Atmospheric disturbances created by hypersonic movers

Request for Information (RFI) DARPA-SN-23-53 Atmospheric disturbances created by hypersonic movers Responses Accepted: Until 4:00 p.m. (Eastern) on May 17, 2023 Point of Contact: Dr. Michael - Orbit Nayak, Program Manager, DARPA DSO/STO Email Address: contact@example.gov The Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) is requesting information related to theoretical hypotheses for physical mechanisms by which objects moving at hypersonic (Mach 3-9) speeds may create mechanical and/or electromagnetic (EM) disturbances in the atmosphere (0-500 km). Based on responses, DARPA may choose to make an initial investment into modeling and simulation work to explore these atmospheric perturbation mechanisms - specifically, their propagation, magnitude, and other actionable insights. BACKGROUND It is well-known that ionized plasmas, consisting of positively charged ions and free electrons, are generated from very fast-moving objects (e.g., bolides, Mach>45).[1] It is also known that ultraviolet radiation may be emitted from hypersonic movers[2] and that ELF/VLF[3] EM waves can be amplified by rocket exhaust plumes.[4] However, it is less clear what physical mechanism or process may generate EM radiation (e.g., from a turbulent plasma) in the radio frequency regime (<30 MHz) for bodies traveling at the lower end of hypersonic speeds (for the purposes of this Special Notice, defined as less than Mach 9). Similarly, for mechanical disturbances, empirical analyses have indicated that large and fast-moving objects like rockets[5] and bolides[6] can produce infrasonic signals that are detectable at thousands to tens of thousands of kilometers, respectively. However, processes that create detectable acoustic and pressure signatures from objects moving at reduced speeds (Mach 3-9) are less clear and have not been explored in detail. This RFI is seeking theories that describe potential atmospheric disturbances generated or created by the transit of Mach 3 to Mach 9 hypersonic movers in either the mechanical (e.g., ground or air-based pressure sensors, magnetometers, Global Navigation Satellite System Total Electron Content (GNSS TEC) measurements) or ELF/VLF/LF/MF/HF[7] EM frequency regimes (1 Hz - 30 MHz). DARPA encourages responses that (1) hypothesize atmospheric signatures caused by hypersonic movers in the regimes specified above; (2) ascribe the reason, process, or physical mechanism behind the creation of the signature of interest and the altitude/regime of the atmosphere[8] where these signals are likely generated; and (3) describe theoretical and/or modeling development that would determine the amplitude, magnitude, and temporal persistence of such signatures of interest (science-up work). Analysis of hypersonic data (data-down work) is out of scope from the focus areas discussed below. Empirical analyses are not of interest to this RFI. Analyses for blunt bodies (a hypersonic mover with a ballistic coefficient less than 10,000 kg/m2) are not of interest to this RFI. Respondents should clearly outline any assumptions, requirements needed, and/or approximations made. Classified responses will be accepted under this RFI. However, respondents are encouraged to propose unclassified work wherever possible and practical. FOCUS AREAS This RFI seeks responses that address the specific two focus areas (FAs) outlined below. Respondents may address both focus areas in a single submission. FA1: Hypotheses for EM disturbance mechanisms This FA seeks hypotheses that describe potential mechanisms for the generation of EM disturbances from hypersonic movers between Mach 3 and Mach 9. An example of such a mechanism for large meteors is the V. A. Bronsht'n model,[9] which describes a magnetohydrodynamic process by which radio waves are generated in ion trails. Alternately, as a hypersonic object moves through the atmosphere, it may ionize the air molecules around it, creating a plasma sheath or "bow shock" in front of the object. This plasma sheath may interact with the Earth's magnetic field, which can generate EM disturbances that propagate from the object over long distances. Additional mechanisms or hypotheses are of interest to this RFI and should explicitly outline each step for the proposed mechanism as well as how each physical process connects to the other, ultimately resulting in emitted EM radiation. Theories should link emissions in the ELF, VLF, LF, MF, and HF regimes back to approximate initial hypersonic mover properties. The amount of emitted EM radiation, how it fluctuates, and how it depends on properties of the hypersonic mover (e.g., mass, composition, velocity, entry angle, etc.) is also of interest. FA2: Hypotheses for mechanical disturbance mechanisms This FA seeks hypotheses that describe potential mechanisms for the generation of mechanical disturbances from hypersonic movers between Mach 3 and Mach 9. Hypotheses should explicitly outline each step for the proposed mechanism as well as how each physical process connects to the other, ultimately resulting in emitted acoustic/pressure perturbations. Potential hypotheses should outline how such a wake may create acoustic/pressure waves that propagate through the atmosphere and hypothesize any distinctive signatures that may feasibly be produced. Theories that show evidence that atmospheric mechanical disturbances created by hypersonic movers, such as vortices, shock waves, or bow waves, can cause measurable fluctuations in air pressure and atmospheric density are of interest. SUBMISSION FORMAT Respondents to this RFI are encouraged to be as succinct as possible, while also providing technically justified insight. Page limits for each section are indicated below. Format specifications for responses include 12-point font, single-spaced, single-sided, 8.5 by 11-inch paper, with 1-inch margins in MS Word or Adobe PDF format. Respondents are responsible for clearly identifying proprietary information. Responses containing proprietary information must have each page containing such information clearly marked with a label such as - Proprietary or - Company Proprietary. Cover Sheet (1 page): Provide the following information. Response Title Technical point of contact name, organization, telephone number, and email address Focus area addressed (FA 1, FA 2, or both FAs) Technical Description (regardless of number of FAs responded to): Not to exceed 8 pages, 3-5 pages preferred. Bibliography (not to exceed 2 pages): All references must be cited in the Technical Description. References (no page limit): Respondents should include copies in PDF format of all cited papers or reports in sequential order as listed in the Bibliography. Respondents are encouraged, though not required, to highlight sections, figures, or statements directly relevant to their technical proposition. SUBMISSION INSTRUCTIONS AND CONTACT INFORMATION All responses to this RFI must be emailed to contact@example.gov. Responses will be accepted any time from the publication of this RFI until 4:00 p.m. (Eastern) on May 17, 2023. Early responses are encouraged. All technical and administrative correspondence and questions regarding this RFI should also be sent to the same email address. Emails sent directly to the DARPA Program Manager may result in a delayed or no response. For classified responses to this RFI, respondents must first send an UNCLASSIFIED email to contact@example.gov no later than 4:00 p.m. (Eastern) on May 8, 2023, indicating their intent to submit a classified response, their CAGE code, and security point(s) of contact. DARPA will subsequently contact respondents to provide details for classified submission. ELIGIBILITY DARPA invites participation from all those engaged in related research activities and appreciates responses from all capable and qualified sources including, but not limited to, universities, university-affiliated research centers (UARCs), Federally-Funded Research and Development Centers (FFRDCs), private or public companies, and Government research laboratories. DISCLAIMERS AND IMPORTANT NOTES This is an RFI issued solely for information and new program planning purposes; it does not constitute a formal solicitation for proposals. In accordance with Federal Acquisition Regulation 15.201(e), responses to this RFI are not offers and cannot be accepted by the Government as such. Responses do not bind DARPA to any further actions related to this topic including requesting follow-on proposals from respondents to this RFI. Submission is voluntary and is not required to propose to a subsequent Broad Agency Announcement (if any) or other research solicitation (if any) on this topic. DARPA will not provide reimbursement for costs incurred in responding to this RFI. Respondents are advised that DARPA is under no obligation to acknowledge receipt of the information received or provide feedback to respondents with respect to any information submitted under this RFI. DARPA will disclose submission contents only for the purpose of review. Submissions may be reviewed by the Government (DARPA and partners) and Scientific, Engineering and Technical Assistance (SETA) support contractors. [1] ReVelle, D. O. (1980) A predictive macroscopic integral radiation efficiency model. J. Geophys. Res. 85, 1803. [2] Caledonia, G. E. (1994). Ultraviolet Emissions Occurring About Hypersonic Vehicles in Rarefied Flows. Defense Technical Information Center. [3] ELF: Extremely Low Frequency; VLF: Very Low Frequency. [4] Bernhardt, P. A. (2021). Strong Amplification of ELF/VLF Signals in Space Using Neutral Gas Injections From a Satellite Rocket Engine. Radio Science. [5] Nambath K. (1971) Characteristics of Infrasonic Signals from Rockets, Geophysical Journal International. Volume 26, Issue 1-4. Pages 135'148. [6] Arrowsmith, Stephen J. (2008) Global Detection of Infrasonic Signals from Three Large Bolides. Earth, Moon, and Planets. [7]LF: Low Frequency; MF: Medium Frequency; HF: High Frequency. [8] For example: lower ionosphere, mesosphere, stratosphere, etc. [9] Bronsht'n, V. A. (1983) A Magnetohydrodynamic Mechanism for Generating Radio Waves by Bright Fireballs. Solar System Research. Vol. 17, No. 2.