content 24-October-2017 07:55:45

Operations and Planning

ESA's second PROBA (PRoject for On-Board Autonomy) satellite carries four scientific instruments: two particle detectors to monitor the plasma environment of the spacecraft (DSLP and TPMU) and two complementary instruments (SWAP and LYRA) which monitor solar activity.

The SWAP (Sun Watcher using APS detectors and image Processing) instrument is an extreme-ultraviolet (EUV) telescope that uses new Active Pixel Sensor (APS) technology to observe the Sun’s outer atmosphere, the corona, in a very narrow spectral band.

On average, SWAP images the Sun every 100 seconds, 7 times faster than the EIT instrument aboard the ESA/NASA SOHO satellite. However, its most significant characteristic is its wide field of view, which enables it to observe solar plasma eruptions as they extend beyond the solar limb and into the corona.

As solar activity increases towards solar maximum over the next few years, SWAP operators will coordinate with other space-based instruments to observe solar flares and coronal mass ejections (CMEs), thereby combining data from solar imagers and coronagraphs.

SWAP images are being used alongside data from the LYRA (Large Yield RAdiometer) instrument, which uses novel diamond detectors that are transparent to visible light but sensitive to extreme ultraviolet.

LYRA consists of three redundant groups of detectors, each capable of measuring solar irradiance - the radiative output of the Sun - in four key UV-EUV spectral bands, with a very high temporal resolution (up to 10 ms).

Until now, units 1 and 3 have only been used for occasional cross-calibration, so they are in pristine condition, whereas unit 2 has been used continuously. As a consequence, the two UV (Lyman-Alpha and Herzberg) channels of unit 2 have suffered from strong degradation.

A special operational programme has been introduced for LYRA. Unit 2 will remain the nominal LYRA unit, with its EUV channels returning science data for continuous monitoring of solar activity. The UV channels of units 1 and 3 will be used on request during scientific campaigns, particularly for studies of Earth’s upper atmosphere, during the yearly eclipse season from November to March.

This operational mode can be maintained until at least 2018, ensuring that LYRA can continue to return data up to, and beyond, the next solar maximum.

Data from all of the instruments on PROBA2 are downloaded to small dish antennas at ground stations in Redu, Belgium, and Svalbard in Norway. There are typically 9 overpasses of these stations every 24 hours, equally spread over the day. This frequent coverage is important because the satellite has limited onboard data storage and the scientific data are overwritten if they are not downloaded in time.

The data are reformatted and sent from the Mission Operations Centre in Redu to the PROBA2 Science Centre (P2SC) at the Royal Observatory in Belgium, typically reaching it within 30 minutes of the contact. Data are then processed into science data products and distributed to the scientific community via the P2SC web server.

Science planning capabilities

The coordination and planning of the PROBA-2 ground and flight segment, especially the operations of the scientific and technology demonstrator instruments, is carried out by the Science and Technology Operations Working Group (STOWG). This group meets every 6 weeks to discuss and plan the main operations in the upcoming three months.

Special campaigns with other space instrumentation or ground observatories are possible, and scientists are encouraged to contact the P2SC with ideas for combined or special operations.

Typically, these are planned a few days to a week ahead. However, the commanding of the SWAP and LYRA instruments is quite flexible and changes to the nominal observational programmes may be made very quickly, as long as there are no conflicts with the operation of the spacecraft and other instruments.

One P2SC duty operator is assigned each week. This operator is responsible for all the scientific operations during that period. However, the satellite usually operates in autonomous mode and commands are only sent when special campaigns are planned.

Should a solar eruption be predicted, the operator can immediately send special instructions via the internet directly to the ground station at Redu, Belgium. Once they have been checked for errors by the ground computer, these commands are uplinked automatically to the satellite for implementation – a degree of flexibility that would be impossible with a much larger, more complex spacecraft.


Last Update: 20 June 2013

For further information please contact: SciTech.editorial@esa.int

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