With 4 days to go, we can start to ask the question: What will the weather be like on Saturday? At the moment there’s a 70% chance of suitable launch weather on either Saturday or Sunday. So things are looking good…
Yesterday we talked about the Sample Analysis at Mars (SAM) instruments. Today we’ll talk about a simpler, but nonetheless important piece of equipment: the Radiation Assessment Detector (RAD). Data from RAD will provide the first measurements of radiation on the surface of Mars (it will also operate during the flight to Mars) and allow us to answer a very important question for any human missions: What would be the radiation dose on the surface? Knowing this answer is a big deal: unlike the Earth, Mars does not have a big magnetic field to shield it, or a thick atmosphere to shield against cosmic rays.
RAD will measure the three main types of radiation, alpha, beta and gamma. Alpha radiation, which is the easiest radiation to shield against, corresponds to particles containing two neutrons and protons (the same as a helium nuclei). Beta radiation, which is slightly harder to shield against than alpha particles, corresponds to high energy electrons or positrons. While gamma radiation corresponds to high energy photons, and, depending upon the energy of the photons, can need inches of lead to provide adequate shielding. In addition to these forms of radiation, RAD will also detect cosmic rays which are made of high energy atomic nuclei stripped of their electrons as well as other particles such as neutrons. For the experts, here is a graph of the energy coverage for each of the different particles RAD will detect:
RAD will sit on top of the body of Curiosity. It isn’t very big, roughly the size of coffee can, and at first take isn’t all that impressive looking. It’s essentially a very short and “stubby” telescope with detectors behind it that will capture the various particles associated with the radiation. The particles are detected by essentially two methods: The first is through a process called scintillation, whereby the energetic particles in the radiation cause a target material to undergo luminescence when hit (the light is then detected). The second method is through striking a semi-conducting material which creates an electric current that can be detected. It’s also possible to use these interactions to determine the overall energy of the incoming particle. In all, RAD contains five separate detectors which combine to give it both an excellent coverage in terms of the energies of incoming particles, and also the specific types of radiation. RAD is sensitive to particles coming in from above through about a 65 degree cone of coverage.
While RADs measurements will enable us to determine how hazardous the Martian environment is for humans, this data can also be used to determine what kind of life could survive on the surface now, and also in the past as well (it’s even possible to calculate how far down into the Martian surface life would have to be to avoid any lethal radiation levels). The radiation levels can also be used to infer what kind of mutation risks the environment presents for lifeforms based on DNA. Lastly, from all the new data it will be possible to determine how much of an impact the radiation background has had on the chemistry and isotopes in the Martian environment.
Bottomline: from the human exploration persepective, RAD well tell us just how inhospitable the Martian environment is!
Tomorrow: the Rover Environmental Monitoring Station (REMS).