-07-01        "        "       +66.47    -0.29
2012-01-01        "        "       +66.60    -0.42
2012-07-01       +35      16       +66.77    +0.41
2013-01-01        "        "       +66.91    +0.27
2013-07-01        "        "       +67.13    +0.05
2014-01-01        "        "       +67.28    -0.10
2014-07-01        "        "       +67.49    -0.31
2015-01-01        "        "       +67.64    -0.46
2015-07-01       +36      17       +67.8     +0.4   (pred)
2016-01-01        "        "       +68.0     +0.2   (pred)
2017-01-01        "        "       +69              (pred)
2018-01-01        ?        ?       +69              (pred)
2019-01-01        ?        ?       +70              (pred)
2020-01-01        ?        ?       +70              (pred)
2021-01-01        ?        ?       +71              (pred)
2022-01-01        ?        ?       +71              (pred)
2023-01-01        ?        ?       +72              (pred)

---------- Post added at 11:47 AM ---------- Previous post was at 11:40 AM ----------

My assumption is:
The difference Terrestric Time to UniversalTime1 = +67.64 seconds.
Thus i think orbiter shows the position of ISS more reliable than the online applets i guess
Because i doubt more common/civil applications just use UTC

BUT:
With the "Heavens above" android app i once predicted the ISS to leave earths shadow and get visible exact to the second.
And it was right in the star-constellation the apps starchart showed.

---------- Post added at 04:35 PM ---------- Previous post was at 11:47 AM ----------

According the "Table of time scales 1972-present, and some predictions" in http://stjarnhimlen.se/comp/time.html for 2010 is a Delta T between UT1 and TT of exactly 66 Seconds. I think thats the reason. But i dont understand whats the advantage if i set my scenario automatically to "now" and the ISS is plottet 1 min 6 sec = 66 sec ahead of the real position of the ISS?