Arecibo Radio Telescope Collapses: A look back at some SDR fun with Arecibo
The Arecibo Radio Telescope has collapsed. Once the largest single dish radio telescope in the world at 305m, Arecibo was mostly used for radio astronomy research. However, the dish was made famous in 1974 for deliberating beaming a message into space as part of a search for extraterrestrial intelligence (SETI) experiment. It also played a part in popular culture, being a part of several famous films such as Golden Eye and Contact.
As part of it's goodbye we thought we'd highlight a few old posts where Arecibo was used together with SDRs for some interesting applications.
Back in 2014 we saw engineers hook up USRP software defined radios to Arecibo in order to contact the lost ISEE-3 NASA spacecraft (Wikipedia Article). The idea was to contact the solar orbiting spacecraft which was last heard from in 2008, and get it to fire it's thrusters in order to reuse it for a new mission. The idea was initially abandoned by NASA, however a crowdfunding campaign raised US$125,000 which funded the project.
The project required finding and researching the original spacecraft documentation, and implementing the modulators and demodulators in GNU Radio. Whilst being successful in communicating with the satellite, ultimately the project failed due to the satellite's nitrogen tanks which had long leaked empty. But the fact that they were even able to find and communicate with the spacecraft using Arecibo was a major achievement. If you're interested in that project, Balint's 2015 talk on YouTube is an interesting watch.
Later in 2017 we saw how Arecibo was used for an Ionospheric heating experiment which involved transmitting 600kW of net power into the Ionosphere. This resulted in SDR users around the world being able to receive the signal. Other posts involve u/moslers Reddit post where he toured Arecibo and showed how they used a familiar program, HDSDR, as part of their monitoring suite.
So goodbye to Arecibo. However, we can look forward to the 500 meter Chinese FAST (Five-hundred-meter Aperture Spherical Radio Telescope) giving us new opportunities for single dish radio observations in the future.
Unlike Arecibo,the chinese dish is receive only. It can’t be used for radar astronomy.
You could place a minuscule pulse radar with a tiny dish in geo-stationary orbit which would reduce the power requirements by a totally insane amount (free space path loss alone at 2380MHz to geo-stationary orbit is 191dB), and it could provide higher performance than Arecibo. The Arecibo antenna (R.I.P.) had a gain of about 60dBi. The higher performance would come from not having to deal with an thick constantly changing atmosphere – no more atmospheric losses (beam-spreading, polarization loss, rayleigh fading, scintillation loss, free-space loss, weather loss), no more rain/fog attenuation, no more ionosphere losses. Without all the sources of distortion, you are going to get a cleaner signal. And there is no need for a NRQZ which is required on earth, because in theory you have about 190dB of attenuation by being away from the planet. And if it was a pulsed radar, it could sit there mostly idle harvesting energy from the sun until enough was collected for a really high power pulse. On paper at least it could be cheaper, and higher performance to have several in space.
geo-stationary orbit is 35,786 kilometers (22,236 miles) above Earth’s equator.
The Free Space Path Loss over 35786 km @ 2380 MHz is 191.0 dB.
It might be difficult for any space agency to justify putting radars in space, but maybe the death of Arecibo, might help spawn a project.