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DTUsat-1: Software
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Software


The Ground Control Center, GCC, is where we will take care of radio contact and communication with the satellite. The parts of the GCC will be a radio, an antenna, a modem, and a PC which will be running the appropriate software. We are responsible for developing the software and setting up the system.

Because of the low orbit of DTUsat we will only have a few windows of communication each day, each window being approximately 15 minutes. Because these windows are few, short and inconveniently placed the GCC should be fully automated to avoid having it manned around the clock.

When the satellite flies across the sky we will need a program to direct the antenna accordingly. This is called tracking, and the program uses information about the satellite orbit and the GCC position to guide the antenna.

At the same time we will have to control the frequency of the radio transmission. Because of the satellites movement relative to the GCC, and the resulting Doppler shift, the frequency will have to be lowered when the satellite is approaching us and vice versa.

These two parts of the software we will get from outside sources and set up on the PC.

Data and Instructions

The software we will develop ourselves will be used to control the contents of the communication with the satellite. Communication from Earth to the satellite consists of instructions, telecommands. The satellite will send data back, telemetrics.

It is important to know if the satellite is functioning correctly, and so the bulk of the telemetrics will be status reports from the different parts of the satellite, e.g battery and computers. Part of the software at the GCC will then log the data received and let the operator know if it appears that something is wrong on the satellite.

Another, and perhaps more interesting part of the telemetrics will be date from the payload. They will give us information about the state of the science mission. The GCC will be able to set up these data so they are easily accessible.

Under normal circumstances the on-board computer will control the satellite, but it will be possible to control most of the systems from Earth. When the operator wants to do special tasks like restarting parts of the satellite or upload new software to the on-board computer, she will place the instructions in a script at the GCC. This can be done will in advance of the next time the satellite is within reach and the software will then automatically make sure that the script is sent when there is radio contact.

Screenshot of NOVA tracking a satellite
The shaded area on the picture is the so-called footprint of a satellite. The tracked satellite is approximately at the same height where DTUsat will be. The footprint is the area where the satellite will be above the horizon, which makes communication possible.