With the global launcher market coming out of an unsettling time, space agencies are tentatively exploring what methods of getting satellites into space could replace current technologies in the next 20 years.
The craft are experimental vehicles and concepts which are being evaluated in order to test out various different technologies required for the various stages of launches.
Space agencies have technologies for next generation launchers
Since Nasa's shuttle disasters, the future path to space for rocket launchers has been cloudy and uncertain, says analyst Luisa Innocenti from Esa's Future Programmes.
"We have gone through a period where launcher vehicle future was linked to reusable vehicles," she explains.
"In Europe and the States, there was lots of work to prepare these new vehicles, but now the situation is changing everywhere."
Dump it or use again?
The impact of the shuttle disasters has been damaging for the US. Nasa's Space Launch Initiative has been subsumed by a wider Next Generation Launcher Technology (NGLT) programme.
But, she says, the US is concentrating on military applications which means not a great deal of information about the programme is in the open.
The big issue for Esa is whether the fleet of launchers that will eventually replace Ariane, Soyuz and Vega, will use expendable - as they do now - or reusable technologies.
As well as the technological considerations, the decision will also be swayed by the wider market conditions, explains Antonio Fabrizi, head of Esa's Launchers Programme.
"Whether we go with full reusability or partial reusability, or again to expendable, is very much dependent on the market because the advantages of reusability is a direct function of the frequency of use."
The more it gets used, the more cost effective it becomes.
"On the other side, if the market remains low, then the next generation launcher will again be expendable.
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"We have also to see another aspect - that is, there is a lot of expectation on what will be the future of exploration.
"This is something that is soon to be analysed to verify what is expected from us, from the launcher providers, in terms of performance."
Europe knows how to build expendable vehicles (ULV), but technical expertise needs to be developed to understand how to build and operate reusable launcher vehicles (RLV).
After a lengthy process which ended in February 2004, Esa was granted approval for their exploratory programme, the Future Launcher Preparatory Programme (FLPP).
This is the multi-million pound EU-funded strategy which will let Esa decide which future launcher technology it should develop after Ariane 5 retires.
The main technological research and development for future launchers needs to include:
With the exception of Vega, which will be in action by 2007, the concepts below are just some of the vehicles which are testing out the technologies under consideration.
- System studies to define the architecture for future space transport
- Rocket propulsion
- Materials and structures
- Launcher health management systems
- In-flight experimentation.
Whatever is chosen, a decision on the new launcher will not be made until 2013, and not operational until 2020.
In three years' time, a new European rocket called Vega will go into action for Esa.
Although satellites are getting heavier, there is still a demand to launch smaller satellites, which weigh in at about 300kg to 2,000kg.
Many of these are sent into polar and Low Earth Orbits (LEO) for scientific and Earth observation missions.
Vega will use the same launch facilities as the Ariane vehicles in Kourou, French Guiana.
At 3m in diameter and 30m in height, it is a single-body launcher, with three solid-propulsion stages. It has an extra liquid-propulsion upper module for attitude and orbit control.
Unusually for a smaller launch rocket, it will be able to carry more than one satellite into space.
STAGES TO SPACE
There are several options which are being explored to decide which parts of a rocket should be reusable, whether it be the whole rocket, the expensive boosters, or other stages.
There are two main options under consideration:
- SINGLE STAGE TO ORBIT (SSTO): Essentially, a rocket is launched in one piece and comes back in one piece. According to Esa, it is unlikely that this option will be chosen for Europe's launchers.
The Hopper is a more likely variation on the SSTO concept, although it does not actually fly to orbit.
- TWO STAGE TO ORBIT (TSTO): This is a two-stage re-usable launch vehicle with rocket propulsion. Ariane 5 is already an example of a two-stage vehicle.
In a TSTO system, the orbiter releases its payload in orbit and then re-enters to Earth's atmosphere and lands.
Ultimately, the low-cost Hopper is the concept that meets most of the requirements for the next generation of European launchers.
It is an unmanned, reusable vehicle which is launched horizontally from the Equator as opposed to the vertical launches that we commonly see.
The "skid sled" would run along a 4km track. The vehicle would have a 27m wing span and would be 50m long.
It would be designed to heft a typical 7.5-tonne satellite into orbit at an altitude of 130km.
The satellite, or whatever the payload would be, is launched from its tail, after which Hopper would return back to Earth. Meanwhile, the payload would travel on to its appropriate orbit on its own - either LEO or GEO (Geostationary Earth Orbit) - depending on its mission.
The craft would land back on European "soil", most likely an Atlantic island.
Nasa's shuttles do a similar job, but they orbit the Earth several times before coming back down.
The Hopper, however, would not need to do that and could be transported back to base by sea.
REUSABILITY VEHICLE (PHOENIX)
Phoenix is a German project which is a one-seventh scale model of the Hopper concept vehicle.
Essentially, it is a flight simulator which has been built to keep the development costs down.
The kind of data it provides is invaluable for engineers, because it lets them examine results that they cannot get from experiments in wind tunnels or by computer simulations.
The aluminium vehicle has a wingspan of 3.9m and weighs in at about 1,000kg.
Its fuselage during testing carries avionics, navigation, data transfer and energy supply systems.
It is also packed with artificial intelligence which helps it keep to the runway and to automatically correct itself if rolling and other anomalies happen.
INTERMEDIATE EXPERIMENTAL VEHICLE (Pre-X)
Pre-X is a vehicle designed to test re-entry technology and capabilities.
It is what is called an "intermediate experimental" demonstrator that is used primarily to test hypersonic aerodynamics, hot structures and thermal protection.
EUROPEAN EXPERIMENTAL RE-ENTRY TEST BED (Expert)
Similarly, Expert is an in-flight aerothermodynamic research programme.
It is not meant to be a concept for a space transportation system or vehicle design.
Its function is to help scientists and engineers test and gather hypersonic data to use in their aerothermodynamics design tools.
The development of improved aerothermodynamics will be critical in future launcher and re-entry programmes.