**1. Introduction**

In the aviation field, great interest is growing in high-speed vehicle design. The increase in manned and unmanned space operations in low earth orbit (LEO) demands an evolution in the vehicle for payloads transportation up to and from LEO to improve the levels of flexibility, affordability and safety of routine accessto-space missions. Today this need is utmost stringent in the light of the NASA Space Shuttle retirement.

On the other hand, in the last few years, the attention to hypersonic travels for civilian application has also increased dramatically. Many start-up industries are focusing attention on hypersonic aircrafts able to fly, e.g., from New York to Sydney in less than 2–3 hours, thus providing a lot of insights on the oncoming market of hypersonic flights.

As a result, over the decades the potential benefit of an operational hypersonic vehicle (HV) has driven continued researches in basic and applied technologies. Indeed, several high-speed aircraft concepts (i.e., lifting and winged vehicles) have been conceived or developed in the USA, Russia (former USSR), Europe, France, Germany, Italy, and Japan to simplify access to LEO and sustained high-speed flight routinely and in a safe way. Most of these projects, however, were just prototypes or developed at the conceptual design stage and linked to flight testing focused mainly on some technologies rather than assessing the effectiveness and the advantages of a cutting-edge design.

A look on the HV research programs developed so far is hereinafter described for each country.
