In the novel Tarkin, Darth Vader is able to track the insurgents by somehow tracking his meditation chamber, which is aboard the stolen Carrion Spike.
He is somehow doing this by reaching out through the Force.
What was so unique to Vader's meditation chamber that he could feel it with the Force?
Short Answer
Vader was tracking his meditiation chamber because he had a strong connection to it through the Dark Side of the Force precisely because he used meditating in it as a mechanism to strengthen his connection to the Dark Side of the Force.
Long Answer
Introduction
A possible explanation for why Darth Vader focused on his meditation chamber within the Carrion Spike while searching for that lost ship can be found in connecting the principles of the Sith in terms of their relationship to the Dark Side of the Force, and how Darth Vader used his meditation chamber. All sources should be Canon except where stated.
The Codes
The Jedi Code states:
There is no emotion, there is peace. There is no ignorance, there is knowledge. There is no passion, there is serenity. There is no chaos, there is harmony. There is no death, there is the Force.
This code taught the Jedi to reject anger, fear, and attachment toward other lifeforms because those emotions eventually lead to you falling to the Dark Side of the Force. This was echoed by Yoda in TPM:
“Fear is the path to the dark side. Fear leads to anger. Anger leads to hate. Hate leads to suffering.”
The Sith embraced this idea, with their own code (N.B.):
Peace is a lie, there is only passion.
Through passion, I gain strength.
Through strength, I gain power.
Through power, I gain victory.
Through victory, my chains are broken.
The Force shall free me.
The Sith believed that by embracing passion they would gain strength. By controlling and expressing their anger, pain and fear, they would master them, and then be able to use them gain even greater power. Emotion was their cornerstone, the first step on the path to the Dark Side and their basic link to it:
Darth Sidious to Anakin Skywaler, ROTS (youtube link)
"I can feel your anger, it gives you focus, makes you stronger"
Darth Sidious to Luke Skywalker, ROTJ (youtube link)
"Good. I can feel your anger ... Strike me down with all of your hatred and your journey towards the Dark Side will be complete"
Count Dooku to Savage Opress, TCW 3x14 (youtube link)
Dooku: "The task is only impossible because you have deemed it so. You must connect with your hatred. Focus on your power building. Do not think about anyone or anything else. That's it, your anger is your strength."
Savage: "I hate you."
Dooku: "Good."
The Meditation Chamber
How this connects with Darth Vader and his meditation chamber is found in the first chapter of the Paul S. Kemp novel, Lords of the Sith:
Vader completed his meditation and opened his eyes. His pale, flame-savaged face stared back at him from out of the reflective black transparisteel of his pressurized meditation chamber. Without the neural connection to his armor, he was conscious of the stumps of his legs, the ruin of his arms, the perpetual pain in his flesh. He welcomed it. Pain fed his hate, and hate fed his strength. Once, as a Jedi, he had meditated to find peace. Now he meditated to sharpen the edges of his anger.
He stared at his reflection a long time. His injuries had deformed his body, left it broken, but they’d perfected his spirit, strengthening his connection to the Force. Suffering had birthed insight.
...
Drawing on the Force, he activated the automated arm. It descended and the helmet and faceplate wrapped his head in metal and plasteel, the shell in which he existed. He welcomed the spikes of pain when the helmet’s neural needles stabbed into the flesh of his skull and the base of his spine, unifying his body, mind, and armor to form an interconnected unit.
When man and machine were one, he no longer felt the absence of his legs or arms, the pain of his flesh, but the hate remained, and the rage still burned. Those, he never relinquished, and he never felt more connected to the Force than when his fury burned.
The first two paragraphs explain that Vader uses his meditation chamber not to meditate on peace, but on his negative emotions; fear, hatred, anger, pain, loss and so on. Inside his meditation chamber, with his helmet removed, not only does he feel the physical pain of his injuries, he feels the emotional pain of their memory. This pain makes him stronger, and strengthens his connection to the Force, through the Dark Side.
The second two paragraphs explain that when he puts his helmet back on and leaves the meditation chamber, Vader is unified with his suit and forgets the physical pain, but the mental pain remains. His meditation chamber is one of his strongest connections with the Dark Side of the Force, it facilitates a nexus for him to draw upon.
Even when he is not in his meditation chamber, the act of meditation draws upon these same elements, from the Lords of the Sith, Chapter Thirteen:
Neither the Emperor nor Vader ate. Instead, both meditated, communing with the Force, Vader standing, his Master seated. Vader, still pondering his Master’s words, drifted into the Force, let its rough currents pull him where it willed. As was so often the case, he saw moments from his past, a series of inchoate, violent, pain-filled images and sounds.
His decapitation of Darth Tyranus, the first kill his Master had asked of him.
Padmé’s screams.
His murder of the younglings in the Jedi Temple, their eyes wide with a fear that only fed his righteous wrath.
Padmé’s screams, her pain.
Treachery.
Mace Windu’s shouts of rage as he’d realized the truth.
Padmé’s screams.
Traitor.
The fires of Mustafar, his hatred for Obi-Wan, who’d feared him and tried to keep him from his destiny, who’d tried to take Padmé from him, who’d put him in the armor.
Padmé’s screams, her despair.
“No, Anakin! No!”
In Legends, Vader uses his meditation chamber to fantasize about 'what-ifs' regarding Padme, but even this dreams end up fueling his negative emotions once he wakes up to his reality (as talked about in this comic book).
Conclusion
From all of the above, the argument can be made that:
When the Sith use the (Dark Side of the) Force, such as in locating a person or an object, they focus on their negative emotions to fuel their strength.
As all objects are connected to the Force, some more strongly than others (as is the case with a Force nexus, and I am not suggesting that Darth Vader's meditation chamber was a Force nexus, I am only using it as an example), this would include the ship, the Carrion Spike, but it would especially include Vader's meditation chamber on that ship.
Not only would his meditation chamber have a strong connection with the Dark Side of the Force, but Vader would have a strong connection with it, and with the Dark Side of the Force through it, thus making it the perfect object for him to focus on in his search for that ship. The Emperor somewhat confirms this in Chapter Thirteen of the novel Tarkin:
No doubt Vader was tracking the Carrion Spike by focusing his attention on his meditation chamber. But why had he not sensed a disruption in the Force when Tarkin’s ship had been taken?
The first half of this quote illustrates that Sidious recognizes the meditation chamber as being the strongest object for Vader to reach out to with the Force in order to find the ship. The second half makes mention of the fact that Vader should, generally have noticed the loss of the ship, and if taken in the context of the first half, may also suggest that Vader should also have noticed the loss since it held an object that Vader himself was strongly connected to through the Force.
N.B. The Sith Code quotation comes from Legends, I don't think the exact formulation of it has appeared in Canon yet.
When a sufficiently skilled Force user needs to find a specific entity, he can meditate on it to pinpoint its location.
The Force is like a search engine (or Siri, if you want to). If you are able to tell the Force exactly what you are looking for, and you pass the skill check, it will return to you the galactic coordinates of the queried entity.
In Episode II, Obi-Wan couldn't find the Kaminoan system in any star chart in the Jedi Archives. So he used the Force. He searched "Force, where is the Kaminoan system?" And the Force replied him with the destination coordinates to jump to.
Same thing for Darth Vader. What is unique about that meditation sphere is that it is Vader's sphere. All Vader needs to do is ask "Dark side, where is my meditation sphere?" And he will instantly receive its current and destination galactic coordinates.
