The harmful biological effects of radiation 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 by the flight crew members and, in the event
of solar flares or other radiation contingencies, the readout and
reporting of the active dosimeters.
There are four types of active dosimeters: pocket dosimeter high,
pocket dosimeter low, pocket dosimeter FEMA and high-rate dosimeter.
All four function in the same manner and contain a quartz fiber
positioned to zero by electrostatic charging before flight. The
unit discharges according to the amount of radiation received; and
as the unit discharges, the quartz moves. The position of the fiber
along a scale is noted visually. The PDH unit's range is zero to
100 rads. The PDF and PDL units' ranges are zero to 200 millirads
and the HRD unit's range is zero to 600 rads.
The rad is a unit based on the amount of energy absorbed and is
defined as any type of radiation that is deposited in the absorbing
media, and radiation absorbed by man is expressed in roentgen equivalent
in man, or rems. The rem is determined by multiplying rads times
a qualifying factor that is a variable depending on wavelength,
source, etc. For low-inclination orbits (35 degrees and lower),
the qualifying factor is approximately equal to one; therefore,
the rem is approximately equal to the rad. In space transportation
system flights, the doses received have ranged from 0.05 to 0.07
rem, well below flight crew exposure limits.
The flight crew's passive dosimeters are squares of fine-ground
photo film sandwiched between plastic separators in a light-proof
package. Radiation striking the silver halide causes spots on the
film, which can be analyzed after the flight. Included in the badge
dosimeters are thermoluminescent dosimeter chips, which are analyzed
Passive radiation dosimeters are placed in the crew compartment
before launch by ground support personnel and removed after landing
for laboratory analysis. Each flight crew member carries a passive
dosimeter at all times during the mission. The remaining dosimeters
are stowed in a pouch in a middeck modular locker. If a radiation
contingency arises, the PDL, PDH, HRD and PDF active dosimeters
will be unstowed, read, and recorded for downlink to the ground.