"The principle's simple enough. You know Newton's Law that to every action there's an equal and opposite reaction. So, if we start a wheel attached to a free-floating object in space turning clockwise, it exerts a rotating moment of equal power and makes the object rotate counterclockwise. If the wheel is much smaller than the object to which it is attached, it will, of course have to turn quite a number of times before the object proper makes one full turn in the opposite direction. Nevertheless, you can turn a body of considerable dimensions, when free-floating in space, with a relatively small, high-speed, electrically driven flywheel or disk. That is, if no very rapid rotation of the body itself is required.
"Our telescope here is equipped with three such inertia disks whose axes are at right angles to one another. This permits it to be turned arbitrarily to any angle in space and to be maintained there."
"We use the same principle in our space ships," said Holt, "to bring them to the proper heading for their various maneuvers. But look, we are making fast."
The pilot of the busy bee had cut in his decelerating motor and skillfully aimed his craft at the opening in a cylindrical shaft that protruded from the great, round ball in a radial direction. The bee slipped into a set of three guide-rails which diverged somewhat at their outer ends. There was a slight clicking sound and the light was blocked off from the great windows. The bee came to a stop with a slight jarring deceleration.
The pilot rose and opened the circular door just above their heads. This was followed by the opening of a second door just above it in which the face of a blond youth appeared.
"Well, Bergmann, I'm glad to see you!" exclaimed Hansen.
"Good morning, Professor. It's good to see you up here with us again. We've a lot of new stuff for you. And you must be Colonel Holt, aren't you?"
"Right. Glad to know you. Since weightless conditions prevailed in the non-rotating sphere of the observatory, they drew themselves hand over hand along a rod which was axially located in the spherical chamber. It led to a room with circular walls which represented the middle floor of the observatory. This room was filled with all sorts of measurement gear and electrical switchboards, and gave the appearance of being a laboratory for electrical experiments.
At one side of it there was an oblong table with a few low chairs near it. Dr. Bergmann introduced two of his youthful coworkers and then they drew themselves down onto the chairs and donned the belts which were necessary to hold them there.
On the table before them lay various documents and pictures which were carefully held onto the surface of the table by steel clamps. This was to prevent their drifting about the room as a result of their weightlessness. Bergmann drew a large, colored photograph from a folder with the statement that it had been made but one week earlier and that it was the best one achieved so far. On, this picture, the image of the planet Mars appeared about a foot in diameter. Of a raw whiteness, the famed south-polar cap of Mars stood out in the upper part of the picture.
Below it and dull bluish-green in color was a large, similarly shaped area, the Mare Australe. As the eye moved towards the Martian equator, the picture became more confused. There were sharply rimmed spots and indefinitely outlined zones of all shadings from reddish brown to dark yellow, alternating with greenish-blue to grayishblue areas. But throughout the whole region there ran a series of fine, dark green lines gracefully curved and following the vaulted shape of the Martian globe. These were the famous and controversial Martian canals. The contrasts on the face of the disc were much paler near the edges. It was apparent that the light at these points had had to travel a much greater distance through the atmosphere of Mars than elsewhere before emerging into interstellar space. This gave an almost plastic and stereoscopic aspect to the photograph.
Holt regarded the image silently and reverentially for a long time, unable to conceal the emotional impact of his thoughts.
Finally he spoke. "It is really a second Earth. But what a mysterious, strange one… The continents float in no oceans. There are no rainy zones, shrouded in cloud. But the view of this picture leaves us almost no room to doubt the existence of intelligent inhabitants. No photograph of this size made from Earth would reveal such obvious testimony of the workings of intelligence."
"You're a member of the planning staff of Operation Mars, are you not, colonel?" asked Bergmann when Holt had again fallen silent.
"Colonel Holt will have command of the expedition!" interrupted Hansen solemnly. The young astronomers present looked upon Holt with surprise followed by joyous enthusiasm. Their questions poured over him in a torrent which lasted until he had answered every one. When it was over, Hansen spoke again. "Dr. Bergmann, please tell Colonel Holt briefly the essential things which we know about Mars in relation to their importance to the expedition. Do not forget any aids to observation and methods of measurement which we have available. We propose to discuss an all-embracing new work plan in relation to what you will have reported."
Chapter 4 — Let's Talk About Mars
Doctor Bergmann began his exposition. "Mars is the fourth of the nine major planets of the Sun. The orbits of Mercury, Venus and Earth lie closer to the Sun than its orbit, while those of Jupiter, Saturn, Uranus, Neptune and Pluto lie outside of it.
"The elliptical orbit of Mars around the Sun is of considerably greater eccentricity than that of the Earth. At perihelion, when Mars most closely approaches the Sun, it is 206 million kilometers away from it; at aphelion, however, the distance is 249 million kilometers. Hence its mean distance is 228 million kilometers. The Earth, whose orbit is nearly circular, has a mean distance of 149V2 million kilometers from the Sun. The Earth's aphelion and perihelion differ from this mean distance by but five million kilometers, roughly.
"The orbit of Mars lies in a plane at an angle of 1 degree and 51 minutes of arc to the plane of the ecliptic, which means that Mars and the Earth rotate around the Sun almost in the same plane.
"Mars requires about 687 Earth days for a full revolution around the Sun, and this may be considered as a Martian year.
"Mars rotates around its own axis once in every 24 hours, 37 minutes and 22.7 seconds, making the Martian day only slightly longer than the Earth day, so that the Martian year has 569.6 Martian days.
"The rotational axis of Mars is inclined to the plane of its orbit by 24 degrees, which is very close to the inclination of the Earth's axis to her orbit, namely 23.5 degrees. This gives Mars seasons like those of the Earth.
"The diameter of Mars at the equator is 6,780 kilometers, while when measured along the polar axis, it is 35 kilometers shorter. This is a little more than half the diameter of Earth.
"The mean density of the planet is only 72 % of that of the Earth. Its mass is proven to be approximately one tenth of that of the Earth, within close limits. These figures yield an acceleration due to gravity at the surface of Mars as equivalent to only 38 % of that of the Earth, or 0.38g.
"Mars has two very small moons, Phobos and Deimos. Phobos is very close to its mother planet, its mean distance from the center of Mars being equivalent to only 2.77 radii of Mars. It circles the planet in 7 hours, 39 minutes and 14 seconds, doing so several times a day, somewhat similar to Lunetta circling the Earth. Viewed from the surface of Mars, it would rise in the west and set in the east. Its orbit is noticeably eccentric. Apparently its diameter is but a few kilometers.
"The other moon, Deimos, lies at a distance from Mars of a scant 7 radii of the latter and requires about 30 hours and 18 minutes to encircle it. We estimate its diameter at 10 kilometers and its orbit is circular within close limits."