The Parker Solar Probe will make its closest approach yet to the Sun
arstechnica.com
arstechnica.com
Light can travel over 34,000km in that time. The great arc distance from LA to Sydney is just over 12,000km. In all likelihood the fiber line connecting them doesn't follow that arc, but it shouldn't be too far out of limits. So about 2/3 of the latency is caused by relays and switching equipment.
it gets even worse for satellite, because (until starlink) communications satellites are in geosynchronous orbit, 35,000km above the equator. so talking on one means a 70km round trip, which causes its path to take over 5x more distance than the linear distance (across the surface) between those 2 cities.
12,000km ?
Not really; the speed of light in fiber optic cable is only about two-thirds of that in a vacuum. That means it takes light about ~60ms to travel the 12,000km great arc distance.
No. There were and are other communication satellites in lower orbits. SpaceX did not invent the concept of low-orbit communications satellites. The first satellites of the 90+ Iridium constellation were launched in the late 90s. That system is still online in low orbit today. Before that there were various military/state-owned satellites. The Soviet Union and Russia were big on providing coms to areas where the geo-stationary relays could not, specifically the north, as far back as the 60s. See the Molnya program.
https://en.wikipedia.org/wiki/Molniya_(satellite)
https://en.wikipedia.org/wiki/Iridium_satellite_constellatio...
It's about 110,000 fathoms per second.
20,000 Leagues, Under the Sea
I think it reads cleaner.
I guess everything with a sun slingshot is going to be impressive.
We'd have 1% speed-of-causality probes by now if it meant better war machines but best they can do with the budget
Vaguely related they did capture light moving with a 1 billion frames per second experiment so Femtosecond Photography is definitely some cutting edge stuff.
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.
either way, very fascinating experiment. i look forward to hearing about the results!
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.
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.
(It's been awhile since I've played KSP, I could be wrong.)
So yes, you can produce a sideways component and let gravity do the rest, but that component can never actually push you towards the sun.
The fact that one has a number of force vectors in varying directions with both sailing and solar sailing, both let you work them together in unison get where you want to go.
Quite often when I am "sailing" the wind is light or dies, and I go to "windward" by timing the currents, and wind at best lets me position for the right currents, but below a sufficient level produces no lift to windward.
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.
...or from my emails; I'm an atrocious writer.
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.
Better, "closest approach" or even "dip into" would say that Parker will keep doing its job afterwards, maybe even lower the next time!
[0] https://www.cbr.com/the-far-side-confusing-comics-like-cow-t...
https://www.youtube.com/watch?v=5Qk9o_ZeR7s
https://en.wikipedia.org/wiki/Ac-Cent-Tchu-Ate_the_Positive
I learnt of this song through the fantastic series "The Singing Detective."
Sun, sun, Mr. Golden sun, sun shine down on me.
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.
Your lateral velocity is what keeps you missing, whether you want to or not.
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.
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.
You can, and I believe this probe will. The Sun’s atmosphere is just much nastier than our own, which means your aerobraking destroys your spacecraft quicker.
There was a bug (or was it?) in the very PC version where by if you had fuel scoops installed, set your view to looking out the rear of the ship, flew toward a star, and ignored all the warnings on your dashboard, you could fly right through the star. If you were being chased at the time you had the additional satisfaction of watching your pursuers' ships explode as they tried to follow you in.
Then gravity crashes you into the sun
While the unfolded mirror is pushed moving away from the Sun, it reflects enough light for the smaller main body to accelerate sunward.
I don't understand why we aren't doing solar + ion drive everywhere (except obviously launch), and instead we settle for slow multi-year multi-grav-boosts trajectories. Current ion drives (by NASA and on Starlink) have 2500-3500 Isp. Which means that even 100+ km/s is easy doable with just 2 stages.
The Parker Solar Probe mass is 555kg. An achievable amount of ion thrust is around 0.5N. Thus, running that thruster would accelerate the craft at 0.0009m/s2.
Getting such a craft to 30km/s of delta-v would therefore take about 33.3 million seconds of thruster time, or about 13 months.
I don't know what the duty cycle is on ion thrusters. Maybe they aren't robust enough to fire for over a year straight?
To be precise for 555kg probe you'd need additional 600-800kg of propellant mass and thus run the thruster(s) at about 1.5N thrust using 40-60KW - 250m2 of solar panels - everything is available at the current state of tech.
https://en.wikipedia.org/wiki/Ion_thruster
"A test of the NASA Solar Technology Application Readiness (NSTAR) electrostatic ion thruster resulted in 30,472 hours (roughly 3.5 years) of continuous thrust at maximum power. Post-test examination indicated the engine was not approaching failure.[75][3][4] NSTAR operated for years on Dawn."
In that case I have a theory. The extra propellant mass, extra solar panel mass, etc, are all more mass against a small amount of thrust. Every bit of additional mass extends that 1-year timeline, and all the extra stuff is extra things that might go wrong.
So instead of a 7 year mission being reduced to 18 months, we have a 7 year mission reduced to maybe 4 years, but then there's possibly a higher chance of failure.
Balancing three years against failure risk, I could see that falling on one side for some missions, and the other side for others. I'm not surprised that they pick the extra time for some missions. I am surprised that they don't pick the faster option more frequently.
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?
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.)
As someone who played before they added patched conics, I'd consider patched conics such a thing.
If you're willing to go for the full n-body package, Principia [0] has a pretty nice flight planner that is quite usable for planning more complicated missions.
KSP Trajectory Optimization Tool [1] is a non-mod alternative with some additional capabilities beyond flight planning as well. I think this one is designed for stock gravity so it should be usable in an otherwise vanilla install.
This is doing the latter.
[1]https://en.wikipedia.org/wiki/Parker_Solar_Probe?wprov=sfti1... [2]https://svs.gsfc.nasa.gov/3966/
In real life they used a set of Venus gravity assists instead. This has allowed them to slowly get closer while observing over time instead of a long wait and then one big bang close up before being shot ridiculously far back out.
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.
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.
* With "eventually" being "assuming a stable state for infinite years" which is of course not how astrophysics actually works.
You’re talking about heat (think ‘amperage’), where temperature is more like voltage.
You can’t get above a specific temperature merely by transferring more heat, or losing less heat, etc.
Upper bounds of temperature is still going to be limited by the temperature/frequency of the input energy, barring energy loss which can reduce it.
The solar atmosphere layers have specific maximum temperatures that limit the maximum temperature of objects exposed to them or the radiation from them.
but you can keep absorbing radiation indefinitely
so the equilibrium temperature will depend on the incoming radiation and ensuing outgoing radiation as dictated by the material makeup of the thingy
Once the object has reached the temperature of the source of the radiation (assuming radiative heat transfer), it reaches equilibrium and it will radiate away at the same rate it is absorbing (as a black body). Per the 2nd law of thermodynamics.
It’s why there is a maximum temperature with concentrated solar too - regardless of magnification, you can’t exceed the temperature of the surface of the sun the light was emitted from. Attempted to do so will actually heat the sun (or some other thing) through radiative thermal heat transfer the other direction.
It’s also why radiative heat transfer can’t be used to produce infinitely high temperatures by having a large emitter near a tiny absorber (like a speck of dust) in a vacuum.
If there is some kind of heat pump or laser or the like which you a providing power, then that doesn’t apply of course, but for pure black bodies it does.
If you have some way to let an object absorb radiation, while emitting no radiation even when it is as hot as the source of that radiation, then you have something pretty special going on eh?
Part of it is due to the ‘Principle of Etendue’ [https://en.m.wikipedia.org/wiki/Etendue#Conservation]
What confuses people I think (practically) is that the actual high temperature (~4500F) is far beyond the limits of a useful highest temperature in 99% of situations we might want in engineering. A spacecraft hitting that temperature is going to be a molten piece of scrap long before it hits that point.
But the limit does actually exist - it won’t somehow hit 10,000F for instance. That is also why we can’t produce infinitely high temperatures with a huge magnifying glass - the highest we can hit, regardless of how big it is, is still ~ 4500F. Higher temperatures need something like an electric arc furnace, or LASER.
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.
https://music.youtube.com/watch?v=ZnIxWznakz8&si=jhjMURGD4S0...
”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”
Neither would I.
Sure, it's close enough to get very hot. But it's not into the sun.
What NASA's Parker Solar Probe discovered in its first 5 years looping the sun - https://news.ycombinator.com/item?id=37128838 - Aug 2023 (1 comment)
A NASA probe has touched plasma and gas that belongs to the sun - https://news.ycombinator.com/item?id=29965805 - Jan 2022 (31 comments)
NASA’s Parker Solar Probe Is Unlocking the Sun’s Mysteries - https://news.ycombinator.com/item?id=21709598 - Dec 2019 (2 comments)
Traveling to the Sun: Why Won’t Parker Solar Probe Melt? - https://news.ycombinator.com/item?id=17743599 - Aug 2018 (121 comments)
Traveling to the Sun: Why Won't Parker Solar Probe Melt? - https://news.ycombinator.com/item?id=17569741 - July 2018 (86 comments)
https://svs.gsfc.nasa.gov/3966/
One probe, Parker I assume, goes through all the planetary flybys to achieve its solar orbit. The other just drops into an even closer solar orbit. Why not do that for both probes?
That's the South Pole. I wasn't aware global warming has gotten that bad yet.
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...
Depending on your scales etc you may wish to group different things into the category of “object”, eg a car would likely be be selected as a valid grouping of atoms as an object by most people in conversation wheres it is mostly empty space at the micro level, and has a bunch of very different densities (many oom) at diff volumes even at the macro scale (eg the air in the trunk vs the engine block).
Well played!