"It's a good question," answered Holt. "Perhaps you didn't notice that we did not increase our speed exactly tangent to the Lunetta orbit, but slightly on a chord-line dipped towards Earth. We'll reach the perigee mid-point of our coasting flight and intersect the Lunetta orbit near the observatory."
"I understand," said Hansen. "But don't we have to compute our flight very accurately in advance so that we shall really hit the observatory and not go wandering off into space somewhere? I am always amazed when we get into these bees without any preparation whatever and push off into nothingness! It doesn't seem to be any different from getting into the car and driving to the market. Why, there isn't even any traffic problem!"
"Professor, you must remember that this is really a very short trip. Space navigation isn't so very different from water navigation. For a transatlantic journey, it's a good idea to do a lot of calculation before you get under way, and to plot your course on the chart.
But you don't go to all that trouble to row across a pond. Our lads up here have soaked up Kepler's laws pretty thoroughly, and these little ferry trips are duck soup to them."
Hansen still wasn't satisfied. "How about the 2,000 kilometer jaunt to the two military stations about which Riley spoke, even if they are in the same orbit? Is that kind of ferry trip just a row across a pond, too? Or is 2,000 kilometers considered quite a respectable ocean voyage?"
"Oh, that's an ocean voyage all right," laughed Holt. "Ferry trips to those stations call for an entirely different brand of navigation from that used on this little hop.
"A busy bee enroute from Lunetta to the Control Station ahead of Lunetta reduces its orbital velocity by about 140 meters per second. This puts it into an elliptical orbit, the perigee of which is only 1,266 kilometers above the Earth's surface. Of course, that's still high enough to keep it clear of the atmosphere's upper limits. When the bee enters upon the second branch of this ellipse, it is again heading for Lunetta's orbit, which it intercepts after a full revolution around the Earth. But this elliptical path is, when averaged, somewhat closer to the center of the Earth than the orbit of Lunetta and her auxiliaries, and according to Kepler's Laws, the time the bee takes to circle the Earth is somewhat shorter than that taken by Lunetta and company.
"For a trip to the Control Station, the bee's ellipse is selected so as to require exactly 274 seconds less than the two hours that Lunetta requires for a complete encirclement. Thus the busy bee, contacting Lunetta's orbit after a complete encirclement of the Earth, is at the exact point to intercept the Control Station, 1,935 kilometers ahead of Lunetta.
Then the bee must perform an adaptation maneuver, exactly like the one we experienced aboard the Sirius, in order to bring its velocity up by 140 meters per second, the amount required to equal the orbital velocity or the station.
"The principle used to reach the Bomb Bay trailing the Main Station is identical. Only, in this case, a complete ellipse is used which, rather than approach the Earth, becomes more distant from it. This causes the time of encirclement of the Earth to become somewhat longer than that in Lunetta's orbit, so that the bee intercepts the trailing Bomb Bay this time."
As Holt finished his explanation, they could see the enormous sickle-like arc of the Earth ahead of them and to the left. Despite the fact that their bee was bathed in the brightest sunlight, the Earth below them was still wrapped in darkness. So brilliant was the illumination of what they might well have referred to as the "crescent Earth" that theycould make out no contrasts where the light fell.
Holt threw a glance at his watch. "We ought to be passing over Alaska in a moment," said he.
"Did you say Alaska?" asked Hansen incredulously.
"Sure, Alaska. We ought to be right over the Northeast Aleutians, headed for Anchorage, Alaska. Look, it's just 23:30, Hawaiian time. Two hours and fifteen minutes ago is just about when we started from Kahului. In the meantime, Lunetta's been around the world once, and a little more, but at the same time, the Earth's rotated to the Eastward some 34 degrees."
Hansen looked puzzled. "I may be an astronomer," said he, "but you'll have to go a little deeper into that one."
"Here's the way it is: the Earth rotates once every 24 hours — 360 degrees; that's 30 degrees for every bi-hourly encirclement by Lunetta. Lunetta makes 12 encirclements every 24 hours. If these were projected onto the Earth, they would make a spiral tracing across the Earth's whole surface between the Arctic and Antarctic circles. That's the joker in the military omnipresence of Lunetta! Lunetta will not be right over Kahului until some 12 hours after her last transit, and then she won't be moving on a Northeasterly course as she was when we took off, but on a Southeasterly one. Due to that, I cannot land back in Kahului until about 12 hours after leaving there.
"But speaking of Alaska, it's mostly heavily clouded over in this region. The sharp illumination you see on the Earth is only the reflection from the upper surfaces of the clouds.
"And did you notice that we were flying for almost an hour through the umbra of the Earth when we were breakfasting with Riley? Now the Sun's ahead of us once more, so we'll have daylight for the next hour."
The busy bee had approached within about a half mile of the observatory, and what had seemed to be a glittering little disc was now a silver sphere with a number of circular port holes. As they drew closer, there was another detail that heretofore had remained invisible against the sepia, star-spangled sky. This was a cylindrical object, apparently of latticework construction. It floated free in space, connected to the sphere only by a cable.
"So that's the 100-inch reflector," said Holt. "When I was stationed in Lunetta we had a dinky, little 60-incher out here. It was a pretty primitive gadget for some of the work."
"This is really a wonderful instrument," said Hansen. "Optically it's far more efficient than the old 60-incher and it's got a lot of other improvements. You'll notice that the 'scope is wholly detached from the observatory proper. We made this arrangement to avoid any shocks to the reflector from people moving in the observatory. With the integrally mounted 60-inch job, we had to keep the whole crew absolutely quiet and even shut off the blower during an observation. If we didn't, the image would flicker."
"Where's the seat for the observer in this case?" asked Holt.
"When an observation is being made, he's in a small cylindrical chamber that moves from the observatory to the 'scope. It has room for two observers and the necessary photographic and spectroscopic equipment. It has a small rocket plant like a bee. The chamber slips into guides attached to the 'scope so that the eye-piece, which is integral with one of the walls, registers properly and accurately with the optical axis. The observer simply replaces the eye-piece with a camera for photographic work."
"Having the 'scope and the observatory separate seems to me tremendously involved," remarked Holt.
"Look, Colonel," answered Hansen, "on Earth we're forced to keep our telescope foundations entirely separate from any other buildings or structures to avoid the transmission of vibrations. We have no heavy foundations here in space and our 'scope would vibrate fearfully if we didn't isolate it from any possible movement of the observatory.
"As you know, stellar observatories on the Earth require complicated suspension systems for their telescopes, and these suspensions are made to follow the apparent movements of the heavens by clockwork or electric drives. No such mechanisms are needed up here in space. When the observer seated in his tank has secured the latter to the telescope frame, he can turn the whole business in any desired direction by means of three electrically driven flywheels, and keep it pointed steadily at its object in the same way.