Another concept for reusable launchers are single-stage-to-orbit (SSTO) vehicles. Such vehicles would provide launch cost saving by eliminating the need for different stages, be they reusable or not. However, SSTOs must try to squeeze out the necessary engine performance, while drastically reducing structural weight, and still be able to reliably deliver a meaningful payload in orbit. Several reusable SSTO concepts have been proposed.
When will a reusable single-stage-to-orbit vehicle deliver a payload to orbit?
This question will resolve on the date that a single-stage-to-orbit vehicle successfully places a payload in orbit (above 100km in altitude), and returns in a condition to be able to be reused. Statements by the Launch provider, National Space Agencies, and credible media reports may suffice as a resolution source.
The payload should be a minimum of 1 kg, and should be operational after being deployed in orbit. If it is determined that the payload has been damaged due to the fault of the SSTO vehicle, that launch will not qualify to resolve; if the payload is inoperational due to no fault of the SSTO vehicle, this will resolve the question.