~ * ~
They approached Titan from an unconventional angle.
Sexdent’s
orbit was in the plane of the ecliptic, while Titan’s orbit was tilted at almost twenty-six degrees because of Saturn’s tilted axis. The burn at Titan was minor, only one minute at three gees. That burn put them into a long elliptical orbit about Titan that took them almost out to Titan’s leading Trojan point. Another minor correction there, and they were stopped among the small collection of ice chunks that had collected at the weak gravity minimum region over the eons.
“There’s a nice egg-shaped hundred-meter iceberg over there,” said Chastity from her pilot’s console. The acceleration couches had been removed from the control deck floor and stored in the airlock and the swivel-arm chairs had been installed in front of the control consoles. “It’s tidally locked to Saturn in all three axes, so its orientation is perfectly predictable.”
“Looks good to me,” said Rod. He had rearranged the icons on the third console so that it was back to being the commander’s console instead of a science console. “Are we ready for separation, Seichi?”
“Rendezvous stage safetied and vernier control tanks full,” reported Seichi from the engineering console.
Rod tapped a red icon on his screen and the clattering sound of clamps releasing rattled through the hull.
“It’s all yours, Chass,” said Rod. “Take the rendezvous stage away a few hundred meters and hold it there ‘til I back
Sexdent
out of the return stage.”
Chastity activated her screen, flew the large empty rendezvous tank out from behind them, and brought it to a halt in the distance. Rod, using the vernier jets on
Sexdent,
brought the nose of the spacecraft up close to the side of the iceberg.
Sexdent
still wore the return stage fuel tank around its “waist,” somewhat like the spare tire Pete wore around his waist.
“Return stage ready, Seichi?” Rod asked.
“Ready.”
Rod pushed another red icon, and another set of clatters indicated that
Sexdent
was now separated from the donut-shaped fuel tank it had been carrying. Carefully, Rod backed
Sexdent
out of the hole in the fuel tank, leaving it floating in front of them, about ten meters away from the hundred-meter block of ice.
“Set the return tank module on autopilot, Jeeves,” Rod commanded. “Maintain present orientation at ten meters’ separation distance.”
“Very good, sir,” said Jeeves, sending commands to a similar semi-intelligent program in the computer that resided on the return stage. Two of the vernier jets on the donut-shaped object fired to stop a small amount of residual rotation that had been left from Rod’s exit maneuver and the tank full of meta became still.
“Now, stay there until we get back,” ordered Rod.
“And don’t get any holes,” added Chastity.
“Okay, Chass,” said Rod. “Fly the rendezvous stage in.”
Chastity activated her control board and brought the nearly empty rendezvous stage up until it was ten meters away on the other side of the donut-shaped tank that contained the fuel that would take them back to Earth. The autopilot on the rendezvous stage was set to maintain station on the opposite side of the return fuel tank from the iceberg. The two large masses would provide shielding for the return stage from incoming space debris objects.
“Okay,” said Rod, turning from the pilot console to look at the watching crewmembers in back of him. “Time for a complete system check before we commit.”
For the next few days, the crew was busy checking every system and item of equipment on the ship—for their lives would depend upon everything functioning properly.
Pete spent most of his time in the meta-manufacturing facility nestled under the spacecraft proper. Since the thirty-five-ton factory would be cut loose and left behind when the spacecraft lifted off from Saturn at the end of their mission, no provision had been made to access the factory from inside the crew compartment. It would have added mass and decreased their chances of completing the mission, so Pete got lots of practice putting on and taking off his spacesuit as he moved back and forth from the factory and the crew compartment.
Mass was at such a premium that “plumber” Dan even emptied out the solid waste storage tank on
Sexdent.
The frozen vacuum-dried brown material was put into storage bags and sent out into space.
“Aren’t you going to at least burn them up by deorbiting them?” asked Chastity primly as she saw the collection of bags growing outside one of the viewports.
“Nope,” said Dan, as he prepared to exit the airlock with another odoriferous reminder of the excellent meals they had enjoyed in the past year. “When they set up a permanent manned station here at Titan to monitor the meta factories down on Saturn, this will be
just
the stuff to fertilize the hydroponics gardens.” Chastity reminded herself not to visit the monitoring station.
After checking all the equipment inside the capsule, Rod, Chastity, and Seichi went outside to check everything there. Seichi examined the heat shield that covered the bottom of the ship. The heat shield had ports that swung aside to allow passage of the exhaust flames during their deceleration bum, then swung back to protect the nozzle bells as the ship entered the upper atmosphere. He activated the doors on each one of the twelve ports, checking to make sure that they seated tightly, then checked the release mechanism that would drop the five tons of heatshield after it did its job. He then checked out all the engine bells and magnoshielded nozzles. Each one took a number of hours, so he too was in and out of his spacesuit many times during the days of the checkout period.
Rod and Chastity helped Seichi with the engine checkout, activating the magnoshield from inside, while Seichi reached up into the nozzle bell with a magnetometer to check the field configuration. The two also examined the parachute, balloon, and shrouds that would bring them to a halt in the clouds and float them there during their six-month stay on the giant planet.
“That’s the trouble,” said Rod with a resigned shake of his head as he and Chastity looked at the neatly laid-out shrouds on top of fold after fold of tough fabric. “The only way to
really
check out a parachute is to jump with it.”
~ * ~
Finally, they were ready. At dinner that night, Rod announced, “Mission Control says they are set up and ready to have us climb down the rings. As soon as Rhea is in the right position, we’ll do a burn at Titan and drop down to our first ‘rung’ on the ladder.”
Sandra, puzzled, asked Rod a question. “What I don’t understand is how come if
Sexdent
is able to climb up out of Saturn’s gravity well using its rockets, why can’t it use its rockets to climb down?”
“ ‘Cause of the extra mass we have to carry down,” said Rod. “If all we had to carry was the fifty-ton main capsule, the hundred and twenty tons of fuel in the tanks of the main capsule would do the job. But we also have to take down the thirty-five-ton meta factory, the five-ton heat shield, and the ten tons of balloon and shrouds—another fifty tons. We’d ran out of fuel trying to slow down that load—and burn up. So we’ve got to take it in steps—using every trick in the book—to climb part of the way down the gravity well using the moons and rings—while saving our fuel for that last big step down into the atmosphere.”
~ * ~
When the orbits were just right, Rod drifted
Sexdent
over to Titan and let it fall in toward the smoggy moon on an essentially parabolic orbit. At the point of their closest approach Rod fired the rockets for about half a minute at one gee.
“We’re on our way,” he reported. “We’ll be at Rhea in five days.”
“Let’s have a party!” suggested Pete, but then he noticed that everyone had a concerned look on their faces. They were committed now ... to a very risky mission ... a mission that might cost them their lives.... He dropped the idea.
~ * ~
As they approached Rhea, Sandra got some good images of the bright, crater-covered moon.
“Just a well-worked ball of ice,” reported Sandra, looking critically at the images she had collected. “Not much different from the bright side of Iapetus.”
Rod brought them to a halt at Rhea with a half-minute burn at three gees.
“We’ll have to wait here until the orbit timing of all the moons we’re going to use is right,” he said.
“Here we are... right outside the E ring,” said Sandra, looking at the fine line across the sky that indicated the plane of the rings, “but I can’t get any pictures—wrong angle. Have to make do with Saturn.”
Soon she and Dan were back at their task of imaging features on the rapidly rotating face of Saturn. The giant planet now covered thirteen degrees of the sky—almost filling the holoviewports.
~ * ~
“Mission Control says the time for the next drop down is early tomorrow,” announced Rod a few days later.
“What’s the next stop?” asked Pete. “Dione? That’s the next big moon inward.”
“Not quite,” said Rod. “We’re going to leave sixty degrees early so we drop down on Dione’s Trojan companion, Helene, instead. It’s just the right size for Chass to try a tether whip maneuver. Save us some fuel.”
The next day, at their closest approach to Rhea, Rod fired the rockets for only ten seconds. But that was enough to drop them downward again. Their trajectory skimmed only a few hundred kilometers above the E ring and Sandra got excellent pictures. For the next two days, they watched as Saturn loomed ever larger in their viewports.
“The white spot is catching up with Brown Spot One again,” reported Dan from the biviewer. “You ought to get a shot of it.”
“As soon as we stop, I’ll take pictures of Saturn, but right now I’d better concentrate on the E ring,” replied Sandra.
“We’re not going to stop,” said Chastity, who was controlling the orientation of
Sexdent
for the two scientists. “With a tether whip, you leave as fast as you came.”
“Oh!” said Sandra. “Then you’d better turn us around so I can shoot Brown Spot now.”
~ * ~
Sexdent
soon caught up with Helene. It was a free-floating potato-shaped megamountain about thirty-five kilometers in diameter. Rod, Chastity, and Seichi were at their stations, while the other three looked over their shoulders from their handholds on the ladder that ran through the center of the ship. The acceleration levels expected during this tether whip maneuver weren’t large, only half a gee, so they didn’t have to strap down on acceleration couches as they did for the rocket bums.
“We’ll be catching up with her at eight hundred meters per second,” reported Rod as the elliptical orbit of
Sexdent
started to intersect the circular orbit of Helene. “It should be a nice easy practice run for you. I’m ready with rockets in case you miss.”
Chastity’s long-nailed fingers flew over the keyboard to bring up a seldom-used menu on her screen. She touched the icon that flipped back the conical nosecone of
Sexdent,
exposing a metapropelled penetrator inside, its sharp tungsten-carbide tip pointing outward. Some hours ago, Jeeves had used its mechbot, Mouser, to move the penetrator from its storage rack on the wall to the launcher, and hook the flame-resistant metal-braid “tail” of the penetrator to the end of the two-hundred-kilometer tether stored on the reel.
Rod, working in concert with Chastity, used the attitude jets to direct the nose of
Sexdent
toward the still-distant moonlet.
“Launch,” said Chastity quietly as the penetrator took off using a low-temperature exhaust of warm helium gas. After the penetrator was well clear of
Sexdent
the exhaust flame brightened into a reddish-purple plasma. The penetrator accelerated toward its target, dragging the tether behind it—the multiline structure automatically dilating to its extended shape as it was pulled from the reel.
Chastity had a plan view of the action on her console screen and a view from the penetrator’s nose camera on the holoviewport. Her manicured right hand was in the controller’s box under the console, directing the flight of the penetrator as her eyes alternated between the holoviewport and the console screen.
“We need to get a little closer, Rod,” she said, tapping the image on the console touchscreen with the tip of a long glittering-gold fingernail. “I want a closest distance of a hundred and sixty.”
Rod tweaked the joyball in the controller’s box under his console. The vernier jets on
Sexdent
gave a short burst, the projected path line of the spacecraft shifted slightly, and the number indicating the distance between the trajectory of
Sexdent
and the trajectory of the asteroid at their point of closest approach changed from 210 to 160. He kept a close eye on that number and his hand ready around the joyball, in case the number started to change, but he couldn’t help glancing out the viewport in front of him as they closed in on the slowly tumbling grayish-white mountain—growing larger each second.
The tumbling gray icerock was much larger in the holoviewport in front of Chastity. Knowing that Rod would keep
Sexdent
on course, she concentrated on the image in front of her, looking for the best place to put the penetrator. If it hit a hard surface, it might not penetrate enough and would be pulled out as tension was applied. If it was placed in a field of rocks, the rocks might cut the tether as it tilted over from the vertical during their turn. The best place was the middle of a small crater, as fresh as possible. She spotted one—and with minuscule adjustments to the joyball in her controller, the cross-hairs on the holoviewport shifted to the center of the crater.