Contents:
Planetary Science Decadal Survey
NASA Small Bodies Assessment Group Findings
National Near-Earth Object Preparedness Strategy and Action Plan
National Preparedness Strategy and Action Plan for Near-Earth Object Hazards and Planetary Defense
National Cislunar Science & Technology Strategy
Planetary Science Decadal Survey
The ngRADAR project is responsive to the findings and recommendations published in the planetary science decadal survey by the National Academies of Science, Engineering, and Medicine entitled "Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032." The planetary decadal collects community input and makes recommendations to the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA) on how to address the key scientific questions in planetary science over the next decade. NASA provided an initial response to the planetary science decadal survey in August 2022.
Recommendation
Page 18-12: “As the steward of ground-based observatories with NEO [near-Earth object] observing capabilities, NSF should support and prioritize critical planetary defense observations of NEOs at its ground-based facilities.”
ngRADAR consists of a transmitter system on the NSF's Green Bank Telescope and receivers at the NSF's Very Long Baseline Array. In the future, the NSF's Next Generation Very Large Array (ngVLA) could also function as a receiving system for ngRADAR, greatly increasing its sensitivity by greatly increasing its receiving area. Establishing the ngRADAR planetary radar system makes use of existing infrastructure at NSF's ground-based facilities and allows a new capability to be realized without the need to construct a new facility.
Finding
Page 18-12: “In order to conduct the required NEO follow-up characterization observations to meet key planetary defense objectives, it would be valuable to expand and extend planetary radar capabilities to obtain coverage over the northern and southern celestial hemispheres.”
ngRADAR expands planetary radar capabilities in the northern hemisphere by making use of the Green Bank Telescope and the Very Long Baseline Array of antennas spread across the United States from Hawaii to St. Croix in the Virgin Islands, which provides complementarity and redundancy to existing planetary radar assets, especially for follow-up physical and dynamical characterization of NEOs.
Finding
Page 21-20: “Development of advanced radar technologies to improve NEO follow-up, tracking, and characterization capabilities would enhance planetary defense preparation.”
ngRADAR makes use of solid-state power amplifiers known as gallium-nitride monolithic microwave integrated circuits (GaN MMICs) that have not been used previously for planetary radar systems. ngRADAR also pushes to a higher transmit frequency (13.7 GHz at Ku band; 2.19 cm wavelength) than other planetary radar systems, is capable of finer resolution resolution (sub-meter) than other planetary radar systems by using up to 600 MHz of waveform bandwidth, and seeks to combine the signals received by multiple telescopes into a radar-receiving array.
Recommendation
Page 20-15/22-45: “NASA and NSF should review the current radar infrastructure to determine how best to meet the community’s needs, including expanded capabilities at existing facilities, to replace those lost with Arecibo.”
ngRADAR, as stated above, makes use of existing NSF facilities by expanding their capabilities to include radar transmission and reception, which will help fill the void left by the loss of the planetary radar system at Arecibo Observatory.
Recommendation
Page 18-12: “NASA and NSF should support studies to develop a plan for ground-based planetary radar capabilities comparable to or exceeding those of the Arecibo Observatory necessary for achieving planetary defense objectives.”
ngRADAR looks forward to supporting discussions and studies by NASA and NSF about the future of ground-based planetary radar capabilities and how ngRADAR can help achieve planetary defense objectives.
NASA Small Bodies Assessment Group Findings
For many years, planetary radar and planetary-radar facilities have featured prominently in the findings of the community-driven Small Bodies Assessment Group (SBAG), which was established by NASA in 2008. SBAG produces findings during biannual meetings of the small-bodies community and passes them along to the Planetary Science Advisory Committee (PAC) to elicit responses from NASA. The SBAG findings from January 2022, once again, included support for planetary radar stating:
Finding: "SBAG commends NASA for supporting additional asteroid radar observations at other facilities in order to meet a portion of the scientific and planetary defense goals previously accomplished by the Arecibo Observatory. SBAG encourages NASA to continue planned upgrades to radar capabilities at the Goldstone and Canberra Deep Space Network sites, and recommends that NASA continue to work with NSF and other agencies to develop new planetary radar facilities. The current efforts to install a planetary radar system at the existing Green Bank Telescope are an example of how such collaborations can aid the development of additional planetary radar capabilities."
The Outer Planets Assessment group (OPAG) concurred with SBAG's finding in support of NASA and NSF working to "develop a concerted plan for new national resources for planetary radar."
ngRADAR presents a way forward for developing planetary radar capabilities using existing infrastructure of the NSF, which can be applied to goals and objectives for planetary science and planetary defense often spearheaded by NASA. Furthermore, the ngRADAR project has been invited to speak at the biannual SBAG meetings on multiple occasions.
The SBAG Goals document "captures the high-priority objectives and unique exploration opportunities related to the Solar System’s small bodies." Mentions of radar are pervasive through the document as a valuable tool in addressing the three overarching themes of (1) Small Bodies, Big Science, (2) Defend Planet Earth, and (3) Enable Human Exploration. ngRADAR can help provide the physical and dynamical characterizations of individual small bodies and probe the small-body population as a whole to support the goals of SBAG.
SBAG also formed the Apophis Specific Action Team (SAT) at the request of NASA to generate a report on observational capabilities and priorities during the close Earth approach of asteroid (99942) Apophis on April 13, 2029. The Apophis SAT report finds that the size and shape of Apophis “could be determined to < 5 m precision by an extensive radar observing campaign.” The SAT report also describes how “sophisticated [radar] polarimetric analysis … can reveal the scale and the shape of surface particles," where “comparison of the polarimetric parameters pre- and post-flyby could reveal changes in surface properties due to tidal resurfacing.”
ngRADAR would be capable of imaging with sub-meter resolution for size and shape determination, providing radar polarimetry through its dual-polarization reception of circularly polarized transmissions, and utilizing multistatic reception for radar speckle tracking to constrain the spin state. The 2029 close approach by Apophis also sets a reasonable soft deadline for having an operational radar system on the Green Bank Telescope. Note, however, even a low-power radar system on the GBT akin to the pilot system (700 W) could provide meter-scale resolution images of Apophis as it approaches well within the orbit of the Moon in 2029.
National Near-Earth Object Preparedness Strategy and Action Plan (2018)
The National Science & Technology Council established the Interagency Working Group for Detecting and Mitigating the Impact of Earth-Bound Near-Earth Objects (DAMIEN) to produce the National Near-Earth Object Preparedness Strategy and Action Plan in 2018, a document outlining how to "improve capabilities for prediction (detection, characterization, and monitoring) and National preparedness (protection, mitigation, response, and recovery)." Among the action items supporting the strategic objective to "improve national capabilities for NEO detection, tracking, and remote characterization" assigned to NASA, the NSF, and the US Air Force was to:
Action: "Identify opportunities in existing and planned telescope programs to improve detection and tracking by enhancing the volume and quality of current data streams, including from optical, infrared, and radar facilities."
Since the announcement of the National Near-Earth Object Preparedness Strategy and Action Plan in 2018, a federal interagency working group led by the NSF and supported by NASA, the US Air Force, and other interested parties has been stood up to review national needs and requirements for planetary radar as a national asset. Also during this time, Arecibo Observatory was decommissioned and ultimately collapsed, leaving a void in the volume and quality of data streams from radar facilities. ngRADAR has the potential to fill this gap in national capabilities for planetary radar, enhancing the volume of observations possible as a complement to the Goldstone Solar System Radar (science), while pushing to new wavelengths and higher resolutions to increase the quality of data streams from radar facilities in the future.
National Preparedness Strategy and Action Plan for Near-Earth Object Hazards and Planetary Defense (2023)
The National Science & Technology Council established the Planetary Defense Interagency Working Group (previously the DAMIEN Interagency Working Group) to produce the National Preparedness Strategy and Action Plan for Near-Earth Object Hazards and Planetary Defense in 2023, a document for improving "our Nation's preparedness to address the hazard of NEO impacts by leveraging and enhancing existing national and international assets and adding important capabilities across government" with a ten-year horizon for its goals and actions. The first action item under the first goal of enhancing detection, tracking, and characterization capabilities reiterates the first action of the 2018 plan, directing NASA, the NSF, the Department of Defense (DoD), and the Department of Commerce over the next two years to:
Action: "Continue to identify opportunities in existing and planned space domain awareness programs to improve detection and tracking by enhancing the volume and quality of current data streams, including from ground-based and space-based optical, infrared, and radar facilities."
A subsequent action under the same goal tasks the NSF, NASA, and DoD to:
Action: "Conduct an interagency assessment to explore interest from key government stakeholders in the coordinated development of current and future deep space radar facilities and identify where these facilities may be useful for planetary defense. Given the loss of the Arecibo Observatory’s 305-meter antenna, provide data to support the newly established interagency group on existing and planned deep space radar capabilities, informing key priorities, investment, and operational opportunities."
As mentioned above, an interagency working group has been initiated, led by the NSF, to explore the use of planetary radar systems for planetary defense. The ngRADAR team was invited, as part of a wider NRAO effort, to speak with the interagency working group taking the above action. Also, the plan itself makes note of the ngRADAR pilot radar system in Appendix C (page 28), listing applicable developments since 2018, noting that: "Preliminary testing on NSF’s Green Bank Telescope of a prototype low-power radar, developed by Raytheon in conjunction with NSF’s Very Long Baseline Array which is operated by the National Radio Astronomy Observatory, resulted in highest resolution images of the Moon collected from ground. NSF is funding conceptual designs of next-generation medium- and high-power radars for potential deployment on current and future radar-capable facilities."
NASA released their own Planetary Defense Strategy and Action Plan in response, expanding on many of the same actions of the national plan from their agency-level, operational perspective as well as complementing the National Cislunar Science & Technology Strategy. These include identifying ways to enhance data streams from current and future space domain awareness programs (including those for cislunar studies) and supporting interagency assessment of current and future radar facilities potentially of use for planetary defense. As part of these objectives, NASA will seek to strengthen partnerships with the NSF and US Space Force in regard to planetary radar. Of note, NASA states that "existing radar capabilities could be augmented with a next generation deep space radar for potentially hazardous object ranging and imaging, which may require interagency collaboration and partnership." The ngRADAR project could provide this augmentation.
National Cislunar Science & Technology Strategy
The National Science & Technology Council established the subcommittee on Cislunar Technology Strategy Interagency Working Group to produce the National Cislunar Science & Technology Strategy, a document that "provides a first interagency strategy to guide the actions of the U.S. government in advancing scientific, exploration, and economic development activities in Cislunar space." Among the four key objectives of the federal cislunar strategy is to:
Objective: "Extend U.S. space situational awareness capabilities into Cislunar space. Space situational awareness is the necessary foundation to enable transparency and safe operations for all entities operating in Cislunar space. As activities in Cislunar space increase, the U.S. government will define requirements for new space situational awareness capabilities, including associated reference systems and data-sharing approaches. The United States will pursue new cost-effective capabilities while improving existing capabilities as necessary. This objective has synergies with efforts to provide early warning for potentially hazardous asteroids."
ngRADAR, by its bistatic (multistatic) nature, will be able to observe without the limitation of having to switch between transmit and receive modes at the same antenna. This opens up a capability of studying targets between Earth and the Moon, including cislunar space debris and close-approaching near-Earth objects. While other systems can study space debris in low-Earth orbit or geosynchronous orbit about the Earth, ngRADAR will have the sensitivity to study space debris in higher (ex-geo) orbits, all the way to the Moon itself. This will help fill strategic knowledge gaps in the amount and type of debris in the cislunar region for space situational awareness (especially as humans return to the Moon) as well as provide tracking and characterization of potentially hazardous natural bodies.
Disclaimer: Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), or other funding agencies.