It wasn't easy to fix a date and the e-mail-exchange therefore dates back quite a while. "We just returned yesterday, tired and weighed down with luggage, from Zwezdny Gorodok, Russia's "Star City"," it said in an e-mail of 30th October 2003. Apparently, preliminary results would be ready in a week. The next message arrived mid-November, "Our analysis will take much longer than expected," and, at the end of January 2004, your correspondent was informed that he would have to be patient for another month. Finally, however, a meeting came off.

Technopark in the new industrial district known as Zurich-West, in the break room of the ETH space biology team (1) . Vlada Stamenkovic and Georg Keller manipulate a noisily functioning coffee machine. We sit at a small table in the middle of the room. "Yes, space. That's it," says Stamenkovic with a sigh. "Of course I could imagine being an astronaut." But before that one needs a specialist education. Stamenkovic from Zurich, with roots in Niederwangen, plumped for physics at ETH Zurich where he met Georg Keller. A stroke of luck. When two people have the same dream the road seems only half as long.

The initial stage of the work is reached in August 2001 and the first step into space can be taken. Together with two other students Vlada Stamenkovic and Georg Keller submit a proposal for an experiment on the mixing performance of liquids in low-gravity environment to the European Space Agency (ESA) and the project is accepted. Training begins for the so-called zero-G-flight, on a parabolic flight with an Airbus-A-300 (2) , where a low-gravity environment is simulated.

Baikonur: Preparing the cell cultures for the flight in a makeshift laboratory.

A further reward beckons: the chance to carry out an experiment in space. Once again Stamenkovic and Keller spend all their free time working on an experiment to send on board a Russian satellite that will spend two weeks in orbit. They are supported by the space biology group and technicians from the ETH Institute of High Energy Physics. The unmanned Foton rocket is launched on 15th October 2002 from the space station Plesetsk in northern Russia – and explodes just 29 seconds after lift-off. Debris from the rocket, which came down in one piece, hit the ground only 800 metres from where the two students were standing. "The students were deeply shocked and then disappointed that all their hard work had come to nothing," says Marianne Cogoli of the space biology group a few days later in an talk with "ETH Life" (3) .

But the two budding physicists get another chance. On 25th December 2002 – "The date sticks in my mind," – Georg Keller receives an e-mail from ESA inviting him to submit a new concept. Data is compiled at lightening speed, because the next planned flight could take place in March 2003.

Vlada Stamenkovic and Georg Keller (from left): The two ETH students are working with ESA on a project.

But plans are disrupted by the explosion, on 1st February 2001, of the Nasa shuttle "Columbia". National and international space agencies are devastated and suspend all flights for an unspecified period.

In the end, however, a new date is set. Though ESA now expects the physics' students to reconstruct their entire experiment. The reason for this is that the cell culture reactor will not, as previously planned, be sent into orbit in an unmanned spaceship but in the manned taxi flight 7S. For Stamenkovic and Keller this means that the incubator has to be reduced by a factor of four, to 500 grams, and made even safer – "safety and security had to be increased from 99 to 99.91 per cent," says Stamenkovic.

Time races by. Two weeks before the start the incubator is finished but the pig bone cells for the culture have not yet been isolated. "It was a hectic period," says Keller, looking back, "especially as we had to go to the Space Research and Technology Centre in Noordwijk, Netherlands time and again." Finally everything was ready. The samples are flown via Moscow to Baikonur. Here the nutrient fluid is changed under difficult conditions, the samples put into the incubator and handed over to the person in charge. Then, on 18th October at 09.38 hours the experiment is sent on its journey into space on board the Soyuz TMA-3, which reaches the International Space Station (ISS) two dates later. "First of all, the batteries had to be changed," says Stamenkovic. "The Spanish ESA astronaut Pedro Duque did that for us. The sojourn at the ISS lasted eight days. After a total of twelve trial days our experiment landed in the steppes of Khasachstan on 29th October 2003."

"Our first task was to immediately stop the growth of the cells. We did this by transferring the new cartilage cells to a transportable vessel filled with a proteinase inhibitor," explains Georg Keller. "We then returned to Switzerland, to the University of Berne." Under the guidance of Shawn Grogan from the university's Osteoarticular Research Group the cells that had developed in space were then examined together with two control groups of cells. On the one hand, they were examined under the microscope for histological and immune-histological information and, on the other, using a PCR reaction of gene expression. "We were able to determine that the cartilage cells that had grown in a low-gravity environment were smoother – more even than if they had developed on Earth," says Keller. "They produce considerably more type II collagen." The latter is responsible for the cohesion of the tissue and an indicator of the stability of the new cartilage. Nonetheless, the results have to be interpreted very carefully, as Stamenkovic and Keller take care to point out. "There are open questions. For example, why does our own cartilage continue to grow regularly despite gravity."

Everyday routine has returned for our two physics' students. Exams are looming and accompanying practical assignments have to be fulfilled. Because the capabilities they've acquired and the time and energy expended on their experiment don't count towards their studies at ETH. The results of the space experiment should appear in the near future in an internal ESA publication.