Adam Laakmann is Chief Engineer at Aerojet Rocketdyne, and has been making a series of interesting and humorous "Rocket Facts" posts on his LinkedIn account. Adam gave me permission to repost them to the forum. Enjoy.
Rocket Facts!
#1: Solid rocket motors pack all their propellant into the combustion chamber, eliminating the need for separate fuel and oxidizer tanks, plumbing, and heat exchangers. This is a large part of why solid rockets are much less costly than liquids. It's also why, unlike their shamelessly gaudy liquid cousins, solid rockets don't need to wrap themselves in a tangle of shiny pipes to look good.
Rocket Facts!
#2: Solid rocket motors survive the intense heat of combustion by torching their guts and spewing out the ashes. (Yum!) The insulators, nozzle throats, and exit cones are ablative and are designed to char and erode away, protecting the underlying material and helping maintain the integrity of the motor during operation.
As a bonus, all of the material that erodes away and exits through the nozzle not only provides a little extra impulse, but also reduces the amount of inert weight the rocket has to carry, allowing for increased range, velocity, and payload capacity. Less ass = more push!
Rocket Facts!
#3: Solid propellants have the consistency of a pencil eraser. This is due to the rubber binders that hold them together.
Unlike a pencil eraser, however, propellant is absolutely terrible at erasing. It mostly just smudges the lead around on the paper, but doesn't remove it. (Don't ask how I know this.) Rubbing faster and harder will improve erasing performance, but it's not optimal because it does so by friction heating the propellant to its autoignition temperature and burning the paper, errant pencil marks and all. And also your fingers. Those will get erased, too.
Say what? Another Rocket Fact??
#4: Solid rockets are able to generate pressure and thrust without the use of turbomachinery, commonly called cheater pumps. How are they able to pull off this miracle, you ask? Why, magic, of course! That magic, however, is supplemented by getting a bunch of hot-and-bothered fuel and oxidizer molecules whipped up into a frenzy -- a chemical orgy, if you will -- and releasing all their pent up energy as a chamber-filling hot gasgasm. Sultry.
More Rocket Facts!
#5: Once solid propellant is cured, it can be stored for years -- even decades -- without suffering from any performance degradation. And when they're ready to fire, they work as well as the day they were harvested from the Rocket Orchard. This is why solid rockets are generally preferred over liquids for defense applications. Because bad guys don't announce ahead of time when they're planning to attack, nor do they acquiesce to requests like "hang on a sec, I've got to tank up my missiles."
Rocket Facts!
#6: Results of a recent survey* show that "Ballistician" is the coolest job title in all of rocketdom. But, what exactly is a ballistician?
In a nutshell, ballisticians are the best looking and most charming people in solid rocket world and are responsible for defining the geometry of the propellant grain -- a task that requires the most intimate knowledge of *all* the shapes they teach you about in kindergarten. They are also responsible for sizing throats and igniters, optimizing nozzle contours, predicting motor performance, and, most importantly, blaming the chemists for making bad propellant when the predicted motor performance doesn't match the test data.
If you're good-looking, charming, and know the difference between a circle and a triangle (or as we call it in the biz, a "pointy circle"), there may be a future in Ballistics for you!
*Survey results based on a single response from me.
Rocket Facts!
Now inspired by drinking at the beach!
#8: While enjoying some time away from work and explaining the finer points of beer tapping (the hitting someone's bottle kind, not the starting into a new keg kind) to my kid, I realized that I had dedicated a whopping seven posts to the greatness of solid rockets but have pretty much ignored all the other types of rocket propulsion that are out there. Maybe this is the beer talking (okay, it's definitely the beer), but I'm going to dedicate this post to showing love to all the other types of rockets out there...and say something nice about each one.
* Solid rockets: sexy; happy to sit around patiently waiting till you're ready for them, but when the mood strikes, they bring the big thrust and lots of it.
* Nuclear rockets: hot; can carry the big loads; will get you there fast and leave you glowing afterwards
* Cold gas rockets: not hot; get even less hot as they blow; but they're clean
* Ion rockets: they may not be the biggest of thrusters, but what they lack in size, they make up for in stamina. They can go all...night...long. And keep going for what seems like forever.
* Tapped beer: low thrust, but lots of sloppy exhaust, usually released prematurely and unexpectedly. Tastes good, though.
* Balloons: good with children, make hilarious farty sounds
* Liquid rocket engines: Moist.
This list is definitely not complete and only marginally educational, but I need another pint of liquid inspiration. Feel free to suggest additions to the list and help me educate (edutain?) the very small corner of the LinkedIn world that has the fortune/misfortune of seeing these posts.
Rocket Facts!
#9: Jack. Parsons.
There are rocket scientists. There are especially eccentric rocket scientists. And then there's Jack Parsons.
One of the OG's of American rocketry, Jack Parsons was involved with what eventually would become JPL and co-founded the world's greatest rocket company, Aerojet. But being a brilliant engineer and expert in explosives was far and away the least interesting thing about this man.
In a nutshell, this cat got in with occultist Aleister Crowley; cheated on his wife, Helen, with her sister, Sara; lost Sara to L. Ron Hubbard (yes, *that* L. Ron Hubbard); got defrauded out of his cashy money by Sara and L. Ron; and died tragically at the tender age of 37 in an explosion at his home that was a (choose one: accident/suicide/murder). And if that's not crazy enough, his birth name wasn't Jack...it was Marvel!
If Jack Parsons was still alive today, the Dos Equis guy would only be the second most interesting man in the world. A very distant second.
Rocket Facts!
#10: O-rings -- the chewiest and least delicious donuts you'll ever eat.
Unbeknownst to few, solid propellants burn really hot. “Cool” propellants burn on the order the of 3000°F, which is sweater weather for your average Floridian. Spicy propellants, however, can burn in excess of 6000°F, midway between “asphalt in Vegas on a hot summer day” and the surface of the sun. At those temperatures pretty much everything used to make a rocket motor will get annihilated. Most of the materials we use offer up their flesh as sacrifices to the fire gods so that they may be allowed to survive long enough to complete the mission. And that works for keeping all the individual components in a motor intact. But what about the spaces between those components?
Rocket motors are typically built up out of various subassemblies. An igniter might get shoved in the front end of the motor. A nozzle and aft closure might get shoved into the back. Where all those different parts mate together, there are gaps. And gaps are bad when you’ve got a bunch of rowdy, hot, gaseous combustion products trying to get out of the motor and you need them to exit in an orderly fashion through the throat. Combustion products do not tend toward being orderly, nor do they care where you *want* them to go. If they see a hole, they’re going in it, whether it’s the right hole or not. (Let my permanent record show that I exercised restraint in not taking this metaphor to the next level.)
Enter the humble o-ring.
By and large, rocket motor o-rings aren’t particularly special. They’re flimsy. They’re thin. They’re not made of exotic materials. They’re cheap enough that a kid could buy some with Tooth Fairy money. And most of them can’t even stand up to temperatures over a few hundred degrees, let alone a few thousand. So how in Goddard’s mustache do these low rent jelly bracelets keep 6000°F gas at bay? Because they BELIEVE IN THEMSELVES!!! Also, clever design work coupled with the physics of heat transfer.
When possible, motor joints are designed to make it a challenge for hot gas to work its way back to the o-ring. Instead of giving the gas a short direct path, designers try to force it to take a more circuitous route. This allows it to lose a little bit of its rambunctiousness and be cooler by the time it runs into the rubber. Once the gas gets there, the pressure driving it now serves to prevent it from traveling any further by pushing on the o-ring and causing it to deform and wedge firmly in the gap, making a nice, tight seal. With it's egress now blocked, the gas has nowhere to go. And like Gandalf staring down the Balrog, the o-ring, brimming with confidence, declares to the now neutered hellfire “sitcho ass down, chump, cuz you ain't passing through here!” Defeated, the hot gas loses its will to transfer heat and crumples in a heap at the feet of the victorious o-ring. Glorious.
Tune in next time for "When O-rings Lose!"
Rocket Facts! #1: Solid rocket motors pack all their propellant into the combustion chamber, eliminating the need for separate fuel and oxidizer tanks, plumbing, and heat exchangers. This is a large part of why solid rockets are much less costly than liquids. It's also why, unlike their shamelessly gaudy liquid cousins, solid rockets don't need to wrap themselves in a tangle of shiny pipes to look good.
Rocket Facts! #2: Solid rocket motors survive the intense heat of combustion by torching their guts and spewing out the ashes. (Yum!) The insulators, nozzle throats, and exit cones are ablative and are designed to char and erode away, protecting the underlying material and helping maintain the integrity of the motor during operation.
As a bonus, all of the material that erodes away and exits through the nozzle not only provides a little extra impulse, but also reduces the amount of inert weight the rocket has to carry, allowing for increased range, velocity, and payload capacity. Less ass = more push!
Rocket Facts! #3: Solid propellants have the consistency of a pencil eraser. This is due to the rubber binders that hold them together.
Unlike a pencil eraser, however, propellant is absolutely terrible at erasing. It mostly just smudges the lead around on the paper, but doesn't remove it. (Don't ask how I know this.) Rubbing faster and harder will improve erasing performance, but it's not optimal because it does so by friction heating the propellant to its autoignition temperature and burning the paper, errant pencil marks and all. And also your fingers. Those will get erased, too.
Say what? Another Rocket Fact?? #4: Solid rockets are able to generate pressure and thrust without the use of turbomachinery, commonly called cheater pumps. How are they able to pull off this miracle, you ask? Why, magic, of course! That magic, however, is supplemented by getting a bunch of hot-and-bothered fuel and oxidizer molecules whipped up into a frenzy -- a chemical orgy, if you will -- and releasing all their pent up energy as a chamber-filling hot gasgasm. Sultry.
More Rocket Facts! #5: Once solid propellant is cured, it can be stored for years -- even decades -- without suffering from any performance degradation. And when they're ready to fire, they work as well as the day they were harvested from the Rocket Orchard. This is why solid rockets are generally preferred over liquids for defense applications. Because bad guys don't announce ahead of time when they're planning to attack, nor do they acquiesce to requests like "hang on a sec, I've got to tank up my missiles."
Rocket Facts! #6: Results of a recent survey* show that "Ballistician" is the coolest job title in all of rocketdom. But, what exactly is a ballistician?
In a nutshell, ballisticians are the best looking and most charming people in solid rocket world and are responsible for defining the geometry of the propellant grain -- a task that requires the most intimate knowledge of *all* the shapes they teach you about in kindergarten. They are also responsible for sizing throats and igniters, optimizing nozzle contours, predicting motor performance, and, most importantly, blaming the chemists for making bad propellant when the predicted motor performance doesn't match the test data.
If you're good-looking, charming, and know the difference between a circle and a triangle (or as we call it in the biz, a "pointy circle"), there may be a future in Ballistics for you!
*Survey results based on a single response from me.
Rocket Facts! Now inspired by drinking at the beach! #8: While enjoying some time away from work and explaining the finer points of beer tapping (the hitting someone's bottle kind, not the starting into a new keg kind) to my kid, I realized that I had dedicated a whopping seven posts to the greatness of solid rockets but have pretty much ignored all the other types of rocket propulsion that are out there. Maybe this is the beer talking (okay, it's definitely the beer), but I'm going to dedicate this post to showing love to all the other types of rockets out there...and say something nice about each one.
* Solid rockets: sexy; happy to sit around patiently waiting till you're ready for them, but when the mood strikes, they bring the big thrust and lots of it.
* Nuclear rockets: hot; can carry the big loads; will get you there fast and leave you glowing afterwards
* Cold gas rockets: not hot; get even less hot as they blow; but they're clean
* Ion rockets: they may not be the biggest of thrusters, but what they lack in size, they make up for in stamina. They can go all...night...long. And keep going for what seems like forever.
* Tapped beer: low thrust, but lots of sloppy exhaust, usually released prematurely and unexpectedly. Tastes good, though.
* Balloons: good with children, make hilarious farty sounds
* Liquid rocket engines: Moist.
This list is definitely not complete and only marginally educational, but I need another pint of liquid inspiration. Feel free to suggest additions to the list and help me educate (edutain?) the very small corner of the LinkedIn world that has the fortune/misfortune of seeing these posts.
Rocket Facts! #9: Jack. Parsons.
There are rocket scientists. There are especially eccentric rocket scientists. And then there's Jack Parsons.
One of the OG's of American rocketry, Jack Parsons was involved with what eventually would become JPL and co-founded the world's greatest rocket company, Aerojet. But being a brilliant engineer and expert in explosives was far and away the least interesting thing about this man.
In a nutshell, this cat got in with occultist Aleister Crowley; cheated on his wife, Helen, with her sister, Sara; lost Sara to L. Ron Hubbard (yes, *that* L. Ron Hubbard); got defrauded out of his cashy money by Sara and L. Ron; and died tragically at the tender age of 37 in an explosion at his home that was a (choose one: accident/suicide/murder). And if that's not crazy enough, his birth name wasn't Jack...it was Marvel!
If Jack Parsons was still alive today, the Dos Equis guy would only be the second most interesting man in the world. A very distant second.
Rocket Facts! #10: O-rings -- the chewiest and least delicious donuts you'll ever eat.
Unbeknownst to few, solid propellants burn really hot. “Cool” propellants burn on the order the of 3000°F, which is sweater weather for your average Floridian. Spicy propellants, however, can burn in excess of 6000°F, midway between “asphalt in Vegas on a hot summer day” and the surface of the sun. At those temperatures pretty much everything used to make a rocket motor will get annihilated. Most of the materials we use offer up their flesh as sacrifices to the fire gods so that they may be allowed to survive long enough to complete the mission. And that works for keeping all the individual components in a motor intact. But what about the spaces between those components?
Rocket motors are typically built up out of various subassemblies. An igniter might get shoved in the front end of the motor. A nozzle and aft closure might get shoved into the back. Where all those different parts mate together, there are gaps. And gaps are bad when you’ve got a bunch of rowdy, hot, gaseous combustion products trying to get out of the motor and you need them to exit in an orderly fashion through the throat. Combustion products do not tend toward being orderly, nor do they care where you *want* them to go. If they see a hole, they’re going in it, whether it’s the right hole or not. (Let my permanent record show that I exercised restraint in not taking this metaphor to the next level.)
Enter the humble o-ring.
By and large, rocket motor o-rings aren’t particularly special. They’re flimsy. They’re thin. They’re not made of exotic materials. They’re cheap enough that a kid could buy some with Tooth Fairy money. And most of them can’t even stand up to temperatures over a few hundred degrees, let alone a few thousand. So how in Goddard’s mustache do these low rent jelly bracelets keep 6000°F gas at bay? Because they BELIEVE IN THEMSELVES!!! Also, clever design work coupled with the physics of heat transfer.
When possible, motor joints are designed to make it a challenge for hot gas to work its way back to the o-ring. Instead of giving the gas a short direct path, designers try to force it to take a more circuitous route. This allows it to lose a little bit of its rambunctiousness and be cooler by the time it runs into the rubber. Once the gas gets there, the pressure driving it now serves to prevent it from traveling any further by pushing on the o-ring and causing it to deform and wedge firmly in the gap, making a nice, tight seal. With it's egress now blocked, the gas has nowhere to go. And like Gandalf staring down the Balrog, the o-ring, brimming with confidence, declares to the now neutered hellfire “sitcho ass down, chump, cuz you ain't passing through here!” Defeated, the hot gas loses its will to transfer heat and crumples in a heap at the feet of the victorious o-ring. Glorious.
Tune in next time for "When O-rings Lose!"
