This computer-generated view depicts the part of Mars at the boundary between darkness and daylight, with an area including Gale Crater beginning to catch morning light. REUTERS/NASA/JPL-CALTECH/HANDOUT

NASA's ambitious Journey to Mars is facing "multiple cost and technical challenges," the space agency's Office of Inspector General (OIG) warned in a new audit report. Moreover, the report also raised doubts over the feasibility of NASA's plans to send crewed mission to Mars in the 2030s or early 2040s, calling for a more detailed operational plan beyond 2021's Exploration Mission-2 (EM-2).

"If the Agency is to reach its goal of sending humans to the vicinity of Mars in the 2030s, significant development work on key systems such as a deep space habitat, in-space transportation, and Mars landing and ascent vehicles must be undertaken in the 2020s, and the Agency will need to make these and many other decisions in the next 5 years or so for that to happen," the OIG wrote in its report, published Thursday. "In addition, to position itself to make wise investment decisions, NASA will need to begin developing more detailed cost estimates for its Mars exploration program after EM-2."

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NASA's planned missions to the red planet rest on two legs — the Space Launch System (SLS) rocket, which is a successor to the agency’s now-defunct Space Shuttle program, and the Orion deep-space capsule. Under the space agency’s current plans, the first uncrewed integrated flight of Orion and SLS — Exploration Mission-1 (EM-1) — is slated to take place no later than November 2018, and the first crewed launch would follow in 2021.

During the first mission of SLS and Orion, NASA plans to send the spacecraft into a distant lunar retrograde orbit — a stable orbit that would involve a flyby of the moon. The space agency says that the challenging mission would help it test maneuvers needed to accomplish future missions to deep space.

However, in its report, the OIG expressed skepticism over whether NASA would be able to meet its deadlines, citing both technical and budgetary hurdles.

"Although the Agency’s combined investment for development of the SLS, Orion, and GSDO programs will reach approximately $23 billion by the end of fiscal year 2018, the programs’ average monetary reserves for the years leading up to EM-1 are much lower than the 10 to 30 percent recommended by Marshall Space Flight Center guidance," the report, published after a nine-month audit by the OIG, warned. "Low monetary reserves limit the programs’ flexibility to cover increased costs or delays resulting from unexpected design complexity, incomplete requirements, or technology uncertainties."

The report comes less than two months after NASA began a feasibility study to consider the risks and benefits associated with adding astronauts to the first integrated launch of the SLS and Orion. If the study, expected to be completed by this spring, concludes that the benefits associated with a crewed flight outweigh the risks, it could push the target date for the first EM-1 mission to mid-2019.