Publications

Two-dimensional histograms of per-orbit RMS density error against drag acceleration for POD-A and EDR, and the difference between them — Per-orbit density error against drag acceleration for the POD-A and EDR methods, with the difference between them.

Constant, C., Brownhall, I., Aruliah, A., Ziebart, M., Bhattarai, S. Empirical Assessment of Storm-Time Thermospheric Density Inversion Methods From LEO POD Data. Earth and Space Science, Vol. 13, No. 8, e2025EA004914, August 2026. DOI

A satellite in orbit above the Earth with the Sun overhead; a blue optimised trajectory reaches a flag while an orange one misses it — A spacecraft design optimised so that radiation pressure carries it to its target (blue) rather than past it (orange).

Constant, C., Bates, E., Bhattarai, S., Ziebart, M., Ritschel, T. Photons × Force: Differentiable Radiation Pressure Modeling. ACM Transactions on Graphics (Proc. SIGGRAPH 2026), Vol. 45, No. 4, Article 82, July 2026. Best Paper Honourable Mention, SIGGRAPH 2026. DOI • arXiv

Schematic of one orbital shell: new launches feed payloads, which become derelicts or are removed; collisions and explosions create debris; objects decay to lower shells — The source-sink model for one orbital shell: launches, post-mission disposal, fragmentation, and decay between shells.

Brownhall, I., Lifson, M., Hall, S., Constant, C., Lavezzi, G., Ziebart, M., Linares, R., Bhattarai, S. MOCAT-pySSEM: An open-source Python library and user interface for orbital debris and source-sink environmental modeling. SoftwareX, Vol. 30, 102062, 2025. DOI

World map coloured by the 3D position difference between NORAD TLEs and the precise orbit of Sentinel-1A, with the largest errors over the southern oceans — 3D difference between NORAD TLEs and the precise orbit of Sentinel-1A over a year, mapped by ground position.

Peto-Madew, F., Bhattarai, S., Constant, C., Brownhall, I. Investigating the Application of the Orbit Domain Calibration Method in Sun Synchronous Orbits. Proceedings of the 9th European Conference on Space Debris, ESA Space Debris Office, April 2025. PDF

Fifteen small time-series panels of semi-major axis through 2024, one per reference satellite, grouped into complex, medium and simple geometry classes — Semi-major axis through 2024 for the 15 reference satellites, grouped by geometry class.

Bhattarai, S., Peto-Madew, F., Constant, C. Toward an On-Orbit Reference Network for Enhanced Ephemeris Quality Testing in Low Earth Orbit. The Advanced Maui Optical and Space Surveillance (AMOS) Technologies Conference, 2025.

Three log-log panels of RMS density error against number of satellites at high, medium and low noise, comparing assimilated and unassimilated densities — Density error against number of satellites, raw and assimilated, at three orbit-noise levels.

Constant, C., Mutschler, S.M., Bhattarai, S., Pilinski, M. Bring the Noise: Three Rules for Improving Thermospheric Density Retrieval From LEO POD Data. The Advanced Maui Optical and Space Surveillance (AMOS) Technologies Conference, 2025.

Time series of neutral density during the May 2023 storm from accelerometer, POD, NRT and EDR methods on top, and JB08, NRLMSISE-00 and DTM2000 models below — Densities from each retrieval method and model against accelerometer values through the May 2023 G2 storm.

Constant, C., Bhattarai, S., Brownhall, I., Aruliah, A., Ziebart, M. Evaluating Near-Real-Time Thermospheric Density Retrieval Methods from Precise Low Earth Orbit Spacecraft Ephemerides During Geomagnetic Storms. arXiv preprint arXiv:2408.16805, 2024. arXiv

Bar charts of mean absolute propagation error in height, cross-track and along-track for nine force-model configurations, low and high altitude, 2019 and 2023 — Propagation error by force-model configuration, at low and high altitude, in 2019 and 2023.

Constant, C., Hanson, B., Brownhall, I., Bhattarai, S., Ziebart, M. An Evaluation of Physics-Based Force Model Performance in LEO: Implications for Next-Generation Space Traffic Management. 45th COSPAR Scientific Assembly, July 2024. NASA ADS

Histograms of argument of latitude at TLE epoch for OneWeb and Starlink, comparing NORAD and supplemental TLEs — Where along the orbit Starlink and OneWeb TLEs are issued: NORAD against operator-supplied supplemental TLEs.

Constant, C., Bhattarai, S., Ziebart, M. Limitations of Current Practices in Uncooperative Space Surveillance: Analysis of Mega-Constellation Data Time-Series. Proceedings of the AMOS Conference, 2023. Abstract

The Photons × Force poster presented at SIGGRAPH 2026 — The poster as presented at SIGGRAPH 2026.

Constant, C., Bates, E., Bhattarai, S., Ziebart, M., Ritschel, T. Photons × Force: Differentiable Radiation Pressure Modeling. SIGGRAPH, 2026. Poster

The Gannon storm poster presented at European Space Weather Week 2024 — The poster as presented at European Space Weather Week 2024.

Constant, C., Brownhall, I., Aguilar, L., Dable, E., Ziebart, M., Aruliah, A., Bhattarai, S. Thermospheric Response and Operational Impacts During the 2024 "Mother's Day" Geomagnetic Storm. European Space Weather Week, 2024. Poster

Strip plots of the reduction in 3D RMS error from each force-model term for ten satellites, in 2019 and 2023 — Reduction in 3D error from each force-model term for ten satellites, in 2019 and 2023. From the interactive presentation.

Constant, C., Hanson, B., Brownhall, I., Bhattarai, S., Ziebart, M. An Evaluation of Physics-Based Force Model Performance in LEO: Implications for Next-Generation Space Traffic Management. COSPAR, 2024. Interactive Presentation

Bhattarai, S., Brownhall, I., Constant, C., Peto-Madew, F., Rotheram, E. Orbit Domain Calibration for Space Surveillance & Tracking (ODC4SST): Design Concept, Network Selection & Initial Validation Tests. COSPAR, 2024.

Brownhall, I., Lifson, M., Hall, S., Constant, C., Lavezzi, G., Ziebart, M., Linares, R., Bhattarai, S. MOCAT-PYSSEM: An Open-Source Python Library and User Interface for Orbital Debris and Source-Sink Environmental Modelling. COSPAR, 2024. ResearchGate

The mega-constellation tracking poster presented at AMOS 2023 — The poster as presented at AMOS 2023.

Constant, C., Bhattarai, S., Ziebart, M. Limitations of Current Practices in Uncooperative Space Surveillance: Analysis of Mega-Constellation Data Time-Series. AMOS, 2023. Poster • Video

The astrodynamics and space geodesy poster presented at GNOSIS 2022 — The poster as presented at GNOSIS 2022.

Constant, C., Bhattarai, S., Brownhall, I., Ziebart, M. Astrodynamics and Space Geodesy for Space Domain Awareness and Sustainability. GNOSIS, 2022. Poster

Radiation-pressure force maps for the CHAMP, GRACE, GPS and Swarm spacecraft, comparing neural, simulated, direct and indirect components — Radiation-pressure force maps for four spacecraft, from the Photons × Force paper the article covers.

Could sunlight help steer the spacecraft of the future? UCL Faculty of Engineering, 2026. Coverage of the SIGGRAPH 2026 Photons × Force paper and the Verra Space spin-out formed to commercialise the work. Article

Nine world maps of the Kosmos 482 lander's ground track over its last 12 hours, coloured by altitude, for three area-to-mass ratios and three drag coefficients — Ground tracks for the Kosmos 482 lander's last 12 hours under nine drag assumptions, from my own propagation.

Cold War Soviet spacecraft to crash "somewhere in Western hemisphere". The Telegraph, 7 May 2025. On the uncontrolled reentry of the Kosmos 482 Venus lander and congestion in low Earth orbit. Article

World map with a probability density of the Kosmos 482 re-entry site from an ensemble of 115 propagations — Re-entry site probability for Kosmos 482 from an ensemble of 115 propagations, from my own analysis.

A Soviet-era spacecraft will crash to Earth in hours — but where? The Times, 9 May 2025. On forecasting where the Kosmos 482 descent craft would come down. Article

Publications

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