Space Exploration: Extravehicular Activity
Since 1972 we’ve just been floating around space
If you’re a little jaded by NASA’s plans for a new moon landing because humans are already spending a relatively large amount of time in space, here’s something to think about. Since the last steps of the Apollo 17 mission nearly 50 years ago, all spacewalks have been in Earth orbit (either on the space station or the retired space shuttle). And although we may have walked on the moon before, humans have only spent a total of just over 80 hours walking (or driving!) on the surface of the moon. Imagine having to learn everything about our oceans with just 3 and half days ever at sea! The term extra vehicular activity or (EVA) refers to those often brief but dramatic moments when an astronaut leaves the safety of the spacecraft and ventures out, sometimes untethered, into space. Only 12 men have ever accomplished this feat on the moon, and it's been over four decades since it happened.
The Apollo astronaut crews only tested leaving the spacecraft once before Neil Armstrong walked on the moon in the Apollo 11 mission EVA. This test was done while orbiting the Earth by two astronauts on the Apollo 9 crew, David R. Scott and Russell Schweickart. Due to a delay when the camera recording the EVA needed to be fixed, Schweickart was afforded five minutes of uninterrupted time to just look at the Earth, and he has said the experience changed his life forever. His profound thoughts during those brief moments staring back at Earth focused on how far the human race had come and what his role in all of it was. He desribed it as, "This is humanity moving out, and you're just the representative on that frontier."
Starting with the Apollo 11 mission and all subsequent ones (aside from Apollo 13) through Apollo 17 each spent a longer time on the lunar surface and covered a greater distance than the one before. The Apollo 11 crew traveled just 200 feet from the Lunar Module, but the Apollo 17 crew were able to tackle a maximum distance of over 25,000 feet, almost 5 miles. In comparison to the distance of the Apollo 17 mission, the Mars Opportunity rover has taken eight years to match this achievement. For all of these excursions a brand new 14-layer spacesuit was required and had to be invented.
And speaking of the unique gift of experiencing the moon, have you ever wondered what the moon smelled like? According to Buzz Aldrin and Neil Armstrong, the moon dust smells like a mixture of gunpowder and wet ash!
Today the astronauts onboard the International Space Station are frequently required to perform an EVA in order to assemble or maintain the ISS itself. Astronauts have clocked in over 1400 hours on over 200 of these spacewalks so far. Other key 'spacewalk' missions include the Hubble Space Telescope. Orbiting 353 miles above the surface of the Earth, it was designed so that astronauts could perform repairs, replace parts, and update its technology during servicing missions - of which there have been five since its deployment in 1990.
The astronauts are physically tethered to the spacecraft and as an extra precaution their suits also carry a jet thruster system called Simplified Aid for EVA Rescue (SAFER) which they can control by joystick to maneuver themselves back to the spacecraft. Recently the engineers at Draper designed a self-return system within a spacesuit capable of determining its precise location. The visual and inertial navigation technology is also equipped with the ability to compute an optimal return path for the astronaut taking into account changing variables like oxygen availability and distance to guide an astronaut, even one that has lost consciousness to safety.
Unlike these ‘floating’ EVAs however, the astronauts on the moon during Apollo missions were totally untethered. The gravity of the lunar surface kept them from drifting off into the abyss, and they could always rely on their own boot tracks in the dust if they got lost. By physically walking on the lunar surface, astronauts were able to sample, test and return home elements of the moon itself. Relying on the self contained life support system of the space suits these EVAs also allowed us to experience for the first time how man could survive in an environment that wasn't Earth. Since the Apollo era ended, we've relied on robots and rovers to perform similar tasks, but none have given us the same sense of accomplishment and thrill as actual manned missions.