HAMNET Report 18th October 2020

The Automatic Position Reporting System (APRS) isn’t only useful to emergency communications operations to help look for missing persons or establish the extent of a disaster.

The ARRL reports on the progress of amateur radio APRS balloons launched by 11 US schools on October 9 with the aim of flying around the world.

Eleven schools across the US launched these helium-filled balloons carrying amateur radio payloads on October 9. The Smithsonian Air and Space Museum live-streamed the multiple launches. The balloons are trackable via ham radio on APRS (144.390 MHz FM or 144.340 MHz FM).

The lighter-than-air vehicles were intended to head east around the globe, although there’s no accounting for upper air currents. Altitudes were expected to be in the 6000– 8000 metre range, with the balloons taking a few days to cross the Atlantic Ocean.

Some of the balloons are already out over the Atlantic, and one, the KS1LAS-1 balloon, launched from Washington, was reported over the Mediterranean on October 14, moving at a speedy 100km/h at an altitude of some 13000 metres.

I’m sure you will be able to view this frontrunner by logging in to aprs.fi and typing the balloon’s call-sign in to the search window.

In a previous bulletin, I mentioned the two airline pilots who consecutively reported a man flying a jetpack at about 300 metres above ground. Well, it has happened again, again near Los Angeles International airport, when a China Air flight crew spotted a bright object that looked like a man flying a jetpack, this time at 2000 metres above ground. The pilots were unable to confirm with certainty whether it was a jetpack-flyer, and a law-enforcement aircraft, which happened to be in the area, and which was asked to go and search the area, was unable to find the so-called UFO.

The pilots of an Emirates flight, about 13 miles behind the China Air flight, did not spot the object, so whether it was actually a man flying a jetpack, or perhaps some sort of drone that looked like that, has not been established.

The biggest problem will be that such small objects will likely not be visible on aircraft radar, and so could pose a potential collision risk to the airliners. The FBI and the FAA are apparently investigating the matter.

South Africa is hugely and justifiably proud of the fact that the major portion of the Square Kilometre Array of radio astronomy receivers is to be installed with epicentre near Carnarvon in the Northern Cape.

However, the SKA global headquarters is applying its mind to the problem of radio frequency interference (RFI) to its extremely sensitive radio telescope receivers, from satellite mega-constellations. They have done an analysis which quantifies this impact and identifies possible mitigations.

What mega-constellations of satellites, I hear you ask? Well, a certain lateral thinking American businessman with roots in South Africa is busy putting a constellation of 6400 satellites into low earth orbit, which will transmit signals within the frequency range covered by the Band 5b receivers of the SKA-Mid telescope array in South Africa. This band is one of seven planned for the array, and covers 8.3 to 15.4 GHz.

Further key points of the analysis are:

  • Without specific mitigation actions by the constellation operators, there is likely to be an impact on all astronomical observations in Band 5b.
  • This impact includes a loss of sensitivity in the frequency range used by the constellations, leading to astronomical observations in that range taking 70% longer.
  • The science impact is most significant for studies of molecular and atomic spectral lines in that range, including complex organic molecules; Class II methanol masers; and a wide range of extragalactic molecular lines.
  • Viable mitigation techniques identified by SKAO can reduce this impact on SKA-Mid by a factor of 10, if implemented by relevant satellite operators.
  • The SKA Organisation (SKAO) remains committed to minimising the loss of scientific discovery through all available avenues. SKAO will continue to work closely with industry on ways to minimise the damage caused by mega-constellation transmissions, and is looking forward to a positive response on these proposed solutions.

Due to their exquisite sensitivity, the two SKAO telescopes will be built in remote locations far away from artificial radio frequency interference. These locations enjoy legal protections, declared as national Radio Quiet Zones (RQZ), which protect them from ground-generated radio signals, such as mobile phones, broadcasting transmitters or Wi-Fi to name a few examples. However, the RQZ status provides no protection against interference from space-borne transmitters.

Radio transmissions from satellite constellations use a frequency range which has been in use by the satellite industry for many years. It sits within the range of frequency observed by the SKA-Mid band 5b receivers, and is immediately adjacent to an internationally protected radio astronomy band. However, radio astronomy has been able to continue to conduct observations in all these frequency ranges due to the small number of (visible) satellites and their fixed position in the sky, most of them being in geo-stationary orbit. The deployment of thousands of satellites in low earth orbit (LEO) will inevitably change the situation as astronomers now face a much larger number of fast-moving radio sources in the sky. Their orbits will be circular and at about 550 km above earth.

In a recent public statement, the CEO of the company deploying the mega-constellation of satellites said that they won’t be seen by anyone unless looking very carefully, and will have about zero impact on advancements in astronomy.

The SKAO study shows that, for radio telescopes in general and for SKA in particular, this is not the case, and specific mitigation actions will be needed to minimize this impact.

SKAO says that there is a possibility of damage to the front-ends of the Band 5b receivers; that strong interfering signals could saturate receive systems, and drown out all other signals; and that the continuous loss of receive sensitivity could impact all astronomical observations in Band 5b within the frequency range of the satellite’s transmissions, unless mitigating actions are implemented.

It may take SKA 70% longer time to acquire the information being investigated in the presence of the RF interference, says the Science Directorate of the SKAO.

Certainly cause for worry!

This is Dave Reece ZS1DFR reporting for HAMNET in South Africa.