12 research outputs found
Hyperbolic limit on the early arrival time of bright pulses from PSR~J08354510 (Vela)
Astronomers have studied the Vela pulsar (PSR~J08354510) for decades. This
study analyses almost one hundred hours of single-pulse data collected over
three consecutive days from 2016 and 2020. The work investigates the
fascinating phenomena of the earlier arrival of brighter pulses with their
increase in peak intensity. We found a hyperbolic relation between them by
constructing integrated pulse profiles using flux density intervals and
examining the relationship between pulse arrival time and intensity. We
identified a phase limit of ~ms for the earliest arrival of
the brightest pulses. This study offers exciting prospects for further
exploring the emission regions responsible for the Vela pulsar's regular and
giant micro-pulses.Comment: 9 pages, 11 figure
Planetary Radio Interferometry and Doppler Experiment (PRIDE) Technique: a Test Case of the Mars Express Phobos Fly-by. 2. Doppler tracking: Formulation of observed and computed values, and noise budget
Context. Closed-loop Doppler data obtained by deep space tracking networks
(e.g., NASA's DSN and ESA's Estrack) are routinely used for navigation and
science applications. By "shadow tracking" the spacecraft signal, Earth-based
radio telescopes involved in Planetary Radio Interferometry and Doppler
Experiment (PRIDE) can provide open-loop Doppler tracking data when the
dedicated deep space tracking facilities are operating in closed-loop mode
only. Aims. We explain in detail the data processing pipeline, discuss the
capabilities of the technique and its potential applications in planetary
science. Methods. We provide the formulation of the observed and computed
values of the Doppler data in PRIDE tracking of spacecraft, and demonstrate the
quality of the results using as a test case an experiment with ESA's Mars
Express spacecraft. Results. We find that the Doppler residuals and the
corresponding noise budget of the open-loop Doppler detections obtained with
the PRIDE stations are comparable to the closed-loop Doppler detections
obtained with the dedicated deep space tracking facilities
Venus Express radio occultation observed by PRIDE
Context. Radio occultation is a technique used to study planetary atmospheres
by means of the refraction and absorption of a spacecraft carrier signal
through the atmosphere of the celestial body of interest, as detected from a
ground station on Earth. This technique is usually employed by the deep space
tracking and communication facilities (e.g., NASA's Deep Space Network (DSN),
ESA's Estrack). Aims. We want to characterize the capabilities of the Planetary
Radio Interferometry and Doppler Experiment (PRIDE) technique for radio
occultation experiments, using radio telescopes equipped with Very Long
Baseline Interferometry (VLBI) instrumentation. Methods. We conducted a test
with ESA's Venus Express (VEX), to evaluate the performance of the PRIDE
technique for this particular application. We explain in detail the data
processing pipeline of radio occultation experiments with PRIDE, based on the
collection of so-called open-loop Doppler data with VLBI stations, and perform
an error propagation analysis of the technique. Results. With the VEX test case
and the corresponding error analysis, we have demonstrated that the PRIDE setup
and processing pipeline is suited for radio occultation experiments of
planetary bodies. The noise budget of the open-loop Doppler data collected with
PRIDE indicated that the uncertainties in the derived density and temperature
profiles remain within the range of uncertainties reported in previous Venus'
studies. Open-loop Doppler data can probe deeper layers of thick atmospheres,
such as that of Venus, when compared to closed-loop Doppler data. Furthermore,
PRIDE through the VLBI networks around the world, provides a wide coverage and
range of large antenna dishes, that can be used for this type of experiments
Planetary Radio Interferometry and Doppler Experiment (PRIDE) for Planetary Atmospheric Studies
Space EngineeringAerospace Engineerin
Analysis of an Interplanetary Coronal Mass Ejection by a Spacecraft Radio Signal: A Case Study
Tracking radio communication signals from planetary spacecraft with ground-based telescopes offers the possibility to study the electron density and the interplanetary scintillation of the solar wind. Observations of the telemetry link of planetary spacecraft have been conducted regularly with ground antennae from the European Very Long Baseline Interferometry Network, aiming to study the propagation of radio signals in the solar wind at different solar elongations and distances from the Sun. We have analyzed the Mars Express spacecraft radio signal phase fluctuations while, based on a 3-D heliosphere plasma simulation, an interplanetary coronal mass ejection (ICME) crossed the radio path during one of our observations on 6 April 2015. Our measurements showed that the phase scintillation indices increased by a factor of 4 during the passage of the ICME. The method presented here confirms that the phase scintillation technique based on spacecraft signals provides information of the properties and propagation of the ICMEs in the heliosphere
Planetary radio interferometry and doppler experiment (PRIDE) for planetary probes
Astrodynamics & Space MissionsPhysical and Space Geodes
The antenna phase center motion effect in high-accuracy spacecraft tracking experiments
We present an improved model for the antenna phase center motion effect for high-gain mechanically steerable ground-based and spacecraft-mounted antennas that takes into account non-perfect antenna pointing. Using tracking data of the RadioAstron spacecraft we show that our model can result in a correction of the computed value of the effect of up to 2×10-14 in terms of the fractional frequency shift, which is significant for high-accuracy spacecraft tracking experiments. The total fractional frequency shift due to the phase center motion effect can exceed 1×10-11 both for the ground and space antennas depending on the spacecraft orbit and antenna parameters. We also analyze the error in the computed value of the effect and find that it can be as large as 4×10-14 due to uncertainties in the spacecraft antenna axis position, ground antenna axis offset and misalignment, and others. Finally, we present a way to reduce both the ground and space antenna phase center motion effects by several orders of magnitude, e.g. for RadioAstron to below 1×10-16, by tracking the spacecraft simultaneously in the one-way downlink and two-way phase-locked loop modes, i.e. using the Gravity Probe A configuration of the communications links.Astrodynamics & Space Mission