# Is there some fundamental limitation that would prevent steam-powered rockets from reaching space?

According to the Discovery Channel (see CNN article below) the latest attempt to use compressed steam propulsion to get to 5000 feet ended in tragedy. It's not yet clear the altitude it reached, previous launches reached 1,374 and 1,875 feet.

The article also says that the Discovery channel says that the eventual goal was the Karman line.

Question: Could this technology have reached the Karman line if suitably funded? I'm not asking if its a useful alternative at this point, but I'd like to know if there was some clear fundamental limitation that would have prevented this from eventually reaching 330,000 feet.

"Our thoughts and prayers go out to Mike Hughes' family and friends during this difficult time. It was always his dream to do this launch, and Science Channel was there to chronicle his journey," the Science Channel said in a statement.

Hughes was scheduled to launch his homemade rocket for a new Science Channel series called "Homemade Astronauts," according to the Discovery Channel website.

Hughes and Waldo Stakes built a steam-powered rocket with the intent of launching Hughes 5,000 feet into the air, the website said.

He eventually hoped to develop a rocket that would launch him 62 miles in the air to where the Earth's atmosphere meets outer space, according to the Discovery Channel.

There's no fundamental physical limitation, but there's certainly a practical one. The rocket equation is $$\Delta V = V_{Exhaust} \ln(M_{Total}/M_{Dry})$$. The exhaust velocity of a typical chemical rocket is around 2500 m/s to 4500 m/s, the exhaust velocity of a steam rocket is only 500 m/s or so.

You need a delta-v of around 2 km/s to reach the Karman line. With, say, a kerosene-burning gas-generator Merlin 1D, you need a mass ratio of about 2.1...slightly more than half your liftoff mass needs to be propellant. With a steam rocket, you need a ratio of around 60.

The Falcon 9 upper stage has a mass ratio of around 30, which is excellent and largely due to it using a dense fuel, while having the light tank construction of a typical turbopump-fed liquid fuel rocket. A steam rocket would have very heavy tanks due to the need to contain superheated water at high pressures. You would need many stages, allowing you to discard that mass as soon as possible, and the vehicle would be huge for its payload even by orbital launch vehicle standards.

• I see, it's because the current design has a strong and therefore heavy pressure vessel and all pressure is stored. As mentioned in this comment perhaps an onboard source of high heat generating pressure and temperature during flight could address this if it weren't also just as heavy.
– uhoh
Feb 25 '20 at 3:32
• That wouldn't be a "steam powered rocket" any more. A nuclear-thermal rocket can use water as propellant and get performance toward the low end of the chemical rocket range, since the exhaust is the same as a hydrolox rocket with suboptimal propellant ratio (stoichiometric rather than fuel-rich), while having lower temperature. The "nuclear lightbulb" mentioned requires cryogenic hydrogen to keep the "lightbulb" from melting. You might get it to work with water, but you'll have lower exhaust temperatures. Feb 25 '20 at 12:21
• @CarlWitthoft I'm not sure you are describing the situation correctly. I thought the reaction mass was steam, not water. Can you cite something that demonstrates that the reaction mass was in fact liquid? Can you also refrain from calling people "stupid" who've recently died in the process of trying to make a living? Thanks!
– uhoh
Feb 25 '20 at 15:00
• @CarlWitthoft the internet is chock-full of places where people can go and write say bad things about other people. Space SE is thankfully not one of them 99% of the time. it stands out here like a sore thumb and looks gauche.
– uhoh
Feb 25 '20 at 15:34
• The classic “steam powered rocket” is actually loaded with high temperature, high pressure liquid water. When pressure is released at launch, the liquid flashes to vapor steam which expelled as a dense (and compared to combustion rockets, slow) stream. Feb 25 '20 at 16:24