How NASA's ATLAS and ROCKY Devices Are Shrinking the Space Gym for Mars

The human body is uniquely adapted to the constant, invisible pull of Earth's gravity. When astronauts leave that gravity well, the physiological consequences are immediate, severe, and compounding. Without the constant mechanical loading required for walking, standing, and lifting everyday objects, skeletal muscle begins to atrophy within days, and bone density plummets at an alarming rate. On Earth, gravity acts as a perpetual resistance machine, forcing the musculoskeletal system to maintain its structural integrity. In the weightlessness of space, the body rapidly discards this expensive tissue, interpreting the lack of physical strain as a signal that dense bones and thick muscle fibers are no longer necessary for survival. Preventing this rapid decay is one of the most critical challenges in human spaceflight, dictating whether a crew can survive a multi-year journey into the solar system.[2]

On the International Space Station, NASA combats this physiological decay with a massive, highly effective orbital gym. The current ISS exercise suite comprises three primary pieces of hardware: a specialized treadmill, a cycle ergometer, and the Advanced Resistive Exercise Device, commonly known as ARED. Together, these machines weigh more than 4,000 pounds and occupy roughly 850 cubic feet of habitable volume—roughly the size of a small bedroom. ARED relies on massive vacuum cylinders to simulate the feel of free weights, allowing astronauts to perform heavy squats and deadlifts. This equipment is undeniably successful; astronauts who spend over two hours a day on these machines are able to preserve the vast majority of their strength during six-month orbital stays, returning to Earth in excellent physical condition.

However, as NASA pivots its focus from low Earth orbit to deep space exploration, the ISS model is no longer mathematically or physically viable. The rocket equation dictates that every pound of payload sent to the Moon or Mars requires exponentially more fuel to escape Earth's gravity. Launching a 4,000-pound gym into deep space would require an unjustifiable sacrifice of life support systems, scientific instruments, or fuel. Furthermore, the spacecraft designed for these deep space journeys are fundamentally different from the sprawling, modular architecture of the International Space Station, requiring engineers to rethink every aspect of orbital living.[1]

The Orion spacecraft, which serves as the primary crew vehicle for the Artemis lunar missions and future Mars transits, has a mere fraction of the internal volume of the ISS. After the massive launch engines cut off and the crew's seats are collapsed to maximize interior space, the astronauts are left with a highly constrained living environment. Packing a room-sized, multi-ton exercise suite into Orion is a physical impossibility. The hardware must fit into the margins of the spacecraft, tucked away near the side hatch without obstructing daily operations or emergency egress routes.[1]

To solve this seemingly impossible geometry problem, NASA's Human Research Program partnered with ZIN Technologies, an aerospace engineering firm based in Middleburg Heights, Ohio. Their mandate was highly specific and seemingly contradictory: they needed to replicate the high-fidelity mechanical loading and heavy resistance of the massive ISS equipment, but they had to do it in a package that was exponentially smaller, lighter, and required minimal electrical power. The device also had to be robust enough to operate for years without the possibility of replacement parts or ground-based maintenance.

The result of this multi-year collaboration is a new generation of electromechanical exercise hardware, spearheaded by two flagship devices: the Advanced Twin Lifting and Aerobic System (ATLAS) and the Resistive Overload Combined with Kinetic Yo-Yo (ROCKY). These devices abandon the bulky vacuum cylinders and heavy physical mass of legacy equipment, turning instead to advanced software, electric motors, and kinetic energy systems to simulate the heavy gravitational loads required to keep human bones dense and muscles strong.

ROCKY represents the extreme end of this miniaturization spectrum. Designed specifically to meet the severe mass and volume constraints of the Orion capsule, the device is astonishingly small—roughly the size of a large shoebox. It measures just 21.5 by 13.5 by 7.5 inches and weighs approximately 25 pounds. This represents a staggering 99 percent reduction in mass compared to the ISS exercise suite, freeing up critical payload capacity for food, water, and scientific equipment on long-duration missions.

Despite its ultra-compact footprint, ROCKY is capable of generating up to 400 pounds of resistive loading through a single-cable system. It achieves this immense force not through iron plates, but through a highly calibrated combination of electromechanical resistance and kinetic yo-yo technology. As the astronaut pulls on the cable, the internal motors and kinetic systems push back, creating a smooth, continuous tension that closely mimics the 'gold standard' biomechanical feel of lifting free weights on Earth.

Crucially, this single mechanism allows astronauts to perform both heavy resistance training and metabolic, aerobic work on the exact same 25-pound device. By adjusting the software and swapping out simple attachments, a crew member can transition from heavy squats, deadlifts, and heel raises to a high-intensity aerobic rowing session. This dual-purpose functionality is essential for deep space missions, where cardiovascular health is just as critical as muscular strength, but carrying separate machines for cardio and lifting is impossible.

For missions with slightly more habitable volume—such as long-term lunar surface habitats or the larger transit vehicles that will eventually carry humans to Mars—NASA developed the ATLAS device. While larger than ROCKY, ATLAS remains remarkably compact compared to legacy ISS hardware. It weighs roughly 250 pounds and features a 50-by-26-inch platform, providing a wider base for complex movements while still fitting comfortably within the tight confines of a deep space habitat.

ATLAS increases the maximum resistance capacity to a staggering 600 pounds and introduces several advanced biomechanical features designed to maximize the efficiency of an astronaut's workout. Chief among these innovations is a capability known as 'eccentric overloading.' This feature allows the device to provide different, highly specific resistance levels during the lifting (concentric) and lowering (eccentric) phases of a single movement, a technique that is difficult to safely replicate with traditional free weights.

Sports science and kinesiology have long established that the eccentric phase of a lift—the controlled lowering of the weight—is critical for maximizing muscle hypertrophy and driving strength adaptation. By allowing the onboard computer to dynamically increase the load as the astronaut lowers the 'weight,' ATLAS can trigger greater muscle preservation and bone stimulation with fewer total repetitions. This efficiency is vital when crew time is one of the most strictly budgeted resources on a space mission.[2]

Both ATLAS and ROCKY rely heavily on a groundbreaking software innovation known as 'virtual racking.' In a traditional terrestrial gym, a lifter must unrack a heavy barbell, step back, perform their set, and then carefully re-rack the weight when their muscles are exhausted. This process introduces significant injury risk, especially in the unpredictable environment of microgravity, where a dropped weight could damage critical spacecraft bulkheads or severely injure a crew member.

Virtual racking entirely eliminates this mechanical danger. Before beginning a set, the software requires the astronaut to perform a calibration rep, establishing their specific, safe range of motion. The device then only applies the heavy working load when the user is safely within that calibrated zone. If the astronaut stumbles, loses their grip, or simply completes the set and lowers the handle, the software instantly drops the resistance to zero. The weight is effectively 'racked' automatically, preventing the cable from violently snapping back.

This software-driven approach to resistance training also allows for seamless, high-fidelity data collection. As the astronaut exercises, the devices continuously log power output, force curves, velocity, and metabolic expenditure. This telemetry is transmitted back to medical teams on Earth in real-time. Flight surgeons and biomechanists can analyze the data to ensure the astronaut is receiving a sufficient 'dose' of mechanical loading, allowing them to adjust the exercise prescription dynamically based on the crew member's physiological response.[2]

The stakes for this technology extend far beyond general fitness or aesthetic muscle retention. When an Orion crew returns to Earth—or when a future crew lands on the Martian surface—they will be subjected to crushing gravitational forces after months of floating in weightlessness. The transition from zero gravity to planetary gravity is violently disorienting, causing orthostatic intolerance and profound physical exhaustion.[1]

NASA mission profiles dictate that astronauts must retain enough functional, real-world strength to unbuckle their harnesses, egress the spacecraft, and survive unassisted in the event of an off-course splashdown or a delayed recovery operation. If a capsule lands in rough seas far from the recovery flotilla, the crew cannot afford to be incapacitated by muscle atrophy. The efficacy of ATLAS and ROCKY directly dictates that baseline survivability, ensuring the crew remains physically capable of saving themselves.[2]

While the electromechanical resistance models are highly promising and have performed exceptionally well in parabolic flight testing, deep space introduces novel, unpredictable uncertainties. The devices must function flawlessly for years, surviving the ambient radiation of deep space and the potential intrusion of highly abrasive lunar or Martian dust, which could easily foul sensitive internal motors and sensors if not perfectly sealed.[1]

Furthermore, researchers are still working to determine if the highly efficient 'dose' of exercise provided by these compact electromechanical devices can fully replace the bone-preserving impact forces generated by the heavy ISS treadmill. Running strikes send shockwaves through the skeletal system that are uniquely effective at preserving bone density, and scientists must ensure that heavy, cable-based resistance can trigger those same osteogenic pathways over a multi-year mission.

As the Artemis program accelerates toward crewed lunar landings and the establishment of a permanent base at the lunar South Pole, ATLAS and ROCKY represent a critical leap in human spaceflight architecture. By replacing tons of orbital iron with smart, software-driven resistance, NASA is solving one of the most stubborn biological bottlenecks of deep space travel. They are ensuring that when the first humans finally step onto the surface of Mars, they will have the strength to walk.[2]