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Two screws
Vibration testing of our satellite was ended preliminarily last week, because two screws become loose during the shaking. To prevent possible damages and to find the cause of the problem, we stopped testing, collected the information gathered and flew back to Finland for further analysis.

The satellite was carefully opened in Jyväskylä on Tuesday 13 July and in addition to two already loosened screws, we also found some other screws almost detached from the mechanical parts of the satellite and experiments. 

Luckily the problem can be solved very easily – just tighten the screws better and lock them with glue.

In satellites everything has to be carefully fastened. Many screws have locking mechanisms or pins holding them in their places, or then a drop of glue or other fastening material is added. Otherwise the screws will open in vibration.

According to an old saying, if you put a bicycle to a rocket and launch it to space, after the launch you have just bicycle parts inside the fairing. The vibration loosens everything, even the pieces you can’t open without a power tool.

WISA Woodsat in Jyväskylä for inspections

Testing is important

Satellites are tested thoroughly many times, because some problems arise practically always. In fact, if nothing is found, it is worrying. 

Because in space nobody can repair the satellite or change the design, it’s far better to find the possible problems already on ground. 

The tests also are harder than actual launch or conditions in space. They are also designed to find out potential errors. 

In our case the vibration test had different tests, made in three main directions, and they probed how the satellite copes with different frequencies of vibrations, many kinds of chocks and random shaking.

The data showed that overall the satellite did well and especially the plywood panels behaved as predicted. But not perfectly: during the inspection some small cracks were found in wood layers. Anyhow, this is not worrying, because the structure of plywood is made to support small damages.

The places where the cracks were found were also very difficult and not important for the integrity of the panels. For instance the area between the solar panel inset and border of the panel is only millimetres, and it has been kept only for aesthetic reasons.

During the test satellite also sported instead of the real solar panels mass simulators, behaving mass-wise in a similar way than the solar panels, but they were not attached like the real panels. This may have contributed to these cracks.

Small tweaks will be done, new tests in sight

Just like with major accidents, also our screw problem has many contributing factors that are individually trivial and harmless, but when put together they cause an issue.

Fixing the problems found seems to be very fast and straightforward. Although the current design of some mechanical parts could have been accepted for the new tests and to be used in the satellite, small changes will be made: measurements will be slightly changed, another type of screws will be used and some screw holes will be placed differently. 

Plywood panels will be cut slightly differently.

There's also one very good outcome of the screw issue: as we need to use new screws in the camera boom, we can now have black ones. These prevent rare, but unpleasant reflections of sunshine from the metallic screws.

As the launches of the Electron rocket have been pushed forward, solving these issues found during the vibration tests are not causing any extra delay. If all goes well now, we’ll be back testing within a month.