The Mars One mission to establish a human colony on the red planet has been delayed by two years, adding fodder for critics who have already cast doubt on the project's selection process, timeline and budget.

The Dutch non-profit group behind the project recently announced that it was pushing back the planned launch to 2027, due to a lack of funds for a robotic mission that was scheduled to precede the first human launch. The aim of the robotic mission is to test out the technologies required for human survival on Mars.

The entire mission, projected by Mars One to cost $6 billion, calls for the use of existing technology and would be funded by a mix of sponsors, ad revenue and private investors. There is also a planned reality TV show/contest that would track the participants as they prepared for their departure.

But it's not just the new delay that's causing concerns about the feasibility of the project.

Physics and astronomy Prof. Paul Delaney says, while the notion of sending humans to colonize Mars isn't far-fetched, the Mars One project has failed to show that it has seriously considered all the other factors required for a successful mission.

"Anybody who has been following this story from the outset, they've all said that the technology is not there, the budget is not there, the timeline is just not realistic," he told CTV's Canada AM on Tuesday.

"While the notion of going to Mars in this sort of incremental way is not that far-fetched… all the other pieces that were going to make it work have never been there."

He said that the soil of the Red Planet is not too dissimilar from that of Earth, meaning that many of the raw materials needed for survival are already there. Unfortunately, the technology required for humans to survive once landed on Mars isn't yet available.

"We don't have the ability at this moment in time to put an inflatable habitat on the surface of Mars and have people survive for years on end. But I don't really think that technology is that far away," he said.

Delaney also said that the project's selection process – involving an online video application, interview, physical and psychological health checks, and various group challenges -- is not nearly rigorous enough to screen for potential astronauts.

"This is playing out a little bit like a TV script and that doesn't equate with the rigour associated with putting people in a capsule for nine months and then going out and facing the unknown," he said.

Delaney isn't alone in his views.

Recently, former Canadian astronaut Julie Payette said the technology to establish a colony on Mars won't be available in time to meet Mars One's timeline. Chris Hadfield has also questioned the expectations that a manned mission to Mars could fly so soon.

Engineers from MIT have analyzed the feasibility of the mission too, and suggested that new technology will be required to keep humans alive once they arrive on Mars.

Mars One addresses criticism

Mars One CEO Bas Lansdorp recently addressed many of the concerns about the mission on the project's website

On the new delay, he said: "I believe we are on track and moving in the right direction. We may have a two year delay now but we show that people are interested in Mars One and in Mars exploration. People want this to happen and it is my conviction that as long as we can show that we are moving in the right direction, that we are getting the right companies under contract, and we are getting these contracts done, then the world will accept that we have a delay in getting our humans to Mars."

He also addressed criticisms on the project's budget, noting that the figure comes from "good discussions that we have had with established aerospace companies from around the world. They have already been building systems for the ISS and for unmanned missions to Mars, which are similar to the ones we need. We are very confident that our budget will be enough."