PHOENIX: Future prospects in space transport through reusable launch systems

Sagging commercial satellite markets and distorted competitive conditions in the launch services sector show that conventional, expendable launch vehicles need to be adjusted to meet the market's demand for improved profitability, efficiency and versatility. Studies prove that Europe's position in the global market and sustained, autonomous European access to space can only be ensured by drastically lowering current transportation costs. This, however, can be achieved by using reusable launch systems.

EADS SPACE Transportation is taking a very active role in the research, technology and development efforts that will support improvements to current launch vehicles and the development of brand-new launcher families. This work covers both conventional, expendable launch vehicles and the planned partially or totally reusable launch vehicles.

For the moment, however, it is still too early to predict what type of launch vehicle will be carrying our payloads aloft in 20 years. EADS SPACE Transportation is currently studying several technological demonstrators such as PHOENIX, Pre-X, Ares or Themis. In doing so, technologies will be prepared that are indispensable for the development of tomorrow's space vehicles.

With PHOENIX, EADS SPACE Transportation concentrates on aspects such as flight characteristics and automatic landing capabilities of such a future reusable space vehicle. PHOENIX is a German project that is intended to strengthen Germany's position in view of the forthcoming Europeanisation.

As early as 1994, the European Space Agency ESA commissioned Dasa (today's EADS SPACE Transportation) within the Future European Space Transportation Investigation Programme, FESTIP, with the development of the most cost-effective and most efficient concept of a reusable space transport system. In 1998, a definite decision was made: the HOPPER concept met all requirements. Development of the system was envisaged in order to be able to offer favourable European launch services in the long run.

In order to be able to reduce development costs, a flight demonstrator is being developed and built first. This flight demonstrator, which was given the name PHOENIX, is a one-seventh scale model of the future space transport vehicle HOPPER. The vehicle particularly serves for acquiring real flight and landing attitude data that cannot be simulated. Since February 2000, EADS SPACE Transportation has being building the PHOENIX vehicle. Within the German development programme ASTRA (selected systems and technologies for future space transport system applications), Deutsches Zentrum für Luft- und Raumfahrt (DLR) appointed EADS SPACE Transportation prime contractor for the technology demonstrator. PHOENIX is financed with the support of the state of Bremen and out of own funds of EADS. The flight demonstrator made in Bremen is indispensable for flight testing. Engineers will be provided with information, which cannot be achieved by means of wind tunnel tests or computer simulations. This procedure will also allow to optimise the future space transport system as quickly as possible and thus reduce development time considerably.

With a span of 3.90 metres, wing and control surfaces of the PHOENIX flight demonstrator, an aluminium structure having a weight of about 1,000 kg, were kept as small as possible to minimise drag during automatic touchdown. During the test flights, the PHOENIX fuselage will be used to accommodate avionics, navigation, data transfer and energy supply systems.

Integration and technological system testing were completed in April 2004. In 2003, PHOENIX was built by EADS and underwent extensive testing in the Deutsch-Niederländischer Windkanal (DNW - German-Dutch Wind Tunnel). Testing completely developed in line with expectations. Initial preparation of the flight testing campaign started in Linköping, Sweden, in September 2003. Owing to the fact that later on a heavy-duty helicopter would tow PHOENIX to an altitude of 2,400 metres and then release it for automatic landing demonstration, it was required to qualify an appropriate hoisting sling first. To this end, a PHOENIX mock-up was attached to the hoisting sling beneath the helicopter to ensure safe landing of the helicopter after having released the vehicle.

The next step was taken at Lemwerder Airport near Bremen in April 2004. PHOENIX has been provided with comprehensive artificial intelligence, which shall contribute to precisely keep the vehicle on the runway and to automatically apply the necessary track corrections. To prove proper functioning, the demonstrator was towed to a speed of about 150 kilometres per hour and then released. During roll, PHOENIX corrected track deviations detected by the navigation system autonomously by means of the steerable nose wheel. Remote control was not possible. At the same time, automatic braking during roll was tested and adjusted.

The objective of the PHOENIX flight testing is to find out how the vehicle behaves during a steep landing approach and subsequent automatic touchdown.

Flight testing is scheduled for May 2004 and will take place at the test airport of Vidsel in northern Sweden near the Arctic Circle. The airport operated within the North European Aerospace Test Range, NEAT, provides best conditions for such test flights.

In March, PHOENIX was carried by truck to northern Sweden where several captive-carry flights were made. With PHOENIX suspended beneath, a helicopter flew along a specified course without releasing the vehicle. During these flights, the aerodynamic characteristics of the helicopter-PHOENIX configuration as well as all onboard systems were tested successfully. After analysis of the test data gained, the engineers gave the go-ahead for the flight test campaign in May 2004.

EADS engineers will put PHOENIX into operation early in May. All systems will be checked first and PHOENIX will be prepared for flight. After a final captive flight, the exact date of first flight will be fixed depending on the data gained, weather conditions and other criteria. At present, first flight is scheduled for 6 May 2004 in the morning.

A special heavy-duty helicopter will tow PHOENIX in the hoisting sling to an altitude of 2,400 metres, which, including the time required for navigation system adjustment, will take about 30 minutes. PHOENIX will be released at an airspeed of 144 kilometres per hour. During the free fall phase, the vehicle will accelerate to a speed of 424 kilometres per hour. At an altitude of a good 500 metres it will then automatically reduce descent speed to touch down at a speed of 255 kilometres per hour. Sensors, the GPS-based navigation system as well as the telemetry and telecommand system will control, monitor and record the mission. The free flight will last about 90 seconds.

Should the first flight be successful, three more flights are planned during which the trajectory will be changed. These flights are intended to acquire as many data as possible.

EADS SPACE Transportation is responsible for project management as well as for the entire software equipment of the system, in which Deutsches Zentrum für Luft- und Raumfahrt, DLR, Braunschweig, is involved. Other partners are Aljo (construction and manufacture of the aluminium airframe), Heggemann Aerospace (landing gear), Wittenstein (actuators/flaps), OHB-System (flight test instrumentation) and RDE Rheinmetall Defence Electronics (ground roll tests). Also involved is DLR Moraba with the development of telemetry and data transfer systems and by supplying the parachute recovery system.

EADS SPACE Transportation has already invested € 8.2 million out of own funds in the PHOENIX project, in which the state of Bremen is also financially involved with an amount of 4.3 million euros. Partner companies such as Bremen-based OHB, DLR and the Federal Ministry for Education and Research are also contributing to the 16 million euros required for the project.

ASTRA is the German contribution to the European development of reusable transport systems. PHOENIX is an integral part of ASTRA. Co-ordinated by DLR and funded to the tune of 40 million euros, the ASTRA programme is intended to gain the necessary system competence for a new space transport system. Programme activities cover a wide spectrum, from ground facilities to payload delivery mechanisms and the creation of maintenance instructions for the transport system. In addition to EADS SPACE Transportation and DLR, companies such as MAN-Technologie, OHB-System and Kayser-Threde, the Centre for Applied Space Technology and Microgravity (ZARM) at the University of Bremen as well as three special research departments of the Technical Universities of Aachen, Munich and Stuttgart are involved in the programme.

In its HOPPER concept, EADS SPACE Transportation has gone for an autonomous transport system that is noted for its high degree of reusability and considerably lower mission costs. The unmanned HOPPER will be launched horizontally on a skid sled running on a four kilometre long track. With a length of more than 50 metres and a wing span of more than 27 metres, the vehicle itself is quite compact. Due to its features, Hopper is intended to transport payloads to orbit at considerably lower cost than conventional transport systems.

HOPPER is designed to carry payloads of up to 7.5 tons – as a rule a satellite on an upper stage booster. At an altitude of 130 kilometres, HOPPER will deploy the payload from its tail and then automatically return to Earth while the payload proceeds independently to its destination in geostationary or low-earth orbit, such as the ISS for instance. HOPPER will be launched from the European Space Centre in Kourou, French Guiana, and, after a flight across the Atlantic Ocean, will land on European territory (e.g. islands in the Atlantic). In comparison to the Shuttle, which orbits the Earth several times before re-entry, HOPPER is indeed a more efficient system. HOPPER can be transported back by ship. Should the ESA decide in favour of the HOPPER concept the space vehicle will be ready for use by the year 2020.

Bremen, May 2004

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