Astronauts at Risk in Solar Proton Storms: STS-117 Atlantis and STEREO Prepare the Way for Safe Space Exploration with 3D

Astronauts are preparing to launch today in NASA's STS-117 Atlantis on a mission to the International Space Station (ISS). Starting at 1:30 P. M. you can watch NASA live TV coverage. Astronauts in space beyond Earth's protective magnetosphere is one step closer to becoming reality, and the threat astronauts will face from radiation sickness is one step closer to being solved.

NASA plans to have a lunar launch in preparation by 2011. The moon's sunlight side is exposed to 10 billion tons of solar proton radiation whenever there is a solar storm spewing coronal mass ejections (CMEs). These go hurtling at one million miles per hour into space. Any astronaut at a lunar station or on an extended mission to Mars would potentially be suddenly hit by 400 rems of radiation, enough to kill a person. What is NASA doing to solve the problem of solar CME radiation?

STEREO, or the Solar TErrestrial RElations Observatory, has begun sending back 3D images of the Sun, tracking solar storms and CMEs. With the binocular or stereoscopic vision of events on the Sun produced by STEREO's twin satellites, scientists can for the first time measure the speed and distance of CMEs and the proton storms that precede them. These measurements provide a crucial step toward predicting upcoming solar radiation events. Astronauts could be warned and given time to run to shelter as a result of advance warnings based on accurate predictions.

Currently, SOHO is the primary source of solar information. It is in a heliocentric orbit (orbiting around the Sun) positioned between Earth and the Sun. SOHO sees events in a straight-on manner from one perspective, so measurements of speed and distance are unreliable because there is no perspective and no corroborating known measurement data.

STEREO overcomes this limitation because STEREO is not one satellite but two almost identical satellites. The Ahead satellite (A) orbits in a heliocentric orbit ahead of Earth and the Behind satellite (B) orbits behind Earth. They are almost aligned on Earths orbits, but A is slightly forward of Earth's orbit and B is slightly further back. Earth orbits the Sun in 365 days, A orbits in 346 days, and B in 388 days. It is these distances and variables that allow STEREO to send back 3D images of the Sun's activity.

Peter Sharon, engineer and designer of STEREO, explains to host Ray Gard, on a radio broadcast of the Australian Broadcast Company, that STEREO was launched into an Earth orbit on one rocket instead of two. He also explains that two separate lunar swing-bys were employed to provide lunar boosts to propel first A and then B into outer space solar orbits. These separate lunar boosts were necessary to position them ahead and behind of Earth. To maintain a heliocentric orbit, the speed of the spacecraft has to be equal to gravitational pull to keep them suspended in a free-fall around the Sun, as accords with the first three Newtonian laws. It is the triangulation achieved via different orbits and different angles that permits STEREO to collect data relevant to the prediction of solar radiation from CMEs. Known values are the speed and location of spacecraft A and B.

NASA's projected lunar expeditions include robotic and manned exploration, prospecting, and building. There will be green houses, power stations, and habitats on the moon. CMEs, and the proton storms that are expelled by CMEs and which travel at even greater speeds, can occur suddenly. The matter and high-speed radiation are hurled at Earth and into space. About one billion tons of solar mass are ejected during a CME. It travels at one million miles per hour. It takes about 20 minutes to reach Earth, but the radioactive particles in the shock wave that precedes the mass reach Earth in under 10 minutes. These hit the moon as well, but the moon is not protected by Earth's magnetosphere. Any astronauts on the moon outside of a shelter during a sudden solar storm, as occurred on January 20, 2005 when an enormous solar flare exploded, would potentially be exposed to death. At best, the exposure would lead to solar radiation sickness with vomiting, fatigue, and low blood counts.

In order for NASA's plans for lunar exploration and outposts to go forward expeditiously, it is paramount that solar storm activity be understood. It is only through the data to be collected by STEREO that precisely accurate predictions can be made and warnings implement to safeguard astronauts, robotics, and equipment, such as those aboard ISS and Atlantis. This is especially true when astronauts are performing Extra Vehicular Activities (EVAs), as they are outside the protection of ISS. You can see STEREO's first images for yourself with the help of a pair of 3D glasses. Just go to http://www.nasa.gov/STEREO.