【这个帖子主要用来收集quora用户C Stuart Hardwick的一些短回答。 Award-Winning Scifi Author, Analog regular 】
SpaceX是否在其太空计划中使用了很多的氦气？ Does SpaceX use as much helium as NASA in their space program?
No. For the new Super Heavy and Starship, Space-X is using autogenous pressurization. All that means is, you pressurize the liquid oxygen tank with gaseous oxygen and the liquid methane tank with gaseous methane.
否。对于新的Super Heavy和Starship，Space-X使用自发加压。 这就是说，您用气态氧气对液氧罐加压，并用气态甲烷对液甲烷罐加压。
I honestly don’t understand why they isn’t already standard practice. I get why it wasn’t used in the early days of the space program as everything was new and rushed, and helium pressurization is mechanically very simple. However, it requires extra high pressure tanks, burst disks, and very expensive helium. It’s also not as trivial as it might at first seem.
老实说，我不明白为什么它们还不是标准做法。 我明白为什么太空计划初期没有使用它，因为一切都是全新的而且时间紧迫，氦气增压在机械上非常简单。 但是，它需要额外的高压罐，爆炸装置和非常昂贵的氦气。 它也不像乍看起来那样麻烦。
Still, autogenous pressurization requires a heater—which usually means piping the pressurant up from the engine, and if there are any leaks, the risk is greater than with helium.
Both systems have their issues, but helium is expensive and Space-X like following the principle that the best component is no component—so no helium.
为什么在发射过程中，巨大的超音速冲击波出现在NASA土星V Moon火箭的中部而不是尖端？Why did a giant supersonic shockwave appear around the middle of NASA’s Saturn V Moon rocket instead of the tip during launch?
You mean this?
That’s not supersonic, and it’s not a shockwave—though it’s related to both.
That’s “vapor cone” or “shock collar.” It’s a transient cloud that forms in the partial vacuum behind the shockwave as a vehicle passes through transonic flight.
Often more than one form, and in this case there are two. The large and obvious one trails the (invisible) shockwave formed where air it deflected off the conical interstage where the stack narrows and transitions from the second stage to the S-IVb. If you look close enough, a smaller shock collar is visible behind the (invisible) shockwave where air is being deflected by the conical Command Model. It’s less obvious because this vapor cone is close the the diameter of the S-IVb and your eye tries to see it as a much large spacecraft than is really up there.
通常是一种以上的形式，在这种情况下有两种。 巨大而明显的一道波在形成的（看不见的）冲击波之后，在那里空气从圆锥形级间偏转离开，在那里，圆锥变窄并从第二级过渡到S-IVb。 如果您看得足够近，则在（不可见的）冲击波后面会看到一个较小的冲击颈，在该处，锥形命令模型使空气发生偏转。 它不那么明显，因为该蒸气锥接近S-IVb的直径，并且您可能会认为看到了比实际略大的航天器。
This is actually typical vapor cone behaviour, in that the cone forms in the low pressure air behind the showwave. Here it is on an Aries-1 test launch in 2009:
Here, vapor cones and trails form aft of the shuttle orbiter, after and dorsal to the ET, trailing from the SRBs, and behind the primary (and invisible) shockwave off the stack a s whole:
Here, vapor cones form aft of shockwaves forming around the canopy, engines, and aerodynamic surfaces of a transonic F-18:
When I was a kid, I had a toy canister you could fill with moisture and a little smoke, then pump up with air and suddenly release the pressure to make cloud. This is exactly the same thing, only at speed that’ll rip your cheeks off.
在日全食时，月球为什么拥有如此精确的尺寸刚好遮住太阳？How did the moon become the exact size to block out the sun perfectly?
The moon is not “the exact size to block out the sun.”
We are of course referring to apparent size here.
When the moon formed, billions of years ago, its was much, much closer—about 18 to 20 thousand miles away, which gave it an apparent size large enough to blot out half the sky. It’s been “the size to block out the sun” ever since.
Ever since it formed, tidal interaction between the Earth and the moon have been lofting the moon into a higher orbit, making it appear smaller—but the whole time, it’s always been “the size to block out the sun.” The moon’s orbit is slightly elliptical, so its apparent size changes by about 10% as it moves through its orbit.
Only recently (in the last 25 million years or so) has the moon gotten far enough away that it is sometimes too small to completely block the sun, and when it’s that far away when it crosses between us and the sun, the result is an annular eclipse.
The rest of the time, it appears bigger. Earth’s orbit is also slightly elliptical, so the apparent size of the sun varies a bit too, but the moon at perigee—at it’s closest to Earth—is always bigger than the apparent size of the sun.
You just don’t see that because the sun’s in the way, and the human mind has a penchant for seeing patterns and parallels, even when they aren’t really there.
It is no magical coincidence that the moon, which started much closer and has been moving farther away, has always been close enough the block the sun. Nor that, tens of millions of years before we arrived, it got far enough away to occasionally fail to do so. Or that, tens of millions of years after we are gone, it will be too far away ever to fully do so.
开始时离地球更近，但之后直向更远处移动的月球，始终足够遮挡太阳，这并不是神奇的巧合。 也不是，在我们的几千万年之后，它距离我们足够远，偶尔会没法完全遮住太阳。 但几千万年离现在的我们还是太遥远了。
为什么NASA的Saturn V月球火箭像花园罩子一样具有波纹状的皮肤？Why did NASA’s Saturn V moon rocket have corrugated skin like a garden shed?
In fact, no part of the Saturn V skin was corrugated, but what you are seeing are stiffening ribs, added to serve exactly the same function as the corrugations you have in mind.
实际上，土星V皮肤的任何部分都不是波纹状的，您所看到的是 stiffening ribs ，并添加了与您所想到的波纹完全相同的功能。
The ribs are on the interstages and skirts between and beyond the propellant tanks. The tanks (filled with liquid hydrogen or oxygen) are smooth, and in fact are insulated with the same polyurethane spray foam insulation as the Space Shuttle external tank, only painted.
Early on, this insulation was too thin and contained void that allowed humidity to pool and freeze behind the insulation, pushing it off in sheets. This was addressed by making it thicker and improving the application procedures.
As to garden sheds, sadly, after cancellation of the failured N1 program, Soviet officials ordered all traces of the great rocket destroyed, and rocket parts and materials were converted into sheds. In the US, after cancellation of Apollo, some interstage adapters were similarly converted into sheds, but unless I’m mistaken, have since been recovered for display.
在太空行走期间为国际空间站服务时，宇航员遇到的最意外的事情是什么？ What is the most unexpected thing astronauts have encountered while servicing the ISS during a spacewalk?
Roscosmos has been conducting a long running study on extremophilic bacteria in which Cosmonauts occasionally swab parts of the outside of the Russian segment of the ISS, then send the swabs back to Earth for study and culture.
This study has provided fodder for clickbait for years, is Russian pronouncements about bacteria found during the study are often quoted (perhaps due to translation, perhaps wishful thinking) the the life form might be from “outer space.”
They are not. All the bacteria found clinging to the outside of the ISS are contaminants from Earth. We know this because if they weren’t, the fact would be obvious the instant the Russians cultured enough of them to get the genome—and in that event it turned out to be alien—not only would we have heard about it in more than click-bait fashion, it would have generated a Nobel prize.
他们不是。 发现附着在国际空间站外部的所有细菌都是来自地球的污染物。 我们之所以知道这一点，是因为如果不是这样的话，那么事实就很明显了，即俄国人培养了足够多的细菌以获取基因组——而这些细菌都是外星细菌——那它们对我们来说就不仅仅是诱饵用的饲料了，这个发现会获得诺贝尔奖。
But in 2015, the Russians claimed to have found plankton—sea plankton—clinging to the hull. Now, since the Russians swabbed all their hardware before launch and since they don’t ship much if any of it by sea like we do, that’s strongly implies that sea plankton (life of some kind that normally drifts in the ocean with little control over its travels) has somehow made it 200 miles straight up.
但是在2015年，俄罗斯人声称发现了附着在外壳上的浮游生物-海上浮游生物。 现在，由于俄罗斯人在发射前就擦拭了所有硬件，并且俄罗斯没有像美国一样经常从海上发射火箭，因此这强烈暗示着海浮游生物（某种生物通常会在海洋中漂移，几乎无法控制 行程）垂直上升了200英里。
That would be remarkable.
On the other hand, I’ve yet to find a link to a translation of an actual paper on this work. “Plankton” could mean anything from a Portuguese Man-Of-War down to planktonic virus particles. Until I see evidence to the contrary, I’m going to assume someone was eating seaweed snack while suiting up for an EVA—or while sealing up the Russian swabs.
另一方面，我还没有找到有关此工作的实际论文翻译的链接。 “浮游生物”可能意味着任何东西，从葡萄牙战警到浮游病毒颗粒。 在我看到相反的证据之前，我将假设某人正在吃海藻小吃，而他们正准备穿好宇航服去EVA或密封俄罗斯棉签。
Here’s a paper about the space plankton: The DNA of Bacteria of the World Ocean and the Earth in Cosmic Dust at the International Space Station. I’m not qualified to assess the quality of the work, and it’s a somewhat questionable journal, so I’ll remain skeptical for now.