Friday has arrived, and the weekly "A Taste of Science for the Weekend" column is here despite the war — issue no. 51.
This week: multistage rockets and solid fuel.
---
On Wednesday, the eyes of millions across the Middle East were riveted to an extraordinary sight.
It was "only" another rocket carrying a warhead of several hundred kilograms — nothing we haven't seen before — but its trail was unlike anything typical.
The mystery was solved later when the Iranian regime announced it had launched the Sejjil: a two-stage ballistic missile powered by solid fuel, reaching a speed of 2,000 km/h, weighing 23 tons, and standing 18 meters tall.
Behind these figures lies a fascinating world of precise science.
---
Conventional missiles are usually powered by liquid fuel.
Liquid fuel can be based on cryogenic liquids — substances that remain in a liquid state only at temperatures below minus 153 degrees Celsius, such as oxygen.
The problem with such liquid fuel is that keeping it cold enough is extremely difficult.
Other liquid fuels are based on chemicals that are liquid at room temperature, but these tend to degrade over time and lose their effectiveness.
For these reasons, fueling with liquid propellant must take place close to the launch site and shortly before launch, using complex fuel-injection systems.
The thermal and chemical signatures of the fuel can be detected relatively easily by various intelligence means, and the fact that fueling occurs near the launch site and time during wartime makes that site especially vulnerable.
---
Solid fuel solves these problems by using a solid compound of fuel, oxidizer, and a binding agent.
The main advantage is that solid fuel retains its stability and integrity over time, meaning a missile can be fueled and stored at a remote launch site years before it is actually fired.
Another advantage of solid fuel is that it stays fixed within the missile's body, unlike liquid fuel, which can shift inside and disturb the missile's trajectory.
---
The second distinctive feature of this missile is its use of stages.
A missile's velocity is described by an equation known as the Tsiolkovsky rocket equation, which shows that the greater the missile's mass, the lower its maximum attainable speed.
Splitting the fuel tank into two stages makes it possible to shed excess weight during flight, so that the remaining fuel accelerates a much smaller mass to a far higher velocity.
Other physical aspects of the missile's design are intended to allow it to survive the enormous speeds and extreme temperatures it is exposed to.
During launch and atmospheric reentry, the missile is subjected to extreme temperature swings — from tens of degrees below zero to thousands of degrees Celsius.
The acceleration forces and aerodynamic drag acting on it can tear apart even exceptionally strong materials, and highly precise engineering is required to prevent the missile from breaking apart in flight.
---
It is worth noting that none of these are technologies unique to the Sejjil.
Other countries possess offensive rockets based on solid fuel, and two-stage propulsion can also be found in civilian applications, such as the launch vehicles of SpaceX and NASA.
---
Despite the beauty of the technology, this time it was unfortunately used in an attempt to strike us.
We hope the war ends very soon, and that we continue to encounter technologies like these only in a civilian context.
Shabbat Shalom 😊
#ATasteOfScienceForTheWeekend #ATasteOfPhysics
Video credit: Abu Ali Express