Arianespace’s Vega rocket conducts Mohammed VI-B launch

by Chris Bergin

Arianespace’s Vega rocket launched the second Moroccan remote-sensing satellite, Mohammed VI-B (MN35-B) 0 building on the footsteps of its twin MN35-A launched also by Vega just over one year ago. Launch occurred at the top of the launch window at 01:42 (UTC) on Wednesday from the European Spaceport in French Guiana.

The MOHAMMED VI – B satellite is the 155th satellite built by Thales Alenia Space to be launched by Arianespace, which has 11 more satellites from this manufacturer in its order book.

It was also the 123rd Airbus satellite to be orbited by Arianespace, which currently has 20 additional Airbus satellites in its backlog.

Produced by Thales Alenia Space as system prime contractor and Airbus as co-prime, the MOHAMMED VI ‐ B satellite had an estimated liftoff mass of 1,108 kg. and deployed it into a Sun-synchronous orbit.

Once in orbit, it will be used primarily for mapping and land surveying activities, regional development, agricultural monitoring, the prevention and management of natural disasters, monitoring changes in the environment and desertification, as well as border and coastal surveillance.

The Mohammed VI-B satellite

It is the second satellite for the Kingdom of Morocco’s MOHAMMED VI ‐ A & B program, following Arianespace’s Vega launch of the MOHAMMED VI ‐ A satellite in November 2017.

Designed to be complementary, the two spacecraft will work together to enable faster coverage of zones of interests.

The final countdown for launch began nine hours and ten minutes before Vega’s scheduled liftoff. In the hours leading up to launch the rocket’s key systems were powered up, with the multi-functional unit (MFU) that controls Vega’s electronics, turned on at the T-6-hour mark in the count.

Twenty minutes later, the rocket’s inertial reference and telemetry systems were activated followed by the Safeguard Master Unit (SMU), after another half an hour. Following removal of pre-flight safing equipment by the four-hour, fifty-minute mark in the countdown, the rocket’s onboard computer was started at T-4 hours, 40 minutes.

About three-and-a-quarter hours before launch, the mobile gantry used to assemble Vega at the launch pad will retract from the vehicle – a process that takes around three quarters of an hour to complete. Once the tower is fully retracted to its launch position, the rocket’s guidance system will undergo final alignment and checkout and the vehicle’s communications systems were activated.

These events occur 145 minutes and 75 minutes before liftoff respectively, with the rocket reaching launch readiness at the fifty-minute mark in the countdown.

Vega rocket ahead of launch – via Arianespace

Following a final weather report ten minutes before launch, the countdown entered its synchronized sequence – the last four minutes of the countdown where Vega’s onboard computers conducted the final checks and operations prior to liftoff.

Once the countdown reached zero, Vega’s solid-fuelled P80 first stage ignited with liftoff occurring about three tenths of a second later. Vega ascended quickly from its launch pad, reaching Mach 1 – the speed of sound – a little over 30 seconds after liftoff and passing through the area of maximum dynamic pressure, or Max-Q, 53 seconds into the flight.

Vega’s first stage burned for about a minute and 54 seconds before burning out and separating. The second stage, a Zefiro-23 motor, ignited about six-tenths of a second after separation and burned for one minute and forty-eight seconds before it too burned out and was jettisoned.

Vega during a previous launch – via Arianespace

Twelve seconds later, Vega’s Zefiro-9 third stage ignited, with the rocket’s payload fairing separating five seconds into the third stage burn.

The Zefiro-9 burned until T+3:38, after which it also separated. Vega then conducted a coast before its fourth stage, Avum, ignited.

The only liquid-fuelled stage used by Vega, Avum burns unsymmetrical dimethylhydrazine, oxidized by dinitrogen tetroxide. Its RD-843 engine was developed by Ukraine’s Yuzhnoye Design Bureau and Yuzhmash production plant, and derives from the RD-864 and RD-869 that powered the third stages of the Soviet – now Russian – R-36 family of missiles.

Avum’s first burn lasted until T+15:33, placing itself and Mohammed VI – B into an initial parking orbit. The burn was followed by a lengthy coast phase until the rocket reached the apogee – or highest point – of its orbit. Avum restarted for its second burn, to circularise the orbit, fifty-two minutes and three seconds after liftoff.

This second burn lasted one minute and 42 seconds, before Mohammed VI – B separated from Vega into its planned sun-synchronous orbit. After spacecraft separation, Avum will make a final disposal burn to deorbit itself – this will begin one hour, 50 minutes and 33 seconds into the flight.

Flight VV13 was Arianespace’s ninth mission in 2018 and is the company’s second this year using a Vega launcher – which is one of three launch vehicles operated by Arianespace at the Spaceport, along with the medium-lift Soyuz and heavyweight Ariane 5. Vega is provided to Arianespace by Italy’s Avio, which is the industrial prime contractor.

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