FIRST STEPS TOWARD SPACE - Smithsonian Institution Libraries

72 SMITHSONIAN ANNALS OF FLIGHT
lift and life? Has there yet been conceived by human genius,
or does it yet exist in embryo, an engine capable of thrusting
a vehicle into the vacuum of space.?
For many years it has been recognized that such an engine
does exist. One need only to think of a machine-gun free
to recoil on its own carriage while launching shells at great
velocity in order to concieve of a propelling unit which
would operate better in a vacuum. In any case, the principle
of the so-called reaction engine is well known. The problem
is to determine whether the energy required to attain this
goal does exist, or whether we here face an insuperable
natural barrier.
It is known that the energy necessary to transfer a body
from the surface of a star to infinity is given by
L-K
mM
where A' is the universal gravitation constant, m the mass
of body, M that of the star, and R the radius of the star.
From this formula, it follows that a body on the Earth's
surface, launched with a velocity equal to or larger than
11,280 m/sec, will not fall back but will continue traveling
indefinitely. For a 1-kg body on the Earth, the energy to
attain this velocity would be 6,371,103 kgm, equivalent to
14,970 cal. Now 1 kg of hydrogen-oxygen mixture contains
a much smaller amount of energy, i.e. 1,420 cal-*; therefore
I kg of such a mixture has not within itself the capability
of transfering even a single gram of its own substance to
infinity.
On the other hand, 1 kg of radium, which contains
2,900,000,000 cal, would have an energy 194,000 times greater
than the amount required of it.
Esnault-Pelterie has shown that a body on the Earth
subjected to a constant force greater than its weight and
directed outwards would attain a velocity sufficient to make
its propulsion superflous at an altitude approximately equal
to an Earth radius.
Let us analyze the order of magnitude of the energy involved
if one were to transfer, for example, a body from the
Earth to the Moon and bring it back again to Earth. Three
phases are to be considered:
First phase: the body accelerates up to an altitude of 5,780
km; then its velocity will be 8,180 m/s and the time spent
24 minutes and 9 seconds;
Second phase: the engine is cut off; the body continues to
move on account of inertia; at the moment where the
attraction of both Earth and Moon become equal, the
velocity will be reduced to 2,030 m/sec and the time spent
will be 48 hours and 30 minutes;
Third phase: the engine is accelerated in the opposite direction
for descent onto the Moon; the time spent during
this phase is 3 minutes and 46 seconds. The total elapsed
time from departure will be 48 hours and 58 minutes, and
that for return will be the same. During this return trip the
engine will operate only 28 minutes, the time being the same
both going and returning.
Now let us assume that the vehicle weight is 1000 kg, of
which 300 are consumable (this ratio is customary for
present-day airplanes). A short calculation shows that the
engine power should be 414,000 hp. Such a vehicle at the
speed of 10 km/sec would spend 47 days and 20 hours to
reach Venus and 90 days and 15 hours to reach Mars.
The analysis of probable sensations of a space traveller
during the trip deserves particular attention. Aside from
difficulties arising from the temperature and space radiations,
there exists a probably serious one of a physiological character.
At a distance of 5,780 km from the Earth the traveller
will feel as though his weight was eleven tenths of his
normal weight; this feeling, though unpleasant, will not be
prejudicial to his organism. But, when, during the second
phase, weightlessness occurs, he will have the feeling of
falling with the vehicle which contains him. Then it would
be necessary to replace the force of gravity by a constant
acceleration of the engine so controlled as to provide an
acceleration that will at every moment replace the loss of
gravitational pull.
This method would eliminate the above mentioned inconvenient,
but would cause a progressive increase of velocity to
61,700 m/sec in the case of a lunar trip, with the advantage
of reducing the required time to 3 hours and 5 minutes; but
the required power would be 4,760,000 hp. Then, even
though the above assumed 300 kg of propellant were dynamite,
it would amount to -r^-o^jr of the propellant necessary;
but if radium were used it would still be 433 times that
required. Travelling at a constant acceleration, Venus could
be reached in 35 hours and 4 minutes with a maximum
speed of 643 km/sec and Mars in 49 hours and 20 minutes
with a maximum speed of 883 km/sec.
The order of magnitude of such velocities is that of the
celestial bodies, and in order to obtain the necessary energy
concentration at the start it would be necessary to seek them
among atomic forces.
If a 1000-kg vehicle had on board 400 kg of radium and
we were able to extract from it the required energy, we
would have available the amount of propellant sufficient to
a round-trip to Venus; but this amount would be hardly
sufficient for an analogous trip to Mars, always assuming a
flight with constant acceleration.
Thus the difficulties that prevent us from achieving this
ultimate human dream are not beyond human reason, but
are dependent only on the possibility of a practical realization
of the necessary means. Having observed the prodigiously
accelerated development of findings in the field of
mechanics, we can therefore doubt but cannot deny such a
possibility.
On the other hand argument and speculation are useless
and unfruitful. The world advances, driven by tenacious
willpower rather than by words and formulae. Perhaps
scientists will still be arguing when the first auto-meteor
penetrates interplanetary space.
Some comments on Costanzi's text seen appropriate.
His clear intuition as to the advantage, from an
economical point of view, of flying at high altitudes,
of the need for jet engines, and of the
enormous propellant consumption required by
space flight, is remarkable.