Astronauts plan final spacewalk of Endeavour mission

Astronaut Christopher Cassidy is seen during the Endeavour crew's fourth space walk. Photo Courtesy: AFP.

Two astronauts will venture into open space again on Monday on a fifth and final spacewalk of the shuttle Endeavour's mission to complete the International Space Station.

Chris Cassidy and Tom Marshburn spent the final hours leading up to their task preparing their spacesuits and tools and reviewing procedures, National Aeronautics and Space Administration (NASA) officials said.

The final spacewalk is expected to run about six and a half hours.

During their fourth walk on Friday, Marshburn and Cassidy installed new batteries on one of the oldest of the four solar arrays that power the space station 350 kilometers (215 miles) above Earth.

The six newly fitted batteries "function as expected," the US space agency said, noting that the old batteries were stored on a cargo carrier that will be placed in Endeavour's cargo barrier later in the day.

On Wednesday, NASA had ordered spacewalking astronauts back into the space station 30 minutes early after a spacesuit was found to be working improperly.

Higher than normal carbon dioxide levels were found in Cassidy's spacesuit due to a problem with its lithium hydroxide canister, the US space agency said, adding he had not been in any danger.

The carbon dioxide removal unit continued to operate in manual mode Sunday.

Cassidy and his partner Dave Wolf managed to replace only two of the six batteries, so part of Friday's outing was to install the remaining four.

Each ISS battery measures 40 inches by 36 inches by 18 inches (101 centimeters by 90 centimeters by 45 centimeters), weighs 375 pounds (170 kilos) and is designed to last 6.5 years.

Endeavour took off from Cape Canaveral, Florida on July 15 for a 16-day mission with a crew of six Americans and one Canadian to help complete construction of the ISS.

On the second Endeavour spacewalk July 19, the astronauts moved equipment from Endeavour onto the ISS and repaired a malfunctioning toilet on the orbiting station.

During a first spacewalk July 18, astronauts completed construction of the Japanese Kibo science lab during an outing that lasted five and a half hours.

The ISS should be completed in 2010, which also is the target date for the retirement of the US fleet of three space shuttles.

Endeavour is expected to land back on Earth on July 31. The launch of the next shuttle, Discovery, to the ISS is planned for August 18 at 4:25 am (0825 GMT).

Meanwhile, in yet another deft maneuver on Sunday, the space shuttle robotic arm grabbed the Japanese Exposed Section cargo carrier from the space station robotic arm, NASA reported.

Endeavour Commander Mark Polansky and Mission Specialist Julie Payette then used the shuttle arm to place the cargo carrier back into the shuttle payload bay.

The cargo carrier was launched with two science experiments and a communication system that were transferred to the Kibo Exposed Facility earlier in the mission

Europe's Mars rover slips to 2018

NEW EXOMARS MISSION CONCEPT Now likely to leave Earth in 2018; primary aim is to search for life Current proposal is to use a US Atlas rocket to launch ExoMars US also to look after the rover's entry, descent and landing Hardware likely to be the same as for US 2013 rover, Curiosity ExoMars would be targeted at key methane hotspots on the planet It will have the capacity to drill 2m into the Martian ground Esa states still have to sign off the plan and a budget Europe's flagship robotic rover mission to Mars now looks certain to leave Earth in 2018, two years later than recently proposed, the BBC understands. The ExoMars vehicle is intended to search the Red Planet for signs of past or present life. The delay is the third for the mission originally planned to launch in 2011. While the switch will disappoint many people, officials say the change will open up a greatly expanded programme of exploration at the Red Planet. The European Space Agency (Esa) will now join forces at Mars with the US space agency (Nasa). The two organisations believe they can achieve far more by combining their expertise and budgets. The basis for this approach was agreed at bilateral discussions in Plymouth, UK, last month. Since then, scientists and engineers on both sides of the Atlantic have been working up the basic architecture for a series of missions in 2016, 2018 and 2020 (launch opportunities to Mars come up roughly every two years). Mass issues The plan, or baseline, for this programme - including its implications for ExoMars - is now starting to emerge. It would see the agencies launch a European orbiter to the Red Planet in 2016. Its main aim would be to track down the sources of methane recently detected at Mars. The presence of methane is intriguing because its likely origin is either present-day life or geological activity. Confirmation of either would be a major discovery. Europe's Mars Express orbiter made the first methane detection from orbit The American Atlas rocket used for this mission would also have capacity to carry sufficient mass to put some sort of static lander on the surface. The European orbiter would act as its data relay to Earth. The 2018 launch opportunity would be taken by ExoMars, again launching on a US Atlas rocket. This mission window is actually one of the most favourable in terms of planetary alignment for many years, and that makes it possible to send a very heavy surface mission. The proposal on the table currently is that ExoMars should be joined by a slightly smaller rover in the class of the US Spirit and Opportunity vehicles that are on the surface today. ExoMars and its smaller cousin could be targeted at the Methane sources identified by the 2016 orbiter. The 2020 launch opportunity would probably then be taken by a network of instrumented static landers. Technological goals Both Esa and Nasa will have tight finances going forward and will have to constrain their ambitions accordingly. Heavy rovers like Curiosity can be landed with a skycrane European ministers pledged sufficient monies at their major triennial gathering last year to take the budget for ExoMars to 850m euros. Esa officials believe the proposals they are formulating with Nasa can broadly match the cost requirements and the technological goals of both parties. For Europe, the primary goals are to land, to rove and to drill on Mars. However, under the plan outlined above, these objectives could not all be achieved during the ExoMars opportunity. In 2018, it is likely the entry, descent and landing (EDL) of Europe's rover would be handled by the Americans, using the "skycrane" system they have designed for their big 2013 rover known as Curiosity. If Europe really does want to do EDL, the option is open for it to take responsibility for the 2016 surface package of instruments. Esa's director-general, Jean-Jacques Dordain, has promised to report to his member states in the autumn with firm proposals for a re-scoped Mars exploration programme. Industrial jigsaw Two months of intensive discussions will now take place in those member states, and in European industry which will be responsible for building the spacecraft systems. If financial contributions to the mission from Esa member states were to change substantially, the space agency might have to re-visit the balance of industrial work allocated to different countries through the process of "juste retour". Esa has rules that govern the distribution of industrial contracts Esa's rules of juste retour ensure the work which returns to a member state reflects the financial contribution it makes to a programme. One senior European space executive called at the recent Paris air show for the whole ExoMars industrial programme to be re-opened to competition. The ExoMars rover was originally conceived as a small technology demonstration mission. It was approved in 2008 and should have been launched in 2011. Then, as ambitions grew and the design was beefed up, the launch was put back. At first, it was shifted to 2013. Last year, a decision was taken to move it even further back, to 2016, because of budget concerns