The airplane is one of the safest modes of transportation in the world thanks to excellent pilot training as well as advanced technologies both onboard and on the ground. This applies even more so to space flights.
KELLER provides sensors for the aerospace industry developed using modern technologies and meeting high safety requirements.
Aviation Safety
Many people feel anxious during flights, unlike traveling by car, even though the risk of being in a car accident is much higher. According to data from the Federal Association of the German Aviation Industry (BDL) and the Aviation Safety Network (ASN) portal, out of 4 billion passengers transported by air in 2017, 79 people died in ten civil aviation accidents. As of 2017, the risk of losing life during commercial flights was the lowest in recorded history.
According to BDL data, airlines transport 13 times more passengers than in 1970. Despite the growing number, in 1970 the statistical probability of dying in an air crash was 1:264,000; in 2017 this figure decreased to 1:92,750,000. These values indicate a 350-fold increase in flight safety. Reports do not include incidents involving military aviation or small aircraft with a capacity of fewer than 14 people onboard. This success is explained by improvements in aviation technologies, airport infrastructure, and air traffic management. Currently, aircraft are generally less susceptible to external influences, which may be due to more thorough selection and strict verification of suppliers and their products.
KELLER Pressure Sensors in the Aviation Industry
Since 1997, KELLER has been a supplier of pressure sensors for various aviation sectors. The main areas are:
• Cabin pressure monitoring
• Hydraulic distributors and filtration systems
• Control valves
• Fuel pumps
• Refueling systems
• Air conditioning systems
• Ventilation
• Emergency oxygen supply for pilots
As shown in the image below, ten different pressure sensors are used in an aircraft. Depending on the type of aircraft, KELLER sensors equip either all compartments or some of them. The description of specialized applications is confidential information. Nevertheless, below are three types of aircraft, whose descriptions give an idea of how much they can differ and, consequently, how broad the list of requirements for pressure measurement technologies is.
The wide-body, double-deck, four-engine A380 aircraft with a capacity of up to 853 passengers is the largest serial civil aircraft in the world. The plane can cover distances up to 15,200 km at a cruising speed of about 900 km/h. Two compact air conditioning systems maintain the temperature at the required level. The output power of the units is about 450 kW. When operating at full capacity, the cabin air is completely replaced every three minutes. Unlike common commercial aircraft, the A380 has only two hydraulic systems. The third hydraulic circuit was replaced by electro-hydraulic drives, which reduced weight due to fewer cables and valves. Fuel tanks are part of the aircraft's load-bearing structure and are located in the wings and stabilizer.
With the controlled fuel consumption system, automatic aircraft centering can be performed throughout the flight, optimizing structural load. The system automatically manages fuel distribution.
The Airbus A400M is intended to replace or supplement the outdated air force fleets of seven European NATO member countries. The aircraft is equipped with four turboprop engines and a cargo ramp at the rear of the fuselage and can take off from short unpaved runways. Although the A400M is already widely used, its technical development is not yet complete.
The Boeing 787 Dreamliner is a long-haul twin-engine aircraft with a capacity of up to 300 passengers. The Boeing 787 is the first wide-body aircraft whose fuselage is predominantly made of carbon-based composite materials. Thanks to reduced weight, as well as new engines and improved aerodynamics, fuel savings are expected to be 20%, and noise levels significantly reduced. A distinctive feature of the engines is the absence of air bleed into the air conditioning system, which prevents engine oil from entering the cabin atmosphere. Each engine is equipped with two 250 kW generators used to start the engines and generate electricity. The air conditioning system is also electric. The Boeing 787 is standardly equipped with an inert gas system that extracts nitrogen from the air using special filters and supplies it to the tanks. This reduces the oxygen concentration to a level where ignition is impossible even if sparks occur.
Spaceflight Safety
The International Space Station with a scientific laboratory in the European Space Agency's Columbus module orbits the Earth at an average altitude of about 400 km at a speed of 28,800 km/h. It takes only 90 minutes for the station to complete one orbit. For astronauts aboard, this means 16 sunrises and sunsets per day. The ISS project combines the efforts of several space agencies: NASA, Roscosmos, the European Space Agency (ESA), the Canadian Space Agency (CSA), and the Japan Aerospace Exploration Agency (JAXA).
Since November 2000, astronauts have lived continuously on the ISS. The station's design is based on a modular principle. Currently, its dimensions are 110 x 100 x 30 m, and its weight is about 450 tons. The station's modules were delivered into orbit by shuttles and then assembled into a single structure. The European module with the Columbus research laboratory was installed in February 2008 by the 16th ISS crew astronauts. Columbus is the largest contribution of the European Space Agency to the station.
Since May 2009, the average number of astronauts working aboard the ISS has been six. The project participants have agreed to operate the station through 2024 inclusive, with an extension under consideration, as technically it can function until 2028.
KELLER Pressure Sensors in Space Exploration
The technical requirements in space exploration are much stricter than in aviation because emergency landings are not possible, and equipment replacement is not as simple as on aircraft. Several years ago, the leading German aerospace company approached KELLER. Absolute and differential pressure sensors were needed for the closed-loop life support system ACLS, which could ultimately be used on the ISS.
The ACLS system's task is to recycle carbon dioxide into breathable oxygen in a closed loop. In September 2018, the system equipped with 37 KELLER sensors was delivered to the ISS aboard the Japanese HTV-7 cargo spacecraft on an H-IIB rocket.
To generate oxygen, the ACLS system extracts CO2 from the space station cabin air. The Sabatier reaction facilitates the reaction of hydrogen with carbon dioxide in the presence of a catalyst to produce water and methane. Then, water condensate is separated from the gas flow and returned to the water management system. Subsequently, water is electrolyzed into hydrogen and oxygen, with methane vented into space.
The ACLS system is designed for a crew of three astronauts and an annual saving of an additional 450 kg of water. Daily, the system absorbs 3 kg of CO2, generates 2.5 kg of O2, and produces 1.2 kg of water, significantly improving efficiency and reducing the demand for supplies from Earth.
As is customary in space exploration, the sensor set for the ACLS system was manufactured twice in advance and delivered for installation in prototypes sent for further improvements and testing. Based on the results, the final version was determined. The samples remaining on Earth will be used for subsequent tests, simulations, and to inform the ISS crew about malfunctions, repair methods, and maintenance of the ACLS system.
Requirements in the Aerospace Industry
Both aviation and space exploration do not use cutting-edge technologies. For both industries, maximum reliability is crucial, and the components used have proven themselves in this regard. Moreover, airplanes are typically in service for 25 to 30 years, and parts used for repair and replacement must be available throughout this entire period.
Based on strict aircraft maintenance guidelines, one part cannot simply be replaced by another – an absolutely identical element from the same manufacturer is required. Therefore, in this case, the use of non-standard products is advisable. KELLER develops solutions taking into account all specific customer requirements to ensure full compliance with the task conditions. Thus, there is no universal solution, but there is a specially designed technology that meets all requirements. This is the only way to ensure the need for the highest reliability under these environmental conditions.
Despite preliminary positive statistics, considering a number of events over the past two years, there is occasionally an impression of reliability requirements being overshadowed by economic interests. KELLER opposes this idea by thoroughly and meticulously studying each client’s task to ensure maximum reliability of all products. Unfortunately, two-thirds of requests are rejected due to incomplete specifications.
Special Technology for Special Purposes
The achievements of aviation and space exploration over the past decade would not have been possible without the use of reliable basic technology. Thanks to its high-precision pressure sensors, KELLER has also been involved in these developments since 1974.
Piezoresistive Technology
The main component of pressure sensors used in aviation and space exploration is the piezoresistive silicon sensor. The sensor consists of a flexible silicon diaphragm that deforms under pressure. The diaphragm bends in both directions depending on pressure differentials, causing mechanical stress on its surface. To measure mechanical stress, resistors are distributed along the peripheral zone of the diaphragm at points of highest stress. Thanks to the piezoresistive effect, the resistors respond to mechanical stress better than strain gauge sensors that track deformation. A major advantage is the extremely high sensitivity combined with good zero-point stability. The latter results from using a solid silicon crystal, which, unlike metal, is unaffected by deformation.
Piezoresistive technology based on silicon chips proves its effectiveness in everyday use and is employed in even more extreme conditions.
Thus, the key to appropriate use lies more in the structural design of piezoresistive chips than in the technology itself. Unlike metal plates, the silicon sensor is less resistant to environmental exposure and can only be used in dry clean air or non-conductive media. However, special housings and corresponding electronic circuits are used to manufacture high-precision, reliable pressure sensors with silicon diaphragms.
Since there is a risk of incompatibility between the environment and one or both sides of the silicon sensor, protection must be ensured. For KELLER, measuring pressure against a vacuum seemed the best option for aviation and space spheres, as only one side would need protection from aggressive media. The electrostatic connection of the silicon sensing element on a glass substrate was provided by vacuum on the opposite side. But without vacuum, the electrostatic connection, based on ion movement between the glass substrate and silicon, could not occur. Even designing oil filling and insulation from the measured medium posed a challenge. Due to the need to control many effects when developing the piezoresistive measuring element, it becomes clear that such a sensor will cost 10-100 times more than a separate silicon sensing element.
“In other words, the customer purchases a comprehensive solution and practically gets the sensing element for free,” concludes Jürg Dobler.
Thanks to their high accuracy and excellent reliability, oil-filled piezoresistive pressure sensors play a leading role in pressure measurements and form the basis of pressure sensors used in aviation and space exploration.
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_80x0_c25.jpeg "Radar Level Meter IZMERKON RL 37")
