The stealthed ship that they had been tracking had taken a slow route to its final destination. It moved in an elongated arc to intercept the rock that allowed it to get a three hundred and sixty degree sensor sweep with all of its potential systems as it moved in. The complexity, and speed, of the sequence of maneuvers took almost eighty hours to complete, from the point they had first detected the craft’s approach.
Drick had deployed a large, thin, fibre net. It was made of an organic compound very similar to silk but with even greater tensile strength. It was sensitive to electromagnetic fields including short range radio signals of the type used for internal control systems on vehicles. It had been strung out from their craft, for hundreds of kilometres. A non-reflective, microfibre mesh that would passively detect the movements of the almost invisible vessel they shadowed.
Drick had tried to explain to Marsh how the passive array worked. Something to do with detecting spatial shifts from electromagnetic sources. Marsh had not fully understood the conversation. What he knew was that you couldn’t make something invisible. Nor could you bend all the possible sources of energy around an object to make it undetectable. So instead you cloaked it. You replicated the signals using an active shield that when viewed from any direction would make it appear as if nothing was there. It was a mixture of absorbing any incoming active signal, masking any outgoing signal, and redirecting any background difference to appear uniform and natural.
Since detection of a vessel in space mostly relied on seeing its outline against the background levels of electromagnetic energy, replicating that energy, and allowing the background to be unimpeded or interrupted, made most sensor arrays ineffective. After that you simply needed to paint the vessel black and use optical dampening to absorb visible light, and it was almost invisible to sight.
At great distances there would be nothing to detect. The further from the object the greater the intervening distortion, with higher levels of interference due to distance and potential sources, and the better the cloak that masked the vessel.
The passive array that they were deploying extended the range and field of the sensors. It allowed them to detect much smaller variances in any of the potential sources from the electromagnetic spectrum. This was how they tracked the cloaked vessel. It was sensitive enough to detect the smallest level of electromagnetic change. It needed to be large enough, to cover as wide an area as possible to allow for comparisons of minute differences, to determine the difference between these signals and naturally occurring changes, and to triangulate a position.
The stealth vessel had used occasional slight course changes and other manoeuvres that flipped its entire trajectory. It was an old style of maneuvering, learned from vessels that needed to determine if another was tracking them covertly, a random change in course will allow you to check if you were being followed. Even walking along streets in a city this technique was utilised. It was particularly useful on a stealthed vessel as its own passive sensors would still operate even if they were cloaked.
Drick kept them far enough away that this behaviour wouldn’t reveal anything. The vessel Drick and Marsh travelled in had similar cloaking technology and light absorbing panels. Whilst undertaking a flight that had complex maneuvers, the stealth vessel wouldn’t be able to deploy as large a passive array as the one Drick was using. Their own large mesh was invisible to almost everything but a similar device.
The stealthed vessel made its final approach on the rock by arcing out to a far point and then flipping and making a direct line for the objective. It was behind the object in regards to the rest of the system, and so invisible to most of the rest of the planets, shielded by the rock as well as its cloaking tech. It had used a small set of thrusters that appeared as bright pinpoints of light to Drick and Marsh, deploying them at the final moment so none of the light would edge around the surface of the rock to anyone on the other side. The large object in front of the craft would completely mask it from any other observer.
Drick had pulled in the large passive sensor net as the ship made its final approach. They were directly behind the vessel and used the flare of the rockets to allow a slight increase in their own speed. They would be using a short burst from the graviton drive to slow them when they were in final approach distance themselves.
Marsh studied the large asteroid that they headed towards and was impressed by nothing. It looked like what it was meant to, a lump of space debris. It was a huge lump of flotsam, suspended in the darkness, many miles from a sun whose warmth would never caress its surface. There were no landmarks on the surface that indicated that is habitation, or ever would have had someone desperate enough to live here. There was no large vessel hiding behind it, hidden from the rest of the system. There was no vessel on its surface masked to scanners by a coating of some type.
Marsh was about to turn to Drick and tell her that it was likely another ruse, that there was something else going on. But he paused. A sequence of lights had played on the surface of the rock. A pattern that suddenly lit up to look like a circle. Then as if by some trickery, a large docking ring had appeared. The lights had now faded to a dim glow that lit a huge circle of rock that was slowly sliding sideways, splitting into segments as it did so which retracted into the surface of the asteroid.
As the ship approached other small lights came on and tracked its descent. They were standard approach lighting. Marsh swore softly in surprise as his brain tried to register what he was looking at.