Orbiting VLBI Tracking Station

Current Schedule

Tracking Station Mission

The Orbiting VLBI tracking station in Green Bank, West Virginia is one of four NASA tracking stations dedicated to support of Very Long Baseline Interferometry satellites. Current and future satellites extend interferometry baselines beyond the diameter of the earth. The trackings stations transmit a maser referenced timing tone to the orbiting satellites. The satellites sample the astronomical signals and transmit the data on a Ku band downlink back to the stations. The tracking stations record the data on wideband magnetic tape and ship it to correlators for further processing. The Observatory and tracking station are located in a valley at elevation 2750' , and are shielded from radio interference by mountains to the east and west. For additional views of the tracking station, click here, or here.

Space VLBI satellites


The Japanese Space agency, ISAS , launched VSOP/HALCA on 97 February 12. VSOP/HALCA has a home page. The VSOP/HALCA mission operations group maintains an interface document page.


The Russian Space agency is building a Radio telescope, RadioAstron , as a part of the spectrum series. RadioAstron is scheduled to be launched after the gamma ray satellite, Spectrum X-Gamma.

Recent RadioAstron compatibility tests on 99 May 23-28 are described in some detail.


  Researchers at JPL and their colaborators are planning a next generation space radio telescope, ARISE, Advanced Radio Interferometry between Space and Earth.

OVLBI Online Documentation

Memo Series

The OVLBI Memo Series contains detailed description of tracking station design considerations. Some memos describe the mathmatical considerations leading to development of station hardware and software. Hardware design documents describe constraints and design specifications. Other hardware memos describe testing of modules during development. The software documents describe the design and testing of the software.

A description of the format of data provided to the VSOG for calibrating data and locating it on the VLBA tapes is available .

The International Mission Operations Group agreements are documented in a memo series kept at JPL.

Software Guide

The software guide describes the offline and realtime programs which control the tracking station. The guide describes the station inputs and outputs and the methode for transfering files to other mission elements.

Hardware Guide

The hardware guide describes the major OVLBI hardware modules and sub-assemblies.

Status Summary

The Green Bank tracking station updates an ASCII status summary of the tracking station activites every 5 minutes. The summary lists the current direction the antenna is pointing, the current activity, wideband data recording status, two way link status and any anomalous hardware states.

MIT NRC Autocorrellation Spectra

The Green Bank tracking station uses the MIT Near Real Time Correllator to regularly generate autocorrellation spectra from the HALCA downlink data. The spectra are updated every 10 minutes.

VLBI Downlink stability

For the VLBI observations using the Green Bank Earth Station, the experiment and the link stability is shown on a pass by pass basis. Plots of the difference between predicted and measured down link frequency show the quality of the orbit prediction. The plots of the RMS during two second fits to the down link phase residuals measure the stability of the link.

Tracking History

A history of tracking passes performed at Green Bank is given.

The Earth Station Milestones:

97 June: HALCA Image

The first high resolution image from HALCA is shown below right. The image on the left is the ground-only image of the radio source. Notice the much improved angular resolution image made using HALCA data.

The two images above are of an extreamly high energy jet of particles ejected from the center of the distant blazar 1156+295. The bright white component in the center of the image is due to material falling onto a giant black hole at the center of the object. Magnetic fields surrounding the black hole accellerate the particles into a narrow jet.

97 May 22: HALCA First Fringes with NRAO VLBA

The alignment in time of astronomical signal from HALCA throught the Green Bank Earth Station and the NRAO VLBA antennas. The radio source 1519-273 was observed at L-Band.

97 May 20: HALCA First Fringes with NRAO 140ft

The first alignment in time of astronomical signal from HALCA throught the Green Bank Earth Station and the NRAO 140ft telescope in Green Bank, WV. The radio source 1519-273 was observed at L-Band

97 April 1+2: VSOP/HALCA First Observations simultaneously with VLBA

The first tracking station data recordings made simultaneously with the VLBA were made at L-Band (1.6 GHz). The strong radio source 1334-127 was observed.

97 March 21: First successful VSOP/HALCA Tracking

The tracking station locked to the Ku band down link from VSOP/HALCA. The decoded VSOP/HALCA telemetry data indicated that VSOP/HALCA was successfully locked to the tracking station uplink tone.

96 October: Doppler Data Exchange

Measurement of the range rate to the Surfsat transponder. A number of software problems were solved and orbit predictions for Surfsat based only on Green Bank data were created at JPL.

97 September 12: Surfsat C Band VLBI

The Surfsat VLBI experiment was repeated successfully (see below), but at a higher frequency. At higher frequencies the stability of the space to ground link is more throughly tested.

96 May: Surfsat S Band VLBI

In collaboration with the NRAO VLBA and Engineers at JPL, the first Surfsat VLBI experiment was performed in 96 May. In this test, the NRAO GB 140' Telescope was used in its normal VLBI mode, but with the maser timing reference signal being transmitted the Surfsat Transponder. The timing tone was successfully recieved at the Tracking station, modulated onto optical fiber and provide to the 140' telescope as the timing reference. Simulatenously, the time corrections data were collected at the tracking station and provided to the VLBA correlator. The VLBA correlator used the timing data to allow successful correlation of the observations with VLBA antennas.

96 March: VSOP Compatability Tests

The Japanese Satellite Sampler,Formatter and Communications model was brought to Green Bank for Compatability Tests. After minor adjustments, the data communications between the tracking station and satellite simulator were found to be compatable.

95 November 5: Tracking Surfsat

The NASA/JPL orbiting test transponder, Surfsat, was first tracked by the Green Bank Earth Station. A two-way link to Surfsat was first established on 95 Dec 15.

95: Tracking Geotail

The Japanese space agency satellite GEOTAIL has been tracked by the Green Bank Tracking Station. This test validated the orbital predition interface to NASA/JPL/DSN.

94: First Light

First dual 8.4 and 14.4 GHz observations of radio sources.

Astronomy with the Tracking Station Antenna

X and Ku Band Surveys

The Green Bank Earth Station is conducting an all Northern Sky Survey at both X and Ku band. This survey program is intended to map the entire Norther sky simultaneously at 8.35 and 14.35 GHz at regular intervals.

A North pole Transient Source Search has recently been completed by Julie Zuber.

X and Ku Band Gamma Ray Burst Monitoring

Dail Frail at the AOC notified Green Bank of a Gamma Ray Repeater in the vacinity of the galactic center. This region has been mapped by the GBES, and an uncalibrated FITS Image is available.

Other Web Sites

VLBA Correlator

NRAO Socorro is developing other hardware and software for the NASA OVLBI project. The latest experiment summaries and fring plots from the correllator are also available.

DRAO Correlator

The Canadian Space Agency Supports both the Russian RadioAstron and Japanese HALCA mission with the S2 Correlator at DRAO .


JPL has a Space Very Long Baseline Interferometry Project home page.

Ground Observatories

The National Radio Astronomy Observatory (NRAO) is a facillity of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

JPL maintains a summary of recent tests .


Last update: 99 May 28