zaterdag 25 oktober 2014

The start of construction of the TUDelft satellite tracking station: DopTrack

Monday 20 October 2014, we started the construction of DopTrack, a satellite tracking station on top of the tallest faculty of Delft University of Technology for students to use in satellite orbit determination. I will try to report on our findings of building it in this blogpost. We are in the process of setting up a dedicated website, but for now you have to do my blog ;)

Project DopTrack
As a master student, I followed several courses on orbit determination and satellite data analyses in the Astrodynamics & Space Missions group. During this time, I also observed the design and launch of two cube-sats of the space system engineering group. I was inspired by what students and university staff could accomplish. Come on, they launched two satellites in space. SPACE!!! However, after launch and succes of the missions the satellites were left alone. It would be cool to combine the use of these satellites and the knowledge from satellite data analyses courses. So I decided, when I became a PhD candidate, to construct a space operations practical that allows bachelor and master students to get hands-on experience with satellite operations and orbit determination. The idea for DopTrack was born!

I found another researcher and a bachelor student mad enough to help me in my adventure. Together, we started to design the tracking station and wrote a proposal for some budget to buy equipment. Because both professors saw this project as a good opportunity to improve cooperation between the groups, the proposal was accepted and we could start ordering equipment.

And before we knew it, the week of construction was showing up in our agenda.

Day 1: Installation of UHF antenna and ground equipment
Monday the weather enabled us to work on the roof. The weather forecast of the rest of the week looked quite bad, with a fall storm coming our way. So, we decided to install all the equipment on the roof and make it waterproof. This meant to check the already installed VHF antenna, placing the (bit smaller) UHF antenna and GPS antennas. we need the GPS antenna for our clock, such that the radio, SDR and computer all have similar frequency stability. We saw in the manual that the clock also calculates the position of the antenna (that is what normal GPS receivers do), so we placed the GPS antenna in between the two radio antennas. The sight was spectacular:

Antenna set-up (from left to right): omni-UHF, GPS, and omni-VHF antennas
Down below, we had managed to place an old network-server cabinet (it was very heavy, and there is no elevator between the 21ste and 22nd level!) for our electronic equipment. We ordered rack mounts for our radio and SDR, while the GPS receiver clock was already in rack mount geometry. After putting the rack mounts together, we placed the equipment in the cabinet. The computer, we have now, is not yet a server rack mount one, but we are trying to get this in the coming months. For now we use a common desktop. It looks like this:

Cabinet set-up with SDR, GPS clock, radio, and computer (top to bottom)
All in all, a good day, but fall was coming!

Day 2: Constructing cables and stormy weather
A big storm had arrived in Holland and at the top floor of this building we could feel this. Worried for the antennas on the roof, we checked their status with a remote video camera pointed towards the antennas. Luckily, everything was fine, we had installed them properly! Despite the horizontal rain fall:

See the movie with HD settings, otherwise it is difficult to see. During this stormy weather, we continued the construction of the set-up. This meant making a lot of cables and soldering the connections. I levelled my soldering skills a lot ;).

Day 3: Making more cables and connecting to the radio
The next day, even more soldering of cable connectors. We also checked if it was possible to remotely operate the radio. And after some internet coding and scripting, we were able to remotely turn the radio on and off again (this is especially useful for trouble shooting, somehow this is important for engineers). 

To be even more in control of the electronic devices, we had installed a power switch, which made it possible for us to remotely turn the power on/off of 8 different devices. This worked and gave use nerdy feelings, when we were turning on/off equipment with our laptop (a bit like the first episode of "The Big Bang Theory"). 

Day 4: Setting up local network and finishing installation of equipment

Finally, all the different cables were made and we could hook up the different components. The radio to the antennas and SDR, and the GPS clock to all the other equipment. In between the antenna and radio we had to put a splitter-board. We ordered antenna splitters, because the antennas would also be used by other setups in the ground station. The initial setup looks a bit like this (we still need to fix it to the wall):

Antenna splitter panels for the VHF, UHF, and S-band antennas
In front of the splitters we placed bias-T amplification, which puts power in the cables to the antennas. This results in less loss in the long (25 meter) cables that run on the floor of the roof. After hooking it all up, we wanted to see if things worked.

First recording of a satellite was a fact!!! You can clearly hear that this signal is moving due to the continuous shifting of the frequency (the tone of the signal constantly changes). A good result of day four.

Day 5: Getting the SDR and GPS clock working

Friday was the last planned day for work on the ground station. This was mainly trying to get remote acces to all the different equipment components. Hours of reading operating manuals, setting up connections from the router/computer to the different ports of the equipment and testing the remote connection on a different laptop. This will we be doing for some more days, but we got connection to the radio and GPS clock:

Remote connection to the GPS clock is established
The GPS clock is up and running and locked to several GPS satellites. The hardware is installed and now we need to fix all the software, before we can test the tracking capabilities of our station. And hopefully we get figures like this:

The Doppler curves in the radio frequency domain of the Delfi-C3 and Delfi-n3Xt (courtesy of Nils von Storch, operator Delfi ground station)
In the end, we will convert this to actual information about the satellite's velocity and position. When you, as a student, are interested in working with this equipment for your master thesis, please send us an email (doptrack[at] Furthermore, this facility will be used in the new Space minor of the Aerospace Engineering faculty of the TUDelft. From a student idea made to an actual education application. 

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