Chinese hackers are suspected of having interfered with the operation of two US government satellites on four occasions via a ground station, according to a report being prepared for the US Congress.

According to Bloomberg, the draft of a new annual report by the US-China Economic and Security Commission includes the claim that in October 2007 and July 2008 hackers used the connection from a ground station to affect the operation of the Landsat 7 and Terra (EOS AM-1) satellites, which are used for earth observation. The allegation was made by the US air force in a closed briefing.

The commission is concerned that the hack might have been carried out by Chinese government-sponsored hackers trying to found out how vulnerable the satellite control systems were to cyber-attack.

The report, which is due to be released next month, warns: "Access to a satellite's controls could allow an attacker to damage or destroy the satellite. An attacker could also deny or degrade as well as forge or otherwise manipulate the satellite's transmission."

The hacks are believed to have been carried out via a commercial satellite station in Spitsbergen, Norway that the US space agency Nasa uses for data transfers over the open internet. It is one of four used for Landsat 7 control; the others are on American soil.

According to the Landsat 7 handbook, the mission operations centre can send data including orbit changes and manoeuvres. That could potentially mean hackers might be able to send faulty data which could make a satellite enter the atmosphere in an uncontrolled manner. That could lead to it burning up, possibly resulting in large pieces landing on Earth at unpredictable locations.

The draft report does not give more detail on the form that the attacks took, and does not directly blame the Chinese government for carrying them out or sponsoring them. But the claims are part of a long-standing pattern in reports from the commission, whose purpose is to monitor and investigate the national security implications of the US's trade with China.

The Landsat 7 satellite saw 12 minutes of "interference" in October 2007; the Terra then suffered two minutes in June 2008. In July 2008 the Landsat 7 had another 12 minutes' interference. Finally in October 2008 the Terra was affected for nine minutes.

In a previous report on China's ability to conduct cyberwar (PDF), the commission noted: "Attacks on vital targets such as an adversary's intelligence, surveillance and reconnaissance (ISR) systems will be largely the responsibility of EW [electronic warfare] and counterspace forces with an array of increasingly sophisticated jamming systems and anti-satellite (ASAT) weapons." At the time, it pointed to China's tests of anti-satellite weapons which could fire electromagnetic pulses at orbiting systems, destroying them.

The Chinese government has repeatedly been accused of being behind hacking attacks against western companies and infrastructure, as well as the hacking of dissident groups. It has consistently denied the accusations.