The Challenge of Meeting Microgravity Requirements

For my main job responsibilities, NASA looks at me to be the expert regarding the requirements the scientists need to do their research. I'm part manager, part engineer, part scientist and part diplomat. The research community (the principal investigators/scientists whose experiments will be on the ISS) and the ISS program are looking to me to be a problem solver. Many times, I am a liaison between the two. The ISS program promises the research community a certain microgravity environment. So, I must be knowledgeable in several areas to make sure all requirements are met -- like structural dynamics, space physics, and how the different managerial processes work, just to name a few.

Vibrations (or what we call accelerations) are all around on the ISS, and are also called G-jitters. G-jitters can affect what's in the surrounding area, like payloads/experiments. We must determine how much vibration is allowable and how to keep it at that acceptable level. Sometimes things must be redesigned to meet the requirements, and others have to be modified with other pieces. Case in point: the exercise bicycles make a lot of vibrations, which cannot be helped, so vibration isolation systems (like a shock absorber) had to be designed, built and fitted to the exercise equipment to lower the vibrations emitted.

Some of the payload racks are equipped with their own shock absorbers, called ARIS, or Active Rack Isolation System. There are computer sensors on the rack that help measure degrees of movement. The racks are attached to the station structure by eight push rods that are connected to actuators so they can move back and forth. When the computer senses movement, it tells the push rods to move in the opposite direction, lessening the vibration, kind of like a push me/pull me routine. This allows the racks to move in "six degrees of freedom" -- moving along X, Y and Z and rotating along X, Y and Z. This is also referred to as 6DOF, for short. These racks are used for payloads that require really low microgravity levels.

I also spend a lot of time working on payload microgravity requirements. This involves structural dynamics -- how the vibration of one rack affects the others around it. In the end, an allocation scheme must be developed covering the allowable vibration limits for all the racks and each attached payload. The rack developer will determine the allowable requirements for the individual experiments housed in them. Of course, writing these requirements is a whole process on its own. It's almost like lawyer language -- for example, the word "shall" means that's the requirement, though "must" and "will" are used sometimes, too.

Once the structural dynamics and the requirements are figured out, then we must make sure we are actually meeting the needs of the research community to do their research. The three of these together is when the diplomat sometimes comes into play. NASA thrives on teamwork. That means it's not always easy when you are working with several different groups of people in different locations.

I am also working with the ARIS, which we talked about earlier. Besides the eight push rods holding the racks in, each rack also has what is called an umbilical (which is a line of connectors) to attach to the power sources of the ISS - power, communications, fluid, gas, or whatever is necessary. Though we have tested these racks on the ground in a simulated environment, we won't really know how they work until we have tested them on orbit on the ISS. The first rack of this kind will go up on ISS Flight 6A. We will perform a test we call the ARIS ICE, which is the ARIS ISS Characterization Experiment. During this experiment, we will test the rack's movement over the six degrees of freedom to see if the ARIS properly isolates the payloads.

I am also a part of the Microgravity Analysis and Integration Team (MGAIT), which is a global team from all the member space agencies that predicts microgravity environments for the ISS. We use computer modeling to do this. This is a big help and can alert us to areas that might have problems later.

I am hoping to chat with you all in January, so look for me on the schedule soon.