Developing a “Water Engine” For Satellites! Pale Blue’s Strength in Confronting Social Issues [Consider the Future of Earth Together with Serika Ito #15]

Warpspace Inc.
7 min readJan 31, 2023

Even though we call it “Space Development”, there are various purposes, technologies, and missions. In this series, we consider the current situation and the future of space development together with our Chief Dream Officer (CDO), Serika Ito.

The theme of this 15th article is solving social issues through the social implementation of technology. We welcomed Ms. Emily Okuhara, who is in charge of public relations at Pale Blue, a startup that develops water-propulsion engines, and asked her why water engines are now attracting attention and what motivates her to work on solving social issues.

The Reason Why Water-Powered Satellite Engines are Attracting Attention

©︎Chuya Koyama/Kodansha

Serika: Nice to meet you, Okuhara-san! I was looking forward to hearing about your “water engine” today. Let me start by asking, what is a satellite propulsion system? Why do you use water as a propellant?

Ms. Emily Okuhara ©Pale Blue

Ms. Okuhara: The propulsion system is an engine that generates the thrust necessary for a satellite in space to change its orbit or maintain its course. If we compare it to the human body, it is like a heart function.

Most of the conventional satellites use hydrazine or xenon as a propellant. However, these propellants are highly toxic, and their handling costs do not match those of small satellites. In addition, hydrazine and xenon must be stored under pressure, which makes the tanks larger and more difficult to install in small satellites. Xenon, a noble gas, was also in short supply, making it impossible to meet the demand for building satellite constellations of tens, hundreds, or even thousands of satellites.

Image of a Water Engine ©︎Pale Blue

So we started developing a water engine that has enough thrust to blow away a tissue, so it’s not quite enough to launch a rocket from the ground, but it can power a satellite in space!

Serika: I heard that the water engine was also used in the EQUULEUS, a Japan micro probe aiming for the moon, which was launched in November 2022 in space with the ARTEMIS I Orion spacecraft!

Ms. Okuhara: The founding members of Pale Blue were involved in the development of the EQUULEUS water engine. It was the world’s first engine using water as a propellant to successfully control orbit beyond low Earth orbit!

Pale Blue’s water engine has already been developed, ground tested, and delivered to customers. We are waiting for more and more satellites equipped with the water engine to be launched. We will continue to accumulate space demonstrations to become a trusted company!

Hybrid Engines that Can be Used for Different Purposes

Serika: Are there other companies besides Pale Blue developing water engines?

Ms. Okuhara: Four companies in the U.S. and Europe are developing water engines that heat water and release steam through nozzles.

Steam-type engines have high thrust, but their fuel consumption is not very good. On the other hand, ion engines have less thrust than the steam type but have superior fuel efficiency. For example, water vapor can be used when higher thrust is required, such as for orbit insertion or orbit change, while ion engines can be used for orbit maintenance. This is how you can efficiently use limited propellant.

Serika: How is the attention from the market?

Ms. Okuhara: Installing a propulsion system will expand the range of satellite applications, and we find an increase in demand. The global emphasis on SDGs is becoming more active in the space industry as well, and there seems to be a movement among international space agencies and space development companies to look for environmentally friendly green propellants. Recently, the number of people who know about Pale Blue seems to be increasing.

When I tell people that we use water as a propellant, they are surprised and at the same time, the conversation about introducing the technology is quickly progressing. I was one of those surprised by the water-powered engine!

Image of a satellite equipped with a water engine ©︎Pale Blue

I Want to Challenge Myself Because it is Difficult. Curiosity with a Researcher’s Spirit

Ms. Okuhara: I got to know about Pale Blue through the news of the Series A round of fundraising in October 2021. At the time, I was working for a company in the automotive industry, and the fuels for engines were gasoline, diesel oil, and electricity. That’s why I thought, “No way!” that they could run an engine on water.

It was interesting, and when I was researching Pale Blue, I saw that they were looking for a public relations position, which I had experience in at my previous job, so I immediately applied and joined the company in February 2022.

Serika: How do you feel now that you have joined the company?

Ms. Okuhara: At my previous job, my main duties were to maintain and improve the communications activities that had already been established, but at Pale Blue, a start-up company, most of the work is built up from scratch. Since I travel overseas almost once a month, I learned a lot from discussionswith executives, engineers and media from across the globe!

Serika: I heard that Pale Blue was founded as a spin-off of a laboratory at the University of Tokyo. Is it still difficult to take the technology created from research and sell it as a product?

Ms. Okuhara: Yes, it is. There is a gap between research and commercialization. The improvements and customer requests that come up in the course of product development are not necessarily bottlenecked by physical phenomena. So, in addition to members who are accustomed to research and development in the aerospace field, engineers from different industries who have experience in product development in the private sector have come together, and we are gradually accumulating know-how.

It is challenging to sincerely meet and respond to the needs of our customers. However, it is rewarding to realize that we are contributing to solving social issues, such as the introduction of water engines that enable satellites to maintain their orbits and extend their lifespan, which in turn leads to the reduction of space debris!

Serika: What do you think is the source of your motivation to take on the challenge of solving social issues?

Ms. Okuhara: The founding members of Pale Blue are very curious, and they are the type of people who dare to take on difficult challenges and overcome them. They enjoy the process of solving social problems that are complicated and intertwined with various events.

The founding members said that when the company grows, it will lead to the creation of jobs for engineers, redistribution of wealth, and the creation of a cycle that will further invigorate research and development.

They also make time to share their thoughts on the business and the company itself with all employees, and I believe that we are able to keep our motivation high because of the proximity between us. The fact that we often have casual conversations and go out to eat that have nothing to do with the business within the company is also important in building the organization.

Inside the company ©︎Pale Blue

In the Future, will there be Gas Stations on the Moon?

Serika: You mentioned earlier that more and more satellites equipped with Pale Blue’s water engine will be launched in the future.

Ms. Okuhara: We have a vision of creating a “space mobility infrastructure” based on water. To achieve this vision, we are first building a mass production system for water engines so that we can receive orders for large-scale projects.

So far, we have targeted hand-held CubeSat satellites and 50 kg-class satellites, but we are also planning to conduct R&D on water engines that can be installed in 100 kg-class satellites and larger, for which demand is now growing dramatically.

Serika: If water can be used as a propellant, then we may be able to refuel on the moon!

©︎Chuya Koyama/Kodansha

Ms. Okuhara: That’s right. That’s the advantage of using water, and that’s where our dreams take us! In the future, if we can build a space gas station and refuel it, satellites may be able to explore back and forth between deep space and relay stations.

The name Pale Blue comes from the “Pale Blue Dot,” a pale blue photograph of the Earth taken by NASA’s solar system probe Voyager 1, and it reflects our desire to create a new industrial structure for research and development on a grander scale than just orbiting the Earth.

The photo was taken by Voyager 1 in 1990 from a point about 6 billion km away from the Earth. The small dot in the center-right is the Earth. ©︎NASA

Serika: That is a wonderful company name that fits your vision. If we can refuel satellites in space, we may be able to aim for deep space, which mankind has yet to reach. Thank you very much!

For the 15th installment of our conversation project with Astronaut Serika, we had Ms. Emily Okuhara of Pale Blue and asked her about water engines and the social implementation of technology born from their research and development.

The next guest will be Daniel Faber, CEO of Orbit Fab, which develops refueling services for satellites in orbit, about market trends and future prospects. Stay tuned!



Warpspace Inc.

Warpspace develops “WarpHub InterSat”, an optical inter-satellite data relay service. We will realize this service for LEO Sat operators by 2025.