Proba-3 stargazing to heat up for corona observations

To take photographs of the photo voltaic corona, Proba-3 carries ASPIICS, brief for Affiliation of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Solar. This instrument, developed for ESA by Centre Spatial de Liège, Belgium, is made up of a big occulting disk mounted on the Occulter spacecraft and a photo voltaic coronagraph system carried by the Coronagraph spacecraft.

Of their most exact formation, the Coronagraph and the Occulter can be flying 150 m aside, sustaining their relative place right down to a single millimetre. The occulting disk will cowl the brilliant physique of the Solar, casting a shadow onto the optical instrument on the Coronagraph spacecraft and permitting it to check the photo voltaic corona.

Following their launch on 5 December 2024, the 2 satellites remained hooked up till their separation on 14 January 2025. The mission management workforce at ESA’s European Area Safety and Schooling Centre in Belgium managed the preliminary in-orbit commissioning.

Whereas the spacecraft have been nonetheless hooked up to one another, the workforce examined the accuracy of the mission’s pointing. Basically, the operators rotated the spacecraft by telling it which stars it must be dealing with. ASPIICS photographs of the star subject have been then used to confirm if the pointing was appropriate.

Andrei Zhukov, Principal Investigator for the ASPIICS coronagraph on the Royal Observatory of Belgium, explains: “We regarded on the star maps to see which stars could be seen for Proba-3 on that particular date. Selecting a single star wouldn’t be sufficient, as a result of then you definately can’t be positive which star you’re looking at. Ideally, you need a minimum of three stars – a triangle like that can provide you full orientation info.

“We selected two shiny stars from the constellation of Ophiuchus – which means ‘serpent-bearer’ in Historic Greek – that are marked with the Greek letters δ (delta) and ε (epsilon). They’re located shut sufficient to suit into an ASPIICS picture, along with just a few weaker stars. The Ophiuchus constellation is definitely seen to the bare eye from wherever on Earth.”

Andrei then requested the management workforce to level the spacecraft in the direction of these stars and to seize a picture of the star subject utilizing the coronagraph’s optical instrument.

“With glorious precision, the spacecraft pointed precisely the place we requested it to. Once we obtained the pictures, we noticed the 2 stars right away. They’re very sharp – that is nice information, as a result of it signifies that throughout the ten seconds it took to seize the picture, the spacecraft have been very secure.”

At the least eight stars are seen on this ASPIICS picture, which is sufficient to affirm the pointing of the telescope. Positioning each spacecraft exactly can be essential for observing the corona. If their alignment is off even by just a few millimetres, the Solar is not going to be totally coated by the occulter, resulting in undesirable mild interrupting the observations.

Within the exact alignment, the 1.4-m giant disc on the Occulter spacecraft – the exterior occulter – will totally cowl the Solar. Even then, nevertheless, so-called ‘stray mild’ will spill over the occulter’s edges, making a haze that might intrude with the corona observations.

To dam the stray mild, the coronagraph is provided with one other, inner occulter. Within the star subject picture, this inner occulter is seen as a black ring, similar to a blackened part of one of many coronagraph’s lenses.

Andrei provides: “You too can see cosmic rays within the picture, marked in purple. That is regular – in coronagraph photographs, cosmic ray hits typically seem like stars. There was a second picture taken a while aside – on this one, the celebrities keep, and the cosmic rays seem in numerous areas.

“General, we have been more than happy with the accuracy of the spacecraft pointing and the standard of the picture. It made us much more excited to see the corona photographs, anticipated as early as March.”

The Royal Observatory of Belgium is internet hosting the ASPIICS Science Operations Centre (SOC) – a devoted workforce answerable for creating operational instructions for the coronagraph based mostly on requests from the scientific group and sharing the ensuing observations.