Observations at X/Ka-band are motivated by their ability to access more compact source morphology and reduced core shift relative to observations at the historically standard S/X-band. In addition, the factor of four increase in interferometer resolution at Ka-band should resolve out some extended source structure. Given these motivations, an X/Ka-band (8.4/32 GHz) celestial reference frame has been constructed using a combined NASA and ESA Deep Space Network. In 176 observing sessions we detected 678 sources covering the full 24 hours of right ascension, α , and the full range of declinations, δ . The resulting XKa median precision is now 67 μas in αcosδ and 95 μas in δ . Comparison of 529 X/Ka sources in common with the S/X-band (2.3/8.4 GHz) ICRF3 produced wRMS agreement of better than 165 μas. There is evidence for systematic errors at the 100 μas level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and terrestrial frame distortions. Actions are underway to reduce all of these errors. In particular, a collaboration between NASA and the ESA deep space antenna in Malargüe, Argentina is reducing weaknesses in the southern hemisphere. By comparing coordinate estimates, we probe the accuracy limits of current celestial frames in an effort to understand the advantages of each frame.

Observations at X/Ka-band are motivated by their ability to access more compact source mor- phology and reduced core shift relative to observations at the historically standard S/X-band. In addition, the factor of four increase in interferometer resolution at Ka-band should resolve out some extended source structure. Given these motivations, an X/Ka-band (8.4/32 GHz) celestial reference frame has been constructed using a combined NASA and ESA Deep Space Network. In 176 observing sessions we detected 678 sources covering the full 24 hours of right ascension, α, and the full range of declinations, δ. The resulting XKa median precision is now 67 μas in αcosδ and 95 μas in δ. Comparison of 529 X/Ka sources in common with the S/X-band (2.3/8.4 GHz) ICRF3 produced wRMS agreement of better than 165 μas. There is evidence for systematic errors at the 100 μas level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and terrestrial frame distortions. Actions are underway to reduce all of these errors. In particu- lar, a collaboration between NASA and the ESA deep space antenna in Malargue, Argentina is reducing weaknesses in the southern hemisphere. By comparing coordinate estimates, we probe the accuracy limits of current celestial frames in an effort to understand the advantages of each frame.

An X/Ka-band (8.4/32 GHz) celestial reference frame has bee n constructed using single baselines from the combined NASA and ESA Deep Space Networks for approx imately 100 sessions each of ∼24-hour duration. The frame solution has dramatically impr oved with respect to the last reported frame due to the inclusion of Southern NASA-ESA bas elines, routine 2-Gbps data rates, and correction of instrumental delays by recently deployed Ka-band phase calibration tones. Comparisons with the S/X-band (2.3/8.4 GHz) ICRF-2 referen ce frame will be presented showing increasing agreement for 525 common sources. About 135 sour ces a e located in the south polar cap (δ < −45) which became accessible for first time with the addition of t he ESA station in Malargüe, Argentina to our project’s network. There is evid nce for systematic errors at the 100 μas level. The known sources of error will be discussed. Frame tie precision with Gaia has been estimated in about ±7 μas (1-σ , per 3-D rotation component) using measured X/Ka position uncertainties and sim ulated Gaia uncertainties. Compared to X-band, Ka-band allows access to more compact radio sourc e morphology and reduced core shift which should reduce these systematic errors compared to a tie of Gaia to S/X-band VLBI. However, there is a great deal of uncertainty in the offset be twe n optical and radio centroids from effects such as optical host galaxy asymmetry which may ulti mately limit the frame tie accuracy.

A celestial reference frame at X/Ka-band (8.4/32GHz) has been constructed using fifty-one 24-h sessions with the Deep Space Network. We report on observations which have detected 436 sources covering the full 24 h of right ascension and declinations down to −45°. Comparison of this X/Ka-band frame to the S/X-band (2.3/8.4 GHz) ICRF2 shows wRMS agreement of 200 micro-arcsec (μas) in \( \alpha cos\delta \) and 290 μas in δ. There is evidence for zonal errors at the 100 μas level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and limited southern geometry. The motivations for extending the ICRF to frequencies above 8 GHz are to access more compact source morphology for improved frame stability, to provide calibrators for phase referencing, and to support spacecraft navigation at Ka-band.

We have constructed an X/Ka-band (8.4/32 GHz) celestial reference frame using fty-nine 24hour sessions with the Deep Space Network. We detected 469 sources covering the full 24 hours of right ascension and declinations down to 45 . Comparison of 450 X/Ka sources in common with the S/X-band (2.3/8.4 GHz) ICRF2 shows weighted RMS (wRMS) agreement of 194 micro-arcsec ( as) in cos and 270 as in . There is evidence for systematic errors at the 100 as level. Known errors include limited SNR, lack of phase calibration, troposphere mismodeling, and limited southern geometry. Compared to X-band, Ka-band allows access to more compact source morphology and reduced core shift. Existing X/Ka data and simulated Gaia data predict a frame tie precision of 10-15 as (1- , per 3-D rotation component) with anticipated improvements reducing that to 5-10 as per component.

This paper is an update of Sotuela et al. (2011) which improves their simulated Gaia frame tie precision by ∼10% by adding three additional VLBI observing sessions. Astrometry at X/Kaband (8.4/32 GHz) using NASAs Deep Space Network has detected 466 quasars with accuracies of 200–300 μas. A program is underway to reduce errors by a factor of 2–3. From our sample, 345 sources have optical magnitudes V < 20 and should also be detectable by Gaia. A covariance study using existing X/Ka data and simulated Gaia uncertainties for the 345 objects yields a frame tie precision of 10–15 μas (1-σ). The characterization of wavelength dependent systematics from extended source morphology and core shift should benefit greatly from adding X/Ka-band measurements to S/X-band (2.3/8.4 GHz) measurements thus helping to constrain astrophysical models of the wavelength dependence of positions.

This paper is an update of Sotuela et al. (2011) which improves their simulated Gaia frame tie precision by approximately 10% by adding three additional VLBI observing sessions. Astrometry at X/Ka-band (8.4/32 GHz) using NASAs Deep Space Network has detected 466 quasars with accuracies of 200-300 micro-arc seconds. A program is underway to reduce errors by a factor of 2-3. From our sample, 245 sources have optical magnitudes V less than 20 and should also be detectable by Gaia. A covariance study using existing X/Ka data and simulated Gaia uncertainties for the 345 objects yields a frame tie precision of 10-15 micro-arc seconds (1 - sigma). The characterization of wavelength dependent systematic from extended source morphology and core shift should benefit greatly from adding X/Ka-band measurements to S/X-band (2.3/8.4 GHz) measurements thus helping to constrain astrophysical models of the wavelength dependence of positions.

In order to extend the International Celestial Reference Frame from its S/X-band (2.3/8.4 GHz) basis to a complementary frame at X/Ka-band (8.4/32 GHz), we began in mid-2005 an ongoing series of X/Ka observations using NASA s Deep Space Network (DSN) radio telescopes. Over the course of 47 sessions, we have detected 351 extra-galactic radio sources covering the full 24 hours of right ascension and declinations down to -45 degrees. Angular source position accuracy is at the part-per-billion level. We developed an error budget which shows that the main errors arise from limited sensitivity, mismodeling of the troposphere, uncalibrated instrumental effects, and the lack of a southern baseline. Recent work has improved sensitivity by improving pointing calibrations and by increasing the data rate four-fold. Troposphere calibration has been demonstrated at the mm-level. Construction of instrumental phase calibrators and new digital baseband filtering electronics began in recent months. We will discuss the expected effect of these improvements on the X/Ka frame.

The NASA Deep Space Network (DSN) requires a broadband VLBI (very long baseline interferometry) correlator to process data routinely taken as part of the VLBI source Catalogue Maintenance and Enhancement task (CAT M&E) and the Time and Earth Motion Precision Observations task (TEMPO). The data provided by these measurements are a crucial ingredient in the formation of precision deep-space navigation models. In addition, a VLBI correlator is needed to provide support for other VLBI related activities for both internal and external customers. The JPL VLBI Correlator (JVC) was designed, developed, and delivered to the DSN as a successor to the legacy Block II Correlator. The JVC is a full-capability VLBI correlator that uses software processes running on multiple computers to cross-correlate two-antenna broadband noise data. Components of this new system (see Figure 1) consist of Linux PCs integrated into a Beowulf Cluster, an existing Mark5 data storage system, a RAID array, an existing software correlator package (SoftC) originally developed for Delta DOR Navigation processing, and various custom- developed software processes and scripts. Parallel processing on the JVC is achieved by assigning slave nodes of the Beowulf cluster to process separate scans in parallel until all scans have been processed. Due to the single stream sequential playback of the Mark5 data, some ramp-up time is required before all nodes can have access to required scan data. Core functions of each processing step are accomplished using optimized C programs. The coordination and execution of these programs across the cluster is accomplished using Pearl scripts, PostgreSQL commands, and a handful of miscellaneous system utilities. Mark5 data modules are loaded on Mark5 Data systems playback units, one per station. Data processing is started when the operator scans the Mark5 systems and runs a script that reads various configuration files and then creates an experiment-dependent status database used to delegate parallel tasks between nodes and storage areas (see Figure 2). This script forks into three processes: extract, translate, and correlate. Each of these processes iterates on available scan data and updates the status database as the work for each scan is completed. The extract process coordinates and monitors the transfer of data from each of the Mark5s to the Beowulf RAID storage systems. The translate process monitors and executes the data conversion processes on available scan files, and writes the translated files to the slave nodes. The correlate process monitors the execution of SoftC correlation processes on the slave nodes for scans that have completed translation. A comparison of the JVC and the legacy Block II correlator outputs reveals they are well within a formal error, and that the data are comparable with respect to their use in flight navigation. The processing speed of the JVC is improved over the Block II correlator by a factor of 4, largely due to the elimination of the reel-to-reel tape drives used in the Block II correlator.

Deep space tracking and navigation are done in a quasi-inertial reference frame based upon the angular positions of distant active galactic nuclei (AGN). These objects, which are found at extreme distances characterized by median redshifts of z = 1, are ideal for reference frame definition because they exhibit no measurable parallax or proper motion. They are thought to be powered by super massive black holes whose gravitational energy drives galactic sized relativistic jets. These jets produce synchrotron emissions which are detectable by modern radio techniques such as Very Long baseline Interferometry (VLBI).