Calculate UT1 to UTC Values

Calculate the difference between principal Universal Time (UT1) and Coordinated Universal Time (UTC) according to International Earth Rotation Service (IERS) by using the Delta UT1 block. Use the Delta UT1 block with these axes transformation blocks:

To calculate the difference between UT1 and UTC, the Delta UT1 block requires the modified Julian date. This example uses the Julian Date Conversion block. However, you can calculate the modified Julian data with other methods. For example, you can use the mjuliandatemjuliandate function from the Aerospace Toolbox software to calculate the date and input the result to the Delta UT1 block.

Use the Delta UT1 Block to Create Difference Values for the Direction Cosine Matrix ECI to ECEF Block

This model shows how a Direction Cosine Matrix ECI to ECEF block uses the output from the Delta UT1 and Julian Data Conversion blocks to obtain the difference between UTC and Universal Time (UT1).

1. Drag these blocks into a new model and connect them as shown:

• Julian Date Conversion

• Delta UT1

• Direction Cosine Matrix ECI to ECEF

• Display

• Three Constant blocks

2. Set up the Julian Date Conversion to convert the date December 28, 2015 to its modified Julian date equivalent. This date must match the one specified in the Direction Cosine Matrix ECI to ECEF.

• For Year, enter 2015.

• For Month, enter 12.

• For Day, enter 28.

• To calculate the modified Julian date for December 28, 2015, select the Calculate modified Julian date check box.

• For Time increment, select None.

3. Leave the default settings for Delta UT1. By default, the block calculates the difference between Universal Time (UT1) and Universal Coordinated Time (UTC) to using the aeroiersdata.mat file supplied with the Aerospace Blockset™ software.

4. Set up the Direction Cosine Matrix ECI to ECEF block to work with the Universal Coordinated Time (UTC) December 28, 2015. This date must match the one specified in the Julian Date Conversion block:

• For Year, enter 2015.

• For Month, enter 12.

• For Day, enter 28.

• For Time increment, select None.

5. Set up the ΔUT1, ΔAT, and polar displacement of the Earth inputs for the Direction Cosine Matrix ECI to ECEF.

• Constant — Set Constant value to 1.

• Constant1 — Set Constant value to l.

• Constant2 — Set Constant value to [.05 .05].

6. Save and run the model. Observe the resulting direction cosine matrix in the Display block.