So what does this have to do with the Hubble Space Telescope?
Here's my story.
I was underwater the first time that I came into contact with the Hubble Space Telescope in the early 90's. As a NASA employee in Huntsville, Alabama, I was currently working as a Space Station Freedom Project Office employee for Marshall Space Flight Center (MSFC). However, all certified divers at MSFC NASA could register at the Neutral Buoyancy Tank to do volunteer work in the Tank. All of these volunteers underwent a rigorous underwater test in order to enter the MSFC Tank that involved donning and doffing scuba diving equipment at the bottom of a pool that contained 1.32 million gallons of clear water as well as maintaining an up-to-date certification in first-aid and cardiopulmonary resuscitation and passing a rigorous physical examination.
On that particular day, I was assigned to take pictures of the HST Goddard Space Flight Center simulation using an underwater movie camera (position usually denoted as "the swim camera"). After the test, the video could be used to review the happenings of the day. Procedures, that would later be followed by the astronauts in space, could be corrected and equipment redesigned in order to enhance extravehicular activity (EVA). During the test, engineers, technicians, and other personnel monitored subjects from a control room which contained several consoles with small monitors and headsets connected to the communications network. These facilities allowed the test director, test conductor, safety, and other personnel to view the test and give instructions to the suited subjects and divers, observer, safety, utility, and photography.
Thus water in the tank was used as the medium for neutral buoyancy to simulate weight-lessness encountered in space. Underwater, the HST equipment that was tested was actually a structural mockup, built for tank environment and specifications. The suited subjects (participants wearing special underwater pressurized space suits that were neutrally buoyant) were able to perform critical EVA functions in preparation for the First Servicing Mission by using this mockup.
Remember the saying, "practice makes perfect". NASA Goddard Space Flight Center (in Greenbelt, Maryland where I now currently work in Operations preparing for the Second Servicing Mission), was using the neutral buoyancy tests as a tool to prepare for the upcoming First Servicing mission by having subjects practice in the simulated weightless environment. Two weeks of on-orbit servicing proved to be a brief interruption to scientific operations compared with having to return the HST to Earth which would have posed significantly greater risk of contamination or damage to the Telescope's delicate components. As a result, unmatched space data and pictures have resulted in increasing our knowledge of the Universe.
So, next time you go swimming (and you are neutrally buoyant as defined in the first paragraph), remember reading this journal and pretend that you are an Astronaut in Space getting ready to perform an EVA. Pick a task, preferably a short one since you'll be holding your breath, that would show you how different it is working in a weightless environment. Remember, you will be allowed to flip upside down while performing this task. Maybe attach small floats to a very heavy object that you would not be able to easily lift on the ground, like a watermelon, and practice moving it from one place to the next.
Who knows, maybe you'll be performing an EVA in space one day!