Documents / Official release
This is a draft paper dated March 1, 2023, by Abraham (Avi) Loeb of Harvard's Galileo Project and Sean M. Kirkpatrick of the All-domain Anomaly Resolution Office (AARO). AARO released it in full in February 2025. The paper derives physics-based limits on how highly maneuverable UAP could be interpreted. It argues that supersonic objects would produce fireballs, ionization and radar signatures. It concludes that when these signatures are missing, the distance and velocity estimates from single-site sensors may be inaccurate.
Constraints on UAP 5 In addition to the thermal, shock, and associated optical signatures of a high velocity, highly maneuvering object, there is also an ionization and associated radio frequency signature from such an object moving through the atmosphere. Studies into supersonic and hypersonic vehicles provide a good basis for comparison. While the ionization density depends on the altitude, shape, material and velocity of the object in motion, some limits can be derived on when a signature would be detected, implying a limit to the object’s motion prior to the fireball threshold. In particular, ionization at high velocities leads to an increase in radar reflectivity along the ionization edge of the object and along the ionization trail. Both give rise to enhanced radio-frequency (RF) reflection for frequencies below the cutoff frequency. Surzhikov calculates the ionization of air in high supersonic and low hypersonic regimes around blunt air- frames (Surzhikov 2018). Figure 2 and table 1 in Surzhikov (2018) demonstrate the lowest end giving rise to a critical electron density of 1010 cm−3 for detection frequencies between 1-10 GHz. Variations of velocity, altitude and shape give rise to electron densities above this threshold, rendering the object detectable for typical radars in the L, S, C, and X radio bands. Dhakal et al. conducted an excellent assessment of constraints on dark matter using radar meteor detectors (Dhakal et al. 2022). While not directly applicable to the current span of UAP sightings, the calculations do address smaller, faster objects at higher altitudes (70-130 km). These objects also exhibit an ionization trail which can be used for detection and measurement using similar radars. This regime is relevant to the mothership/probe scenario discussed above, indicating a detectable signature prior to the onset of a fireball as shown in Figures (1) and (11) of Dhakal et al. (Dhakal et al. 2022). 6. CONCLUSION The considerations in this paper imply a useful limit on observations of UAP which bound the hypothetical expla- nations and can support limitations on interpretations of data. For example, one of the most common sets of data within the military holdings comes from FLIR (forward looking infrared) pods. These sensors provide an accurate resolved image of relative thermal measurements across the scene. Typical UAP sightings are too far away to get a highly resolved image of the object and determination of the object’s motion is limited by the lack of range data. The range is usually estimated using the flight dynamics of the platform and some fixed points in the scene - if either are available. The error in estimating the range gives rise to a significant variation in the calculated velocity and is subject to human bias and error. Claims of objects exceeding the transonic to supersonic range should be evaluated against the above known physics of ionization, radar reflectivity, temperature, sonic booms, and fireballs (Loeb 2022b). All of which can more effectively and accurately bound the velocity, and hence drive the range calculation. This will, in turn, when matched with the specifics of the sensor, allow for better estimates of the size, shape, and mass of the object in question. ACKNOWLEDGEMENTS. This work was supported in part by Galileo Project at Harvard University and con- ducted in partnership with the Department of Defense, All-domain, Anomaly Resolution Office. We thank Richard Cloete for assistance and comments on the manuscript. REFERENCES 2021, ODNI UAP Report], USG. https://www.dni.gov/files/ODNI/documents/ assessments/Prelimary-Assessment-UAP-20210625.pdf Bracewell, R. N. 1960, Nature, 186, 670, doi: 10.1038/186670a0 Brown, P., Spalding, R. E., ReVelle, D. O., Tagliaferri, E., & Worden, S. P. 2002, Nature, 420, 294, doi: 10.1038/nature01238 Bryson, S., Kunimoto, M., Kopparapu, R. K., et al. 2021, AJ, 161, 36, doi: 10.3847/1538-3881/abc418 Dhakal, P., Prohira, S., Cappiello, C. V., et al. 2022, arXiv e-prints, arXiv:2209.07690, doi: 10.48550/arXiv.2209.07690 Ezell, C., & Loeb, A. 2022, arXiv e-prints, arXiv:2209.11262, doi: 10.48550/arXiv.2209.11262 Freitas, R. A., J. 1980, Journal of the British Interplanetary Society, 33, 251 Freitas, R. A., J., & Valdes, F. 1985, Acta Astronautica, 12, 1027, doi: 10.1016/0094-5765(85)90031-102Page determined to be Unclassified Reviewed by Chief of Staff, AARO IAW FY24 NDAA, Section 1841 (a)(1)(C) Date: 2/5/2025
Official release, from the nara collection. The PDF is mirrored here; the original link is above. 6 pages are in the text index: search them above, or from the library's search.