An unmanned Russian space capsule returned to Earth on Monday after six weeks in orbit for microgravity research, but officials said five geckos flown for space sex experiments perished on the journey.

The Foton M4 landing craft after touchdown Monday in the Orenburg region of southern Russia. Credit: Roscosmos
 
The Foton M4 spacecraft's pressurized return capsule, derived from the Vostok capsule flown by Yuri Gagarin on the first human spaceflight in 1961, re-entered the atmosphere and parachuted to a landing in the Orenburg region of southern Russia. Landing occurred at 0918 GMT (5:18 a.m. EDT) Monday, according to a statement from Roscosmos, the Russian Federal Space Agency.

Recovery teams reached the capsule, opened the hatch to access its interior, and began extracting research specimens and other gear.

Experts are assessing when and why the geckos died, Roscosmos officials said.

Scientists sent up the geckos to keep track of their sexual habits in space, research that officials say could yield information on how reproductive behavior might be altered during long-duration space missions.

Officials reported no other problems with the mission's experiments, which included 1,900 pounds of specimens and support hardware inside the Foton M4 spacecraft.

A colony of fruit flies weathered the mission well, according to Roscosmos, and successfully developed and bred in space.

Scientists also planned to study dried seeds and silkworm eggs inside the Foton space capsule to determine their response to cosmic radiation, and the satellite carries several experiments for research into microbes.

A joint Russian-German experiment inside the capsule is designed to measure the growth of semiconductor crystals in microgravity, an investigation scientists hope will lead to advancements in solar cells, light emitting diodes, transistors and other applications in the electronics industry.

"The goal is to produce crystals with the highest possible quality," said a statement by DLR, the German space agency.

Recovery technicians swarm the Foton M4 capsule after its landing Monday. Credit: Roscosmos
 
Three types of materials were to be heated up inside a Russian-made furnace housed inside the Foton M4 spacecraft. Once melted, the samples will crystallize as scientists study the influence of magnetic fields and vibrations on their growth.

Preflight plans called for the samples be divided among Russian and German scientists at the end of the mission.

Once technicians retrieve the experiments from the spacecraft, the equipment will be handed over to researchers for analyses in laboratories.

The capsule launched July 18 on a Soyuz rocket from the Baikonur Cosmodrome in Kazakhstan, but the mission ran into problems hours after liftoff. The craft stopped responding to commands from ground controllers and missed a rocket burn to raise its orbit to the planned 575-kilometer (357-mile) altitude.

Roscosmos announced a week later that engineers restored communications with the capsule, but the satellite never boosted its orbit.

Officials shortened the mission from its planned two-month duration to about 44 days.

The mission is the 16th flight of a recoverable Foton spacecraft since 1985.

Engineers introduced several upgrades on the Foton M4 mission to extend the duration of the flight, including solar panels to generate electricity and a new propulsion module to adjust its orbit.

Follow Stephen Clark on Twitter: @StephenClark1.