**4. Future developments**

*Hypersonic Vehicles - Past, Present and Future Developments*

perform full atmospheric reentry.

numbers.

**3. Present developments**

capsule operated by Russian Federation [9, 27, 28].

Advanced Research Projects Agency (DARPA).

concepts and in-flight experimental sensors.

to accumulate practical flight experience. To this end, ESA has undertaken the design of the intermediate experimental vehicle (IXV) also promoted within the FLPP framework [22]. It was derived by the Pre-X concept investigated early by CNES [23]. The IXV holds the distinction of being the first ever lifting body to

German studies refer to the SHarp Edge Flight EXperiment (SHEFEX) program of DLR for the development of future reentry and hypersonic technologies [24]. The goal is to set up a flying laboratory to gain knowledge of the physics of hypersonic flow, complemented by numerical analysis and ground-based testing. SHEFEX flight experiments were an excellent laboratory to test new technological

In Italy there was the unmanned space vehicle (USV) program [25]. Within the ongoing USV project, CIRA conceived a family of flying test beds (FTB's) for in-flight experiments in the fields of aerodynamics, aerothermodynamics, flight mechanics, control, and aeroelasticity. The first phase of the USV Program consisted of the design and realization of two laboratories (i.e., FTB-1). The FTB-1 concept was based on a winged slender-body vehicle able to address in-flight experiments and low atmosphere maneuvered flights at supersonic, transonic, and low subsonic Mach numbers, referred to as dropped transonic flight test (DTFT) missions. The flight test success demonstrated the ability of designing and implementing robust guidance and control laws up to low subsonic Mach

Japan contributions to unmanned RLVs' design refer to programs of National Space Development Agency of Japan (NASDA) and, later, by the Japan Aerospace eXploration Agency (JAXA). Hypersonic Flight Experiment (HYFLEX) was a NASDA unmanned reentry demonstrator which was launched in 1996 from the Tanegashima Space Center by a J-I expendable rocket. It was a successor of OREX and was a precursor for the HOPE-X concept [26]. HYFLEX was a lifting body

To date there are only two servicing HVs, namely, the X-37 and the Soyuz spacecrafts. As discussed before, the former is a US unmanned reentry spacecraft (winged-body) close to the Space Shuttle, while the latter is the only human-rated

The Soyuz spacecraft was designed for the Soviet space program by the Korolev Design Bureau in the 1960s, and it is still in service today. It is currently the only manned space vehicle in the world to support flight to and from the ISS. The spacecraft consists of three parts, namely, orbital module (OM), service module (SM), and reentry module (RM). The OM is a spheroid spacecraft's segment which provides accommodation for the crew during mission. The cylindrical spacecraft's segment is the SM. It features solar panels attached and contains the instruments and engines. Finally, the RM is a small capsule which returns the

The X-37's aerodynamic design was derived from the Shuttle Orbiter, and hence the X-37 has a similar lift-to-drag ratio (L/D). The X-37 is the smallest and lightest lifting winged vehicle flown to date. It features a forwarded double delta wing and a butterfly tail [9]. The X-37 re-enters Earth's atmosphere and lands automatically. It is the second reusable spacecraft to have such a capability, after the Buran shuttle [14]. The X-37 is now operated by the USAF being transferred to the Defense

laboratory to gather data on aerodynamic heating and pressure loads.

**6**

crew to Earth [27, 28].

As future developments in HVs, there are Dream Chaser and Space RIDER (both lifting bodies) concepts. They are being developed by the USA and Europe, respectively [13, 29, 30].

The Dream Chaser is a reusable lifting-body spaceplane that can fly autonomously to resupply the ISS with both pressurized and unpressurized cargos. The vehicle is designed to be launched on expendable rockets, return from space by gliding, and autonomously land on conventional runways. The potential further development of the spaceplane includes a human-rated version which would be capable of carrying up from two to seven people to and from LEO. Dream Chaser design is derived from NASA HL-20 lifting body which was itself like the Soviet BOR-4 [1, 14, 31].

The experience and data obtained by Europe so far on Hermes, FESTIP, and FLPP programs served as stepping stones toward a vehicle called Space Reusable Integrated Demonstrator for Europe Return (Space RIDER), underdeveloped by ESA [29]. The Italian Space Agency (ASI), with the project being led by the Italian Aerospace Research Centre (CIRA), presented its own Programme for Reusable In-orbit Demonstrator in Europe (PRIDE) to develop the prototype named Space RIDER [30]. It is an unmanned spacecraft aiming to provide the ESA with affordable and routine access to space.
