Why Did Isaac Clarke Go to the Ishimura?

Isaac Clarke went to the USG Ishimura for two reasons. Officially he was the ship systems engineer on a CEC repair crew, sent aboard the shuttle USG Kellion to fix whatever had silenced the planet cracker. Personally, he went for Nicole Brennan, his girlfriend and the Ishimura's senior medical officer, who had sent him a distressed message he couldn't bring himself to watch to the end. (Dead Space)

The job: a silent planet cracker#

The Ishimura was the CEC's biggest planet cracker, working over Aegis VII in 2508. After Marker 3A was brought aboard, the outbreak tore through the crew, and the ship went silent and then issued a distress call. The CEC's answer was a routine-looking maintenance call: send a shuttle, find the fault, fix the comms. (Dead Space; Dead Space: Downfall)

The Kellion carried security chief Zach Hammond, computer specialist Kendra Daniels, two corporals and Isaac, whose job was to repair the ship once they got there. The Ishimura didn't answer their hails. The automatic docking failed, the Kellion crashed onto the Flight Deck, and within minutes the first Necromorphs had killed everyone but Isaac, Hammond and Kendra. (Dead Space)

Dead Space: Downfall adds a darker layer. Security officer Alissa Vincent launches the distress signal before she dies, believing she's warning the outside world. In the film the Marker is manipulating her through a hallucination, so the call that brought the Kellion was, in a sense, the Marker asking for more people. (Dead Space: Downfall)

The real reason: Nicole#

Isaac had his own reason to be on that shuttle. Nicole was aboard. As the Kellion approaches, he watches a video message from her. She's upset and apologising, and the message cuts off before the end. Isaac doesn't watch the rest. (Dead Space)

Once he's aboard, finding her becomes the thread that pulls him through the ship. Hammond gives him repair jobs deck by deck, and Isaac keeps looking for Nicole on the way, following glimpses of her and, later, her voice. (Dead Space)

What he found#

Nicole was dead before the Kellion arrived. With the Medical Deck overrun, she had recorded her last message to Isaac and taken her own life. The Nicole who guided him was a hallucination from the Marker, which used his grief to get him to carry it back to its pedestal. Kendra makes him watch the end of the message on Aegis VII, and the page on what happened to Nicole Brennan covers it in full. (Dead Space)

So the honest answer has a sting in it. Isaac went to rescue Nicole, and the thing that made him go was the same grief the Marker then turned against him. That's our reading of the story's design, and it's the reading Dead Space 2 builds on when the Nicole hallucination returns. (Dead Space)

What the 2023 remake adds#

The remake tells the same story with the same date and the same mission. Two things change how Isaac's reason lands. (Dead Space (2023))

First, Isaac talks. In 2008 he was silent and his motive came only from the video. In the remake he speaks and argues with Hammond and Kendra, so he reads as a person with his own stake in the mission rather than a player stand-in. The page on why Isaac was silent covers that change. (Dead Space (2023))

Second, the remake's logs fill in their history. Nicole met Isaac while treating his mother, and when the post of senior medical officer on the Ishimura opened in 2507, Isaac pushed her to take it. He went to the ship partly because he'd helped send her there. (Dead Space (2023))

Kendra, it turns out, had her own reason too. She was an EarthGov agent sent to get the Marker. (Dead Space)

Read more: the full Dead Space story explained and the Isaac Clarke biography. (Dead Space; Dead Space (2023))