Mars One, a Netherlands-based nonprofit, aims to send four people on a one-way trip to the red planet every two years.
Three Indians, 29-year-old Taranjeet Singh Bhatia, who is studying computer science at the University of Central Florida, Ritika Singh, 29, who lives in Dubai, and 19-year-old Shradha Prasad from Kerala, are among the 100 finalists for the Mars mission announced last month.
Out of these 100 finalists, 24 will train to go to the red planet.
The delay was necessitated by a lack of investment funding, which has slowed work on a robotic precursor mission that Mars One had wanted to send toward the Red Planet in 2018, Mars One CEO Bas Lansdorp said.
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The robotic mission aims to launch a lander and orbiter to Mars, to test out technologies needed for human settlement.
Mars One awarded contracts to aerospace firms Lockheed Martin and Surrey Satellite Technology to work on the lander and orbiter, respectively, 'SPACE.Com' reported.
"Unfortunately, the paperwork of that deal is taking much longer than we expected," Lansdorp said.
"I now think that it will be done before the summer of this year. That means that we will not be in time to finance the follow-up study that Lockheed Martin needs to do for our first unmanned mission in 2018, which unfortunately means that we will have to delay that mission to 2020," he added.
In the video, Lansdorp also responded to an article critical of Mars One that Matter magazine posted last week.
In the article, astrophysicist Joseph Roche, a former Mars One astronaut candidate, alleges that the organisation has been picking its astronauts at least partly based on how much money they donate to the private colonisation effort.
Roche also said that Mars One's selection process is flawed. The article author Elmo Keep alleges that Mars One received just 2,761 applications from prospective red planet settlers, not the 202,000 claimed by the organisation.