How can a satellite send a text message to an unmodified android phone?

An unmodified android phone is one which is not designed to perform some specific tasks. For instance, in context of satellite communication our basic android phones are considered unmodified.

Then, how this basic phone can receive a text message from satellite?

Well, this was considered impossible until couple years ago. But now this has become possible because a space startup ‘LYNK’ has made it happen. A team lead by Charles miller was working on this technology since 2017 and in February 2020 they succeeded in sending and receiving a text message.

How did they do it?

To make it possible, new kinds of satellite which act like terrestrial towers for phone have been deployed in space. As we are talking about our basic phones which have inbuilt antennas that too very small with limited range, these satellites can’t be deployed in any other orbit like geostationary or medium earth orbit but Low Earth Orbit (LEO) at 500 kilometer or lower altitude. Also, the antenna on the space tower should have narrow bandwidth with higher gain and lower slant range. Narrow band communication promises stable long range communication. One more thing that is required to set up the link is the use of Sub-1 GHz frequency spectrum. It provides range more than 100 kilometer. Also, this spectrum has minimum power consumption and it avoid interference and provide better gain. Once the link is set, communication becomes feasible and data can be sent. Moreover to send and receive the text message, it is necessary for both the mobile phones transmitter and the receiver to have link with the satellite tower. That’s how a basic android phone turns into a satellite phone.

However, only one satellite in LEO cannot cover the entire earth. As a single satellite covers approximately 45˚ angle, a huge number of satellites are needed to be deployed.

What are the pros of having this technology?

The benefit of having this technology in common mobile phones is that it is possible to switch back to ground towers whenever required. And also satellite phones are pretty expensive, not everyone can afford them. This very technology will be helpful in case of disasters like tsunami or earthquake etc.