Digital marketing tycoon Chris Brown originally planned to go on Sunday's submersible tour of the Titanic wreckage but withdrew due to safety concerns. His friend, Hamish Harding, is among those aboard the missing vessel.

Brown, who described himself as a "modern day adventurer," admitted that he knew "very little" about the tour operator, OceanGate Expeditions, prior to signing up. But he said the deep-sea trip initially sounded "like a great idea."

"The Titanic's obviously an iconic wreck," Brown told ABC News' Michael Strahan during an interview Wednesday on "Good Morning America."

"OceanGate had put forward this program to go down and do a 3D scan of the wreck," he added. "So it's a chance for an expedition, exploration and adding a bit of science into the situation."

Brown said safety concerns ultimately led him to pull out of the trip, but he declined to go into detail.

"I'm not really sure that this is the time to be going into that sort of thing," he added. "I think that the focus right now has to be on trying to rescue these people. It's not fair on the families and friends to be making speculation about what might've happened or how it happened at this point."

Brown said he feels "no" apprehension about joining similar projects in the future but noted that it's important to "think about all the risks."

"If you don’t have an appetite for those risks, then you might not go ahead," he said. "You may try and mitigate those by bringing in some expertise from outside. You might have other risks or dangers that could be mitigated by changing the time of when you go out there."

The submersible that was reported missing while on a tour of the underwater wreckage of the Titanic is an unorthodox vessel with a relatively unproven history, according to company press materials and experts familiar with underwater vehicles.

News of the vessel's disappearance prompted a flurry of interest in the company OceanGate Expeditions and its deep-sea submersible called the Titan.

The company's founder and CEO, Stockton Rush, who is one of the five people aboard the missing vessel, manned the Titan's first "validation dive" to 4,000 meters in 2018, according to the company. The company then began offering tourists the opportunity to dive to the depths of the Titanic in the following years, selling tickets for the 2023 journey for $250,000.

Here's what we know about how the submersible operates.

-ABC News' Peter Charalambous

A source familiar confirmed to ABC News that there were reports of "banging" that were picked up by sonar in the search area on Tuesday morning, but nothing has yet been found.

The U.S. Coast Guard had said early Wednesday that an aircraft with sonar capability "detected underwater noises in the search area," but remotely operated vehicles were unable to find the origin of the sound.

-ABC News' Luke Barr

Magellan, an international exploration company that digitally mapped the Titanic wreckage last year, said Wednesday that it is "ready to support" the search for the missing submersible and is "fully mobilized to help."

The U.K.-based company told ABC News that it was contacted by the submersible’s operator, OceanGate Expeditions, early Monday and "immediately offered our knowledge of the specific site and also our expertise operating at depth considerably in advance of what is required for this incident."

"We have been working full-time with U.K. and U.S. agencies to secure the necessary air support to move our specialist equipment and support crew," Magellan said in a statement.

When asked for comment about media reports that U.S. authorities have failed to give Magellan the necessary permits to participate in the search, the company told ABC News it "does not not wish to comment on any specific media report."

-ABC News' Emma Ogao

Samad Dawood, the brother of Shahzada Dawood, one of the passengers who died in the submersible, said losing his brother and nephew, Suleman Dawood, is heartbreaking.

"This is beyond what you could ever imagine in terms of the kind of hardships and struggle that we've had. I think what we've seen is enormous tragedy and devastation and a lot of emotions. Obviously we were hoping to hear some good news about the rescue and them coming back. It was heartbreaking to find out that that's not the case," Samad Dawood told ABC News.

Samad Dawood said his brother had a strong sense of adventure and curiosity about the world.

"He was always the kind of person who has this incredible love for the world," Samad Dawood said.

"He inspired us curiosity. And he was a guy who just wanted to go out there, experience what the world had to offer, even though he he himself pushed himself to do it. So they made adventures to go to Antarctica, to go to Greenland and to go to Africa and go to the rapids," Samad Dawood said.

This sense of adventure was passed on to Shahzada Dawood's son, 19-year-old Suleman Dawood, who was also in the submersible. Suleman Dawood had traveled to all seven continents, according to Samad Dawood.

"He was so filled with humbleness and gratitude," Samad Dawood said.

"We're deeply grateful for all the support and the love and the effort that the people have made, working tireless nights being optimistic in giving a sense of hope, giving that transparency to us. But obviously we were devastated as a family ... that we couldn't get them back safe," Samad Dawood said.

-ABC News' Octavio Cadenas, Dr. Jennifer Ashton and Victor Ordonez