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Could a hydrogen-powered Starship outperform a Raptor-powered one? We design “Hydra,” crunch the numbers, and compare the costs, challenges, and potential of hydrogen and methane on Earth, the Moon, and Mars. Plus, a surprise Starship critique. Which fuel wins? Watch and find out!
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👉 This channel was created in collaboration with https://www.youtube.com/@marschroniken
0:00 - Why Rockets Chose Methane
4:44 - Hydrogen Performance and Engine History
12:00 - Hydrogen’s Density and Mixture Challenges
18:12 - Optimizing Starship’s Design
24:27 - Hydra Versus Raptor
27:01 - Fuel Costs and Off-Earth Propellant
32:05 - Conclusion: The Case for Hydra
#SpaceX #Starship #RocketScience
Subscribe for more spaceflight deep dives.
Comment what you liked most from the video!
👉 This channel was created in collaboration with https://www.youtube.com/@marschroniken
0:00 - Why Rockets Chose Methane
4:44 - Hydrogen Performance and Engine History
12:00 - Hydrogen’s Density and Mixture Challenges
18:12 - Optimizing Starship’s Design
24:27 - Hydra Versus Raptor
27:01 - Fuel Costs and Off-Earth Propellant
32:05 - Conclusion: The Case for Hydra
Category
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TechTranscript
00:00In November 2012 Elon Musk took the stage in London and said a sentence that shapes
00:06spaceflight to this day, SpaceX's next big engine will burn methane. Yet Raptor started out as a
00:14hydrogen engine and on paper hydrogen is the best chemistry has to offer. Around 20% more specific
00:22impulse than methane. No soot, no coking. A Raptor with hydrogen that is full flow staged combustion
00:31at 350 bar would be the pinnacle of chemical rocket propulsion. There's only one problem.
00:38This engine doesn't exist. Nobody built it and nobody is building it. So today we're designing
00:44it ourselves, at least in our minds, and we'll call it Hydra. To do this I got some help from
00:50Aeneas who has been calculating rockets and engines in his own models for years. Feel free to follow
00:56him, check out X if you want to know more about rockets and the energy sector. We compare Hydra
01:02with the Raptor, vaulted underneath a starship and at the end asked the question whether Musk and his
01:08team back then really made the right call. My name is Silvan and this is Mars Chroniken.
01:18We live in a methane world. Methane and oxygen deliver among the common chemical propellants the
01:24second highest specific impulse right behind hydrogen and oxygen. Specific impulse is something
01:33like an engine's standard fuel consumption rate. It tells you how much thrust you get out of each
01:39kilogram of propellant and is specified in seconds. For the sake of completeness it should be said that
01:45even more is possible. If you replace oxygen with fluorine the specific impulse increases noticeably
01:51with hydrogen by around 5% and with methane even by more than 10%. It's just that pure fluorine is
02:00pretty much the nastiest oxidizer you can imagine. It reacts with almost everything and does so at room
02:06temperature. A tank leak and disaster is inevitable. On top of that there are the exhaust fumes. If
02:14fluorine burns with hydrogen what comes out the back is practically pure hydrogen fluoride. With methane
02:20a large portion of the exhaust is still made of it. Dissolved in water the stuff is called hydrofluoric acid
02:28and both are insanely dangerous. You definitely shouldn't be spreading thousands of tons of that
02:33all over a launch pad and into the atmosphere. They tried it anyway. In the US they experimentally modified
02:39the RL10 upper stage engine to use fluororine as its oxidizer back in the 60s.
02:46The Soviet Union ran the RD301 fluorine engine on a test stand. Neither of them ever flew.
02:55Oxygen remains the oxidizer of choice for good reason. That leaves the question of fuel and today methane
03:02dominates. Raptor has long been in good company. Blue Origins BE-4, Stokes Spaces Zenith, Land Spaces TQ-20
03:13and Longyun-70 that Zhou Zhou Yunjian is building for space epochs rocket all burn methane. The same goes for
03:22New Frontier Aerospace's Mjolnir which is intended to power a hypersonic aircraft. Are we living in a methane
03:29world because a single man once decided that hydrogen was too difficult? Perhaps. The others of course
03:36might have reached the same conclusion independently. With Starship, the choice of methane was also largely
03:42based on the fact that methane can be produced from the Martian atmosphere. However, for decades the
03:49standard for anyone who found hydrogen too demanding was kerosene. When it comes to a specific impulse,
03:55that's almost as good as methane. It's just that kerosene produces soot and when it comes to reusability,
04:01that's a problem. SpaceX notices this too with the Falcon 9 whose engines have to be cleared of soot
04:08between flights. So Musk probably shaped the market less through the methane decision itself than by the
04:14fact that he and his engineers made reusability financially viable. Although the space shuttle was
04:22already reused, it certainly wasn't a financial advantage. Calcreated over the entire program,
04:28each freight cost around 1.5 billion dollars adjusted for inflation. Why? Aeneas and I broke that down in
04:37our technical critique of the space shuttle. Naturally, I'll link the video below. What hydrogen promises?
04:44Hydrogen doesn't produce soot either and when it comes to specific impulse, it's in a league of its own.
04:50Why? That is stated in the Tsiolkovsky rocket equation which Konstantin Tsiolkovsky published in 1903.
04:58It states that the achievable change in velocity of a rocket, the so-called delta v, depends on exactly
05:04two things. First, on the velocity at which the gas exits the nozzle. Second, on the natural logarithm of
05:13the ratio of initial mass to final mass. That sounds academic, but it's simple. The faster the gas
05:21shoots out the back, the faster the rocket moves forward. And the larger the proportion of propellant
05:26in the total mass, the better. The exhaust velocity depends on the temperature in the combustion chamber
05:33and on the mass of the exhaust molecules. The lighter the molecules, the faster they move at the same
05:38temperature. This is precisely where hydrogen shines. When burned with oxygen, it produces water vapor at
05:4518 grams per mole. Because hydrogen engines run fuel-rich, unburned, feather-light hydrogen, additionally
05:53mixes into the exhaust. On average, you end up at about 14 grams per mole. Methane, on the other hand,
06:01leaves
06:01behind water vapor, carbon dioxide and carbon monoxide. On average, 20 to 23 grams per mole. This difference
06:10affects the exhaust velocity through the square root. In numbers, it looks like this. The RS-25,
06:17the space shuttle's main engine, achieves a specific impulse of 452 seconds in a vacuum. For the vacuum
06:25Raptor, SpaceX is aiming for 380 seconds. That is a difference of 72 seconds or around 19%. The American
06:35upper stage engine, the RL10, even manages around 465 seconds in its best version. That's a good 22%
06:44more. And what does the Hydra need? At a combustion chamber pressure of 350 bar, the value achieved by
06:51Raptor 3 on the test stand and full-flow staged combustion with two pre-burners, we get around
06:58430 to 440 seconds in a vacuum, depending on the nozzle and mixture ratio. That's 50 to 60 seconds,
07:07more than the vacuum Raptor. It might not sound like much, but because of the exponential nature of
07:12the rocket equation, it makes quite a difference. And that's despite hydrogen needing significantly larger
07:18tanks and turbopumps due to its low density. Roughly speaking, a hydrogen stage requires about 1.7 times
07:27as much dry mass per ton of properant as a methane stage. Even with that, a large, lightweight,
07:34high-energy stage with 8,000 meters per second of delta-V can be roughly 23% lighter than a
07:42comparable
07:43methane stage. And that's including propellant and payload. The heavy lift launch vehicle that carries
07:49this stage can then also turn out 23% lighter. Launch vehicles cost real money, so saved weight
07:56quickly pays off. If you want to go even further and stack two such high-energy stages, you even save
08:03around 40%. That's how much lighter the large launch vehicle can then be compared to two stacked methane
08:11stages. On top of that, hydrogen burns absolutely cleanly. No carbon, no soot, no clogged injectors.
08:20For an engine that's supposed to fly dozens of times, that's a strong selling point. Besides,
08:27hydrogen burns very quickly and evenly, which helps with the pressure buildup in the combustion chamber.
08:34Measured by pure engine performance, oxygen is therefore the best that chemistry has to offer.
08:40Why? There's nothing comparable. With so much potential, such an engine should have existed long ago. In
08:47fact, today, hydrogen is primarily at home in smaller engines with low chamber pressure and large nozzles,
08:54that is, in upper stages. The most famous large hydrogen engine is the RS-25, which we looked at in
09:01detail just recently. It is linked below. While it operates on stage combustion, both preburners run fuel rich.
09:10So it is not a full flow engine. It is old and at over 100 million dollars apiece, absurdly expensive.
09:18Besides, it is a so-called sustainer engine. Like the VUKAN 2.1 of the Ariane 6 or the LE9
09:28of the Japanese H3. It burns from the ground almost into orbit and has to work in thick as well
09:35as in thin air. So it is not a modular engine that you use in multiple stages. The most powerful
09:41hydrogen engine that ever flew was the RS-68 of the delta stages. In its final configuration, the RS-68A,
09:48it delivered around 320 tons of thrust at sea level and a good 360 tons in a vacuum. That translates
09:56to about 3560 kN. Impressive! Raptor 3 reached 280 tons on the test stand and currently flies with around 250.
10:08So only a future Raptor generation could beat the RS-68, if at all.
10:14Except, with its open gas generator cycle, the RS-68 has an embarrassingly low specific impulse for hydrogen of around
10:23410 seconds in a vacuum. At the same time, it is heavy, partly because its nozzle is ablatively rather than
10:31regeneratively cooled. It burns away in a controlled manner during operation. Reusability was never an option here.
10:39We should also mention the RS-83. We should also mention the RS-83. In the early 2000s, it was
10:44supposed to build on experience gained with the RS-25, be reusable and achieve a high specific impulse with fuel
10:52rich staged combustion.
10:54It never made it past the development stage. NASA cancelled the program.
10:59The closest thing to our Hydra was a project hardly anyone knows about. The Integrated Powerhead Demonstrator. IPD for short.
11:08Starting in the 90s, the US Air Force Research Laboratory and NASA had the core of a fuel flow staged
11:15combustion hydrogen engine developed, meaning the turbo pumps and pre-burners.
11:19Between 2004 and 2006, the IPD ran on the test stand at Stennis, reaching full power for the first time
11:27in July 2006. It was designed for a thrust level of just over 110%. After that, there was no more
11:35money for a complete flight engine and the project was shelved. So we wouldn't have to start from scratch for
11:41Hydra.
11:41In short, a quick request of my own. If you like this kind of calculation adventure, then please give the
11:48video a thumbs up and hype it.
11:49That's just two clicks below the video and it helps us out a tongue with the algorithm. If you want
11:54to support the channel directly, become a channel member and you'll get to see every video before anyone else.
12:00Thank you. And now, things are getting dense. Or rather, exactly, they're not. The dense density problem.
12:07So hydrogen does have advantages, if it weren't for all the disadvantages. I've already mentioned the low density, but it's
12:14only with numbers that the scale really sinks in.
12:17One cubic meter of liquid hydrogen weighs around 71 kilograms. For methane, it's about 423 kilograms. For liquid oxygen, it's
12:281142 kilograms.
12:32Hydrogen stands out here for how much space it takes up. Now you always need significantly more oxidizer than fuel.
12:38The stoichiometric ratio at which fuel and oxygen react completely with each other is 8 to 1 for hydrogen.
12:47So for 1 kg of hydrogen, there are 8 kg of oxygen. For methane, it's 4 to 1.
12:56If you compare these two mixtures, the hydrogen mixture comes to 427 kilograms per cubic meter and the methane mixture
13:04to 852.
13:05So for the same mass, the hydrogen mixture needs twice as much space. But that's not all. These densities apply
13:13close to the boiling point.
13:15If you cool the liquids down further, they become denser. Near the freezing point, hydrogen reaches 77 kilograms per cubic
13:23meter and methane 452.
13:26Oxygen reaches 1,282 at 60 Kelvin, a few degrees above its freezing point. That saves space and it's already
13:37being done to some extent.
13:39SpaceX has been fueling its rockets with subcooled propellants for years. Theoretically, the hydrogen mixture thus increases to 468 kilograms
13:49per cubic meter and the methane mixture to 938.
13:52I deliberately say theoretically. Especially with hydrogen, this additional density is very expensive.
13:59Its boiling point is less than 20 degrees above absolute zero. The freezing point at 14. That's only 6 degrees
14:08below.
14:09But so close to absolute zero. Every single degree costs a disproportionate amount of energy.
14:16For our comparison, we therefore choose a reasonable middle ground. We cool the hydrogen down to just 20 Kelvin, which
14:23is minus 253 degrees Celsius. So right near the boiling point.
14:29The oxygen, on the other hand, will cool down to 60 Kelvin, just above its freezing point of 54 Kelvin.
14:36That way, the temperature difference between the two tanks is smaller and the insulation between them becomes less of a
14:42headache.
14:43With methane, we do the opposite. We cool the methane down to 91 Kelvin, just above its freezing point. And
14:50we leave the oxygen at around 90 Kelvin at its boiling point.
14:55Both liquids are then practically at the same temperature and you can almost completely skip the insulation between the tanks.
15:01That brings our methane mixture to 857 kilograms per cubic meter and the hydrogen mixture to 426.
15:10I'll give you a quick moment now.
15:13Yep, anyone who just calculated it or rewound a few seconds will notice that something isn't right.
15:19With the colder and denser liquids, both values should actually be higher.
15:25That's true. The hydrogen mixture should end up at 443 kilograms per cubic meter and the methane mixture at 875.
15:34Actually, why are we running 7.5 to 1?
15:38The truth is, almost all rocket engines run fuel rich, meaning with more fuel than the oxygen can burn.
15:47That's because the specific impulse depends significantly on the molecular weight of the exhaust gas and extra fuel usually lowers
15:55this weight.
15:57To put it simply, you could open a whole can of worms with this topic, but we are not going
16:02to do that today.
16:03Maybe in another video we'll talk about why rocket engines work the way they do.
16:08If you're interested in that, please let me know in the comments.
16:11Experience has shown that the optimal mixture for methane is around 3.6 to 1 and for hydrogen around 5
16:20.5 to 1.
16:22That varies depending on chamber pressure, expansion ratio, cycle and cooling concept, but it works as a rough general guideline.
16:29With 3.6 to 1, the 857 for methane makes sense.
16:35And did you calculate it again?
16:37For hydrogen, it still doesn't add up.
16:39With 5.5 to 1, the mixture should be at 354 kilograms per cubic meter, but we say 426.
16:49That's because we deliberately don't work with the optimal mixture.
16:53We use 7.5 to 1.
16:56That's unusual even for an industry that sometimes even uses a ratio of 6 to 1.
17:02We have our reasons.
17:03Of course, you can get lost in the nitty-gritty, nerdy details and push for the maximum specific impulse or
17:09the greatest thrust.
17:10But in the end, it's all about money.
17:13Transporting payloads into space has to become as cheap as possible and we can't lose sight of that here.
17:20Hydrogen is damn expensive and damn bulky.
17:24The less of it you need, the better.
17:26Aeneas determined in his models that although the specific impulse decreases with the linear mixture because the exhaust gas gets
17:35heavier,
17:36the advantages of smaller tanks and smaller turbo pumps outweigh that.
17:40Still, we are not running completely stoichiometric.
17:43A slight excess of fuel ensures that the oxygen burns completely and doesn't get the idea of reacting with the
17:51copper in the combustion chamber at these temperatures.
17:53Because then the flame quickly turns green and the engine is toast.
17:58That's why 7.5.
18:007.5.
18:01For precisely these kinds of questions, Aeneas has built models over the past few years for scaling rockets and engines.
18:08They at least give us a rough idea of where things are heading.
18:12For Hydra to fly, we ultimately need a rocket too.
18:16And the choice there is simple.
18:18The Starship architecture is probably the cheapest thing we'll see in space transport over the coming years.
18:24The focus is on mass production and reusability.
18:28With minor or no changes at all, the upper stage works for low Earth orbit, for sun synchronous and geostationary
18:35orbits, for the Moon, Mars and high energy destinations.
18:39That helps SpaceX mass produce and continuously refine the design.
18:45Almost every insight from a flight advances all variants at the same time.
18:50On top of that, there's a shared engine power head for the booster and the upper stage.
18:55Whether this architecture flies with Raptor or with Hydra, it should stay.
18:59In his modeling, Aeneas actually noticed that SpaceX is currently making strange compromises.
19:06That's why today you're getting a quick technical critique of Starship as a bonus.
19:11The problem is easy to pinpoint.
19:14Super Heavy is too thin.
19:17For rocket stages, there's an optimal ratio of length to width.
19:21The wider a tank is, the thicker its steel must be to withstand the internal pressure.
19:26On the other hand, it holds more volume relative to its surface area and the load from above is distributed
19:33over a larger ring.
19:35A sphere has the best surface area to volume ratio, it's just not very good at carrying a payload.
19:41That's why the gold standard is rather wide but not too wide cylinders.
19:46The Falcon 9 is also too thin.
19:49However, for logistical reasons, its stages travel on public roads and with a diameter of 3.7 meters, they max
19:58out what's allowed there.
19:59Starship doesn't have this problem.
20:01With a diameter of 9 meters, it wouldn't fit on any normal road anyway.
20:06SpaceX is building the necessary infrastructure itself.
20:09But that very infrastructure is the catch.
20:12Manufacturing, development and launch facilities are all designed for 9 meters.
20:18Meters for the ship itself, by the way, that's a good compromise.
20:21At least with version 3.
20:23Version 4 might already be too slim again.
20:27A constantly wider rocket would mean having to extensively manufacturing and a launch pad every time.
20:34Growing ever taller is simply easier.
20:36We wouldn't rule out Starship becoming significantly wider in a few years during a truly major developmental leap.
20:45Right now, SpaceX has other priorities.
20:48First of all, the system needs to reach orbit and return reliably, if it hasn't already done so by the
20:54time this video is released.
20:55The effort required for a wider rocket seems so vast that SpaceX is even making massive compromises with Raptor.
21:03The nozzle is way too small.
21:05Otherwise, the narrow booster couldn't accommodate enough engines to produce the planned thrust.
21:10According to Aeneas' calculation, the exhaust gas leaves the nozzle of Raptor 3 at about 1.3 bar.
21:17Optimal first stage engines expand to around 0.6 bar instead.
21:23Although this costs some specific imparts at liftoff, the engine gains disproportionately more in the thinner air higher up.
21:30That more than compensates for the losses at ground level and the heavier, because larger, nozzle.
21:35In numbers, that means the following.
21:37At sea level, the specific impulse of a 0.6 bar Raptor drops from 334 to 332 seconds.
21:46In a vacuum, it rises instead from 350 to 361 seconds.
21:53At roughly 1002 meters altitude, both variants are already neck and neck.
21:58Above that, the large nozzle takes the lead.
22:01To be fair, there is a counter-argument.
22:04A small nozzle lets the engine swatter down further at ground level without flow separation occurring inside the nozzle.
22:10And that's precisely what the booster needs during landing.
22:12The landing engines in the center would therefore presumably keep their small nozzles.
22:18The optimal width for Super Heavy in Aeneas' model, at least for version 3, is around 12.5 meters.
22:25Beneath that, the 0.6 bar Raptor fits as well.
22:29And that is precisely our benchmark.
22:31This optimized booster is also 7% lighter.
22:35Together, that yields a solid, a good 10% more payload into low Earth orbit.
22:41Aenea comes up with 180 tons for today's design and 200 tons for the optimized one.
22:48The official numbers are lower, but we are calculating at the limit.
22:52For example, we don't throttle the engines around Max-Q, that is, at the moment of maximum aerodynamic stress.
22:58For now, that's done for safety reasons.
23:00But we are relatively sure that with enough experience, Starship can fly full throttle through this phase.
23:06The slightly higher drag losses are more than offset by significantly lower gravity losses.
23:12We are also assuming only one percent remaining fuel.
23:16And the target orbit is at an altitude of only 180 kilometers.
23:21A satellite there would deorbit after just one to two days.
23:25A heavy aerodynamic upper stage, like Starship, will stay up significantly longer though.
23:32Long enough to be refueled by tanker flights and set off on a high energy mission.
23:37Fully refueled again, Starship could, for example, send about 200 tons of payload toward Jupiter,
23:45if you sacrifice the Starship in the process.
23:48That opens up completely new possibilities for science.
23:51But that's a topic for another video.
23:53That leaves the objection regarding air resistance.
23:56Yes, a wider rocket has more of it.
23:59The value almost doubles.
24:01It's just that air resistance on today's Starship is already hardly worth mentioning.
24:06A doubling is significantly overcompensated for by the higher specific impulse and lower dry mass.
24:13During re-entry, the larger width could even save fuel.
24:17Super Heavy is then much lighter than at launch, with the ship and payload on top.
24:22So that should make a significantly bigger difference.
24:27Hydra versus Raptor.
24:29This optimized Starship with the optimized Raptor is our benchmark for the Hydra Starship.
24:35Heads up!
24:36Here comes a barrage of numbers.
24:37The Hydra version is 25% lighter at launch, even though its stages are 20% heavier without propellant and
24:45payload.
24:46Hydrogen takes up a lot of space.
24:48That makes the Hydra version 17 meters longer than the optimized Raptor Starship, which only measures 100 meters.
24:57The booster is also half a meter wider and the ship a full meter.
25:03A minor side effect.
25:04This gives the ship more room for payload, because the payload bay stays the same length at about 20 meters.
25:11Super Heavy's thrust is only about 14% lower, even though the rocket is 25% lighter.
25:19That is because the Hydra version gets lighter more slowly, since it consumes less propellant per ton of thrust.
25:27Here, the higher specific impulse actually becomes a bit of a disadvantage.
25:32Without countermeasures, the average thrust to weight ratio over the entire flight would be worse, which would mean more gravity
25:38losses.
25:38So, we are adding a bit more thrust.
25:41Version 3 with Raptor 3 reaches a thrust to weight ratio of just under 1.6 at liftoff.
25:48Hydra reaches about 1.8.
25:50That 1.6, however, assumes the full 280 tons of thrust per engine.
25:57So far, SpaceX has been flying the Raptors slightly throttled back at around 250 tons.
26:03Just as an aside, the engine itself, on the other hand, fares worse.
26:07Hydra's own thrust to weight ratio is about 30%, 30% lower than that of the Raptor, because the size
26:15of the turbopumps depends on the volume they have to pump.
26:18This is where the low density of hydrogen really hits hard.
26:21And that's already an optimistic estimate for our modern design, since the aging RS-25 doesn't even reach half of
26:29the Raptor's value.
26:30On the other hand, hydrogen has an enormous heat capacity, which makes cooling the engine easier.
26:38It also burns even faster than methane, which slightly increases the efficiency in the combustion chamber.
26:44In general, Hydra would be a completely new engine of its own.
26:49Hydrogen makes many metals brittle, so it requires different materials and coatings.
26:55The lines around the turbopumps and in the cooling circuit also need to be sized completely differently.
27:02After all, with the IPD, I have a reference in the archives for what the propellant costs.
27:08Is that better or worse now?
27:10Now I'm going to get briefly legal on you.
27:13Because it depends.
27:15First of all, all these numbers are rough estimates.
27:19You can certainly refine the optimization further.
27:22And our assumptions are probably not the perfect choice either.
27:27With that thought in mind, we can say the following.
27:30Right now, methane is clearly the better choice.
27:33Because it comes directly from very cheaply available natural gas, at least in the US.
27:39On top of that, liquefaction is significantly easier with methane.
27:43A full tank for the methane version currently costs about $1.2 million.
27:48For the hydrogen version, about $2.4 million.
27:52That doesn't have to stay that way.
27:53Methane has long been liquefied on a large industrial scale at every export terminal for liquefied natural gas.
28:01The hydrogen side, on the other hand, still has great potential for development.
28:05If you had to supply thousands of launches a year, that would be a job for a highly developed heavy
28:11industry.
28:11However, methane is not CO2-free.
28:15Hydrogen isn't either, because it's still mainly obtained from natural gas.
28:19If we want to produce all fuel in the future using CO2-free electricity, such as from solar or uranium,
28:26then the amount of electricity becomes the decisive cost driver.
28:30For production, we calculate 46 kWh per kg of hydrogen, and just under 1 per kg of oxygen.
28:38Methane is more complex to produce than you might think.
28:41Every kg contains half a kg of hydrogen from electrolysis, and that alone accounts for 23 kWh.
28:49On top of that, there's an additional step, the Sabatier process, which turns hydrogen and CO2 into methane in the
28:55first place.
28:55And you have to extract the CO2 from the air first.
29:00Bottom line, we end up at about 27 kWh per kg of methane.
29:05Then, everything still needs to be liquefied.
29:08For methane, that costs 0.4 kWh per kg.
29:12For hydrogen, 9.
29:14Yes, you heard that right.
29:16Liquefying hydrogen is really energy intensive.
29:20Oxygen, at just under a kWh by the way, is already liquid.
29:25Crunching these numbers, the Raptor version needs around 34 kWh of electricity per launch.
29:32The Hydra version, a good 27.
29:35That is the annual consumption of 8 to 8,000 households.
29:40Hydra is therefore about a fifth ahead, even though hydrogen per kg guzzles way more power.
29:46The reason is simple.
29:47When it comes down to it, there is more electrolytic hydrogen in the methane of the Raptor version than the
29:52Hydra version fuels up on in total.
29:55Hydra still doesn't get that for free, though.
29:57Hydrogen requires better insulated tanks and lines, more tank volume and the more complex engine.
30:04The methane side, on the other hand, needs additional facilities for synthesis and capturing CO2.
30:09On Earth, Hydra would enter the race with a head start as soon as emitting CO2 is no longer allowed.
30:17That said, it wouldn't be decided just yet.
30:20Some time ago, Aeneas worked out with Moritz from Senkrechtstarter that under certain conditions, methane might not even be the
30:27best choice on Earth today.
30:30Propane, the fuel chosen by ESA Aerospace, offers some interesting advantages.
30:35I'll link the video down below for you guys.
30:37But back to the topic at hand, the Moon and Mars.
30:40What do things look like beyond Earth?
30:43Sure, hydrogen is colder, Moon then does require more insulation and possibly active cooling technology to prevent it from boiling
30:49off.
30:50Blue Origin, however, seems confident that it can solve, or rather has already solved, precisely these issues using solar-powered
30:58cryocoolers for the Blue Moon lander.
31:00The vacuum of space insulates exceptionally well anyway.
31:04It requires a good sunshield and proper management of thermal bridges to the rest of the spacecraft.
31:10Hydrogen can be produced on the Moon and on Mars, because there's water on both.
31:15Carbon for methane, however, is only offered on a large scale by Mars with its CO2 atmosphere.
31:22On the Moon, only traces of carbon compounds have been found in the polar craters.
31:27So there, Hydra would clearly take the lead.
31:30Oxygen is provided directly through electrolysis, with almost 8kg of it generated for every kilogram of hydrogen.
31:38And here's the kicker.
31:40In the beginning, we talked about how saving mass quickly pays off.
31:44Because expensive launch systems can be smaller.
31:48Hydra Starship, which is refueled in low Earth orbit, needs about 20 fewer tanker flights.
31:54That turns the advantage in electricity use into a decisive advantage.
31:58And it multiplies when the fully fueled Hydra Starship in Earth orbit refutes other hydrogen spacecraft itself.
32:06Conclusion and Assessment
32:08My honest take clearly labeled as an opinion.
32:11Musk and his team probably made the right call back then.
32:14Methane was cheaper and significantly easier to handle.
32:18For a company that still had to invent a reusable giant rocket, that was worth its weight in gold.
32:23In the medium to long term, that could look different.
32:27If carbon avoidance becomes more important and fuel production starts up on the Moon and Mars,
32:33Hydra could be an economically attractive next step.
32:37Maybe the solution also lies in a hybrid.
32:39In terms of energy, it makes total sense to use a fuel with low specific impulse in the first stage.
32:45That's been proven.
32:46It's not for nothing that, historically, hydrogen has flown primarily in upper stages,
32:51while kerosene burned down below.
32:52Take the Saturn V for instance or the Atlas V.
32:56Solid rocket boosters with even worse specific impulse often help out as well.
33:00In our calculation, a Starship with Raptor in the booster and Hydra in the ship requires around 28 GWh of
33:08electricity per launch.
33:09That is virtually on par with Hydra alone and about 6% less than with Raptor alone.
33:15So you would get almost the full benefit but would only have to tame the bulky hydrogen in the upper
33:20stage.
33:21Maybe that way, the integrated powerhead demonstrator will still find its way into the future after all.
33:26For transparency, because SpaceX is the benchmark for everything in this video.
33:31As of the time of publication, I personally hold a position in SpaceX stock and I expressly do not make
33:36any buy or sell recommendations.
33:38This video is a journalistic analysis, not investment advice.
33:42My name is Sirwan and this was MASH Chroniken.
33:45Thanks for tuning in.
33:47Per aspera ad astra.
33:52It was my name and this video.