Q&A: Chandra Mission

Q:
What X-RAY danger was there to the astronauts who placed Chandra in orbit?



A:
First, remember that Chandra is not an X-ray machine, but a telescope. Its mission is to detect and map X-rays produced by cosmic X-ray sources.

The X-ray photons that Chandra detects are very few in number, so they posed no threat to the astronauts. However, radiation from the Sun, especially in the form of high-energy particles produced in large solar flares, present serious dangers. Astronauts do not venture outside the space shuttle during a solar flare.

The harmful biological effects of radiation from the Sun must be minimized through mission planning based on calculated predictions and monitoring of dosage exposures. Preflight requirements include a projection of mission radiation dosage, an assessment of the probability of solar flares during the mission and a radiation exposure history of flight crew members. In-flight requirements include the carrying of passive dosimeters — little wafers of photographic film — by the flight crew members and, in the event of solar flares, the readout and reporting of the active dosimeters.

The radiation absorbed by humans is expressed in roentgen equivalent in man, or rems. In space shuttle flights, the doses received have ranged from 0.05 to 0.07 rem, well below flight crew exposure limits. For comparison, the exposure from a typical medical X-ray is 0.05 rem, and a 500 rem dose is usually fatal. A large solar flare can deliver 100 rem/hour or more.

For more information, visit: http://spaceflight.nasa.gov/shuttle/reference/shutref/crew/radiation.html (on NASA's site on Human Space flight)