RMU electronics

The the work of the RMU electronics can be divided into several steps:

  1. Conceptual design
  2. Electrical schematics
  3. PCB layout
  4. Verification of hardware
  5. Firmware implementation

We are currently at step 3. PCB layout means that we are creating a drawing of were every component will be placed and how all the connections will be routed.

The RMU electronics is quite similar to the FFUs. As you can see in the conceptual diagram below, the backbone is a FPGA and it features sensors. The main task for the RMU electronics is to split the communication from our data connection into the experiment out to the four FFUs. This is handled inside the FPGA. The RMU electronics will also be able to control a camera that will be mounted inside the RMU.

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Mech. design changes

Hello MUSCAT-eers! (registered trademark)
We’ve had an interesting development in the mechanical design last week when we got a message from our friends at DLR stating that the pyrocutters we were planning on using for our ejection mechanism were not supported and we would have to change to another type of pyrocutter.

Suffice to say, this caused a bit of a problem for us, as our pyrocutter bracket and accompanying assembly were fully designed and drawings had been sent to manufacturing companies.
Fortunately, the bracket had not been greenlighted yet, so we were able to change the design to accommodate the new component. Below you see the (hopefully) final version of the pyrocutter assembly with the new TRW pyrocutter!

New pyrocutters ready to go!

Surface mounting

Dear followers and the rest of the world!

Today, you will get two blog posts! This post is unfortunately not about composites but about small part of the amazing world of soldering.

Many readers might not know what soldering is but Wikipedia has an article about soldering which is quite informative. There are many ways to solder but I’m only going to tell you about the soldering process for MUSCAT.

You might know that the MUSCAT experiment has two PCBs in each free falling unit (FFU) which we identify by naming them top and bottom PCBs. We start with soldering the bottom PCBs which are more complicated to solder than the top ones. In the figure above you can see one side of the bottom PCB. As you can see it is a green board with some small places where it is shiny, some are golden and other look like silver (but are actually tin and lead blend) which are called soldering pads. The long lines however are not soldering pads, they are just lines that carry the signals. In space soldering one does not want to have gold plated pads since they can cause short circuits when it suffers some mechanical stresses, e.g. thermally induced stresses, which basically means that it can destroy our experiment. For this reason we pre-tin the pads. But we can’t use pure tin because the same thing happens if it is pure and that is why we use a 63/37 (Sn/Pb) tin-lead blend for the actual soldering of the components, but for pre-tin purposes I use 60/40 (Sn/Pb) blend. What we do is that we use flux which removes oxide and then I apply the tin blend to the pad with a soldering iron. When the gold film gets heated with the tin blend the tin sucks it up and they blend together. Next I use soldering wick to clean the tin/gold blend away. The soldering wick is a braid of copper with flux in it so it sucks up all the tin and gold when heated with a soldering iron. So far I have pretined Doc, Sleepy and half of Dopey and one third of Sneezy so I only need to finish Dopey, Sneezy and Bashful and then all the PCBs are ready for soldering.

Next step is soldering the components on to the PCB. But first one needs to practice. I have been practicing for at least two weeks now and finally today I went on to soldering components on to the PCBs we are going to use. First we solder the 3.3 V voltage regulator and then we solder all the capacitors, then all the resistors and so on. Today I soldered 6 capacitors on to Sleepy (one of our PCB) and it took me an hour, but fortunately I am not alone doing the soldering, Marcus Lindh soldered  about 39 capacitors on Doc (another of our PCB) yesterday in an hour and Markus Fjällid was also soldering this evening but it is not confirmed how many capacitors he solders in an hour, but he is quite quick at it. But as they say, practice makes perfect so probably at the end of the soldering phase I will manage to solder around 40 capacitors in an hour with high quality, but we will see.

Unfortunately I do not have pictures of my soldering today (because my phones memory was full) but so that you can get a better idea of what I was doing today I have included links to some cool youtube videos I found that show how to surface mount various things.

The first one shows what I was doing today, i.e. soldering a capacitor, although this person does not apply extra flux as I do and I also use another method, i.e. first I place the component on the pad, place a holder on top of it so that it will not move and then I apply flux. Finally I use the soldering iron and tin connect the capacitor to the pad. This guy makes it look so easy that I am thinking about if I should practice more in order to become good at this method.

The next video is a tutorial on how to solder and I think it is quite good and shows well what I am going to be doing for the next few weeks.

Then I found this and I thought it was quite cool and I wish we could just place all our capacitors on the board and it would just melt like that  so I decided to share it with you:

I hope you enjoyed this post. Take care!

Best regards,

Ólafía

The MUSCAT experiment loves composites

As you may know the MUSCAT experiment is manufacturing the shell of the FFUs with composite material in glass fiber/epoxy. It has been quite hard to reach the desired result in the manufacturing process but now it is working. However now we are in the stage where the shells have to become mass produced. 

The VARTM process used by the MUSCAT experiment in the manufacturing, it is becoming more important  in the aerospace industry. Nowadays, there is no better exponent of the composite intensive used than the 787 Dreamliner. Therefore, the MUSCAT team had to go and visit this wonderful composite toy.

The MUSCAT mechanical team visited the 787 Dreamliner at Arlanda airport. Here you can see the pictures were taken in the visit.

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It should be mentioned that Boeing is using RTM process to manufacture the flaps of the wings. This process is the pressurized version of the VARTM that MUSCAT is using for our “mass production”. Here you are the picture that illustrates the “mass production” of MUSCAT

ImageWe are getting done!!

Hope you enjoy the pictures, composites are fun.

Naming our PCBs

Hello!

As you know by now, we lost one of our FFUs in the high altitude drop test. Chances of recovering it are low, so it is likely that we will not see Oj again. But we still have Glad and Arg, and soon we will have a total of seven FFUs for our experiment. It is a good idea to have names, because it becomes a lot easier and intuitive to discuss each piece of our experiment and the tests that they go through, and even to write about them in our blog posts. Therefore, since we are going to have seven FFUs, it was decided that our FFU PCBs should be named after the Seven Dwarfs in Snow White. First, Glad and Arg would have English names, and are now called Happy and Grumpy. Then, the other five will be SneezySleepyDopeyDoc and Bashful.

Besides from the FFU PCBs, there are also PCBs in the RUM and in the umbilical connections. To keep it coherent, these PCBs should have names as well, and they could also be from Snow White. So, the umbilical PCBs that connect the RMU to the four FFUs that will in the rocket are called The PrinceThe HuntsmanThe Poison Apple and The Kiss. Finally, there are two main RMU PCBs: the flight board and the spare board. Naturally, to the main PCBs the main names were attributed: Snow White and The Evil Queen!

Components for the FFU cages arrived

Hej! Last week we received a package with all the components we ordered for the cages of the FFUs. Lets take a look on them!

 

Other new components are almost complete or will be delivered in the next weeks. We will keep you updated!

Tito and Darri

The drag coefficient

Hello everyone!

I am responsible for some of the aerodynamic considerations in this experiment. This is my first blog post. I will today share one of the things I have contributed to the experiment. To obtain an accurate density and temperature profile in the atmosphere it is essential to know the drag coefficient of the falling spheres (FFUs). The drag coefficient depends on the Reynolds number and Mach number of the flow. I have gathered several hundred tabulated values of the drag coefficient of a sphere for different Mach numbers and Reynolds numbers from reports on the subject. A polynomial fit with terms up to the third order was subsequently made. The result is illustrated below in the form of a contour graph with lines of constant value of the drag coefficient. A trend is seen in the graph of increasing drag coefficient for lower Reynolds numbers. Due to the lines getting very closely packed I have chosen to only show contours for a drag coefficient up to 2.

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