Drop Tower w Bremen. Fot. Dante (CC BY-NC-ND 2.0)

Drop Tower w Bremen. Fot. Dante (CC BY-NC-ND 2.0)

PW-Sat2 team has another marvelous message we can share with you! Our team has qualified for the Drop Tower Experiment Series (DropTES) organized by The United Nations Office for Outer Space Affairs! Soon, the deorbitation sail will be tested in conditions of zero-gravity state and very low pressure, during drops inside specially designed and built tower, in ZARM, in Bremen. Due to the sail dimensions (2 × 2 m after deployment) our experiment is not going to use the available in the Centrum capsule, but will be dropped from altitude of approximately 13 m. High speed cameras in the chamber and acceleration sensors attached to the sail will record the whole process. The experiment is planned to be executed in November 2017, before putting PW-Sat2 in orbit on board od Falcon 9 rocket, but after finishing of satellite assembling and handing it over to launch providing company

DropTES campaign is organized by United Nations Office for Outer Space Affairs (UNOOSA), in collaboration with the Center of Applied Space Technology and Microgravity (ZARM) and German Aerospace Center (DLR).

Why Drop Tower?

A successful testing of our sail has never been an easy task. Since we have started our works with prototypes of our device in 2014, we have been looking for a way to simulate behavior of the sail during its deployment. We had many ideas, but the most promising have been two of them – parabolic flight or drop from large altitude. Both of them can provide conditions of temporary weightlessness (similar to zero-gravity state). Unfortunately, both are  expensive.

Eventually, we have focused our efforts to get an access to the Drop Tower, because this solution, aside from the transient zero-gravity state, gives us opportunity to deploy the sail in conditions of very low pressure. It is particularly important, because the large surface of sail (4 square meters after a deployment) results in a relative big aerodynamic drag. In practice, the sail during an opening acts as… a sail or a parachute and air effectively changes and reduces the dynamics of its motion.

By courtesy of many people met abroad during scientific and business meetings, we were able to attract attention of Drop Tower Representatives. Despite the fact that our experiment does not follow a classical scenario of tests, and the deployed sail would not fit in tower (with internal diameter of approximately 1 m) they quickly offered their help, time and experience to make our experiment possible. We collaborate very closely with Deputy Scientific Director of ZARM, from whom we receive remarkably lot of support and valuable, substantive remarks in the process of the preparation of experiment

How is our experiment going to look like?

NThe record of a one of the tests of deorbitation sail deployment system, in a vacuum chamber, at the Space Research Centre of the Polish Academy of Sciences

The procedure of our experiment differs from typical tests performed in the Drop Tower. Most of them take place inside the special capsule, which is shot to the height of more than 100 meters and then falls freely into a huge tank, where it slows down. Such a process can be seen in this video.

Our sail will be placed on the top of the lower chamber, at the height of approximately 13 m. Just after the release of a locking mechanism the sail opening will occur. Free fall is expected to last about 1,5 s. Even thought this is extremely short time, even under the atmospheric pressure, the sail opens in about 0,8 s. We have performed successful tests of the sail deployment system, with attached special container, inside of a vacuum chamber. The tests took place at the Space Research Centre of the Polish Academy of Sciences. We expect that the same system is going to work effectively under conditions of the Drop Tower experiment.

We are going to make four “drops” inside of the Drop Tower. Three of them are going to reflect the real model of the sail behavior. A sail for the fourth test will be a little heavier, therefore we will measure the effect of moment of inertia of the sail deployment system on the dynamics of its rotation during an opening.

What is the purpose of the experiment?

During tests in the Drop Tower our sail will be placed in the mass simulator of PW-Sat2. Therefore, there is a very high chance of a successful examination of the effect of sail opening on the dynamics of the satellite, especially its rotation. Then, we are going to compare the collected data with the measurements acquired in the process of the sail opening in the Earth orbit, after PW-Sat2 launch at the beginning of 2018.

We are expecting that the Drop Tower experiment will confirm our results of ground tests of opening of sail. Thus far, we have tested it, with success, during falls from height of several meters (in air) and on surfaces with a low friction coefficient. The video recordings and results obtained from accelerometers will have a tremendous value.

We want to compare the results collected during this test with data acquired from PW-Sat2 (after its launch) and then to publish them. So far, we did not find full and comprehensive study on subject of opening such structures in space and its effect on a satellites’ dynamic. We feel obliged to share this results with scientific community.

How is our work going on?

We are extremely busy now and what’s more the next two months are expected to be tremendously demanding. This time is scheduled for satellite assembling and finishing the last tests before PW-Sat2 is handed over to launch provider. In parallel, we are deeply engaged in working on many issues: satellite and ground station software, assembling of deorbitation sails, manufacturing and assembling of mechanical structure, manufacturing of solar panels deployment mechanism, manufacturing and calibration of the Sun sensor, tests of all prepared (so far) systems.

We are facing now the most intensive and challenging stage in the history of the project. Keep your fingers crossed for us and – if you like it – please share this message further!

Translated to English by Grzegorz Daszykowski


Background image: Peter Gorges (CC BY-NC-ND 2.0)