Electrolysis Propulsion

Electrolysis Propulsion Operation

The centerpiece of the Cislunar Explorers program is the use of water as a green, dense, and effective propellant. Hydrogen and oxygen have been used in rockets from the early days of space exploration, including the upper stages of the Saturn V used in the Apollo program. Historically, the two are stored separately on the launch vehicle or spacecraft, as cryogenic liquids. To carry enough hydrogen, in particular, necessitates the use of extremely high pressures and extremely low temperatures. It takes a complex apparatus to achieve this: pumps, pressure vessels, and heavy insulation to keep the storage units cold.

There is another way. Zapping H2O with electricity can overcome the bond between hydrogen and oxygen, decomposing the liquid into a gaseous mixture that readily combusts. Instant rocket, just add water!

A successful demonstration of electrolysis propulsion opens the door to future spacecraft gathering water from the surface of distant worlds to refuel themselves. The abundance of water throughout the Solar System has become increasingly clear in recent years. Our mission will demonstrate the untapped utility of all this water, along with robust, inexpensive supporting technologies. Water has been vital to exploration and settlement here on Earth; we believe it will be equally indispensable in space.

Thermal Vacuum Chamber, used to test our hardware in the extreme environments of space.

We are engaged in ongoing, extensive performance and environmental testing of the electrolysis propulsion system. Our electrolysis propulsion thruster, pictured below, has fired hundreds of burns in the thermal vacuum chamber here at Cornell. It's made of a 3D printed titanium alloy, and has weathered the simulated extremes of space inside our thermal vacuum chamber. After years of tweaks to the design and operational procedures, we are fabricating a new generation of thruster components to form the centerpiece of our final spacecraft.

3D Printed Titanium electrolysis propulsion thruster

Symbiotic Subsystems

Our shiny new spacecraft hull

The Cislunar Explorers spacecraft leverage simple physics and symbiosis between several subsystems. The concept is a single rectangular 6U structure that splits into two L-shaped spinning spacecraft with a spring loaded separation mechanism. Each spacecraft has a tank of water in the bottom of the “L,” off-center from the spin axis. The spacecraft spin helps separate the combustible gas electrolyzed from the inert water like a centrifuge.

We mount the spacecraft electronics on the faces of the propellant tank, which will serve as a heat sink for waste energy produced during the mission. This helps keep our electronics from overheating and our water from freezing. Either would cause the end of the mission.

Symbiotic subsystems greatly simplify the design and operation of the spacecraft: key aspects of the mission work for each other’s benefit instead of needing to be solved independently. Synergy reduces complexity, and a streamlined spacecraft is a safe and inexpensive spacecraft.

The splitting of our two 3U spacecraft from each other.

Optical Navigation

Optical Navigation Geometry Example

Celestial navigation is an ancient art. Explorers have found their way by the Sun and Moon for millennia. The Cislunar Explorers will be using a similar technique to tackle a new problem in an old way.

The motion of the Sun, Earth, and Moon are very predictable. One can look up the future motion of these bodies, or "ephemerides," many years in advance. We use several inexpensive cameras to take images all around our satellite as it zips through cislunar space, and compare the apparent size and position of the Sun, Earth, and Moon with their known ephemerides at the time each picture is taken. Using our knowledge of where the three bodies *are*, together with where the *appear to be* from the spacecraft's point of view, we can puzzle together the spacecraft's position and attitude: the one place in space where it could see the view that it sees, at the time that it sees it. In this way, we are able to find the spacecraft's position down to within tens of kilometers.

Attitude determination by reference to celestial bodies has been in use on spacecraft for a long time. Star trackers and sun sensors, for example, can determine which way a spacecraft is pointing. But they can not tell where in space it is located.

Our method is uniquely able to simultaneously determine position and attitude on board a spinning spacecraft. This technique can function with any three celestial bodies, at least one of which is resolvable as a discrete disc; these need not be the Sun, Earth, and Moon. In the future, another possible application of this technology could be exploring the moon systems of gas giants.

Optical Navigation Cameras

Optical Navigation Image Examples

Accessible Design

Raspberry Pi usage

Wherever possible, the Cislunar Explorers design makes use of inexpensive, off-the-shelf components. Our flight computer is a Raspberry Pi Model A+ (512 MB model). Our power subsystem was bought completely off the shelf rather than made in house. Certain components, such as 3D printed titanium and high efficiency solar panels, are unavoidably expensive, but the cost of both is dropping every year.

Our ultimate goal is to make space exploration accessible for anyone. By choosing inexpensive components, open-sourcing our design, and publishing our extensive test results, we will make all our lessons learned from the design process available for the world to build on. In doing so, we hope others will be able to follow our success--but we need your help to succeed, first.