Eric Flint: Threshold

Sure, keep the rocket on it long enough and we'd probably damage something, but we're not firing it that long." Maddie nodded. "Munin, are your reaction mass tanks fully loaded?" "Yes. Glad that where we are going there is a lot of ice, because otherwise we would all be very short of water when this is done." "Good. Everyone strapped in?"

The others reported in. "Mia, I want you and Jackie to keep a really close eye on everything. We can't afford glitches." "Understood. We are watching." Madeline rubbed her eyes and took several deep breaths before putting her helmet on. This being a critical maneuver, she'd also taken a stimulant. She simply hadn't had enough sleep, and this was not the time to have slowed reflexes. There were only two good aspects to the situation. One, obviously, was the low gravity of Europa, less than one seventh of Earth's, which meant a gravity well of just slightly over two kilometers per second-withinMunin 's capacity to handle even with the added mass ofNebula Storm. That was critical, because not only did they need to land, they neededMunin to be able to lift them off of Europa eventually, because the nebula drive wasn't capable of lifting off from anything larger than a smallish asteroid. The second good thing was that Europa had no atmosphere to speak of. This jury-rigged double ship had the aerodynamics of a falling bridge, and were there any atmosphere-even one as thin as Mars'-the pressure variations during reentry would probably rip them apart. Aside from the gravity well itself, she'd be able to treat the maneuvers as being the same as in deep space. That gave them a chance. Not a great one… but I'd better make it good enough, she thought. "All right, everyone. We are almost there."

Europa now loomed before them, eclipsing even Jupiter in size as the combinedMunin/Nebula Storm overtook it in its orbit at a differential of less than a kilometer per second. Smallest of the Galilean moons, it was still immense, half again as wide as Luna, far more massive, far more complex. From their current altitude, it looked as smooth and polished as a billiard ball, an ivory cueball with multiple browned lines like cracks from age covering its surface. Somewhere below that surface, Maddie knew-depending on the scientist you asked, anywhere between two and fifty kilometers below-there was a dark ocean that covered the entire moon to a depth ten times greater than the deepest parts of Earth's ocean. The smoothness was deceptive. Europa might be the smoothest object in the solar system, but there were still plenty of ridges, blocks, edges, hills, and chasms, and they had only minimal control over their landing site. In the few hours they had, A.J. and Larry had gone over the available imagery and what they could make out with the onboard instruments and picked their best guess as to a landing trajectory that might offer decent landing topography… but it was still a crapshoot. "About to begin maneuvers. I'm going to ask everyone to either cut out radios or stay quiet unless they have something I need to hear. This is going to take all my concentration, and I don't need even a gasp, a curse, or a prayer distracting me." "Understood,"A.J. acknowledged. She saw some people drop out of the network-mostly the formerOdin crewmembers that she hadn't had time to get to know yet, and who weren't engineers involved in this maneuver. Helen and Larry also dropped out. Larry had done all he could, and Helen was not going to be able to do anything more, either, now that the gruntwork of putting the whole contraption together was over. "Here goes…" Munin's rockets coughed and then began a low, rumbling roar at minimal power. She wanted-needed-to get a feel for the clumsy dual ship before she kicked in full power. It was sluggish… wobbly… still some imbalance… but there, A.J. and Horst's programming was kicking in, automatic compensation based on the accelerometers all over the ships. The departure from projected optimal course was minimal. "Working so far. Full de-orbit burn coming up in three, two, one…" Now the rockets gave vent to full-bore thunder, sending a shudder of vibrations throughoutNebula Storm."Ice seal under stress… holding, but I'm seeing cracks starting to build. Think it will hold, but be ready," A.J. said quietly. "Cables?" "All well within limits. No shifting yet. The torque on the hab section connecting tubes and supports is getting awfully near their design limits, but doesn't seem to be increasing any more." "Burn almost done… in five, four, three…" Just as theMunin ceased its rumbling, there was a reverberatingcrunch. "What was that?" "Ice seal shifted and broke. We're only held together with the string and duct tape now. On the positive side, we don't need to worry about making sure that part breaks when it comes to the time to separate." "Any advice?" Horst answered."When we do the other burn for landing preparation, begin very slowly, as before, then taper slowly.

This will let any slack be taken up and stress the cables least.

Backing down slowly will let the strain off the cables evenly-I hope-so there will be no great shifts." "I understand." She leaned back. "It will be a while before we come to the landing decision.

Larry, A.J., I want you to keep watch ahead of us and refine our landing site as much as possible. As we know from our little landing inJohn Carter, you don't have to hit at kilometers per second to ruin your day." "We're on it. Take it easy for now." She reached out and took Joe's hand. Even though the contact was just glove-to-glove, it felt good. "You okay?" he asked privately. "Scared to death. I practiced alot after that crash, and Bruce said I was getting pretty good, but I'm not half as good as he is, and I think he'd find this a hell of a challenge." "You're my Supergirl. You'll do it." She giggled. "Yeah, I'll just fly out and catch us if something goes wrong." "I almost believe you could." He smiled at her fondly. "I'd try, anyway." "Maddie, all that matters is we're doing our best. And if anyone can get us down safe and sound, it's going to be you." Once more his words made all the difference. She stopped worrying. If the worst happened, it happened.

Chapter 47 It was no longer a moon. Europa wasdown, now; a planet of ice, of jumbled ridges, occasional craters, scattered blocks the size ofOdin stuck in the center of smooth, featureless frozen white, all rolling by underneath them at a tremendous speed. "Without atmosphere, we're having to kill our speed directly. According to Larry and A.J., we will be landing near the area called the Conamara Chaos. There's no good way to predict smooth landing spots, if any, so we just have to wing it. Everyone make sure they are securely strapped in." She did not allow her voice to betray any uncertainty. Her review of the Conamara region didn't encourage her; "chaos" was a good description of the area, but outside of it wasn't much better. On a planetary scale, Europa was smooth; on a human scale, it was some of the most rugged-looking terrain she'd ever had to look at. Plenty of areas of Mars were smoother to land on. But… there were a few possibilities. If she could just get lined up right. "Combined landing burn coming up." The rocket came on again at minimal power, slowly building to maximum. Scraping noises and vibrations echoed through both ships as, despite the cables, the two shifted slightly with respect to each other. Horst and A.J.'s balancing application was strained to its limit, and Maddie could feel the combined ship moving toward some catastrophic adjustment that would send them spinning out of control. Instinctively she eased off on the thrust, watching the projections of time and velocity. She had to get their relative velocity with respect to Europa's surface down to less than a hundred meters per second. Five hundred meters per second, and descending.

Altitude ten thousand meters. Four hundred meters per second.