Good luck Parker Solar Probe

I've really been enjoying the coverage of this project. It's really very exciting. The technology is amazing, and the research is fascinating.

I've always struggled a bit with the physics here. Perhaps @bwilson4web can help.....

Surely, to get to the Sun, you just need to get the probe travelling around the sun close to where we are, but a bit slower. Then its velocity won't be enough to keep it in orbit, and it will spiral toward the Sun. I get why it takes energy to get out to Mars, because you're "going up" in relation to the sun. But to get to the Sun, don't you just need to "fall"?

 

I think it was fuzzy1 who explained somewhere, how difficult a target the Sun is. Defies my level of understanding, but ...

Parker is going to do some whips past Venus and get up to new-record speed. Which is nice. When it sends data home, that will get collected by deep-space network. I further imagine that their big parabolas might have to slew pretty fast to keep on target.

 

Tor Johnson @20 never made a movie worse by appearing in it.

 

This is the key. Even if it is difficult, if they mess it up, they can always send the probe back in time and do it again.

 

Ahha. Thank you! That makes sense.

 

black body radiates@25. Well, yeah. Don't even point your big dish at sun, unless seeing smoke come out of a block converter is your goal.

 

Johanes Kepler never made any science worse by appearing in it.

 

To get to the sun, you need to go a lot slower from here, not just a bit slower. Our velocity is for a circular orbit. For highly elliptical orbits similar to Bob's illustration, the objects are going very fast when close to the sun, but very slow on the far end, near us in this case.

For objects coasting on ballistic trajectories, without continuous thrust (e.g. rocket, chemical or electric) or drag (e.g. atmospheric entry to the earth or sun), there are no 'spiral' orbits, only conic sections such as ellipses.

Objects in orbit possess considerable energy (kinetic and potential combined) and angular momentum relative to the central body. In basic Newtonian mechanics, both of these elements are conserved quantities. An object can't gain or lose either without some sort of external action. In the vacuum of space, in the absence of collisions or close approaches for 'gravitational slingshot' maneuvers, there isn't anything natural to create any large amounts of such action. (There are a bunch of little things, but they act too slow to be visible on human lifespan scales.)

Getting to the sun from here requires shedding nearly all of the probe's angular momentum. This requires either a big loss of speed, or a change of direction. Either action requires a huge amount of rocket energy. While the satellite loses a lot of energy with respect to the sun, the humans can do this only by applying (negatively in the orbital equations) a huge amount of energy to the object.

Note that the universe doesn't actually lose any energy or momentum here. The heavy gas cloud of rocket exhaust gets blasted forward with all the energy and momentum that the satellite loses.

Here is another description, from NASA - https://www.nasa.gov/feature/goddard/2018/its-surprisingly-hard-to-go-to-the-sun:

"It's Surprisingly Hard to Go to the Sun

The Sun contains 99.8 percent of the mass in our solar system. Its gravitational pull is what keeps everything here, from tiny Mercury to the gas giants to the Oort Cloud, 186 billion miles away. But even though the Sun has such a powerful pull, it's surprisingly hard to actually go to the Sun: It takes 55 times more energy to go to the Sun than it does to go to Mars.

Why is it so difficult? The answer lies in the same fact that keeps Earth from plunging into the Sun: Our planet is traveling very fast — about 67,000 miles per hour — almost entirely sideways relative to the Sun. The only way to get to the Sun is to cancel that sideways motion.

Since Parker Solar Probe will skim through the Sun's atmosphere, it only needs to drop 53,000 miles per hour of sideways motion to reach its destination, but that's no easy feat. In addition to using a powerful rocket, the Delta IV Heavy, Parker Solar Probe will perform seven Venus gravity assists over its seven-year mission to shed sideways speed into Venus' well of orbital energy. These gravity assists will draw Parker Solar Probe's orbit closer to the Sun for a record approach of just 3.83 million miles from the Sun's visible surface on the final orbits.

Though it's shedding sideways speed to get closer to the Sun, Parker Solar Probe will pick up overall speed, bolstered by Sun's extreme gravity — so it will also break the record for the fastest-ever human-made objects, clocking in at 430,000 miles per hour on its final orbits."

 

For now....

 

That's the ticket, fuzz.

Imagine my joy reading words that ellipses are conic sections. You betcha - just not parallel to the base. Far too many kids learning such stuff lack access to such insights. And my buffoonery.

What a shame. Let's figure out how to get students back to science with >billion expenditures such as this. Educational bang from nerd bucks.

 

Voyager II is going 'thataway' at >15 km/sec. One could scarcely hope for more with chemical rockets, because of specific impulse or whatever.

Parker will exceed 191 km/sec in its moments of glory. Stealing momentum from big gravity balls works, if one's aim is good enough. It must go into the hot zone to attain such velocity, so perhaps impractical to attain such speed to exit solar system.

Little lightsails may go faster, someday, pending solution of serious technological problems. Ion drives also, if one packs enough Xenon and energy to blow it out the back.

Put this into perspective that lightspeed is 300,000 km/sec. Universal speed limit unless space itself can be squished. Moving at that speed one can get to nearest maybe habitable planet in 10 years. Or do the whole galaxy in 100,000 years.

Space is big and we are still slow. Parker solar probe will be a million times faster than a typical snail. Four orders of magnitude faster still, and you are talking about enough speed to check out habitable planets within one or few lifetimes of very lucky, far-in-future crew.

 

I want to discuss how to 'buy' new technology.

WWI greatly advanced aeronautics, tanks, the internal combustion engine, ships etc. It cost money, but more importantly it cost 14 million lives.

Technology slows until WWII, which again advances many technologies, at huge costs in money and lives. (36 million lives)

In the 60's, NASA and the space race has also sped up human technologies, and cost some minor fraction of going to war. Importantly, fatalities were in the low tens of people.

I feel way better about squandering money to go to the sun that advances our knowledge about climate, solar storms, computing, rockets (You can call your booster "Heavy", but not your wife) Than I do invading somewhere. In my mind it is a 'cheaper' way to advance.

YMMV

 

That is one. Others include:

* the solar system has many gravitating objects, N-body, whereas our simple orbital equations are for just 2-body systems, i.e. the central object and the satellite only, excluding perturbations from the other objects;
* the sun and planets rotate, so are not perfectly spherical, so their gravities don't really act as true point sources;
* sunlight causes radiation pressure, a real force that is significant for small objects. Reflected light creates different forces than does absorbed light / radiated heat. And for slowly rotating objects with a cooling backside, this radiated heat may be asymmetric;
* the solar wind means that interplanetary space is not a true vacuum, but has a very thin 'atmosphere' with very high speed variable winds.

I'm sure there are more ...

 

Visionaries suggest that getting humans onto extrasolar planets is our necessary future. Stated as a logical extension of our exploratory spirit.

Not to disparage our exploratory spirit, but doing this entire planet happened centuries ago by crossing oceans at about 0.002 km/sec. Snail speed times 10. Now we jet around at almost 0.3 km/sec.

Extension of exploratory spirit to extrasolar scale will require much more than has been demonstrated.

 

Remarkable advances in computation and machine-interface control put this entire solar system (robotically at least) under human eyes. Much has been learned that informs about what other habitable planets are like, much much much further away. None of those are accessible to us. Not for a very long time.

This century may show that humans can sustain themselves on nearby places. It seems that scarce money is needed both to 'extend', and to keep this one&only available place in good condition.

In my view and perhaps controversially, most of scarce money needs to be spent towards earth.

 

Not mentioned here that Parker probe goes into solar corona during sunspot minimum when corona is least frisky. When last it was most frisky, we were not ready to do it.

It is a matter of debate whether next solar (sunspot) max will be small. But either way, in 2023 or 2024, there might be found another 1.5 billion for Parker II.

 

A ground-based solar imaging effort in Inner Mongolia has offered to collaborate with Parker Probe

China's radio heliograph may cooperate with NASA's spacecraft in solar observation: scientist

Which I presume would be useful. However (US) NASA has rules against collaboration with China. Unclear how it will proceed.