He spent over three hours underwater with the model of the robotic arm, which was built in 1998, but is nevertheless in perfect condition.

Impressive

The impressive robotic arm is over 11 metres in length and weighs 630 kg. Once ERA reaches the International Space Station (ISS), the Russian Multipurpose Laboratory Module (MLM) will be its home base. With the help of seven joints, a variety of tools and its electronics, the astronaut's aid can move insect-like around the Russian ISS segments and will be used for a variety of tasks.

ESA's ERA project manager Philippe Schoonejans said: "ERA can work with the Russian airlock, which means that astronauts will no longer have to venture outside the Space Station to install certain pieces of hardware. Using video cameras, the arm can perform inspections of the outside of the Station, it can move experiments and supplies and even serve as a crane for astronauts."

Kuipers tested the Weightless Environmental Test model of ERA, known as the 'WET model'. This model was built in 1998 by a consortium of companies led by Dutch Space, from the Netherlands. Originally ERA would have been launched on the Space Shuttle in 2001, but due to circumstances its launch has been delayed. Last summer it was decided that the robotic arm would be launched in November 2007 on board a Russian Proton rocket together with MLM.

There is work to be done before then though. Last week, in an underwater exercise lead by Kuipers, the WET model was dismantled and then reassembled. Together with Russian Dmitry Verba, Kuipers also checked the manual controls, which serve as a backup to the automated system.

According to the Dutch astronaut: "the exercise was heavy going, it took a lot of patience. We had to make lots of rotational movements during the manual control of the arm; not an easy task underwater."

The arm functioned well. Although Schoonejans concluded that there are some improvements to be made. Some one-handed operations had to be performed by Kuipers using two hands, or with the help of Verba, as the astronaut had no means of stabilising himself. One possible solution for this would be to use a mobile attachment mechanism. A set of spanners will also have to be modified, as they kept releasing during tightening of the bolts, wasting valuable time. Isolation material, which at times obstructed the video cameras, will also have to be better secured.

Perfection

For the coming year, the Russian company Energia, as well as the European partners who built ERA, will be working to perfect the robotic arm. From mid-2006, once new procedures are ready, future ISS expedition crews will train with ERA for the first time. They will become fully familiarised with ERA before its launch in 2007.