A NASA probe has touched plasma and gas that belongs to the sun | Hacker News Reader

A NASA probe has touched plasma and gas that belongs to the sun

theatlantic.com

84 pointsworldvoyageur31 comments

At its launch, the Parker Solar probe surpassed all prior records of speed. And it will continue to break its own record over the 7 years after 7 consecutive encounters with Venus that will lower its trajectory to 9.86 Solar Radii

While a lot of it will be eventually achieved due to orbital mechanics, most of the push was given to it by the Delta IV Heavy. For those who may not be familiar, the launches are always spectacular due to the pre-flushing of Hydrogen through the system. NASA has an HD video that you can download, https://www.youtube.com/watch?v=AlyuSwRSVHU

The PSP's speed is impressive without context, but it's even more impressive in context. Here are phenomena in the same range as the PSP.

The Earth rotates around the sun at a speed of,

    29,800 m/s or 0.01% the speed of light

Our galaxy approaches the Messier 98 https://en.wikipedia.org/wiki/Messier_98 galaxy at a speed of,

    140,000 m/s or 0.04% the speed of light.

PSP is faster than both of these at,

    163,000 m/s or 0.05% the speed of light.

Due to the quirks of orbital mechanics, by the end of its life, the probe will be even faster and it will reach,

    192,000 m/s or 0.06% the speed of light

It's 8,000 m/s shy of our solar system's orbital velocity around the galactic center.

The design is a stunning accomplishment of engineering and daring. If you would like a detailed overview of how the mission trajectory was designed, the navigation team has written an excellent explainer that you can read here, https://trs.jpl.nasa.gov/handle/2014/47575

I was confused at first because the article mentions that "a spacecraft bound for the center of the solar system would need to slow itself down" and "engineers must take Parker past Venus seven times throughout the mission, so that the spacecraft can use that planet’s gravity as a brake", but you mention that PSP is traveling very fast (and indeed I've always understood that items orbiting closer to the center travel faster). Is this just a dumbing-down in the article's verbiage, or is it common to think of shrinking the perihelion as "braking"?

Think about it as a vector. Imagine if you were a god, and you placed a particle in the same orbit as Earth. Now imagine you wanted to smash it into the sun. How would you do it?

For the particle to fall straight "down" to the sun, in a straight line, you would have to cancel all of its orbital velocity.

That's why it's difficult to get close to the sun and it requires a lot of energy. You have to subtract out a large part of Earth's orbital velocity.

But that's just one part of the explanation. It's not intuitive per se (I imagine it as a play between kinetic and potential energies), but the closer you are to a body, the faster your orbit. The farther out the "slower" your orbit.

It's the opposite of a disc.

Ah, thanks.

If I get you right, the braking slows the orbiting object down. But that slow-down causes it to move to a lower orbit, losing potential energy in exchange for increased orbital velocity. And the velocity you drop in high orbit, you gain with interest as you move to low orbit.

So braking makes you go faster.

Passing by Venus is lowering the spacecraft's periapsis, increasing the orbit's eccentricity. The lower the satellite goes, the faster it will be at periapsis. Those speeds the GP comment is refering to are, in all likelihood, velocity as periapses.

Yes, indeed! It's the magnitude of its velocity around the sun at closest approach.

There we go, thank you, that's the mental model I needed to bring it together

"Reaching the sun is, remarkably, more difficult than reaching the outer planets, or leaving the solar system altogether."

A fact that I independently stumbled upon in Kerbal Space Program when I was trying to fly my Kerbals directly into the Sun. It was surprisingly difficult (still haven't achieved it - no spoilers please!), but obvious after a few moments thought.

I don't know much about celestial mechanics, but Newtonian conservation of energy should mean that not only did we 'boop the Sun', but we also pushed the Sun a tiny, tiny, tiny bit away from where it was. I wonder if that would be measurable.

This Grand Theft Pluto: New Horizons Gets a Boost From Jupiter Flyby [1]

"For New Horizons to speed up, of course, Jupiter must slow down. "That's conservation of energy," he says. But no one will notice. The change in Jupiter's orbit around the Sun due to the flyby is fantastically small. New Horizons will absorb about 1/1025 of Jupiter's orbital energy. That's like "taking a single drop out of the ocean," says Farquhar. "

[1] https://www.nasa.gov/mission_pages/newhorizons/news/jupiter_...

1/1025 of Jupiter's orbital energy sounds absolutely huge.

Of course, it's supposed to say 1/10²⁵, which is quite different.

THANK YOU!!! I re-read that so many times :-)

That was my fault for not double checking my copy / paste. Sorry about that.

My fault. I didn't verify it when I pasted it. Thanks for correcting it!

I once saw a calculation that Voyager's slingshot past Jupiter slowed the planet's motion by one foot per trillion years.

It's measurable, if you've got a long enough time scale.

And a stable enough ruler.

If the vessel was started at day, the earth was also pushed away from the sun

Cool way to fix the global warming problem. Just push the sun away.

Cue the classic meme: “we should take Bikini Bottom and PUSH it somewhere else!”

https://youtu.be/ubePTrs2VJc

Would”t that be true of any voyage through the solar system?

I just read and watched a video about the Parker Solar probe (very cool) thanks to The Orbital Index email newsletter: https://orbitalindex.com/

I am not affiliated, but enjoy very much getting my weekly space news!

Why didn't the probe burn up in the coronasphere? It went at night!

It had a face mask.

Reply on news.ycombinator.com