A new generation of missions

The study of the earth magnetosphere has been a major field of study since the first steps of space exploration and its still a hot topic in the scientific community. In order to understand the physical phenomena happening there, data that can only be collected by spacecrafts is needed, such as plasma density or electric and magnetic field strength and direction at different altitudes. Development of technology and capabilities on space engineering has made possible to develop very complex missions based on formation flights of identical payloads, such as CLUSTER (left image) from the European Space Agency or the upcoming MMS mission from NASA . Data collected by those missions is extremely important as they provide information about how the different parameters change with time and space.

Some of the most interesting magnetospheric phenomena happen at relatively low altitudes, such as the auroras, which take place over 100km above earth's surface. Those altitudes can be reached by sounding rockets, providing a short suborbital flight to the payloads launched on them. Inspired on the missions mentioned above, the Royal Institute of Technology (KTH) of Stockholm is developing a mission consisting on the launching of several identical payloads on a sounding rocket, in order to perform magnetic and electric field measurements on the ionosphere.

A spinning problem

Electric field measurements are typically carried out with several probes (usually four in order to maintain the stability of the spacecraft) attached to the main body of the payload with a flexible wire, that must be deployed several meters in radially opposite directions. On a suborbital flight, and due to the relatively short time that the spacecraft stays in orbit, the deployment must be carried out as fast as possible in order to have more data collecting time.

When the deployment is carried out on a spinning spacecraft, the centrifugal force acting over the probe will not be aligned with the rotation axis, as the trajectory followed by the probe will be a spiral. On fast deployments this effect becomes more important, and due to the flexibility of the wire it can be shown that if the deployment is performed at constant velocity, once the probe is completely deployed it will remain oscillating . This effect will have a big impact on the quality of the measurements carried out by the probes and must therefore be minimized.

One of the goals of the SQUID mission is to test a new deployment strategy that will reduce, and ideally cancel out this residual oscillations (see diagram on the left), ensuring high accuracy of the electric field measurements.