ESSP: select focused missions for Earth-science questions

NASA’s Earth System Science Pathfinder program, ESSP, supports Earth-science investigations designed around specific scientific objectives. Its documented portfolio includes whole orbital missions, instruments carried on other platforms and suborbital investigations. Those are different ways of obtaining evidence, not ranks in which a larger spacecraft is automatically more scientifically useful.

Competitive investigations bring teams together around a proposed measurement and an explanation of why it matters. Principal investigators carry scientific and project responsibilities, supported by engineering and program oversight. ESSP also has legacy and directed projects; describing every item in its history as the result of one identical competition would erase real differences in how projects began.

CloudSat and CALIPSO launched together in 2006 and are examples of focused ESSP missions. CloudSat used radar to investigate cloud structure. CALIPSO, a NASA–CNES partnership, used lidar and supporting instruments to study clouds and aerosols. Their different responses helped build a more informative vertical picture than treating a cloud as only the bright outline in an overhead photograph.

A radar return and a lidar return do not have identical sensitivity or penetration. Combining them requires knowledge of their geometry, timing and response to particles. The CALIPSO launch-preparation image shows a protective fairing section for the shared launch. That structure protected the payloads; it was not itself a cloud radar or a science image of the atmosphere.

A focused investigation still needs development, integration, launch arrangements, calibration, operations, data analysis and preservation. A proposal with a strong idea but no credible plan for obtaining interpretable measurements has a missing link. Program management considers scientific value alongside cost, schedule, technical performance and risk because each can affect whether the planned evidence becomes available.

Imagine a fictional team choosing between an airborne campaign and an orbiting sensor. The aircraft may sample a process closely during selected events, while an orbital instrument may provide broader repeated coverage. The better choice depends on the question and the required sampling. ESSP teaches that an investigation should be sized and organized around its scientific task, with realistic limits stated from the beginning.