Satellite data relay is a network of satellites that passes data from one satellite to another until it can be sent down to the ground. Customers reach the whole network through one API: a fixed set of instructions that a customer's software sends to the relay network, such as "deliver this image to my server".
A satellite in low orbit circles the Earth about once every 90 to 100 minutes. It can send data to a ground station only while it passes overhead, for about 10 minutes at a time. A satellite operator may own only a few ground stations. So data collected over one region often waits hours before the satellite passes over its station again. For many uses, such as flood maps or crop damage reports, a delay of hours is too long.
A relay network removes most of the wait. Its satellites sit in orbits chosen so that one of them is almost always within reach of the customer's satellite. The customer's satellite sends its data to the nearest relay satellite. The relay satellites pass the data between themselves, by radio or by laser satellite communication, until one of them is over a ground station. That station sends the data to the customer over the internet.
Imagine a crop insurance company in Jaipur. Hail damages wheat fields in a district of Rajasthan at 3 p.m. An Earth observation satellite that the insurer buys images from photographs the district at 10:15 the next morning. Without a relay, its next pass over the operator's ground station is at 6 p.m., so the images arrive in the evening. With a relay, the satellite hands the images to a relay satellite at 10:20. By 10:40, they reach the insurer's server. The claims team starts assessing the damage before lunch, almost a working day earlier.
The relay satellites carry software-defined radios. Much of how such a radio works is set by software. So the operator can change a relay satellite's frequencies and signal formats by sending a software update from the ground, even after launch. This lets one network serve customers' satellites that use different radios.
For the customer, all of this sits behind the API. Its engineers do not book ground stations or plan passes. Their software requests a delivery and receives the data. Relay networks belong to the newer, low-orbit side of space, explained in LEO and GEO satellites. The delivered images then go to satellite imagery analytics, which turns them into maps of the damage.