Our first, less than modest, Sounding Rocket

Our story begins on January 1st, 1951. We've been tasked with creating a fledgling space rocket program by the newly formed Council of Europe. The USA and USSR have managed to 'poach' many of the top German scientists and already have established own space programs (though NASA is a way off existing yet). We, on the other hand, have been dumped in the desert of Africa with a seemingly endless supply of exotic fuels and an ahead-of-its-time ability to simulate rocket flights.

We start with 50,000 funds and a dream.

Our first strategic objective from the European Commission for Really Cool Space Flights is to get off the ground, but I have much larger ambitions than that (which will no doubt be the death of me or, at least, some of our crews).

Sounding Rockets are research rockets, designed to take measurements on the nature of rocketry and space itself. Their research is intended to be used to 'sound out' the feasibility of space travel. In RP-1, we'll start with a very modest sounding rocket, test out our hardware under controlled conditions and...

Nah, scrap that. Let's send our first tiny rocket straight up in to space.

Space is defined by the Kármán line. Precisely where it starts is a matter of debate, but 100km is a widely agreed upper bound. I'll be aiming for about 120km with our first flight. The Kármán line is the point at which the Earth's atmosphere ends and space begins. A sounding rocket that makes it up to 120km will not only have more time to collect telemetry for our space program, but will also provide our first data from space itself. It'll also make for fantastic headlines, which means more funding. Hurrah!

Historical aside: The first rocket to make in to space beyond the Kármán line was MW 18014, a German V2 rocket, in 1944. The astrophysicists of the world did na'zi this coming. German rocket engineers were in extremely high demand after World War 2. The American military ran Operation Paperclip to smuggle as many of them out of Germany as possible before the Soviets arrived or the Nazis killed them to prevent their knowledge being re-purposed.

The tools we start with are pretty meager. Our first rocket is powered by a hypergolic fuel mixture of Aniline, IRFNA-III, and Furfuryl (raw distilled essence of furry) and will deliver a 'mere' 7733N (Newtons) of thrust, but that's okay. A hot tip for rocket science is that if your rocket isn't powerful enough, just make your payload smaller (a corollary of the tyranny of the rocket equation).

Our tiny rocket is only 30cm in diameter (you could hug it, although it's not recommended) and has no guidance system. Aside from a barometer, thermometer, an antenna, and some basic electronics to support them, the rest of our rocket is entirely dedicated to the problem of going upwards in a large gravity well. The lack of guidance system means once we leave the pad we have no direct control over this rocket, but that's fine too.

The mod FAR models aerodynamics in great detail, so it's also important that our rocket is stable. Rocket aerodynamics is too complex a topic to go in to here, but the basic idea is that by putting wings ('fins') on the bottom of our rocket, we create a set of surfaces that oppose any movement away from pointing straight up. I'm hand-waving a lot of complexity here but our sounding rocket is fairly simple and we can get away with this for now. We'll come back to this later.

We have another problem to tackle too. Our game models a potential issue with our rocket called ullage, a tricky concept which effectively means we need to force our fuel down on to our engine in order to be able to ignite it.

The easiest way to do that is to strap another rocket on to the bottom which isn't affected by ullage. We ignite this 'first stage' booster, throwing our rocket in to the air. This will force all the fuel in our tanks to drop the bottom of the tanks. We then detach ('decouple') it from the rest of the rocket and fire the 'second stage' rocket. (Technicality: We actually start both rockets at the same time, since the second stage takes a couple of seconds to fire up).

To avoid ullage for this design I have chosen to strap a 'Tiny Tim' air-to-surface rocket to the bottom of our rocket. This World War 2 weapon is perfectly suited to the task of kickstarting our rocket and is (not entirely co-incidentally) almost exactly 30cm in diameter as well.

There are a couple of snags with this plan. The first is that our rocket engine is barely rated for the flight we're asking of it. Unlike an everyday car engine, which is designed to run for years without breaking down, our rocket engine it isn't built to run for long periods of time. In fact, less than a minute, according to the datasheet (which was a pain to get shipped to the middle of the Saharan desert in 1951). This shortcoming is one of the inherent issues with funneling a massive controlled explosion down through a piece of crude metal. In order to achieve our comfortable 120km target, we're going to have to run our rocket engine very slightly longer that it is rated for.

Since we're using the TestLite mod, we already run the risk of engine failures. By running the rocket longer that it is rated for, I'm accepting a large degree of risk with our rocket design. Most of the costs of this rocket will go in to tooling (that is, setting up our factories and production lines), rather than the parts themselves. My theory is that, since we don't have any astronauts crew, we can afford to build plenty of these rockets for cheap and expecting some of them to fail. Even if the rocket somehow fails catastrophically a third of the time that's still perfectly acceptable to our space program.

There's also another issue I can't avoid mentioning. Our 1951 fins aren't made of the fanciest materials and are only rated for subsonic flight (Mach 1 or below). Due to our ambitious goal to head straight up really, really, fast we will probably end up going faster than these fins are rated for and hitting the sound barrier. As a result, it is expected they will disintegrate due to the heat of the launch towards the end of the rocket burn. Simulations tell me that this won't affect the mission in any significant way, but it's something to bear in mind as we build new rockets (and perhaps very early prototype spaceplanes) in the future.

Historical Aside: The closest analogy in real life to this sounding rocket is the Aerobee sounding rocket family, which some parts of the rocket are explicitly designed after.

Phew. That's more than enough talk, let's build our SR-1 rocket system:


The vital statistics:

Time to build (inc. tooling): 67 days (First unit ETA 9th March 1951)

Tooling cost: ~2,500 funds

Unit cost: 85 funds

Now that we have our sounding rocket (looking very fancy if I do say so myself, and I do), it's time for our first test flight. In the next post!

Next post: SR-1 Launch Day

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