 Humanity has always looked up at the stars with nothing but a deep desire to travel to them. For decades, we have yearned to sail through the great cosmic ocean, unlocking mysteries of other worlds. But to conquer the cosmos, we first need a way to travel across it. And with modern space technology, we have a long way to go before this becomes a reality. One big obstacle between humans and their space empire is fueling the rocket to travel such fast distances. An intraplanetary trip will require a spacecraft to carry an extremely large fuel supply, which may not be a viable option in the long term. So what are our alternatives? Well, one is fusion-powered rockets, especially those powered by Helium-3. But then that raises the question, will Helium-3 meet the energy needs to fulfill our space colonizing dreams? To understand where we currently are, let's take a look at NASA's Artemis-1. Artemis-1 is the beginning of NASA's long-term goal to put a sustained human presence on the moon. The propulsion for Artemis-1 involves using over 750,000 gallons of ultra-cold liquid hydrogen and oxygen. Combining the hydrogen and oxygen results in a violent combustion reaction, with temperatures north of 2700 degrees Celsius, this reaction produces nearly 8 million pounds of thrust, which is the equivalent weight of 16 Boeing 747 aircrafts. Quite impressive indeed. But how would Helium-3 stand up the competition if used as a fuel source? A Helium-3-powered rocket would work by fusing together deuterium, an isotope of hydrogen, with Helium-3. A kilogram of Helium-3 in deuterium fuel can produce nearly 4.2 million times more energy than a kilogram of hydrogen. Because of this fuel efficiency, a Helium-3-powered spacecraft could carry significantly less mass than its traditional chemical propulsion-based counterparts, even when accounting for the weight of the Helium and deuterium, as well as the fusion engine. This weight reduction is really handy when we are talking about interplanetary trips. It gets even better. The products of Helium-3 and deuterium fusion are Helium-4 and Neutron, compared to other types of fusion reactions. Helium-3 and deuterium releases far less energy in the form of neutrons, making it less radioactive. Additionally, because most of the energy emitted from Helium-3-deuterium fusion is in the form of charged particles, such as Helium-4, an ion collector, or a similar apparatus, could be used to convert these particles into electrical energy, which could then be used to power certain components of the spacecraft. Approximately 60-70% of the potential electrical energy from this fusion is estimated to be usable. Now, in terms of thrust, fusion reactions such as Helium-3 and deuterium do indeed have a lower thrust-to-weight ratio than traditional chemical fuels like liquid, hydrogen, and oxygen. The thrust-to-weight ratio is the ratio of the thrust force of the spacecraft as it accelerates to the weight of the spacecraft itself. A higher thrust-to-weight ratio is more desirable. However, it is also worth mentioning that the exhaust velocity of fusion reactions is far greater than that which is provided by chemically powered means. This means that Helium-3 is far more efficient as a fuel source. But Helium-3 doesn't come without its drawbacks. For starters, Helium-3 and deuterium fusion is possible only under very high temperature conditions, and building an engine that can facilitate this fusion will cost a hefty amount. After all, we need a design that is an appropriate size and weight, and can supply the level of energy needed to facilitate Helium-3 deuterium fusion and withstand the resulting reactions as well. There's also the question of abundance. Helium-3 is very hard to come by here on Earth, and is primarily created through the radioactive decay of tritium, an isotope of hydrogen which can be found in nuclear warheads. However, Helium-3 is available in large quantities on the moon in the lunar regolith, as discussed in our previous Helium-3 video. Also, the gas giants of our solar system contain an abundance of deuterium in Helium-3. So, if we ever need to refuel on interplanetary expeditions, we could potentially count on our cosmic neighbors to pitch in. Of course, the technology required to mine from these gas giants is out of reach currently, and may not be available until a couple of decades or even centuries from now. So, how exactly are we going to build a fusion-powered rocket that can withstand the extreme conditions of fusion and fulfill our interplanetary dreams while not draining our wallet? Such a feat is something which requires its own separate video, which is why you should stay tuned for the next installment in the Helium-3 series, where we examine how it could be possible to create the technological marvels to make our dreams of spreading humanity amongst the stars and beyond possible. In the meantime, be sure to explore more wonders of the cosmos here on The Science Universe, and as always, stay tuned for more science videos.