As NASA and other space agencies are gearing up to return to the moon, there is significant interest and opportunities in detecting and tracking small objects, both manmade and otherwise, in cis-lunar space, a vast void between terrestrial orbits and the moon. This paper investigates the feasibility and performance of using NASA's Deep Space Network (DSN) tracking stations and the Goldstone Solar System Radar (GSSR), currently the world's most capable planetary radar transmitter, to detect and track Cis-Lunar targets. In 2022, the JPL GSSR team performed three CisLunar radar experiments using DSN Open Loop Recorders (OLRs). Observations were made by illuminating the targets with continuous waveform (CW) and Pseudo Random Noise (PRN) codes at X-band with the 450kW transmitter on DSS-14, a 70-m diameter antenna at Goldstone, and detecting the targets' reflection echoes at DSS-13, DSN's 34-m diameter R&D antenna in Goldstone, CA, using an open-loop recording system. We evaluate the performance of Cis-Lunar target detection by comparing observations with the Doppler frequency estimates derived from spacecraft's orbital dynamics, lunar noise temperature impacts, Moon clutter effects, and Signal-to-Noise Ratio simulations. This investigation will improve our understanding of engineering and science constraints for future detection and tracking of Cis-Lunar targets, including satellites, debris, asteroids, and surface assets on the moon.

With NASA's new focus on returning to the Moon, there is a need to build the capability to detect and track objects or debris that may threaten future missions in cis-lunar space. This paper analyzes the feasibility of detecting and tracking objects in cis-lunar space using NASA's Deep Space Network's (DSN) Goldstone Solar System Radar (GSSR) and the Green Bank Telescope (GBT). The GSSR is a 70-m antenna that can transmit X-band signals at $450kW$ . The cis-lunar space debris radar (CSDR) is a bistatic radar with the GSSR transmitting the signal and either the GBT (100-m diameter antenna) or a DSN 34-m antenna receiving the returned signal. The analysis will determine what object sizes are detectable under specific conditions and bistatic setups. Several GSSR, GBT, and DSN experiments were conducted to observe spacecraft in lunar orbit and xGEO (beyond GEO). The data from these experiments provide examples of detection versus tracking performance. Known spacecraft orbital dynamics will be compared with the radar estimated Dopplers, range, and signal-to-noise ratios (SNR). This analysis will look at the tradeoffs of waveforms traditionally used by GSSR, continuous wave (CW), and pseudorandom number (PN) codes and new ones considered for this application. With targets close to the Moon, return signals of certain waveform types are susceptible to interference from moon clutter.

Understanding and predicting the evolving spin states of defunct geosynchronous (GEO) satellites and rocket bodies is important for space situational awareness, active debris removal, satellite servicing, and anomaly resolution. There is clear evidence that many defunct GEO satellite spin states are predominantly driven by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect. The YORP effect is spin state evolution due to solar radiation and thermal re-emission torques. Observations are crucial to understand how YORP drives spin states and to validate dynamical models. Unfortunately, GEO satellites are non-resolved from ground-based telescopes and extracting spin states (spin periods, rotational angular momentum vector, instantaneous attitude) from ubiquitous photometric light curve data is challenging. Even for well-known objects, light curve inversion often yields several or more well-fitting spin state solutions within the measurement noise and modeling uncertainty (i.e. detailed satellite geometry, reflective properties, etc.). Also, there is strong evidence that the YORP effect drives satellites from uniform rotation to non-principal axis tumbling. Such tumbling states further complicate the light curve inversion process because the motion is driven by two independent periods rather than one. To aid complete spin state analysis, particularly for the tumbling case, Doppler radar observations collected at NASA Goldstone Deep Space Communications Complex are incorporated. Observing the well-documented retired GOES 8–12 weather satellites, the radar data yielded unambiguous spin period estimates for all targets and greatly narrowed pole solutions, independent of light curve data. Significant changes in spin rates and pole directions were observed over a two month span. These findings are consistent with YORP-driven evolution.

We have detected a bright radio burst from FRB 20200120E with the NASA Deep Space Network (DSN) 70 m dish (DSS-63) at radio frequencies between 2.2 and 2.3 GHz. This repeating fast radio burst (FRB) is reported to be associated with a globular cluster in the M81 galactic system. With high time resolution recording, low scattering, and large intrinsic brightness of the burst, we find a burst duration of ∼30 μs, comprised of several narrow components with typical separations of 2–3 μs. The narrowest component has a width of ≲100 ns, which corresponds to a light travel time size as small as 30 m. The peak flux density of the narrowest burst component is 270 Jy. We estimate the total spectral luminosity of the narrowest component of the burst to be 4 × 1030 erg s−1 Hz−1, which is a factor of ∼500 above the luminosities of the so-called “nanoshots” associated with giant pulses from the Crab pulsar. This spectral luminosity is also higher than that of the radio bursts detected from the Galactic magnetar SGR 1935 + 2154 during its outburst in April 2020, but it falls on the low-end of the currently measured luminosity distribution of extragalatic FRBs, further indicating the presence of a continuum of FRB luminosities. The temporal separation of the individual components has similarities to the quasiperiodic behavior seen in the microstructure of some pulsars. The known empirical relation between the microstructure quasiperiodicity timescale and the rotation period of pulsars possibly suggests a possible pulsar as the source of this FRB, with a rotation period of a few milliseconds.

ANITA's fourth long-duration balloon flight in 2016 detected 29 cosmic-ray (CR)-like events on a background of 0.37_{-0.17}^{+0.27} anthropogenic events. CRs are mainly seen in reflection off the Antarctic ice sheets, creating a phase-inverted waveform polarity. However, four of the below-horizon CR-like events show anomalous noninverted polarity, a p=5.3×10^{-4} chance if due to background. All anomalous events are from locations near the horizon; ANITA-IV observed no steeply upcoming anomalous events similar to the two such events seen in prior flights.

Estimating and predicting the spin states of defunct satellites and rocket bodies is important for space situational awareness, active debris removal, and satellite servicing. Observations show that the spin states of defunct geosynchronous (GEO) satellites are diverse and can change significantly over time. Spin state evolution for many defunct GEO satellites is primarily driven by solar radiation torques via the Yarkovsky-O’Keefe-RadzievskiiPaddack (YORP) effect. To better understand the YORP-driven evolution of these objects we obtain spin state estimates from a combination of Deep Space Network (DSN) Doppler radar echoes and optical light curves. The resolved nature of Doppler radar echoes allows for clear identification of satellite spin periods and can greatly constrain possible spin pole directions. Observations of the defunct GOES 8-12 GEO weather satellites demonstrate ongoing spin period evolution and pole motion consistent with YORP theory. Observations of two spent upper stage rocket bodies yield spin periods, center of mass offsets, and constraints on spin pole directions.

We report on simultaneous radio and X-ray observations of the repeating fast radio burst source FRB 180916.J0158+65 using the Canadian Hydrogen Intensity Mapping Experiment (CHIME), Effelsberg, and Deep Space Network (DSS-14 and DSS-63) radio telescopes and the Chandra X-ray Observatory. During 33 ks of Chandra observations, we detect no radio bursts in overlapping Effelsberg or Deep Space Network observations and a single burst during CHIME/FRB source transits. We detect no X-ray events in excess of the background during the Chandra observations. These non-detections imply a 5 sigma limit of <5 x 10(-10)erg cm(-2)for the 0.5-10 keV fluence of prompt emission at the time of the radio burst and 1.3 x 10(-9)erg cm(-2)at any time during the Chandra observations. Given the host-galaxy redshift of FRB 180916.J0158+65 (z similar to 0.034), these correspond to energy limits of <1.6 x 10(45)erg and <4 x 10(45)erg, respectively. We also place a 5 sigma limit of <8 x 10(-15)erg s(-1) cm(-2)on the 0.5-10 keV absorbed flux of a persistent source at the location of FRB 180916.J0158+65. This corresponds to a luminosity limit of <2 x 10(40)erg s(-1). Using an archival set of radio bursts from FRB 180916.J0158+65, we search for prompt gamma-ray emission in Fermi/GBM data but find no significant gamma-ray bursts, thereby placing a limit of 9 x 10(-9)erg cm(-2)on the 10-100 keV fluence. We also search Fermi/LAT data for periodic modulation of the gamma-ray brightness at the 16.35 days period of radio burst activity and detect no significant modulation. We compare these deep limits to the predictions of various fast radio burst models, but conclude that similar X-ray constraints on a closer fast radio burst source would be needed to strongly constrain theory.

— The growing inactive satellite population near geosynchronous Earth orbit (GEO) motivates improved understanding of these satellites’ dynamical evolution. Proposed active debris removal and servicing missions will require accurate spin state knowledge and predictions to capture and de-spin these large, inactive satellites. Spin state estimation from ubiquitous non-resolved ground-based optical measurements is very challenging due to complex satellite geometry and reflections. In this paper, we investigate how spin state estimates can be achieved through radar observations of inactive GEO satellites by the Deep Space Network (DSN). Leveraging time-varying viewing geometry due to Earth’s rotation and limited satellite geometry knowledge, we find that we can greatly constrain a satellite’s inertial spin pole. Analysis of 2017 Doppler echoes for the Echostar 2 satellite yielded pole solutions consistent with earlier optical studies. In addition, we have developed a radar observation model and unscented batch filter for radar-based spin state estimation.

The spectra of repeating fast radio bursts (FRBs) are complex and time-variable, sometimes peaking within the observing band and showing a fractional emission bandwidth of about 10%–30%. These spectral features may provide insight into the emission mechanism of repeating FRBs, or they could possibly be explained by extrinsic propagation effects in the local environment. Broadband observations can better quantify this behavior and help to distinguish between intrinsic and extrinsic effects. We present results from a simultaneous 2.25 and 8.36 GHz observation of the repeating FRB 121102 using the 70 m Deep Space Network radio telescope, DSS-43. During the 5.7 hr continuous observing session, we detected six bursts from FRB 121102, which were visible in the 2.25 GHz frequency band. However, none of these bursts were detected in the 8.36 GHz band, despite the larger bandwidth and greater sensitivity in the higher-frequency band. This effect is not explainable by Galactic scintillation and, along with previous multi-band experiments, clearly demonstrates that apparent burst activity depends strongly on the radio frequency band that is being observed.

The spectra of fast radio bursts (FRBs) encode valuable information about the source's local environment, underlying emission mechanism(s), and the intervening media along the line of sight. We present results from a long-term multiwavelength radio monitoring campaign of two repeating FRB sources, FRB 121102 and FRB 180916.J0158+65, with the NASA Deep Space Network (DSN) 70-m radio telescopes (DSS-63 and DSS-14). The observations of FRB 121102 were performed simultaneously at 2.3 and 8.4 GHz, and spanned a total of 27.3 hr between 2019 September 19 and 2020 February 11. We detected 2 radio bursts in the 2.3 GHz frequency band from FRB 121102, but no evidence of radio emission was found at 8.4 GHz during any of our observations. We observed FRB 180916.J0158+65 simultaneously at 2.3 and 8.4 GHz, and also separately in the 1.5 GHz frequency band, for a total of 101.8 hr between 2019 September 19 and 2020 May 14. Our observations of FRB 180916.J0158+65 spanned multiple activity cycles during which the source was known to be active and covered a wide range of activity phases. Several of our observations occurred during times when bursts were detected from the source between 400-800 MHz with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope. However, no radio bursts were detected from FRB 180916.J0158+65 at any of the frequencies used during our observations with the DSN radio telescopes. We find that FRB 180916.J0158+65's apparent activity is strongly frequency-dependent due to the narrowband nature of its radio bursts, which have less spectral occupancy at high radio frequencies ($\gtrsim$ 2 GHz). We also find that fewer or fainter bursts are emitted from the source at high radio frequencies. We discuss the implications of these results on possible progenitor models of repeating FRBs.

Magnetars are young, rotating neutron stars that possess larger magnetic fields (B ≈ 10¹³-10¹⁵G) and longer rotational periods (P ≈ 1-12 s) than ordinary pulsars. In contrast to rotation-powered pulsars, magnetar emission is thought to be fueled by the evolution and decay of their powerful magnetic fields. They display highly variable radio and X-ray emission, but the processes responsible for this behavior remain a mystery. We report the discovery of bright, persistent individual X-ray pulses from XTE J1810-197, a transient radio magnetar, using the Neutron star Interior Composition Explorer (NICER) following its recent radio reactivation. Similar behavior has only been previously observed from a magnetar during short time periods following a giant flare. However, the X-ray pulses presented here were detected outside of a flaring state. They are less energetic and display temporal structure that differs from the impulsive X-ray events previously observed from the magnetar class, such as giant flares and short X-ray bursts. Our high frequency radio observations of the magnetar, carried out simultaneously with the X-ray observations, demonstrate that the relative alignment between the X-ray and radio pulses varies on rotational timescales. No correlation was found between the amplitudes or temporal structure of the X-ray and radio pulses. The magnetar's 8.3 GHz radio pulses displayed frequency structure, which was not observed in the pulses detected simultaneously at 31.9 GHz. Many of the radio pulses were also not detected simultaneously at both frequencies, which indicates that the underlying emission mechanism producing these pulses is not broadband. We find that the radio pulses from XTE J1810-197 share similar characteristics to radio bursts detected from fast radio burst (FRB) sources, some of which are now thought to be produced by active magnetars.

We report the detection of multiple bright radio bursts from therepeating fast radio burst (FRB) source FRB 121102 using the 70 mdiameter Deep Space Network (DSN) radio telescope (DSS-43) inTidbinbilla, Australia [1]. We carried out a continuous 5.7 hour observation of the position of FRB 121102 [2, 3], starting at 06 September 2019 17:27:55 UTC, following alerts that the source is now in an active state (e.g., ATels #13064, #13073, #13090, #13098).