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VGOS updates: McDonald signal chain build weblog


7 MAR 2019   Congratulations to the whole team, including our ISI colleagues, for a successful Site Acceptance Test (SAT) of the new VGOS dish! (Photo credits C. Ruszczyk and G. Rajagopolan.)

positioner, ETU in boxes


positioner, ETU in boxes 

19 FEB 2019  A mini photo album from McDonald Observatory in Texas, documenting the successful installation of the positioner and the ETU (Engineering Test Unit) last week! The antenna passed its pointing verification test, and moves on to the Site Acceptance Test (SAT). Looking great — both technology and location! (Photo credits C. Eckert and A. Burns.)

positioner, ETU in boxes


positioner, ETU in boxes 

positioner, ETU in boxes

positioner, ETU in boxes

positioner, ETU in boxes

4 FEB 2019  Big day for the ETU and the positioner: they are currently being loaded on a truck destined for McDonald Observatory in Texas as part of the next NASA VGOS antenna.

These boxes weigh more than 650 pounds each, smell like Christmas trees, and are decorated with shock sensor tags to help ensure that they aren't jostled overmuch on their journey.

positioner, ETU in boxes

22 JAN 2019   Another positioner video! This time it's in the midst of some earlier software testing. It has been sped up slightly, but moves very smoothly and quietly, and the software controls were passing muster.

8 JAN 2019   Happy new year! The hub box, containing what's properly called the NED (network electrical distributor), is currently undergoing an intense testing, verification, and validation process. Under the microscope during this process is basic functionality of the HUB box, along with the verification of its first external interface: to the drive motor on the positioner. Once the drive communication and functionality are verified and validated, the positioner will be packaged and shipped, with the ETU to MGO. The ETU feed has already gone thru extensive testing and verification and is awaiting shipment to McDonald Observatory.

hub box night testing

hub box diagram

21 DEC 2018   Individual components of a front-end elements, the dewar, seen here a short while ago during construction. The dewar cryogenically cools the feed and the low-noise amplifiers (LNAs) for the VGOS signal chain to minimize noise.

dewar component

dewar component

9 DEC 2018  The ETU (Engineering Test Unit) frontend RF component is itself being tested. Haystack engineers took it outside on a recent weekend to check cold sky ETU measurements. Receiver temperatures were satisfactory, and the ETU will continue its trek toward McDonald Observatory and NASA's next VGOS station.

testing the ETU

14 NOV 2018  Things are getting wired here in the Westford technical lab! Literally: at right are the hub box wiring (top), an electrical work of art, and limit switch wiring (bottom). The limit switch is constructed as part of the positioner; it keeps the sled that moves instruments back and forth within the positioner from traveling too far and overstepping its bounds.

hub box wiring

limit switch wiring

22 OCT 2018  The Engineering Test Unit (ETU) RF frontend component has been integrated with its mechanical payload simulating the original signal chain frontend. The plot shows the receiver temperature measured using the Y-factor method. Microwave absorbers at room (295K) and liquid nitrogen (77K) temperatures were used as hot and cold loads. And, as a bonus, please admire our VLBI-branded laboratory stepstool.

ETU in the lab

RF testing plot for ETU

VLBI inked on a stepstool

18 OCT 2018   One stage in the machining process for the VGOS front end radome, which covers the feed components, shown at right. The holes are part of the fixturing jig Haystack engineers use to hold the radome as they machine it to the correct height.

VGOS front end radome
1 OCT 2018   In the video at right, the Engineering Test Unit (ETU) sled is seen in motion within the production VGOS positioner. The ETU and positioner will soon be be installed at McDonald Geophysical Observatory. The ETU contains the electronics for a feed and a single-band, single-polarization signal that is transmitted over fiber to the backend equipment and field system computer.

The positioner, ETU, and supporting backend equipment will be installed in February 2019 at McDonald Observatory for pointing verification as part of the antenna Site Acceptance Test (SAT). The ETU includes a mass equivalent to that of the VGOS feed; the black weights shown are carefully calibrated to match the frontend feed. Installing the ETU before the actual frontend feed will allow NASA to test the pointing capability of the McDonald VGOS antenna.

As shown in the video, the payload (in this case, the ETU) can be moved in and out of position mechanically — saving wear and tear on the human operators. The ETU can also be moved into position manually.

After the successful completion of the antenna SAT, the positioner will remain in Texas, awaiting the installation of the VGOS signal chain.

12 SEP 2018   An interesting detail of signal chain builds that might be overlooked by outside observers is the intricate cable harnessing work. Here, macro and micro cable arrangements are made with intense attention to detail at the Westford testing laboratory. Cables are sorted and selected based on build plans that include color coding to indicate different purposes and specifications.

feed horn testing 


testing results

25 SEP 2018   We welcomed MGO operatives Chevo and Jerry to Westford and Haystack last week! They went through extensive training on VGOS telescope operation, including participation in observations at Westford and lectures about VLBI from Haystack scientists and engineers — and managed to remain cheerful throughout. The McDonald Observatory telescope will be in good hands.

feed horn testing  

testing results

29 AUG 2018   The Westford technical lab welcomed students visiting from the University of Massachusetts–Lowell yesterday! These students from the Lowell Center for Space Science and Technology are working on their own CubeSat in the NASA-sponsored SPACE HAUC program, and spent some time yesterday learning from and collaborating with Haystack engineers.

Visiting UML students
16 JUL 2018   One of the test components of the ETU (Engineering Test Unit). The ETU, in the testing process at the Westford technical lab, contains a subset of the signal chain and once installed, will allow engineers to test an antenna's pointing capability earlier in the process than was previously possible.

ETU test component
29 JUN 2018   The signal chain progress continues; today we see a couple of the (meticulously organized!) staging areas for various components in the build process. Included here are some of the innards of the CDMS, or cable delay measurement system, that will be installed on the new VGOS antenna at McDonald. The CDMS, which was also successfully deployed at KPGO, is designed by Haystack to measure variations of the delay in the cable carrying the reference frequency from the hydrogen maser to the phase calibration generator. The CDMS design corrects for transmission of the reference frequency over an optical fiber or coaxial cable. The cable delay value is an essential component of the final geodetic estimation. The phase cal board is mid-installation in the top photo; in the bottom image is one of the gear couplings (hand model: Larry).

CDMS being built  

gear coupling

22 JUN 2018  The RDBEs (ROACH Digital Backend System) are looking good, as seen in one of the Haystack technical laboratories yesterday! Several of these RDBEs are destined for the next VGOS site, located at McDonald Observatory in Texas.

RDBE, or ROACH Digital Back End
18 JUN 2018   Last week, we said farewell to the ETU Vibration Monitoring System, but we took a few photos before it went out the door. Destined for the new VGOS antenna at McDonald, Texas, by way of Goddard, the ETU Vibration Monitoring System is a set of very sensitive sensors that use accelerometers to measure any vibration on the antenna's dish once they are attached; the accompanying LabVIEW software shows graphs of even tiny motions and logs data to files on a field laptop for McDonald engineers to monitor.

feed horn testing  

testing results

12 JUN 2018   In a collaborative effort between GSFC and MIT Haystack, the radiation pattern of the X-band feed horn for the Engineering Test Unit (ETU) is measured at an antenna test facility within GSFC in Greenbelt, Maryland. The top figure at right shows the setup inside the anechoic chamber; the bottom figure at right, a representative 3D rendition. Below is a plot of the pattern at the VGOS band D frequency of 10.2 GHz. As designed, the corrugated conical horn feed pattern exhibits excellent agreement between E and H plane patterns with very low cross-polarization levels.


testing results

feed horn testing  

testing results

23 MAY 2018   The assembly process for many of the MGO VGOS antenna components is not merely highly photogenic but very carefully organized; once sourced or machined, parts are labeled and arranged for the most efficient and accurate assembly.

Coming up soon is the next stage in their life cycle!

ETU arrival  

ETU arrival

16 MAY 2018 It's only fitting that an image of the accelerometer going into testing is a little shaky. These devices are part of the system that will be located at the new VGOS station at McDonald to monitor antenna vibrations. The testing phase for the accelerometers is designed to ensure highly accurate calibration. ETU arrival  

25 APRIL 2018   Earlier this month, we received the corrugated conical horn feed for the X-band Engineering Test Unit (ETU). The ETU is a 8.2–12.4 GHz room-temperature receiver chain designed and built to test the pointing capability of the 12-meter ISI antenna to be constructed at McDonald Observatory. The engineering department reports that an early check of its impedance match looked good, particularly at VGOS band D frequencies (centered at 10.44 GHz). The ETU build continues! (Photo credit: Ganesh Rajagopalan) ETU arrival  

9 APRIL 2018   A momentous anniversary for VLBI: in April 1968, fifty years ago this month, observations were held between MIT Haystack Observatory and the Onsala Space Observatory in Sweden. We threw VLBI a transatlantic birthday party at Haystack and Onsala, complete with cake, champagne, and Swedish fish! Several scientists and engineers who helped develop this technique attended at both observatories and shared their memories of early VLBI work. Shown here are Alan Whitney, Jim Moran, and Alan Rogers; a Mark I tape from 1968; and today's Haystack VGOS group.

For more on this historic scientific anniversary, see MIT News:

Alan Whitney, Jim Moran, Alan Rogers  

Mark I tape, historic documents  

Haystack VGOS group, 2018  

3 APRIL 2018   The MGO build includes a number of custom parts CNC machined by the experts here in Westford. Here a 3D CAD model is converted from virtual to reality, from the original design drawing, through the machining process, into the finishing stages. The white liquid is a cutting fluid that also cools and flushes out the chipped-out pieces to be discarded from the final product.

Coming soon: VLBI anniversary celebration, plus an update on the ETU (engineering test unit) progress!

MGO CNC machining part, #1  

MGO CNC machining part, #2  

MGO CNC machining part, #3  

MGO CNC machining part, #4  

21 MARCH 2018   QRFH feed in the house! Build progress continues on the NASA SGP VGOS antenna's signal chain, to be located at McDonald Observatory in Texas. The shiny, artwork-quality object shown here is the quad-ridge flared horn (QRFH) feed. This feed is a main component of the cryogenic front end of the antenna's signal chain. The design of the QRFH shown here is optimized for the VGOS 2.3–14 GHz frequency range; it collects radio waves from the 12m antenna's dish (via the subreflector) and converts the signal to an electrical current to be amplified by cooled, ultra-low-noise amplifiers. The ridged and flared design allows for signals to be gathered in dual linear orthogonal polarizations over a 6:1 wide-frequency range. [Feed model QRFH-45-62P3, Cosmic Microwave Technology Inc.; hand model: C. Eckert]

More on the antenna, the low-noise amplifier, and the rest of the front end coming soon!

testing system temperature
7 MARCH 2018 Progress continues on the NASA SGP McDonald VGOS antenna's signal chain; here, the positioner alignment and assembly is nearing completion at the Westford build site. [Photo credit: Michael Poirier] MGO positioner assembly, #1  

MGO positioner assembly, #1

1 MARCH 2018 The signal chain build for the new VGOS antenna at McDonald Observatory in Texas is well underway! The front-end positioner — which houses mechanical and electrical elements such as the antenna feed, receiver payload, receiver cryogenics and vacuum, and calibration and monitoring systems — is nearing completion at the Westford instrumentation facility. [Photo credit: Michael Poirier]


MGO positioner build MGO positioner build

MGO positioner build


MGO positioner build

27 FEBRUARY 2018 Earlier this month, our VLBI/VGOS science and engineering team met with colleagues from NVI and NASA’s Space Geodesy Project (SGP). Haystack and NVI have a long history of successful collaboration on VLBI data and science! Together, we reviewed the VGOS progress over the last few years, and produced a tentative plan for the rollout of the VGOS network that will cover the period between 2018-2020. [In photo: Pedro Elosegui (Haystack), Chester Ruszczyk (Haystack), Dirk Behrend (NVI), Ganesh Rajagopalan (Haystack), Frank Lemoine (NASA/SGP Project Scientist), Ed Himwich (NVI), John Barrett (Haystack), and John Gipson (NVI), at MIT Haystack Observatory] testing system temperature
23 FEBRUARY 2018 Recently, a team from Haystack tested the system temperature of the broadband receiver of the VLBI antenna at Goddard Geophysical and Astronomical Observatory (GGAO), after servicing it and before transporting it back from Westford, Massachusetts, to GGAO, Maryland. This engineer looks cold, but he’s more interested in how the New England weather affected the receiver’s performance (only a few dBs above the noise floor of the spectrum analyzer) than keeping himself warm. The radome in the background houses the Haystack 37-m radio telescope. [Photo credit: Ganesh Rajagopalan]

testing system temperature
21 FEBRUARY 2018 Welcome to the VLBI weblog at MIT Haystack Observatory, where we’ll cover highlights of our latest work in regard to very long baseline interferometry (VLBI), which we use for geodesy and astronomy. We’ll share updates from our Westford radio telescope and some of our collaborations with other VLBI institutions and stations around the world, as well as progress on the signal chain for NASA’s next cutting-edge VGOS station, at McDonald Observatory, Texas—following in the footsteps of the Space Geodesy Project’s popular Koke'e Park Geophysical Observatory (KPGO) Blog.


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