Kourou Space Center, French-Guyana in 2020 Ariane 6 will be lifting off in a few minutes.
Finally! Yet, it was an ambitious schedule as the road from the drawing board to the final launcher or, more precisely, the space transfer vehicle took only five years.
Ariane 6 is to embark on its maiden flight today. Key elements such as the tank and structural components have been provided by OHB subsidiary MT Aerospace. Typical payloads carried by Ariane 6 include OHB’s Galileo satellites. Over a period of 30 years, the space transfer vehicle will provide a European gateway to space, while the Galileo satellites will ensure European independence from the US GPS system. This makes the Ariane 6 an extremely efficient space transfer vehicle, which is to be launched an average of once a month, thus marking a further milestone in the history of space transportation.
THE HISTORY OF SPACE TRAVEL IS A HISTORY OF TRANSPORTATION
The 20th century: from the 100-km limit to the lunar landing
“Scotty, beam us up!” – Back in 1966, Captain James T. Kirke of the Space Ship Enterprise issued his chief engineer Montgomery Scott this command for the very first time on TV. At this stage, it is still three years before Neil Armstrong becomes the first man to set foot on an extraterrestrial object. This historical event marks the peak of the ideologically-driven technological race to space. The successful lunar landing is preceded by many milestones:
In 1947, fruit flies become the first creatures to fly beyond the atmosphere’s 100-km limit, while the first ape achieves this feat in 1948. 1957 sees a major breakthrough in the space race, when the Soviet Union place their first satellite, “Sputnik 1”, in an orbit around the earth, while Laika the dog on board Sputnik 2 becomes the first living creature to go into orbit. Finally, in 1961, Russian cosmonaut Yuri Gagarin becomes the first man to orbit the earth once and to experience weightless conditions in space.
The United States quickly catches up, closing the initial gap: The much-quoted call by President John F. Kennedy to “land a man on the moon and return him safely to the earth” is quickly put into practice. And so it is that in 1969 a man is transported to the moon using what at the time is the most powerful launch vehicle ever built. Weighing almost 3,000 tons, the “Saturn V” carried three men and their equipment to the moon. 600 million people watched the lunar landing on their TV sets.
The 21st century: partnerships instead of competing super powers
Half a century after the lunar landing, beaming living material is still science fiction. However, that’s just about the only thing that hasn’t changed. The cold war is over. Space programs are no longer confined to national borders. The competition between the super powers has given way to multilateral alliances such as the International Space Station ISS. Cosmonauts, Taikonauts and Euronauts fly to space together. In addition, commercial initiatives to explore the stars generate new momentum. At the same time, the focus increasingly shifts to harnessing specific benefits: the experiments and observations on board the International Space Station ISS are directly incorporated in research activities on the earth, in programs aimed at making life on earth better, more convenient and safer. Our modern life styles would be unthinkable without the fleet of communications, weather and navigation satellites orbiting the earth. However, satellites must first be transferred to their orbit. In Europe, this is primarily done using Ariane launchers. Thus, space transportation is no longer a question of prestige on the part of competing nations but provides genuine benefits for people on earth.
In the 21st century, space transportation will become more frequent, turning into a daily occurrence. This is because more and more objects are being placed in space: large satellites, “cube sats”, rovers and space ships, material and crews for the International Space Station ISS as well as other space projects.
ARIANE - A EUROPEAN SUCCESS STORY
MT Aerospace has been a supplier of components from the outset
For decades now, space transportation in Europe has primarily gone by a single name: “Ariane”. While there are other European launchers, Ariane is the most powerful. MT Aerospace has been involved in Ariane ever since the earliest days of the series back in 1979. These days, MT Aerospace is part of OHB SE. As a result, OHB’s share in the Ariane program has grown: Since 2011, Ariane 5 has also been transporting the Galileo satellites that are, in turn, assembled by OHB System AG.
OHB is involved in the assembly of the transporter itself and typically also in the payloads that it carries.
The Ariane launch vehicle was developed in the Cold War with the aim of conducting space transportation independently of the United States and the Soviet Union. Between the maiden flight in 1979 and the end of 2017, the Ariane program achieved a reliability rate of 90 percent. With a share of around 10 percent in the components, OHB is the largest German supplier, delivering booster cases and tank domes for the central and upper stage of the space transfer vehicle. The Ariane 5 ES ATV version carries ESA’s 19-ton ESA ATV-4, which is responsible for sending supplies to the ISS.
Ariane 6: A European replacement for the Soyuz launcher
Ariane 6 is to embark on its first qualification flight in 2020. In Bremen, employees at OHB subsidiary MT Aerospace are welding the upper stage tanks for Ariane 6, using new Industry 4.0 production processes, among other things (/de/magazin/ausruester- fuer-den-raumtransport/#c9252). One of the aims of the Ariane 6 program is to achieve an enormous reduction in launch costs per mission. The space transfer vehicle is to be 40 percent cheaper than its predecessor. With its modular structure, it can be fitted with two or four boosters depending on the size of the payload to be transported.
A further aspect demonstrating that Ariane 6 is a model for a New Space approach is that never before has a space agency like ESA transferred so much responsibility - and also risk - to private-sector companies. OHB not only holds development and definition responsibility for all the launcher’s metallic structures but has also been named a risk-sharing partner, meaning that it is liable for any risks that may occur. Consequently, OHB is assuming greater responsibility than ever before for the parts that it supplies. The transporter has a launch mass of either 500 tons or 900 tons, permitting a payload of 5.5 or 11 tons. An average of 12 starts per year are planned from 2023. A further decisive point helps to secure Europe’s independence in space travel: the launch pad at the ESA space center in Kourou will be available for Ariane 6 from 2020, allowing it to replace the Russian Soyuz launcher.
„Ariane 6 is cheaper, it will be replacing the Soyuz, can be deployed flexibly and can be re-ignited.“
This heightens Europe’s independence and opens up new possibilities for it in space: A European space transfer vehicle carrying European navigation satellites will be lifting off from a space center operated by the European Space Agency. OHB is involved in all three elements - partially also via its subsidiary OHB System AG. Incidentally, MT Aerospace Guyane is also operating the launch pads.
The Space Launch System and space ship “Orion”
OHB is also a supplier of components for manned space travel. MT Aerospace has been awarded a contract for the aluminum segments of the fuel tanks and the upper-stage dome components of the Space Launch System (SLS), NASA’s most powerful space transfer vehicle to date. This vehicle will be used for manned and unmanned missions, including to the moon and Mars. With a payload of 130 tons, the SLS is to carry a further project in which OHB is involved, namely the Orion spaceship. OHB Sweden was tasked with the assembly, integration and testing of the propulsion qualification model for the spaceship, successfully completing these activities in the first quarter of 2017. A preliminary manned flight of the Orion is planned for August 2023. The space ship will be transferred to space on board the SLS and is to carry a crew of four. The mission objective is to orbit the moon for a period of 8-21 days. Here as well, OHB is participating in a project that will leave decisive marks on space technology for many decades to come.
ENERGY! HOW SPACE TRANSFER VEHICLES ESCAPE THE PULL OF GRAVITATION
The recoil principle as a basis
The successful launch of a firework rocket gives the person lighting the fuse a sense of power, while everyone around him is in awe of the spectacle. The structure of a firework rocket is not really any different from that of a large launcher, comprising as it does the launch pad (empty bottle), a rocket filled with propellant and stabilizers (black powder and a wooden stick) as well as the payload (the pyrotechnical effects).
The acoustic energy given off by the launch can be felt as a tremble in the ground even at a distance of several kilometers.
These launches are louder than 140 decibels – far in excess of even the loudest rock concert. An Ariane 5 has a beam power of 30 million horse power.
The saying “it’s not rocket science” is frequently used to designate simple processes. Yet, the principle underlying a rocket is indeed pretty straight forward: The fastest possible ejection of the support mass at one end generates a driving force (“thrust”) in the opposite direction.
Due to this recoil principle, rockets function both in the earth’s atmosphere and in the vacuum of space. The combustion of the propellant produces a very energy-rich exhaust, which exits at high pressure through one or more nozzles and thus generates thrust.
This simple recoil principle allows an Ariane 5 ES ATV to transport a payload weighing 21 tons to a low orbit around the earth. In fact, the SpaceX “Falcon Heavy” can carry more than 60 tons. However, NASA holds the record: The “Saturn V” was able to lift a payload of more than 133 tons into space, the most prominent example being Apollo 11 on its journey to the moon.
A lot of hot air – the role played by propellant in space transfer vehicles
After the launch vehicle lifts off from the pad, it increasingly gains velocity and speed as the propellant is burned. Two aspects converge here: during the launch phase, several tons of propellant are consumed per second. This means that the vehicle’s weight constantly drops, as a result of which the largely unchanged thrust must accelerate less and less mass. Consequently, the launcher increasingly picks up speed on its voyage into space as the thrust remains the same while the mass simultaneously lessens. Ultimately, the same amount of thrust transports an almost empty and, thus, substantially lighter vehicle compared with the immediate post-launch phase.
However, the vehicle faces an obstacle, namely air resistance. The friction caused by the molecules in the earth's atmosphere at a speed many times that of sound heats the front components enormously, while at the other end the combusted propellant generates temperatures of several thousand degrees. For this reason, the materials used in rocket engineering must be extremely resilient, capable of withstanding not just heat. Liquid fuel is usually made up of extremely refrigerated substances, known as “cyrogenic gases”. The cryogenic tank systems supplied by OHB must be sufficiently insulated to keep the liquids at a temperature of as low as -253° C, while simultaneously being highly resistant to pressure.
This means that system competence plays a crucial role when it comes to engineering space transfer vehicles. The components must be tested, conditions simulated and sources of errors taken into consideration. This calls for a holistic approach throughout the entire process. It also means factoring in dynamics outside the individual engineer’s field of expertise. Although he or she does not have to be able to solve such problems, it is important always to be aware of them. To give an example, the material of the Ariane 5 is so thin that it would collapse under its own weight if the vehicle were to be placed in an upright position without the tank first being filled. It is only after the tank has been filled that the main stage of the transfer vehicle becomes stable. This makes it possible to use very thin walls. At the same time, it means that the propellant performs a function for which it was not designed, namely to provide static support. Only an engineer who sees the “big picture” is capable of coming up with such an idea.
Uncle Phaeton and his niece – popular namesakes
In Greek mythology Helios, the sun god, steered his chariot across the sky. His son Phaeton gained notoriety, sustaining an accident with his father’s chariot. Despite this great mishap, several technological innovations bear his name. Phaeton’s niece also held a position in the Pantheon of gods: She is “Ariadne”, the goddess of fertility (Greek for “Ariane”).
Where does space begin?
Depending on the luminary, there is a different answer to this question. The frontier is defined by the transition of the celestial body´s atmosphere to the high vacuum of space. For luminaries with no atmosphere, space begins directly on their surface. For earth, a commonly accepted definition defines the beginning of space at a height of 100 kilometres (Kaman line). Objects flying higher than 100 kilometres have officially crossed the border to space.The reason: Objects are no longer held on their orbit by speed but by centrifugal forces - due to the very thin air.
Do launchers need to be hot when they lift off?
It is striking that rocket launch sites are mostly situated on the southern hemisphere. But why does the European ESA start their billion dollar space projects in South America? Why does the Italian Space Agency (ASI) use the space launch site in Kenia? The reason are two site-related factors: Firstly, earth´s torque is strongest at the equator. Rockets use of this torque when they start eastwards with earth´s rotation “in their back“. The closer a launching spot is situated towards the equator, the more fuel can be saved. In Kourou, rockets get an additional boost of 460 metres per second by being near the equator. Secondly, rockets need a launch place a few hundred kilometres away from any settlements.This is because any rocket will lose parts that fall down to earth – even if launched properly.
THE MATERIAL OF THE FUTURE FOR SPACE TRANSPORTATION
Paper and wood is all you need for a fire-work rocket. The materials used to engineer a launch vehicle such as the Ariane 5 are rather more demanding. In the 20th century the main materials were stainless steel and particularly also aluminum alloys and titanium. In the last few years, they have been joined by carbon-fiber reinforced plastics (CRRP), lithium and ceramics. MT Aerospace has already used the new material for the Ariane 5 for demonstration purposes. However, the prefabricated booster cases are still being made from steel. Among other things, it is engineering, building and delivering CFRP booster cases for Ariane 6. “Fiber ceramic composites”, which are patented under the name “Keraman”, are being used for components which must be particularly low-weight or extremely temperature-resistant (or both).
„Successful testing of the new kind of CFRP booster casings marks an important step in the development of the Ariane 6 launch vehicle.“
When a launch vehicle is designed, it is necessary to find a viable compromise between many parameters. For one thing, the components need to be as light as possible. Until such time as we are able to build and launch rockets in space, space transfer vehicles must be laboriously pushed out of the earth’s atmosphere. The less the launcher weighs without propellant and payload, the heavier it is possible for its cargo, e.g. a (weather) satellite. All employees involved are thus expected to be able to think in systemic terms. Materials must work together under the toughest conditions and without exception. Thinking in terms of individual parts or isolated activities is not the right course of action.
One of the prime imperatives for space pioneers is weight reduction.
By the same token, the space transfer vehicles must be stable enough to withstand the incredible forces arising during the launch phase. The structure of the vehicle must be able to withstand enormous weights during all phases of the mission. It faces enormous air resistance in the atmosphere while traveling several times the speed of sound. When the jets are ignited at launch, the material is exposed to massive acceleration forces from the very first second. Many rockets have exploded on the launch pad due to the failure of one part of the structure. The materials used also play a crucial role in this respect.
ACCURATE TO A TENTH OF A MILLIMETER – STATE-OF-THE-ART PRODUCTION AT OHB
Processing material at the microscopic level.
To give an idea of the precision required in engineering space transfer systems: When a pigeon leaves droppings on the roof of a 20-floor building, no-one would consider this to pose a risk to the structure of the building. Yet, the difference in height caused by the pigeon leaving its droppings on the building exceeds the maximum permitted tolerance in the construction of space transfer vehicles by a factor of more than 20. Incidentally, the tank systems for satellites for the Eurostar and Alphabus platforms as well as the water tanks for Boeing and Airbus aircraft are subject to the same stringent requirements. A launch vehicle is made up of thousands of components of many different sizes and performing many different functions.
Many of these components – such as the thermal protection subsystems – can now be produced using near net-shape processes. These processes entail only a very small number of steps. The manufactured component must be revised to only a very minor extent. This is important as the fewer the steps required the less likely is the risk of flaws of only a few tenths of a millimeter occurring. The near net shape process aims to create a component which is “perfect” from the outset without the need for any interim steps.
MES and FSW – how OHB is building the space transfer vehicle of the future
OHB and its subsidiaries are working in a state-of-the-art production environment using the possibilities afforded by “Industry 4.0”. This means an inseparably close link between production equipment and IT and communications systems going far beyond mere computer-based control of the machinery. Rather, the production process is completely networked and reports automatically generated, while algorithms link data intelligently at the right place. One aspect of this new infrastructure at MT Aerospace is the “manufacturing execution system” (MES). This system digitally maps the complete production of the product. Digitization of industrial processes permits swifter access to data and statistics.
The leap into Industry 4.0 era triples the productivity of space transfer vehicles in many areas.
The world’s most expensive stations – more than high-tech scaffolding
Space transfer vehicles need to reach their target orbit with the greatest possible precision. As far as possible, subsequent adjustments and corrections to the trajectory should be avoided. This is why the launch pad systems at the space center play a decisive role on the launch day. The launch pad for the Ariane series is located in French-Guyana. Whereas Ariane 5 uses the ELA-3 launch pad, a new launch pad is already being designed for Ariane 6. The large mechanical arms fitted to the launch pad play a crucial role as they help to guide the launcher into the atmosphere. The launcher is positioned with great precision and supplied with power up to shortly before launch.
„The mechanical systems fitted to the ELA-4 launch pad account for a significant part of the entire ground infrastructure for Ariane 6.“
MT Aerospace Guyane S.A.S. and MT Mechantronics GmbH, both subsidiaries of MT Aerospace AG, are responsible for planning, delivering and commissioning the mechanical systems. This is also to be the case with Ariane 6.
„There will be a number of changes in Kourou. This is related to the fact that with the transition [...] to Ariane 6 the number of service providers will drop to fewer than half a dozen. At MT Aerospace our goal is obviously to remain within this handful of operators.“