Final Countdown for PVT-GAMERS microgravity flight

The improved Pressure-Volume-Temperature GAuging Method for Electric pRopulsion Systems (PVT-GAMERS) is already on the sprint of the last weeks prior to the Fly Your Thesis! (FYT) parabolic flights 2018 campaign at Bordeaux, France. PVT-GAMERS was one of the only two proposal accepted in the competitive European call that took place last year. The experiment is meant to test in real microgravity conditions the PVT method to accurately determine the propellant content in the tanks of modern spacecrafts equipped with Electric Propulsion thrusters.

Within less than one year the PVT-GAMERS team has designed the flight model, built prototypes for laboratory testing and software development, and is now on the final stages of Flight Model assembly and testing. During the month of September, the team had a review visit from FYT! 2018 in the LTU campus in Luleå to show the status of the experiment and is now implementing the last modifications to comply with all the recommendations and be ready for the flight campaign that will take place soon, between the 22nd of October and the 2nd of November.

The PVT-GAMERS experiment is a small-size demonstrator for reduced gravity conditions which will be used to increase the Technical Readiness Level (TRL) of a novel method for propellant retrieval that was developed by the GAS group. The FYT! parabolic flight campaign will allow to test all the range of gravity values that a spacecraft tank may be exposed to: from the characteristic microgravity of an orbit around Earth, to the hyper gravity due to the accelerations suffered by the tanks during the spacecraft manoeuvres.

The PVT-GAMERS experiment being finished
Credit: GAS

After the selection of the experiment, the PVT-GAMERS team (Álvaro Soria-Salinas, Riccardo Lucchese, Erik Nyberg, and Tobias Hultqvist) and the endorsing professor, María-Paz Zorzano developed a completely new arrangement to adapt it to the particular requirements of this campaign. The PVT-GAMERS experiment consists of a rack containing three sets of two connected chambers each, mounted in parallel along an axis that allows to rotate the configuration with a certain angle. This feature permits to control the effects, if any, of the position of the tanks with respect to the acting accelerations on the retrieved mass measurements. Each chamber has between 5 to 7 sensors, to monitor temperature, pressure, and acceleration. Between two of the chambers of one of the sets, there is a flux meter for controlling the amount of gas transferred from one to another when reproducing a thrusting manoeuvre. The initial amount of gas is 5 g in each chamber and it is a true challenge to be able to resolve this tiny amount under such changing environmental conditions and within a heavy experiment with a large thermal inertia. The preliminary tests on ground have so far been successful and the team is looking forward to testing it on the air.

The FYT campaign consists of three series of flights along three days, comprising 30 parabolas each. Every parabola lasts a minute, with 30 seconds of hyper gravity (2g), and some 20 seconds of microgravity (1/10g). During the first series of parabolas, the chambers will be kept in horizontal position and the measurements will be done on constant mass content in them. During the second series, the following day, changes in the angle of the sets of chambers will be introduced in successive parabolas, and the third day will be devoted to measuring after transferring gas between the chambers, while the three sets of chambers remain in vertical position (with respect to the airplane floor). During these last weeks at the LTU campus, the team is finishing the tasks of calibration and assembling of the experiment.

The improved PVT method, which is based on universal Physics and Thermodynamics principles and a differential form of the Redlich-Kwong equation of state (an empirical, algebraic equation that relates temperature, pressure and volume of gases), was conceived to provide, with maximal accuracy, at every given moment along the duration of a mission, the amount of remaining propellant in the tank of an Electric Propulsion spacecraft. This project started within the Group of Atmospheric Science three years ago, and it has been tested and validated in different experiments carried out in the laboratory, by using a specifically built supercritical pressure chamber filled with CO2. The method can be equally applicable to Xenon (which is the most used propellant for the EP thrusters) and to other different gases as well used as propellants, such as krypton (Kr), argon (Ar), helium (He) and nitrogen (N2), and it is scalable, so that it can be easily adapted to any tank size. The method, at this point, has shown to improve the accuracy of the standard retrievals by a factor 8, measuring the amount of propellant with an error margin of only 0.1% of the initial mass for any remaining amount.

The Flight-Model of the experiment will leave the LTU campus and be sent to Bordeaux on October the 11th. We are all excited about this final sprint and happy that we reached this milestone of the project! Go PVT-GAMERS go!

PVT-GAMERS' rack showing the main components of the experiment. Credit: GAS

Wacht these videos on PVT-GAMERS explanation and mounting. Credit: GAS