The Twin ANthropogenic Greenhouse Gas Observers (TANGO) mission is a pioneering satellite mission comprising two satellites, TANGO-Carbon and TNAGOTANGO-Nitro flying in loose formation. The mission concept is developed through ESA’s SCOUT program and currently consolidated to be ready for a timely launch. TANGO envisages a unique European contribution to monitor globally and independently the emission of the anthropogenic greenhouse gases over the period 2025-2028. To this end, breakthrough technology will be used to quantify emissions of the greenhouse gases methane (CH4) and carbon dioxide (CO2) at the level of individual industrial facilities and power plants. The mission will demonstrate a distributed monitoring system that can pave the way for future larger constellations of small-satellites allowing for enhanced coverage and temporal resolution. The TANGO mission consists of two agile small-satellites, each carrying one spectrometer. The first satellite measures spectral radiances in the shortwave infrared part of the solar spectrum (1.6 µm) to determine moderate to strong emissions of CH4 (≥ 10 kt/yr) and CO2 (≥ 5 Mt/yr). The instrument has a field of view of 30 x 30 km2 at spatial resolutions small enough to monitor individual large industrial facilities (≤300 x 300 m2), with an accuracy to determine emissions on the basis of a single observation. Using the same strategy, the second satellite yields collocated NO2 observations from radiance measurements in the visible spectral range, supporting plume detection and exploiting the use of CO2/NO2 ratio. In essence, TANGO will provide surface fluxes of specific emission types based on the combination of CH4, CO2 and NO2 observations at a high spatial resolution following strictly open data policy. Mission operation will be based on scientific input on target selection. In doing so, TANGO aims to uniquely complement the large current and planned Copernicus monitoring missions like Sentinel-5(P) and the CO2M mission by providing unrivalled high-resolution monitoring of the major anthropogenic greenhouse gas emissions at on a regular basis.

Monitoring and understanding the Earth’s magnetic field and the ionospheric environment is key for both fundamental science and multiple applications. The Earth’s magnetic field protects our planet from incoming energetic charged particles and organizes the way the near outer space (the magnetosphere) and the ionized upper layers of the atmosphere (the ionosphere) respond to solar activity. This response can produce strong magnetic signals that can affect ground technology such as power transmission networks, radiation hazards that can affect satellites in the near outer space, and multiple ionospheric perturbations that can severely affect radio transmissions, radars and GNSS systems (hazards collectively known as space weather hazards). Monitoring Earth’s magnetic field and ionospheric environment is crucial for investigating all these phenomena. Identifying and understanding Earth’s magnetic field multiple sources is also crucial to aid precise navigation, reveal properties of the shallow and deep Earth, and provide key information for geophysical surveying for minerals.

The very successful on-going ESA Earth Explorer Swarm constellation revealed the considerable science value of using a well-conceived satellite constellation for such investigations. Building on Swarm’s achievements, NanoMagSat has been designed to demonstrate the ability of New Space technology to bring such studies to the next level of success.

The constellation will consist of an innovative low-Earth orbit (LEO) constellation of three 16 U nanosatellites, with a current baseline of two 60° inclined and one polar orbits, allowing much faster local time coverage of all geographic locations up to 60° North and South latitudes than is currently possible with Swarm. This constellation would also allow even better coverage, should NanoMagSat be launched while Swarm is still in operation. Each satellite will carry an identical payload consisting of an advanced Miniaturized Absolute scalar and self-calibrated vector Magnetometer (MAM) combined with a set of precise star trackers (STR), a compact High-frequency Field Magnetometer (HFM), a multi-needle Langmuir Probe (m-NLP) and dual frequency GNSS receivers. This payload will allow the production of absolute vector magnetic data at 1Hz sampling, scalar and vector magnetic data at 2 kHz sampling, electron density data at 2 kHz sampling, electron temperature data at 1 Hz sampling, as well as TEC and ionospheric radio-occultation data.

As already demonstrated in the context of the NanoMagSat Scout consolidation phase carried out in 2020, this combination of data, particularly those acquired at higher rates than on Swarm, and the proposed new constellation configuration, will allow improvement of the type of monitoring and investigations Swarm (and previous missions such as Oersted and CHAMP) achieved, also bringing entirely new science opportunities.

Science primary objectives begin with the precise recovery of the field produced by the geodynamo within the Earth’s core. This field, also known as the Earth’s main field, is critical to characterize and understand the way the Earth reacts to the incoming flux of energetic charged particles (the solar wind). Its precise knowledge is also used for many practical applications, both ground-based and space-borne. Recovering its fast dynamics is a top priority, as our still-limited knowledge of this dynamics severely hampers present efforts, relying on data assimilation and advanced numerical dynamo models, to predict main field evolution at the level requested by users. Twenty years of space-born observations by Oersted, CHAMP and Swarm, combined with ground observation data, has allowed great progress, making it possible to study inter-annual changes as well as abrupt changes known as geomagnetic jerks. Thanks to recent progress in numerical dynamo simulations, we now know that further observations are needed to fully characterize and understand these phenomena, since much faster changes can occur. It has not been possible to study such rapid variations with the existing satellite constellations. NanoMagSat will have the ability to considerably improve the situation by capturing core field signals with periods of as short as three months.

A second set of primary objectives will be to also improve our ability to recover fast changing planetary scale ionospheric and magnetospheric fields. These also need to be better monitored and understood. The mid and low latitude ionospheric field typically varies on a daily and seasonal basis, but significant day-to-day variability occurs in response to solar activity. In contrast to Swarm, NanoMagSat will have the ability to recover such variability. The magnetospheric field shows even stronger and faster dynamics. The ability of the NanoMagSat constellation to cover all local time scales at mid-latitudes over its orbital period will also make its recovery much easier. Characterizing both these fields, and the companion fields produced by the electrical currents they induce in the solid Earth, will not only help understand the way the Earth responds to solar activity, but also help reconstruct the still poorly known conductivity structure of the solid Earth.

A third set of primary objectives will take advantage of the innovative payload combination of NanoMagSat to investigate the ionospheric environment. As demonstrated by the experimental “burst mode” of the absolute magnetometers (ASM) on board the Swarm satellites (scalar data acquired at 250 Hz), whistlers produced by lightning strikes in the neutral atmosphere can be detected at LEO altitude and used to sound the state of the ionosphere below the satellites. NanoMagSat will have an extensive ability to even better do so, thanks to the 2 kHz sampling rate of its vector magnetometers. Such information, together with the TEC data, ionospheric occultation data (which Swarm lacks), and local electron density data will provide a powerful means to monitor the state of the ionosphere, to both investigate its dynamics and improve ionospheric models, such as the International Reference Ionosphere (IRI) model. Investigation of the local smaller scale dynamics of the ionosphere will also be made possible thanks to the joint use of 2kHz sampling vector magnetic and electron density data. This will provide access to ionospheric meter-scale plasma density structures and allow monitoring of the electrical currents testifying for the energy input that feeds them from the magnetosphere.

Additional secondary, but equally important, science objectives have also been identified. Some are already addressed by Swarm, but would considerably benefit from both longer (ideally permanent) satellite observations and could also greatly benefit from the joint use of NanoMagSat and Swarm data, should NanoMagsat be launched while Swarm is still in operation. This is the case for the magnetic signals produced by oceanic lunar tides. NanoMagSat would allow these minute signals to be recovered faster and more accurately. As already demonstrated, these signals can be used to sense the electrical conductivity of the uppermost regions of the solid Earth. On the long term, they could also potentially be used to assess the evolution of the temperature of the oceans (the magnitude of the tidal signals being sensitive to ocean temperature), thus contributing to monitoring one key parameter of climate global change. Additional signals produced by the global ocean circulation and its variability could also potentially be investigated, at time (month to interannual) and length scales expected to be accessible with NanoMagSat.

Another important secondary science objective that could benefit from NanoMagSat, especially if operated jointly with the Swarm constellation, is the recovery of the magnetic field signals produced by magnetized rocks within the lithosphere. Maps of these provide invaluable information about the nature and thermal state of the lithosphere and its deep- seated rocks, as well as about their tectonic history. This objective requires making the best of all missions, as it benefits from the accumulation of data over long periods. The Swarm constellation (with two satellites side-by-side) was optimally designed for that purpose. However, the much better local time coverage provided by NanoMagSat could be taken advantage of in order to better remove signals produced by all other sources and assist in better isolating this lithospheric signal.

Many additional possible secondary objectives are also now under study, thanks to the support of the science community, following a dedicated NanoMagSat brainstorming session organized in Athens in October 2021, as a follow-up of the 11th Swarm Data Quality Workshop. In particular, exciting ideas have emerged that could take advantage of the ability of the NanoMagSat payload to study ionospheric-magnetospheric dynamics, as a stand-alone mission or in conjunction with other missions.

In this invited talk, we will strive to illustrate all the numerous science objectives NanoMagSat could achieve, also reporting on E2E simulations that will have been run by the time of the meeting. Since we just learned that following successful negotiations with ESA, the NanoMagSat project will soon (January 10, 2022) kick off a new technical phase of Risk Retirement Activities for a period of 18 months, we will also report on how we have started backing up this phase with appropriate science preparation activities. All scientists willing to contribute to this effort to further enhance the science return of the NanoMagSat mission and demonstrate the potential of New Space for such science are warmly welcome to join. Beyond this initial mission, NanoMagSat could indeed be used as a stepping-stone for permanent low-cost monitoring of the Earth’s magnetic field and ionospheric environment.

Scout missions are a new Element in ESA’s FutureEO Programme, demonstrating science from small satellites. The aim is to tap into the New Space approach, targeting three years from kick off to launch, and within a budget of €30m, including launch and commissioning of space and ground segments. The Scout missions are non-commercial and scientific in nature; data will be made available freely using a data service delivery approach. HydroGNSS has been selected as the second ESA Scout Earth Observation mission, primed by Surrey Satellite Technology Ltd, with support from a team of scientific institutions - Sapienza University of Rome, Institute for Space Studies of Catalonia, Finnish Meteorological Institute, Tor Vergata University of Rome, “Nello Carrara” Institute of Applied Physics, National Oceanography Centre and University of Nottingham. The microsatellite uses established and new GNSS-Reflectometry techniques to take four land-based hydrological climate variables; soil moisture, freeze/thaw, inundation and biomass. The initial project is for a single satellite in a near-polar sun synchronous orbit at 550 km altitude that will approach global coverage monthly, but an option to add a second satellite has been proposed that would halve the time to cover the globe, and eventually a future constellation could be affordably deployed to achieve daily revisits.

GNSS Reflectometry has been developing rapidly as an L-Band remote sensing technology suitable for small satellites, a form of passive bi-static radar that uses GNSS satellites as radar sources, and it continues to find applications over ocean, ice and land. The UK TechDemoSat-1 and NASA CYGNSS missions were primarily flown to target wind speed over the ocean but enabled demonstration of the potential for cryospheric and hydrological applications. Over rough surfaces, for example oceans, a resolution of approximately 25 km is expected, but over flat surfaces such as sheltered rivers, the signal becomes coherent and the resolution achieved can be better than 1 km, while the resolution achievable over land varies between 1 km and 25 km depending on the characteristics of the terrain. The ESA Scout-2 HydroGNSS mission will use established and new measurements, including Galileo signals, coherent reflection sensing, dual polarisation and dual frequency reflectometry exploration to improve the resolution and separation of hydrological measurements. Although targeting land, measurements will also be collected over ocean and ice, with the prospect of a number of secondary applications.

The instrument is a development based on technology used on TechDemoSat-1 and CYGNSS missions, upgraded to allow for additional measurements. The nadir antenna uses 2 x 2 array of metal patches to implement an efficient dual frequency dual polarisation antenna. Low noise amplifiers incorporate cavity filters and calibration switches and the receiver is able to collect multiple GPS and Galileo reflections simultaneously at dual polarisation and at dual frequencies, L1/E1 and L5/E5. Signal processing uses open loop predictions to target reflections at each specular point and collect measurements in the form of Delay Doppler Maps (DDMs). The platform is a 55kg implementation of the SSTL-Micro, incorporating many features advantageous to a GNSS reflectometry mission. The accurate and agile attitude capability is enabled by an attitude control system using star trackers and wheels. Propulsion allows for collision avoidance and phasing and maintenance of a future constellation. A large capacity data storage and high rate X-band downlink allows acquisition of targeted raw sampled captures in addition to the routine on-board processed DDMs.

The ground segment makes use KSAT station in Svalbard for both telemetry, telecommand and control link as well as payload downlink, where the high latitude frequent passes could be an enabler for fast data availability for future weather applications. SSTL’s ground station in Guildford is available as backup. The data is processed by the Payload Data Ground Segment (PDGS), which prepares different levels of products. The Level 1 data comprises of GNSS DDMs and coherent measurements, and are made available with sufficient metadata for calibration and recovery of surface reflection coefficients at the specular reflection points. Level 2 operational processors are supplied to the PDGS by scientific partners, and these will allow the operational recovery of the climate variables, soil moisture, inundation, freeze/thaw and biomass, plus secondary products over the ocean of ocean wind speed and sea ice extent. Level 1 and Level 2 products will be shared publically with registered users over the web using a similar platform to “MERRByS” that shared the TechDemoSat-1 data.

The project is now underway – the HydroGNSS mission contract was signed between ESA and SSTL on 11th October 2021, and a ride-share launch in 2024 is currently being negotiated. Upon launch, there will be a concerted effort to commission the satellite, payload and PDGS and undertake preliminary validation of all the Level 2 products within 6 months. HydroGNSS will continue to explore the technique of GNSS-Reflectometry while laying the foundations for a future constellation offering high spatial-temporal resolution observations of the Earth’s weather and climate.

HydroGNSS is a mission concept selected by ESA on 2021 as the second Scout small satellite in the frame of the FutureEO Earth Observation programme. The satellite is planned to be launched in 2024 after a 3-year development phase and is being developed by Surrey Technology supported by a scientific team composed by Sapienza University of Rome, IEEC in Barcelona Spain, NOC in Southampton UK, Finland Meteorology Institute, CNR/IFAc in Sesto Fiorentino Italy, Tor Vergata University of Rome.
The mission targets the hydrological cycle and is based on the GCOS requirements for monitoring Essential Climate Variables (ECV). Water is a natural resource vital to climate, weather, and life on Earth. It manifests itself in or on the land in different ways, for example, moisture in the ground, wetlands and rivers, snow and ice, and vegetation density. Global knowledge of land water content and state is important in its different forms for many reasons:
• Soil moisture knowledge is needed for weather forecast, hydrology, agriculture analysis, and wide scale flood prediction
• Freeze / thaw state is an important variable that helps understand permafrost behaviour in high latitudes, a key issue in climate change as a methane source.
• Above Ground Biomass feeds into understanding of carbon stock in forests and a sink in the carbon dioxide cycle, and it also has a coupling to biodiversity
• Wetlands are fragile ecosystems that also can be sources of methane, and often hidden under forest canopies
Increasingly complex and accurate models are used to characterise and forecast hydrological processes. Earth System Models (ESMs) are used for climate, and Numerical Weather Prediction (NWP) models for weather forecasting. A better knowledge of these processes requires hydrological observational data to be assimilated into models to ensure correspondence with the complexity of the real world.
The HydrGNSS mission is based on the GNSS Reflectometry (GNSS-R) technique that collects the signal transmitted by the navigation satellites and scattered by the Earth surface in the near specular direction. GNSS-R has consolidated applications for ocean monitoring, which have been demonstrated by past and current missions (UK TEchDemosat-1, NASA CyGNSS) but land applications have been also proved. Specifically, the target Level 2 products for HydroGNSS are surface soil moisture, inundation/wetland, freeze/thaw state and forest above ground biomass, which are partially coincident with ECV’s (moisture and biomass) or strictly related to them (freeze / thaw and wetland).
This presentation illustrates the products that will be delivered by HydroGNSS, the requirements dictated by GCOS and the performances expected from HydroGNSS based on the state of art of the GNSS-R technique. The development of an End to End simulator is a first step to demonstrate the mission is capable to achieve the Scientific Readiness Level 5 and the achievements in this field by the research group will be presented.

Earth is changing at an unprecedented pace. Awareness of the socio-economic impact of climate change has also been growing and so has the international consensus on the urgency of understanding and limiting the impacts. To do this successfully, we need to understand and quantify the processes driving the change and its future, and particularly the role played by the atmosphere.
The composition of the Upper Troposphere and Stratosphere (UTS) plays a significant role in controlling the Earth’s climate, but there are still poorly explored feedbacks within the Earth System. This region is coupled to the surface and the free troposphere both dynamically and radiatively. Its composition is strongly affected by anthropogenic emissions of greenhouse gases (GHG) and pollution precursors, and is subject to changes via radiative, dynamical, and chemical processes. As the Earth’s atmosphere is changing, so is the UTS. The rapid vertical and horizontal variations in the abundances of trace gases and aerosol around the tropopause, as well as strong and differing trends either side of the tropopause, have made trend detection challenging in this region with a knock-on effect on estimates of their climate impact.
The overall goal of CubeMAP is to study, understand, and quantify processes in the UTS, study its variability, and contribute to analysis of trends in its composition and the resulting effects on climate and vice-versa. The mission focuses on tropical regions, which are most critical for UTS processes, as the strong vertical transport in these latitudes means this is effectively the “gateway to the stratosphere”.
The space sector is also changing at a fast pace, which ought to benefit innovation for science missions. CubeMAP embraces a high level of innovation and studies the UTS processes with a unique combination of high accuracy, high vertical resolution, and enhanced geographical and temporal coverage, owing to a novel sounding approach that leverages small satellite benefits. These measurement characteristics are achieved by measuring high spectral resolution atmospheric transmission spectra at the limb, exploiting the high signal to noise ratio delivered by solar occultation. The limited coverage usually associated with solar occultation limb sounding is obviated through the deployment of a nanosatellite constellation of identical sounders, equally distributed in one orbital plane.
The mission makes uses of GOMSpace 12U cubesat platforms, with electric propulsion and enhanced pointing control. The CubeMAP fleet is made of three spacecrafts. Each spacecraft embarks three thermal infrared laser heterodyne spectrometers for high spectral resolution atmospheric transmittance spectroscopy, miniaturized using hollow-waveguide integration technology. The scientific payload also includes a solar disc imager required for determining the pointing knowledge of each spacecraft, which also provides hyperspectral atmospheric transmittance data over 16 channels in the visible and infrared by using a multi spectral focal plane mosaic array.
In addition to its immediate scientific objectives, CubeMAP contributes to developing a novel resilient approach to atmospheric observation to be scaled up: it offers a high level of deployment flexibility and system modularity, as well as economy of scale, through the use of identical payloads and platforms but targeted towards specific Earth observation goals. CubeMAP is highly complementary to the existing nadir sounding infrastructure and will add value by enhancing its outputs and exploitation.

The chemical composition of the upper troposphere and lower stratosphere – the UTLS – is spatially and temporally highly variable and determined by a range of factors such as transport, chemistry, and tropopause dynamics. The UTLS is also thought of being very sensitive to climate change. The tropopause in particular has been dubbed the canary of the climate system due to its sensitivity to radiative forcing. Because of long radiative timescales, a small forcing leads to a large response, with knock-on effects on transport and composition. However, given a rather sparse sampling (in space and/or time) and limited precision of available observations, accurately quantifying UTLS composition variability and trends and identifying their drivers poses a considerable challenge.

CubeMAP – CubeSats for Monitoring of Atmospheric Processes – focusses on exactly addressing this challenge. To this end, CubeMAP is putting forward a flexible, fast to implement, and highly innovative modular measurement system which will make observations at tropical and sub-tropical latitudes. It will observe chemical trace gases such as water vapour, carbon dioxide, methane, ozone, and nitrous oxide and their isotopologues, as well as aerosols – all of which play a key role in radiative forcing and climate change and which will shed light and help quantify diverse climate processes.

In this contribution, we will review open science questions CubeMAP will help to address, including how natural and anthropogenic emissions (e.g. from wildfires, deep convection, long-range transport) will affect UTS composition, how water vapour in the UTS will change in response to climate change, how these changes will feed back on climate, how climate change will alter transport in the stratosphere and impact the ozone layer and its recovery, and how knowledge of the vertical distribution of greenhouse gases will help improve the quantification of estimates of their surface emissions.