Data availability
Endurance ephemeris data and all science data presented in this article are available at the Space Physics Data Facility of NASA (https://spdf.gsfc.nasa.gov/data_orbits.html) through the Coordinated Data Analysis Web (CDAWeb) tool (https://cdaweb.gsfc.nasa.gov/) by selecting ‘Sounding Rockets’ from the data sources.
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20 May 2025
A Correction to this paper has been published: https://doi.org/10.1038/s41586-025-09144-2
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Acknowledgements
We thank the 100+ strong team of engineers, scientists and technicians who made the Endurance rocketship mission a success. We thank A. P. Collinson for the useful discussions in preparing and editing the paper. Endurance was funded through the NASA grant 80NSSC19K1206. EISCAT support was supported through the National Environment Research Council grant NE/R017000X/1. EISCAT is an international association supported by research organizations in China (CRIRP), Finland (SA), Japan (NIPR and ISEE), Norway (NFR), Sweden (VR) and the UK (UKRI).
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Extended data figures and tables
Extended Data Fig. 2 Example spectra from the Photoelectron Spectrometer.
Data calibrated but uncorrected for spacecraft potential. a, PES Scan 72 showing standard resolution (black) and high resolution (red). b, PES Scan 72 zoomed in to the He-II photopeaks showing a gaussian fit (blue) to the primary N2 A2Πu dominated photopeak. c,d, The same for PES Scan 38.
Extended Data Fig. 3 Conversion from peak energy of photopeaks to planetary potential drop below Endurance.
Upleg, top panels; downleg, bottom panels. a,d, Peak energy of N2 A2Πu dominated photopeak as measured. b,e, Energy of photopeak after correction for S/C potential from SLP. c,f, Potential drop below Endurance (as Fig. 2a,b).
Extended Data Fig. 4 Measurements by the Swept Langmuir Probe.
Area denotes ±1σ error. a, Colour-coded timeline of Endurance mission (as per Fig. 1a, Fig. 2a). b, Altitude versus time. c, Total Electron density (m−3). d, Electron temperature (K). e, Potential difference between Endurance and ambient plasma. The periodic (70 s) firing of the ACS thrusters (amber, panel a) temporarily perturbed the plasma environment around the spacecraft. The resulting erroneous measurements by SLP have been cut from the dataset.
Extended Data Fig. 5 Supporting Measurements by the FIELDS instrument.
a, Colour-coded timeline of Endurance mission (as per Fig. 1a, Fig. 2b). b, Mean potential between the two pairs of electric field probes.
Extended Data Fig. 6 Radar measurements from the EISCAT Radar in black compared to in situ measurements by the SLP instrument in gold.
a,b, Plasma density; c,d, Electron temperature. e,f, Ion temperature; g,h, Ion velocity. These plots were made by time-averaging measurements from the upleg and downleg portion of the flight. Error bars represent the standard deviation. EISCAT data were truncated above 500 km in Fig. 3 owing to the large error bars but are shown here in full. The good agreement between independent measurements of \({n}_{e}\) and \({t}_{e}\) by EISCAT and SLP give good confidence in our SLP data analysis.
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Collinson, G.A., Glocer, A., Pfaff, R. et al. Earth’s ambipolar electrostatic field and its role in ion escape to space. Nature 632, 1021–1025 (2024). https://doi.org/10.1038/s41586-024-07480-3
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DOI: https://doi.org/10.1038/s41586-024-07480-3