|Contract award||EADS, German Aerospace Center|
Hopper was one of several proposals developed by the ESA to function as a European reusable launch vehicle (RLV), which was envisioned to be used for the inexpensive delivery of satellite payloads into orbit as early as 2015. A prototype of Hopper, known as Phoenix, was a German-led European project which involved the construction and testing of a one-seventh scale model of the larger Hopper. On 8 May 2004, a single test flight of the Phoenix was conducted at the North European Aerospace Test range in Kiruna, Sweden.
From the 1980s onwards, there was growing international interest in the development of reusable spacecraft; at this time, only the superpowers of the era, the Soviet Union and the United States, had developed this capability. European nations such as Britain and France embarked on their own national programmes to produce spaceplanes, such as HOTOL and Hermes, while attempting to attract the backing of the multinational European Space Agency (ESA). While these programmes ultimately did not garner enough support to continue development, there was still demand within a number of the ESA's member states to pursue the development of reusable space vehicles. During the 1990s, in addition to the development and operation of several technology demonstrator programmes, such as the Atmospheric Reentry Demonstrator (ARD), the ESA were also working on the production of a long-term framework for the eventual development of a viable reusable spacecraft, known as the Future Launchers Preparatory Programme (FLPP).
Under FLPP, the ESA and European industrial partners performed detailed investigations of several partially-reusable launch vehicle concepts; the aim of the program was to prepare a suitable vehicle to, upon a favourable decision by the ESA's member-nations, proceed with the production of a Next Generation Launcher (NGL). A total of four launch concepts were studied, these were named as the Horizontal Take-Off (HTO) Hopper, the Vertical Take-Off (VTO) Hopper, the Reusable First Stage (RFS), and the liquid fly-back booster (LFBB). Each of these concept vehicles consisted of a reusable winged booster, which was paired with an expendable upper stage, to deliver a payload in geostationary transfer orbit (GTO).
The HTO variant of Hopper was designed for horizontal take-off, the first portion of which was to be achieved via a rocket sled arrangement. It possessed relatively conventional wing-body configuration, one atypical feature was the nose of the spacecraft, which possessed a deliberately low camber so that the required size of the elevons for desired trim functionality could be reduced while also resulting in an improved internal structure, such as in the accommodation of the nose gear. Aerodynamically, the HTO Hopper configuration features a rounded delta planform wing at a 60-degree leading edge sweep, which was matched with a central vertical stabilizer and a flat-bottomed underside for the purpose of maximising the spacecraft's performance during hypersonic flight.
The alternative VTO variant of Hopper was designed for vertical take-off, being launched conventionally via an expendable launch system. It features a relatively traditional slender missile-like body, but differed in the presence of a small delta wing at a 45-degree leading edge sweep and a central vertical stabilizer arrangement. In terms of its structure, the VTO Hopper possessed a circular cross section complete with a loft fillet on the underside of the craft which functioned to accommodate both the wings and bodyflap; it also featured a booster which was designed to carry on the payload upon the nose of the fuselage. Studies determined that both the HTO and the VTO Hopper concepts possessed a relatively similar reentry load environment.
The HTO version of Hopper was adopted for further development work under another ESA initiative in the form of the FESTIP (Future European Space Transportation Investigations Programme) system design study. During 1998, it was decided the design of Hopper fulfilled all of the established requirements. At this point, the spacecraft was to be composed of a single-stage reusable vehicle which would not attain orbital velocity itself. Hopper reportedly held the promise of delivering lower cost orbital deployment of payloads. An EADS spokesperson stated that a reusable launch vehicle like Hopper could halve the cost of sending a satellite into orbit, which reportedly had been determined to be around $15,000 USD per kilogram of payload in 2004.
The envisioned mission profile of Hopper would have involved several phases. The launch phase was to be achieved by using a 4 km magnetic horizontal track, which was to be purpose-built for the craft at the Guiana Space Centre in French Guiana, that would accelerate the spacecraft up to launch speed. Upon reaching an altitude of 130 km, the vehicle would fire an expendable rocket-powered upper stage in order to attain orbital speed; once it had achieved the necessary high and speed, it would have released its satellite payload, which would then independently ascend higher still to reach the desired orbit. Reportedly, Hopper was designed to deliver 7.5 tonne satellites into an orbit of 130 km above the surface of the Earth. Following the release of its payload, the vehicle would have then glided down in a controller descent; it was intended for the spacecraft to land at a pre-prepared island facility in the Atlantic Ocean, after which it would have been transported back to French Guiana by ship for further flights.
Multinational aerospace conglomerate EADS was responsible for project management on Hopper, as well as for the development of the entirety of the project's software-based elements. A number of other partner companies were also involved in the spacecraft's development. Reportedly, both the ESA and EADS had originally intended to complete development of Hopper between 2015 and 2020. After the first glide test using the Phoenix prototype on May 2004, no further updates on the programme were forthcoming; it is believed that work on Hopper has been eventually discontinued.
The Phoenix RLV launcher, the prototype of Hopper launcher, was developed and produced as a portion of the wider ASTRA programme of the German Aerospace Center (DLR), a €40 million project founded by the German Federal Government, EADS Astrium Space Transportation and the state Free Hanseatic City of Bremen. Reportedly, EADS and the State of Bremen invested at least €8.2 million and €4.3 million in the ASTRA programme, respectively. A further contribution of €16 million was sourced from partner companies on the programme, such as the Bremen-based OHB-System, the DLR and the Federal Ministry for Education and Research. During 2000, construction of the prototype commenced.
The Phoenix RLV prototype was 6.9 meters (23 feet) long, had a weight of 1,200 kilograms (2,600 pounds), and a wingspan of 3.9 meters (13 feet). During its design, an emphasis had been placed on minimising drag by making the vehicle as small as possible. The interior space of the craft's fuselage was occupied by various avionics and onboard system, providing navigation, data transfer, energy supply, and artificial intelligence functions to allow it to automatically perform its data-gathering mission. The final version of the vehicle was expected to be able to support the reentry forces, generated heat, and be able to glide from an altitude of 129 kilometers (80 mi). During April 2004, integration and systems testing work upon the Phoenix prototype had been completed.
On Saturday 8 May 2004, the Phoenix prototype underwent a large-scale drop-test at the North European Aerospace Test range in Kiruna, 1,240 km (770 mi) north of Stockholm, Sweden. The vehicle was dropped from a height of 2.4 kilometres (7,900 ft), having been lifted to the appropriate altitude by a helicopter. Following a guided 90 second glide, the prototype reportedly landed with precision and without incident. The primary aim of the test was to assess the glider potential of the craft. More specifically, the Phoenix explored various methods of performing automatic landings that would not involve any intervention by human controllers; as such, guidance was provided by cues from multiple means of navigation, including GPS satellites, radar and laser altimeters, as well as various pressure and speed sensors. According to EADS spokesmand Mathias Spude, the prototype had landed within three centimeters of the intended target.
In addition to the initial drop-test, further tests had already been scheduled, including three that were planned to occur during the following two weeks, which were to built towards the testing of more challenging landings, said to involve the spacecraft being dropped from different angles or orientations relative to the landing site. Furthermore, the project had an anticipated milestone of eventually releasing the prototype from an altitude of 25 kilometres within three years. In the long term, if successful and viable, the landing technology tested on Phoenix was to be incorporated into a follow-on re-usable vehicle, which was to be named Socrates. While not envisioned to serve as an orbital vehicle, Socrates was to be capable of flying at up to 10 times the speed of sound, as well as of performing very rapid turnaround times between flights as a stepping stone towards reusability. However, EADS noted prior to the flight that further flights of Hopper would be pending on the craft's performance during the initial flight. As no such further flights occurred, it can be assumed that the performance may not have been satisfactory and thus little value was seen in conducting further flight tests.
- McKee, Maggie. "Europe's space shuttle passes early test." New Scientist, 10 May 2004.
- "Launching the next generation of rockets." BBC News, 1 October 2004.
- "The Atmospheric Reentry Demonstrator." European Space Agency, October 1998. BR-138.
- G. Pezzellaa et al. 2010. p. 36.
- G. Pezzellaa et al. 2010. p. 37.
- G. Pezzellaa et al. 2010. pp. 38-39.
- "Possible Future European Launchers, A Process of Convergence - ESA Bulletin Number 97." ESA, March 1999.
- "PHOENIX: Future prospects in space transport through reusable launch systems." Airbus, 10 May 2004.
- "Phoenix Flight Day." Swedish Space Corporation, 8 May 2004.
- G. Pezzellaa, M. Marinia, P. De Matteis b, J. Kauffmann c, A. Daprad, C. Tomatisd. "Aerothermodynamic Analyses of Four Reusable Launchers in the Framework of ESA Future Launchers Preparatory Programme ." Aerotecnica Missili & Spazio, The Journal of Aerospace Science, Technology and Systems, Vol. 89, No. 1. January 2010. pp. 36–46.