Methods | Science Mission Impact

The challenges of bibliometrics for space science missions

Space is hard, as the saying goes. So is measuring a space mission’s scientific output.

There is no perfect collection of science publications associated with a mission; there are only degrees of correctness. Large missions, like the Hubble Space Telescope, dedicate staff time to identifying science papers and distinguishing results from engineering descriptions and speculative work. A European team studying ESA’s space science missions describes a transition from manual review to machine learning and natural language processing, with scientists still validating the selections. Such assessments can require access to the full text of large numbers of publications, often shielded by paywalls.

Exactly how one defines “science” varies, and many judgment calls are required. For this study, we used a simpler approach also used in many peer-reviewed publications, such as Fiore & Elvis (2026): querying NASA’s Astrophysics Data System (ADS)/SciXplorer database by mission name and the names of its primary instruments. ADS is the leading repository of space science publication and citation references. This approach assesses the signal of a mission within the abstract literature, using publications as a proxy for scientific productivity and citations to those publications as a proxy for impact.

We tailor each query to filter out obvious false positives from name or acronym collisions: TRACE, for example, is both a space mission and a very common word. We also compared our query outcomes to the managed collections of several missions with hand-curated publication sets. They generally agree within 10%–25% of publication records, with a single exception, GALEX, differing by a wide amount due to the pattern of not reporting the mission name in many abstracts. Since we’re primarily comparing mission costs across orders of magnitude, this is well within acceptable limits. We tested our outcomes with curated mission collections and found the overall comparative outcomes remained consistent.

Our aim is to identify broad patterns in the research associated with these missions. We call these records “tracked publications” to make their scope clear: they capture the papers we found, while leaving room for omissions and corrections.

What we included

This dataset contains 134 projects primarily built and funded by NASA’s science directorate, launched from 1980 to 2021, spanning five divisions. It focuses on US-led, free-flying missions with mature publication windows. The default comparison allows papers the publication year and three following calendar years to accrue citations.

Comparisons stay within each division. Research communities differ in size, publishing practices, and citation rates, so a higher count in one field does not mean its science is more valuable.

Tracked publications

Tracked publications are the peer-reviewed research papers we found for each mission. They are not necessarily its full publication record. The snapshot contains 146,808 distinct tracked publications across the study.

We use mission-specific searches in NASA’s Astrophysics Data System (ADS), now available through SciX. Searches look for mission and instrument names in titles, abstracts, and keywords, with topic restrictions to distinguish ambiguous acronyms. Mission bibliographies help identify omissions; additions and exclusions are reviewed individually.

This approach will miss papers that use mission data without naming the source in those fields. A name match alone also does not establish that a paper used the data. In essence, we are measuring the signal strength of a mission's name in the ADS's abstract fields.

What we exclude

We have general exclusions for non-refereed material, conference proceedings, news articles, and records for datasets or catalogs.

When tracking begins

Queries are time-bound by the first full month after prime science operations start, or launch date if no prime mission start is published. This reduces pre-launch and overview material; it does not eliminate every false match. For missions with long cruises or flyby results, we include results published before the prime mission start.

Comparison windows

Older papers have had more time to collect citations. Windowed comparisons give each paper a defined citation period, while lifetime totals show the accumulated record.

Active Mission Window

The default comparison covers publications from a mission’s operating life and allows two years after mission end for results to appear. Each paper’s citations count from its publication year through the three calendar years that follow. A window counts as mature three months before its last citation year ends, so the most recent papers’ final citation year is counted only through the as-of date (at least nine of its twelve months), and their counts can still grow slightly. A mission still operating, or one that ended too recently, is cut at the latest window end that is mature on the as-of date; a cut window shorter than two years is not scored.

Prime Mission Window

This comparison follows the prime phase, with two years after prime mission end for results to appear. Its length varies by mission.

Lifetime

All tracked publications and their reported citations to date.

Mission costs

Costs come from the NASA's reported life-cycle costs at launch. We include documented partner contributions where available. These generally cover development, payloads, launch, and prime operations. Values are adjusted to 2025 dollars using NASA’s New Start Inflation Index.

Corrections

If you find a missing or misattributed paper, a wrong date or cost, or any other error, write to casey.dreier@planetary.org. Mission pages list the query and every tracked publication, which makes a specific correction easy to check.

Image credits

NASA/ESA.