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108 OUR ANCESTORS CAME FROM OUTER SPACE
puters establish the navigation data and corrections of trajectory,
which are transmitted by radio. Even the astronauts in Apollo
spacecraft who had a sextant and a telescope linked to
an onboard
computer did not make the slightest move without previous
approval from the Houston Space Center. The crew was advised
of all necessary maneuvers and the astronauts carried these
orders out without questioning them.
But the day is not far away when interplanetary spacecraft
will roam so far in space that they vdll be impossible to guide by
radio or check by radar from earth. What then? Again, the same
principle discovered by Austrian scientist Christian Doppler in
1842 and used for the first time by French physicist Armand
Fizeau to measure the relative speed of stars will come to our
aid. We will use the powerful radio signals transmitted by some
emitting stars to guide our spaceships. These invisible radio stars
are very powerful transmitters in space. Some keep sending continually
in the 21-cm band, on the frequency of atomic hydrogen,
1,420 MHz. Three of these sources that have been chosen to
guide our future spaceships are situated in the constellations of
Cassiopeia, Sagittarius, and Taurus respectively. The distribution
of these sources on the celestial vault is very favorable to the
navigation of interplanetary spacecraft, which are always
launched in a plane close to that of the ecliptic. Negative or positive
Doppler frequencies obtained with the aid of a computer
will guide our vehicles v^th great precision automatically, being
compared all the time with the real course with the program and
checked against the radio space markers of the stars. The radio
source of Cassiopeia, which is the strongest one and always "visible"
to radio telescopes at 40° N, is
subject right now to intensive
studies.
It is true that our forefathers did know electricity. Thousandsof-year-old
electrical batteries have been found around Baghdad,
Iraq, and a design for an electrostatic generator was discovered
in Dendera, in Upper Egypt. But they did not use electronic
gear to navigate around the world. Much simpler means were
available. They used currents and winds that year after year
flowed and blew in the same directions at the same time of
the year. Just like the travelers of not so long ago who had to
change from one steamship line to another to go to fara-