Neutral buoyancy simulation as a training aid

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An astronaut training at the Neutral Buoyancy Laboratory at the Johnson Space Center. NASA Neutral Buoyancy Laboratory Astronaut Training.jpg
An astronaut training at the Neutral Buoyancy Laboratory at the Johnson Space Center.

Neutral buoyancy simulation with astronauts immersed in a neutral buoyancy pool, in pressure suits, can help to prepare astronauts for the difficult task of working while outside a spacecraft in an apparently weightless environment.

Contents

History

Extra-vehicular activity (EVA), working outside the space vehicle, was one of the goals of the Gemini Program during the 1960s. The astronauts were trained in the “zero gravity” condition by flying a parabolic trajectory in an aircraft that caused reduced gravity for thirty second intervals.

Pioneers without sufficient training

The Russian cosmonaut Alexei Leonov was the first to egress his vehicle while travelling in orbit above the Earth. Shortly after, Ed White, Gemini IV, was the first American astronaut to egress a vehicle while in space. These were demonstrations of a capability to get out of and back into the vehicle but included no EVA tasks. The next three flights to demonstrate an EVA capability were Gemini IX-A, X, and XI. Each of these flights exposed problems with performance of EVA tasks. Working in pressure suits while in the constant weightlessness of orbital spaceflight was more complex and difficult than had been anticipated. NASA determined that training for EVA tasks required further development. [1]

Origins of neutral buoyancy training

In July 1966 the Gemini Program joined in a NASA Langley Research Center contract to include an evaluation of Gemini EVA tasks. [2] The contractor, Environmental Research Associates of Randallstown, MD had already begun developing a neutral buoyancy simulation capability in 1964. This capability for pressure suited subjects was initially developed in 1964 by utilizing an indoor swimming pool at a private school (McDonogh School near Baltimore). [3] Initially, these early underwater simulations were simply designed to test the ability of subjects to move about mock-up airlocks and weights were not attached to the subjects. [4] Quickly, Environmental Research Associates' submerged testing evolved into proper neutral buoyancy simulation, featuring weighted subjects and numerous safety divers on hand during given sessions. [5]

First evaluation by astronauts

Scott Carpenter was the first astronaut to evaluate the contractor's operation, in a "wet workshop" simulation. The task was to remove bolts while in a submerged simulated airlock. The bolt removal task was designed to create access to a spent S-IVB dome. Carpenter's evaluation of the simulation was favorable and NASA quickly provided mockups of Gemini vehicles and docking components to facilitate further development of EVA capabilities via neutral buoyancy training. Astronaut Gene Cernan first visited the McDonogh School indoor pool facility for post-mission evaluation of problems that he encountered during his Gemini IX-A EVA. NASA then modified the contract to include pre-mission training of Gemini XII astronaut, Buzz Aldrin. Astronaut Cernan also participated in this pre-mission training, as he was in a backup role to Aldrin as pilot of Gemini XII.

Gemini XII EVA training

Aldrin trained for the original Gemini XII EVA version which was then revised to eliminate the task of using a manned maneuvering unit. Aldrin returned to the McDonogh facility and trained for the final version of his EVA. NASA considered the flight EVA to be a total success, and Aldrin again returned to McDonogh to perform a post-mission evaluation of the EVA. The post-mission evaluation verified the value of using neutral buoyancy simulation training before attempting all of the EVA tasks while wearing a pressure suit and working in the hostile environment of space. Aldrin himself recognized some minor flaws of neutral buoyancy training, but described the method to have a "considerable advantage" over Keplerian trajectory aircraft. [6]

Beyond Gemini

After the successful EVAs in the Gemini XII mission, NASA constructed tanks for neutral buoyancy simulation: The Water Immersion Facility at the Manned Spacecraft Center and the Neutral Buoyancy Simulator at Marshall Space Flight Center. Following use of those facilities during the Apollo and Skylab programs, NASA eventually constructed the Weightless Environment Training Facility at the Manned Spacecraft Center in Houston and later the Neutral Buoyancy Laboratory, where Shuttle and Space Station astronauts are trained in neutral buoyancy. Astronauts and cosmonauts also train at the Yuri Gagarin Cosmonaut Training Center near Moscow. These accomplishments were summarized in a feature article published by the Baltimore Sun newspaper in 2009. [7] In September 2011, the Gemini XLV Symposium included a review of these accomplishments by G. Samuel Mattingly and featured remarks by astronauts Richard Gordon, Tom Jones, and Buzz Aldrin.

Rescuing Skylab

During the Skylab 2 mission, astronauts Conrad and Kerwin successfully opened a solar panel that had not automatically deployed after launch. To perform this task, the astronauts trained underwater in the Neutral Buoyancy Simulator at the Marshall Space Flight Center. However, due to differences between the design of the mock-up used for training and what they found at Skylab, the astronauts used makeshift tools and redesigned how they would accomplish the task while they were in outer space. [8]

Characteristics

Need for simulation

Astronauts rehearse extra-vehicular activity tasks in underwater neutral buoyancy before attempting those tasks in space to gain an understanding that they cannot use their weight to provide a force and that they may move or reposition themselves if they provide a propulsive force in any vector, either planned or inadvertent. Articles describing neutral buoyancy simulation generally point out that the astronaut's spacesuit is made neutrally buoyant but that the astronaut still feels gravity inside the spacesuit so the fit of the suit is very important, and that moving around in water, a viscous fluid, creates drag that is not present in EVA. [9]

Normal gravity experience

The main purpose for an astronaut to egress the vehicle and go EVA is often to provide a force to push, pull, crank, squeeze or transport an object. While living in normal earth gravity people do not generally recognize the use of their weight to provide a force. The simple task of opening or closing a door, for example, is complicated when an individual is standing on a slick sheet of ice, so the individual's weight does not provide a frictional coupling to the ground. The application of force is an action requiring a reaction and if the individual's feet are slipping, the force application is limited or non-existent. The individual feels gravity standing on the ice but they cannot use their weight to provide traction and they cannot shift their weight to provide force in a horizontal vector so they cannot force the door. Giving the door a shove and sliding back is using mass inertia and not using the individual's weight. Mass inertia can also be used during EVA, but doing so in a pressure suit can produce unintended results.

Comparison

As stated above (in Need for simulation), the astronaut feels gravity inside the pressurized suit while immersed in water. However the astronaut-spacesuit combination, when properly balanced in neutral buoyancy as when in EVA, is weightless so the astronaut is, similar to standing on ice, unable to use weight to provide a force in any vector. The vector of any force is similar, if not exactly the same in EVA and in neutral buoyancy. The magnitude of the force, if static, is very similar and if dynamic is still similar although the force and vector used in moving large objects must be carefully studied and planned to make the simulation realistic. It is the inability to use weight in any vector in EVA coupled with the encumbrance of the pressure suit that makes task performance difficult.

Drag

Drag is the other major concern identified in articles on neutral buoyancy simulation. Any motion in the water is subject to drag and requires a little more time (seconds) and a little more force (ounces) to compensate for drag compared to the same motion in EVA. Early in the history of neutral buoyancy simulation there was consideration of providing the immersed astronaut with small motors to compensate for water drag, but this was soon dismissed as an unnecessary complication. Only a small percentage of time is spent in translating to a new location, usually at low velocity, generally less than 6 inches per second. Even such low velocities are subject to drag but it becomes difficult to measure amid the minor currents in the water caused by other astronauts, divers and the water circulation system that add to or subtract from drag.

Task performance

In EVA, most work is done slowly, carefully and methodically not because of the neutral buoyancy training but because that is how a task must be performed by a pressurized astronaut in weightlessness. It takes more force to accelerate a mass to a higher velocity, and then to slow the mass back down, than to move it slowly to its destination. It is also easier to control its movement if it is moving slowly. Thus, the drag of water on movement in neutral buoyancy simply necessitates a slowness of movement that is also appropriate to spaceflight.

Visual differences

There are other less obvious but important features that must be considered in underwater EVA training, such as the visual differences due to refraction at the air-water interface at the helmet's visor and position or attitude in the suit relative to the task. The personnel at the Neutral Buoyancy Laboratory in Houston plan and evaluate their simulations meticulously. Experienced EVA astronauts observing a simulation can advise as to how realistic is the task performance and recommend modifications.

Usefulness to EVA astronauts

Learning and rehearsing an EVA task in neutral buoyancy gives an astronaut or EVA specialist confidence that the planned task may be accomplished. The timeline developed for task performance is similar to the time required in EVA. In general, it is considered that a task performed and practiced in neutral buoyancy simulation can also be performed in EVA. Neutral buoyancy, properly planned and conducted, works because it is a realistic simulation of the physical requirements of performing a task in EVA.

Comparison with reduced gravity aircraft

The other major method used to simulate microgravity is flight in a reduced gravity aircraft (a so-called "vomit comet"), an aircraft which performs a number of parabolic climbs and descents to give its occupants the sensation of zero gravity. [10] Reduced-gravity aircraft training avoids neutral-buoyancy training's drag problem (trainees are surrounded by air rather than water), but instead faces a severe time limitation: periods of sustained weightlessness are limited to around 25 seconds, interspersed with periods of acceleration of around 2 g as the aircraft pulls out of its dive and readies for the next run. [11] This is unsuitable for practicing EVAs, which usually last several hours.

Related Research Articles

Extravehicular activity Activity done by an astronaut or cosmonaut outside a spacecraft

Extravehicular activity (EVA) is any activity done by an astronaut outside a spacecraft beyond the Earth's appreciable atmosphere. Normally, the term applies to what has been termed a spacewalk outside a craft that is orbiting Earth. However EVA also applies to lunar surface exploration, as performed by six pairs of American astronauts in the Apollo program from 1969 to 1972. A Stand-up EVA (SEVA) is when an astronaut does not fully leave a spacecraft, but is completely reliant on the spacesuit for environmental support. Its name derives from the astronaut "standing up" in the open hatch, usually to record or assist a spacewalking astronaut. The Soviet Union/Russia, the United States, Canada, the European Space Agency and China have all conducted EVAs.

Space suit Garment worn to keep a human alive in the harsh environment of outer space

A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, and are necessary for extravehicular activity (EVA), work done outside spacecraft. Space suits have been worn for such work in Earth orbit, on the surface of the Moon, and en route back to Earth from the Moon. Modern space suits augment the basic pressure garment with a complex system of equipment and environmental systems designed to keep the wearer comfortable, and to minimize the effort required to bend the limbs, resisting a soft pressure garment's natural tendency to stiffen against the vacuum. A self-contained oxygen supply and environmental control system is frequently employed to allow complete freedom of movement, independent of the spacecraft.

Buzz Aldrin American astronaut and lunar explorer (born 1930)

Buzz Aldrin is an American former astronaut, engineer and fighter pilot. He made three spacewalks as pilot of the 1966 Gemini 12 mission, and, as Lunar Module Eagle pilot on the 1969 Apollo 11 mission, he and mission commander Neil Armstrong were the first two people to land on the Moon. He is the last surviving crew member of Apollo 11.

Johnson Space Center NASA field center for human spaceflight

The Lyndon B. Johnson Space Center (JSC) is NASA's center for human spaceflight, where human spaceflight training, research, and flight control are conducted. It was built and leased to NASA by Joseph L. Smith & Associates, Inc. It was renamed in honor of the late US president and Texas native, Lyndon B. Johnson, by an act of the United States Senate on February 19, 1973.

Jim Lovell American astronaut (born 1928)

James Arthur Lovell Jr. is a retired American astronaut, naval aviator, test pilot and mechanical engineer. In 1968, as command module pilot of Apollo 8, he became, with Frank Borman and William Anders, one of the first three astronauts to fly to and orbit the Moon. He then commanded the Apollo 13 lunar mission in 1970 which, after a critical failure en route, circled the Moon and returned safely to Earth.

Gemini 12 1966 NASA crewed spaceflight

Gemini 12 was a 1966 crewed spaceflight in NASA's Project Gemini. It was the 10th and final crewed Gemini flight, the 18th crewed American spaceflight, and the 26th spaceflight of all time, including X-15 flights over 100 kilometers (54 nmi). Commanded by Gemini VII veteran James A. Lovell, the flight featured three periods of extravehicular activity (EVA) by rookie Edwin "Buzz" Aldrin, lasting a total of 5 hours and 30 minutes. It also achieved the fifth rendezvous and fourth docking with an Agena target vehicle.

Reduced-gravity aircraft Fixed-wing aircraft that provides brief near-weightless environments

A reduced-gravity aircraft is a type of fixed-wing aircraft that provides brief near-weightless environments for training astronauts, conducting research and making gravity-free movie shots.

Project Gemini 1961–1966 US human spaceflight program

Project Gemini was NASA's second human spaceflight program. Conducted between projects Mercury and Apollo, Gemini started in 1961 and concluded in 1966. The Gemini spacecraft carried a two-astronaut crew. Ten Gemini crews and 16 individual astronauts flew low Earth orbit (LEO) missions during 1965 and 1966.

Artificial gravity Use of circular rotational force to mimic gravity

Artificial gravity is the creation of an inertial force that mimics the effects of a gravitational force, usually by rotation. Artificial gravity, or rotational gravity, is thus the appearance of a centrifugal force in a rotating frame of reference, as opposed to the force experienced in linear acceleration, which by the equivalence principle is indistinguishable from gravity. In a more general sense, "artificial gravity" may also refer to the effect of linear acceleration, e.g. by means of a rocket engine.

Neutral buoyancy Equilibrium between buoyancy and weight of an immersed object

Neutral buoyancy occurs when an object's average density is equal to the density of the fluid in which it is immersed, resulting in the buoyant force balancing the force of gravity that would otherwise cause the object to sink or rise. An object that has neutral buoyancy will neither sink nor rise.

Space Systems Laboratory (Maryland) Neutral buoyancy facility at the University of Maryland

The Space Systems Laboratory (SSL) is part of the Aerospace Engineering Department and A. James Clark School of Engineering at the University of Maryland in College Park, Maryland. The Space Systems Laboratory is centered on the Neutral Buoyancy Research Facility, a 50-foot-diameter (15 m), 25-foot-deep (7.6 m) neutral buoyancy pool used to simulate the microgravity environment of space. The only such facility housed at a university, Maryland's neutral buoyancy tank is used for undergraduate and graduate research at the Space Systems Lab. Research in Space Systems emphasizes space robotics, human factors, applications of artificial intelligence and the underlying fundamentals of space simulation. There are currently five robots being tested, including Ranger, a four-armed satellite repair robot, and SCAMP, a six-degree of freedom free-flying underwater camera platform. Ranger was funded by NASA starting in 1992, and was to be a technological demonstration of orbital satellite servicing. NASA was never able to manifest it for launch and the program was defunded circa 2006. For example, Ranger development work at the SSL continues, albeit at a slower pace; Ranger was used to demonstrate robotic servicing techniques for NASA's proposed robotic Hubble Servicing Mission.

Neutral Buoyancy Laboratory NASA astronaut training facility in Houston, Texas

The Neutral Buoyancy Laboratory (NBL) is an astronaut training facility and neutral buoyancy pool operated by NASA and located at the Sonny Carter Training Facility, near the Johnson Space Center in Houston, Texas. The NBL's main feature is a large indoor pool of water, in which astronauts may perform simulated EVA tasks in preparation for upcoming missions. Trainees wear suits designed to provide neutral buoyancy to simulate the microgravity that astronauts would experience during spaceflight.

EASE/ACCESS Pair of Space Shuttle flight experiments

The Experimental Assembly of Structures in EVA and the Assembly Concept for Construction of Erectable Space Structures, or EASE/ACCESS, were a pair of space shuttle flight experiments that were performed on STS-61-B, on November 29 and December 1, 1985. The purpose of the experiments was to study how quickly astronauts would become proficient at assembling space structures during extravehicular activity, and how quickly they would become fatigued, and to explore various construction and maintenance techniques. In particular, researchers studied the applied moments of inertia arising in the manual assembly of a large space structure.

Neutral Buoyancy Simulator Historic astronaut training facility

The Neutral Buoyancy Simulator was a neutral buoyancy pool located at NASA's George C. Marshall Space Flight Center (MSFC). Engineers and astronauts developed hardware and practiced procedures in this tank from its completion in 1968 through its decommissioning in 1997. Marshall recognized the need for underwater simulations of extra-vehicular activities (EVAs) and developed three successively larger tanks for the purpose. The Neutral Buoyancy Simulator contributed significantly to the American crewed space program. Skylab, the Space Shuttle, Hubble Space Telescope, and the International Space Station have all benefited from the Neutral Buoyancy Simulator. Until Johnson Space Center constructed the Weightless Environment Test Facility in the mid-1970s, MSFC had the only NASA-owned test facility that allowed engineers and astronauts to become familiar with the dynamics of body motion under weightless conditions.

Weightlessness Absence of stress and strain resulting from externally applied mechanical contact-forces

Weightlessness is the complete or near-complete absence of the sensation of weight. This is also termed zero-G, although the more correct term is "zero G-force". It occurs in the absence of any contact forces upon objects including the human body.

Astronaut training Preparing astronauts for space missions

Astronaut training describes the complex process of preparing astronauts in regions around the world for their space missions before, during and after the flight, which includes medical tests, physical training, extra-vehicular activity (EVA) training, procedure training, rehabilitation process, as well as training on experiments they will accomplish during their stay in space.

Terrestrial analogue sites are places on Earth with assumed past or present geological, environmental or biological conditions of a celestial body such as the Moon or Mars. Analogue sites are used in the frame of space exploration to either study geological or biological processes observed on other planets, or to prepare astronauts for surface extra-vehicular activity.

Diver trim Balance and orientation skills of an underwater diver

The trim of a diver is the orientation of the body in the water, determined by posture and the distribution of weight and volume along the body and equipment, as well as by any other forces acting on the diver. Both static trim and its stability affect the convenience and safety of the diver while under water and at the surface. Midwater trim is usually considered at approximately neutral buoyancy for a swimming scuba diver, and neutral buoyancy is necessary for efficient maneuvering at constant depth, but surface trim may be at significant positive buoyancy to keep the head above water.

Hervé Stevenin European aquanaut at the European Astronaut Centre

Hervé Stevenin is a European aquanaut leading ESA Neutral Buoyancy Facility Operations and the EVA Training Unit at the European Astronaut Centre (EAC) in Cologne, Germany. He served as an aquanaut on the NASA Extreme Environment Mission Operations 19 crew.

Neutral buoyancy pool Pool of water in which neutral buoyancy is used to train astronauts

A neutral buoyancy pool or neutral buoyancy tank is a pool of water in which neutral buoyancy is used to train astronauts for extravehicular activity and the development of procedures. These pools began to be used in the 1960s and were initially just recreational swimming pools; dedicated facilities would later be built.

References

  1. ↑ Barton C. Hacker and James M. Grimwood, On The Shoulders of Titans: A History of Project Gemini. NASA Special Publication-4203 1977 (p. 356 of original hardback publication).
  2. ↑ Otto F. Trout, Jr., Harry L. Loats, Jr., and G. Samuel Mattingly "NASA Contract NAS1-4059 with supplemental agreements" Archived 2011-10-25 at the Wayback Machine , January 1966
  3. ↑ Otto F. Trout, Jr., Harry L. Loats, Jr., and G. Samuel Mattingly "Water Immersion Technique of a Pressure-Suited Subject Under Balanced Gravity Conditions", 1964
  4. ↑ Michael J. Neufeld and John B. Charles, "Practicing for space underwater: inventing neutral buoyancy training, 1963-1968." ScienceDirect 39, no. 3-4 (2015): 149-150.
  5. ↑ Michael J. Neufeld and John B. Charles, "Practicing for space underwater: inventing neutral buoyancy training, 1963-1968." ScienceDirect 39, no. 3-4 (2015): 151.
  6. ↑ Reginald Machel, Summary of Gemini Extravehicular Activity.NASA Office of Technological Utilization, 1967: 7-35.
  7. ↑ Frank D. Roylance "Historic Mark", The Baltimore Sun July 19, 2009
  8. ↑ David J. Shayler, FBIS, Walking in Space, 2004, p. 213, Praxis Publishing Ltd.
  9. ↑ G. Samuel Mattingly, with John B. Charles, "A personal history of underwater neutral buoyancy simulation". The Space Review, February 4, 2013.
  10. ↑ Rafiq A, Hummel R, Lavrentyev V, Derry W, Williams D, Merrell RC (August 2006). "Microgravity effects on fine motor skills: tying surgical knots during parabolic flight". Aviat Space Environ Med. 77 (8): 852–6. PMID   16909881 . Retrieved 2008-08-27.
  11. ↑ Pletser V (November 2004). "Short duration microgravity experiments in physical and life sciences during parabolic flights: the first 30 ESA campaigns". Acta Astronautica. 55 (10): 829–54. Bibcode:2004AcAau..55..829P. doi:10.1016/j.actaastro.2004.04.006. PMID   15806734.
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