Launch vehicles, or rockets, are essential for putting satellites and space probes in space. Once they have served their purpose, they are usually removed. But with the annual number of new satellites expected to grow fourfold in the next decade, researchers are now developing more sustainable and less expensive reusable launchers.
The first reusable launch system, where some or all of the components are recovered, was NASA’s space shuttle, in use from 1981 to 2011. All of its parts were reused, except for the external fuel tank that would burn up in the atmosphere. But maintenance costs were high, leading to the view that it was cheaper to use expendable systems.
Ansgar Marwege of the German Aerospace Center (DLR) and his colleagues think that reusable rockets can be profitable if they land upright. “The space shuttle was very complex because it had wings, etc.,” Marwege said. “With a vertical landing, you want to simplify all of that.”
One of the advantages of landing upright is that the load during takeoff and landing is similar, which is easier in terms of design. Although more fuel is required for the descent compared to other landing setups due to braking maneuvers, Marwege says it would have little impact on overall cost as fuel is relatively cheap.
Marwege and his team, along with other research and industry partners, are investigating the key technologies needed to land a rocket vertically after a mission as part of the RETALT project. They are looking to land a rocket using retro-propulsion, where the vehicle decelerates by generating thrust in the opposite direction of its movement. They will also examine how to drive a vehicle during landing. Since the base of a rocket is expected to heat up, one of the project partners is designing cork thermal protection.
Launchers
The team has concepts for two different types of pitchers. One is a heavy-lift launcher that can carry a payload of up to 14,000 kg, like a weather forecast satellite, to an orbit about 36,000 km above the Earth’s surface . The second design is for smaller loads of up to 500 kg that must be transported over distances of up to approximately 140 km . “This setup could theoretically be used for zero-gravity experiments or demonstration flights,” Marwege said.
So far, the researchers have started all the technical work, such as the initial designs for the landing legs. In the next year, they will conduct structural tests and wind tunnel experiments to test aerodynamic behavior using scaled-down models of their launchers. An experiment will test rocket motors in the wind tunnel using hot combustion, which is challenging and not done often. However, the use of hot gases better mimics how engine power is generated in real life.
In addition to reducing costs, Marwege and his colleagues hope that their technologies will have a positive environmental impact. Expendable systems create waste when they break down into the atmosphere, where some parts fall to the ground while others remain in space. Reusable systems will pollute the environment and space much less, according to Marwege.
Currently, in Europe, there are no launchers available to put small satellites into orbit.
When a small satellite needs to be transported into space, it is usually found in a heavy launcher with a larger satellite. But that means the departure date and orbit are chosen by the contractor that ships the largest load.
“It’s like a bus going a little bit out of its orbit, so they need a propulsion system to get to their desired orbit,” said Xavier Llairo, co-founder and COO of Pangea Aerospace in Barcelona, Spain.
Service
Currently, the US-New Zealand company: Rocket Lab offers a small satellite launch service . Although it allows for personalized service, it is more expensive than carpooling in a heavy launcher. And Europe is determined to have its own small rockets so that it can control its access to space. “It is important for geostrategic reasons,” Llairo said. “And since it is a new market, it would be great to create growth and provide opportunities in Europe.”
For a project called RRTB, Llairo and his team aim to create a small rocket that is profitable and can be reused at least ten times. They are developing a novel landing system using electrically ducted fans, a propulsion system currently used in drones and UAVs. It allows for a smooth and precise landing, which is important if the system is to be reused.
“The technology is already proven and exists in other sectors, so it is not very expensive,” Llairo said.
The main engine is not used to landing, which limits thermal stress and increases reusability.
The project, which started last month, is now looking at how to make fuel tanks reusable, as they are expensive components in a rocket. The team is also beginning to investigate how to control the vehicle during re-entry into the atmosphere using simulations. It’s a challenging part of the mission due to the weight and high speed and will require generating some lift or finding a way to slow the vehicle down. “We are analyzing different scenarios and we will choose the most promising one,” continues Llairo.
In addition to transporting small satellites into space for scientific, commercial and civil uses, Llairo believes that some of its components could also have other applications . The lightweight aerospike engines they are developing, for example, could also be adapted as propulsion systems for satellites in space. And its landing system could be used to provide aid to disaster areas. “Right now, you have planes with parachutes to land (supplies), but our system could be used to have a more precise landing,” the expert clarifies.
Having less environmental impact is one of its objectives as well. In addition to the greener credentials obtained by being reusable, the rocket will use liquid oxygen and liquid methane as propellants, where 80% of the emissions will be simply water. And your aerospike engines should be about 15% more efficient than current designs. “We believe that (sustainability) is the way forward in this market,” says Llairo. “In 10 or 20 years from now, it will be absolutely common.”
Original article
This article was originally published in Horizon, the EU Research and Innovation Magazine
