"What's that?" asked Dan as the back of the probe came into view. The surface was a metallic gray, similar to battleship gray, and as smooth as a polished marble. A silvery metal structure jutted out from the rear of the probe. Nancy switched to magnification 10 for a better view.
"It's a parabolic dish," declared Garvin, "and it's gimballed. See how it doesn't point straight back from the sphere; it's tilted at an angle." His fingers flew across the keyboard, pulling up a series of star charts. "This won't surprise you; it's pointed at Arcot."
"Not surprising at all." agreed Nancy. "Two way communication is impractical; it must be a telemetry downlink. For the past 8,000 years this probe has been sending its status back to its home world. If it failed halfway to Earth, they could send another one."
"Sure," said Dan, "but the information it is sending right now won't get back to Arcot for 6,000 years."
"Well, it's better than nothing." Nancy switched the screen back to normal magnification and the probe was once again a small gray sphere with a silver metal dot in the center. After a moment's thought she changed the magnification back to 5. "We'll be gliding in behind the dish; maybe we can get a good look at the transmitter." The leading edge of the structure was just coming into view, as though a bird were flying in front of a satellite dish. Suddenly Garvin grabbed the controls and pulled the stick hard over. Everyone groaned as 9 G's hit them from behind. They were all experienced pilots, with high G training, but it was still a shock when it came without warning. Nancy tightened her diaphragm in the classic anti-G stress maneuver. Dan also did his best to avoid a blackout. In a slow motion response that was almost surreal, the ship turned and skirted the edge of the giant dish. Garvin let the stick return to center and everyone breathed a sigh of relief.
"I'm sure you have an explanation." Nancy growled.
"When I was a boy, I lived near a long distance microwave communication tower. That beam was capable of carrying thousands of simultaneous phone calls across hundreds of miles. My friend said you could put a raw egg in that beam and it would cook in under a minute. An instant hard boiled egg. I never tried it, but that image has stuck with me. This dish is sending telemetry across 6,000 light years. It has to be putting out megawatts of power, on a frequency that we can't even begin to guess. If we flew into that beam, we'd be toast."
"That's a good explanation. I don't know why I didn't think of that." She looked embarrassed and grateful at the same time. "Thank you."
Dan was still straightening his back. "I'm going to need a chiropractor when we get back to Earth."
The ship sailed on in silence, crossing the terminator from back to front. The smooth metal surface became pitted and cratered. Nancy switched to magnification 100. Individual craters were still hard to see, as there were few larger than four feet across, but the entire surface looked rough, and it became more pitted as they moved around to the front. She switched back to normal magnification as several structures were coming into view. "Analysis, quickly." she commanded, not wanting to make another mistake.
"More parabolic dishes, but much smaller." Garvin was quick and concise. "These are probably passive telescopes - keeping an eye on our sun and its planets. I think they are harmless."
"No matter, we seem to be gliding in between two of them. But what's that coming up?" Nancy was pointing at a large metal plate that was near the front of the probe.
Garvin paused for almost a minute. "That's a phased array radar. It sends out pulses in various directions and waits for echos. But it's most effective looking straight ahead."
"Does it use radar to fix the locations of the planets and moons in our solar system?" Dan asked.
"Perhaps, but I think it has a more important mission." Garvin explained, as they flew across the top left corner of the array. "Asteroid detection in interstellar space. It's black as night between the stars, and if you smack into an asteroid at near light speed, you're in a world of hurt."
"What can they do about it?" Nancy asked.
"There's too much mass to change course. They can't move out of the way. But if they can see the asteroid from a great distance, they will try to deflect or destroy it. In fact that looks like a kinetic energy weapon coming up." A long metal tube extended straight out from the shell, like a solitary tree in the desert. Slowly, as they watched, the entire structure, over a mile long, leaned to the left. "Of course it's gimballed." stated Garvin. "It would have to be."
Nancy grabbed the stick and pulled it over. For the second time in a half hour, the three crew members felt 9 G's pulling their bodies into the contour seats. The ship curved to the left as a metal projectile shot out of the tube at near light speed. If they had been a mere rock, subject only to orbital mechanics, the aim would have been spot on. A 20 kilogram iron ball tore through the ship's projected position, followed by a tiny nuclear bomb. The flash filled the bridge with light, and temporarily blinded the occupants, who were still straining under the G forces. The million degree heat vaporized most of the outer hull on the starboard side, and melted a section of the inner hull adjacent to supply room 3. A stream of air shot through the 6 foot hole in the wall, carrying several cartons that were not tied down. Inner doors closed in response to the drop in pressure, effectively sealing off the supply room. Nancy released the stick out of reflex and the ship returned to its zero G orbit. alarms rang out, but the crew had to wait ten seconds for their eyes to recover. It seemed like a very long time. Finally Nancy was able to read the display and survey the damage. She began with a deliberate understatement, an attempt at humor.
"That's not good." She turned to Garvin. "Is it going to shoot at us again?"
"No." replied Garvin. "We're in a very tight orbit, and we've already past the angular resolution of the radar. It can't see us any more. The system is designed to detect and vaporize asteroids that are a thousand miles out in front and closing fast. We're not a typical threat object."
"So, it calculated our trajectory precisely, and it knew we were in orbit, and would not collide with the surface. Why did it need to destroy us?" Dan asked a valid question, and Garvin had to think for several minutes.
"An object in orbit won't stay safely in orbit if the probe accelerates, or changes direction. Destroying it is a sensible course of action. Besides, nobody expects an asteroid to contain life forms. I don't think the Arcots expected a ship to come out and greet them before they arrived at Earth. In any case, we're going to have the same problem in 41 minutes, when we circle back around to the front of the probe."
"No we're not." declared Nancy as she pulled the stick gently to the left. "We have plenty of fuel; I'm going to change the plane of our orbit. We'll circle the terminator, the line between front and back, where there are no defensive weapons, and no communications beams." The 7 minute 1.5 G turn seemed mild compared to the last two maneuvers. Soon the ship was traveling along the probe's virtual equator, with the sun off to the left. At this distance the sun was merely the brightest star in the sky. You could look straight at it, but nobody paid much attention, because all eyes were on the probe. At magnification 100, streaks became visible, where interstellar pebbles grazed the sides of the probe at high speed. They would have formed pits and craters if they had hit the probe head on.
Nancy took a deep breath, trying to regain her composure and take stock of her situation. She smoothed her long blonde hair back with her hands, looked into the camera embedded in the console, and spoke directly to Mission Control. She took some comfort in these virtual consultations, even though the response would not arrive for 26 hours.
"Houston this is Explorer 29. I hope you're having a better day than we are. We've been on open mike, so you've heard our conversations, and you've seen the telemetry. The Arcots took a shot it us, but I believe it is an automated asteroid defense mechanism. An electromagnetic rail gun shoots an iron projectile into the asteroid at high speed, breaking it into pieces, or at least punching a hole into it if the asteroid is large. Then an atomic bomb vaporizes the pieces, or breaks a large rock into smaller rocks, whence the process begins anew on each piece. Well they missed, except for the damage to our starboard hull and supply room 3. We got off pretty light. I'm sure the telemetry is showing you the status of the ship. When we return to Earth, reentry may not be an option. You may have to send a shuttle craft to rescue us, then repair the ship at one of the outposts. But that's tomorrow's problem." She leaned back and watched the weathered surface of the sphere race by. "Houston, this technology is immense. Even if the Arcots are benevolent, we could be destroyed simply by being in the wrong place at the wrong time. It's a bit like having a pet gorilla in the house. I wish we could talk to you in real time; maybe we wouldn't make so many mistakes. We'll try to be more careful out here." She turned to Garvin. "I think I'm going to leave the mike open for a while - everything we say might prove helpful to someone on Earth."
"I agree. I'll try not to swear when the two-headed monster jumps out at me."
"What was that?" asked Dan. It flew by so fast they almost missed it.
"You keep your eyes on the landscape, and your hand on the stick," Nancy directed, "and I'll rewind the video." She pressed three buttons and turned a knob, and the surface of the sphere slid backwards across her screen in slow motion. Soon the unusual feature came into view. Concentric colors formed a bull's eye, with a red ring in the center. Inside this ring sat a glass window with a control panel to one side. "It's a portal!" Nancy announced excitedly. "That's the way inside."
"Yeah, assuming you know the secret code to type into that keypad." mumbled Dan.
"That's where you come in." replied Nancy. "You know the Arcots better than anyone on Earth. Start thinking about what kind of code they might use." Dan leaned back and sighed, recognizing the task as impossible.
The next orbit revealed 4 portals around the equator, evenly spaced at 90 degree intervals. Another orbit revealed nothing new, and the crew finally began to relax. "Folks, we need a good night's sleep before we enter the probe, or try to enter the probe. When we land, it's going to be almost 2 G's. Personally I'd rather sleep in freefall than 2 G's. So I'm going to leave the ship on automatic. If the probe accelerates, or changes direction, our orbit will be perturbed. The autopilot will sound an alarm; believe me, you'll hear it. But I don't expect this to happen. And we won't get an update from Earth for a full day, So let's get some sleep."
Dan and Garvin agreed. They left the bridge and headed to their quarters. On her way back to the cabin, Nancy stopped outside supply room 3. It was her ship, and she felt obligated to inspect the damage. She peered through the glass in the door, but all was darkness inside, except for a field of stars on the far wall, almost 6 feet across. Nancy had imagined a neat clean circle, but the hole was jagged around the edges. She could almost see the stars rotating as the ship turned in its orbit. It took a couple of minutes before she remembered how to turn on the lights in another room. She tried several combinations at the panel on the wall, until the lights snapped on. The stars were lost in the glare, leaving a black hole against the white background of the ship's wall. The edges were curled inward, melted in the heat. The metal was charred in places, as superheated air rushed past. The carton immediately below the hole was melted into a grotesque plastic sculpture. Other storage containers had minor deformations, as the heavy duty plastic succumbed to the nuclear fireball. "I'll have to pry some of those lids off." thought Nancy as she turned off the light. She went back to her cabin and crawled into bed, but sleep didn't come easily. "Not every day you get to see an atom bomb explode a few hundred yards away." She pulled her arms out of the sheet and let them float free. "In air or water, the blast would have killed us all. Good thing space is a vacuum." After several minutes she pulled her arms back inside the sheets. "I'm glad nobody was looking out the starboard window at the time. They would certainly be blind." She turned to float on her stomach, rather than her back. "That's a first for me - a nuclear blast from an alien race some 6,000 light years away. I suppose there will be many more firsts before this mission is over."