The Rocket Builder’s Handbook of the Twenty-First Century

Tuesday, December 29th, 2015

Elon Musk and his SpaceX team threw out the Rocket Builder’s Handbook of the Twentieth Century and started from scratch with their own designs:

Instead of using a foundation of flight-tested but badly outdated designs, they designed a brand-new rocket, built using modern materials and techniques.

Instead of building high-performance rocket engines with exotic alloys to squeeze out every ounce of performance, they sacrificed some performance for a large reduction in cost.

Instead of building a larger, more powerful rocket engine for the booster stage, they designed it to use nine smaller ones.

Instead of using expensive radiation-hardened computers, they chose a low-cost design using three redundant computers built from ‘off the shelf’ components.

Instead of using flight computers in the uppermost stage alone, they used identical avionics in both stages to facilitate booster stage recovery.

Not only did using nine booster engines provide assurance that a launch would succeed even if an engine failed, it opened up options to recover the booster stages at some later date. By using virtually identical engines on both the booster and the second stage, they would also get more engine performance data per launch while reducing both cost and design complexity.

SpaceX also designed the booster stage of the Falcon 9 to have far more power than was required to launch the most common medium-weight payloads into space. This extra power provided the margin SpaceX needed to develop a recovery system without having to take a future hit on the vehicle’s payload capacity. Even as an expendable launch vehicle, the Falcon 9 is already one of the lowest-cost in its class, putting the company ahead of its competition even without reusability.

SpaceX Falcon 9 Launch Profile

The recovery system that SpaceX finally arrived at was nothing more complicated than fuel, landing legs, grid fins, and updated flight software. This system took advantage of the vehicle’s extra fuel capacity and lighter weight to create a reusable booster stage out of an expendable one. Reusability could then be achieved with minimal structural changes to the existing booster stage.


  1. James James says:

    “they sacrificed some performance for a large reduction in cost”

    I’m curious, in space rocketry, what other measure of performance is there other than cost?

  2. Assuming a set Delta-V, payload fraction is the main area you can compromise. A few large-chambered engines specialized for the first-stage role are a more efficient use of mass than 9 small general-purpose ones, for instance. 3 redundant COTS computers are probably heavier than 1 radiation-hardened one. So on and so forth. The general rule for components and systems in rocketry is cheap = heavy.

  3. Isegoria says:

    Whoops! A typo ate the text of the link (“their own designs”). Fixed it.

  4. Slovenian Guest says:

    Fun fact, from

    “The Falcon 9 rocket costs about $16 million to build … but the cost of the propellant, which is mostly oxygen and a gas, is only about $200,000,” Musk said. “So that means that the potential cost reduction in the long term is probably in excess of a factor of a hundred.”

  5. Slovenian Guest says:

    And Just a Tinkerer (John Gardi) on How Elon Musk Can Build the Hyperloop for a Tenth the Cost of High-Speed Rail.

    He and Musk are even Twitter buddies. La di da!

  6. Admittedly, building the Hyperloop at a tenth the cost of high-speed rail isn’t as much of a feat as it sounds. Much of the cost of modern high-speed rail projects have nothing to do with engineering. I’m confident that the America of the ’50s gifted with the technology of today could build high-speed rail systems at maybe 1/20th the expense of their modern counterparts.

  7. Candide III says:

    I always reference this post on Hyperloop to counter the hype — and this update on costs.

  8. Our illustrious ancestors would probably build a hyperloop to the moon, which would confuse the heck out of Elon Musk.

    The real trick in rocketry is to decide exactly where you can economize. Deciding to use three COTS computers instead of one custom might save you 90% on cost but cost you x2 on weight. Deciding to use a cheaper (weaker, heavier) alloy might save you 90% on cost because it’s not only a cheaper material, it’s easier to work with. But it might fail catastrophically and your rocket goes ‘splodey.

    Scipio answered my semi-rhetorical question on one of the other SpaceX posts. Rockets are hard, I am impressed with Musk and SpaceX’s achievement. And to a lesser extent, with Tesla.

    Musk has made real what many have talked about for decades. And while many of the ideas have been there, it’s not like he walked into the rocket design store and picked the Falcon 9 design off the shelf and went back to his garage and built it. He and his team designed it, and made it work, and more – returned it to earth.

    He has accepted government contracts, and government loans. That’s the environment we live in. Does that make him a rentseeker? He’s actually built a reusable rocket, the which Boeing, Lockheed, and countless government contractors have not despite half a century and probably trillions of dollars.

  9. “Our illustrious ancestors would probably build a hyperloop to the moon, which would confuse the heck out of Elon Musk”


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