Modern life would hardly be possible without satellites. Many of the comforts people on Earth rely on today depend heavily on what’s happening high above their heads—from monitoring wildfires, deforestation and sea surface temperatures to new mobile technologies such as 5G in hard-to-reach areas.
A sign of the growing trend is the recent wave of cheaper miniature satellites sent into close orbits of 500-1,000 kilometers above the Earth’s surface, such as those by Elon Musk’s SpaceX and UK-based OneWeb.
Less is more
Some of these satellites, the size of a shoebox or even smaller, manage to monitor the entire land area of the planet or provide unprecedentedly detailed information. Over the next decade, more than an average of 2,500 such satellites are expected to be launched each year.
To reach space economically, small satellites often have to share the journey with larger rockets. Designing smaller rockets would enable faster and more personalized access to space and open the market to a wider range of specialized service providers.
“Small satellites can travel on large launch vehicles, but there are problems, such as the time it takes to reach orbit, because you have to make your reservation so far in advance and find a shuttle aimed exactly where you want your satellite to go.” says Xavier Leiro, chief commercial officer and co-founder of Pangea Aerospace in Barcelona, Spain. “Companies that launch such technology need precise access to outer space.”
The European Union-funded RRTB project, led by Pangea, is investigating cost-effective ways to launch small-sized rockets that can carry payloads of up to 500 kilograms into space. The hope is to have a flight-ready engine available by 2025.
The key to this is finding ways to reuse microlaunchers by minimizing the damage they suffer on re-entry into the Earth’s atmosphere and by ensuring a safe landing. This would also be much more environmentally friendly compared to single-use media.
“Through reuse, you can reduce the investment, use less production materials and achieve a higher launch frequency,” says Leiro.
According to the RRTB project, whose three-year term expires this month, Europe does not currently have a proven method to achieve this goal.
The first degree
The RRTB focuses on the reuse of the first stage of the rocket located in the base. This stage provides most of the thrust immediately after launch, before it separates and falls to Earth, most often in the ocean. Now with less weight, the other stages of the rocket move forward and carry the payload to orbit.
The first stage can be damaged not only by its high-speed fall through the Earth’s atmosphere, but also by salt water. The difficulty and expense of finding and returning the rocket to the spaceport may prove unwarranted.
“Getting into the ocean makes the possibility of reuse very, very small,” Leiro says.
The solution, he says, lies in finding a way for the first stage to safely return to Earth’s atmosphere and land on a dedicated station near the spaceport or on a floating barge.
In the meantime, the rocket design must allow for the carriage of a large enough payload to make the operation economically viable.
To find ways to reduce damage to microlaunchers during re-entry and landing, the RRTB team tested a scale model of a small-sized rocket in a wind tunnel.
According to Leiro, the optimal goal for smaller launch vehicles is to avoid re-entry engine ignition. This will allow a larger initial payload to be carried and reduce the weight of fuel they must carry.
The team encountered difficulties with the traditional bell-shaped nozzle around the engine and subsequently found that the conical shape had more potential. This “air wedge” nozzle helps distribute the heat in a way that reduces the damage the vehicle takes.
“Atmospheric penetration is smoother,” Leiro says. “This applies to both smaller and larger launch vehicles. The find was unexpected because we weren’t looking for it deliberately.”
Leiro says that while the fuel consumption of wedge-shaped engines is lower than that of traditional engines, their benefits have so far not been able to compensate for the complexity and cost of their design, including difficulties in cooling them. However, techniques such as 3D printing used by Pangea are making this type of engine more affordable.
“Wedge technology will change how we get to space and how we get back to Earth,” says Leiro. “It is a key factor in the reusability of missiles.”
He also says that the engine the team intends to use is powered by naturally occurring methane.
Another goal is to make individual parts of the missile with improved reusability, for example using aluminum-based materials for the tanks.
“To be economically viable, as many rockets as possible must be landed safely and as many of their components as possible must be reusable,” Leiro said.
Ready to take off
While the RRTB focuses on rocket reuse, UK aerospace company Orbex is preparing to debut its own lightweight and environmentally friendly micro launch vehicle.
As part of the European Union-funded PRIME project, in May last year Orbex unveiled the prototype of its 19-meter rocket, intended to be Europe’s first small-satellite micro-orbital rocket.
The rocket is designed so that parts that do not burn up in the atmosphere can be collected and reused. While the company is not yet revealing exactly how this will be done, a representative of Orbex said that the method will be “completely unknown before”.
The company hopes that the Prime rocket will be able to take its maiden voyage as early as this year, although certain prerequisites have yet to be met, such as obtaining a launch license.
“We have already sold launch reservations to several commercial satellite providers, but we have not yet announced the date of the first launch,” said Orbex CEO Chris Larmer. He was also the coordinator of the PRIME project, which lasted three years until June 2022.
A greener rocket
The rocket will use pure biopropane fuel, obtained as a by-product in the production of biodiesel, which is derived from sources such as waste vegetable oils and used cooking oil.
It will be combined with liquid oxygen, “cryogenic rocket fuel” – a gas cooled to below freezing and condensed into a highly flammable liquid.
Through these measures, the rocket could reduce its carbon emissions by up to 96 percent compared to smaller, fossil-fueled launch vehicles.
“Orbex Prime aims to be the world’s greenest space rocket powered by renewable biofuel,” says Larmer.
The tanks are made of carbon fiber, which combines great strength and light weight.
Orbex predicts that Prime weighs about 30% less than traditional carriers, thus providing the high efficiency and performance that are vital to small satellites. The rocket is designed to leave no debris either on Earth or in orbit.
The company expects to be able to launch up to 12 rockets a year from a spaceport in Sutherland on the north coast of Scotland. The facility is also expected to be carbon neutral during both construction and operation.
It also benefits from its relative proximity to Glasgow and its booming space industry — the city is Europe’s largest producer of satellites. Orbex believes that all this will offer the right prerequisites to help key individuals in the region gain access to space.
“The satellite industry and its needs for carriers to put satellites into specific orbits has grown in recent years and continues to grow exponentially,” says Larmer. “This creates a huge need for specialized and sustainable launch vehicles.”
The research in this article was funded by the EU. This article was first published inHorizonthe EU research and innovation journal.