A trio of Space Station experiments this week are zeroing in on the sources of vibrations that could disturb future delicate microgravity experiments.

Three Active Rack Isolation System - ISS Characterization Experiment (ARIS-ISS) hammer tests were conducted last Friday with realtime video downlink during the first two tests. Flight Engineer Carl Walz set up the camera to give excellent close-up views of the locations where he tapped with a small hammer. The video provided the science team on the ground with new insight into their experiment results to date. Scientists observed on the video that Walz occasionally bumped into the data umbilical between the rack and the Station structure, which corresponded to occasional disturbances observed in the data of previous hammer tests. That knowledge will be useful in analyzing Friday's hammer tests. ARIS was developed by The Boeing Company. The ARIS-ICE experiment was developed by NASA's Johnson Space Center.

On Monday, the crew helped the Space Acceleration Measurement System (SAMS) team by performing a microgravity disturbance test. To help track down some unexplained vibrations registered by the SAMS sensors, the crew practiced entering and exiting their Temporary Sleep Station restraints four times while the ground team monitored.

The Microgravity Acceleration Measurement System (MAMS) this week is downlinking acceleration data from one of its low frequency sensors. This allows the science team to archive and monitor the Station's low frequency acceleration environment. The main influence at these frequencies is aerodynamic drag caused by altitude and attitude and mass distribution. The higher frequency sensor is currently disabled. MAMS will be recording during the upcoming Shuttle docking and Station robot arm operations in preparation for a planned spacewalk. Both SAMS and MAMS are managed by NASA's Glenn Research Center in Cleveland, Oh.

Gas, nutrient and condensate samples continue to be taken from the Advanced Astroculture experiment. Scientists have been changing the growth conditions inside the plant chamber to encourage the plants to flower and produce seeds. The final sampling of the plants themselves will occur today, with the sample placed in a fixative and then into the Biotechnology Refrigerator (BTR).

The crew is scheduled to deactivate the crystallization cylinders in the Protein Crystal Growth Single Thermal Enclosure System (PCG-STES) Unit 10 on Thursday. The growth cylinders in the companion unit, STES 7, have already been deactivated.

Locations scheduled to be photographed this week for the Crew Earth Observations research program include: land clearing and wetlands activities in the Irrawady River Delta, Bombay, India, Congo-Zimbabwe vegetation burning, harvesting and vegetation clearing in the Parana River area in South America, and lake levels in the Rukwa Transforma area of Tanzania.

During upcoming joint Shuttle/Station operations, when the Station solar arrays are turned to accommodate Shuttle docking, the Payload Operations Center will turn off two experiment racks to conserve power. EXPRESS Rack 1 will be powered down on Sunday and powered up prior to the Shuttle undocking when the Shuttle undocks. EXPRESS Rack 2 will be powered down Thursday and powered up on April 12.

When Space Shuttle Atlantis launches Thursday on mission STS-110, it will carry the final five experiments planned for Expedition Four aboard the Space Station. All five are scheduled to return on the STS-111 Shuttle mission planned for late May.

The PESTO (Photosynthesis Experiment and System Testing and Operation) experiment will be traveling inside the Biomass Production System - an engineering development unit for a future Station plant habitat. PESTO will study and determine whether plants will photosynthesize and transpire at the same rates as on Earth.

The Protein Crystal Growth-Enhanced Gaseous Nitrogen (PCG-EGN) Dewar experiment, which has flown to the Station on three earlier Shuttle missions, is a passive experiment containing about 500 plastic tubes with specific crystal growth experiments with potential applications in medicine and agriculture. Students from California, Illinois, Indiana, Michigan, Ohio and West Virginia helped prepare some 290 samples as part of their classroom studies.

Also going up is the Commercial Generic Bioprocessing Apparatus (CGBA). It contains experiments to characterize the effects of long-term exposure to weightlessness on the process of fermentation, used in the production of antibiotics. Antibiotic compounds are naturally produced by microorganisms and can be used to fight a variety of infections. This experiment will examine bacterial growth processes used to produce actinomycin D. This class of antibiotics is used to treat certain types of cancer.

The Commercial Protein Crystal Growth (CPCG) experiment will be making its second trip to ISS. The middeck locker-sized payload can carry up to 1,000 different samples of various proteins and other compounds, with the goal of growing samples of greater quality. These higher quality - or better-organized - crystals, are important to researchers who use techniques such as X-ray crystallography, to determine the molecular structures of the various compounds.

Atlantis will also carry the first samples for the Zeolite Crystal Growth (ZCG) experiment. The furnace unit launched last December on STS 108, and has been checked out onboard the Station. The samples will be loaded into the furnace about one week after the Shuttle undocks and will grow for about two weeks. This experiment will be the first operational use of the Active Rack Isolation System in EXPRESS Rack 2.