[HN Gopher] We're about to fly a spacecraft into the Sun for the...
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We're about to fly a spacecraft into the Sun for the first time
Author : pseudolus
Score : 80 points
Date : 2024-12-20 11:23 UTC (11 hours ago)
(HTM) web link (arstechnica.com)
(TXT) w3m dump (arstechnica.com)
| pavel_lishin wrote:
| > _Now, you might naively think that it 's the easiest thing in
| the world to send a spacecraft to the Sun. After all, it's this
| big and massive object in the sky, and it's got a huge
| gravitational field. Things should want to go there because of
| this attraction, and you ought to be able to toss any old thing
| into the sky, and it will go toward the Sun._
|
| Yes, yes, speak orbital dynamics to me!
|
| > _The problem is that you don 't actually want your spacecraft
| to fly into the Sun or be going so fast that it passes the Sun
| and keeps moving. So you've got to have a pretty powerful rocket
| to get your spacecraft in just the right orbit._
|
| What?! No! I mean, yes, you _don 't_ want your spacecraft going
| right into the sun itself, but that's not the major reason why
| it's difficult! It's that at launch, the spacecraft is already in
| orbit around the sun - since it came from the Earth. And left to
| its own devices, it won't want to "fall" into the sun any more
| than it already is, any more than the Earth is falling into it.
| Changing orbital parameters that much is expensive in terms of
| delta-V!
|
| As I recall, the "cheap" way of getting into a low-enough orbit
| to get that close to the sun is to counterintuitively first
| _expand_ your orbit massively, and then do a retrograde burn at
| the highest point. (But I 'm guessing the Parker Solar Probe used
| gravity assists.)
|
| I wonder if some editor cut a large part of this paragraph.
| zomg wrote:
| i was thinking the same but with respect to this entire article
| -- feels like we're missing the second half and/or much more
| detail. feels like the article was due in to the editor by 11pm
| and the author forgot and started writing it at 10pm. :x
|
| either way, very fascinating experiment. i look forward to
| hearing about the results!
| Ancalagon wrote:
| would a solar sail be a feasible - albeit long time scale -
| method of getting the delta-v to decrease the orbit? Just point
| it retrograde and wait a long time?
| tifik wrote:
| I might be missing something, but here is my thinking... the
| radiation coming out of the sun would always be perpendicular
| to your direction of travel around the sun at any given
| moment, so it would only ever be able to add delta-V and
| increase your orbit, not reduce it.
|
| Unfortunately you can't do upwind sailing in a vacuum.
|
| That being said, you can still use it for the method
| described in parent post, but you'd still need a different
| propulsion method to slow you down at the apogee.
| floxy wrote:
| You should be able to tilt your mirror/sail at 45deg, so
| that the reflected light heads off in the direction of your
| travel, so that the momentum it imparts works against your
| current velocity, slowing you down, and degrading your
| orbit. Right?
| emilamlom wrote:
| They can be used to decrease orbit as well. Since you just
| need to bleed off the speed from Earth's orbit, you could
| angle the sail diagonally so the the reflected light is
| pushing against your direction of orbit (sort of like how
| the fins on a pinwheel are angled).
|
| While I was googling, a couple places likened it to tacking
| into the wind, but that's a different kind of phenomenon
| that works because of friction and pressure differences.
| pavel_lishin wrote:
| I think that if you're constantly being thrusted radially
| out, you don't actually gain delta-v or increase your orbit
| - you just shift it. Your apoapsis increases, but your
| periapsis decreases.
|
| (It's been awhile since I've played KSP, I could be wrong.)
| josho wrote:
| Sailors have figured this out centuries ago to travel
| against the wind (called tacking). Some of the same
| principles apply, like orienting the sail so that photons
| push against the sail reducing the angular momentum.
| andrewaylett wrote:
| Tacking works because you have resistance against two
| media (air and water) which are travelling at different
| velocities -- you need a keel in the water. Solar sails
| don't have an analogous second medium.
| emilamlom wrote:
| They can eventually decrease orbit toward the sun. They just
| need to be angled in such a way that the thrust is retrograde
| (not the sail itself). It would be incredibly slow though.
| happytoexplain wrote:
| I absolutely hate that AI is the first thing I think of
| whenever I see things like this now.
|
| Yes, innocent mistakes happen in writing and editing all the
| time. But look at that whole paragraph you're quoting. It does
| exactly what sloppily-guided AI does: It's using words in an
| order that sounds relationally intuitive, but taken as a whole
| it's ping-ponging across completely unrelated concepts. It _can
| 't_ have come from a human, unless, like you said, parts were
| removed in editing without re-reading the result.
| GauntletWizard wrote:
| I disagree. I have encountered tons of humans who do exactly
| that - Use "words in an order that sounds relationally
| intuitive, but taken as a whole it's ping-ponging across
| completely unrelated concepts". It's not unique to AI, it's
| fairly common across bullshitters of all stripes. But perhaps
| more tragically, it often happens to actually big thinkers
| whose brain is connecting dots so fast that they're eliding a
| bunch of important hops along the way, and while the former
| is more common, it's easy to confuse for the latter.
| pavel_lishin wrote:
| Hey, sometimes you get called on in standup when you're
| trying to do some work, and you just have to glue some
| words together. I'm just glad nobody's writing those words
| down and publishing them!
| adolph wrote:
| Thats improv, not standup; granted, one must be agile
| either way.
| strongpigeon wrote:
| You would think Eric Berger (who's a pretty seasoned space
| writer) would have played Kerbal Space Program. That game took
| my understanding of orbital dynamics to a whole other level. I
| was immediately bothered by that paragraph as well.
| daveslash wrote:
| I'm not a KSP pro, but I have tried and tried to fly into the
| sun and have yet to succeed. Even if I do my best to lose as
| much of the planet's orbital velocity as I can until I'm out
| of fuel, and I begin to fall towards the sun.... I still
| always miss and then just go into an elongated elliptical
| orbit. It's really hard.
| Filligree wrote:
| You'll want a bi-elliptic transfer orbit. And probably a
| larger rocket.
| LorenPechtel wrote:
| I would suspect that a slingshot at Jool would do it but
| I've never tried.
| vikingerik wrote:
| Yes, Parker used gravity assists, several passes by Venus.
|
| The cheapest way in terms of delta-v in the real solar system
| is actually to use Jupiter, launch to there and slingshot
| against your incoming velocity to cancel it out and drop
| towards the sun. Parker considered this, but decided not to
| because it would complicate the spacecraft design to handle
| operations at Jupiter (cold) and at the sun (hot).
|
| And yes, without assists, it's harder to get from Earth to the
| sun than to anywhere else. Solar escape velocity is 42 km/s at
| the altitude of Earth's orbit. Earth's orbital speed is 30
| km/s, closer to escape velocity than to the near-0 you would
| need to drop all the way to the sun.
| imglorp wrote:
| I'm not wild about the title either. In English, "fly into the
| sun" implies permanence and they exploited that for title bait.
|
| Better, "closest approach" or even "dip into" would say that
| Parker will keep doing its job afterwards, maybe even lower the
| next time!
| hnuser123456 wrote:
| It sounds like for large changes in orbit, a bi-elliptic
| transfer can beat Hohmann:
| https://news.ycombinator.com/item?id=42357272
| buildsjets wrote:
| Soundtrack for appropriate ambiance.
|
| https://music.youtube.com/watch?v=ZnIxWznakz8&si=jhjMURGD4S0...
| Qem wrote:
| I was thinking about Adagio in D Minor, because of Sunshine
| (2007).
| grecy wrote:
| Soundtrack to "Sunshine" also seems very appropriate.
|
| https://www.youtube.com/watch?v=AXzqJucLae8
| vardump wrote:
| I was thinking about Red Dwarf theme:
| https://youtu.be/zV0hwZwNQZc?si=NcQULlVtqBX_V7wm
|
| "It's cold outside
|
| There's no kind of atmosphere
|
| I'm all alone
|
| More or less
|
| Let me fly
|
| Far away from here
|
| Fun, fun, fun
|
| In the sun, sun, sun"
| hinkley wrote:
| They don't literally mean _in_ the sun.
| lizzas wrote:
| They mean Fiji
| wormius wrote:
| Came here looking for this. :)
| koops wrote:
| You could also go with this:
| https://www.youtube.com/watch?v=juq0_2Oj5qw
| zimpenfish wrote:
| Came here to post exactly this. Mainly for the sample of
| Jo'Bril, obviously.
| amelius wrote:
| Of course it is completely evaporated before hitting anything
| that remotely resembles a surface.
| detritus wrote:
| Is there even a surface?
| amelius wrote:
| Yes, if you zoom out enough you see it. Like with ordinary
| objects.
| shwouchk wrote:
| Most ordinary objects have the property that the density of
| object mass has a very sharp gradient near some 2d surface
| that encloses a compact domain, and outside that is close
| to 0. However not identically 0, since eg the object is
| constantly releasing vapor of atoms of itself. If you zoom
| out enough out out of anything it looks like that,
| depending on how sharp you wish the gradient to be to call
| it a "surface".
|
| For objects where the gradient at the boundary is not great
| relative to our size we would subjectively experience no
| surface when coming close eg to a cloud.
|
| Does a galaxy have a "surface"? We can often also "clearly
| see" the edge of it...
| amelius wrote:
| How do you define density?
| adolph wrote:
| _The photosphere is the visible surface of the Sun that we
| are most familiar with. Since the Sun is a ball of gas, this
| is not a solid surface but is actually a layer about 100 km
| thick (very, very, thin compared to the 700,000 km radius of
| the Sun)._
|
| https://solarscience.msfc.nasa.gov/surface.shtml
| alnwlsn wrote:
| To be clear, it's not the end of the mission as far as I'm
| aware. It will come around again and do 4 more sun flybys next
| year.
| ceritium wrote:
| No if they go during the night
| alnwlsn wrote:
| _Yeah, it 's going to get pretty hot. Scientists estimate that
| the probe's heat shield will endure temperatures in excess of
| 2,500deg Fahrenheit (1,371deg C) on Christmas Eve, which is
| pretty much the polar opposite of the North Pole._
|
| That's the South Pole. I wasn't aware global warming has gotten
| that bad yet.
| blindriver wrote:
| I don't know if I'm shocked or not shocked that the temperature
| is 2500F 4 million miles away from the Sun. Part of me expected
| it to be much much hotter than that, but I guess it is 4 million
| miles. Considering we are 90 million miles away, and the
| temperature still gets up to 120F on the Earth, maybe that makes
| sense?
| thisisbrians wrote:
| you're probably getting downvoted because there isn't really a
| temperature 4 million miles away from the Sun (it's mostly just
| empty space being bombarded by radiation)
|
| 2,500o F is merely the temperature the probe is expected to
| _reach_ at that distance. if it were to stay at that distance
| indefinitely, it would grow much, much hotter as it absorbed
| more energy from the sun.
| tomnicholas1 wrote:
| No not necessarily - it will keep growing hotter until the
| black body radiation emitted by the probe matches the power
| of the radiation hitting the probe. Then it will stay at
| constant temperature.
|
| It's a standard undergraduate problem to work out what this
| equilibrium temperature is for a flat plate at a distance
| from the sun equal to the Earth's orbital radius.
|
| Interestingly the result is only a few 10's of degrees less
| than the average temperature of the real Earth - the
| difference is due to the Greenhouse Effect.
|
| For the probe one could easily do the maths but I could
| believe that at 4 million miles that equilibrium temperature
| is 2,500F.
| feoren wrote:
| Temperature is so wibbly-wobbly. The probe will reach an
| equilibrium energy-in vs. energy-out temperature depending on
| its distance from the sun, its surface area facing the sun,
| and the materials being lit, vs. its surface area facing
| away, the thermal radiation rate of various materials, and
| other factors. You could give an aerospace engineer almost
| any temperature between the CMB and the surface of the sun
| and they could probably design a (at least theoretical) probe
| that would reach that temperature eventually* at almost any
| distance. My guess is that 2500 oF probably is the
| equilibrium temperature of the probe at that distance.
|
| * With "eventually" being "assuming a stable state for
| infinite years" which is of course not how astrophysics
| actually works.
| lizzas wrote:
| Depends on the object receiving the heat. Walk outside in
| bearfoot in summer. You will soon notice some surfaces are way
| hotter than others. This depends on how efficiently heat can
| transfer. Convection, radiation, conduction I think are the 3
| ways.
|
| The air temp is heated by the sun, those surfaces then the
| atmosphere is preventing heat escaping. A lot going into that
| 120F!
|
| That is why things like climate change and urban heat islands
| don't need a closer sun.
| FredPret wrote:
| If KSP is to be believed, this is shockingly difficult to do
| lizzas wrote:
| The same gravity that wants to pull you in keeps you in orbit.
| And any object we launch starts off in the suns orbit.
| FredPret wrote:
| It's only the v0 you start off with from being in orbit
| already that makes it hard. Earth (and Kerbin) orbit at a
| very high speed.
| feoren wrote:
| > The same gravity that wants to pull you in keeps you in
| orbit
|
| I would say it's your velocity that keeps you in orbit.
| Without the velocity, you fall into the star. Without the
| star's gravity, you keep going away in a straight line. Any
| object we launch starts off with Earth's velocity.
| beAbU wrote:
| In order to 'land' on the sun, or any celestial body, you need
| to get rid of your orbital speed. Higher orbital speed means
| higher orbit altitude. Landing on earth is comparatively easy,
| because you can use the atmospheric drag to slow down. It is so
| difficult to land on Mars because of it's thin atmosphere.
| Alternatively you need a shitload of fuel to burn to kill that
| velocity.
|
| Earth's orbital velcity is ~30km/s. So by extension, anything
| that comes from Earth will at least have that speed. So the
| probe needs to find 30km/s delta v in order to actually get
| close to the sun.
| FredPret wrote:
| I wonder if you can use atmospheric drag to pull you into the
| Sun / a different star / Kerbol.
|
| Long ago, playing Elite if I remember correctly, you could
| fly close to a star and scoop up a load of hydrogen for later
| resale. I'd be interested to see a graph of gas density vs
| tendency to melt spacecraft compared to distance from the
| core for a typical star.
| nostromo wrote:
| You could use a solar sail to project a satellite towards the
| sun.
| aziaziazi wrote:
| In SpaceFlight Simulator it's quite easy IIRC (it's been a
| while):
|
| 1. Orbit yourself around low earth
|
| 2. When entering the transfer window (opposite side of the sun-
| facing earth, i.e. above midnight longitude) booooost
|
| 3. For orbit, aim for tangent with your target. For sun
| discovery, aim for sun center. Choose but don't change.
|
| The game is in 2D and you got nice auto-calculated transfert
| windows and trajectories. Is it one of those game
| simplification that makes it easy or there's more difficulties?
| LorenPechtel wrote:
| The math is simple enough, it's just the delta-v requirements
| are brutal. Or you take the slingshot approach at which point
| the math requirements are brutal.
|
| And I'm not aware of any KSP mod that helps you plan
| slingshots. And even if there was a slingshot maneuver
| requires a lot of precision because your ejection angle is
| highly sensitive to exactly how close you came.
|
| The Parker probe was sent outward to Jupiter and used it to
| slingshot away much of it's energy. (We normally think of
| using a planetary encounter to gain energy but it works both
| ways. Ejection velocity from a slingshot at Jupiter can be
| anywhere from hitting the sun to solar escape. It's just most
| probes are heading out, not in.)
| kccqzy wrote:
| There's a difference between flying directly into the sun as if
| landing there, and orbiting the sun but so close that the
| spacecraft is inside the solar atmosphere.
|
| This is doing the latter.
| kfogel wrote:
| Most of the comments so far are about the temperature and the
| closeness to the sun, and, hey, I get it: those are both amazing
| to think about. But to me even more amazing is... 0.16% of the
| speed of light?? Yikes.
| verzali wrote:
| Pretty sure it's 0.064%, not sure why the article got it wrong,
| still impressive though
| caseyohara wrote:
| Still. ~200,000 m/s (= ~430,000 mph) is unfathomably fast.
| verzali wrote:
| This article is about 3 years late, Parker first flew through the
| Sun's atmosphere in 2021. This is its closest approach but
| definitely not the first time it's doing it.
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