China successfully launched and orbited a Pakistani remote sensing satellite, the PRSS-2, on Sunday, in addition to two other satellites. Generally, remote sensing satellites gather Earth data, aiding in environmental and geographic changes used in many ways, including weather forecasting and detection of forest fires.
However, the launch raises the question:
What’s the difference between a remote sensing satellite and a spy satellite? Both are clearly in orbit, and rely on various sensors, but spy satellites generally have optical and infrared sensors with far greater resolution, enough to support resolutions from 5 to 15 centimeters, according to reports supplied by intelligence officials. That would mean a spy satellite could discern a baseball-sized object from orbit.
Payloads in spy satellites are set up for intelligence, surveillance and reconnaissance, known as ISR. In addition to high-resolution optical and infrared cameras, they may also deploy synthetic-aperture radar for all-weather images and signals intelligence (SIGINT) equipment for spying on communications. The SIGINT gear is not usually part of a payload for a remote sensing satellite, which may be used for weather forecasting, environmental monitoring, resource management and scientific research. A remote sensing satellite may be able to discern objects of less than a meter, not down to the resolution of a spy satellite.
There’s a big difference between the two different satellites in how data is treated. With the remote sensing satellite, data is usually shared with the public or used commercially and used for agriculture or climate science work. A spy satellite’s data is usually encrypted and kept secret. Governments and defense industry companies rarely share details about spy satellites, leading to widespread speculation about what nations are up to.
Satellite examples from as early as the Cold War
Some spy satellite images have been declassified or leaked. President Donald Trump tweeted a classified image of the aftermath of a failed test of Iran’s Safir rocket in 2019, for example. Spy satellites give reconnaissance such as missile early warning, which can rely on space-based infrared systems. They can also detect nuclear detonations from space, as with Project Vela developed in the 1970s. A spy satellite can detect signals such as radio waves, and SOLRAD, sponsored by the US Navy in the 1960s is one example. SOLRAD-1, launched in June 1960 was dual-purpose, serving as a military intelligence satellite (as GRAB 1) and a scientific solar observatory.
Optical imaging satellites could be both remote sensing satellites or spy satellites and can include spectral imaging. The CIA and US Air Force operated the CORONA program from 1959 to 1972. Space-based radar satellites can be used at night or through cloud cover. The US-A (Upgravlyaemy Sputnik Aktivnyy) was a series of 33 Soviet reconnaissance satellites launched from 1967 to 1988 to monitor NATO and merchant vessels using radar. The western world knew US-A as Radar Ocean Reconnaissance Satellite or RORSAT. A RORSAT was launched in 1987 , called Kosmos 1867. It was powered by a TOPAZ 1 nuclear reactor and had a mission life of about 11 months, according to reports.
The Pakistani remote sensing satellite recently launched could be used to collect data on temperature changes in oceans, cloud patterns, volcanic activity, urban growth, farmland growth and even the topography of the ocean floor, which provides data for the US Geological Survey, according to reports. The launch took place at a commercial aerospace innovation pilot zone in northwest China, according to the China’s Xinhua news agency. The Lijian -1 Y8 carrier rocket placed the PRSS-2 and China’s AIRSAT 03 and 04 into their planned orbits, the agency said. China earlier deployed two Pakistani satellites in 2018, according to Times of India.
In addition to intelligence concerns about satellites in orbit, there are now such a large number deployed that scientists worry about collisions, space debris, light pollution from reflected sunlight and the impact on research and atmospheric and radio signal interference. A potential for a chain reaction of collisions is known as the Kessler Syndrome. In 2015, there were about 1,300 satellites in orbit, a number that has risen to above 8,000. In 2023, the FCC had pending applications for 60,000 new satellites.
Jonathan McDowell, an astronomer at Harvard-Smithsonian Center for Astrophysics said that year that the sheer number of satellites and different organizations that own the satellites “gets to the point where a collision ends up being pretty inevitable.”