Wikipedia:Reference desk/Archives/Science/2019 July 1

= July 1 =

Time to space in Gemini 8
I was watching First Man and noticed that the sequences from liftoff of Gemini 8 to reaching space (or orbit, I don't remember) lasted a  few minutes, they seemed as if intending to represent real time. The Gemini 8 article has March 16, 1966, 16:41:02 UTC as launch time and March 16, 1966, 22:14 UTC for the docking with Agena. But I don't see the time for reaching the space (or orbit). Do space flights usually take just some minutes to reach space?

Launch and Early Orbit phase is very small. Space launch says:
 * the edge of space is defined by convention, often the Kármán line of 100 km. Other definitions have been created as well, in the US for example space has been defined as 50 miles.

I do not have a preference for a definition. Anything that works in a movie to establish "the ship reaches space" is enough for me. It also says:
 * It is not generally recognized by the public that the increase in potential energy required to pass the Kármán line is only about 3% of the orbital energy (potential plus kinetic energy) required by the lowest possible Earth orbit (a circular orbit just above the Kármán line.) In other words, it is far easier to reach space than to stay there

--Error (talk) 00:19, 1 July 2019 (UTC)
 * Orbital objects are going some 17,000 mph in LEO. While they are not going that fast earlier in flight, they are still booking. Depending on your definition of the boundary of space and your launch vehicle, it only takes a couple minutes to reach space.  Kees08  (Talk)   01:07, 1 July 2019 (UTC)


 * Reaching space (using whatever definition of space) usually isn't very interesting. It's about reaching orbit, which is when the engines are shut off and (apparent) microgravity begins. On some launches there may be a half-orbit coast phase followed by a few seconds circularization burn. From launch to orbital insertion last somewhere between 8 and 15 minutes on most launches.
 * The Titan II GLV used in Project Gemini had a rather high acceleration (up to about 6g, according to our article), so it reached orbit quickly. Our article mentions 156 seconds first stage and 180 seconds second stage burn, indicating it reached orbit in slightly less than 6 minutes. PiusImpavidus (talk) 08:42, 1 July 2019 (UTC)
 * Depends if the vehicle is manned or not. If not, like a Minuteman, around 3 minutes are needed. But this require too much acceleration for a human being, so it takes ~3x more time, for instance, for Space_Shuttle to reach orbit. This is still less than 10 minutes. Gem fr (talk) 08:45, 1 July 2019 (UTC)


 * To see how long it takes to reach space (as defined however you would like to define it yourself), you can watch an old live stream of a SpaceX launch on youtube such as this one. 139.194.66.147 (talk) 11:19, 1 July 2019 (UTC)
 * In the case of STP-2, at T+00:03:13 the vehicle reached an altitude of 100km. At T+00:08:27 it reached a speed equal to LEO velocity. So the answer to whether space flights usually take just some minutes to reach space, yes, space is reached within minutes. 139.194.66.147 (talk) 12:49, 1 July 2019 (UTC)


 * Thank you all. Your answers satisfied my curiosity. --Error (talk) 23:01, 1 July 2019 (UTC)

Oddly enough, there was a comedy movie once where this bit of rocket science formed a plot point. In The Mouse on the Moon (1963), the spaceship from Grand Fenwick takes off slowly and intends to take weeks to get to the Moon. And Prof. Kokintz explains that they have no need to hurry because they have plenty of energy available from their special fuel. (That's not a direct quotation, but it's the essence of his point.) Real-life rockets generally accelerate rapidly to their final speed because fuel burned for any purpose other than accelerating the payload is essentially wasted, and if there is fuel available to waste, more fuel is spent accelerating it. This all ties in with the Tsiolkovsky rocket equation. --76.69.117.113 (talk) 06:15, 2 July 2019 (UTC)


 * A wonderful reference is NASA publication SP-4203: On The Shoulders of Titans: A History of Project Gemini, a zero-cost full-length book available from NASA's history website.
 * On Page 199 there is a brief accounting of times for Gemini 1 (also called Gemini-Titan 1):
 * Two and a half minutes after liftoff, the 118 tonnes (130 tons) of propellants in its first stage exhausted after driving Gemini-Titan 1 64 kilometers high and 91 kilometers downrange, GLV-l's first-stage engines cut off. The sec­ond-stage engine flared into life, and the four bolts that had held the two stages together exploded as they were designed to, cutting the spent first stage loose from the still-accelerating second stage and spacecraft. Five and a half minutes after launch, the second-stage mo­tor stopped, its 27 tonnes (30 tons) of propellants gone. Now 1000 kil­ometers downrange and 160 kilometers high, coasting at a speed of 7888 meters (25 879 feet) per second, Gemini Spacecraft 1, with the second stage of GLV-1 still attached, was in orbit.
 * A similar accounting is provided for each launch. For example, Gemini VIII - as the original question posed - is described around pg. 309 and of course involves two different types of rocket with two distinct launch timelines.  Bear in mind that there was a "time-to-orbit" for each spacecraft, and then a time to the "correct" orbit (for rendezvous) which occurred a few hours (several orbits) later.
 * Similar details are provided, e.g., for Gemini IX-A, pg. 332, and so on; and culminating with Gemini XII, pg. 374, in which a NORDO radio problem meant that certain exact technical details in the early-phase-of-flight are probably lost to history.
 * This is a great book, and was informed by interviews with astronauts, engineers, flight specialists, and senior program officials; it also has reference appendices with short data summaries for the interested readers.
 * Cited by this resource are many dozen more technical publications, including of course NASA SP-4002 Project Gemini: Technology and Operations (1969), which contains the wonderful Appendix 1, Table B: Gemini Program Flight Summary Data - Orbital Operations (and similar tables), in case you're planning a mission and need to pop these into your favorite ephemeris calculator.
 * Nimur (talk) 14:56, 2 July 2019 (UTC)

Just a science question if there's an official record
Hi all, is there an official source stating the weight of Kim? I read articles about him having problems with one of his legs and guessed this. Is that information available? Thanks all. --LLcentury (talk) 02:39, 1 July 2019 (UTC)


 * Kim who?--Shantavira|feed me 05:53, 1 July 2019 (UTC)


 * I suspect the OP probably means Kim Jong-un. I doubt there is any reliable official source because the North Korean government generally just makes up whatever they feel suits. I mean the situation in North Korea is nuts enough that it's hard to know whether even Kim knows his weight, or his doctors have a proper record of it or they were afraid of annoying him in some way and so use a purposely miscalibrated scale or whatever. Kim has traveled to various places but recording the weight of leaders visiting your country isn't something countries tend to do at least officially. (I mean theoretically the Russians, Chinese, Singaporeans, Vietnamese etc could have hidden scales in stuff he stood on, but they're not going to tell us what they learnt.) According to [//asia.nikkei.com/Spotlight/N-Korea-at-crossroads/Seoul-uses-3D-images-to-monitor-Kim-Jong-Un-s-health] South Korean intelligence have actually tried to track his health including weight from video footage and estimated it was 130kg at one time but I'm doubtful that sort of thing is any more accurate to within 20% or so, and probably less. Nil Einne (talk) 08:20, 1 July 2019 (UTC)


 * I suppose rapid weight loss could be a sign of serious illness, and since him dying and leaving NK's nukes in the hands of somebody potentially even more crazy than him would have serious implications, I wouldn't put it past a security agency to put strain gauges under the floor of a hallway he was to walk down during a visit, to measure his weight as accurately as possible. Of course, they wouldn't publicize this fact, nor the results. SinisterLefty (talk) 12:55, 1 July 2019 (UTC)

Yes, my apologies, I was referring to Kim Jong-un. - --LLcentury (talk) 10:38, 1 July 2019 (UTC)


 * If Trump's weight is known, someone could probably do an estimate of Kim's from their side-by-side photos. ←Baseball Bugs What's up, Doc? carrots→ 18:46, 2 July 2019 (UTC)


 * Trump is a lightweight, being mostly hot air and inflated ego, with nary a fact to weigh him down. SinisterLefty (talk) 17:47, 5 July 2019 (UTC)
 * Ref Desk is not the place to seek medical advice, so expressing here a Trump derangement syndrome wont help you. However, psychological projection is certainly a place to start. Gem fr (talk) 07:27, 6 July 2019 (UTC)

Crossing Over in Genetics
I'm trying to teach myself the basics of genetics. One very basic question that I'm not clear on is whether (let's limit to humans for simplicity) genetic diversity is always a matter of combination of individual chromosomes or whether alleles from different chromosomes can be mixed together. E.g., suppose we have chromosome C1 and the Father's genome is C1F1 and C1F2 and the mothers C1M1 and C1M2. My understanding is that in Meiosis we get four haploid daughter cells with the values for C1 being: C1F1, C1F2, C1M1, and C1M2 and that the new fertilized egg will have one of these from the father and one from the mother. However, it also seems there is something called Crossing Over where alleles from one chromosome get swapped with the homologous (I think that's the correct term) alleles from another. So that the child could end up with a C1 chromosome that was a combination of say C1M1 and C1F1. I hope my question is clear and I'm not butchering the terminology. Also, just to be clear, I'm aware there are also other factors that are very important such as epigenetics, the environment in the womb, etc. but I'm just trying to make sure my basic understanding of Meiosis in humans is correct. Thanks for any help. --MadScientistX11 (talk) 22:25, 1 July 2019 (UTC)


 * You have it correct. This is diagrammed in the image at the top of Meiosis, for a hypothetical organism with two chromosome pairs. For ease, in that diagram the paternal and maternal chromosomes are different colors. As you can see, the gametes that come out of meiosis have one full copy of each chromosome, but it is a mix of red sections and blue-grey sections. In that diagram, as is actually very typical, crossing over only happened on one member of each pair of sister chromatids. However, that is not actually a rule. It could happen by chance, but both sister chromatids can experience crossing over. Someguy1221 (talk) 22:52, 1 July 2019 (UTC)
 * did you read chromosome allele Chromosomal crossover Unequal crossing over ?
 * Gem fr (talk) 23:02, 1 July 2019 (UTC)
 * Thanks. I read the Chromosomal crossover article but not the others, I'll take a look at them. Part of the reason I was confused is that a professor told me the opposite, but she was not a biology professor and she was teaching genetics as one part of a larger class. And it's such an important concept (it really increases the combinatorics of possible genotypes) that I wanted to make certain I was understanding it correctly. Thanks a lot for the quick response. --MadScientistX11 (talk) 03:09, 2 July 2019 (UTC)
 * What do you mean, she told you the opposite? What specifically was she talking about, do you remember? I might know what she meant. Someguy1221 (talk) 04:28, 2 July 2019 (UTC)
 * What do you mean, she told you the opposite? What specifically was she talking about, do you remember? I might know what she meant. Someguy1221 (talk) 04:28, 2 July 2019 (UTC)