JuanCastillo29/space-mission-intelligence-data huggingface dataset:
a defined search strip of the sky centred on the spacecraft’s ephemeris, and searching
for radio sources inside this search strip. All these sources could be used as prospective
PRIDE experiment calibrators and the proper selection of calibrators has an impact
on the VLBI data quality. Figure 7 depicts the PRIDE observation planning chart for
CReMA 5.0 during the cruise phase of the JUICE mission. These results are utilized
to detect instances of in-beam phase referencing observation [43] possibilities or, in
general, PRIDE observing opportunities.
The PRIDE JUICE project relies heavily on the ecliptic plane densification of
these sources along the ecliptic plane is insufficient for high-accuracy VLBI spacecraft
tracking, according to the current list of phase calibrators as shown in Fig. 6 [53].
Before arrival in the Jovian system, we will perform dedicated observational campaigns
to create a dense grid of calibrator sources around Jupiter’s orbit in order to achieve
sub-nano radians accuracy in the spacecraft’s lateral positioning.
To create and distribute schedules to VLBI telescopes and correlator, and orga-
nize an observation campaign for the discovered opportunity, the custom-developed
planning tool’s output is loaded into pySCHED. Many VLBI scheduling tools, such
as pySCHED, have difficulty incorporating satellites as observation targets in the nec-
essary control files, since these tools have been used for spacecraft observations only
on relatively few occasions. Our setup allows operational VLBI data acquisition and
processing systems to be used for direct satellite signal observations, similar to those
Residual frequency [Hz]

2.455M 2.45M 2.445M 2.44M 2.435M
18.5k 19k 19.5k 20k 20.5k 21k 21.5k 22k
0.02
−0.02
18.5k 19k 19.5k 20k 20.5k 21k 21.5k 22k

[Figure: Fig. 10 Topocentric frequency detections and Doppler noise at Ka-band as detected at Mopra on April 11, 2022, three 20-minute-long scans that were alternated with reference sources.The horizontal axis represents time, measured in seconds since the beginning of the day on April 11, 2022. This axis delineates the duration of observations conducted at the Mopra facility. Each point along this axis corresponds to a specific moment in time during the observations. The vertical axis depicts the detected frequency in kHz at the Ka-band. This frequency axis illustrates the variations in the detected signal over time due to the Doppler effect and noise. The Doppler shift, totaling 22 kHz over the 3600-second observation period, is represented on this axis.]
spacecraft communications and tracking. However, until recently, the technique had
only demonstrated results at S- and X-bands. We have used the tools and methodology
from Sections 3.1 and 4.1 to plan, schedule and execute the BepiColombo observa-
as a dry run and preparatory activity for the more extensive PRIDE–JUICE opera-
tions. As JUICE’s and BepiColombo’s radio communication systems and radio science
instruments are very similar, BepiColombo is the most suitable choice for testing and
preparations.
The primary objective of the experiment was to detect the BepiColombo radio sig-
2021 and 2022. In the specified epoch we consider here, we conducted a session in par-
allel using the radio telescopes from University of Tasmania (UTAS) Ceduna (Cd) in
South Australia, Katherine (Ke) in North Territory, and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) telescope at Mopra (Mp) in New South Wales. Figure 8 shows the BepiColombo-PRIDE experiment settings, the Molleweide projection, and the zoomed-in finding chart. Figure 9 shows the SCHED elevation time plot for the telescopes used in this campaign, as an illustration of the output of the tools we have developed. The Cd and Ke tracked the downlink signal of the spacecraft at X-band, while Mopra tracked the radio signal at Ka-band. The spacecraft was operating in two-way mode with the ESTRACK ground station at New Norcia (NNO) in Western Australia. The uplink frequency was locked with an X/Ka transponder on board (locked at 7.1 GHz). We generated the schedule files for all three antennas, and we recorded data in VLBI Data Interchange Format (VDIF) for Ke and Cd, and LBA data format for Mp. The topocentric frequency detections at Mopra are shown in Fig. 10. As shown in Fig. 9, the observation was at a lower elevation; therefore, we only obtained 3 Mopra scans. The session was extended for three scans of 20 minutes. The Doppler noise or stochastic noise for the session was in the range of 10 mHz (as in Fig. 10). This section shows the results of an observation campaign that was performed using our planning and scheduling software for the specific case of BepiColombo. These specially designed modules aid in the meticulous scheduling to make sure the spacecraft is in the observable region of the telescopes during the planned observation time. Furthermore, the software makes it simple and feasible to modify the observation plan in (near) real-time when unforeseen changes in spacecraft operations take place. These modules enable easy collaboration between mission operators, ground-based observatories, and VLBI correlators to ensure successful and effective observations. For our science operations in the Jovian system, the VLBI data quality will be of the utmost importance to maximize PRIDE’s impact on the science data products. Our first opportunity for an end-to-end test of our software and methodology, up to and including the processing of the VLBI data for use in improved ephemerides, will be the JUICE Venus flyby in 2025. In Section 4.4, we will present the results of a numerical simulation to quantify how VLBI data quality – and, therefore, proper planning and scheduling – will propagate into science data product quality.
preparation for the JUICE Venus flyby

JUICE will perform a Venus flyby (experiment PRIDE-EXP2; see Table 3 and Section 3.3) that will take place on 2025 Aug 31 (Table 2). Our plan to perform PRIDE observations (when JUICE is transmitting a radio signal before, during or after this flyby) has a number of reasons. Apart from offering a unique opportunity for a full dress rehearsal of PRIDE operations to be conducted later in the Jovian system, PRIDE-EXP2 has a potential scientific value in its own right, by promising an accurate independent validation of the ephemeris solution for Venus (see Section 4.4 for more details). To improve the radio background near the Venus flyby, a preparatory VLBI experiment has been designed and conducted with the EVN (project EP129, PI: K. Perger).
of nearby phase calibrator sources [48] with positions accurately linked to ICRF [44],
during the 5-day period centred on the date of the Venus flyby (Fig. 11). There are
further 9 known VLBI-detected sources at X band in this celestial area found in the
RFC [53]. To use some of the latter as reference objects for JUICE VLBI measure-
ments, their coordinates have to be linked to ICRF by means of relative astrometric
observations (nodding-style phase referencing) to the neighbouring ICRF sources. For
this purpose, we selected 3 RFC sources (J0832+1953, J0839+1921, and J0846+1735;
ferent neighbouring ICRF sources and supplement well the existing ICRF sources in
the area, serving as nodding-style phase-reference sources for PRIDE-EXP2. Another
RFC source, J0817+1958, would be an important potential phase-reference object at
the beginning of the period where the sky chart in Fig. 11 is sparsely populated with
its position. Therefore, the current radio background of JUICE near the Venus flyby
could limit the quality of the VLBI data that could be acquired. Our preparatory
experiment will mitigate this issue.

[Table: Table 4 Known and potential calibrator sources for PRIDE-EXP2 to be conducted at around the JUICE Venus flyby in 2025. The five ICRF sources (top) and four additional RFC sources (middle) have already been detected with VLBI at X band, while the suitability of nine potential in-beam calibrators (bottom) needs to be verified in a dedicated preparatory VLBI experiment. A sky chart with the source positions is shown in Fig. 11.]
Flux Density (mJy)

J0829+1754 08 29 04.828611 +17 54 15.86399 30 ICRF [44] J0832+1832 08 32 16.040283 +18 32 12.13313 50 ICRF [44] J0836+2139 08 36 16.216892 +21 39 03.58055 100 ICRF [44] J0839+1802 08 39 30.721364 +18 02 47.14274 120 ICRF [44] J0842+1835 08 42 05.094174 +18 35 40.99051 200 ICRF [44] J0817+1958∗ 08 17 05.49328 +19 58 42.8985 30 RFC [53] J0832+1953∗ 08 32 00.15804 +19 53 12.1757 40 RFC [53] J0839+1921∗ 08 39 06.94389 +19 21 48.6850 30 RFC [53] J0846+1735∗ 08 46 00.03366 +17 35 25.1140 20 RFC [53] J0822+1930∗ 08 22 44.877 +19 30 43.40 2† VLASS [58] J0828+1908∗ 08 28 39.432 +19 08 40.64 2† VLASS [58] J0835+1844A∗ 08 35 17.235 +18 44 50.96 6† VLASS [58] J0835+1844B∗ 08 35 52.393 +18 44 10.02 2† VLASS [58] J0841+1821∗ 08 41 42.3106 +18 21 56.774 2† mJIVE [59], VLASS [58] J0841+1826∗ 08 41 01.6482 +18 26 02.421 1† mJIVE [59] J0843+1816∗ 08 43 08.5839 +18 16 05.078 1† mJIVE [59] J0843+1814∗ 08 43 08.5839 +18 14 00.373 1† mJIVE [59] J0843+1815∗ 08 43 32.5761 +18 15 31.062 1† mJIVE [59] Notes: ∗– accurate position to be linked to ICRF; † – VLBI detectability to be checked in the EVN experiment EP129
(J2000)

[Figure: Fig. 11 Radio sources from the mJIVE-20 and VLASS catalogues within 4′ of the trajectory of JUICE (indicated by a dashed line) during 5 days around the Venus flyby. Their total flux densities at the L band (1.4 GHz) are coded with colours. Known VLBI calibrator sources from the ICRF and/or RFC within ∼2◦are also shown. Sources marked by filled symbols are potential phase-reference calibrators in in-beam (circles and squares) or nodding styles (triangles). The list of their coordinates is given in Table 4.]
trajectory would allow in-beam phase-referencing observations before and/or after the
Venus flyby with a network of ∼ 32-m or smaller antennas. To search for candidate
objects, we checked the mJy Imaging VLBA Exploration at 20 cm (mJIVE-20) [59]
list containing VLBA-detected sources at 1.4 GHz, and the second-epoch Very Large
Array Sky Survey (VLASS) [58] catalogue at 3 GHz. The latter sources are only
detections with a short-baseline connected-element interferometer, the Karl G. Jansky
Very Large Array (VLA), having yet unknown milliarcsecond-scale structure and VLBI
detectablity. There are a total of 12 radio sources, with flux densities up to about
24 mJy, along the JUICE trajectory in mJIVE-20 and/or VLASS. Out of them, 3
sources were found to have extended lobe-dominated morphology on arcsecond scale
and thus dropped from the sample. The remaining 9 sources (Fig. 11, Table 4) can be
considered as candidate in-beam phase reference calibrators. Their detectability with
VLBI and suitability as calibrators for JUICE have to be checked by means of prior X-
band imaging observations. For the candidate in-beam reference source J0822+1930,
we planned phase-referencing observations to the closest ICRF source (J0829+1754, 2.26◦) as well as the RFC source J0817+1958 mentioned before as potential phasereference source in the period preceding the Venus flyby. This way, upon successful detection of J0822+1930, the position of J0817+1958 could indirectly be linked to ICRF. The 10-h preparatory EVN experiment was conducted on 2024 Feb 23–24. At the time of writing, the data are being prepared for correlation. After correlation, calibration and data analysis, the results will become available for planning PRIDEEXP2. In particular, this experiment will improve the quality, diversity and density of phase-reference sources, thereby allowing more accurate VLBI observations of JUICE to be acquired close to the Venus flyby. The potential scientific implications of this are discussed in the next section.
Improving planetary and satellite ephemerides is a key objective of PRIDE for the JUICE mission. As mentioned in Section 3.1, the Venus flyby performed by the JUICE spacecraft during its cruise phase will represent an excellent opportunity to test the PRIDE technique, the data analysis procedures to provide input data points to ephemerides, and quantify the improvement that PRIDE observables can bring to ephemerides solutions (PRIDE-EXP2, Table 2). We will be able to provide a very accurate normal point (local state solution) for Venus at the flyby epoch, which will help us verify our methodology, and offers an additional validation opportunity for Venus’ ephemeris. In this section, we simulate this Venus flyby experiment and analyse the influence of accuracy levels for PRIDE VLBI measurements on Venus’ state solution. This provides a direct quantification of the impact of scheduling and planning on science return. Since the science return (in terms of ephemeris improvement) from PRIDE will be made primarily from data acquired at the flybys [45], the Venus flybys are of prime interest. To quantify the accuracy of the local state solution achievable for Venus, we used the Tudat3 software [60] to perform a covariance analysis. We simulate PRIDE Doppler data [every 60 s, with a noise level of 35 µm s−1; 10], as well as independent VLBI measurements every 20 minutes. We assumed a tracking arc of 2 h centered at the closest approach. We considered different VLBI noise levels, adopting identical PRIDE VLBI error budgets4 as in [45], to test the impact of various data quality scenarios on the state estimation [see similar analyses in 27, 46]. The detailed descriptions of VLBI simulations for the Jovian system are provided in [45]. Different phase calibrators identified in Table 4 were investigated, their ICRF position uncertainty being included as a systematic error (i.e., bias) to the VLBI observables [45], and added as consider parameters in our analysis (see below). More precisely, we selected the four RFC calibrators identified within 2 degrees of JUICE, and two ICRF ones, picked such that we sample a representative range of ICRF position errors (see Table 5). Potential in-beam calibrators listed in Table 4 were not selected since their suitability as phase referencing sources is yet to be confirmed (see Section 4.3 about the selection
3https://docs.tudat.space/
4Poor VLBI case: 0.6 and 0.9 nrad noise level in right ascension and declination, respectively. Good VLBI case: 0.2 and 0.3 nrad in right ascension and declination. In-beam VLBI case: 0.1 nrad in both right ascension and declination.
cases will provide information on the added value of expanding more effort to improve
observation planning.
From the simulated PRIDE observables, we estimated both JUICE’s and Venus’
states at the flyby epoch. No a priori constraint was applied to the state of the JUICE
spacecraft, while a priori uncertainties for Venus’ state were set to three times the
differences between the INPOP21 [61] and DE440 [62] ephemerides solutions, used as
a conservative estimate of Venus’ ephemeris error. This led to a priori constraints of
10 m (radial), 480 m (tangential) and 630 m (normal), the radial position being very
well constrained by the Magellan and Venus Express data.

[Table: Table 5 Formal uncertainties in Venus’ position at the time of JUICE flyby using different phase calibrators and VLBI noise levels. The VLBI biases are defined by the calibrator’ position uncertainties, reported in the second and third columns. The resulting Venus’ state solutions are provided in last three columns, in RTN (Radial; Tangential; Normal) coordinates.
Phase calibrator σ(α) [mas] σ(δ) [mas] VLBI noise σ(R) [m] σ(T) [m] σ(N) [m]
J0817+1958 0.19 0.23 poor 10 260 250 good 10 260 240 in-beam 10 260 240
J0832+1953 0.59 0.92 poor 10 840 960 good 10 840 960 in-beam 10 840 960
J0839+1921 0.16 0.25 poor 10 230 270 good 10 230 260 in-beam 10 230 260
J0829+1754 0.14 0.19 poor 10 200 210 good 10 200 200 in-beam 10 200 200
J0842+1835 0.11 0.11 poor 10 160 140 good 10 150 120 in-beam 10 150 110
no VLBI 10 480 630]
eters to ensure that their current uncertainties are accounted for in our estimations
[63]. Venus’ gravitational parameter, spherical harmonic gravity field coefficients up to
degree and order 10 rotation rate, and pole orientation were included, and their uncer-
tainties were based on the formal uncertainties derived from Magellan data analysis
[64] and ground-based observations [65]. A factor of 3 was, however, systematically
applied to the published formal errors, as suggested in [64]. Empirical accelerations
acting on the spacecraft, estimated every hour during tracking, with a consider uncer-
for the Venus state change minimally when we use an a priori value that is 10 times
higher. Finally, VLBI biases were added with a consider uncertainty equal to the
calibrator position uncertainty.
[Table: Table 5 displays the formal errors in Venus’ position obtained for various VLBI random noise levels and calibrator position uncertainties. It must be noted that, as expected, Doppler measurements do not noticeably contribute to Venus’ state solution, which remains constrained to their a priori values when no VLBI is included. Adding VLBI, however, significantly reduces the a priori uncertainties in the tangential and normal directions. Only Venus’ radial position cannot be improved beyond its a priori uncertainties (irrespective of the error budget). It is interesting to note that the influence of the PRIDE VLBI random noise level is rather limited. The choice of phase calibrator, on the other hand, is critical: the accuracy with which its ICRF position is known, by directly affecting the systematic error in the VLBI measurement of JUICE’s angular position, drives the quality of the resulting state solution for Venus. These results provide a very strong motivation for the thorough analysis of available calibrators, including the possibility to use multiple calibrators or performing a dedicated campaign to extend/enhance the available calibrator sources. In particular, reducing the systematic bias in VLBI measurement induced by the error in the calibrator’s position is essential. The tools developed for PRIDE and presented here allow analyses of the feasibility and scientific return of such activities to be performed with minimal effort.]
Over 35 single antenna experiments of JUICE have been conducted from the University of Tasmania since its launch in April 2023. Observations were scheduled similarly to the PRIDE VLBI, however track the spacecraft continuously. The data for each observation was subsequently processed using the Spacecraft Doppler Tracker software (SDtracker)8, along with a series of Python tools (pysctrack)9. This enables sub-Hz precision detections of the topocentric frequency detections, along with reconstructed and residual phases of the carrier signal [15]. In particular, these observations have applications in the analysis of space weather [1].
The JUICE spacecraft carrier tone along with the residual phases is shown in Figure 4, as well as the topocentric frequency detections versus time in Figure 5.
4 https://ssd.jpl.nasa.gov/horizons/app.html 5 http://astrogeo.org/calib/search.html 6 https://s2e2.cosmos.esa.int/bitbucket/projects/SPICE_KERNELS/repos/juice/browse/kernels/spk 7 https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/ 8 https://gitlab.com/gofrito/sctracker 9 https://gitlab.com/gofrito/pysctrack Stations Distance (AU)

[Figure: Figure 4: Left: JUICE spacecraft integrated carrier tone and subtones from the Ceduna 30m radio telescope on 12/10/2023. Right: Residual phases from a 20-minute scan of JUICE from the Hobart 12m antenna on 21/05/2023. At the time of the observation, the spacecraft was at a distance of 0.06 AU and a Sun-Observer-Target elongation angle of 132 degrees.]

[Figure: Figure 5: Revised frequency detections of the JUICE Doppler tracking from the Ceduna 30m antenna on the 19/08/2024, during the Lunar flyby. Transmission switched from two-way to one-way mode just prior to lunar occultation, which resulted in the frequency jump before it was lost soon after 20:30 UTC.]

[Table: Table 1: Summary of PRIDE Doppler observations of JUICE from the University of Tasmania. Observations were conducted in X-band in three-way mode. Distance and SOT
values obtained from Horizons.]
PRIDE, as one of eleven JUICE experiments, aims to enhance the mission’s science return by applying VLBI and Doppler tracking techniques. In 2031, JUICE spacecraft will arrive in the Jovian system and conduct extensive observations of Ganymede and flyby observations of Europa and Callisto. The two primary goals of PRIDE are to improve the ephemerides for the Jovian system and study the Jovian atmosphere and the ionosphere of the Galilean moons using radio occultation observations. In this work, we have reviewed the PRIDE operations and engineering interactions with the JUICE spacecraft. Furthermore, a step-by-step procedure was presented for planning and scheduling PRIDE observation campaigns in a manner that automates many of the steps in the process. By selecting the celestial regions of interest for JUICE’s near-field VLBI (PRIDE) during various mission stages, notably during the cruise period, we showcase the significance of scheduling and its impact on the experiment’s science return. For JUICE, a finding chart for extragalactic radio sources from the Radio Fundamental Catalogue was created. The ESA’s BepiColombo spacecraft was observed as a training target for prospective optional Ka-band PRIDE operations. The initial results on PRIDE Ka-band Doppler shift detections are demonstrated. This example demonstrates the flexibility of the scheduling approach and PRIDE’s readiness for operations on any planetary mission, which proved to enhance the process and boost the scientific return. Additionally, we have presented a numerical simulation of the PRIDE contribution to potential science return from Venus flyby, in which we took into account different tracking durations and noise levels for VLBI observations. This allowed us to test various acquisition and error budget scenarios while also, and perhaps more importantly, quantifying their impact on the final ephemeris solution. The simulations also demonstrated that by lowering PRIDE VLBI noise (for instance, using Ka-band or in-beam tracking), one would further improve the state solution for the flyby body.

Additionally, choosing a phase calibrator is crucial; its ICRF position accuracy directly influences the error in measuring JUICE’s position through VLBI, thus impacting the accuracy of determining the Venus state solution. These results strongly recommend an examination of calibrators, which may involve using multiple ones or organizing specific campaigns to expand/improve the calibrator options. It is essential to reduce biases in VLBI measurements caused by errors in calibrator positions. This indicates the need for effective planning and scheduling of PRIDE–JUICE observations during the Galilean moon flyby tour to ensure maximum VLBI data quality and, as a result, provide the best possible scientific contribution of the PRIDE experiment in improving our understanding of icy satellite origins, interior and evolution.
The EVN is a joint facility of independent European, African, Asian, and North American radio astronomy institutes. The involvement of the University of Tasmania in the observations presented here was enabled by Geoscience Australia and the Australian Government via the National Collaborative Research Infrastructure Strategy (NCRIS). J.F., S.F., and K.P. acknowledge the ESA PRODEX support (project PEA 4000136207). We express our gratitude to Olivier Witasse, Claire Vallat, Nicolas Altobelli, and the ESA team (MOC and SOC) for the cooperation provided for supporting PRIDE observations of JUICE and BepiColombo missions. We acknowledge Chris Phillips (CASS) for supporting and conducting the observations at Mopra. We appreciate the anonymous referees for their valuable comments and corrections.