The start of the European mission “Proba-3” is approaching, in which for the first time two artificial objects that move in a precise pattern will be used. “Tandem allows you to check the accuracy of artificial satellite groups and provide a detailed survey of the Sun,” said Tomasz Barczynski, an expert of the space research center of the Polish Academy of Sciences. Poland has a big share in this mission.
It is planned to launch the Proba-3 mission of the European Space Agency on December 4. As the head of the laboratory of mechatronics and artificial robotics, Dr. Tomasz Barczynski assured, a truly advanced system will be launched into space at the space research center of the Polish Academy of Sciences.
– This is the first such precise configuration. It will consist of two satellites. One of them is used by a coronagraph – a telescope designed to observe the crown of the Sun. The second acts as a so-called occulter – an element that covers the solar disk and causes eclipses like the Moon. Anyone who has taken pictures will notice how difficult it is to photograph a scene with very bright and dark objects next to each other – for example, taking a picture with the sun behind you. The disk, which is millions of times brighter than the corona, blinds the coronagraph detector, so we have to cover it with an occulter, explained the expert.
“We will observe space that reaches almost the surface of the Sun”
Coronagraphs have already been sent into space, for example in the SOHO mission. But earlier, the occulter was located a few meters away from the telescope installed on the same satellite. In the case of Proba-3, about ten times the distance allows for a much more accurate image of the crown.
– We can descend to the very deep regions of the crown, where the matter ejected from the Sun into space is “catapulted”. This area was previously only accessible during a rare and almost momentary total eclipse of the Sun by the Moon. We will observe the space that almost reaches the surface of the Sun, starting from eight percent of its radius, said Dr. Bartsinsky.
The large distance of the occulter from the coronagraph is designed to reduce the problem of diffraction (bending of the wave) which distorts the image. – The wave nature of the light causes the photons of the solar disk to “bounce” from the edge of the occulting disk and fall into the telescope. By moving the shield, we reduce the intensity of this phenomenon, – explained the expert.
An excuse to test the technology
As Dr. Bartsinsky noted, the main goal of the mission is not to study the solar disk.
– “Zond-3” is described as a “technological mission”. In fact, the use of a coronagraph and an occulter is an excuse to test the extremely precise technology of keeping two satellites in a constant position. Both elements will be at a distance of 150 meters, with an accuracy of a few millimeters. In this way, the angular orientation of the satellites is kept accurate – the deviation does not exceed a few seconds of arc (1 second of arc is 1/3600 degrees). It should be remembered that the tandem is always in motion and moves in an elliptical orbit. In fact, due to the distance between them, both elements will move in two different, although they have the same orbits. This means that they tend to move away from each other, so their position and direction must be constantly adjusted. It will be a very difficult task in front of management systems, – explained the specialist. Scientists and engineers hope that the technology tested on Proba-3 can be used in future space flights – any mission that requires high precision and coordination between two satellites. – These, for example, will be the programs of the so-called space garbage collection vehicles, in which a robot-manipulator picks up an unusable satellite for removal from orbit. Apparently, the captured satellite rotates almost chaotically around its axis. Therefore, the robot must not only approach with great precision, but also start orbiting the satellite to capture it, said Dr. Barczynski.
Proba-3 mission – ESA visualization
Space tankers will do the same. – Refueling in orbit had such requirements. The fuel vehicle must connect a suitable cable to the satellite or other vehicle. Such precision will be needed here as well, the expert added. This type of technology is also used in fundamental space research that uses gravitational waves. – In the planned European mission LISA (Laser Space Antenna), three satellites will be placed about 2.5 million kilometers apart, forming an equilateral triangle. They send laser pulses to each other and tell the satellites about their relative position. Gravitational waves disturb this position slightly. To detect these changes, the satellites must maintain their position very precisely. In short, many potential applications of the approach have been tested in the Proba-3 mission – the CBK PAN expert emphasized.
“We have become an even more recognized band in Europe”
The Center team was primarily responsible for two parts of the system. – One of the elements we prepared was the computer that controls the coronagraph, the heart of the main instrument of the mission. Space computers are specific – they have to meet specific requirements, but are similar in many ways. Therefore, we use technologies that we have already developed and adapted them to this specific mission, – described Dr. Barczynski.
The second element was a part of the telescope itself, which operated on the satellite. – We also made a tool called a filter replacement wheel. As the name suggests, it is a wheel with optical filters placed in front of a light-sensitive detector. By turning this wheel, these filters can be selected depending on the radiation band that is being checked, explained the expert.
– The most difficult thing was putting the filters on the wheel. It seems like a simple task, but it is not. The filters are made of glass, which we need to attach to the metal. Vibration during the flight, the vacuum of space, temperature changes, the need to maintain the utmost cleanliness of the optical instrument – these difficulties forced us to develop a special assembly technology. We installed the glass filters in a flexible system to strictly control the pressing force of the glass. Preventing the filter from breaking or even breaking. Another difficulty was that it was a moving mechanism, and organizers of space flights are always afraid of such elements. “If something moves, you need an engine, a control system, a power supply system, a failure detection system, etc.,” explained the specialist.
The developed technology can probably be used in other applications as well. – This mission allowed us to deepen the skills needed to work on European Space Agency projects. Thanks to our participation in Proba-3, we became an even more recognized group in Europe – as a group that was able to cope with this difficult space mechanism. “Our team, including the group of mechanics for whom I am responsible, showed itself very well,” he said.
Polish companies also cooperated with CBK PAN, which managed the Polish part of the project – Astri Polska, N7 and Creotech Instruments.
Tomasz Barczynski specializes in control theory and mechatronics. He leads the teams working on the most important space missions with the participation of Poland, including the Proba-3 mission, the construction of the ATHENA X-ray space telescope and the Comet Interceptor probe, designed to intercept comets from outside the Solar System. He also worked on the Space Debris Vehicle project in the ESA ClearSpace program and Poland's EagleEye observation satellite.
Main image source: ESA
