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Elon Musk hit gigantomania

UNITED STATES (OBSERVATORY NEWS) — Experts continue to discuss new grandiose plans voiced by Elon Musk. This time, he promises to launch Starship into orbit within six months. And this despite the fact that we are talking about the launch of a superheavy rocket, more than the Saturn-5 and Energy. It is intended for flights to the moon and to Mars. How realistic are such statements?

Starting a story about the Starship project is worth the ideas that were originally laid down in its concept. It is difficult to discuss specific technical details in the case of the offspring of Elon Musk, which is dictated by the specific approach to creating Starship. In the nine years since the first announcement of the start of the development of the superheavy rocket, SpaceX has already radically changed its appearance several times. And often the information of the next, new presentation fundamentally contradicted the data from the previous one.

It was almost impossible to achieve anything intelligible as an explanatory comment from SpaceX or personally from Elon Musk, since the Starship program was developed and implemented at SpaceX’s own funds – unlike the quite fully documented and described joint programs with NASA or the Pentagon.

In addition, the very process of creating Starship looked intimidating for old space industry professionals (both in Russia and in the United States). It seemed that SpaceX engineers had before their eyes only a certain outline design of the desired product, but they had to think up everything else on the go, assembling the ship from the components most suitable in meaning and available to them in reality.

After the start of the Starhopper project, which was the first demonstration and test stand of the program, Starship even began to compare it with the popular computer toy Kerbal Space Program. In it, the player is invited to assemble their rockets in the style of the LEGO constructor, going through the painful trial and error path and simultaneously sending little cherubs knots into the world of another, whose fate was the test of unsuccessful products on the way to a real flying rocket.

However, back to the ideas. What does Elon Musk want to launch into orbit? In rocket technology, as in many other industries, the so-called cube law applies. In a visual representation, it is formulated as follows: when the linear dimensions are doubled, the average cost of materials for the structure grows four times (the square of linear growth), but the useful volume of the product is already eight times (the cube of linear growth).

A simple fact follows from this: a heavier rocket does not just put more load into orbit – it does it with better weight efficiency. After all, it turns out that the cube grows much faster than a square – and, for example, the weight of the fuel and oxidizer tanks becomes proportionally less than the weight of the components of the chemical fuel pumped into them. And this, in turn, allows you to transfer the “freed” weight to the payload.

Hence the desire of Elon Musk to make a rocket, powerful and heavy as ever. It’s enough to mention that in the framework of the latest “edition” of the project it was announced that the starting weight of Starship should be about 5,000 tons, which is almost twice as large as the largest “classic” American lunar rocket Saturn-5. According to preliminary calculations, this will make it possible to put about 150 tons of payload into orbit. And this is without taking into account the very second stage of the rocket, which is thought by Elon Musk to be not only manned and orbital – but also reusable, with the possibility of returning to Earth and reusing.

In general, in the bold idea, Starship should become an almost magical all-in-one shampoo that should make space rockets and flights on them look like modern civil aviation – cheap, affordable and reusable. It looks smooth and beautiful on paper, but what about ravines?

How to teach a water tower to fly

It cannot be said that the idea of ​​a “bigger rocket hammer” came only now in the bright mind of Ilon Mask. The concept of big dumb booster (BDB, translated from English – “big stupid (dumb) carrier”) has been known since the early 1960s.

In 1973, Boeing Corporation calculated the ambitious Boeing Space Freighter project , whose launch mass was supposed to be 11,000 tons of cyclopean (twice as much as Mask with Starship planned today). The development of Boeing even visually resembles the current images from the presentation of the Mask, with the slight exception that the first step of Space Freighter also resembled an airplane and had to land on a regular airfield, “in the air.” To match the size, there was also a load on a low Earth orbit – almost 420 tons, together with the second stage, a spaceplane.

The second ideological ancestor of Starship can be called another Boeing project , presented a little later, in 1976, and called Boeing LEO.

A classic rocket scheme was chosen for him. The huge starting weight of this monster, which amounted to about 10,000 tons, allowed him to reach the orbit without multi-stage, using the entire rocket for landing after putting the payload into orbit. Boeing LEO was supposed to land “rocket-like,” as the first stages of the Falcon rocket do today. However, in this case, no landing poles could stand it – Boeing LEO was offered to be planted in a huge artificial lake. And the circuit with one step also had its own price – only about 200 tons were put into orbit by LEO, half as much as the Space Freighter comparable to it in size.

What did Boeing engineers face in those years – and why did these monster missiles remain in draft designs? Indeed, from the point of view of the economy, everything was on the level there – the same LEO, according to calculations, was to ensure the cost of delivering cargo to near-Earth orbit in the region … $ 45 per kilogram! For comparison, launching a payload on a Falcon 9 rocket, created by SpaceX itself, costs about $ 2,700 per kilogram: 22.8 tons of cargo on it in low Earth orbit can be launched for $ 62 million.

The main problem in these projects was materials. The missile during its flight is in very different physical conditions: some of its parts will be very hot, others will be just as cool from contact with the cryogenic components of the fuel. The entire design of the rocket will experience overloads, longitudinal and transverse forces arising at the start and during a decrease, and the operation of the main engines will also add destructive vibration at the time of launch, which also grows in a cube from the linear size of the rocket.

By the way, vibrations were encountered even when rockets reached a starting weight of 3,000 tons. In the Soviet lunar rocket N-1, vibrations several times led to the failure of individual engines. In the last launch of Saturn 5, which launched the Skylab station into near-Earth orbit, the vibration simply tore off one of the solar panels, after which the station was even considered lost for some time, and then could not work out its assigned resource.

In view of the above, sooner or later, some materials in the design of the launch vehicle begin to “fail”: overheat, lose strength or other physical properties. Indeed, no “cubic miracle” happens to them: the properties and capabilities of the same structural material of a tank on a rocket weighing 500 tons or 5000 tons are equivalent and identical.

The problem of materials has already been faced by Elon Musk himself. Starship’s original design involved the use of durable and heat-resistant carbon fiber. However, an attempt to make the Starship case out of it ran into an unexpected problem that Musk himself described . One kilogram of carbon fiber costs about $ 135. When creating a rocket hull, the entire volume of the initial material cannot be used due to the specific properties of carbon fiber, therefore

about 35% goes to marriage, and a kilogram of a finished tank costs $ 200 already. In this version, Starship would have turned out to be just “gold”.

When this fact was realized, SpaceX made a compromise, starting to use ordinary sheet steel in the design, which costs only three dollars per kilogram. But this, in turn, gave rise to another problem – the “stainless steel” simply does not withstand heating during braking of the Starship during its descent from orbit.

So far, they will try to avoid overheating of stainless steel by bleeding off cryogenic fuel residues. Cryogenic fuel will be supplied between two layers of stainless steel sheathing and will float out through many micro-holes in the outer shell. Thus, they plan to organize an ablation effect around Starship, which is organized on ordinary disposable capsules by burning out a special ablative “coating”. How this system will be working is an open question; no one has conducted full-scale tests of such a cooling scheme. In general, the Kerbal Space Program, not only on computer screens, but in reality – with stainless steel, methane and liquid oxygen. True, fortunately, it seems to be without kerbonauts-maskonauts.

Now for the good

Firstly, it’s worth saying that SpaceX is quite capable of creating a reusable system with a starting weight of two to three thousand tons. Such launch vehicles have already been launched from the Earth several times in the past, and their strengths and weaknesses are well known. The American Saturn-5 rocket and the Space Shuttle reusable system were created in this size. In the USSR, the Energia launch vehicle and the N-1 nearly-flying moon rocket had a similar launch mass.

By the way, this kind of “road to reality” can also be traced in the sketch designs of Elon Mask, published as of “for now.” The first project, the predecessor of Starship, which was called ITS and presented in 2010, had a starting weight of 10,500 tons, being exactly in the “danger zone”, where the hope of creating adequate materials and a working structure looks especially illusory. Now, Starship has shrunk to a starting weight of 5,000 tons, which is much closer both to the past, successfully flying missiles, and to the possibilities and prospects of improving rocket technology, taking into account tried and not “desired” technologies.

Secondly, Mask and his company have a lot of important “details” that greatly facilitate the implementation of the main idea – launching a rocket that is superior in weight to all developed ones. In particular, three Raptor methane-oxygen engines were already delivered to Starhopper, which, according to Mask, will be able to provide a specific impulse of 330 seconds at sea level and about 380 seconds in vacuum. For comparison, the best Russian RD-180 engines operating on kerosene and oxygen today have specific impulses of 311 and 337 seconds, respectively. Thus, Raptor in this parameter is somewhere around 6-12% more effective than the best Russian developments.

“Terra incognita” in the case of Starship, however, so far it looks much more extensive. So far, in the orbital flight of the new offspring of Elon Musk there are much more unknown or “dark spots” that can make these steps if not impossible, then certainly associated with a lot of improvements, trials, failures and a tedious search for the necessary solutions. Unless, of course, such solutions are found and possible in principle.

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