Day of Action Deep Prep: Planetary Science Division

Planetary exploration is a core enterprise of The Planetary Society. However, due to the significant programmatic and policy differences between robotic and human planetary exploration (robotic missions are much cheaper and more frequent and are driven by scientific consensus, human missions are generational projects that are driven by coalitions and international politics), we generally consider them as separate issues.

NASA's Planetary Science Division (PSD) is the science side of planetary exploration in the U.S. It's responsible for all robotic missions to solar system destinations except for the Sun and Earth. It funds the development and operations of planetary spacecraft, supports the national infrastructure for Plutonium-238 power systems, and is the primary source of research funding for the nation's professional planetary science community. Historically, it has received about 10% (or less) of NASA's total budget.

Though it faced significant budget cuts in the early 2010s, the Planetary Science Division — in part due to the ongoing work by The Planetary Society and its members — has seen its fortunes improve in the past 5 years. Its FY 2021 budget and 5-year projection proposed in Biden's FY 2022 budget request achieve historical levels of investment:

NASA's planetary science budget, with Biden's FY 2022 proposal. Data adjusted for inflation and normalized to maintain consistent accounting of launch costs and to remove Deep Space Network infrastructure costs between 2002 and 2007. Inflation-adjustment made using NASA's New Start Index. Source: Planetary Science Budget Dataset, compiled by Casey Dreier for The Planetary Society (accessible on Google Sheets or downloadable as an Excel file).

There are nine major program areas within the Planetary Science Division:

  • Discovery
    Competitively selected, small-scale (~$500M each) spaceflight program with a goal of launching a new mission every 2 - 3 years. Current development projects include Psyche, DAVINCI, and VERITAS.
  • New Frontiers
    Competitively selected, mid-scale (~$1 billion each) spaceflight program with a goal of launching once per decade. Current development project is Dragonfly.

  • Mars Exploration Program
    This manages all existing Mars spacecraft and funds Mars-related technology and scientific research efforts. There are no projects in active development.
  • Mars Sample Return
    Due to the prominence of MSR, this project was elevated to its own high-level program that reports directly to upper-level NASA management. At the conclusion of the MSR project, this program will end. This is the highest planetary science priority for The Planetary Society right now.

  • Lunar Discovery and Exploration
    The scientific part of the Artemis effort. Includes the Commercial Lunar Payload Services program and upcoming VIPER mission.
  • Outer Planets and Ocean Worlds
    Currently developing the Europa Clipper spacecraft and related technology development for exploring the ice-moons of the outer solar system.
  • Planetary Defense
    Funds ground-based NEO observations and manages a flight program consisting of DART (impacting this Fall) and developing the NEO Surveyor asteroid-hunting spacecraft. See our deep prep page on Planetary Defense for more information.
  • Radioisotope Power
    Funds the production of Plutonium-238 and related components, a critical power source for deep solar system and Mars surface exploration spacecraft (or any destination that can't use solar power).
  • Planetary Science Research
    Funds nearly all research by professional planetary scientists in the U.S.

The Decadal Survey

The scientific priorities of the Planetary Science Division are guided by the Decadal Survey, a once-per-decade report published by the National Academies of Sciences, Engineering, and Medicine. The survey is a product of a community-wide effort to define the highest-priority scientific questions facing the field and then identify the missions that could address them in a 10-year period.

The current decadal survey was released in 2011 and covers the years between 2013 and 2022. There is a new decadal survey report in the works, with a planned release of April of this year. We do not know what will be in this report, so there is no action needed on your part prior to its release. Next year's Day of Action will certainly address its key recommendations.

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Our top priority: Mars Sample Return

Mars Sample Return (MSR) is a complex, multi-mission, multi-agency effort to return samples of the Martian surface to Earth. It was identified as the highest-priority effort in the past decadal survey, and NASA has stated its intent to follow through on those recommendations in the coming decade.

Securing funding for Mars Sample Return is our top priority for robotic planetary exploration.

Fortunately, there is widespread support for MSR. Both the Trump and Biden White Houses blessed the program with formal budget requests. Congress approved initial funding for it in FY 2021, and continued to do so in its draft funding bills for FY 2022.

The project is currently in an early development and planning phase.

The Problem: In order to meet its launch goal in 2028, MSR needs to grow and grow fast. NASA's FY 2022 budget requested $653 million for MSR, a 2.5x increase from FY 2021. Congress incorporated this increase into its draft appropriations bills, but these have not been passed into law.

We are halfway through fiscal year 2022 but Congress has not passed a FY 2022 appropriations bill. A current stop-gap funding measure expires in March. The options are for Congress to continue its stop-gap funding for the entire year (a "full year continuing resolution") or pass actual FY 2022 appropriations. The downside of a stop-gap funding plan is that it only provides funding at the previous year's level. It would not support significant growth in MSR funding.

We need Congress to pass NASA's FY 2022 funding in March or run a real risk of delaying this mission. Due to limited launch opportunities to Mars (every 26 months), the onset of seasonal dust storms at Mars, and aging telecommunications relay satellites at Mars, any delay will have significant consequences for both cost and difficulties of the mission.

NASA's spending on Mars Sample Return, current 5-year projections Data adjusted for inflation Source: Planetary Science Budget Dataset, compiled by Casey Dreier for The Planetary Society (accessible on Google Sheets or downloadable as an Excel file).


The House and Senate have both released versions of their FY 2022 appropriations legislation. The House version provides $688M for Mars Sample Return, $34M more than the request. The Senate version provides the requested $653 million. The House version is preferable, obviously, but not necessary. Either number would be fine.

At the time of writing, the Senate and House appropriations committees are working on a compromise version of their legislation. We urge Congress to (1) pass FY 2022 appropriations, and (2) to fund MSR at the requested level of $653 million.

Planetary Science Division Additional Reading

Goals for the reader

  • To understand the scope, major program elements, and upcoming projects within NASA's robotic planetary exploration efforts

  • To be able to convey the importance of funding Mars Sample Return in a timely manner, and to connect it with near-term legislative action

  • To understand how programmatic priorities are determined in planetary science

Day of Action

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