Where do spent missiles land

Space travel : Recycle for missiles

The rocket takes off into the sky with a lot of noise. It releases a satellite in space. It spins, re-ignites its engines, slows down, re-enters the earth's atmosphere, maneuvers, maintains its upright position and finally lands gently not far from the launch pad. To all this, the basses of the British band Muse are throbbing. "Uprising" - "Aufruhr" is the name of the programmatic song.

The animated promotional video of the recurring rocket is a vision of the future for the SpaceX company. All launch vehicles used today are disposable. They transport their cargo into space and break if they fall back to earth, burn up or fall into the sea. It's like flying from Berlin to London and then scrapping the brand new machine, a huge waste.

Elon Musk, founder and chief developer of the Californian rocket manufacturer SpaceX, wants to change that. The next generation of his “Falcon” rocket should not burn up after its work, it should instead be able to be used hundreds of times: safely, reliably and significantly cheaper than current rockets.

The South African, who made his billions by selling the Internet payment service PayPal, wants to use the new technology to turn space travel upside down. "If we can reuse rockets as efficiently as airplanes, that would reduce the cost of a flight into space by a factor of a hundred," says Musk. "That would be the long-awaited breakthrough to revolutionize access to space."

The fuel costs are only a tiny fraction

Anyone who wants to start with a conventional “Falcon 9” from SpaceX currently has to pay 56 million dollars (about 40 million euros) according to the official price list. Three quarters of this is accounted for by the first stage, which returned to Earth for the first time during the test in mid-April. The cost of fuel, on the other hand, is only about $ 0.2 million. Musk argues that if a rocket could be used a thousand times, the cost per launch would drop to $ 50,000. Even after adding up the fuel and maintenance costs, the flights would be many times cheaper than today's take-offs.

A successful test flight in April showed that SpaceX is technically on the right track. The video that is supposed to prove the progress is nowhere near as slick as the advertising animation. It is out of focus, it has dropouts. And yet it shows, at least in outline, a premiere in space travel. It gives an idea of ​​how a rocket stage developed by SpaceX crashes in a controlled manner over the Atlantic, then ignites its engines again, stirs up water and finally hits the stormy surface of the sea. "Our flight computers were still delivering data eight seconds after contact with the water," tweeted Musk after the test.

Outwardly, Musk's new rocket hardly differs from the company's current flagship, the "Falcon 9". The reusable variant also has two stages, can heave almost five tons into earth orbit, and flies with kerosene and liquid oxygen. Only the four fold-out landing legs made of carbon fibers, which nestle against the slim fuselage of the rocket when it takes off, bear witness to a special mission.

Small nozzles steer the rocket back to the launch site

It begins at an altitude of around 80 kilometers. The burned-out first stage, just separated from the rest of the rocket and traveling at six times the speed of sound, rotates 180 degrees and re-ignites three of its nine engines. The speed, originally 11,000 kilometers per hour, is decreasing rapidly. The cylinder inevitably crashes into the increasingly dense layers of the atmosphere, is further decelerated and stabilized by its control nozzles. Where ordinary rockets tumble and break, the reusable variant falls in a controlled manner towards the earth. Small nozzles guide them back to the starting point. The rocket unfolds its almost eight-meter-long landing legs, prances on the exhaust jet and finally touches down gently.

As early as this fall, a burnt-out rocket stage could fly back to its launch site from a height of 80,000 meters and initially ten times the speed of sound. The first used rocket could then take off next year.

It would be one of the greatest innovations in the history of rocket construction. Rockets have brought people to the moon and now routinely transport satellites into space and astronauts to the International Space Station (ISS). The underlying principle has hardly changed since the US researcher Robert Goddard catapulted the first liquid fuel-fired rocket at a height of 14 meters in March 1926. Regardless of whether it's Goddard's mini rocket or the 3000-ton Saturn V that flew to the moon in the 1960s: fuel is burned on board the rocket and ejected at great speed. Due to the mass that is thrown backwards, the rocket is accelerated forwards, similar to a balloon that is inflated and then released.

The heavier a missile, the more fuel it takes. But the additional fuel, which only burns gradually, increases the weight again. It is precisely this physical problem that troubles Elon Musk: To escape earthly gravity, so much energy (and therefore fuel) is required that with typical rockets only three percent of the total mass is left for the payload, e.g. for the satellite, the should be brought into space. In the case of reusable missiles, this reserve is consumed by the fuel for the return flight, the weight of the landing legs and stronger, heat-resistant structures.

SpaceX wants to compensate for this with particularly light and stable materials. Nevertheless, a reusable “Falcon 9” will be able to transport around 40 percent less payload than its one-way version. However, a lower payload means less income and thus less profit. "I'm not saying our success is guaranteed," says Elon Musk. "But we will definitely try."

Technically and economically not feasible, say critics

He is the only one. While one or the other start-up company tries to break new ground with airplane-like reusable transporters (see box), the long-established rocket builders do not believe in reuse: "We have studied such concepts for many years," says Stefano Bianchi, Head of rocket development at the European Space Agency Esa. "So far we have come to the conclusion that something like this is technically and economically not feasible."

Musk's calculation only works if he launches many, very many missiles. Only then, in view of the lower payload, the lower prices and the associated lower margins, can SpaceX gradually recoup the high development costs. For years, however, the market for commercial satellite launches has been hovering around 20 to 25 orders per year. Experts see little upside potential.

Musk thinks differently. He is thinking of launch costs of just 150 euros per kilogram (compared to the estimated 10,000 euros for the European “Ariane 5” rocket) - and of many interested parties for whom space was previously too expensive, but who, given such prices, suspect a business model.

New markets, new customers. Musk copied the idea from space tourism: the first vacationers in space, such as the US entrepreneur Dennis Tito, who spent seven days on the ISS in 2001, had to pay dearly for their flight opportunities. Tito is said to have spent around $ 20 million on his seat in the Russian "Soyuz" capsule, the spaceship that even professional astronauts use to fly into space. The space airline Virgin Galactic of the British billionaire Richard Branson, on the other hand, aims at a broader market and wants to help up to six passengers to make a short detour into space for an initial 200,000 dollars, provided that the project, which is well behind its own schedule, finally gets underway.

Musk relies less on tourists than on new satellite customers. Significantly cheaper starts could attract companies that want to offer Internet access from space, sell photos of the earth or seek cheap research in earth orbit and are deterred by the current costs.

The heat shield of the space shuttles proved to be extremely in need of maintenance

However, this presupposes that reusable missiles, such as airplanes, can take off again without losing much time. “However, we have to be able to guarantee the same reliability every time we start. That is only possible with a thorough overhaul or with additional safety reserves, ”warns Stefano Bianchi. The Esa engineer is thinking primarily of the American space shuttle: the space shuttle with its solid rocket was also considered reusable. Ultimately, however, it was so time-consuming to check the drive every time and to set it up again that disposable boosters would not have been much more expensive. In addition, the space shuttle, with its heat protection, which made it possible to re-enter the earth's atmosphere, was so complex that engineers spent most of their time on maintenance work. Instead of days, months passed between two shuttle launches.

SpaceX has even more ambitious plans. In the future, less than ten hours should elapse between the landing of a used rocket and the restart, according to Elon Musk. That would be almost as fast as with today's large-capacity jet, which has to be cleaned, refueled and reloaded after a successful landing, which can also take several hours.

How realistic all of this is will be seen when SpaceX can analyze the first stage returned from space in detail. "It works on paper," says Musk. “Now we have to prove that simulation and reality match.” You could also say: The time for promotional videos is over.

The company SpaceX manufactures the "Falcon" rocket series. The next generation should be able to land back on earth after their work is done. The hope: space travel could become cheaper this way.

Other companies are therefore pursuing completely different concepts. For example, they build missiles that travel part of the way on the back of an airplane.

The missile must have additional fuel and landing legs on board. This leaves even less space for the payload that is to be brought into space.

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