Norwegian Reusable Rocket Concept Rivaling SpaceX?
A revival of the old Sea Dragon concept. The advantages of launching space rockets from the ocean
I was recently made aware of a very interesting space company called Ripple Aerospace, based in my native Norway. I would like to detail some of the reasons why the concept they are working on is very promising.
Comparing this to SpaceX is of course a bit hyperbolic I admit. But that is mainly because ideas are cheap and execution is everything. SpaceX is where they are today not merely due to their ideas but because of the ability of Elon Musk to get stuff done and raise capital.
However as a concept, what Ripple Aerospace is working on is at least as exciting if not more so than what SpaceX is doing. I am only speaking of the rockets concept itself.
Paper Rockets and Execution
While it takes a lot to be the next Elon Musk, Ripple Aerospace is not just all concept drawings. They have actually built and successfully launched rockets. Not large scale of course, but they are certainly well on their way.
That is why I think the company concept warrants some attention.
What is the Big Deal
Ripple is pursuing sea based rocked launches. By that I don’t mean launching from a platform at sea but actually towing the rocket itself out to sea. The rocket is then floating in water before getting launched.
This is not as crazy as it sounds. There is a long history of sea based launches. Submarines already do this. NASA explored this extensively in the past and did many rocket launches from the sea:
Oceanic launch systems have been in development for the past 55 years, with over 120 successful test flights of varying design.
The benefits of this approach over using a launch pad is that you can launch from anywhere. You could tow the rocket to the equator for optimal launch location.
Rational and Historical Background
The rational for such an approach was first described by American rocket engineer Robert Truax back in the 60s when he proposed the Sea Dragon rocket as an alternative to the Saturn V, which eventually took America to the moon.
Truax had observed that one of the major drivers of cost is complexity, and that the cost of complexity increase much faster than the cost from scale. His idea was that instead of getting more payload into space by making a rocket more efficient, one could compensate by simply making the rocket much larger.
He theorized that a very large simple rocket would be cheaper to make than a smaller but more complex one.
However building very large rockets is impractical because of the difficulty of transport. Truax solved that problem by suggesting that the Sea Dragon would be built in a dry dock just like a ship or submarine. Dry docks are basically large basins at a shipyard which can be filled with water or drained. That means you can build a large structure in it such as a ship, submarine or rocket, then flood the dry dock to move the large structure out. We already build enormous ships in dry docks, so existing shipyards already have the capacity to build enormous rockets.
A submarine already has to deal with many of the same challenges as a rocket, such as withstanding high pressures. Building a rocket using shipbuilding techniques means you can utilize well established and well understood technologies and building techniques thus lower cost.
This does not provide optimal efficiency, but remember that will be offset by the ability to build at much larger scale.
How is the Sea Serpent different from the Sea Dragon?
The rocket being built by Ripple Aerospace is called the Sea Serpent in homage to the Sea Dragon which inspired it.
However while many of the basic concepts are the same, the Sea Serpent still seems like a very different rocket. They seem to aim for a more efficient and smart rocket.
Just by glancing at the Sea Serpent, you will notice one major difference. Do you see the cone shape underneath it, in place of the bell?
What on earth is that? This is called an aerospike toroidal engine. Aerospike engines are much more efficient than traditional bell shaped engines. Regular bell shaped nozzles reduce the thrust in particular at sea level. Rocket use different nozzle shapes at different altitudes to compensate. E.g. the optimal nozzle geometry for a bell in vacuum is quite different from what you need at seal level pressure.
Of course there is no way of changing the nozzle geometry while a rocket ascends continuously. You can only use different nozzles for each stage.
But if Aerospike engines are so great, why aren’t everybody using them? From what I can gather from researching this topic online, there is a significant problem with heating up the cone. Cooling it down sufficiently so it does not get damaged is a major problem, in particular at launch time.
Ripple Aerospace has not spelled it out, but my guess would be that they made this choice because they are launching from sea water. That means the central cone is getting plenty of cooling, thus making a aerospike engine a much more viable option.
The shape of the nozzle is just one part of engine design. How fuel gets fed to the combustion chambers would be interesting to know. A normal problem with sea based recovery of rockets is that sea water flooding a turbo pump creates a lot of problems. The original Sea Dragon circumvented this problem by using simple gas pressure to push the fuel and oxidizers into the combustion chambers, that is rather inefficient however.
SpaceX vs Ripple Rocket Reuse Strategy
SpaceX avoided the whole problem of sea water flooding into the engines by landing on a barge or on land. Getting the rocket to land without tipping over and exploding was quite a challenge. Another problem is that there seems to be no easy way to recovering the second stage in this fashion as it re-enters at much higher velocity.
A sea based splash down likely requires less effort to get right. The problem is the damaging effect of salt water, but being built for a maritime environment from the get go may turn this into a lesser problem for Ripple.
It also means the second stage recovery will be easier to accomplish.
Another crucial benefit of this approach is that by using the sea for launching you got essentially infinite number of launch pads. Getting the cost of launches down through reuse depends on rapid turn around, launching rockets as frequently as possible. A limited number of launchpads which need to be prepared for each launch means they can become a significant bottleneck.
Ripple rockets also need to be prepared for each launch somewhere, however there are far more dry docks available in the world than launch pads. Also rockets likely don’t have to wait for extended periods of time in a dry dock waiting for a proper launch window. As soon as you are done servicing the rocket you can take it out to sea making space for another rocket.
Why Build These Rockets in Norway?
Norway has the longest coastline in Europe. Ever since Viking times Norway has been a maritime nation. Most of the population live along the coast and for centuries we have lived of what the coast offers. Norway has poor conditions for agriculture and hence fishing has historically been very important.
Later shipping was a major part of the Norwegian economy. At one point Norway had the largest merchant fleet in the world and there where shipyards dotted all along the coastline. When I was a child in the 80s I remember the sound of metal against metal in the morning coming from the local shipyard.
Then the maritime industry started dying out outcompeted by lower wage Asian countries. Our salvation was the discovery of oil in the North Sea. The harsh weather, deep water and generally difficult conditions of oil drilling in the North Sea mean that there was a need for skilled maritime engineering. This gave our maritime industry something to adapt to and utilize. In place of ship building we build up a large oil service sector, which build specialized ships and oil platforms. Some of the largest dry docks in the world are in Norway.
Now the oil industry is at the beginning of its end. The oil industry has made Norway very wealth and help build up the worlds largest sovereign wealth fund, controlling over 1 trillion dollars in assets. This was intentionally built up knowing that the oil industry would not last forever. This is the money needed to transition to a new industry.
As before, it makes sense to utilize existing expertise. Subsea technology has a lot in common with space technology. You need to deal with high pressures and generally harsh environments without any quick access to a repairman. Equipment needs to be robust and durable.
Venturing into the growing space industry makes sense for Norway. It is already an industry growing fast in Norway. The Norwegian space industry is already bigger than the much older and more established forest industry. There has been a natural symbioses for space industry and maritime industry in Norway. Satellites have been used to monitor the seas, and rockets have been launched far north to study arctic areas.
I think Ripple Aerospace sees the potential in this context. Going the maritime route with their rocket technology allows them to utilize the strong maritime engineering traditions in Norway. It is also something the Norwegian government is likely to want to push economically, as they are searching for alternative industries, which can take over from the oil industry.
We already have examples of this happening. Norwegian oil company statoil has engineering experience in building large offshore structures such as oil platforms. They have been able to utilize this expertise in successfully building large offshore windmills off the coast of Scottland.