sorry kshacker, I may have thrown you off the scent here. My explanation of the slingshot effect is right, but it doesn't look like slingshotting is what the spacecraft is using to increase its speed:
tl;dr:
the spacecraft is just falling into the Sun, which is why it speeds up. It isn't gaining speed relative to anything else, and it loses that speed again once it flies away from the Sun. It is using Venus to get closer to the sun each time around by damping its angular momentum, which works but I don't know how to explain that in an ELI5 way.
so it's actually a little anticlimactic.
BlarfMcFlarf and pfdietz got this right below in their comment thread:
"What the Venus flybys did was not add energy so much as remove angular momentum. The hard part about getting close to the Sun is that conservation of angular momentum prevents it."
...and icehawk and vl correctly point out that you can't really use the Sun to increase your within-solar-system speed. Thanks to them for prompting me to look into this further. The cool slingshot maneuvers all involve planets, not the sun.
...but I think the key answer that none of us quite articulated to your question:
How is the spacecraft using the slingshot effect to increase its speed each time around?
...is that it isn't!
...the article dramatically describes it as "picking up speed" each time it goes around the sun, but that is misleading. It is just getting closer to the sun every time around, so of course it goes faster the closer it gets.
the cool part if any is how it uses Venus to get closer to the sun (by sapping angular momentum), but that's hard to explain in a nutshell and doesn't really relate to your energy question.
so that is hopefully now a better answer to this mystery that brings together what some of the other commenters have pointed out.
hey icehawk -- so you can use any celestial object in the solar system to maneuver; all you're doing is basically changing your direction. But you're right, there's something strange going on here. The original article doesn't actually have any information about what this spacecraft is doing, but it links to another one about the speed. I'm looking at that now, gonna add an addendum (or edit the old comment if i can figure out how to do that)
i was wondering too! Do you think it might be because of citing family as a source? I barely ever post here, so don't have a good muscle memory for norms and best practices.
(also both scared and curious of what might result from dropping below 0 karma)
>there actually is no objective answer as to which body gained and which lost energy! Energy is always conserved, but which way the transfer happened depends on your reference frame!
this isn't too difficult to demonstrate: pick an inertial reference frame A such that the spacecraft is at rest following the "collision" (aka the slingshot). In this frame, the spacecraft has 0 kinetic energy post-slingshot; therefore, it lost energy in the slingshot, which was transferred to the Sun. Likewise, pick a frame B such that the Sun is at rest after the slingshot (this would be the more usual frame to pick). In this case, it's the Sun that lost energy, and the spacecraft that gained it.
(depending on one's mechanics background this might appear anything from obvious to very weird and unintuitive)
That's correct, the energy comes from the body the spacecraft is slingshotting around (the Sun in this case). It's not mass or gravitational energy or anything weird like that, it's actually just a momentum transfer, the same as if the two objects had collided and bounced off each other elastically (i.e. without loss of energy to heat). So a (miniscule amount) of momentum (velocity x mass) is being transferred from the Sun to the spacecraft, and that's where the energy comes from.
(source: I studied physics and had a grandparent at NASA who worked on Voyager II and talked about this issue with me; but it's been a while since both of those things, so anyone with more fresh experience feel free to chime in!)
I'm not sure what the best way to link a source on HN is, but I'll do my best.
McCrae and Costa did a study in the 1980s that looked at correlations between MB and FFA, as part of a larger, longitudinal study on aging. There were 468 participants.
As you can see, these are extremely strong, and the reason F/T and J/P are in the 0.40s is the cross-correlation I was mentioning, with part of the T/F prediction being tied to intra/extraversion (0.19), and part of the P/J prediction being tied to openness (0.30), which is intuitively just what you'd expect.
The full table of 16 correlations is available here:
McCrae, Robert R; Costa, Paul T (1989). "Reinterpreting the Myers-Briggs Type Indicator from the Perspective of the Five-Factor Model of Personality". Journal of Personality. 57 (1): 17–40
...so that's one of the sources for the correlations I mentioned, though there have been other such studies. But as I said, the strange thing is that this information has been publicly available and is even referenced on both the M-B and FFA Wikipedia pages (i.e that M-B and FFA are more or less measuring the same thing) and yet the popular narrative remains that one is dogma while the other is pseudo-science.
(and sorry, yes indeed, the article directly says M-B has been discredited, which is part of the point I'm making. It SAYS that, but it doesn't offer any support for that claim, and the only data it cites shows the opposite)
(edit: author does cite one source, a Vox article, which has the same problem of not citing any data and also plugs the FFA, saying "the newer, empirically driven test focuses on entirely different categories" which suggests the Vox author has also not delved into the research. Most of the people quoted in both pieces make statements like "[using the M-B] would be questioned by my academic colleagues," which may suggest the echo-chamber nature of the problem)
You're exactly right, I think, as to the reason most people are attracted to Myers-Briggs.
That said, it's odd that the narrative persists of M-B having been discredited, when, as the article mentions but doesn't explore, the opposite is true. Myers-Briggs traits strongly correlate with the categories in the FFA, which is the dominant model in psychology, as the article states. But this doesn't even include the cross-correlations between the 4 MB traits and the 4 main FFA traits (minus neuroticism)
Myers-Briggs is in fact basically identical to FFA but in a different eigenbasis, and minus the "neuroticism" dimension. This information is available in every major source on MB vs FFA, including just on Wikipedia. And yet, the "MB as horoscope" idea continues, despite having been scientifically discredited, so to speak.
the mapping is roughly this:
E/I <=> Extroversion
N/S <=> Openness
F/T <=> Agreeableness
J/P <=> Conscientiousness
But it is fun to make fun of the MB-scale (and its enthusiasts) as a horoscope and it's also fun to USE its categories as horoscopes, and the first meme feeds off the second, so both persist.
"What is elementary, worldly wisdom? Well, the first rule is that you can’t really know anything if you just remember isolated facts and try and bang ’em back. If the facts don’t hang together on a latticework of theory, you don’t have them in a usable form.
You’ve got to have models in your head. And you’ve got to array your experience—both vicarious and direct—on this latticework of models."
talk was previously linked from:
http://www.ycombinator.com/munger.html
but no longer available. Spent 20 minutes just now searching for it in frustration; here it is for anyone similarly afflicted!
no comments yet - how strange! seems like a major change, assuming he can follow through on it, which might be hindered by all the other stakeholders FB is beholden to. i have NEVER really used it for social engagement (ie always passively) so i won't notice any effect, but curious if it does make things substantially better
what did H.P. know that we did not??