OPEBIMG THE 3PACB FRONTIERS
It is almost impossible to state precisely where the frontier of space begins - it could be anywhere in a region between 621 miles and 1.988 miles above Earth. "ithln it, the random collision ( CTOJIKHOBeHie ) of atmospheric gas Molecules ia neg-
llglble (He aHaHZT ) and the partloulate density of matter varies greatly. Also the region, the lighter gas molecules can escaps the gravity of Earth. From a historical viewpoint, however, the frontier can be considered as being at a much lower altitude:
some 99 miles. There, the atmosphere becomes very tenuous and the laws of aerodynamics give way to those of astrodynaaioa.
It ie this.region that was first probed by rocket as man began his systematic exploration of space, a voyage that took him from Earth's upper atmosphere, then into cislunar apace, to the Moon, and finally, to the sister planets of the Solar System.
Por many years, scientists were denied the investlganion of the upper reaches of the atmosphere except by observations from Earth and instruments lifted by aeroplane and sounding balloon. Earth observation had obvious limitations. Only a few "windows" were open in the atmosphere tor the receding of data, generally those in the optical wavelengths. Additionally, with time, the atmosphere at lower levels above the regions accessible to such observations started to become opaque because of both man-made particulate pollution as well as light pollution from his expanding cities. By the end of world War 2 nultl-en-gine aircraft had a ceiling of only 5 to 6*2 miles and the scientific sounding ballon could reach at beat some 19*9 alias. Geophysical Year, instrumented sounding rockets were launched in the USA from an altitude of some 18-6 miles by utilising balloons to lift them to that altitude before launch. Such rockets carried pay loads of 19'8 Ib to altitudes of 62'1 miles.
with the end of the war, both the USA and USSR found tif-selves with the means of penetrating to the upper reaches '/at the atmosphere with sizeable scientific payloads.
It was the A-4 (V-2) rocket.