The tyranny of the rocket equation | Don Pettit | TEDxHouston 2013
Why Space Exploration Stack Exchange recommends it
Space Stack Exchange users link it as a plain-language, authoritative explanation of why rockets are mostly fuel and why the rocket equation limits mission design.
Recommended by 2 people across 2 different months, 2016 to 2025.
What it is
A 12-minute TEDx talk by NASA astronaut Don Pettit on the rocket equation and why getting mass to orbit is so hard. He explains how most of a launch vehicle must be propellant and how that shapes spaceflight, including a worked example for travel to Mars.
What people said
Recommends kim holder · 2016-01 · Space Exploration Stack Exchange · on “Engineering difficulties towards near-perfect rockets?”
The main problem is that in order to have enough thrust to get a rocket out of the atmosphere and up to orbital velocity, 85% to 90% of the rocket has to be fuel. So you have a controlled explosion, essentially, in which thousands of pounds of fuel is combusting each second and the force of that is being directed out of nozzles, pushing a rocket upwards with forces of several gravities, through supersonic winds, and you have to make the structure and engines that support all those forces as light as possible. This is a good overview on the topic by astronaut Don Pettit: Even very minor failures can cause payload to fail to reach orbit or the loss of the vehicle, because there is so little ma
Recommends Slarty · 2021-03 · Space Exploration Stack Exchange · on “Mars in 30 Days”
This sort of discussion can easily get stuck as there are a lot of different connected issues. But the heart of the problem is the rocket equation and understanding what it means. In layman’s terms what it means is that the faster you go the harder it gets to go faster still. If you burn 90% of the rocket as propellant to go at one speed, in order to go twice as fast you must burn 99% of the rocket as propellant. Try this link [this video] and see how you get on. I suspect what you think should happen would only happen if extra propellant could be found in orbit.
Cites user12102 · 2018-09 · Space Exploration Stack Exchange · on “3* Tonnes Unaccounted for in Falcon 9 FT Weight Wikipedia Calculation?”
NASA Astronaut Don Pettit's Tyranny of the Rocket Equation [LINK] as well as the underlying Tsiolkovsky rocket equation [LINK] dictate that most of a rocket's mass when launched from Earth is propellant. Very roughly it's 90% but it varies by mission and by vehicle. [LINK] Does this 3* tonne difference relate to propellant density? So the tl;dr might be yes, while the dry weights might be more stable (as they are for say cars), the total weight spec for rockets is mostly that of the propellants. However without the actual detailed tallies used in each case, it's almost impossible to be sure if there aren't several different part-per-thousand effects that add up to 5 parts per thousand. The f
Cites Roger Wang · 2019-11 · Space Exploration Stack Exchange · on “Velocity of a rocket needed to get to Mars”
At 2:16 in this video [this video] , Don Pettit says he used the Rocket Equation to determine the velocity of the rocket needed to travel to Mars, which was 16 km/s. I am not sure as how he did it though, and was unsure if he used the escape velocity of Earth, the Hohmann Transfer, and also if that was only that velocity computed needed to be obtained once or through some timeframe. Also, the velocity of the rocket needed to travel to the Moon was 14 km/s, so I was also wondering how much the gravity of the Sun mattered as well.
Cites BrendanLuke15 · 2021-12 · Space Exploration Stack Exchange · on “Which deorbit trajectory minimizes reentry heating?”
@ChristopherJamesHuff is right, [LINK] many assumptions need to be made to make this feasible, but assuming a ballistic Crew Dragon entry [LINK] from a 400 km circular orbit is enough to demonstrate some important concepts. Working off of the "pick a velocity and drop" mantra, here is a plot of the key metrics as a function of the (atmosphere intersecting) transfer orbit periapsis (i.e., how much you wish to slow down): [LINK] Note the logarithmic scale on the right plots. The tyranny of the rocket equation [this video] pretty much constrains us to the right hand extremes of the X-axis (and the relative squishiness of most payloads limits max g-forces). As @RusselBorogove points out [LINK] the ma
Cites BrendanLuke15 · 2022-01 · Space Exploration Stack Exchange · on “Elon Musk's ITS Travel Time to Mars Estimate”
What is unique about the ITS that would make the travel time so much shorter? Is the propulsion method described in existence today? The current manifestation of the ITS is Starship [LINK] , and the performance estimates of such a vehicle have shrunk considerably since the public reveal of the ITS [LINK] (it is very much so a different vehicle though so not an apples to apples comparison). The propulsion system on all manifestations of ITS/BFR/Starship is not exactly revolutionary. It uses chemical rocket engines the same way that the Apollo missions did 50+ years ago (albeit with different propellants and significantly better cost & mass efficiency). The in-space long term storage, transfer
Cites David Hammen · 2025-04 · Space Exploration Stack Exchange · on “What prevents solar sails from being used?”
@Mithoron The appeal is that solar sails are one of the very, very few ways we humans have discovered that escape the tyranny of the rocket equation [this video] .