On April 25th, 2018, at 17:57 UTC a Russian Rokot/Briz KM rocket launched from Site 133, pad 3 from Plesetsk Cosmodrome. Aboard was Sentinel 3B, an Earth observing satellite, part of Europe’s Copernicus environmental monitoring network. This marks the final commercial Rokot Launch, and the final Eurokot mission. There are some more Rockot launches planned for the Russian government though, after which it is reportedly that the repurposed missile launch system will be retired.
Sentinel 3B is a Thales Alenia Space Prima Bus satellite, designed to measure ocean temperatures, colour, surface height and the thickness of sea ice. While it is over land it can measure the height of rivers and lakes, monitor wildfires, provide maps of land use and monitor vegetation. The satellite has been designed for many uses. Created for the European Space Agency, the satellite will join Sentinel 3A in orbit to symmetrically monitor the Earth. The data will be primarily fed into the Copernicus Environmental Monitoring Service, where the applications can be developed from to use the data.
The satellite carries many payloads to track the huge amount of data it is recording, these include:
OLCI (Ocean and Land Colour Instrument)
SLSTR (Sea and Land Surface Temperature Radiometer)
SRAL (Synthetic Aperture Radar Altimeter)
MWR (Microwave Radiometer)
LRR (Laser Retroreflector)
GNSS (Global Navigation Satellite System)
Thales Alenia Space was the prime contractor, responsible for constructing the spacecraft and the SRAL instrument, as well as contributing to the supply of the SLSTR instrument. Many European companies were involved in supplying the SLSTR instrument, including SELEX Galileo, RAL (Rutherford Appleton Laboratory), Jena-Optronik, Thales Alenia Space, ABSL and ESA-ESTEC. EADS CASA Espacio was contracted to provide the MWR instrument. CNES was contracted to provide the DORIS instrument.
At 17:10 UTC on the 9th of March 2018, Arianespace launched its second rocket of the year from Guiana Space Center at Kourou. Designated VS18, the Soyuz rocket launched four O3b Satellites into orbit more than 3 years after the last O3b launch. Controlled by a Russian ground crew from the Soyuz Launch Complex (ELS) near Sinnamary, there was a 33 minute delay to the start because of bad weather. The Soyuz used was a Soyuz 2-1b/Fregat placing the satellite in Medium Earth Orbit (MEO).
A somewhat complex launch, the first ascent lasted 9 minutes and 23 seconds placing the launcher in a sub orbital trajectory. After separation the Fregat performed a 4 minute burn to reach 160 x 205 km x 5.16 deg parking orbit. Coasting for 8 minutes, the Fregat performed its second burn for 8 minutes and 36 seconds to enter a 190 x 7,869 km x 3.88 deg transfer orbit. Then after a coast of 1 hour and 21 minutes to the apogee, the Fregat fired for its third and final time for 5 minutes and 6 seconds, to enter its 7,830 km x 0.04 deg insertion orbit.
After the third burn, the satellites were release two at a time, with opposite satellites released at the same time. The first were released 2 hours into launch, and the second set 22 minutes later after a short firing of the Altitude Control System. The rocket then performed 2 more burns to lower its orbit to 200 km below the O3b release point. This was a disposable orbit, intended so that it will not interfere with working satellites.
The Ka band satellites are the fourth set of O3b to be sent up, making the total constellation 16. Arianespace intend to launch the next set of four in 2019. “The new Ka-band satellites will join the existing O3b constellation to deliver high-speed connectivity to people and businesses in the growing mobility, fixed data and government markets,” Arianespace officials said in a statement. It was reported that the launch was a success, and the Luxembourg based satellite operator SES Networks now have control of the O3b’s.
The second launch of the year, Arianespace delayed the launch from the original March 6th launch date. This was postponed to conduct extra checks, likely inspired by the partial failure of the Ariane V earlier this year. On January 25th the company lost contact with the upper stage of the rocket. The 3 satellites on board did reach orbit despite the anomaly, but Arianespace have been quiet on the condition of them.