Rocket Engine Test on the ESA's Test Bench For Large Solid Propellant Boosters

The thrust of the booster is around 4650 kN. Thunder strikes the rainforest; the noise is deafening. The deep rocky drench at the foot of the launch tower is forcefully filled with large clouds of fire and smoke. The trees along the edges are swaying heavily. It is only fired for 135 seconds, but the power of the solid rocket motor is overwhelming.

P120C, the motor tested measures 13.5 meters in length and 3.4 meters in diameter. Packed with 142 tons of solid propellant, the engine was ignited and produced a flood of flames. All to validate its design – to monitor, measure, and document all functions and parts with 600 parameters – simulating the complete burn time from liftoff and through the first phase of flight.

The scene is the European Spaceport located around 10 km to the North-West of Kourou in French Guiana, South America. On the 28th of January 2019, the CNES (National French Space Agency) facilities test-fired its second P120C solid rocket motor, a step toward the initial launches of the Vega-C light satellite launcher late this year and the Ariane 6 heavy satellite launcher in 2020.

The static hot firing was a success – one more important step in the joint European space program to make sure that multi-million payloads reach orbit safely and cost-efficient – and Dewesoft data acquisition products played a key part.

Clemessy and Dewesoft - the test solution

In the run-up to the test, all the main components of the motor – such as nozzle, igniter, solid propellant, and insulated motor case – had already been tested separately.

This static firing is designed to prove these technologies, materials, and production techniques in combination and validate the behaviour of the assembled motor

noted ESA ahead of the test.

In 2015 CNES on behalf of the ESA put forward the task to improve the Ariane rocket test bench by replacing analog data acquisition with high-end conditioning and digitizing data acquisition. The provider would face the challenge to interface with the existing test bench and providing high-reliability control commands.

This challenge was accepted by CLEMESSY as a system integrator, even with a hard deadline and limited time to complete the project: the firing test date was fixed, and whatever happened, teams had to put the data-acquisition and control command fully operational for the test.

CLEMESSY is a French company specialising in the engineering and implementation of industrial technical installations. CLEMESSY, a subsidiary of EIFFAGE, was to deliver the system to be used when testing the booster on the Ariane launch and to be in charge of the maintenance of the installations.

For data acquisition CLEMESSY selected Dewesoft. On the hardware side, Syclone ensures the interfaces with the operator, and performs the server, and real-time sequencer, whereas Dewesoft is interfaced with the process. The originality is that the Dewesoft data acquisition and control systems are not only used for data acquisition but also serve data to the Syclone control system in real time.

Kourou - the European spaceport

The test took place in French Guiana, at the Guiana Space Centre (CSG) - the European spaceport, which has been operational since 1968. This overseas region of France is the size of Portugal – 98% is covered by tropical rainforest – and has a little more than 250.000 inhabitants. The industry is centred around the spaceport and an estimated 15% of the working population is directly or indirectly involved with the space industry.

 Geographically, this location fulfils the two major requirements of a spaceport:

• It is near the equator, meaning less energy is required to manoeuvre a spacecraft into an equatorial, geostationary orbit. Rockets can be launched into orbit with an inclination of as low as ~6°.

• It has an open sea to the east, meaning lower stages of rockets and debris from launch failures are unlikely to hit human habitations. Rockets launch to the east to take advantage of the angular momentum provided by Earth's rotation.

The European Space Agency (ESA), the French National Space Agency (CNES), and commercial companies like Arianespace conduct launches from Kourou. The spaceport was used by the ESA to send supplies to the International Space Station. ESA pays two-thirds of the spaceport's annual budget and has also financed upgrades made during the development of the Ariane launchers.

The day-to-day life of CSG is managed by CNES. CNES provides all needed range support, requested by Arianespace, for spacecraft and launch vehicle preparation and launch. The facilities can process several spacecraft of different customers at the same time, with large clean rooms and supporting infrastructures. The spacecraft and launch vehicle integration and launch are carried out from launch sites dedicated to special projects; Ariane, Soyuz, or Vega.

Ariane 6 - the launcher

The test is all about the Ariane 6 launcher project. ESA’s goal is to ensure and maintain independent access to space for Europe. Beginning in 1973, the development program is working with the CNES as a prime contractor. The maiden flight of Ariane 1 took place on 24 December 1979.

ESA works with an industrial network, led by ArianeGroup, of more than 600 companies in 13 European countries, including 350 small- and medium-sized enterprises, to fine-tune the design and start production. Meanwhile, CNES is preparing its launch facilities at CSG.

The overall mission is to make a cost-effective, reliable, unmanned vehicle that provides affordable access to space – a tool to launch satellites for mobile communication, television broadcasting, meteorology, earth observation, and other uses.

The exploitation cost of the Ariane 6 launch system is its key driver for development. The final design of Ariane 6 was selected in December 2014, favouring a liquid-fueled core with large solid rocket boosters over the initial solid-fuel rocket design. Ariane 6 is to replace Ariane 5 at half the cost and allow double the number of launches each year.

The Ariane 6 consists primarily of these components:

• A Lower Liquid Propulsion Module equipped with the Vulcain 2.1 engine.

• An Upper Liquid Propulsion Module equipped with the Vinci engine.

• Two or four Equipped Solid Rocket depending on the configuration of the Launch Vehicle: Ariane 62 or Ariane 64.

• A payload fairing.

• Depending on the mission requirements, a variety of different adapters/dispensers / dual launch structures or carrying structures may be used.

• Carrying structures for micro, mini satellites, and nanosats.

The Ariane 6’s Vulcain 2.1 engine is built with fewer parts while holding a greater efficiency, while the improved Vinci upper stage will allow for additional orbital destinations for more flexibility via a wider reignition capability.

Beap - the test bench

Unlike a lot of solid motor tests, this firing was conducted in a vertical position on the test stand. The test facility is continuously improved to accommodate European launcher evolution. The all-new P120C solid rocket and testbed were equipped with sensors to gather data on over 600 parameters, mounted the stand, and fired for 135 seconds in the test.

The Solid Booster Test Bench (BEAP) is the unique test pad at the Guiana Space Centre. Since 1993, it has performed the testing of Ariane 5 Solid Booster Stage (EAP) motors. None was actually intended to lift off and the facility is equipped with safety systems to prevent a booster from breaking loose from the test bench and leaving the ground. In this case, large blades would cut its envelope open, allowing the solid propellant to burn freely without providing any thrust.

BEAP is used to test the boosters of the European ARIANE 5, VEGA, and the future ARIANE 6 launchers to ensure they perform properly. The test bench acquires the measurements and controls the nozzle in order to check the operation of the onboard electronics

P120C - the booster

The P120C is designed and built by a European consortium involving a joint venture known as Europropulsion, a venture between ArianeGroup and Avio.

The P120C booster has a thrust of approximately 1 million pounds. It has the world’s largest monolithic carbon-fiber composite solid rocket booster casing. The motor’s case is one, single, component designed to lower the cost of flying payloads.

The booster is the first stage of the Vega-C, a new launcher developed by ESA, which is expected to debut in 2020, increasing performance from Vega’s current 1.5 t to about 2.2 t in a reference 700 km polar orbit. It will also work as the strap-on booster for the Ariane 6 series – either two or four of these boosters can be affixed to the Ariane 6 launcher to provide the thrust required for liftoff.

The P120C, co-developed by ArianeGroup and Avio on behalf of their 50/50 joint venture Europropulsion, consists of two principal parts. The first is the structural casing, built by Avio, an international group engaged in the construction and development of space launchers and solid and liquid propulsion systems for space travel. The casing is made of carbon fiber (filament-wound, automated fabric layup pre-impregnated epoxy sheets).

The second part is the nozzle, built by ArianeGroup and made of various composite materials, including carbon/carbon; it allows high-speed ejection of the extremely hot gases (3,000°C) generated by the motor, thus creating thrust by transforming the combustion gas energy into kinetic energy. The nozzle can also pivot, which enables the launcher to be piloted. Propellant casting and motor final integration are performed in French Guiana.

While Vega-C will continue to launch from the current Vega pad at the spaceport, a new launchpad complex is being built for the Ariane 6, called ELA-4.

For a launch campaign, the core stages will be integrated and prepared horizontally in the Launcher Assembly Building, less than a mile from the launch zone. The central core is then moved to the pad and erected vertically in the mobile gantry. There, the boosters, payloads, and fairing are added, before the mobile structure allows for platforms to access the different levels on the pad. The gantry is moved shortly before launch.

Two further test stand firings will follow to qualify the solid motor before the first flight of Vega-C in 2019 and that of Ariane 6 in 2020.

Syclone - the test control system

The system now implemented on BEAP integrates SYCLONE by CLEMESSY (Syclone), a fully scalable control-command software operating like a toolbox, which makes it possible to develop a customized solution adapted to needs and environments. The software structure combines the worlds of supervision, real-time process control, and physical hardware.

The Decision Support System provides operators at the Guiana Space Center with map support for danger zones during risky operations such as launching a rocket. The objective of the system is to analyze and cross-check meteorological and pyrotechnical parameters over an area of 2,200 km² and display information in real-time for up to 10 dangerous operations conducted simultaneously for coordination purposes.

In the early phase of the project, advanced features were requested by the end customer; one, to see the global system as if it was only one measurement unit, and two, to have a cross trigger which triggers all the units on the same event. Lastly, cybersecurity requirements are very high and were dealt with since the beginning of the project.

When testing rocket launcher boosters or engines, the uniqueness and the high added value of the units tested, as well as the high pyrotechnic risks, require optimal safety and reliability of the control command for a system that must be able to be used for several decades.

In this case, the Product Under Test is unique and has a value of around 50 M€. The test cannot fail, it has to be right for the first time – and naturally, the safety of the teams involved is a mandatory concern.

Syclone has to ensure data acquisition and real-time measurement as well as to control and monitor the entire rocket testing process. The tests carried out may require up to 1000 channels with 64 at 200k samples per second.

Once processed the drive front-end transforms the network frame into an analog signal. Imagine an ignition firing signal. All the 500 analog channel starts. These data are acquired in the data acquisition software at a very high speed up to 200 kHz per channel, fully synchronized, and is at the same time available to the control system with less than 500 microseconds latency including the sigma-delta group delays.

Data are processed in the controller in order to generate the test case prepared: What are the tank pressures? What is the position of the nozzle? What is the next step in the sequence? 400 microseconds required.

Lastly, a delay is induced by the drive front end. The consequence is a processing loop time of 1 ms on a network of about 4 kilometres. 1 ms of loop processing time is important, but there are also other key features to consider.

To fulfil the requirements of such impressive tests, the real-time measurement and monitoring system has to reach very high levels of performance - keeping in mind that the data acquired are directly used to drive the nozzle. The test bench reaches high levels of speed for loop processing, even if the equipment is distributed over kilometres of networks. The loop time between the sensor event and the action on the nozzle must be about 1 ms.

Data acquisition is interfaced with the sensors and signals are acquired on the Dewesoft DAQ system, SIRIUS and R8rt - both communicate perfectly via an EtherCAT network.

Thanks to the integrated EtherCAT bus, data are collected over the networks and are calculated in the real-time controller.

SIRIUS and SBOX R8 - the data acquisition

Data acquisition systems from Dewesoft were used during the test. They are now an integrated part of the European Solid Booster Test Bench (BEAP) and the French space agency CNES (National Centre for Space Studies) is to equip Ariane 6 launch pad with 800 channels SIRIUS data acquisition system with isolated STG analog inputs in 19” racks.

The solution also includes the R8rt, which offers a unique and key functionality - the dual-mode data bus. High-speed analog data is streamed and saved in the data acquisition supervisor and at the same time also send to the real-time controller via the real-time, low-latency EtherCAT bus.

R8rt instruments are high channel count, standalone DAQ systems with built-in powerful data processing computers, and SSD data logging capabilities, designed for maximum portability.  Systems can be configured with up to eight SIRIUS DAQ amplifier slices for a total of 128 analog inputs for virtually any sensor. R8rt DAQ systems include an EtherCAT slave port with built-in synchronization for connection and extension of an EtherCAT-based DAQ system like SIRIUS or KRYPTON DAQ modules.

On the data acquisition, only SIRIUS STG isolated amplifiers and signal conditioning modules are used. Firstly, it covers a wide range of sensors at a very high level of performance. Secondly, to have a modular approach on the 16 test benches and to have only one reference to handle during the maintenance phase.

The SIRIUS DAQ instrument – appropriately named after the brightest star in the sky, the Dog Star - is well-suited for the task. It comes with DualCoreADC® technology, which solves often-faced problems with signal measurement - input overload, noise, and artificial frequencies in the signal caused by aliasing. Each channel amplifier has two ADCs that always measure the high and low gain of the input signal. This prevents the signal from being clipped and keeps results in the full measuring range of the sensor.

With this technology, SIRIUS achieves more than 130 dB signal-to-noise ratio and more than 160 dB in dynamic range - 20 times better than 24-bit systems and 20 times less noise.

The SIRIUS instrument also comes with high galvanic channel-to-channel, channel-to-ground isolation (CAT II 1000V with ranges up to 1600V), and includes isolated sensor excitation. Such isolation allows for measuring high voltage potentials. Measurements, like vibrations, temperatures, or any other measurement where non-isolated sensors are placed next to a high voltage potential against the DAQ system ground, are safe.

The hardware can read different signals like the voltage, strain, ICP/IEPE, charge, CAN, counter, encoder, and digital. With the included DewesoftX software, data are acquired and combined from additional interfaces like GPS, FlexRay, Ethernet, Serial, PCM telemetry, and many more. Though each data source may have different sampling rates, timing and GPS synchronization technologies ensure that all data are perfectly synchronized.

SIRIUS data acquisition system utilizes a patented technology called SUPERCOUNTER® in every counter/encoder input. Counter inputs can measure the RPM and angle of rotating machines. Supercenter inputs are able to extract accurate values like 1.37, 1.87, 2.37, etc. fully synchronized for time and amplitude. The counter inputs are fully synchronized with analog, CAN bus, and other data sources enabling even the most demanding applications, even rocket booster tests.

Aerospace - the future

Becoming part of the ARIANE project has been a step-by-step process. In 2016, 16 Dewesoft DAQ channels were qualified as part of SYCLONE by CLEMESSY – and by the test, in January 2019 up to 600 DAQ channels were used. CNES intends to use the same technology for Ariane 6 and especially the firing test in French Guyana of the Vulcain 2.1 rocket motor.

Furthermore, comparable projects are being addressed worldwide and not only in booster firing tests. Dewesoft and SYCLONE by CLEMESSY combine the best of both worlds: high-end data acquisition and control front-ends with efficient and full-performance control-command software solutions. The high level of quality required by the National French Space Agency and more generally the European Space Agency has increased Dewesoft and SYCLONE by CLEMESSY solutions maturity and robustness for large test benches with hundreds of channels.

One more test stand firing will follow to finalize the qualification of the solid booster P120C before the first flight of Vega-C and that of Ariane 6 in 2020. The thunder of the motor will roar again, and trees and bushes will have to bow as fire and smoke fills the rocky drench in Kourou. At the same time, loads of data are streaming at extreme speed to ensure control and monitoring of the test. The partnership of CLEMESSY and Dewesoft boosts the lift-off.