Archive for the ‘SKA project’ Category

Freezing cold antenna in the desert (SKA 4)

Thursday, March 25th, 2010
Sun beating down on KAT radio telescope

Sun beating down on KAT radio telescope

Imagine you are in the middle of the desert with the scorching sun beating down on you with no shade-cover, no water, no electricity and temperatures rising above 50 degrees Celsius? This is more or less the circumstances under which the elements of the Karroo Array Telescope (KAT) have to operate. The only difference is that the antenna feed needs to be cooled down to 20K ( -253 deg C), which is potentially a difference of more than 300 degrees. The cooling of the feed is necessary to reduce total RF noise in the system as every 7 degrees adds 0.1 dB RF noise.

I spoke with one of the project engineers who said that the easy part is to cool the feed to 50 K. They’re using a Gifford-McMahon helium gas cooler for the first cooling stage which can absorb up to 50 Watt of heat energy. The tricky part is cooling it down from 50 to 20 K. This has to be done inside a vacuum otherwise the smoke and dust particles would freeze and clog up the cavity. This creates another challenge, because gasses behave differently under very low temperatures and particles don’t collide as usual. This is overcome by using an ion pump cooling system which uses a strong magnetic field to positively charge all the particles, accelerating them to sputter against the cathode plates and extract the molecules to form a vacuum. See http://www.gammavacuum.com/operation.asp for a more detailed, graphic explanation.

To view previous blogs on the SKA project, please click here.

Author: Robert Kellerman

SKA – single element overview

Thursday, February 11th, 2010
Single Meerkat radio telescope element

Single Meerkat radio telescope element

The image above shows a single telescope forming part of the Meerkat project which is planned to form part of the future +- 500 telescope Square Kilometer Array.

The feed consists of two dual-polarised horn antennas, five conical deflector cones (where future horns could be inserted), cooling components, LNA’s and RF- to-fibre modulators. The struts are also designed to maintain strict tolerances on the feed position relative to the parabolic reflecting surface.

The 12m dish is made of a resin-foam composite and has a parabolic shape with 0.38 F/D ratio. It has to maintain its shape within millimeter tolerances and remain an almost perfect electromagnetic reflector while withstanding harsh environmental conditions like temperature variations, rain and strong winds etc.

The dish mount is an altitude-azimuth system and rests on a concrete pedestal. Another challenge is constantly stabilising the telescope, compensating for external forces like wind, gravity or metal expansion (and contraction due to large temperature changes) which can pull the whole structure off target or cause unwanted spillover.

In the next few blog entries I will discuss these interesting and potentially challenging topics in a bit more detail.

Author: Robert Kellerman

$2.5 billion on space research!

Tuesday, January 26th, 2010
Could one justify spending $2.5 bill on the Square kilometer array (SKA)?

Could one justify spending $2.5 bil on the Square kilometer array (SKA)?

There is a lot of controversy about the multimillion dollar SKA project. People are asking questions like, ?is it really worth spending 2.5 billion dollars just to listen to the sky while there are poor people living in shacks? How many houses could we rather build with that money? Others say, ?One mustn?t confuse research with helping the poor. Each year there are millions of dollars spent on R&D around the globe which leads to job creation.?

Both of these are valid points of view and one could argue both ways but from an antenna engineer?s point of view the SKA project is probably one of the largest global antenna related projects in history which already attracted a lot of interest from large academic institutes as well as stimulating the antenna industry.

Read the previous SKA project blog entry here.

Author: Robert Kellerman

Square Kilometer Array (1)

Wednesday, December 23rd, 2009
Artistic impression of SKA

Artists impression of SKA

I just had the most interesting conversation with one of the antenna engineers currently working on what is going to be the largest Radio astronomy telescope the world has ever seen, the Square Kilometer Array (SKA). There is so much that can be said about this topic so I decided to break it up into a few blog posts.

The image above is an artists impression of the planned telescope which will consist of a few thousand reflector antennas forming a huge array with a +- 0.01 degree beamwidth, The array will be constantly scanning the sky, ?listening? to whatever signals are coming from outer space. The data collected from each fraction of a degree will be processed to produce ultra-high resolution images of objects in space like in the ones shown below – these are images of the famous Crab Nebula taken by the Palomar radio telescope (left) and the optical Hubble Space telescope (right).

Crab Nebula taken by Palomar radio telescope (left) and Hubble Space telescope (right).

Crab Nebula taken by Palomar radio telescope (left) and Hubble Space telescope (right).

The main drive behind SKA is for scientific researchers to learn what lies beyond the borders of our galaxy, to study dark energy, dark matter and to try and solve the mysterys and questions like what happened ?in the beginning?.

South Africa and Australia are in the run to host the SKA and have started working on smaller demonstration projects like Meerkat and ASKAP. Both these countries?have great locations available for the SKA construction and the final decision of who the host country will beis primarily a political one (the announcement of the host country will be in 2011). Should South Africa win the draw, the center of the array – where most of the antennas will be located is in the Great Karoo (a semi-desert region well known in radio astronomy circles as a ?quiet? spot ? in terms of RF noise) and will stretch over nearly all countries in Africa, south of the equator.

Here are some of the tight specifications for each reflector antenna in the array:

  • 2:1 bandwidth
  • 1 degree main beamwidth
  • practically no backlobe (< 30 dB)

and

Each 2 ton antenna must be kept physically stable despite changes in the elements (Sun, Rain, Wind etc.) to reduce possible noise that might reflect from the ground.

There are numerous other challenges like cooling down the feed, creating affordable vacuums, manufacturing tolerances, data processing etc. which I will touch on in future posts.

Feed of the Meerkat reflector antenna.

Feed of the Meerkat reflector antenna.


12m radio telescope reflector antenna in the Karoo, South Africa.

12m radio telescope reflector antenna in the Karoo, South Africa.

Author: Robert Kellerman