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I’m almost done…there.  We’re all set.  You can swap the cartridges now, Susan.”
    “Copy that, Paul.  I’m swapping them out now.” Susan removed the test cartridges that had been inserted before launch and replaced them with another set that would be retrieved once they were back on the ground.  Paul would need to recalibrate the system for these new cartridges and she would have to tend to the unit to make any necessary adjustments.  The process was a bit tedious and would take many iterations.
    “Susan, you have about ten minutes before I’ll need you again,” Paul said.
    “Call me when you need me,” Susan said.  She looked out of the cargo bay as the shuttle passed into the shadow of the earth and the stars stood out boldly against their black backdrop, no longer having to compete with the glare of the sun.  Her sense of foreboding grew the more she stared into the void.  Susan fought the urge to return to the airlock and argued with herself that she was just over-reacting.  Susan snapped out of her musings when she heard Mission Control talking to Jill about the replacement panels she was having trouble attaching. 
    “Roger, I had some difficulty removing the mounting screws when I removed the original plate in position X4.  The material on the plate seems to have reacted with the screws and the new screws are just not going in quite as easy.” Jill moved back and surveyed the satellite for a moment.  “Jerry, can you raise SCIEXSAT about a foot or so?  It’s a little awkward getting at this lower panel.”
    “Roger that, Jill,” Jerry replied. “How’s that?”
    “Great! That’s much better. Thanks.”
    Mission Control cut in, “Jill, tech support wants to know if you can reuse the old screws.”
    “They are pretty useless at this time.  They came out pretty hard and the heads are shot.  I’m going to try a little more elbow grease on this one.  Hang on.”
    “We copy that, Jill,” CAPCOM replied.
    Susan watched as Jill applied more force to fasten the stubborn screw and her body rotated while the satellite remained stationary, as if she were a white pinwheel attached to the glistening satellite.  Newton’s third law of motion was in full force: For every action there will be an equal and opposite reaction .  Jill let out a gasp of exasperation and Susan floated over to give her a hand. 
    “Try this, Jill.” Susan braced herself on a support strut that was installed for the CRV and let Jill prop her foot against Susan’s foot.  From this position, Jill was able to tighten the screw without rotating around the screwdriver.
    “Thanks, Susan,” Jill said.  “I think I need a refresher course in Physics 101.”
    “No problem,” Susan said.  “It’s amazing how we take gravity for granted.”
    “That’s for sure.” Jill gave all the screws one more check to make sure that everything was tight.  “Mission Control, that’s the last panel, everything looks good.  Ready to toss this baby overboard for another year.” Jill’s fatigue echoed in her voice.  It could be quite exhausting working in micro-gravity and after two hours of wrestling with the satellite she was ready to call it a day.
    “Jill, telemetry looks good for the new panels.  You are cleared to release SCIEXSAT.  You did a great job.”
    “Thanks, Houston, couldn’t have done it without you, or Susan.  Jerry, you heard the man, let’s unload this beast so we can come in for lunch, I’m starving.”
    “Roger that, Jill, that makes two of us.” Jerry scanned the cargo bay to make sure the astronauts were at a safe distance. “All clear from SCIEXSAT?”
    “Roger, all clear,” Susan and Jill echoed.
    “Okay. Let’s raise this nice and easy.” The satellite rose out of the payload bay in a smooth motion as Jerry manipulated the controls for the arm.  “We are at maximum elevation and now I am rotating ninety degrees to proper release attitude…Ready to