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Floating space ports for future rockets

While early prototypes for SpaceX’s Starship have exploded fairly regularly at the company’s test facility in Texas, the overall program has moved forward at an amazing pace. The towering spacecraft that CEO Elon Musk believes will be the key to building a sustainable human colony on Mars has gone from CGI rendering to flight hardware in a few years. It’s fast even at conventional rocket conditions, but then there’s a bit about Starship that anyone would dare call conventional.

An early Starship prototype is assembled.

Almost all components of the deep space vehicle are either a technological leap forward or a departure from the norm. Its revolutionary full-power staged internal combustion engines, the first of their kind ever to fly, are so complex that the rest of the aviation industry gave up trying to build them decades ago. To support rapid recyclability, Starship’s slim hull abandons fine – grained carbon fiber to much harder (and heavier) stainless steel; a material that has not been used to build a rocket since space-time.

Then there’s the big size of it: when Starship is mounted on top of the matching Super Heavy booster, it will be taller and heavier than both the iconic Saturn V and NASA’s upcoming Space Launch System. When lifted, boosters’ 31 Raptor engines will produce an incredible 16,000,000 pounds of pressure, releasing a terrible pressure wave on the ground that would literally be fatal to anyone who got too close.

Which leads to an interesting question: where could you safely launch (and land) such a massive rocket? Even under ideal circumstances, keep people several miles away from the pillow, but what if the worst were to happen? It’s one thing if a single engine prototype goes up in flames, but if a fully powered Starship stack explodes on the pad, the resulting fireball would have the equivalent energy of several kilotons of TNT.

Thanks to the stream of consciousness that Elon often unloads on Twitter, we may have our answer. While responding to a comment on previous efforts to launch orbital rockets from the sea, he casually mentioned that Starship would likely operate from floating space ports once it started flying regularly:

While the story warns us against looking too deeply at Elon’s comments on social media, the potential benefits of launching Starship from the Sea are a little too much to dismiss at hand. Especially since it’s a proven technology: the Zenit rocket, to which he refers, made more than 30 successful orbital launches from its unique floating pad.

Last of the Soviet rockets

The Zenit rocket was developed in the 1980s and was intended to replace the aging Soyuz and Proton launchers that were the backbone of the Soviet space program. Similar in size and specifications to the early versions of SpaceX’s Falcon 9, the liquid oxygen and refined petroleum-powered Zenit would be cheaper and safer to operate than its predecessors. Its ability to act as a strap-on booster for larger vehicles, another similarity shared with the Falcon 9, also promised to further streamline space logistics to the Soviet Union.

Of course, that never happened. Before all the bugs could be worked out by the new booster, the Soviet Union collapsed and the program was caught up in politics. Not only did the Russian Federation lack the means to simultaneously operate Soyuz, Proton and Zenit to their full potential, but there was concern about launching sensitive payloads on a rocket now being manufactured in newly independent Ukraine. After several high profile errors in the 1990s, the Zenit program was almost completely canceled.

One if on land, two if by sea

While the dissolution of the Soviet Union ultimately prevented Zenit from replacing Soyuz and Proton, it also provided some exciting business opportunities. When the Cold War was officially over, an international coalition of companies from the United States, Russia, Ukraine and Norway was formed to offer Zenit to commercial customers. Instead of having to decide which nation would serve as the rocket’s permanent home base, a modified version of the vehicle would fly from a self-propelled offshore launch pad that started life as an offshore oil kingdom. This revolutionary new service was aptly called Sea Launch.

Zenit-3SL at Sea Launch’s Ocean Odyssey platform.

In addition to the political aspect of not being tied to any nation, the launch from the sea offered a number of compelling benefits. First, it was much safer if the rocket exploded on the pillow or failed shortly after liftoff. This was especially important given Zenit’s somewhat tarnished track record. It would also allow transmissions from near the Earth’s equator, giving the vehicle greater tangential velocity during ascent and directly translating into increased payload capacity.

The initial boost provided by the Earth’s rotation can be approximated by taking the planet’s rotational speed at the equator and multiplying it by the cosine at the launch site latitude:

While the gains offered by equatorial launching may seem small compared to orbital speeds (approximately 28,000 km / h), the rocket equation is unusually unforgivable. Even a small reduction in the acceleration required to reach the circuit allows more of the vehicle’s mass to be set aside for payload instead of propellant. In addition, this means that payloads destined for equatorial orbits, such as geosynchronous communications satellites, do not need to adjust their slope after separation from the booster. This further reduces the propellant requirement and gets the satellite faster in its final operational orbit, resulting in a longer service life.

An experiment cut short

A total of 36 Zenit rockets were launched from Sea Launch’s floating pad between 1999 and 2014, 32 of which successfully delivered their payload to orbit. The most serious failure was in January 2007, when the rocket with the NSS-8 satellite failed a few seconds after ignition and engulfed the launch pad in a fireball.

Due to the design of the floating launch pad, the rocking rocket fell through an opening in the platform and sank; causes only superficial damage to the infrastructure on board. As part of the normal operating procedure, there was no staff on board Ocean Odyssey platform at the time of launch so that no damage was done. The platform was repaired and ready for its next launch just six months after the incident.

From a technical point of view, Sea Launch showed that there was a definite promise of sea-launched orbital rockets. The handful of failures that the program experienced were in no way related to the logistics of transporting the rocket to the equator or the unique nature of the floating launch pad. The only failure was not on board either Ocean Odyssey enough to postpone the program very long, much less stop it completely. If anything, the NSS-8 explosion demonstrated the inherent safety of ocean broadcasts in the event of a catastrophic failure.

Unfortunately, Sea Launch was eventually killed by the same thing that made it possible in the first place: political unrest. The 2014 annexation of Crimea by Russia strained the country’s relations with Ukraine, and while Sea Launch publicly denied that the situation had any impact on their operation, staff were dismissed within a few months, and Ocean Odyssey and its support ship was milled.

Rockets on the high seas

SpaceX has already gained significant experience landing their rockets on floating platforms, which is undoubtedly a harder feat than lifting from one. The Sea Launch project proved without a doubt that the concept worked, it just needs to be scaled up. As Elon pointed out, the Starship and Super Heavy booster is a far larger vehicle than the Zenit, but that doesn’t mean the core technology has to be any different.

Each spacecraft will be refueled in the orbit of several tankers.

The overall Starship architecture is built around the concept of gasoline refueling, meaning that each mission will actually consist of multiple launches in quick succession. Up to five or six in case of a trip to Mars, all launched within a few days in a row.

Equatorial shipments would help streamline this process as much as possible so that the maximum amount of propellant can be delivered to Starship and waiting in orbit for the least amount of time. The winnings per. Flight will not be much, but SpaceX is clearly playing the long game. At the very least, it would help keep the incredible amount of noise that such an operation would produce as far away from civilization as possible.

Or as we have previously learned with SpaceX, it may never happen. Perhaps the cost of building a fleet of giant floating space ports will end up being so high that the benefits gained from ocean launches will be nullified. With all the changes the Starship design has undergone in a few short years, very little can be said about this futuristic craft with absolute certainty. Many doubted it would ever get this far.

But even if SpaceX does not go ahead with the launch of Starship from the Sea, there is still hope for the concept of sea-going rocket. The Russian space agency Roscosmos has announced that they plan to get the sedative Ocean Odyssey running again, this time using only domestic technology. Like stainless steel rockets, it looks like ocean-going launchers are coming back in style for the New Space Race.

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