# Five veteran astronauts tested a weighted suit and electrical balance stimulation, and said the combination recreated up to 90 percent of postflight disorientation

> Astronauts returning from long missions may need to walk, escape a spacecraft, or respond to an emergency soon after landing. Yet Earth's gravity can leave them unsteady, dizzy and unsure where their feet are going. Researchers have now built a portable ground...

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Published: 2026-08-22T08:45:03+00:00
Categories: Explainer, Space

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Astronauts returning from long missions may need to walk, escape a spacecraft, or respond to an emergency soon after landing. Yet Earth's gravity can leave them unsteady, dizzy and unsure where their feet are going. Researchers have now built a portable ground test that recreates key parts of this difficult postflight period.

The system sends mild electrical signals near the ears and adds carefully placed weight to the body. Five experienced astronauts said the combination produced many of the balance problems and feelings of heaviness they remembered after returning from the International Space Station.

The [Frontiers in Physiology study](https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2024.1369788/full), published on April 18, 2024, describes a **Sensorimotor Disorientation Analog**, or SDA. The NASA-funded project could help researchers test safety equipment, improve landing procedures and prepare crews for their first steps on Earth or another world.

## Why astronauts struggle after landing

Months in orbit change how the brain handles information about movement and body position. On Earth, gravity provides a steady downward reference. In orbit, astronauts float, so the brain gradually learns to control movement without that familiar pull.

Several senses work together during walking. The **inner ear balance organs** detect head motion and acceleration. Muscles and joints tell the brain where the arms and legs are positioned. Vision supplies clues about direction, speed and nearby obstacles. The brain combines these signals to keep the body upright.

After landing, gravity returns in full, while the brain still uses some movement strategies learned in orbit. Astronauts can experience motion sickness, balance loss, unusual feelings of movement and poor control while walking. Arms and legs may also feel much heavier than expected because the muscles must once again support their weight.

Recovery begins quickly, although the first hours can create serious concerns. A crew landing far from help might have to leave a capsule, cross rough ground, or perform emergency tasks while their balance system is still adjusting.

## How researchers recreated postflight disorientation

Space agencies have several ways to study the effects of weightlessness on Earth. Volunteers can remain in tilted beds for long periods, float in water, or take part in immersion studies. Large centrifuges can also expose people to changing forces. Such projects require major facilities and may take days or weeks.

The research team wanted a test that could be carried into a laboratory or field setting and used for a short period. Their SDA combined disturbances aimed at different parts of movement control. Electrical stimulation affected balance signals, special goggles changed vision and added weights altered the sense of body position.

The electrical part used two round electrodes placed behind the ears over bony areas called the mastoid processes. A small device delivered changing current through the electrodes. The signal followed a random pattern based partly on measurements of capsule motion, which made it harder for participants to predict the direction of the disturbance.

Researchers prepared a lower setting to resemble performance about 24 hours after landing, known as R+1. A stronger setting was designed to resemble the hours immediately after landing, called R+0. Each part could be adjusted after the astronauts described how closely it matched their memories.

## Five astronauts tested the analog

Five astronauts who had previously lived aboard the International Space Station joined the study. Four were women and one was a man. Their average age was 45 and their latest missions had lasted an average of 249 days.

Each astronaut had already completed similar movement tests after an actual spaceflight. Before using the SDA, they watched videos of their earlier postflight performance. The recordings helped them recall how their bodies felt immediately after landing and again about one day later.

The astronauts then completed baseline tasks without any disruption. One task required them to rise from a chair, walk toward a cone, step across an obstacle, circle the cone and return. Another used a **heel-to-toe tandem walk**, similar to walking along a narrow line. They performed the tandem walk with their eyes open and closed.

Testing followed an adjustable process. The astronauts tried separate parts of the system and later used combinations. After each block, researchers asked which postflight period the experience resembled and whether changing the strength improved the match. The study's [PubMed record](https://pubmed.ncbi.nlm.nih.gov/38699143/) identifies the project as an exploratory study, reflecting its small group and early stage.

## Electrical stimulation produced the closest match

The strongest results came from **galvanic vestibular stimulation**, usually shortened to GVS. The changing electrical current interferes with nerve signals linked to the inner ear. While a person walks, the brain receives misleading information about head movement and balance, which can cause swaying or uncertain steps.

All five astronauts selected the standard 2 milliamp signal as the best match for the R+1 period. Three of the four astronauts who evaluated the immediate postflight level selected a standard 3 milliamp signal. The fourth chose a modified 2 milliamp pattern with stronger changes between parts of the signal.

Four astronauts said GVS by itself recreated roughly 80 to 90 percent of their remembered postflight experience and performance. The fifth estimated a 50 percent match. In the discussion, the researchers wrote, "GVS alone was the best at replicating postflight experience after long duration missions."

Complex movements were especially sensitive to the electrical disturbance. Walking heel to toe with closed eyes became harder because participants could no longer rely on vision to correct misleading balance signals. Head movement also played a role, since looking down at an obstacle or standing up changes the signals sent by the balance organs.

## A weighted suit recreated postflight heaviness

Added weight addressed a different part of the landing experience. Astronauts often describe their limbs as unusually heavy when they return to gravity. Their brains and muscles have spent months moving arms and legs that require little effort to support in orbit.

The study's **weighted suit** used a vest along with wrist and ankle straps. Weight was placed symmetrically and distributed according to the relative mass of each body area. Researchers could raise or lower the load as the astronauts compared it with their memories.

The final lower setting added weight equal to 15 percent of body weight. The stronger setting added 30 percent. Individual preferences varied, with astronauts choosing between 10 and 20 percent for the R+1 condition and between 25 and 40 percent for the immediate postflight condition.

Ankle weights were particularly useful for three astronauts. The extra load made foot placement harder to judge during the tandem walk and changed how the leg swung during a step. The vest reproduced a general feeling of heaviness, although its position near the body's center sometimes helped stabilize the wearer.

All five participants felt that added weight belonged in the final analog. They estimated that it reproduced another 5 to 40 percent of their postflight experience. The combination worked better because GVS disturbed balance while the suit recreated effort, heaviness and changes in the sense of limb position.

## Visual disruption goggles fell short

Researchers also tested goggles designed to disturb vision. The goggles are commonly used to demonstrate levels of impairment associated with alcohol. They blur or shift the visual scene, making it harder to use sight for balance.

Four astronauts said even the weakest goggles produced a visual experience that was too disruptive or unlike what they remembered after landing. Two chose not to complete movement tasks with them, either because the effect was uncomfortable after standing or because testing time was limited.

Only one astronaut felt that the goggles helped fine-tune the analog. For that participant, adding the goggles reduced correct tandem-walk steps and brought the strongest test condition closer to the person's immediate postflight performance. At the lower setting, however, the goggles caused a larger decline than the astronaut had experienced one day after landing.

Postflight visual effects can involve the apparent movement of the body or surrounding scene when the head tilts. Standard distortion goggles create a different experience. A future version could use **virtual or augmented reality** to make the visual world move with a slight delay or exaggerate its motion in response to a head turn.

## Balance tests matched key postflight effects

Researchers scored each tandem-walk step from video. A step could be marked incorrect if the feet crossed, the moving foot touched down more than once, or the person made a wide swing. Long pauses and large gaps between the heel and toe also counted as errors.

At the lower SDA level, the astronauts averaged 74.4 percent correct steps with their eyes open. Earlier postflight data from a larger group showed an average of 84.6 percent one day after landing. With eyes closed, SDA performance averaged 18.8 percent, compared with 25.3 percent in the earlier postflight results.

The strongest condition produced 7.6 percent correct steps with eyes closed. Actual immediate postflight data had averaged 9.9 percent, a difference equal to much less than one step in a short test. The **eyes-open R+0 test** produced a weaker match, with SDA participants scoring 53.3 percent compared with a postflight average of 33.5 percent.

Vision may explain part of the difference. Astronauts can use visual landmarks to correct uncertain balance signals and people vary greatly in how well they use that information. Actual R+0 scores with open eyes had ranged from zero to 100 percent, showing how differently individuals can respond during the first hours back in gravity.

The small sample requires caution. Five astronauts can provide detailed personal comparisons, although their results cannot describe every crew member. Test order may also have influenced some answers and every possible combination of electrical current, weight and goggles was not completed.

## A portable tool for training future crews

A compact analog could help engineers examine what astronauts can safely do during the first minutes and hours after landing. Teams could test capsule exits, emergency equipment, protective clothing, or movement across uneven ground without waiting for a crew to return from orbit.

Training is another possible use. Three of the five astronauts independently suggested that the electrical stimulation could help first-time flyers experience temporary balance problems before launch. A trained astronaut might learn to move more slowly, use stable handholds and limit sudden head movements while the body readjusts.

Researchers could also use the system to compare countermeasures. Exercise programs, balance training, footwear and landing procedures could be tested under repeatable conditions. Because the effects of GVS fade quickly after the current stops, several approaches could be studied without producing long-lasting disorientation.

The project received support from the **NASA Human Research Program**, which studies risks to astronaut health and performance. NASA's [funded-science report](https://www.nasa.gov/wp-content/uploads/2025/03/final-fy24-hrp-funded-science-002-1.pdf) includes the work among its research on protecting crews during exploration. Co-author Michael C. Schubert's [Johns Hopkins record](https://pure.johnshopkins.edu/en/publications/development-of-a-ground-based-sensorimotor-disorientation-analog-/) also lists the peer-reviewed study and its institutional partners.

Further testing with more astronauts could show how the settings should change with mission length, individual balance ability, or time since landing. Head-linked electrical signals and improved visual effects may also bring the analog closer to the experience of returning from space. Future crews traveling to the Moon or Mars could face similar problems when entering gravity after months in transit. A refined **postflight disorientation analog** would give mission planners a practical way to study those first uncertain steps while remaining safely on Earth. Broader mission context is available from [NASA's Human Research Program](https://www.nasa.gov/hrp/).