Safe Return for Astronauts on Space Walks: The Role of SAFER and Orbital Mechanics

Introduction: Spacewalks are vital for the maintenance and construction of space stations, but they are also fraught with potential dangers. One of the most critical risks is the untethering of an astronaut. This article discusses how astronauts would not simply rely on Earth's gravitational pull to return to safety, but instead, they use specialized equipment, such as the SAFER (Simplified Aid for EVA Rescue) device, to maneuver back to the spacecraft.

Gravitational Pull and Orbital Mechanics

While Earth's gravitational pull does exert a force on objects in space, it does not "pull" astronauts back to the planet directly. In the vacuum of space, there is no air resistance, so an untethered astronaut would continue to drift away from the spacecraft at the speed they were moving at the moment of untethering. The astronaut would start to orbit Earth, albeit in a slightly different orbit compared to the ISS. This orbit is governed by Newton's laws of motion and the principles of orbital mechanics.

Orbital Degradation and Re-Entry

If an astronaut were to become untethered and drift into lower Earth orbit, atmospheric drag would eventually slow down the object. This slowing would cause the astronaut to drop to a lower, denser part of the atmosphere where the thickening air would create more resistance, potentially leading to re-entry. However, the likelihood of such an event is extremely low due to the risk of the astronaut drifting to higher, safe orbits before re-entry occurs.

The Role of SAFER: A Lifesaving Tool

For astronauts in distress, there is specialized equipment designed to help them return to safety. The SAFER (Simplified Aid for EVA Rescue) device is crucial in such situations. SAFER is a self-contained, motorized backpack that uses gas thrusters to propel an astronaut back to the spacecraft. This technology was developed to assist astronauts who may have issues with their tether lines or need to navigate in the vicinity of the station.

NASA has not always relied on SAFER. Initially, the Manned Maneuvering Unit (MMU) was planned to be used for similar purposes, but it was deemed too risky. Now, astronauts are equipped with SAFER packs, which also include thrusters for self-rescue. NASA is currently working on enhancing this technology to include a 'return-to-home' capability, making it even safer for astronauts.

Orbital Decay and Astronomical Re-Entry

Even if an astronaut manages to stay in orbit without re-entry, their orbit would eventually decay due to the thin atmosphere in low Earth orbit (LEO). As the astronaut slows down due to atmospheric drag, they would drop to a lower orbit with even more atmospheric drag, leading to re-entry. Since these orbits often do not match the angle and orientation of re-entry paths used by spacecraft, the astronaut would not experience a controlled re-entry like a spacecraft. Instead, the body would quickly burn up due to the intense heat generated by atmospheric friction.

Conclusion

Astronauts on space walks do not rely on Earth's gravitational pull to return to safety. Specialized equipment such as the SAFER device is essential in preventing untethered astronauts from drifting away. While the possibility of re-entry exists, especially in lower orbits, the use of SAFER or equivalent equipment ensures the astronaut's safe return to the spacecraft. Understanding the principles of orbital mechanics and the role of specialized tools like SAFER is crucial for ensuring the safety of spacewalks.