As the Expedition 40 crew members head into their final weekend together aboard the International Space Station, the six astronauts and cosmonauts spent Friday preparing for the arrival of a cargo craft and Wednesday's departure of three crewmates after nearly six months in space.

Flight Engineers Alexander Skvortsov and Oleg Artemyev got an early start on the day, waking up a half hour before the crew's usual 2 a.m. EDT reveille to conduct a test of the Soyuz TMA-12M spacecraft's motion control system.

Soyuz Commander Skvortsov, Artemyev and Expedition 40 Commander Steve Swanson will undock their Soyuz from the Poisk module on the space-facing side of the station on Wednesday, Sept. 10 at 7:02 p.m. for a parachute-assisted landing on the steppe of Kazakhstan a little less than 3 0.5-hours later. These three crew members have been aboard the station since March 27.

View NASA TV schedule of Expedition 40 departure events.

Following the crew's daily planning conference with the flight control teams around the world, Skvortsov and Artemyev spent the remainder of the morning conducting Lower Body Negative Pressure training. The two cosmonauts took turns donning a special outfit that simulates the effects of gravity by drawing fluids to the lower half of the body.

In addition to conditioning cosmonauts for the return home, this device provides Russian researchers with data to predict how the cosmonauts will react to the full force of Earth's gravity at the end of their mission.

Swanson and Flight Engineers Reid Wiseman, Alexander Gerst and Max Suraev all began the day with medical specimen collections. Throughout their mission, crew members provide saliva and blood samples for various experiments that track the effects of long-duration spaceflight on the human body.

After Swanson stored his blood sample in the Minus Eighty-degree Laboratory Freezer for ISS, or MELFI, for further study, he observed that the doors on the NanoRacks CubeSat deployer mechanism were open. That mechanism, which is currently attached to the end of the Japanese robotic arm on the exterior of the Kibo module, is designed to eject CubeSats into orbit.

Flight controllers determined that two CubeSats had been inadvertently deployed. No crew members or ground controllers saw the deployment, and no views of the deployment were found on the video footage recorded by the station's cameras.

The deployment appears to have occurred sometime overnight or possibly hours after Japanese flight controllers "jiggled" the robotic arm in an effort to get the doors to open. The deployer mechanism has been out on the arm since late last month when previous efforts to deploy the CubeSats were unsuccessful. Flight controllers are assessing whether to return that mechanism to the Kibo module's airlock or make another attempt to deploy the remaining CubeSats.

Wiseman and Gerst teamed up for some computer-based training as they get set to capture the SpaceX Dragon cargo vehicle with the 57-foot Canadarm2 robotic arm. The SpaceX-4 commercial resupply services mission is targeted to launch from the Cape Canaveral Air Force Station in Florida no earlier than Sept. 19, which would result in a rendezvous with the station on Sept. 20.

SpaceX-4 will deliver crew supplies and science cargo, including the ISS-RapidScat instrument, a replacement for NASA's QuikScat Earth satellite to monitor ocean winds for climate research, weather predictions, and hurricane monitoring.

Meanwhile, Suraev collected surface samples in the Russian segment of the station for research into the biodegradation of the surfaces in materials used in station construction. Russian researchers are looking into the kinds of microorganisms that may be colonizing those surfaces to determine the best methods for preventing corrosion and damage.

After a break for lunch, Swanson, Skvortsov and Artemyev spent the afternoon conducting a Soyuz descent drill to review the operations for Wednesday's undocking and landing. Their departure will signal the end of Expedition 40 and the start of Expedition 41, under the command of Suraev.

Suraev, Wiseman and Gerst, who will remain aboard the station until November, got together to review their roles and responsibilities in the event of an emergency aboard the complex.

Afterward, Wiseman briefly checked in on the Binary Colloidal Alloy Test, or BCAT, to download images and set a timer for this experiment that studies colloids - mixtures of small particles distributed throughout a liquid.

Wiseman then inspected components of the Combustion Integrated Rack and removed the alignment guides to prepare the rack for more ground-commanded research into the behavior of ignited fuels in microgravity.

Wiseman also retrieved a pair of acoustic dosimeters and downloaded their recorded data so the ground team can keep track of the noise levels the crew is exposed to throughout the day.

Gerst spent some time removing and replacing a recycle tank for the Environmental Control and Life Support System's Water Recovery System.

Suraev meanwhile conducted routine maintenance on the life-support system in the Zvezda service module. He rounded out the day with the Uragan Earth-observation experiment, which seeks to document and predict the development of natural and man-made disasters on Earth.

Over the weekend, the station's six crew members will take care of weekly housekeeping chores as they wipe down surfaces and vacuum dust. They also will continue their daily 2 0.5-hour workouts to stay fit and to prevent the loss of muscle mass and bone density that occurs in microgravity.

Back on Earth, the three Expedition 41 flight engineers who will return the station's crew to its full six-person complement after the departure of Swanson, Skvortsov and Artemyev have wrapped up their qualification exams at the Gagarin Cosmonaut Training Center in Star City, Russia.

NASA astronaut Butch Wilmore and Russian cosmonauts Alexander Samokutyaev and Elena Serova are scheduled to launch aboard the Soyuz TMA-14M spacecraft from the Baikonur Cosmodrome in Kazakhstan on Sept. 25. The trio participated in a news conference Friday morning before making the traditional trip into Moscow to visit Red Square and lay flowers at the memorials of Russian space icons interred there.