## Posts

### My education experiment: deconstructing Satellite Laser Ranging (part 1)

Imagine a spacecraft the size of your car travelling at an altitude of 600 km with a velocity of 7.6 km/s. Now try to determine where the spacecraft is and how fast it is flying, also called its dynamic state. There is no speedometer (no wheels turning) or a pitot tube like in an aircraft (no air to measure). So, we, as astrodynamicists (yes, I think that is a word), have different techniques to accurately determine the state of the spacecraft. Highly accurate measurements of distances (also called range) between the satellite and ground stations are used, as well as the changes in these distances (called range-rate). If you follow this blog a little bit, you know that we work on building a ground station at the TU Delft that measures these range-rates with respect to cubesats. With some complicated, but very elegant mathematics, these measurements are transformed into very precise orbit determinations of satellites. Some of my colleagues can tell you within one cm accurate where thei

### Determine the shape of the Earth 200 years ago with gravity

A colleague of mine pointed me to a PhD dissertation of Petrus van Galen. He wrote this dissertation in 1830 and two copies can be found in the Tresor of the TU Delft Library. The title of this dissertation is “ Disputatio Mathematica Inauguralis d e Pendulo Ejusque Applicatione ad Telluris Figuram Determinandam ”. Loosely translated: A Mathematical Essay about the Pendulum and its Application to Determine the Figure of the Earth. Of course, as soon I heard about this, I made an appointment with the librarian responsible for the collection in the Tresor for a viewing session. I also found a  link  in Google books, showing almost the complete dissertation, but I wanted to smell the old pages. Furthermore, the appendices of the dissertation were not scanned properly, so the data, that Petrus van Galen used, were not yet available to me. A week later, I cycled to the Library (appointed as one of the 10 most beautiful libraries of the world and known very well to me due to th

### Geology and Whisky on Islay

Few weeks ago, I visited the Queen of the Hebrides, or better known as the isle of Islay. My dad and I organised the trip for some friends of ours with the main objective to show them the many beauties of the island. Two years ago my dad and I made a ‘reconnaissance’ trip to explore those beauties.  Machir Bay viewed from the old abandon RAF radio station. Photo credit: Maurits Kok. Being true to my blog, which is a more scientific-orientated blog, I will not make this post a travellers log, but lets just say we visited several distilleries (even one that is now under construction), enjoyed the cuisine (which was quite high standards in the hotel we stayed), and made many long walks through the fantastic and overwhelming landscapes of the Scottish island. This island keeps surprising me with its fascinating history, incredible geology, and beautiful whiskies. Whisky Wharehouse tasting at Bruichladdich. Photo credit: Maurits Kok Before the trip I bought a book about the

### Paving the way for our presence on the Moon

Reading the books and watching the TV series “the Expanse” awoken my old boyish-dreams of our presence on the Moon. Growing up with a dad that introduced me to the fantastic worlds of Larry Niven, Brian Aldiss, Isaac Asimov, Jack Vance, and Arthur C. Clark, gave me hope for the future and it motivated me to start my studies in Space Engineering. The science fiction became real-life science and engineering and I began to understand why the future was not yet achieved. We have made space engineering very complicated and expensive, which allowed only nations to perform this type of activities. But, I am living in the future of my old heroes of words and spaceflight has a permanent role in our daily life.  And more and more young engineers want to participate, because space is not that complicated anymore. We evolve as humans, such that complicated problems in the past are simple issues in the future. James S. A. Corey (A.K.A. Daniel Abraham and Ty Franck) hints to this as well in the

### Delfi-C3 is feeling the power of Spring

All the trees have blossom, baby ducklings are rooming the ponds, and we get more Sun: we survived the winter! Spring is here to give us our much needed vitamine D.  Spring on the campus of TU Delft Not only on the surface of the Earth this is felt, but also in outer space. The Delfi-C3, now more than 9 years orbiting our Earth, notices that spring has arrived on the Northern Hemisphere. During winter, our ground station (DopTrack) only receives data during the morning and mid day (between 8:00 and 13:00 CET). Starting from April, we start receiving signal around 20:00 CET. Fraction of a 24 hour day (UTC) at Time of Closest Approach (TCA) of the Delfi-C3 with DopTrack. We saw this already last year, when in April the telemetry of Delfi-C3 started appearing in the evening. The Sun was already set on the ground, but at 560 km height light was still shinning on the solar cells of the satellite. The satellite is designed such that when sunlight hits the solar cells and enough

### Interacting of the SDR with Matlab during my classroom tutorial

This year was the second time I gave my tutorial with an SDR dongle. The idea behind this tutorial is to simulate ground-station-to-satellite interaction in the radiowave spectrum. The ground station is replaced by the SDR dongle and the student's computer. For the satellite, I use a radio beacon designed and built by a colleague of mine. The device transmits an FSK modulated signal at a certain frequency. During the tutorial, the students learn to develope software that interacts with the SDR, such that they can process the digital stream observed by the SDR. I made a small video of the signal with GQRX software, such that you can see the signal in the frequency spectrum and listen to the FSK modulation. Last year, I was using an open-source software package "gnuradio" for the signal processing part, but I found out that this introduced a lot of trouble-shouting in the first few hours, because of students having: different operating systems and versions (every s

### The day the Earth changed its rotation-rate

This week I saw a great article in Wired.com about the static test of one of the solid boosters for the SLS rocket. So I tweeted: "The Earth rotated a little bit faster that day! #rocketengine". I should have known that I cannot make these kind of statements without proving them first. One of my friends called my bluff. So, I replied with "Challenge accepted!". The blog post will report on my investigation and show how much the Earth speed up/slowed down by the QM-2 test of the SLS booster rocket. My investigation consists of three parts: the model, the search for reliable information, and my conclusions. Model of the Earth with an attached booster By igniting their propellant, rockets can produce thrust that normally propel them upwards towards space. If you fix them on the Earth they could speed up or slow done the rotation of the Earth, depending on  the direction of its thrust. Ok, hold your horses! Of course this will have a small effect, but I st