Over the next few years, NASA plans to get back to launching its own rockets again, with two deep-space missions that will take new hardware and people in the vicinity of the Moon. Those launches are tentatively scheduled for 2018 and 2021, but most likely they won't get off the ground on time, thanks to high costs and technical challenges. That's the conclusion of a new report from NASA's Office of Inspector General.

The two inaugural missions are part of NASA's long-term plan of sending people to Mars in the 2030s. They'll involve two key pieces of hardware the space agency is developing: a giant rocket called the Space Launch System and a crew capsule called the Orion. The first SLS flight, scheduled for November 2018, will launch an empty Orion capsule into orbit around the Moon. The second flight, slated for no earlier than 2021, will launch a crew of four on an eight-day journey, also around the Moon.

The programs supporting these first couple of flights are not being funded at recommended levels

Right now, NASA is also working on all of the hardware on the ground that is meant to support launches of these vehicles. That includes building a new mobile launch platform that the SLS will take off from, and making modifications to certain buildings at NASA's Kennedy Space Center in Cape Canaveral, Florida.

But the OIG report points out that all of the programs supporting these first couple of flights are not being funded at recommended levels. That means that if an issues pops up, there isn't enough money to cover for it. Meanwhile, the development of a few other key systems, such as the software needed for the flights, are behind schedule. All of these issues combined make it pretty unlikely that the first flights of SLS will happen when NASA says they will, the report argues.

Another problem is that the overall plan for these launches could change. NASA has said it might do away with the uncrewed SLS mission, and just go with the crewed one first. The agency is studying what it'd take to pull this off, and such a move would seemingly delay the first SLS flight until 2019 at the earliest. However, this change hasn't be confirmed just yet, and so the original two-flight plan still stands for now.

The report also looked at the larger NASA Mars mission beyond these first two flights, and criticized the space agency for not having much of a plan. A couple of weeks ago, NASA's Bill Gerstenmaier, the associate administrator for human exploration and operations, gave a rough outline of the missions NASA hoped to do in preparation for a crewed Mars mission. The timeline involved launching a number of habitats and modules into an area around the Moon. These modules will be put together to create what NASA is calling the Deep Space Gateway — a place for astronauts to visit and train. Once that station is built, NASA will launch the Deep Space Transport vehicle — the spacecraft that will actually take people to the vicinity of Mars.

The cost of pulling off a comprehensive human mission to Mars at NASA is could be astronomical

Though that outline represents the first major details of the Mars mission NASA has announced in a while, it still doesn't specify when these vehicles will be made and how much they'll cost. And what about the habitats for astronauts to live on the Red Planet, or the vehicles needed to transport them to and from the planet's surface? Those details are missing too, the OIG reports says. Given all this uncertainty, the OIG recommends that NASA come up with more rigorous schedules, establish objectives for the things it needs to accomplish, and figure out better cost estimates for what this whole thing will take.

Because the cost of pulling off a comprehensive human mission to Mars at NASA is could be astronomical — so coming up with better budget estimates is crucial. Up until this point, NASA has spent more than $15 billion on its Mars efforts, but the OIG says that everything associated with the human exploration of Mars will exceed a cost of $210 billion by 2033. For that reason, the OIG recommends that the space agency figure out ways to save money on its Mars mission — either by partnering with other government space agencies or the private space industry.

This isn't the first time that NASA's been criticized for lacking a clear plan regarding its Mars initiatives, and it's not even the first time that the OIG and other advisory committees have cast doubts on the schedule for the first launches of the SLS. And 2018 is fast approaching too, so we'll soon find out if all this forecasting of delays turns out to be true.