Last year's budget delivered the first budget of the new administration. It projected a drop in future planetary funding to enable additional funding for Earth science missions. At the time, I projected that this budget would mean that NASA could not afford Flagship missions to both Mars and the outer planets. Subsequent analyses provided by NASA bore out that assessment.
This year's budget proposal recommends further budget cuts. In the near term, those cuts are borne by the Mars program while the New Frontiers and Discovery programs fund a mission development each. At the end of the five year window, the Mars funding is restored but the New Frontiers and Discovery programs are cut. With the budgets forecast by this proposal, it appears that NASA cannot afford both the Mars program at its current or restored levels and active development of both New Frontiers and Discovery missions.
I rarely editorialize in this blog, but I will here. I believe that robust funding of the New Frontiers and Discovery programs are essential to a balanced program that includes the entire solar system. If necessary, funding for these programs should be maintained by reducing the increase for the Mars program, which should still enable two or more substantial ("medium class") missions to Mars per decade. (An increase to the planetary science budget would also do the trick -- hint to Congress.)
In an era of constrained budgets, Mars makes sense as a focus. It is easy to reach, relatively easy to land on, has a fairly benign environment (at least compared to, say, the surface of Venus or the radiation fields at Europa), and NASA has substantial investments in technology to enable missions.
I am disappointed that there appears to be no way to begin development of a substantial NASA mission to any of the icy moons in the outer solar system in the next decade. That leaves me hoping for the selection of the TiME Titan lake Discovery mission and the European Ganymede orbiter with Europa and Callisto flyby mission. (I'm very impressed by the other two Discovery proposals in competition, but TiME must be selected for the next Discovery mission to arrive while the northern lakes are in a position for it communicate with Earth after landing.)
Ryan Anderson at the Martian Chronicles blog pointed out some smaller but key cuts that I had overlooked. This year, NASA is spending $70M to continue operations of the Mars Odyssey orbiter, Opportunity rover, and the Mars Reconnaissance orbiter in addition to supporting American involvement for the European Mars Express orbiter. Next year's proposal will cut that amount to $54 million (-24%). The outer planet budget, which funds the Cassini orbiter along with future mission planning, will drop by 31%. These cuts suggest substantial reductions in support for these continuing missions as hinted at by the angst over the upcoming review of these missions (also see here for Cassini). (Funding levels for operating Discovery missions also drop, but it is hard to tell whether this is because of increased efficiencies in operations that occur as a mission gains experience, different mission phases, or because of planned cuts in science returned. Also, what is that sudden jump in Dawn mission funding in 2017 after it has completed its mission at Ceres? Is this a hint of an extended mission?)
If the budget levels in this proposal are implemented, NASA will still have the most capable program of planetary exploration in the solar system. But between this and last year's proposals, that program and the portion of the solar system it can reach will be much smaller than we expected two years ago.
Here is a list of other good articles to read about the new budget proposal:
NASA Budget Pushes Science to the Brink (Planetary Society)
ESA To Press Ahead with ExoMars (Space News)
Proposed NASA Budget Cuts Mars Exploration by $226 Million (Martian Chronicles blog)