from the what-goes-up-must-come-down-oops dept.
It seems that China has done it again, they have a history of dropping rocket parts on their own people. This time no one was hurt, but Tech Review mentions some previous events that didn't have a happy ending.
It's the latest incident in China's long history with falling rocket parts causing destruction below. The most infamous crash occurred in 1996, when the first Long March 3B launch saw the rocket veer off course and crash into a village, killing an unknown number of people (possibly hundreds, by some Western estimates).
"Any time you have stuff going up, there's a possibility it's going to come down where you don't plan for it," says Victoria Samson at the Secure World Foundation. "So there's a reason why you don't fire over populated land." That's why most countries launch over water.
So why doesn't China? "This entire issue is down to geography," says Thomas Roberts, a former aerospace security fellow at the Center for Strategic and International Studies. All three of China's main spaceports are located in the mainland, including the Xichang site. They all save money by flying missions east (which requires less fuel to get into space), but that route takes them over vulnerable populations.
China issues evacuation notices to communities downrange, but even if people aren't harmed or killed by the physical impact of a crash or by direct exposure to rocket fuel (which can lead to severe organ failure or cancer), the wreckage could pollute nearby rivers and streams used for irrigation and drinking water. Launches from the Soviet Union's old Baikonur Cosmodrome in Kazakhstan, built in 1955, have caused more than 2,500 tons of debris to rain down on the surrounding region, leading to health problems for thousands.
[...] China could also just change its flight paths. For example, Israel's Palmachim Airbase can't launch to the east because of obvious geopolitical conflicts. So it sends rockets over the Mediterranean Sea and through the Strait of Gibraltar. This requires putting a satellite in a retrograde orbit—one that moves in the opposite direction of Earth's rotation. This requires much more fuel, but it entirely avoids populated areas.
(Score: 2, Informative) by Anonymous Coward on Sunday December 01 2019, @01:44PM (22 children)
Rocketry is surprisingly limited. It turns out of the radius of Earth was just about 50% larger, it would simply be impossible to get off this planet with any known technology.
Without getting into the specifics, you can look at each rocket having one critical value. And that's it's deltaV - the max amount it can change its velocity by. It's not just something you can increase with more money or more fuel. It's something is hard capped under perfect conditions and will require substantial improvements in technology to meaningfully improve. The earth rotates at different rates of speed depending on where you're at. On the equator it moves the fastest, at about 1000 miles per hour. So when you launch at the equator you basically get a free 1000mph added to your speed. And that is huge. Going against the rotation of the Earth requires vastly more deltaV which means some objectives are simply impossible to do. Suffice to say that a negligible risk to an isolated group of areas versus no space is an obvious choice. However, why they have their launch facilities [apparently?] in Xichang near the center of China as opposed to e.g. some place around Shanghai (coastal + east side) is something that I have no clue about.
Also the stuff about the dangers of rocket fuel is nonsense. Rocket fuel isn't some magic poison. RP-1 the most common propellant is little more than a refined kerosene. In the future rockets will probably be going with plain old methane. Well that alongside some liquid oxygen which is even less harmful. Probably don't want to take a bath in it, but it's not like you're suddenly going to croak for some once in a lifetime ambient exposure. The exhaust? Even better. It's wator vapor and CO2 and far lower concentrations (that the ground would be exposed to) than you're huffing while sitting in a traffic jam. The biggest danger would be hydrazine (used for maneuvering thrusters) which is some really nasty stuff, but there's a very limited amount of this on board a rocket, and it's going to be extremely secure contained since it's hyper toxic and hyper unstable.
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @02:13PM (19 children)
deltaV is the amount of force needed to overcome gravity's pull on the mass (rocket) that keeps it glued to the ground. It's not a hard capped value. And... if the Earth was 50% bigger you're not stuck on the ground with no possible way to escape gravity. Rockets have plenty of power and actually have to throttle back at mach to prevent catastrophic disassembly from friction with the atmosphere. And again... Most rocket fuels are highly toxic. RP-1 is old technology, the good stuff will melt your skin and give you 3 headed children.
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @02:25PM (9 children)
delta-V is not a unit of force.
You're right about the planet: https://arxiv.org/abs/1804.04727 [arxiv.org]
The industry is moving towards liquid methane + liquid oxygen using the Raptor and BE-4 engines.
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @02:43PM (3 children)
That paper is probably accurate. A 50% increase in diameter is an 8x increase in volume, thus mass. Then you have the atmosphere to deal with on Earth - haven't read the paper, but assume they're speaking of atmosphericless planets for simplicity (otherwise you need to know all sorts of things about its composition, or making assumptions about such). And 50% was an off the cuff figure. Not giving specific figures relating to detalV/etc because I'd like our enlightened fellow above to answer my questions. ;-)
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @04:01PM (2 children)
A 50% increase in diameter is actually 1.5x1.5x1.5=3.375x volume. But mass increases significantly more than volume, because the density is not constant -- solid matter compresses when there's a planet sitting on it.
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @05:28PM
Yeah, there's a conversation chain down below on that. Glad to be posting on an AC account at times like this.
Awesome insight on the point about density not being constant. I recalled the datum of 50% radius from an article [nasa.gov] on the rocket equation, but when running it, the numbers were a little off. Saturn V had a delta-v of about 18k. 50% radius yields an escape velocity of about 17k. That 18k is ideal and without a payload so it'd certainly be well below 17k in practice, but that's close enough a figure that it seemed, at the minimum, quite debatable for such a shocking statement. But now since, as you mention, the density would not be constant the 50% radius datum is probably spot on since that'd pump up the escape velocity enough to make it plainly unviable.
(Score: 2) by FatPhil on Sunday December 01 2019, @10:28PM
*And* the amount of inner core is way smaller than the amount of planet that's not inner core, as volumes scale with the cube, so that <10% increase at the centre would only be a tiny fraction of the planet's mass.
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @02:56PM (4 children)
∆v is indeed the amount of force needed to maneuver mass against gravitational forces. It's not a fixed value because it depends on the mass of the object being moved, the gravity acting against it, and the aerodynamics from atmospheric drag.
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @02:59PM
And he doubles down on dumb. Isn't the internet awesome?
(Score: 1) by khallow on Sunday December 01 2019, @03:19PM (2 children)
No. Gravitational losses are a thing, but delta-v still is not a force. And no matter how awesome your engines could be, you're limited by how much force your payload can endure and in turn that acceleration limit constrains just how much you can reduce gravity losses. For example, humans just aren't going to handle 250 G of acceleration without pancaking, so there is always going to be some loss of delta-v to gravity losses (effectively 100-200 m/s out of 7-8 km/s to orbit with max acceleration under 5 G, IIRC).
(Score: 2) by FatPhil on Sunday December 01 2019, @10:51PM (1 child)
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2, Interesting) by khallow on Monday December 02 2019, @02:14AM
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @02:27PM (8 children)
You have absolutely and positively no clue what you are talking about, whatsoever. To provide some entertainment:
- What would the escape velocity of Earth be if it had a 50% larger radius?
- What is the highest deltaV ever achieved by any rocket?
- What are the two primary components in any rocket fuel?
- What fuel does SpaceX use?
- What fuel does the RS-25 (space shuttle engine, will be used on the Senate Launch System if it ever leaves ground as well) use?
- What do you get if you combine the answers from #2 and #4?
I do not expect answers.
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @02:39PM
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @02:50PM (6 children)
Meh, question 1+2 were originally one question. Decided to make them two, but didn't adjust my numbers. Final question should be "What do you get if you combine #3 and #5?"
"What are the two primary components in any rocket fuel?"
"What fuel does the RS-25 (space shuttle engine, will be used on the Senate Launch System if it ever leaves ground as well) use?"
Wikiable question, but informative nonetheless.
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @03:02PM (3 children)
Lol. Shit. Diameter also - 50% greater diameter. Not radius. Meh.
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @04:04PM (2 children)
Do you know some way to increase the radius of a sphere without increasing its diameter in the same proportion, or vice versa?
(Score: 2) by Runaway1956 on Sunday December 01 2019, @04:14PM
I was hung up on that one for a second or two. I'm like, "What's the difference here? Have I forgotten some basic geometry, or what?" I'll laugh at AC and myself over that one, LOL!
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @04:25PM
Hahaha, oh boy. It's times like this that make me happy to be posting as an AC account. ;-)
I was aiming for about an 8x volume/mass increase => doubling the radius. We can get there. Let's just turn it into a riddle. Increase the radius of Earth by half its diameter!
(Score: 1, Interesting) by Anonymous Coward on Sunday December 01 2019, @03:08PM (1 child)
The solid propellant of the old SLS boosters was Ammonium perchlorate. It's fumes smell like sweet black pepper.
RS25 main engines are liquid oxygen/liquid hydrogen.
Back in my rocketry days Aerotech made a hybrid engine, a solid chuck of Ammonium perchlorate with a hollow core and Nitrous oxide sprayed through the center. It was a big boost of go go juice.
(Score: 2, Funny) by Anonymous Coward on Sunday December 01 2019, @03:22PM
Come on guys, this isn’t rocket science ...
... oh!
(Score: 4, Informative) by Rich on Sunday December 01 2019, @03:37PM
Long March 3 runs on UDMH/N2O4, like Proton and the early Ariane versions. Everyone on a budget would rather use RP1/LOX, and everyone looking for performance LH2 as the propellant. But if you're a state without proper rocket technology, particularly when aspiring to get ICBMs with storable fuels, it's the toxic hypergolic and non-cryogenic stuff. One could research why historically von Braun went for LOX, and Glushko for N2O4 as oxidator, or rant how the French try to make the rest of Europe pay for their visions of grandeur (cf. the Europa 2nd state, which led to Ariane 1), but this leads a bit far now.
(Score: 4, Informative) by sjames on Sunday December 01 2019, @07:20PM
RP-1, H2, or methane combined with LOX are popular for booster stages now, but boosters derived from ICBMs (including Long March) use UDMH or hydrazine and nitrogen tetroxide (N2O4). Those are used because they are liquid at room temperature and pressure and will self ignite. The missile can be kept in a fueled and ready state for long periods of time. They are also every bit as nasty as described in TFA.
If you have seen a shuttle landing, you may have wondered why it just sat there for so long before the astronauts came out. Part of that was waiting for any fumes from the OMS and RCS to dissipate.
(Score: 2) by Username on Sunday December 01 2019, @01:45PM (4 children)
Isn't the pacific ocean east of China?
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @04:06PM (3 children)
Yes, but half of China is also east of [the point in] China [where they launch rockets from]. They don't fall in the Pacific unless they make it past China first.
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @05:30PM (2 children)
I think he was implicitly asking why they don't launch from a facility closer to the coast instead of in the middle of the country. Very easy to speculate about many possible reasons, but I'd also like to know the reason if it's publicly known.
(Score: 0) by Anonymous Coward on Sunday December 01 2019, @05:45PM
Probably worried about collisions among all the Russian and American Trawlers.
(Score: 3, Interesting) by KilroySmith on Sunday December 01 2019, @07:21PM
>>> why they don't launch from a facility closer to the coast instead of in the middle of the country
https://arstechnica.com/science/2019/11/china-keeps-dropping-toxic-rocket-parts-on-its-villages/ [arstechnica.com]
"China built three of its major launch centers away from water during the Cold War, amid tensions with both America and the Soviet Union. For security purposes, it built the sites at inland locations."
Basically, their launch facilities are repurposed Cold War ICBM R&D sites. They didn't want to build them on the coast for fear that the US or Soviet submarines could blow them up with zero warning.
(Score: 2) by corey on Sunday December 01 2019, @08:32PM (2 children)
Ugh that article highlights the pain of overlays. Half my mobile screen was eaten up by some subscribe nag and cookie acceptance. I didn't look hard enough if the article had pictures.
(Score: 0) by Anonymous Coward on Monday December 02 2019, @10:20AM
https://addons.mozilla.org/en-US/android/addon/behind_the_overlay/ [mozilla.org]
(Score: 0) by Anonymous Coward on Monday December 02 2019, @10:31PM
did you read the article?
I mentally would try to ignore the nag and ad stuff, but your comment about pictures was really funny to me. they may be worth a thousand words, but not on a wannabe tech site...
(Score: 2) by Phoenix666 on Monday December 02 2019, @11:01AM (1 child)
Xichang is a poor choice of a launch site. Chongqing and a couple other major cities are downrange.
Xinjiang in the northwest would make more sense, because it's largely unpopulated; if anything falls, it'll fall in the desert or perhaps the empty grasslands of Inner Mongolia. Or they could put it in Jilin Province in the northeast, whose eastern border is spitting distance from the Pacific coast.
Washington DC delenda est.
(Score: 0) by Anonymous Coward on Monday December 02 2019, @05:07PM
There's a lot of factors that go into a desirable launch site. An important one is how closer it is to the equator. Earth spins the fastest along its equator thus giving you the biggest free delta-v boost on your launches which is critically important.
Part of the reason that in some hard sci-fi novels (Artemis in particular) places like Kenya become key critical destinations in space. You not only hit the Africans checkbox for your Hugo Award, but it also really is a super logical place. Right on the equator, great weather, Indian Ocean is right to the right, etc. Only problem is the country is about as stable and safe as hydrazine, and that doesn't seem to be changing any time soon. Africa in a nutshell - so many resources, so much potential, but complete chaos leaving it all to waste.