Distance Learning Module: Astronauts and Aquatics
This week’s Distance Learning theme is AQUATICS. For today’s lesson, we’re making connections between deep sea and deep space by exploring the “how” and “why” of underwater astronaut training. Let’s “dive in” and get started!
Gravity and Weightlessness
Vehicles in spaceflight operate in an environment of microgravity. In this situation—often referred to, inaccurately, as “zero gravity”—objects and people react as though they are weightless. This is why astronauts and equipment appear to be floating in photographs of space missions.
Astronauts Shane Kimbrough and Sandy Magnus play with floating food during the STS-126 shuttle mission (Image Credit: nasa)
The existence of weight depends on the presence of gravity. When we measure the weight of an object on Earth, we’re actually measuring the force exerted on that object by the Earth’s gravitational field. Humans feel the sensation of our own weight as gravity pulls us downward because our bodies are coming into contact with the ground, floors, and objects all around us.
astronauts in “zero-gravity” training (image credit: nasa)
Most spacecraft operate at a distance where they are still impacted the Earth’s gravity. According to NASA, the typical orbital spaceflight takes place about 120-360 miles above Earth’s surface—while Earth’s gravitational field is still 88.8% as powerful at a distance of 250 miles as it would be at the surface. So, objects in orbit still have mass, and they are still acted upon by gravity. The difference is that astronauts on orbiting spacecraft do not feel their weight because their bodies no longer have contact with the ground, floors, and objects that would be pushing against them if they were on the Earth’s surface.
In the vacuum of space, where there are no air molecules creating forces such as friction and resistance, gravity is the only force acting upon astronauts. The astronauts, in this state, are said to be in freefall. The International Space Station is in perpetual freefall above the Earth. Its forward motion just about equals the speed of its "fall" toward the planet, so the astronauts inside the ISS are not pulled in any particular direction: they float.
You may have experienced momentary freefall yourself, if you ever went over a big “hump” on a roller coaster. You can see another explanation of the way that weightlessness happens in this video, using the example of an elevator with a broken cable.
Simulating Weightlessness
It’s important to be able simulate weightlessness on Earth, so that astronauts can more easily adapt to conditions in space. Weightlessness impacts astronauts’ spatial orientation, head-eye and hand-eye coordination, balance, and locomotion—and can even cause motion sickness. Space suits are bulky, so it is beneficial for astronauts to practice their mobility in an Earth environment that closely replicates space travel.
physicist stephen hawking experiencing weightlessness on a modified boeing 727 parabolic flight (Image credit: Jim Campbell/Aero-News Network)
Reduced-gravity aircraft create weightlessness by following a parabolic flight path. Essentially, a plane travels in a path shaped like an upside-down U, rising and then descending at steep angles. Passengers on these flights experience temporary weightlessness —but the effect is brief: a number of seconds, or roughly half a minute, of freefall per flight. This is helpful for some types of research, but it does not allow astronauts to complete prolonged training in weightless conditions…For that, we use water!
Neutral Buoyancy: Simulating Weightlessness in Water
As we explored in last weekend’s raft building STEM Challenge, buoyancy is the force that allows an object to float in water or air. For example, a boat floating in the ocean is impacted gravity pulling it down, and also by buoyancy pushing it upward. The force of gravity is dependent on the weight of the boat, and the force of buoyancy is dependent on the weight of water that the boat displaces.
Neutral buoyancy occurs when an object's density is equal to the density of the fluid in which it is immersed, resulting in a balance between the upward and downward forces being simultaneously exerted. An object that has neutral buoyancy will neither sink nor rise.
Scientists create neutral buoyancy environments to simulate the weightlessness of spaceflight. In a neutral buoyancy pool, humans and equipment are placed in water, and weights are added to their suits until they hover in place. In the United States, NASA uses neutral buoyancy to train astronauts at its Neutral Buoyancy Laboratory in Houston, Texas, and at the Space Systems Laboratory at the University of Maryland. Similar services are available at the Gagarin Cosmonaut Training Center’s Hydrolab in Star City, Russia.
These facilities are impressive feats of engineering. For example, NASA’s Neutral Buoyancy Lab includes a massive pool, measuring over 200 feet long and 100 feet wide, which contains 6.2 million gallons of water! That pool contains full-scale mock-ups of real spacecraft and equipment, including multiple ISS modules and payloads. It once even contained a full-scale mock-up of the Hubble Space Telescope, to train the astronauts for servicing missions. Take a video tour here:
Top image: gigantic training pool at the Neutral Buoyancy Lab (Image credit: NASA)
Lower image: cosmonauts training in neutral buoyancy pool at Hydrolab
Neutral Buoyancy Training
To train in a neutral buoyancy pool, astronauts wearing spacesuits are lowered into the water using an overhead crane. Support divers in the water gradually add weights to the astronauts’ suits until the astronauts neither sink nor rise: they are suspended in place, similar to the experience of floating in a low-gravity space environment.
Neutral buoyancy is not identical to weightlessness. Gravity still acts on objects in a neutral buoyancy tank, and water exerts a drag force that is not present in the vacuum of space. Astronauts in neutral buoyancy training still feel their full body weight within their spacesuits—but the weight is well-distributed, similar to a swimmer floating on the surface of the water.
Neutral buoyancy training is an important aspect of preparing astronauts to maneuver their bodies, suits, and equipment during extravehicular activity (EVA): any project (such as a spacewalk) conducted completely outside the shelter of a spacecraft. Swedish astronaut Christer Fuglesang, of European Astronaut Corps, explains the regimen required for spacewalks on the ISS: “For each specific spacewalk, there are several training units to be completed. One EVA run lasts around 5 hours, and the standard right now is that you spend five to seven times as long in the NBL at Houston for each EVA, depending on the difficulty.”
Immerse yourself in this video demonstration of an aquatic spacewalk training in action:
