The president's 2013 budget, released today, asks for modest increases for some federal science agencies but trims funding to NASA. The request takes a deep bite out of Mars and outer-planet science exploration in particular.

NASA's funding would fall to the lowest level in four years, with a total budget of $17.71 billion. The president's request projects a flat budget through 2017, with no growth to even account for inflation.

"We are having to make tough decisions because these are tough economic times," said NASA administrator Charles Bolden during a press conference Feb. 13.

As expected, planetary science – in particular Mars exploration and outer-planets missions – is the biggest loser, getting a $309 million decrease compared to last year. This means NASA will not be able to maintain previous commitments to the European Space Agency for dual Mars missions in 2016 and 2018, Bolden confirmed at the conference.

The hit to outer-planet exploration means a lack of funding for any new mission to study the moons of Jupiter or a Uranus orbiter, two projects that received high priority in last year's planetary science decadal survey. The reduction might also affect ongoing missions such as the Cassini spacecraft that is currently exploring Saturn and its moons, though this will depend on the outcome of NASA's senior reviews later this year.

The budget does include some winners. Manned exploration would get a boost of $200 million. This includes $2.8 billion for a new heavy-lift rocket system, which continues much of the work from the canceled Bush-era Constellation program that would take astronauts beyond low-Earth orbit.

The long-delayed and over-budget James Webb Space Telescope would get $627.6 million, which is a more than $100 million increase over last year. This mission will require continued funding until its launch date, currently pegged at October 2018.

Other scientific agencies are also getting modest increases. The National Science Foundation would be given a 5 percent increase, receiving $7.4 million. While Obama promised to double the NSF's budget back in 2009, the difficult fiscal environment doesn’t seem to make this possible. The U.S. Geological Survey could also be getting a $34.5 million boost compared to last year, bringing its funding to $1.1 billion.

The president's budget request is just a taste of what may come. Congress has to agree on what the actual federal budget looks like, and legislators and the White House don't see eye to eye on many issues.

One major area of contention is the requested $830 million for private spaceflight companies. Many Congress members, particularly those whose districts include traditional spaceflight companies such as Boeing, have scoffed at previous private spaceflight requests, eventually providing around half of the requested amount.

But the new private companies are looking to prove their worth. SpaceX will launch its Dragon capsule to dock with the International Space Station this year.

The budget request also makes no mention of the failure of last year's bipartisan congressional subcommittee that was meant to find $1.2 trillion in deficit reductions. Members of this committee were unable to compromise, triggering an across-the-board cut to all government agencies. Congress will have to figure out what to do with this legislative requirement before starting deliberations on the final 2013 budget.