Before I write my post on an upcoming planetary mission (promised in my last post), I wanted to complete my reporting on the Outer Planet Analysis Group (OPAG) meeting last week and the portion of the Small Bodies Analysis Group (SBAG) that I listened to Monday. These analysis groups (with their Mars and Venus counterparts) review NASA's planetary science program and provide feedback.
I picked up one key point in Monday’s meeting while listening to James Green, the head of NASA’s planetary science program. In reviewing his program’s projected budget, his team believes that it can start two additional New Frontiers missions ($1B each) and a single Discovery mission ($500M) in the next ten years. The balance between the two programs is NASA's choice; for approximately the same funding it could select one New Frontiers and three Discovery instead.
The Discovery program has been incredibly successful -- just look at the currently operating MESSENGER mission at Mercury and the Dawn spacecraft that just left Vesta headed for Ceres. However, many of the easy (read inexpensive) exciting missions have been done. And it is hard to fit an outer planets mission, and I suspect many potential comet and asteroid rendezvous missions, in its budget.
Alfred McEwen at the University of Arizona proposed an Io Discovery mission for the recently completed selection competition. He is also principle investigator for the HiRISE camera on the Mars Reconnaissance Orbiter. McEwen provided a proposal to the OPAG meeting to help make Discovery missions more competitive in future Discovery selections. In the justification, he said that the Discovery program as currently structured doesn’t provide sufficient funding for outer planet missions with adequate budgetary reserves. (His proposal was to help mitigate this problem by adjusting the Discovery cost cap by the length of time required to conduct the selected mission.)
If that remains true, the Discovery program may remain an inner solar system (say from Venus to the asteroid belt) program. However, in the last Discovery competition many Venus missions were proposed but none made it as far as the finalists list, suggesting that the next step for Venus may require a larger New Frontiers class mission. NASA is looking to fly approximately five new missions to Mars starting in 2017 (see my previous post) outside of the Discovery program. So the single new Discovery mission may target another inner solar system destination.
Two New Frontiers missions gives an outer solar system mission, a comet sample return, a Trojan asteroid mission, and a Venus lander mission better chances of being selected. I don't know if NASA used this reasoning in laying out it's roadmap, but it's a balance between New Frontiers and Discovery that I agree with.
A couple of other points from the OPAG meeting:
I have often wondered why the Europa multi-flyby proposal (nicknamed the Europa Clipper) has been estimated to cost $2B when ESA can fly a Ganymede orbiter with Callisto and two Europa flybys for ~$1.2B and NASA estimates a multi-flyby mission for Io would cost ~$1B. The answer may be as simple as, “it’s the radiation”. In a recap of the multi-flyby Europa concept, the presenter mentioned that the Jupiter Juno New Frontiers mission (perhaps $1B in 2015 dollars) will receive around 1/10th (worst case 1/3rd) the radiation of the Europa mission. Those thirty or so Europa flybys the Clipper would do would expose the spacecraft to an incredible radiation load, and that may drive the cost difference compared to the other missions.
The availability of plutonium 238 for power supplies for future planetary missions has been a concern for the last several years. An update on the situation at the OPAG meeting stated that NASA has on hand two additional Curiosity radioisotope systems (MMRTGs), one of which will be used for the 2020 rover mission. The second set could be used by the Europa mission or potentially another mission. In addition, NASA continues to develop the next generation of power supplies (ASRGs), and plans to have one available for a New Frontiers or Discovery mission. However, the Pu-238 supply is becoming old and out of spec. It’s essential that production of new Pu-238 begin to enable missions in the next decade.
A closing note: Curiosity has hit the jackpot, already. Water flowed across its landing site, possibly multiple times. If you haven’t read Emily Lakdawalla’s post on the latest Curiosity news, I encourage you to do so. Remember, this is just the start of what promises to be an incredible stroll through Martian history. And we can look forward to equally exciting locations for ESA’s 2018 ExoMars rover and NASA’s 2020 rover to explore.