Deep Space Network Stations Research Articles

Nitrogen Abundance Distribution in the Inner Milky Way

We combine a new Galactic plane survey of hydrogen radio recombination lines (RRLs) with far-infrared surveys of ionized nitrogen, N+, to determine nitrogen abundance across Galactic radius. RRLs were observed with the NASA Deep Space Network Station 43 70 m antenna and the Green Bank Telescope in 108 lines of sight spanning −135°< l < 60°, at b = 0°. These positions were also observed in [N ii] 122 μm and 205 μm lines with the Herschel Space Observatory. Combining RRL and [N ii] 122 μm and 205 μm observations in 41 of 108 samples with high signal-to-noise ratio, we studied the ionized nitrogen abundance distribution across Galactocentric distances of 0–8 kpc. Combined with existing solar neighborhood and outer Galaxy N/H abundance determinations, we studied this quantity’s distribution within the Milky Way’s inner 17 kpc for the first time. We found a nitrogen abundance gradient extending from Galactocentric radii of 4–17 kpc in the Galactic plane, while within 0–4 kpc the N/H distribution remained flat. The gradient observed at large Galactocentric distances supports inside-out galaxy growth, with the additional steepening resulting from variable star formation efficiency and/or radial flows in the Galactic disk, while the inner 4 kpc flattening, coinciding with the Galactic bar’s onset, may be linked to radial flows induced by the bar potential. Using SOFIA/FIFI-LS and Herschel/PACS, we observed the [N iii] 57 μm line to trace doubly ionized gas contribution in a subsample of sight lines. We found negligible N++ contributions along these sight lines, suggesting mostly singly ionized nitrogen originating from low-ionization H ii region outskirts.

The radioscience LaRa instrument onboard ExoMars 2020 to investigate the rotation and interior of mars

LaRa (Lander Radioscience) is an experiment on the ExoMars 2020 mission that uses the Doppler shift on the radio link due to the motion of the ExoMars platform tied to the surface of Mars with respect to the Earth ground stations (e.g. the deep space network stations of NASA), in order to precisely measure the relative velocity of the lander on Mars with respect to the Earth. The LaRa measurements shall improve the understanding of the structure and processes in the deep interior of Mars by obtaining the rotation and orientation of Mars with a better precision compared to the previous missions. In this paper, we provide the analysis done until now for the best realization of these objectives. We explain the geophysical observation that will be reached with LaRa (Length-of-day variations, precession, nutation, and possibly polar motion). We develop the experiment set up, which includes the ground stations on Earth (so-called ground segment). We describe the instrument, i.e. the transponder and its three antennas. We further detail the link budget and the expected noise level that will be reached. Finally, we detail the expected results, which encompasses the explanation of how we shall determine Mars' orientation parameters, and the way we shall deduce Mars' interior structure and Mars’ atmosphere from them. Lastly, we explain briefly how we will be able to determine the Surface platform position.

A comparison of atmospheric effects on differential phase for a two‐element antenna array and nearby site test interferometer

AbstractPhased arrays of reflector antennas can be used to obtain effective area and gain that are much larger than is practical with a single antenna. This technique is routinely used by NASA for receiving weak signals from deep space. Phase alignment of the signals can be disrupted by turbulence in the troposphere, which causes fluctuations in the differences of signal delays among the antennas. At the Deep Space Network stations, site test interferometers (STIs) are being used for long‐term monitoring of these delay fluctuations using signals from geostationary satellites. In this paper, we compare the STI measurements with the phase variations seen by a nearby two‐element array of 34 m diameter antennas tracking 8.4 GHz and 32 GHz signals from the Cassini spacecraft in orbit around Saturn. It is shown that the statistics of the STI delay fluctuations, after appropriate scaling for differences in antenna separation and elevation angle and conversion to phase at the spacecraft frequencies, provide reliable estimates of the phase fluctuations seen by the large antennas on the deep space signal. Techniques for adaptive compensation of the phase fluctuations are available when receiving a sufficiently strong signal, but compensation is often impractical or impossible when using the array for transmitting. These results help to validate the use of long‐term STI data for assessing the feasibility of large transmitting arrays at various sites.

The 2014 Earth return of the ISEE-3/ICE spacecraft

In 1978, the 3rd International Sun–Earth Explorer (ISEE-3) became the first libration-point mission, about the Sun–Earth L1 point. Four years later, a complex series of lunar swingbys and small propulsive maneuvers ejected ISEE-3 from the Earth–Moon system, to fly by a comet (Giacobini–Zinner) for the first time in 1985, as the rechristened International Cometary Explorer (ICE). In its heliocentric orbit, ISEE-3/ICE slowly drifted around the Sun to return to the Earth׳s vicinity in 2014. Maneuvers in 1986 targeted a 2014 August 10th lunar swingby to recapture ISEE-3 into Earth orbit. In 1999, ISEE-3/ICE passed behind the Sun; after that, tracking of the spacecraft ceased and its control center at Goddard was shut down. In 2013, meetings were held to assess the viability of “re-awakening” ISEE-3. The goal was to target the 2014 lunar swingby, to recapture the spacecraft back into a halo-like Sun–Earth L1 orbit. However, special hardware for communicating with the spacecraft via NASA׳s Deep Space Network stations was discarded after 1999, and NASA had no funds to reconstruct the lost equipment.After ISEE-3׳s carrier signal was detected on March 1st with the 20m antenna at Bochum, Germany, Skycorp, Inc. decided to initiate the ISEE-3 Reboot Project, to use software-defined radio with a less costly S-band transmitter that was purchased with a successful RocketHub crowdsourcing effort. NASA granted Skycorp permission to command the spacecraft. Commanding was successfully accomplished using the 300m radio telescope at Arecibo. New capture trajectories were computed, including trajectories that would target the August lunar swingby and use a second ΔV (velocity change) that could target later lunar swingbys that would allow capture into almost any desired final orbit, including orbits about either the Sun–Earth L1 or L2 points, a lunar distant retrograde orbit, or targeting a flyby of the Earth-approaching active Comet Wirtanen in 2018.A tiny spinup maneuver was performed on July 2nd, the first since 1987. A 7m/s ΔV maneuver was attempted on July 8th, to target the August lunar swingby. But the maneuver failed; telemetry showed that only about 0.15m/s of ΔV was accomplished, then the thrust quickly decayed. The telemetry indicated that the nitrogen pressurant was gone so hydrazine could not be forced to the thrusters.The experience showed how a spacecraft can survive 30 years of space weather. The spacecraft flew 18 thousand km from the Moon, resulting in a heliocentric orbit that will return near the Earth in 2029.

Regionalized Lunar South Pole Surface Navigation System Analysis

Apollo missions utilized Earth‐based assets for navigation, since the landings took place at lunar locations in constant view from the Earth. The new exploration campaign to the lunar South Pole region will have limited Earth visibility, but the extent to which a navigation system comprised solely of Earth‐based tracking stations will provide adequate navigation solutions in this region is unknown. This article presents a dilution‐of‐precision‐(DoP‐) based stationary surface navigation analysis of the performance of multiple lunar satellite constellations, Earth‐based deep space network assets, and combinations thereof. Results show that kinematic and integrated solutions cannot be provided by the Earth‐based deep space network stations. Also, the surface stationary navigation system needs to be operated as a two‐way navigation system, or as a one‐way navigation system with local terrain information, while integrating the position solution over a short duration of time with navigation signals being provided by a lunar satellite constellation.

Goal‐driven automation of a deep space communications station: a case study in knowledge engineering for plan generation and execution

Abstract: This paper describes the application of Artificial Intelligence techniques for plan generation, plan execution, and plan monitoring to automate a Deep Space Communication Station. This automation allows a communication station to respond to a set of tracking goals by appropriately reconfiguring the communications hardware and software to provide the requested communications services. In particular this paper describes: (1) the overall automation architecture, (2) the plan generation and execution monitoring AI technologies used and implemented software components, and (3) the knowledge engineering process and effort required for automation. This automation was demonstrated in February 1995, at the DSS13 Antenna Station in Goldstone, CA on a series of Voyager tracks and the technologies demonstrated are being transferred to the operational Deep Space Network stations.

Precise orbit determination of high-earth elliptical orbiters using differenced Doppler and ranging measurements

Recent advances in NASA's Deep Space Network station calibration methods have led to renewed interest in the use of differenced radio metric data types for interplanetary navigation, particularly differenced Doppler and range. An orbit determination error analysis is described which compares the performance of these differenced data types when used in concert with conventional two-way Doppler for precise navigation for high-earth orbiters. Three highly elliptical orbits were investigated, with apogee heights on the order of 20000, 70000, and 156000 km. The analysis assumes that each orbiter's downlink antennas has no ground footprint limitation in the near apogee regime. Results indicate that the most significant navigational accuracy improvements are seen for the lowest altitude orbit by using differenced Doppler measurements in conjunction with two-way Doppler. The results for the two higher-altitude orbits, although less dramatic, suggest accuracy improvements can also be achieved when differenced range measurements are combined with two-way Doppler.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spacecraft Doppler tracking with a VLBI antenna

Accurate measurements of the Doppler shift of the Voyager 2 spacecraft (26 A. U.) have been performed in the period 23/7/88-12/8/88 with the 32m VLBI antenna at Medicina (BO). The device which allows the use of VLBI instrumentation for precision Doppler tracking is basically an open-loop receiver and is called digital tone extractor (DTE). Simultaneous measurements were performed at NASA's Deep Space Network (DSN) stations of the Madrid complex, using a different technique (closed loop). In the most interesting tracking configuration, the signal was transmitted inS-band (2.1 GHz) from the 70 m DSN station at Canberra (Australia), retransmitted back coherently from the spacecraft inX-band (8.4 GHz–19 W) and received 7h 6min later at Medicina and Madrid. The main purpose of the experiment was to test the capabilities of this new system and to characterize its performances. This taks has been successfully accomplished with the acquisition of high-quality data, which are presently under analysis. We plan also to compare and correlate the data with the ones acquired at Madrid stations, in order to separate out different noise contributions to the measured signal. The use of Medicina antenna as a listen-only station is planned for the gravitational wave experiment of the Ulysses spacecraft (ESA), in 1992.

An Extragalactic Reference Frame From DSN VLBI Measurements–1989

Assessment of the impact of recent improvements in Deep Space Network (DSN) instrumentation, as well as of joint data analyses, provide a prognosis for the accuracy level to be expected in future realizations of an inertial radio reference frame. Intercontinental dual-frequency radio interferometric measurements during 68 sessions (including two recent sessions employing Mark III instrumentation) from 1978 to 1989 using NASA's DSN stations in California, Spain, and Australia give 8900 pairs of delay and delay rate observations. Analysis yields a catalog of positions of 200 extragalactic radio sources north of —45° declination. The resulting source position formal uncertainty distributions peak below 1 milliarcsecond, with three fourths being smaller than 2 mas. Comparison with independent measurements shows some evidence for systematic errors at the milliarcsecond level.

Astrometric results of 1978-1985 Deep Space Network radio interferometry - The JPL 1987-1 extragalactic source catalog

An astrometric radio reference frame has been determined from intercontinental dual-frequency radio interferometric measurements. These measurements were carried out on a regular basis during 1978-1985 between NASA's Deep Space Network stations in California, Spain, and Australia. Analysis of 6800 pairs of delay and delay-rate observations made during 51 sessions produced estimates of 1300 parameters. The most significant of these are geophysical quantities and positions of extragalactic sources. The source catalog resulting from this analysis includes 106 sources fairly uniformly distributed over the celestial sphere, north of -45 deg declination. Almost all of the resulting source positions have formal uncertainties between 0.5 and 3 milliarcseconds (mas), with rms values of 2 mas in both angular coordinates. Internal consistency checks, as well as comparisons with independently determined source catalogs of comparable quality, indicate that relative source coordinates determined by VLBI contain systematic errors at the level of 1 to 2 mas.

The JPL 1986–3 Extragalactic Reference Frame

Intercontinental dual-frequency radio interferometric measurements were carried out during 1978 to 1985 between NASA's Deep Space Network stations in California, Spain, and Australia. Analysis of 6800 pairs of delay and delay rate observations made during 51 sessions produced a catalog of positions of 106 extragalactic radio sources, fairly uniformly distributed over the celestial sphere between −45° and +85° declination. Almost all of the resulting source positions have formal uncertainties between 0.5 and 3 milliarcseconds, with their distributions peaking somewhat below 1 mas. Root-mean-square uncertainties are 2.1 and 2.0 mas for RA and declination, respectively. Evidence is found for a long-term drift of the Earth's rotation axis in inertial space, relative to the 1984 IAU precession and nutation models. Tests for time variability of positions of 32 frequently observed sources place limits at the 1 mas/yr level. Comparisons with independently determined source catalogs of comparable quality show differences of positions of common sources that amount to a few mas, and may indicate the level of systematic errors in VLBI source position measurements.

Radio Reference Frame Stability from VLBI Data

Intercontinental radio interferometric measurements between NASA's Deep Space Network stations yield a catalog of positions of 106 extragalactic radio sources, uniformly distributed between −45° and +85° declination. Almost all of the source positions have formal uncertainties between 0.5 and 3 milliarcseconds. Estimates of three independent sets of 32 source coordinates at average epochs 1980.0, 1983.2, and 1984.5 assess the level of stability of the reference frame over a five-year period. Comparisons of the three sets of source coordinates show a number of cases of &gt; 2σ differences, particularly betwen the 1984–85 and 1981–83 periods. No sources, however, show 2σ shifts among both pairs of epochs. Upper limits of the order of 1 mas/yr can be placed on the time rates of change of the 32 source coordinates.

Measurement technique for the Giotto radio science experiment

The paper describes the technique used to record time delay and waveform measurements for the Giotto radio science experiment of ESA's mission to comet Halley. The data were taken by using either two-way measurements (during pre- and post-encounter) or one-way measurements (during encounter with comet Halley), the downlink of the radio signal of the Giotto spacecraft being received at 8.4 GHz by the 64 m tracking stations of NASA's Deep Space Network (DSN). The waveform measurements were obtained at a sampling frequency of 50 kHz with an open-loop receiver assembly at DSN station Canberra as recently used for the Voyager/Uranus fly-by. Performance and calibration data are given as relevant to the radio subsystems on the ground and aboard Giotto.

Application of the Deep Space Network (DSN) to the testing of General Relativity

Over the past two decades, radar and radio observations of planets and spacecraft have been made by stations of the Deep Space Network (DSN), which by the unprecedented nature of their accuracy have produced the most accurate tests of general relativity available. We review the history of the instrumentation and data analysis of the first spacecraft test, the three percent determination of the effect of solar gravity on radio signals between DSN stations and the two spacecraft, Mariner 6 and Mariner 7 (Anderson et al., 1975), as well as later more accurate tests using the Mariner 9 spacecraft anchored to Mars (Reasenberg and Shapiro, 1977; Anderson et al., 1978) and the Viking orbiters and landers (Shapiro et al., 1977; Hellings, 1985). We also review tests of the metric nature of gravity using radar, optical observations, and radio astrometry of the planets (Anderson et al., 1978; Reasenberg, 1985; Hellings, 1985) and the limits placed on the variability of the gravitational constant G (Hellings et al., 1983). Finally, we discuss the prospects for improved accuracy through ongoing upgrades of DSN instrumentation and show the results of covariance analyses for a possible future NASA mission to the Sun (Solar Probe) in the mid 1990's (Mease et al., 1984) and the next NASA mission to Mars, the Mars Observer mission planned for launch in late 1990.

Spectral-line sky surveys from the NASA-JPL SETI project

The Jet Propulsion Laboratory (California Institute of Technology) has recently begun preparations for a modest SETI (Search for Extra-Terrestrial Intelligence) project at radio wavelengths. The proposed project is two-fold: (1) to search the entire sky visible from Goldstone, California (site of one of the NASA Deep Space Network Stations), i.e. that north of δ ∼ −30°, at all frequencies between 1 and 24 GHz using a horn receiver and (2) to carry out a more sensitive sky search at a few selected frequency bands, using dedicated 26 and 10m antennas. The search will be for signals of the type unlikely to be produced by natural causes, e.g. narrow spikes in frequency space. The basic rationale behind this search is discussed by Murray, Gulkis and Edelson (1978).