The US Air Force X-37B mini-shuttle/reusable spacecraft not only broke its own mission duration record on its fifth flight, its unannounced release of unidentified spacecraft, if true, would make it illegal under international law, explains guest writer and spaceflight expert Jonathan McDowell.

The US Air Force Rapid Capabilities Office’s X-37B spaceplane was on its fifth mission, OTV-5, from 7 September 2017 to 27 October 2019, ending in an automated landing at Kennedy Space Center. The flight is thought to be the third mission of the X-37B No. 2 vehicle and was the longest duration OTV mission to date.

X-37B lands at KSC. Courtesy: US Air Force

In the post-landing press release, Randy Walden, director of the USAF RCO, said: “This mission successfully hosted Air Force Research Laboratory experiments, among others, as well as providing a ride for small satellites.”

The implication is that at some time during the mission the X-37B released multiple sub-satellites – probably cubesats, but maybe larger payloads. These sub-satellites have not been included in the US Satellite Catalog and have not been registered with the United Nations.

If true, this is an apparently unprecedented violation of UN Resolution 3235 (XXIX), Convention on Registration of Objects Launched into Outer Space. Transparency of space activities was a hard-won achievement of the 1960s negotiations between the US and the USSR following concerns over unannounced satellites launched by the USSR in 1962 (which turned out to be failed interplanetary probes stuck in parking orbit).

Secret satellite deployments are a threat to the safety of flight and to international security. We don’t know how many satellites were released or when they were released, or whether they are still in orbit.

Update on 14 February 2020: US Space Command has subsequently noted that USA 295, 296 and 297 were deployed from craft during mission.

Jonathan McDowell is an astrophysicist working at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, USA. He is also a spaceflight and orbit expert who publishes Jonathan’s Space Report: The opinion expressed is his own and not that of his employer.