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Introduction

The stratosphere and mesosphere are critical components of Earth’s climate system, playing a central role in regulating atmospheric composition, radiative balance, and surface weather through tightly coupled chemical, dynamical, and transport processes. These regions host the ozone layer, which shields life from harmful ultraviolet radiation, and contain stratospheric aerosols that can strongly influence climate. Variations in aerosol loading, for example following major volcanic eruptions, can measurably perturb the global radiative balance and surface temperatures. Dynamically, the middle atmosphere is closely linked to the troposphere, with changes in stratospheric circulation capable of modulating jet streams, storm tracks, and regional weather patterns.

These atmospheric layers are also increasingly influenced by expanding space activities. Rocket launches, upper-stage disposal, and satellite re-entries inject reactive gases, metallic and carbonaceous particles, and combustion or ablation products directly into this region. The impacts of these emissions on ozone chemistry, aerosol evolution, polar stratospheric cloud formation, and climate forcing remain incompletely characterised.

Europe has strong heritage in high altitude balloons, sounding rockets, and emerging High-Altitude Pseudo-Satellite (HAPS) platforms. Balloons provide long duration background observations and seasonal statistics; sounding rockets offer rapid access to higher altitudes and event driven sampling; and HAPS systems support persistent observations and technology demonstration in the upper troposphere and lower stratosphere. Together with satellite remote sensing missions, these platforms form the backbone of Europe’s atmospheric observing capability.

However, the physics of the upper stratosphere and mesosphere presents inherent access challenges. Aircraft cannot operate above the lower stratosphere. Balloon systems, while offering long-duration sampling, are altitude limited and lack precise manoeuvrability. Sounding rockets provide access to higher altitudes but only for short durations and under high velocity conditions. Current HAPS platforms operate well below the upper stratosphere. As a result, sustained, repeatable in-situ measurements across this critical region remain difficult to achieve.

At the same time, satellite observations, while indispensable for global monitoring, cannot directly resolve certain key parameters such as ultrafine particle populations, detailed aerosol chemical composition, and highly reactive trace species without in-situ validation. Consequently, many processes governing aerosol evolution, metal vapour chemistry, nanoparticle formation, heterogeneous reactions, and gas particle partitioning remain constrained primarily through laboratory studies and indirect inference. This creates a growing mismatch between the rapid expansion of space activities and the maturity of the observational system required to assess their atmospheric impacts.

This campaign addresses these challenges by advancing innovative platforms and instrumentation to strengthen Europe’s access to, and understanding of, the stratosphere and mesosphere. The strategic objective is to integrate and extend existing capabilities into a coherent atmospheric access architecture, with particular emphasis on enabling sustained and targeted in-situ measurements above approximately 45–50 km altitude.

Strengthened European access to this region will support:

• improved understanding of aerosol microphysics, heterogeneous ozone chemistry, and upper atmospheric particle formation
• enhanced calibration and validation of current and future Earth observation missions
• quantitative assessment of launch, disposal, and re-entry impacts

Expected Ideas

Background

Europe maintains significant capability in atmospheric research across multiple platforms. Long duration scientific balloon programmes provide stable stratospheric observations up to typical float altitudes of 35–40 km, delivering high quality measurements of background composition, aerosol properties, and trace gases. Sounding rockets offer access to the mesosphere and lower thermosphere, enabling targeted campaigns and technology demonstration at higher altitudes. High Altitude Pseudo Satellite (HAPS) systems are emerging as promising platforms for persistent sampling in the upper troposphere and lower stratosphere.

In parallel, satellite remote sensing missions provide global and continuous monitoring of atmospheric composition, temperature structure, and aerosol distributions. Instruments operating in limb and nadir geometries deliver valuable vertical profiles and long-term datasets that underpin climate and ozone assessments.

However, despite this strong foundation, routine and controlled in-situ access to the upper stratosphere and mesosphere remains limited. Balloon systems are inherently altitude constrained and lack precise vertical manoeuvrability above float ceilings. Sounding rockets provide only short duration measurements at high ascent and descent velocities, limiting sampling time and introducing challenges for microphysical characterisation. HAPS platforms currently operate well below the upper stratosphere.

Remote sensing, while indispensable, cannot directly resolve particle composition, nanoscale aerosol formation processes, or reactive species partitioning without in-situ validation. In particular, models describing metal vapour chemistry, nanoparticle formation, heterogeneous reactions, and ablation product evolution rely heavily on laboratory studies and indirect inference.

At the same time, launch activity, upper stage disposal, and satellite re-entry are increasing in frequency and scale. Existing emission inventories and ablation models remain only partially validated, and systematic in-situ observations in the upper stratosphere and mesosphere are sparse.

Consequently, Europe possesses strong but fragmented capabilities. The opportunity now is to integrate these strengths into a coherent architecture enabling sustained, controlled, and repeatable in-situ measurements across the upper stratosphere and mesosphere

ESA's Discovery programme, through the Open Space Innovation Platform (OSIP), provides an established mechanism for sourcing early-stage concepts from the broader innovation ecosystem. The collaboration framework with ARIA offers a pathway to advance promising concepts beyond feasibility study toward demonstrator development, creating an end-to-end innovation pipeline for this capability gap.

Process

1. Campaign launch on 27th February 2026
2. Campaign closing on 30th March 2026
3. Proposal phase for studies (budget 100k max, 6 months duration)
4. Proposal Evaluation May 2026
5. Parallel studies kick-off (Common Kick-Off event)
6. End of studies phase in Nov/Dec 2026 (Common Final Presentation Day)

ESA's Discovery programme, through the Open Space Innovation Platform (OSIP), provides an established mechanism for sourcing early-stage concepts from the broader innovation ecosystem. 

Campaign Process Details

First Step: Idea

The first step, is to enter an idea through this Campaign. Ideas considered within the scope of the Campaign will be evaluated according to the below evaluation criteria. Please also take note the Special Conditions applying to the submission as listed below. 

Any questions to the Agency relating to the first step shall be addressed exclusively via OSIP. If required, the Agency may request clarifications via OSIP.

Authors have at any moment full visibility of the status of their idea (visible above the title of the idea). Ideas move from "qualification" to "community discussion" to "evaluation" to "selection".

Ideas start in draft status and can be stored as such in case information for mandatory fields is still missing. Draft ideas are only visible to authors. As soon as all mandatory information is available, even if not final, authors are encouraged to submit the idea. You can still work on your idea until start of the evaluation.

Second Step: Proposal

All retained ideas will be invited to the second step to submit a Full Proposal via esa-star. This includes:

• Write and submit a Full Proposal through esa-star;
• ESA will evaluate your proposal against evaluation criteria that will be stated in the data pack from the Call For Proposals which will be published on esa-star publication. (Evaluation criteria of the second round are foreseen to be (but may be subject to change - always consult the TA package of the Call for Proposal once publish to find the final set of evaluation criteria):
  • A) Relevant background and experience,
  • B) Innovation, quality and suitability of the technical and/or scientific content of the proposed activities,
  • C) Adequacy of time dedication, planning, and the organisation of the work, compliance with administrative tender conditions)
• Successful proposals will be invited to a negotiation meeting and possibly lead to a cooperative agreement award (please see a draft cooperative agreement in the attachments of this Campaign).

This Campaign follows the ESA Call for Proposals process with Cooperative Agreements.

References

Ongoing Discovery activities

• BALLOON-BORNE SPACE DEBRIS AEROSOL FETCHING EXPERIMENT
• Impacts of space Debris ablation on Earth's Atmospheric System
• Insights into the Chemistry of Atmospheric Re-entry of jUnked Spacecraft
• Overcoming atmosphere-blindness - In-situ resonance lidar measurements of re-entering space debris enabled by an Alexandrite laser

Other References

• 2nd Workshop - Atmospheric Impacts of Spacecraft Launch and Re-entry (23-25 September 2025): Overview · Indico at ESA / ESTEC