lnd-time-converter 2.1.3

A Python class that allows for convenient conversion between different date and time formats/units

time_converter

A Python class that allows for convenient conversion between different date and time formats and units. The library supports both general-purpose Earth-based time units (such as Python's datetime type, Day-of-year or POSIX time) as well as time units useful for working with data from the Mars Science Laboratory and Chang'e 4 space missions. It can be easily extended to support additional units.

Note

This package is a maintained fork of the original time-converter by Johan von Forstner, who developed it in 2019 while working on the MSL and LND missions. As Johan has since left the space science field, the original package is no longer actively maintained. This fork is actively maintained by Zigong Xu and is the recommended version for use with LND_loader and Chang'e 4 data analysis.

Changes from the original:

• Updated Chang'E 4 local time data (change4_localtime.dat) to support lunar days through 2032
• Fixed lunar day off-by-one bug with spiceypy >= 6.0.0: lunarday=1 now works as direct input
• Fixed NumPy compatibility (np.float removed in NumPy 1.20+)

The conversion between spacecraft clock and UTC is based on a pure Python reimplementation of the SCLK kernel functionality from NASA's SPICE library, together with the SCLK kernel file (msl.tsc) baked into the library.

Especially if very high accuracy (on the order of a few seconds or better) is required and/or the dependency on compiling the SPICE library is not an issue, I would instead recommend using SPICE directly for MSL SCLK conversions. In Python, this can be done with SpiceyPy.

Installation

pip install lnd-time-converter

Usage

from time_converter import Time

Time(2019.5, 'decimalyear').to('dt')
# > datetime.datetime(2019, 7, 2, 12, 0)

you can also supply list-like objects as input, the output will be a numpy array.

Time([2018.0, 2018.1], 'decimalyear').to('dt')
# > array([datetime.datetime(2019, 1, 1, 0, 0),
#          datetime.datetime(2019, 2, 6, 11, 59, 59, 999997)], dtype=object)

Supported units

Earth-based time units

Unit	Example	Name	Abbreviated Name
Python datetime (UTC)	datetime.datetime(2019, 1, 1, 0, 0)	datetime	dt
DoY Tuple (year, day of year)	(2019, 1.0)	doy
Decimal year	2019.0	decimalyear	dy
POSIX time	1546300800	posix

Mars Science Laboratory

The MSL spacecraft clock (sclk) measures the number of seconds since January 1 2000, 11:58:55.816 UTC. However, due to drifting of the clock, some corrections need to be applied based on a file supplied by NASA, which this tool uses to do the conversion between sclk and other units.

Unit	Example	Name
MSL mission sol	2276.8306983767375	sol
MSL spacecraft clock	599570768.5720837	sclk

Chang'E 4

For Chang'E 4, the conversion of spacecraft clock time to datetime has already implemented, so it does not need to be included in time_converter. But we have implemented a converter for the lunar day number and local solar time at Chang'E 4's landing site:

Unit	Example	Name
Local solar time at Chang'E 4	(1, datetime.time(7, 32, 30))	ce4lst

Lunar day numbers start from 1 and can be used directly:

Time((1, datetime.time(8, 30)), 'ce4lst').to('dt')
# > datetime.datetime(2019, 1, 2, 4, 20, 28, 400000)