When viewed, it’s hard to forget the spectacular display the Space Shuttle’s solid rocket boosters put on during every launch. This powerful type of booster is relatively simple to manufacture but also potentially dangerous.
The primary danger and drawback of using solid rocket boosters is that they cannot be stopped once ignited. After ignition, the rocket cannot be switched off, throttled down, or restarted. Unlike a liquid propellant rocket, it burns at maximum thrust until all the solid propellant is depleted.
Before continuing, it has to be unequivocally stated that all rockets are dangerous and unsafe to some extent. There hasn’t been a single orbital rocket launch, crewed or uncrewed, that didn’t carry a significant amount of risk with it.
With that said, it is very noticeable that the vast majority of modern rockets are liquid propellant launch vehicles, and solid rocket boosters are mainly used to assist the central core and provide additional thrust during liftoff.
There are several reasons why solid rocket boosters are not the launch vehicle of choice when it comes to orbital rockets. Much of it has to do with the characteristics of this form of propulsion and, as the following section will illustrate, the dangers these rockets pose.

Why Solid Rocket Boosters Are Considered Unsafe And Dangerous
Solid rocket boosters can be a real blessing for launch service providers. They are relatively simple to produce and transport, with a superior thrust-to-weight ratio compared to their liquid propellant counterparts.
Whenever the payload requirements of missions exceed the capabilities of a single launch vehicle or need to be placed into a higher orbit, adding a couple of solid rocket boosters can make an otherwise impossible task very doable and make it look almost “effortless.”
Companies like United Launch Alliance (ULA) and Arianespace routinely use solid rocket boosters (SRB) to increase the payload capacity by providing additional thrust to their Atlas and Ariane launch vehicles, respectively.

No discussion of solid rocket boosters will be complete without mentioning the solid rocket boosters used during the Space Shuttle Program. They were the biggest and most powerful SRBs ever made and produced 85% of the launch vehicle’s thrust during liftoff.
However, although solid rocket boosters have proven to be a reliable and cost-effective way of getting launch vehicles into Low Earth Orbit and beyond, they come with some significant dangers that make them less safe than liquid propellant rockets.
Before delving into the details of what makes this form of propulsion potentially more dangerous and unsafe, one first needs to define what exactly a solid rocket booster is and how it functions:
What Is A Solid Rocket Booster?

A solid rocket booster (SRB) or solid-propellant rocket works on the same principle a liquid-propellant rocket does in the sense of blowing hot gases at high velocities out its nozzle to propel the rocket forward.
The primary difference between the two engines is that an SRB uses a solid fuel/oxidizer mix for combustion, unlike a liquid-propellant rocket that carries its fuel & oxidizer in separate internal tanks, which are also mixed and ignited in a separate combustion chamber.
The fuel/oxidizer mix is applied to the inside of the rocket’s shell and runs the full length of the rocket. The fuel typically consists of aluminum powder, while the oxidizer is a type of ammonium perchlorate. They are combined in a rubber-like substance.
A cylindrical hole also running the full length of the rocket acts a the combustion chamber, from where the hot gases are expelled through the rocket’s nozzle.
When the rocket is ignited, the combustion takes place throughout the length of the cylindrical combustion chamber, with the surface area of the surrounding walls (consisting of the solid propellant and oxidizer) acting as the burn surface.
As a result, the solid propellant burns from the rocket’s central axis towards the outside covering. In a typical cylindrical hole this will result in the burn area expanding as the fuel burns through the inner walls of the central chamber.
(Much research has been conducted on various forms apart from a simple cylindrical shaped combustion chamber, though, resulting in specifically designed shapes to allow for various burn rates during the rocket’s operation.)
Solid rocket boosters have several advantages and disadvantages, but there are three major drawbacks of this type of rocket propulsion that make it especially dangerous and unsafe.
1) Once Ignited, A Solid Rocket Booster Cannot Be Switched Off
Once the ignition charge starts the rocket, it cannot be switched off and burns until the fuel is completely depleted (usually after approximately 2 minutes.)
This means if any malfunction or other serious problem occurs, there is no way of shutting the rocket down. With a liquid propellant rocket, shutting down the flow of fuel can stop the engine or at the very least, allow time for contingency protocols to be activated.
(Learn more about the difference between liquid and solid propellant rockets in this article.)
2) A Solid Rocket Booster Cannot Be Throttled Down Or Restarted
A solid rocket booster also cannot be throttled down or restarted at a later stage. It essentially means an SRB can only be used once during launch & left to burn until the fuel is spent. (Primarily why it is used as a first-stage booster and jettisoned after fuel depletion.)

On 28 January 1986, the Space Shuttle Challenger was destroyed when the O-ring seals failed in a joint of its right solid rocket booster, causing the external fuel tank to explode, destroying the shuttle. (The two solid boosters’ were remotely detonated seconds later.)
If the solid boosters had a form of throttle control, shutting or throttling the right thruster down might have prevented the joint from opening and the hot gases from escaping long enough for the vehicle to jettison the solid boosters away safely.
(Solid rocket boosters are by no means the only reason rockets fail and sometimes explode in spectacular fashion. Learn more about why rockets explode in the following article.)
3) The Fuel And Oxidizer Are Mixed Together During Manufacturing
The fuel and oxidizer are also mixed together as a solid rubber-like substance during the rocket’s manufacturing, which means any accidental ignition or sudden compromise of the vehicle’s structure can result in instant catastrophic combustion.
On 22 August 2003, the Brazilian Space Agency suffered a major disaster when one of the four solid rocket boosters accidentally combusted on the launchpad, destroying the launch vehicle & entire launch platform and killing 21 technicians working on the site.
The Advantages And Disadvantages Of Solid Rocket Boosters
Much of the emphasis so far has been on the disadvantages or dangers associated with solid rocket boosters. It is important, however, to provide a balanced view of this form of rocket propulsion by highlighting both its advantages and disadvantages:
Advantages Of Solid Rocket Boosters
- Cheaper And Easier To Manufacture
- Simpler Design With Fewer Components
- Greater Power-To-Mass Ratio Compared To Liquid Propellant Rockets
- Premixed Solid Fuel/Oxidizer Propellant Allows For Easier Transport
- Provides Additional Payload and Orbital Capacity To Existing Launch Vehicles
Disadvantages Of Solid Rocket Boosters
- A Solid Rocket Booster Cannot Be Switched Off Once Ignited
- It Cannot Be Throttled Down Or Restarted
- Danger Of Accidental Detonation Due To Solid Fuel/Oxidizer Mix
From this comparison, it may seem that there are more advantages than disadvantages to using solid rocket boosters. It is undeniable that there are several reasons why using them will make perfect sense. This, however, does not negate their inherent dangers.
Conclusion
As stated during the introduction, all rockets are dangerous and unsafe to some extent. There hasn’t been a single orbital rocket launch, crewed or uncrewed, that didn’t carry a significant amount of risk with it.
Solid rocket boosters fulfill a crucial role in the space industry, and their advantages are undeniable. However, the dangers associated with them always have to be taken into consideration, especially when very sensitive launches like crewed missions are planned.
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