NASA is going to send a probe to with in 4 million miles of the Sun’s surface.
More NASA information here.
The Earth orbits at about 100 million miles above the Sun’s surface.
…so the probe is going to close 96% of the distance.
That’s pretty awesome.
Wikipedia link.
Now, one thing that’s a bit hard to wrap one’s head around is that “falling into the sun” (or, if you’re in earth orbit, “falling down to Earth”, is a lot of hard work. If you’re not used to thinking about orbits (or even if you are), you might be inclined to think “OK, I’m already pretty close, and the gravity wants to pull me in …so I just have to let it.
The thing is, though, you’re not just looking at a 2-D or 3-D space; you’re looking at a 4-D (or, arguably, 6-D) state space, where your velocity vector is as important as your location.
…and in this state space, your orbital velocity, which is sufficient to keep you from falling into the center mass, is a huge deal.
It’s easier to get from the Earth to Jupiter’s orbit than it is to get from the Earth to the sun. To get to Jupiter’s orbit, you merely (“merely”) achieve escape velocity from Earth, and then drift at 1 mile per hour out to Jupiter.
To get from the Earth to the Sun, you have to kill all of your forward orbital velocity.
“Good enough” isn’t good enough. Kill just some of it, and you fall in to a somewhat lower orbit … but an orbit none-the-less.
How fast is the Earth moving with regard to the sun?
If you remember your They Might Be Giants and recall that we’re 8 light minutes from the sun, and you also remember that a year has ~ 365 days, you can do the math yourself (c=2πr, etc.). The answer – I recall from the last time I worked it out – is something like Mach 90. Looking it up … yup ~30 km/s.
That’s three times the escape velocity out of Earth’s gravity well.
So, let’s talk about brute forcing it.
Think about a giant multi-stage stack booster that gets an Apollo mission out of Earth’s well.
…and now realize that you’ve now got that payload in solar orbit.
You now have to accelerate to Mach 90.
That’s a lot of work, and you’re using a huge percent of your solar-orbit payload for fuel and rockets.
…which stinks.
So, what’s the smart solution?
Early conceptual designs for the Solar Probe mission used a gravity assist maneuver at Jupiter to cancel the orbital angular momentum of the probe launched from Earth, in order to drop onto a trajectory close to the sun. The Solar Probe + mission design simplifies this trajectory by using multiple gravity assists at Venus
Cool.
My previous musings on gravity assist maneuvers.
My review of the movie Sunshine.