Sam Hooke

Tour of MRAO (Part 1): Lord's Bridge station and AMI Large Array

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Perhaps best known for the discovery of the first pulsar, by Jocelyn Bell Burnell, the Mullard Radio Astronomy Observatory (MRAO) is located on the outskirts of Cambridge, located on the site of a former WWII munitions storage facility. The MRAO is home to many radio telescopes and antennas, with some equipment dating back to the 1950s, scattered across the several miles wide site. While most of the pre-1990s equipment is now decomissioned, there is still a lot of active work being done by the more recent arrays and telecopes.

The facility is owned by Cavendish Astrophysics, who were pioneers in this field from 1945, and opened the MRAO in 1957 (supported by Mullard Ltd. and the Science Research Council). While the many of the dishes are clearly visible from the A603, which runs right though the middle of the site, the facility is not open to the public. However, they do occasionally run guided tours, and I was fortunate enough to take part in one.

Station §

We began the tour at the old Lord’s Bridge railway station, which closed on New Year’s Eve 1967. A single length of the eastbound platform remains, with the station building and goods shed.

Outside §

An old station building.
Standing northeast of the station building, looking southwest at the main entrance. The “platform” is through the gap on the left.
An old station platform, with no railway track, and the old railway station building in the background.
Standing where the old railway track would have been, looking northwest at the station building.
An old station platform, with no railway track, and an antenna and the old goods shed is in the background.
Same again, but looking northeast at the old goods shed.

Inside §

Entering the station, you pass by a little museum, with cabinet full of radio equipment dating back to at least 1949 (and possibly earlier - I didn’t manage to read it all).

A large, old cabinet, filled with various old radio equipment.
The museum cabinet.

Going past the little museum, there is a “lecture theatre”, which is the size of a typical classroom with about as many chairs. At the back of the lecture theatre, on the wall, is a magnificant map of GALACTIC RADIO EMISSION AT 38 Mc/s.

If I were to hazard a guess, this map comes from the paper Results of a Survey of Galactic Radiation at 38 Mc/s, published in 1957, which gives its thanks to “Mr M. Ryle” (of the former Ryle Telescope at MRAO). The diagrams in the paper are black and white, but this diagram illustrates the radio emissions much more clearly with range of blue and orange hues.

J. H. Blythe, Results of a Survey of Galactic Radiation at 38 Mc/s, Monthly Notices of the Royal Astronomical Society, Volume 117, Issue 6, December 1957, Pages 652–662, https://doi.org/10.1093/mnras/117.6.652

A wide, old poster, with speckled hues of blue, orange and red.
Poster of GALACTIC RADIO EMISSION AT 38 Mc/s.

Among the many other interesting things shown in the lecture theatre, the following two stood out, which relate to the military history of the site: during WWII it was used as a munitions storage facility.

First is a map of the former facility, which indicates where the BOMB STORES were, and the railway tracks. While the tracks are long gone, much of the original road structure remains, as can be seen in the composite map I created.

The map used to be secret information, hence the RESTRICTED label at the top, but I’m assured that’s no longer the case.

An old black & white map, which displays the locations of railway lines, buildings and roads at Lord's Bridge.
A map of what I believe was called Lords Bridge Air Ammunition Park. See the composite map I created for how the old railway sidings fit with the modern day MRAO.

Second is a photo of a photo of some of the old munitions: the munitions are of course no longer there, but when the MRAO was first being constructed, they did find some left over from the war that needed disposing of safely! Again, I’m assured that’s no longer the case.

Four grey tubes on large gravel.
If I recall right, these were canisters of mustard gas dating to WWII, which had to be cleared from the site at Lord’s Bridge prior to the establishment of MRAO.

Map §

To help illustrate where things are, following is a map of MRAO that I made (see this post for more details about the map).

SITE 1.ADMINISTRATIONCambridge RoadWimpoleRoadHaslingfieldRoadBarton RoadLord's BridgeStationAMI Small ArrayCOASTAMI Large Array†Pulsar Array4C Array†Half-Mile Telescope (small) & †One-Mile Telescope (large)†One-MileTelescopeTrack continues 1km eastwardse-MERLIN†CLFST†CATUnknown?Unknown?†SKA†HERAUnknown?†SKAPrototypearrayPrototypeindividualPrototypeRyle ControlRoomOne-MileControlRoom(Previously site of †Ryle Telescope)(Track is shared)Name†NameLong BrookBourn Brook𝕳𝖊𝖞 𝕳𝖎𝖑𝖑𝕽𝖔𝖒𝖆𝖓𝕭𝖆𝖗𝖗𝖔𝖜NSITE 6.SEWAGE DISPOSALSITE 2.BOMB STORESSITE 4.F.F.D.4.1 Mile1 Kilometerhttps://sam.hooke.me/mraoJune 2024Mullard Radio AstronomyObservatory (MRAO)KeyFormer railwayTelescope railwayMain roadMRAO tarmac roadMRAO trackTelescope (static)Telescope (on track)Telescope (approx. area)Telescope (active)Telescope (inactive)MRAO (approx. area)

We left the station building (Lord’s Bridge Station, in the middle near the top) and drove east along the road that follows the old east-west railway line. The road passes underneath a bridge (Haslingfield Road / Barton Road), and then we stopped at the AMI Large Array.

AMI Large Array §

Here there are eight dishes, which together form one radio telescope, the AMI Large Array.

Six dishes. Five are in a line, following the old east-west railway track. One is off to the left.
Six of the eight dishes. The nearest one, and the one to the furthest left, are both fixed in position. The other four are all track mounted.

The nearest dish was the only clean one, the others were all rather grubby. Our guide informed us that the dishes were due for cleaning, and so the cleaning process had begun, however a film crew contacted the MRAO wanting to use the AMI Large Array for their location. The film crew were keen that the dishes looked dirty, so the cleaning process was postponed until after filming was complete. I don’t know what film it was (or will be), but perhaps it’s going for post-apocalyptic vibes?

A photo of the clean dish.
A front view of the nearest dish.
A photo from behind the clean dish. Latticework is visible.
After a few minutes, the dish started moving, and gradually rotated to point higher and higher up. I walked around and got a photo from underneath.

Track §

Four of the eight dishes are mounted on a railway track.

Four large dishes on a large track.
The four track mounted dishes.
A close view of the track.
As mentioned earlier, these dishes have intentionally not been cleaned.
A closer view of the four track mounted dishes.
Another view.
A straight road vanishing into the distance, with a track running parallel.
Looking straight down the maintenance road that runs parallel to the track.

Next part §

To carry on with the tour, see here for part 2.

All trips at this location: