What Else Makes Observing Cosmic Rays Hard?
About 90% of the cosmic ray nuclei are hydrogen (protons), about 9%
are helium (alpha particles), and all of the rest of the elements
make up only 1%. Even in this one percent there are very rare
elements and isotopes. These require large detectors to collect
enough particles to say something meaningful about the "fingerprint"
of their source. The HEAO 3 Heavy Nuclei Experiment, launched in 1979,
collected only about 100 cosmic rays with charges between 75 and 87
in almost a year and a half of flight, and it was much bigger than
most scientific instruments flown by NASA currently. To make better
measurements requires an even larger instrument, and the bigger the
instrument, the greater the cost.