February 1983:the Neutral Buoyancy Simulator

Working in space beyond the protection of a spacecraft cabin is still a complex and dangerous business. American and Soviet astronauts spend hundreds of hours practising the work in large water tanks to simulate the weightlessness of orbital activities. With the advent of the Space Shuttle, the Neutral Buoyancy Simulator in Huntsville has become a vital tool for preparing astronauts for such work. Here is a first-hand account of what it is like to go into space a few feet under water...

Underwater

There I was, floating outside the cargo bay of the Space Shuttle. It was tiring to work in weightlessness, particularly while wearing a bulky space suit. Was I really out in space? No. I was underwater in a huge tank, known as the Neutral Buoyancy Simulator, at the Marshall Space Flight Center in Huntsville, Alabama,which is often used by astronauts and engineers to practise working in weightlessness.

J was taking part in an evaluation of the procedures used to set up a “space platform”. To gain familiarity with tank tests, I was first sent in with Scuba diving gear to observe a tank “run”. Since the tank is totally above ground, I took the lift up to the surface where I met the NASA divers who were also preparing to dive. We checked the pressure in our air tanks, then I donned my tank, mask and fins. It was a pleasant surprise to jump into such warm water after training for this dive with wet suits in cool Canadian lakes.

Below me, as I descended, was a full scale model of the Space Shuttle. The roof was opened, exposing the cargo bay which ran the length of the fuselage. Inside, there were two astronaut subjects wearing space suits, accompanied by their many support Scuba divers. It seemed as though we were all floating in space; the water was so clean it was invisible.

The Remote Manipulator System (RMS) of the Shuttle was controlled by an operator looking into the tank through a porthole. He guided the arm, unfolding a 5 m cube made of tubing (see photograph). It was stacked in the bottom of the cargo deck, with other similar folded cubes. Breathing with Scuba gear creates quite a noise, but between breaths I could hear the conversation between the astronauts and the test director over the underwater speakers.

“Ready to release your side, Steve?” the test director asks one of the astronauts.

"OK here but the RMS is seven inches off centre.” To correct this, the RMS grappling hand was moved over. Then it lifted a cross bar, unfolding the cube.

“We’ll have to translate it a bit farther before we can start rotation.” “You’ll have to move over to the C-plus side,” observed the test director in the control room, as he watched from many angles through TV cameras in the tank. Several people monitor the tank simulations in a large control room full of consoles and TV screens.

“I can’t reach it,” Steve complained as he prepared to connect two of the cubes together.

“Wait till I strap myself on here. Did you get a good picture, Dennis?” asked Steve as the NASA photographer floated by. There were other photographers in the tank, including a US Navy team and a diver with a mobile TV camera to transmit live close-ups to the control room. Another diver guided the cable from this camera, while yet another held a light for filming.

There were 18 people in the tank. Each astronaut had two safety divers to assist in the event of a suit malfunction. They also watched the line that supplies air and cooling water to the suit, to ensure that nothing became tangled. Another four divers retrieved and positioned equipment. Two additional safety men were on standby, swimming on the surface. This first dive of mine was made in standard Scuba equipment; now I was ready to wear an EVA suit.

Although I had been previously trained in space suits, there was more to learn about the safety procedures for using them underwater. Glenn Dobbs, my suit technician, has been working with astronauts for a long time. He explained that when working with a suit underwater, a perfect fit is essential. Otherwise, the wearer could end up “bouncing” around inside the suit. So, before my tank run, I went through a sizing check. Each suit is custom made to fit one of the astronauts, but slight adjustments can be made. I was helped into a suit used by one of the Skylab astronauts and the proper length of the arms and legs were recorded so that slight adjustments could be made later.

Next to my skin I wore a liquid cooling garment, which carries 100 m of tubing to circulate cooling water. This particular one had been worn by astronaut Pete Conrad. He is now in, what he told me, a more challenging career trying to sell DC-10s. He obviously had his own way of doing things: the cooling garments are not made with collars, but he wanted one so he made his own and sewed it on.

Wrist bands were also worn as protection from rubbing on the metal couplings where the gloves were attached. When my space helmet was on, I could maintain my discussion with Glenn via the “Snoopy Cap”, the communications carrier with earphones and microphones. Last to be put on were my helmet and gloves which had double locks so they could not accidentally disconnect.

As soon as the helmet was locked on the suit began to pressurise, inflating like a balloon. It became rigid and could only bend at the shoulders, elbows, waist and knees where there were joints. Also, the wrist section is free to rotate. Glenn gave me a dexterity test to demonstrate some of the difficulties involved in working with the suit on. Using a screwdriver was difficult because the glove fingers were wide and did not bend much. After checking the suit at higher pressure, Glenn brought it back down to ground pressure. A glove was taken off first because, if the helmet were to come off first, a slight excess pressure could send it flying away.

A few days later, I was ready. This time, I was the astronaut and more than 20 people were involved in the simulation. Normally only 15 are required to support a single suited diver, but others were needed to tape styrofoam to some tubes that had leaked and filled with water. A heart rate sensor attached to my ear was monitored in the control room, but they were having trouble picking up the signal. Adjustments were made and the signal improved. Meanwhile, technicians attached weights to my ankles and wrists to hold me down in the water. Before I entered the water, a communications and status check was made. While I stood partially submerged on a platform,weights were added to my chest, and my backpack was attached. By then, I carried 67 kg of weights to hold down the inflated suit! As I submerged onto another platform, I was amazed to be underwater yet totally dry. Neither sinking nor floating, I was in a state of neutral buoyancy. I was suspended. To balance my suit, the divers “trimmed me out”. They rotated me so that I was lying flat to check that I didn’t tip to one side, then they spun me upside down. Assured that I was trimmed, they pushed me out and down towards the Shuttle.

To maintain the air pressure inside the suit at a pressure higher than the surrounding water, the suit pressure was increased as I descended. Every three metres we stopped to allow my ears to adjust to the higher pressure. This gave me a chance to look around and appreciate the excellent view afforded by the bubble helmet. Being accustomed to the restricted view of a Scuba diving mask, it was a new experience. Handrails along the outside of the Shuttle made it easy to move around using a hand-over-hand method. Once I began to move in one direction, I would maintain that course with almost no effort other than making sure 1 didn’t let go. A few times I did and I would drift back a bit. Optical distortion underwater makes things look closer than they really are, so a handrail that semed to be within reach was sometimes too far away. I would then be stranded; one of the safety divers would give me a push.

Generally, working in the suit takes some adjusting to because of the restrictions on movement. For example, to reach something above, where one can normally just reach up and grab, is not possible in the suit because the shoulders do not rotate forward easily. But that does not mean it cannot be reached. In fact, in weightlessness it’s easier. I could simply push myself "up” and then reach forward. The work is not more difficult, but definitely different.

Sometimes it is more convenient to work upside down. With the suit and extra weights, I had a mass of 152 kg! So, a large effort was required to turn over.

Footholds are provided at workstations in the Shuttle cargo bay and slipping space suit boots into them is a skill that takes practice. Before 1 tried this, I was tipped forward by a safety diver to have a good look at the grapplng system; then 1 was tilted back up. f was then floating just above them. I had to push my body “down” along a straight line, hook my boot toes in, and turn my heels out slightly. At first, I didn’t even know I was hooked in because the platform flexed slowly. Only one of my boots was in and when I tried to put the other one in I ended up tumbling away. But, 1 eventually succeeded.

To attach an experiment to the Shuttle, two metre long “card table legs” had-to be unfolded. I found that it took only a very small force with one hand to swing the large tubes. Sometimes, moving one of these tubes would start me rotating randomly. This was hard to stop unless there was something secure to hold on to. The safety divers made sure I didn't crash into the equipment because sharp edges could rip the suit. Also, the equipment was actual space hardware scheduled to fly in two years to develop the technology for building large structures.

Although suspended in the water, I was not actually weightless. My inner ear could tell my brain which way was up. I could recognise the difference beteen this and true weightlessness, having experenced the latter in fast aircraft. Still, the difference is subtle. Psychologically, I could develop a sense of up and down in true weightlessness. Conversely, working in the tank, I would sometimes forget which way was actually up. But up and down was neither here nor there. In the tank, as in space, I could work with my body in any orientation.

At one point, I looked past my feet and I could see the sky through the skylights in the roof. It was like working on the experiment in space, looking down on the Earth. It was time to leave the Shuttle and the safety divers pushed me up slowly. The sky beckoned. The hardware was ready to fly.