The first launches of SQUID: Spring and RID testing

Yesterday the rocket interface disc, RID, finally arrived. This is the piece that actually mounts the free-flying unit, FFU, to the rocket. The custom made wave spring that will eject the FFU arrived a couple of weeks ago, and now we could finally mate them together.

The rocket interface disc (RID) with the ejection spring

However it soon became apparent that the spring had a tighter fit in the spring gully than we had expected, and to determine whether this would affect the ejection or not me and Mikko carried out some spring testing.

Soon half of the team had gathered around to watch and help out as we covered a sturdy table down in the workshop with foam and devised a clever way of holding the bottom plate of the FFU down against the spring. An unlucky Mario was selected sit under the table and cut a rope going down through a hole in the bottom plate and rid, and down through the table where it was hooked up to a tightening mechanism. To document the ejection we borrowed a Casio high-speed camera from the department of mechanics.

We did two “launches” today, and while the launches weren’t as straight as they could have been the results seem positive, especially since the weighted-down bottom plate was not perfectly balanced. However, since the radius of the spring is slightly lower than expected the very top part of it easily gets jammed between the bottom plate of the FFU and the RID. More testing will be done soon, but until then enjoy the fancy high-speed videos! Sorry for not having turned them right way up, but this would decrease the video quality.

The flickering is due to the flourescent lighting in the room,  and the towel in the first video was an attempt at catching the falling plate. 🙂

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Parachute load test with an unexpected outcome

Last Thursday it was time to determine once and for all how much the parachutes we use in the landing system could handle. Having failed to break them in both the car towing test and the actual drop test, me and our supervisor Gunnar Tibert resorted to more brutal methods.

One of the 70″ parachutes was hung upside down from a hook in the Structures Lab at KTH, supported by a single line of paracord which was to brake the fall. This is the same type of cord that was successfully used in the drop tests above Esrange. The parachute was loaded with about 19 kg of extra load, and dropped with 1.5 m of slack paracord.

Sometimes it's best to use what you have closest at hand! 19 kg of old newspapers have just the right density to fill out the parachute nicely.

Much to our surprise, it turned out the paracord, which we thought was rated to the equivalent of a couple of hundred kilograms in force, was the weakest link:

View from the hook of the crane, filmed with the GoPro HD Hero.

420 FPS high speed footage shot using a Casio consumer camera. This doesn’t show the paracord breaking, but is cool nontheless!

Right now we’re trying to determine the speed right before and after the line broke so we can calculate the force in the cord. At any rate, it is likely we will switch this cord for the real system to be sure that the same won’t happen during our flight! However, the cord still needs to be flexible so the shock to the experiment isn’t too great.

The art of making streamers

Jacob writes

After two presentations at Bergtorpsskolan in Täby and two more at Naturvetargymnasiet in Södertälje the school visit part of our outreach plan is done for the time being. All work is now focused on the tasks that need to be finished for the Critical Design Review in the beginning of June!

One such task is choosing the proper streamer for the landing system.

In order to minimize the risk of the parachute getting entangled with the free-flying-unit (the ejected part of the experiment), it needs to be pulled out and away from it. We hope to be able to do this with a simple streamer, which is kind of like a long ribbon of cloth or plastic.

Streamers are commonly used on model rockets in place of parachutes, but we haven’t found any good info on them being used for anything bigger. This means we have to do some testing! What we’re mostly interested in is how the drag from the streamers varies with speed, the weight of the material, and the dimensions of the streamer itself.

This weekend I have a great opportunity to test just this my holding them out on a stick from a car, but first I need something to test! During lunch today I headed to a hobby store which just happened to have some streamers for model rockets at hand… including some big 7*70 inch ones!

The model rocket streamers are very light while the info we’ve found on the subject says that a heavier streamer might provide a lot more drag. However, thanks to the LAPLander team we have a lot of thick, heat- and tear-proof airbag cloth lying around at the lab, so I immediately got to work cutting out more streamers of various dimensions from that.

It’s going to be fun sitting in the back seat of a convertable testing all these during the weekend, I’ll write up a post about how it went next week!

Oh, and here’s a pic from one of the presentations we held at Bergtorpsskolan. It’s been great fun and the students have been really interested, and haven’t been afraid of asking us tricky questions! Hopefully we can go out and do this again after summer.

David and a group of students at Bergtorpsskolan

MEFISTO Vibration test

One of the main objectives of the SQUID project is to deploy several wire booms. The system in charge of deploying these wire booms is called SCALE, and a very similar system called MEFISTO is being developed at KTH for the BepiColombo mission from ESA/JAXA, which will be launched to Mercury in 2014.

Last Thursday we performed a vibration test at Kista, where the instrument was subjected to a very severe vibration test in order to prove that it will survive to the launch. The instrument we tested was not the final design, and it was used mostly to validate the FEM model and detect possible problems on the design.

The test went really well, showing that the design was very robust and only some minor weak points where detected. The video posted below shows one of the hardest vibration tests the dummy had to withstand, and it is specially interesting to see how at the end of the test the door of the system (left side) starts bending and some “white things” start falling from the instrument. Those “white things” where actually pieces of adhesive that where used to attach one of the parts, which obviously wont be case in the final design, but due to some manufacturing problems it was not possible to screw the parts before the test, so a fast and improvised solution was made. The adhesive however, was not good enough to survive to the test:

As you can see, vibration is an important thing to consider when designing space hardware, and with SQUID we will also have to deal with it!