This week on MOTE I swapped prompts with Fiona Grey, receiving: “It’s caterpillar time.”
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The Scalpel was the latest prototype from Jupiter Spacecraft Fabricators. Its hull was made from special materials that absorbed sensor rays, but that wasn't new. Spy ships and satellites had been made using those materials for a long time. The problem, so far unsolved, was that any attempt to enter orbit around a planet or asteroid involved the firing of engines, which sprayed hot gases as exhaust fumes, easily spottable by thermal sensors. Once the thermal sensors had located an unknown object, the visual sensors could confirm what it was, and it could be tracked.
The Scalpel had been launched from Jupiter, and was currently approaching Earth. Overtly, should anyone ask, its maiden voyage was an attempt to win a prize, the Stealth Ship Prize, for the first spaceship to travel from orbit around one body to orbit around another, and then transmit data to the ground, receive a reply and leave orbit without being spotted.
Not that Jupiter Spacecraft Fabricators were seriously interested in claiming the prize. If the Scalpel could do all this without Earth's authorities ever being aware that the attempt had been made, the design would be much more valuable to the Jupiter authorities, and JSF would make much more money out of this voyage.
No, the real reason for the trip was to practically test the systems that JSF hoped would make the class the premier spy ship in the solar system. The class that Jupiter would then purchase for all their intra-solar spying needs.
As noted, the biggest problem with the previous set of stealth ship designs were the engines, spewing out hot gases easily detectible by thermal sensors. So the Scalpel had been designed with a caterpillar engine, that used the power generated by a fusion generator to propel ionised gases out of the craft at much lower temperatures. These temperatures were far below the minimum relevant settings of the thermal sensors.
The one slight problem was that the exhaust gases were visible to visual sensors, and the primitive AI that ran the automated checks of these would flag up such a plume as suspicious due to the long cross-referencing with the thermal sensors.
So, the approach to Earth had been arranged to ensure that the Scalpel passed into the Earth's shadow. It was in the Earth's shadow for long enough that it could be slowed down sufficiently in order to obtain a stable orbit. Then, each time it passed through the shadow it would slow down further in order to tighten the orbit to the point where the signals could be sent and received.
After this the Earth's shadow would be used as the cover for the acceleration that would eventually enable it to break orbit, and return to Jupiter.
But now the Scalpel was still on Earth approach and had yet to enter orbit. The cockpit was very constrained, with barely enough room for the two pilots. Over 90% of the ship was taken up with the fusion reactor and the caterpillar drive (including the gas stores). On top of that there needed to be sleep facilities, a galley and so on. There wasn't much room left in which to put the cockpit.
Gerald Smith a'Ganymede was in charge, with Peter March a'Io in the copilot's seat. The seconds were counting down.
"One minute to Earth's shadow. Power up the caterpillar drive."
"Drive powered up," responded Peter.
"Thirty seconds to Earth's shadow. Confirm drive set to forward exhaust."
"Drive set to forward exhaust."
"Fifteen seconds to Earth's shadow. Open forward external exhaust vents, and release gas into the acceleration chamber."
"Vents opened, and gas vented."
"Initiate caterpillar drive."
"Drive activated. It's caterpillar time."
Gerald studied the gauges at his station. "Deceleration is observed. We are still on a fly-by trajectory."
The seconds ticked away. The Scalpel was slowing, but it only had so long to slow enough that the Earth captured it into orbit. The boffins back at JSF had calculated that they had long enough before they exited out of the planet's shadow to do this, but the only way to test it was to make the attempt.
Gerald continued to study the displays. "Deceleration continuing. Orbit achieved. Ten seconds of shadow left. Turn off the caterpillar drive."
"Drive deactivated."
"Close the external exhaust vents."
"Exhaust vents closed."
"Make the drive safe and power it down."
"Drive is safe. Drive is powered down."
"Good," said Gerald. "We are now in a highly elliptical orbit of Earth. As far as I can tell we have not yet been spotted. The computer calculates that we will re-enter Earth's shadow in approximately 50hrs time.
"Stage one is complete. You have the helm."
"I have the helm," replied Peter.
Gerald got up and left the cockpit. Once in his bunk, he opened the ship's log and noted down that Earth orbit had been achieved. Over the next week or so they would try to tighten their orbit enough to get into reliable signal range of the test transmitter.
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I’m looking forwards to reading what everyone else comes up with.