In 1768, the french author François-Marie Arouet, also known under the nom de plume Voltaire, composed a verse epistle. He addressed it to the anonymous author of The Three Impostors. Voltaire felt like he needed to reply to this virulently atheistic work that denied the existence of god. By doing so he uttered the famous adage the words “Si Dieu n’existait pas, il faudrait l’inventer”. Or in English “If God did not exist, it would be necessary to invent him.”
Voltaire was a bit coy about human nature. That we needed something higher, a belief system that held us back from living out our primitive nature.
That said, when it comes to markets we still tend to give our most primitive urges free rein. And this seems to be so no matter how religious a person is.
Many people want to believe in the big pot at the end of the rainbow so they never stop chasing what does not exist. Hence, in business culture, there is another saying. “If it looks too good to be true, it’s because it is”.
And I would almost always run with that. Yet, at times, very rarely we still stumble upon something that feels like serendipity smiling down on us. A solution for so many problems, it really looks too good to be true. Sometimes the solution to many of our problems literally flies in our faces. Yet, we are so stubbornly glued to what we think we have that we can’t see the forest for the trees.
Last week we took a nosedive into the current issues with rocket fuels and combustion. The launch of Crew Dragon and its docking with the International Space Station triggered this. But the issue had festered with me for quite a while.
Let’s look at what we saw last week. There are essentially two liquid fuels for rockets in use today. One is really good for lifting stuff out of Earth’s deep gravity well and pushing it through the lower atmosphere. But it’s also filthy stuff that gives the engine a run for its money.
The other is great fuel outside the atmosphere but has low thrust and volume issues and is also hard and expensive to procure and store.
If you want a fully reusable rocket and one single rocket engine for all your push-work, neither of both is an ideal solution. But methane really seems to fill this slot.
This opens up 3 possibilities for any rocket man:
- Kerosene / Liquid Oxygen (KERALOX) engines – good for single shots from the surface;
- Hydrogen / Liquid Oxygen (HYDROLOX) engines – good for space travel and acceleration in a vacuum;
- Liquid Methane / Liquid Oxygen (METHALOX) engines – pretty good in both environments,
But I am just starting with the good stuff. Hang on.
The use of kerosene is not a problem if you discard every single rocket after launch. The engines are messed up but who cares, they are scrap.
Thats very different if you want to reuse the first stage booster – or even more of the rocket.
OK. let’s clear up one misconception. SpaceX’s KERALOX boosters are not reusable. Yes, I know you are stomping the ground now. We have all seen those boosters land and fly several times over.
They don’t fly after refueling and a cleanup. After every landing, they are extensively refurbished. That costs time and money. And it affects the profitability calculations.
If the booster is in better shape after launch, it arguably costs less to refurbish it and relaunch. And looking at the announcements of Elon, he aims at instant turnover. Fuel up and off you go again. I don’t think this is in the cards with a KERALOX booster.
If someone thinks of an airline like service with fuel up plus cabin cleanout between launches, engines must remain in good working order without refurbishing. Carbon deposits in the rocket engine just won’t do.
You can, of course, use hydrogen and there are indeed some rockets that do. But hydrogen is bulky so you get a really fat lower booster. Hydrogen is also hard and expensive to produce and to store. It’s a very aggressive substance that makes everything it touches brittle. This means that tanks, pipes, and engine parts that get in touch with the hydrogen have a pretty limited life. This makes refurbishing a pain plus safety checks in case of reuse will be on the very pokey side.
In comes methane. Like hydrogen, it does not leave any deposits during combustion as it burns so very cleanly. But better still – Methane does not have procurement and storage problems. It can simply be bought from a very large and thriving international market in liquid form (LNG) on the cheap. It can also be produced directly at the launch site with off the shelf technology, a pipeline connection, and moderate investment. It is non-toxic and non-corrosive so parts that come in touch with it suffer zero degradation.
Also, it is much easier on your mind and on the budget when it comes to reuse and safety checks.
Oh, I forgot. LNG also does not explode if handled well. If there is a leak the worst that will ever happen is a flame that can be handled. It certainly won’t explode as hydrogen does. Thats also very nice if it needs to be produced and stored in space or on other planets.
And you really want your brownie points with the green bunch, you may use biogas and go zero carbon. You imagine, one of those big explosive sticks lifts you into space carbon-free. Not that I would ever worry about carbon emissions but there are such people I heard.
Methane combines some of the best of the two dominant liquid fuels in today’s rocketry. Good thrust, good specific impulse, easy to produce and store, very safe. And it’s great if you want to use your gear many times over with minimal maintenance.
But wait, there is more. Remember the Challenger explosion? One of the O-Rings of one of the solid fuel boosters broke and a hot flame cut into the liquid hydrogen tank.
Hydrogen needs to stored in liquid form to save space. And for hydrogen to be a liquid you need to cool it down very close to absolute zero. Thats ridiculously hard and expensive and its also very, very hard to store a cryo-fuel that is so incredibly cold. Insulation is a major issue.
On top of that, Hydrogen is a very small molecule which means that the most microscopic of cracks will suffice for it to escape. Also, Hydrogen makes anything it touches brittle which is also not great from a safety and maintenance point of view.
Seals for hydrogen need to withstand very extreme conditions which makes them very exotic and hence expensive. And you want your hydrogen to remain where it is as otherwise – remember the Hindenburg?
One does not have that problem with methane.
However, all that pales when we look at it from another angle. One of the most significant drawbacks of spacetravel has always been that everything we need to survive out there needs to be brought from Earth. And Earth is the most massive rocky gravity well in the solar system so lifting anything out of it is a monstrous effort. And expensive.
Imagine it this way. When humans went to the moon, they needed to bring everything to sustain humans including air. But also fuel for the liftoff from the lunar surface and for the trip home.
If some of the bulk could be harvested en route or at the destination, that would improve the economics a whole lot further. And make space dwelling humans resilient on top. Hydrogen can be harvested from almost any celestial body but as we have seen its really hard to produce and store.
But CO2 also exists in interesting quantities on many celestial bodies in some form. By using the Sabatier process, hydrogen and CO2 can be transformed into methane.
This makes storage alone much easier. Methane is a liquid at comparatively balmy minus 161 degrees Celsius. Open space close to Earth is minus 100 degrees celsius cold in the shade and the vacuum of space acts as a great insulator.
Methane engines are not the strongest. They are also not the cheapest. Or the biggest. On every single metric, there is an engine using another fuel that will beat METHALOX engines. But none of them will have such a great sum of all parts equation.
If Methane did not exist in the first place, one would have to invent it.