APOD: Launch of the Parker Solar Probe (2018 Aug 15)

[APOD Robot]

Launch of the Parker Solar Probe

Explanation: When is the best time to launch a probe to the Sun? The now historic answer -- which is not a joke because this really happened this past weekend -- was at night. Night, not only because NASA's Parker Solar Probe's (PSP) launch window to its planned orbit occurred, in part, at night, but also because most PSP instruments will operate in the shadow of its shield -- in effect creating its own perpetual night near the Sun. Before then, years will pass as the PSP sheds enough orbital energy to approach the Sun, swinging past Venus seven times. Eventually, the PSP is scheduled to pass dangerously close to the Sun, within 9 solar radii, the closest ever. This close, the temperature will be 1,400 degrees Celsius on the day side of the PSP's Sun shield -- hot enough to melt many forms of glass. On the night side, though, it will be near room temperature. A major goal of the PSP's mission to the Sun is to increase humanity's understanding of the Sun's explosions that impact Earth's satellites and power grids. Pictured is the night launch of the PSP aboard the United Launch Alliances' Delta IV Heavy rocket early Sunday morning.

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[Boomer12k]

Go, Baby, Go!!!!

:---[===] *

[Fred the Cat]

It's the photographer that needed a shield. Let alone his camera. Sure his aperture was only open a whisper.

[suicidejunkie]

I like to use that same angle for launching from KSC. The ship looks awfully familiar too. I gotta get a high rez texture mod like this image.
Good to see they added the extra boosters and struts too

[Uwe]

Of course the best time to launch a probe to the sun is .. on a sunday

[MarkBour]

Since we have not sent anything that close to the Sun before, I wonder a little if they are right about the temperature that the shielded part will experience. I'm sure they've modeled it based on the knowledge we already have of the solar wind and corona. I hope it goes smoothly and gathers lots of interesting data.

[neufer]

Since we have not sent anything that close to the Sun before,
I wonder a little if they are right about the temperature that the shielded part will experience.

Black Body radiation is pretty well understood.

Parker Solar Probe shield Temp. = 0.89 x [Photosphere Temp.: 5,772 K) / sqrt(distance in R_☉)]

[MarkBour]

Since we have not sent anything that close to the Sun before,
I wonder a little if they are right about the temperature that the shielded part will experience.

Black Body radiation is pretty well understood.

Parker Solar Probe shield Temp. = 0.89 x (Photosphere Temp.: 5,772 K) / sqrt(distance in R_☉)

But the Parker Solar Probe will get into the corona, right?
The gases therein are evidently not heated by blackbody radiation.
Helping figure out how that works is why it is being sent there ...

[Chris Peterson]

Since we have not sent anything that close to the Sun before,
I wonder a little if they are right about the temperature that the shielded part will experience.

Black Body radiation is pretty well understood.

Parker Solar Probe shield Temp. = 0.89 x (Photosphere Temp.: 5,772 K) / sqrt(distance in R_☉)

But the Parker Solar Probe will get into the corona, right?
The gases therein are evidently not heated by blackbody radiation.
Helping figure out how that works is why it is being sent there ...

The corona is "hot" in the same way that the Earth's thermosphere is. That's where the ISS orbits, and the temperature is over 2000° C. The ISS does not need a heat shield. The corona where the Parker probe will dip has a density of around 10⁹ particles per cubic centimeter. That's a pretty good vacuum. What that means is that very little heat is transferred. "Hot" means very energetic particles as well as x-ray emission. That's what they had to be concerned about. The heat shield protects the probe from ordinary solar radiation. Other measures are used to protect from radiation and energetic plasma in the corona itself.

[CurtT]

Wouldn't it be better to launch at local noon? At that point in time and space the Earth's 67,000 mph speed is decreased by 1040 mph at the equator, maybe 900 at the cape, thanks to Earth's rotation. That reduces total energy by almost 1/67th.

[neufer]

Wouldn't it be better to launch at local noon? At that point in time and space the Earth's 67,000 mph speed is decreased by 1040 mph at the equator, maybe 900 at the cape, thanks to Earth's rotation. That reduces total energy by almost 1/67th.

Spacecraft must first go into circular orbit at ~17,000 mph... which is easiest done from the equator heading due East (but at any time of day) .

The spacecraft then gives a burst of thrust at ~17,000 mph for maximum power (= F x v) to go into a hyperbolic orbit that places it on a path either in the direction of Earth's motion around the Sun (by starting the maneuver in the evening-time) or (for Parker say) in the opposite direction (by starting the maneuver in the morning).

It is all done in stages such that each stage provides the maximum power (= F x v) at its start while the final stage ends up going in the proper direction.