Russia: The European Space Agency’s Sentinel 5 Precursor satellite was launched aboard Russia’s Rokot carrier rocket. Liftoff, from the Plesetsk Cosmodrome in Northern Russia took place at 12:27 Moscow Time (09:27 UTC).
Sentinel 5 Precursor, commonly known as Sentinel-5p, is a small scientific satellite that will contribute to the Europe’s Copernicus programme, dedicated to Earth science. Sentinel-5p will focus on the planet’s atmosphere, detecting and monitoring trace gases in the troposphere – the lowest layer of Earth’s atmosphere.
The satellite will a void, leading to resurgence of capabilities lost when the Envisat spacecraft stopped operating in 2012 before a new generation of instruments begins launching in the early 2020s.
Copernicus, formerly the Global Monitoring for Environment and Safety (GMES), is an ambitious project being undertaken in partnership between the European Commission and the European Space Agency (ESA) to launch a fleet of satellites and instruments in space which will gather data on Earth and its environment. The European Commission manages the project, while ESA is responsible for its space component – which it is executing through its series of Sentinel missions.
Sentinel consists of six different types of satellites or instruments, each providing different insights on an aspect of the Earth. Sentinel-1 satellites carry synthetic aperture radar (SAR) payloads providing all-weather radar imagery of the surface.
Sentinel-2 satellites carry high-resolution multispectral optical imaging payloads to capture images of the planet at various wavelengths.
Sentinel-5p will be the sixth Sentinel satellite to launch. Two Sentinel-1 satellites are currently in orbit, having been deployed by Soyuz-2-1a rockets in April 2014 and April 2016, while a pair of Sentinel-2 satellites were launched by Vega rockets in June 2015 and March this year. Sentinel-3A was deployed in February 2016 by a Rokot.
Unlike the planned Sentinel-5 missions, which will be integrated with MetOp-SG spacecraft, Sentinel-5p is a free-flying satellite. Constructed by Airbus Defence and Space – formerly EADS Astrium – the satellite is based on the AstroBus-L 250M platform.
Weighing-in at 820 kilograms (1,800 lb) at launch, the spacecraft is expected to operate for at least seven years. Sentinel-5p’s three solar arrays will provide at least 1,500 watts of power, and the satellite’s average consumption expected to be around 430 watts.
Sentinel-5p’s PM-22 propulsion system provides maneuvering capabilities, with a tenth of the satellite’s liftoff mass consisting of hydrazine propellant. The satellite is three-axis stabilized, with an attitude and orbit control system (AOCS) using star trackers, GPS receivers, magnetometers and an Earth sensor to determine its position and orientation – while reaction wheels and magnetotorquers will deliver attitude control.
Scientific data will be collected aboard the satellite, via the Payload Handling and Transmission subsystem (PDHT) which has 480 gigabits (equivalent to 52.5 gigabytes) of onboard storage capacity. When passing over a ground station, data will be downloaded via an X-band transmitter with a data rate of up to 310 megabits per second. The satellite also carries two S-band transponders for telemetry and control.
The Tropospheric Monitoring Instrument, or Tropomi, is the only scientific instrument aboard Sentinel-5p. A multispectral imaging spectrometer, ESA describe it as the most advanced instrument of its type to have been flown to date. Tropomi operates in three different bands of the electromagnetic spectrum: 270-500 nanometres, 675-775 nanometers and 2,305-2,385 nanometers.
The first of these bands covers parts of the near-ultraviolet and the blue end of the visible spectrum, while the other bands are in the infrared – covering the near infrared and short-wave frequencies respectively.
Tropomi will measure the spectra of light that has been reflected from the atmosphere and of sunlight. Comparing these spectra will allow it to highlight absorption lines, caused by particular wavelengths of light being absorbed by chemicals in the atmosphere. Different chemicals have unique signatures, so by studying which absorption lines are present scientists will be able to identify which gases are present in the atmosphere.
At the wavelengths Tropomi will observe, it is expected to be able to detect absorption lines caused by bromine oxide, carbon monoxide, chlorine dioxide, formaldehyde, glyoxal, iodine oxide, methane, sulphur dioxide, nitrogen dioxide, atomic and molecular oxygen, ozone, water – including semi-heavy molecules with a single deuterium atom – and some aerosol compounds.
Developed by ESA in conjunction with the Netherlands Space Office, Tropomi has a mass of 220 kilograms (485 lb). The instrument will help Sentinel-5p to study pollution in the troposphere, providing high-resolution data on the presence of chemicals that play a major role in pollution. Its observations will also contribute to monitoring of volcanic ash in the atmosphere and forecasting ultraviolet radiation levels.
Sentinel-5p will operate in a circular sun-synchronous orbit, at an altitude of 824 kilometers (512 miles, 445 nautical miles), an inclination of 98.7 degrees and a local time of ascending node of just after 13:30. In this orbit, the satellite will complete sixteen revolutions per day and revisit the same point on the surface every sixteen days, or 227 orbits.
This orbit has been chosen to coordinate observations with Suomi, a US weather satellite that launched in 2011. Sentinel-5p will follow closely behind Suomi, using the US satellite’s cloud cover observations to calibrate its observations. Suomi is expected to be replaced by the JPSS-1 satellite, which is to be launched next month.