TLE Line 1 Epoch is Based on UTC. Should this be Corrected for the UTC to UT1 Offset?
The OREKIT code that generates TLE line 1 calculates the TLE based on UTC calculations. Should this be corrected for the offset between UTC and UT1?
A snippet of the OREKIT code is as follow:
/**** Build the line 1 from the parsed elements.
* @exception OrekitException if UTC conversion cannot be done
*/
private void buildLine1()
throws OrekitException {
:
:
:
buffer.append(' ');
final TimeScale utc = TimeScalesFactory.getUTC();
final int year = epoch.getComponents(utc).getDate().getYear();
buffer.append(addPadding(year % 100, '0', 2, true));
final double day = 1.0 + epoch.durationFrom(new AbsoluteDate(year, 1, 1,
utc)) / Constants.JULIAN_DAY;
buffer.append(f38.format(day));
The time system for TLE epochs is Mean Solar Time. This is described by Dr. T.S. Kelso:
“An epoch of 98001.00000000 corresponds to 0000 UT on 1998 January 01—in other words, midnight between 1997 December 31 and 1998 January 01. An epoch of 98000.00000000 would actually correspond to the beginning of 1997 December 31—strange as that might seem. Note that the epoch day starts at UT midnight (not noon) and that all times are measured mean solar rather than sidereal time units.”
http://celestrak.com/columns/v04n03/#FAQ03
The best implementation of Mean Solar Time is UT or UT1. It is described at the US Naval Observatory:
Universal Time (UT) is counted from 0 hours at midnight, with unit of duration the mean solar day, defined to be as uniform as possible despite variations in the rotation of the Earth. UT0 is the rotational time of a particular place of observation. It is observed as the diurnal motion of stars or extraterrestrial radio sources. UT1 is computed by correcting UT0 for the effect of polar motion on the longitude of the observing site. It varies from uniformity because of the irregularities in the Earth's rotation."
http://www.usno.navy.mil/USNO/time/master-clock/systems-of-time
(from redmine: issue id 168, created on 2014-03-28, closed on 2014-03-28)