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Author of blog piece seems to be very confused about how staged rockets work, and appears to think that a two stage rocket is somehow inherently more efficient

by cstross 14y ago

Author of blog piece seems to be very confused about how staged rockets work, and appears to think that a two stage rocket is somehow inherently more efficient than a three stage rocket! Which is just plain wrong. http://en.wikipedia.org/wiki/Multistage_rocket http://en.wikipedia.org/wiki/Multistage_rocket What he might be getting is that, if Iran had stuck a third stage on top of a pre-existing two stage IRBM in order to put a tiny wee satellite into orbit, then it would imply that the rocket in question was borderline-capable and not really amenable to being upgraded further. But the Safir-2 is apparently a 2-stage rocket with the ability to reach orbital velocity, implying that by adding boosters or a third stage to it a much larger payload could be launched.

mistercow 14y ago
I was thinking that might be what he meant, but then he says this: >While a three-stage rocket is simple and is limited on how much of a weight threshold it can lift, the more advanced two-stage can be expanded for larger weights. The first part of that is, I'm pretty sure, the opposite of true. The second part is sort of true, but the "expansion" in question would be... adding a third stage. I think he heard the Geoffrey Forden quote and misunderstood the point, which is admittedly subtle. I think what Forden meant was: "If they need three stages to do just this, then they'll never be able to use this to launch a human, because a four-stage rocket is completely beyond them. But if they can do this with only two stages, they could get a human to space with three stages."
- cstross 14y ago
  Yup, that was my reading, too.
ChuckMcM 14y ago
"Confused" is probably not the correct word here, if this journalist is similar to western journalists then I would expect them not to have any idea how rockets work or even a passing knowledge of physics. Combine that with a language translation stage and well, accuracy is probably not high. The book "Rocket Propulsion Elements" [1] which is pretty much everything known about rockets that isn't classified, is pretty dense for a reason. I certainly don't hold it against the journalists who are trying to do their job as best they can. That said, because launching heavy things into space can also be used to launch heavy things around the globe and into other peoples territory, there are aspects of the technology that are closely watched. One of them is cryogenic turbo pumps. These are pumps which can pump a cryogenic fluid at high pressure and flow rates. Those are an essential part of the space puzzle because once you get a functional cryogenic rocket engine you can add additional engines and fuel at a relatively constant mass/payload ratio. And then that means if you have a payload of mass X, and an orbit of O (or sub-orbit if you're talking ICBM) you can build a delivery system to make that work. Of course other controlled technologies are guidance systems and launch 'racks'. If Iran was looking for something more than a PR ploy I think they should host a middle east space conference with peer reviewed papers. To get to where SpaceX is, and where Iran wants to be, is rocket science but it is also achievable rocket development. Open discussion would lend an air of legitimacy to the research (today most westerners assume its simply a quest for missile technology) and probably advance their programs more effectively. [1] http://www.amazon.com/Rocket-Propulsion-Elements-George-Sutton/dp/0470080248/ http://www.amazon.com/Rocket-Propulsion-Elements-George-Sutt...
ucee054 14y ago
When the author says the three stage rocket is simple, he is saying that that rocket is simple, not that three stages is simple. The author's English is correct with the meaning but can be misread. He hasn't used English that can be unambiguously parsed, presumably because he is not a native English speaker - I assume he is a native Persian speaker. The author is obviously saying that the rocket currently being deployed in two stages is more advanced than the rocket currently being deployed in three, which is why the former will be capable of more when it too is deployed in three stages. You just chose to parse it the wrong way, and then call the author's writing just plain wrong.

by cstross 14y ago

mistercow 14y ago

I was thinking that might be what he meant, but then he says this: >While a three-stage rocket is simple and is limited on how much of a weight threshold it can lift, the more advanced two-stage can be expanded for larger weights. The first part of that is, I'm pretty sure, the opposite of true. The second part is sort of true, but the "expansion" in question would be... adding a third stage. I think he heard the Geoffrey Forden quote and misunderstood the point, which is admittedly subtle. I think what Forden meant was: "If they need three stages to do just this, then they'll never be able to use this to launch a human, because a four-stage rocket is completely beyond them. But if they can do this with only two stages, they could get a human to space with three stages."

cstross 14y ago
Yup, that was my reading, too.

ChuckMcM 14y ago

"Confused" is probably not the correct word here, if this journalist is similar to western journalists then I would expect them not to have any idea how rockets work or even a passing knowledge of physics. Combine that with a language translation stage and well, accuracy is probably not high. The book "Rocket Propulsion Elements" [1] which is pretty much everything known about rockets that isn't classified, is pretty dense for a reason. I certainly don't hold it against the journalists who are trying to do their job as best they can. That said, because launching heavy things into space can also be used to launch heavy things around the globe and into other peoples territory, there are aspects of the technology that are closely watched. One of them is cryogenic turbo pumps. These are pumps which can pump a cryogenic fluid at high pressure and flow rates. Those are an essential part of the space puzzle because once you get a functional cryogenic rocket engine you can add additional engines and fuel at a relatively constant mass/payload ratio. And then that means if you have a payload of mass X, and an orbit of O (or sub-orbit if you're talking ICBM) you can build a delivery system to make that work. Of course other controlled technologies are guidance systems and launch 'racks'. If Iran was looking for something more than a PR ploy I think they should host a middle east space conference with peer reviewed papers. To get to where SpaceX is, and where Iran wants to be, is rocket science but it is also achievable rocket development. Open discussion would lend an air of legitimacy to the research (today most westerners assume its simply a quest for missile technology) and probably advance their programs more effectively. [1] http://www.amazon.com/Rocket-Propulsion-Elements-George-Sutton/dp/0470080248/ http://www.amazon.com/Rocket-Propulsion-Elements-George-Sutt...

ucee054 14y ago

When the author says the three stage rocket is simple, he is saying that that rocket is simple, not that three stages is simple. The author's English is correct with the meaning but can be misread. He hasn't used English that can be unambiguously parsed, presumably because he is not a native English speaker - I assume he is a native Persian speaker. The author is obviously saying that the rocket currently being deployed in two stages is more advanced than the rocket currently being deployed in three, which is why the former will be capable of more when it too is deployed in three stages. You just chose to parse it the wrong way, and then call the author's writing just plain wrong.