Now, they have to deal with a subtle but definite problem of space travel: low gravity...
"Argh!" A.J. said with articulate precision.
Joe looked over at his friend, who was currently settling back down to Europa's surface, still clinging to one of the wrenches designed for use in space-walk conditions. "Didn't lock yourself down again, eh?"
A.J. muttered something that didn't sound at all friendly. "I keep getting focused on getting the work done and forget where I am. Stop grinning at me!"
"I'm smiling at how well the centrifuge is shaping up," Joe countered, the broad smile still on his face. "Not mocking your inability to remember basic procedure. No, not at all."
"What about the time you –"
"—I know exactly what you're going to bring up, and that was about ten years ago, and I did it once. This is the third time I've seen you wrench yourself right up off the surface of Europa."
"Be kind to him," Helen said, but her image wasn't showing grave, serious concern either. "I'm using his only Locust right now, with the others having to do slow sequential recharge, so he can't sit in his master control center and have his robotic servants do his bidding."
"Focus on the tasks at hand, please," Madeline said calmly from her position on the other side of the centrifuge assembly. "We need to be sure everything is done properly. A.J., how's your IAA program tracking?"
The Integrated Automated Assembly application monitored the entire process of construction; similar programs had been in use throughout the assembly of all the current generation of spaceships – and, for that matter, planes and ships back on Earth. They made sure the right fasteners were tightened in the right order, grounding contacts properly made, and so on.
After a pause, A.J. answered. "Looks like… I have to give this one another tug or two, not surprising since I didn't really get a good grip last time." Joe managed to keep from interjecting anything else, not that this was an easy thing to do. "Maddie, one of the fasteners on module 7 – I'm highlighting it in your view – is overtorqued. Back it off until the display shows green."
"No change since we started full assembly, despite that one big ground tremor. Looks like those got planted good, so it shouldn't walk on us."
"Is everyone clear for takeoff again?" Horst's voice interrupted.
Madeline did the official checkoff. "Yes, Horst, we're all over here with the centrifuge assembly, except for Helen, who's running her excavation and Athena, and Petra, who's relaxing in Hotel Europa. All clear."
So far, things are going smoothly, Joe thought to himself, then spent a few quiet seconds kicking himself for even thinking that. Still, the basic thought was correct. Having someone like Brett along to make sure the entire design was workable and help figure out the best way to assemble things sure helped. And Dan had pointed out – in another of the "we should have thought of that weeks ago" moments – that the best way to keep Munin shuttling back and forth would be to set things up so that the Nebula Storm's tanks could be emptied directly into Munin's; then Munin could take off, bring additional reaction mass to Odin, have the crew do some more work on the giant EU vessel, and then come back to tank up without having to wait for Athena to do the whole job. This way, when the time came, they wouldn't have to wait for more than the time it took to fill Nebula Storm back up.
So now Munin was taking off – there she went, impractical wings and all, straight into the black sky – only about four days after she'd brought the components back. And they were getting close to finishing the assembly of the magnetic-drive centrifuge.
"I know it's gonna be a pain," Joe said, "but I'm actually kind of looking forward to spending some time moving around in real gravity for a while."
"I think the novelty's going to wear off really fast," A.J. said, "but me too. I haven't been able to do decent exercises since we came here; the old 'dynamic tension' method doesn't cut it, and I've got at least an inch of padding I didn't have before."
"Not quite that much," Petra Masters said from her comfortable position in the artificially sun-drenched room of Hotel Europa, "but the little you have gained feels – and probably looks – like much more given the rather unforgiving designs of your suits."
"Thought you were on vacation, getting away from it all."
"I'm still interested in your progress. But think of it as a phone call from this marvelously sunny vacation flat. By the way, I compliment you, Dan – this really does feel like actual sunlight."
"Thanks, Petra," Dan Ritter said after a few seconds' pause, as Dan was still aboard Odin. "Visual triggers and biological ones for the light cycle are pretty important and widely studied; I just followed their advice."
"Well, wherever the basic idea came from, it is a capital one; I feel more… myself, somehow, than I have in some time."
"You have trouble with SAD back home?"
"I do indeed. Seasonal Affective Disorder is common in my family."
Joe nodded to himself. "I guess that's more of a problem out here where the sun doesn't seem itself at all."
"That's got it," Maddie said from the other side of the structure. "A.J., how about yours?"
"Done. Was that the last one?"
"I certainly hope so, or my beloved husband has been slacking terribly over the last few minutes. Instead of asking me –"
"—I should just check the screen… okay, yes. We should be ready to connect up the power and test her out with a dummy load. Joe, would you go get in?"
"Is that supposed to be a demonstration of your brilliant wit? Helen, I think he's going senile." As he continued the usual banter, Joe went to retrieve the test load which, for his usually obscure reasons, A.J. insisted on naming "Buster".
"I've got the test dummy; putting it in place." He picked up the stuffed spacesuit and entered the spin assembly, making his way to the acceleration chamber. The interior was adapted from one of the shelters in Odin's storage, meaning that it would have its own atmosphere and, within the very limited space, afford several options for exercise (pushups, tracked weights, chin-up bars, and about a 10-foot span for walking back and forth). He stripped off the suit, hung it on the rack set next to the airlock, and dumped the dummy in the middle of the floor.
A minute later he stepped down, having made sure the door was fully secured. "Okay, I'm out."
"Maddie, check the balancing readout. How much excess weight you reading in the acceleration chamber?"
"Just a moment, A.J." A pause, then, "I make it one hundred thirteen point four kilograms."
"Excellent," A.J. said. "Buster with his suit actually weighs, according to my own numbers, one hundred thirteen point four two. Well within accepted margin of error and the balance limits that Dan and Brett gave us. All right, I'm loading that much weight into the opposite balance chamber."
A few minutes later A.J. said "All set. Everything shows green on my end. Anyone else see anything off?"
Joe checked his own systems. "No warning lights here. Power's set."
"Then we're ready for a spin test," Madeline said. "Everyone back to Nebula Storm. I'm sorry, Petra, that includes you – you'll get your additional hours back. But if anything goes wrong with something that large spinning fast enough to make a one-gravity equivalent field inside, it could send very heavy pieces scattering over the surface, and Nebula Storm's the only absolutely safe location in that case. Helen, shut down the Locust and Athena, just in case."
It took about half an hour for everyone to wrap up and assemble in the now rather cramped confines of Nebula Storm's control room.
"All right, Joe. Start her up."
Joe fed power to the centrifuge. It was a simple enough design in concept, using modified magnetic acceleration components from Odin's drive spines (and the hidden coilguns) to spin the modules around a track which was constructed at a precise angle. When the centrifuge reached the speed at which the side acceleration was approximately one gravity, the combined lateral acceleration and the slight contribution of Europa's downward gravity vector would make the floor of the acceleration chamber seem to be precisely down. "Centrifuge on."
Outside, the forty-meter wide, spidery structure showed movement inside the wire-cage openwork which was the main accelerator. "Acceleration as predicted. Power draw is within one percent of theoretical. Increasing power."
The rotating component was a cross-shaped structure in the center, two carefully balanced weights at the end of each of two crossarms, the other crossarm having the acceleration chamber at one end and the counterweight chamber at the other. The display showed the spinning, like the spokes of a wheel – except in this case the wheel stayed stationary while the spokes moved faster and faster. "Up to two RPM now – nearing one-third gravity." The 20-meter radius would require the assembly to spin at nearly seven RPM to reach the desired acceleration – non-optimal, because some of the crew might find that unpleasant, but there was no practical way to build the thing larger; Joe had been skeptical of their ability to construct something this large, and Dan and Brett had spent a lot of time figuring out a design which would be practical. Dr. Masters thought there were ways to minimize the vertigo or nausea, and that the benefits of acceleration outweighed the risks of discomfort for a few hours.
"Very little. Anchors are holding. Okay, guys, I'm taking her up the rest of the way."
Faster and faster the rotating chamber passed by. Once every twenty-five seconds. Twenty seconds. Fifteen. "Almost there, rotational speed forty-two… forty-five…"
A green light blinked and a chime sounded in all their helmets. Joe heard a small cheer from the others. "One full gravity, spinning at fifty point four kilometers per hour. Congratulations, Dan, Brett – she works!"
"Then let's put her into service," A.J. said. "So all of us can… take our turns."
Joe resolved to wait until A.J. got out of his suit before he kicked him in the shin.