Construction of a flying telescope

This positioning system is used as a mirror adjuster for a telescope suspended from a helium balloon, which ascended to an altitude of 24,000 meters to observe the sun as part of the SUNRISE mission of the Max Planck Institute for Solar System Research (MPS). The linear stage with a drive that consists a ball screw and stepper motor is used for high-precision adjustment of the planes of the 3rd and 4th deflection mirrors in the "Sunrise" solar observatory.

This is necessary because the structure of the telescope bends depending on its position due to its suspension on a wire. These positioning systems compensate for these deformations by moving the mirrors back to the optically correct position. These two actuators are supported by the M2 three-axis actuator for the secondary mirror.

 

Environments almost like in space

The positioning solution installed in the telescope had to prove its specification under extreme conditions such as heat, cold, humidity, vibration and shock. A lubricant-free ball screw from August Steinmeyer still achieved smooth running for optimum repeatability. The surface topography of the screw threads was additionally improved by new thread grinding processes. The ground ball screw ensures smoother running and thus less friction, resulting in higher precision as well as longer lifetime.

Highest reliability under temperature fluctuation, vibration and shock was required. This was achieved by an additional encoder for redundant feedback on motor position. High-ratio stepper motor drives assured 1 µm steps in full-step operation and thus also achieved excellent standstill accuracy. In addition, the gear unit was heated so that it could still be driven by a very small motor at low temperatures.

The positioning solution is characterized primarily by its rigidity, very high power reserves, high efficiency and its compact, small and therefore lightweight construction.

Comprehensive documentation

High documentation requirements included extensive qualification in the development phase and verification in production, including application-oriented tests on specially developed test benches.

Field of application

Aerospace, research, vacuum (HV, UHV), metrology, linear actuators, mirror actuators

References

SUNRISE | balloon carried solar observatory | https://www.mps.mpg.de/sonnenforschung/sunrise