Vacuum testing at ESA

In this blog post, I am going to present shortly our vacuum test campaign performed at ESA. The campaign was necessary in order to validate the correct behavior of all the pod’s systems in vacuum. This was going to be the first time that the pod was subjected to competition conditions, with all the major systems assembled and connected. Thus, any problems identified during the campaign, could be solved before the team departs for the US.

The Delft Hyperloop team performed the tests at the VTC1.5 vacuum chamber, from 11-22 May. The launcher vehicle was subjected to the three tests outlined below, along with a preliminary test on the battery box. The pressure and temperature conditions were regulated to 10 mbar and 40C, to better represent the competition conditions on a sunny day. In order to monitor the complete status of the pod, the on-board sensors were used along with 18 thermocouples, placed in areas of importance.

In order to give more insight on the kind of tests performed, a brief description is given along with some results and conclusions. Overall, the test difficulty increased gradually, so that any problems identified could be easily debugged and traced back to the last component or system added. The team performed the following tests:

  • Initial validation of leak tightness of the battery box: This was a preliminary test performed before entering the vacuum facility in order to verify that the battery box will not leak more than expected, during the future tests. Any exposure to vacuum or near vacuum levels, could irreversibly damage the cells. The method used was leak detection using helium gas. The helium was inserted to the battery box and a leak rate of 7e-6 mbarL/s was found by using a helium sniffer, which was quite low. Moreover localized leak tests were performed using a vacuum pump and measuring the airflow.
  • Validation of Electronics & Battery Box: This was the first test performed, with the goal of verifying the proper functionality of all on-board computers and sensors. In addition, the Battery box was mounted pressurized, but without any battery cells inside. This was necessary in order to identify any potential leaks in competition-conditions, without the danger of exposing the LiPo cells to dangerous pressure levels.
  • Low-voltage battery test: During this test, the low-voltage batteries were placed inside the vacuum-proven box. The purpose of this test was to validate the pod's internal low-volt battery, along with the power delivery system. The health status of all cells was monitored continuously by the Battery Management System (BMS), while the computers recorded data from all sensors. The successful completion of this test, meant that the team could move on to place the high-voltage battery and perform the propulsion tests, while knowing that all electronic components work as expected.
  • Propulsion tests: The last part of the testing campaign involved the propulsion unit. In total there were multiple motor runs (0-17000rpm), while the pressure inside the vacuum chamber was dropping. Since the pod was constrained inside the vacuum chamber using an external frame, the wheel was free to spin. Although spinning the wheel with no load did not replicate the competition conditions, it provided useful information with respect to the heating of the drivetrain unit and the 3-phase cables. Propulsion tests were performed at 100, 50, 30 and 23 mbar. As soon as the pressure dropped below 30mbar, arcing occurred and the test had to be stopped. The issue was investigated by the Delft Hyperloop team and the manufacturer and was attributed to the insulation of the high-voltage system. Several fixes and modifications were performed, before the team departed for the US.

Concluding, the vacuum test campaign proved beneficial for the team as there was a set of issues unveiled and the team actively worked to fix them. In the end, the pod was validated fit for vacuum application and the battery case and electronics performed well. Also, the test campaign was a good rehearsal for the actual competition, since the team used similar procedures in terms of tests preparation and execution. This proved to be beneficial for completing the necessary SpaceX tests on time and in a professional way.

- Konstantinos Karavelas