The wrench in this plan is the two-year delay in the previously selected Discovery mission, the InSight Martian geophysical station. As you’ve probably heard, the key instrument for this mission wasn’t ready in time to allow the planned launch this year. Instead, under a just-announced new plan, the mission will lift off in 2018 when Earth and Mars next align for launch. As a result of the delay, the costs of launch and operating the mission that had been planned for the next two years are pushed out to 2018 to 2020. This is when NASA wants to start development on the next one or two Discovery missions. In addition, a substantial group of engineers and scientists need to be paid from now until launch in 2018 to fix the instrument problem and retain the core group needed to prepare the mission for launch and flight.

When NASA’s director for its planetary science program, Jim Green, announced the new InSight plan at a recent meeting, one of the earliest questions was whether or not this meant that NASA would still be able to select two Discovery missions. An article on the journal Nature’s website poses the same question.

NASA has not formally released an estimate of the additional costs required under the new plan, saying that those figures will be available this coming August. At a recent meeting, the InSight mission’s principal investigator stated that flying the mission later would cost $150M. It’s not clear from his statement what all is included in that figure. NASA had ~$150M budgeted for InSight for the next two years to cover launch and mission operations. Those costs will need to be shifted out two years. There will also be new costs for the 2016-2017 period to fix the instrument and to keep the core team together, and it’s not clear if this spending is included in the $150M estimate.

Because the federal budget operates on a cash basis, any money not spent in the current fiscal year returns to the treasury. So NASA can't simply bank the money it had planned to spend in 2016-2017 and spend it two years later. The agency’s managers may have some flexibility, though, subject to many rules that I don’t pretend to understand in any detail:

NASA may be able to sign long term contracts with an outside company or organization (which would include the Jet Propulsion Laboratory, which is developing and will later operate the InSight mission). In some cases, money committed to a contractor counts as spent by the government when the contract is signed but the contractor can spend the transferred money later.

NASA’s managers may be able to shift money among projects. For example, they might be able to spend money in the next two years originally earmarked for InSight on the Mars 2020 rover project. Then in 2018-2019, the agency might be able to spend money originally planned for the rover on InSight.

The $150M is less than half of what NASA is projected to be spending on Discovery mission development per year by the end of the decade. In theory, delaying the start of the next Discovery mission(s) by around six months might solve the cash flow problem and allow the selection of two Discovery missions. Jim Green has said that mission timing will be crucial, and all the teams currently in the Discovery competition have been asked to identify alternative launch dates.

I am convinced that NASA’s managers would like to fly InSight and select two new Discovery missions if fiscally possible. The kinds of options that I've mentioned above probably just scratch the surface on the kinds of ideas they are exploring. We will know more when NASA’s managers release the final budget plan for InSight this August and when they announce in late this year whether or not they selected one or two new Discovery missions.

In the meantime, veteran space reporter Jeff Foust has tweeted that Science Mission Directorate head John Grunsfeld (Jim Green’s boss) told him that the option to select two missions is still on the table. We can hope that he and his managers find a solution to select two.

The other problem, how to enable missions to Saturn’s moons Titan and Enceladus may not have such a clean path to a resolution. A spate of new discoveries have raised interest in exploring these worlds as possible abodes of life. These discoveries caught the attention of key members of Congress who have directed NASA to establish an Ocean Worlds program to explore these two moons along with Europa. (There are other ocean moons in the outer solar system, but they are less likely to be abodes of life or would be harder to explore.)

The Congressional mandate directed NASA to explore these worlds through a mixture of low-cost (Discovery program), medium cost (New Frontiers program, ~$850M), and high cost (Flagship, >$1B) missions. Planning for a Europa mission with a Flagship mission is underway (although there’s no agreement on when the mission should launch). NASA is left to find a way to send new missions to Titan and Enceladus to fulfill the Congressional mandate.

Unfortunately, neither of these moons was highly ranked as targets by the most recent Decadal Survey, which represents the consensus of the scientific community on exploration targets. (Europa was highly ranked.) The Survey examined missions to land on the lakes of Titan and decided that the scientific return for the estimated approximately $1B cost was not high enough. A mission to orbit Titan, land on a lake, and fly a balloon was estimated at an astronomical cost of $6.7B. Mission concepts, primarily orbiters, were examined for Enceladus, found to be expensive at $1.9B and were not a priority at that cost.

Fortunately, mission concepts such as multi-flyby spacecraft instead of more expensive orbiters have been more fully developed, giving mission planners lower cost options. In recent competitions for Discovery missions, two teams have proposed multi-flyby missions to fly through Enceladus’ plumes to search for clues to habitability and in one of the proposals to also map Titan’s surface at higher resolution. A third team proposed a lander for a Titan lake. All of these proposals were for missions at a fraction the cost of the Decadal Survey cost estimates for similar (but to be fair, more capable) missions.

Unfortunately, per a comment by Green at a recent meeting, while these Discovery missions proposed compelling science, they were judged by reviewers of being unlikely to fit within the Discovery cost cap. Green implied that similar missions could fit within the New Frontiers budget cap (further implying costs substantially lower than their Decadal Survey cost estimates).

Given NASA’s current budget level and missions in development, the agency has no ability to add another major Flagship mission to the queue of missions before the mid-2020s. That leaves NASA’s New Frontiers program as the only potential home for an Enceladus and/or Titan mission in the next ten years or so. But there’s a problem using this program, too. While Discovery proposals can target any world in the solar system except the Earth and sun, candidate missions for the New Frontiers program competitions were pre-selected by the Decadal Survey. The list was carefully examined to ensure that the missions are scientifically compelling, affordable, and balance the wide interests of planetary scientists. Because NASA is mandated to follow the Decadal Survey in setting its priorities, the list of recommended missions carries weight. One purpose of the list is to prevent teams from lobbying outside the Decadal Survey for their favorite New Frontiers candidates to NASA’s senior managers and Congress. (There’s no mechanism to prevent Congress from imposing its favorites on NASA, though.)