Pointing in the (b)right direction
Attached to the top of a floating platform at the European Space Agency’s Orbital Robotics Laboratory is an essential component of the upcoming CubeSpec mission: a precision pointing system designed to enhance the accuracy of the spacecraft’s attitude control system.
CubeSpec is a 12U CubeSat – a microsatellite about the size of a shoebox weighing less than 30 kg.
It will fly as an in-orbit technology demonstration, with the aim of becoming the first CubeSat to carry out high spectral resolution spectroscopy of visible light. These measurements help scientists study the internal structure of stars, and obtaining them will make CubeSpec ESA’s first astronomy CubeSat.
To take the measurements, the tiny spacecraft will carry a telescope, which will need to remain pointed at a target star with extreme accuracy – orders of magnitude more accurate than the current state of the art for CubeSat platforms.
“To achieve this level of accuracy, the spacecraft’s attitude control system is augmented by a High-Precision Pointing Platform (HPPP), developed by KU Leuven within the frame of this project,” explains Leonardo Peri, PhD researcher at KU Leuven.
The High-Precision Pointing Platform (HPPP) features a fine steering mirror that can be tilted rapidly and precisely to redirect incoming starlight towards the mission’s spectrograph – an instrument that splits light into its components (or wavelengths) to record a spectrum, in a way a rain droplet splits light to form a rainbow.
To test the system in conditions resembling space as closely as possible, Leonardo made use of the ORBIT facility at ESTEC, ESA’s technical heart.
ORBIT is part of ESA’s Orbital Robotics Laboratory and consists of a 43 m2 ultra-flat floor replicating frictionless orbital dynamics. The height difference between the floor’s lowest and highest points is less than a millimetre.
The facility operates similarly to an air hockey table: its testing platforms are equipped with air bearings, which create a stable air gap between the platforms and the floor. This gap, only a few tens of micrometres thin, allows the platforms to hover above the floor with minimal friction, reproducing orbital dynamics in two dimensions.
“A prototype of the HPPP was mounted on top of a floating platform, and a fixed laser source was placed in front of it to represent an observed star,” adds Marti Vilella, ESA’s automation and robotics engineer. “The HPPP tracked the laser beam and maintained a stable spot on the image sensor, compensating for the platform’s attitude error in the same way it will in flight.”
The CubeSpec mission is developed by KU Leuven, in Belgium, in the frame of ESA’s General Support Technology Programme Fly Element, and with funding from the Belgian Federal Science Policy Office (BELSPO).
[Image description: An indoor laboratory scene shows a person crouching beside a compact, circular robotic platform standing on the floor to the left of him. The platform has exposed mechanical components and wiring. On the right, there is a telescope-shaped instrument mounted on a tripod. The left half of the wall in the background is covered with a black curtain; the right side has a dark blue banner with the European Space Agency logo on it.]
