The final launch of the space shuttle Endeavor hit yet another snag , forcing eager scientists to wait up to another week before their experiments hitch a ride to space.

The NASA space shuttle was first scheduled for lift-off last Friday afternoon in its historic final flight, but now officials are expecting the shuttle to launch no earlier than May 16, marking the second delay since its original April 29 target date.

The set-back also delays the $2bn Alpha Magnetic Spectrometer particle detector reaching the International Space Station.

The device is designed to give scientists their first detailed study of the electrically charged particles streaming through the universe.

It could also reshape modern understandings of the universe in a similar way that the Hubble Space Telescope pioneered new frontiers in astronomy.

The pictures painted by AMS, which was assembled at the CERN physics research center near Geneva, could bring to light the universe's so-called dark matter -- material that is so far unaccounted for but necessary to explain what is observable.

Several other, lower profile experiments are also slated to take the ride to space.

The nonprofit Planetary Society is putting six types of microbes inside sealed tubes that will fly on Endeavour's middeck. The various microbes will be studied to see how they are able to adapt to the extreme environments of outer-space.

NASA has made room for several experiments set up by students.

Technicians this weekend will continue to repair and retest the electrical system to determine what caused a circuit to short out.

NASA repair crews have already replaced a distribution box that shorted out a circuit supplying power to heaters for the orbiter's hydraulics system.

Endeavour is the second-to-last shuttle mission for the 30-year US program. Atlantis will mark the end to the program in in June and July.

NASA is winding down its space shuttle operations this summer as it tries to save money, which will leave American and European astronauts with only Russian rockets as options for going into space.