It became apparent early in the program that the X-15's could perform
a valuable function, not foreseen in the original planning, as reusable
carriers for a wide variety of scientific experiments. Some 15 such experiments
which have returned useful data are tabulated below:
Ultraviolet stellar photography
Simultaneous photographic horizon scanner
Optical degradation measurements and earth-resources photography
Infrared exhaust signature and earth radiance
Ultraviolet exhaust plume
Atmospheric density measurements
Rarefied - gas experiment
High altitude sky brightness
Solar spectrum measurement
Saturn thermal protection
A quick scan of the list reveals that all but a few of the experiments deal
with space problems.
Multiple experiments were carried on many flights, and the X-15 system,
unlike space rocket testing, permitted full recovery of the equipment,
recalibration, and repeat runs where needed. In nearly all cases use of
the X-15 was the least costly and quickest means of achieving the desired data.
Figure 18. Solar spectrum instrumentation in wing-tip pod.
An illustration of the solar spectrum equipment is shown as an
example in figure 18. The equipment is mounted in a wing tip pod, and
is exposed after the aircraft reaches the high altitude environment. A
second type of experiment involved testing the insulation of the Saturn
booster on the dive brakes of the X-15 where the severe real-environmental
heating situation of the Saturn could be duplicated (fig. 19).
Figure 19. Saturn insulation on X-15 dive break showing
flow-field rake and photographic reference grid..