Peter Layton, a visiting fellow at the Griffith Asia Institute at Australia's Griffith University, offered a scenario similar to Balbi's: If the vessel had sunk but was still intact, Layton said, the crew would have about a week to 10 days of oxygen.
The San Juan entered service in the Argentine Navy in 1985, but underwent an extensive "mid-life update" from 2008 to 2013 - a refit that was reportedly plagued by delays due to a shortage of funds.
Officials have suggested that the submarine is likely on the ocean floor, where even the best scenario would mean it has only seven days worth of air if it can not resurface.
The submarine had reported an electrical problem and was heading back to its base in Mar del Plata when it disappeared on Wednesday almost 300 miles off the coast.
The Atlantis started aiding search operations, using multi-beam sonar and underwater communications systems, around 2 p.m. Tuesday.More news: Iranian Man Charged In HBO Hack That Released 'Game Of Thrones' Script
Frank Owen, from the Submarine Institute of Australia, told news.com.au that the crew could still be underwater and hoping they are brought to the surface.
"Our concerns about the oxygen reserves on board are growing", navy spokesman Enrique Balbi said. "We trust in God", said one sign.
In its last contact with its naval base last Wednesday, the submarine had given word of a battery glitch, Captain Gabriel Galeazzi, another navy spokesman, said. The oxygen situation could be helped, even if the vessel bobs adrift on the surface with the hatch open.
The submarine was originally scheduled to arrive Sunday in Mar del Plata, a navy base about 250 miles southeast of Buenos Aires.
Maria Victoria Morales, the mother of Luis Garcia, an electrical technician aboard the vessel, said: "Today is a critical day". "This is why we are deploying all resources with high-tech sensors".More news: Arsenal midfielder Mesut Ozil demands huge signing bonus to join Barcelona
Other experts say the Argentine submarine, which mysteriously disappeared last week, may be at the bottom of the Mar del Plata. "At this time, we have not received a request for military assistance", he added.
Cards, banners with slogans and placards have been strung up on the outside of the Mar del Plata base's wire fence, expressing solidarity with the families tensely waiting for any news.
The Argentine navy had one more interaction with the captain before the submarine went missing, said Galeazzi.
Reports emerged that crews searching for the missing sub had detected a heat signal beneath the waves - however the vessel has still not been found.
Her sister Silvina Krawczyk told Reuters: "They are working very hard to find them". But the raft is a different model than what would be carried on the San Juan, and a white flare is not typically used by the crew.More news: Former Braves GM John Coppolella is now banned from baseball for life
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