Astronomy Cast Ep. 468: Simulations for Science and Fun

Astronomers depend on simulations to study the Universe. From relatively straightforward orbital simulations to vast simulations that try to recreate the large scale structure of the Universe from the Big Bang. Today we’re going to talk about some of those simulations, as well as tools you can use simulate the Universe.

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Flying Into the Sun? NASA’s Parker Solar Probe Mission

Into The Sun!


If you’ve read enough of our articles, you know I’ve got an uneasy alliance with the Sun. Sure, it provides the energy we need for all life on Earth. But, it’s a great big ongoing thermonuclear reaction, and it’s right there! As soon as we get fusion, Sun, in like, 30 years or so, I tell you, we’ll be the ones laughing.

But to be honest, we still have so many questions about the Sun. For starters, we don’t fully understand the solar wind blasting out of the Sun. This constant wind of charged particles is constantly blowing out into space, but sometimes it’s stronger, and sometimes it’s weaker.

What are the factors that contribute to the solar wind? And as you know, these charged particles are not healthy for the human body, or for our precious electronics. In fact, the Sun occasionally releases enormous blasts that can damage our satellites and electrical grids.

How can we predict the intensity so that we can be better prepared for dangerous solar storms? Especially the Carrington-class events that might take down huge portions of our modern society.

Perhaps the biggest mystery with the Sun is the temperature of its corona. The surface of the Sun is hot, like 5,500 degrees Celsius. But if you rise up into the atmosphere of the Sun, into its corona, the temperature jumps beyond a million degrees.

The list of mysteries is long. And to start understanding what’s going on, we’ll need to get much much closer to the Sun.

Good news, NASA has a new mission in the works to do just that.

The Parker Solar Probe logo. Credit: NASA/JHUAPL

The mission is called the Parker Solar Probe. Actually, last week, it was called the Solar Probe Plus, but then NASA renamed it, and that reminded me to do a video on it.

It’s pretty normal for NASA to rename their spacecraft, usually after a dead astronomer/space scientist, like Kepler, Chandra, etc. This time, though, they renamed it for a legendary solar astronomer Eugene Parker, who developed much of our modern thinking on the Sun’s solar wind. Parker just turned 90 and this is the first time NASA has named it after someone living.

Anyway, back to the spacecraft.

The mission is due to launch in early August 2018 on a Delta IV Heavy, so we’re still more than a year away at this point. When it does, it’ll carry the spacecraft on a very unusual trajectory through the inner Solar System.

The problem is that the Sun is actually a very difficult place to reach. In fact, it’s the hardest place to get to in the entire Solar System.

Remember that the Earth is traveling around the Sun at a velocity of 30 km/s. That’s almost three times the velocity it takes to get into orbit. That’s a lot of velocity.

In order to be able to get anywhere near the Sun, the probe needs to shed velocity. And in order to do this, it’s going to use gravitational slingshots with Venus. We’ve talked about gravitational slingshots in the past, and how you can use them to speed up a spacecraft, but you can actually do the reverse.

The Parker Solar Probe will fall down into Venus’ gravity well, and give orbital velocity to Venus. This will put it on a new trajectory which takes it closer to the Sun. It’ll do a total of 7 flybys in 7 years, each of which will tweak its trajectory and shed some of that orbital momentum.

Parker Solar Probe's trajectory including Venus flybys. Credit: NASA/JHUAPL
Parker Solar Probe’s trajectory including Venus flybys. Credit: NASA/JHUAPL

You know, trying to explain orbital maneuvering is tough. I highly recommend that you try out Kerbal Space Program. I’ve learned more about orbital mechanics by playing that game for a few months than I have in almost 2 decades of space journalism. Go ahead, try to get to the Sun, I challenge you.

Anyway, with each Venus flyby, the Parker Solar Probe will get closer and closer to the Sun, well within the orbit of Mercury. Far closer than any spacecraft has ever gotten to the Sun. At its closest point, it’ll only be 5.9 million kilometers from the Sun. Just for comparison, the Earth orbits at an average distance of about 150 million kilometers. That’s close.

And over the course of its entire mission, the spacecraft is expected to make a total of 24 complete orbits of the Sun, analyzing that plasma ball from every angle.

The orbit is also highly elliptical, which means that it’s going really really fast at its closest point. Almost 725,000 km/h.

In order to withstand the intense temperatures of being this close to the Sun, NASA has engineered the Parker Solar Probe to shed heat. It’s equipped with an 11.5 cm-thick shield made of carbon-composite. For that short time it spends really close to the Sun, the spacecraft will keep the shield up, blocking that heat from reaching the rest of its instruments.

And it’s going to get hot. We’re talking about more than 1,300 degrees Celsius, which is about 475 times as much energy as a spacecraft receives here on Earth. In the outer Solar System, the problem is that there just isn’t enough energy to power solar panels. But where Parker is going, there’s just too much energy.

Now we’ve talked about the engineering difficulties of getting a spacecraft this close to the Sun, let’s talk about the science.

Coronal holes are regions in the sun’s atmosphere or corona where solar plasma can stream directly into space. Often a hole will a couple rotations, inciting repeat auroras approximately every 4 weeks. Credit: NASA

The biggest question astronomers are looking to solve is, how does the corona get so hot. The surface is 5,500 Celsius. As you get farther away from the Sun, you’d expect the temperature to go down. And it certainly does once you get as far as the orbit of the Earth.

But the Sun’s corona, or its outer atmosphere, extends millions of kilometers into space. You can see it during a solar eclipse as this faint glow around the Sun. Instead of dropping, the temperature rises to more than a million degrees.

What could be causing this? There are a couple of ideas. Plasma waves pushed off the Sun could bunch up and release their heat into the corona. You could also get the crisscrossing of magnetic field lines that create mini-flares within the corona, heating it up.

The second great mystery is the solar wind, the stream of charged protons and electrons coming from the Sun. Instead of a constant blowing wind, it can go faster or slower. And when the speed changes, the contents of the wind change too.

There’s the slow wind, that goes a mere 1.1 million km/h and seems to emanate from the Sun’s equatorial regions. And then the fast wind, which seems to be coming out of coronal holes, cooler parts in the Sun’s corona, and can be going at 2.7 million km/h.

Why does the solar wind speed change? Why does its consistency change?

Parker Solar Probe's instruments. Credit: NASA/JHUAPL
Parker Solar Probe’s instruments. Credit: NASA/JHUAPL

The Parker Solar Probe is equipped with four major instruments, each of which will gather data from the Sun and its environment.

The FIELDS experiment will measure the electric and magnetic fields and waves around the Sun. We know that much of the Sun’s behavior is driven by the complex interaction between charged plasma in the Sun. In fact, many physicists agree that magnetohydrodynamics is easily one of the most complicated fields you can get into.

Integrated Science Investigation of the Sun, or ISOIS (which I suspect needs a renaming) will measure the charged particles streaming off the Sun, during regular solar activity and during dangerous solar storms. Can we get any warning before these events occur, giving astronauts more time to protect themselves?

Wide-field Imager for Solar PRobe or WISPR is its telescope and camera. It’s going to be taking close up, high resolution images of the Sun and its corona that will blow our collective minds… I hope. I mean, if it’s just a bunch of interesting data and no pretty pictures, it’s going to be hard to make cool videos showcasing the results of the mission. You hear me NASA, we want pictures and videos. And science, sure.

And then the Solar Wind Electrons Alphas and Protons Investigation, or SWEAP, will measure type, velocity, temperature and density of particles around the Sun, to help us understand the environment around it.

One interesting side note, the spacecraft will be carrying a tiny chip on board with photos of Eugene Parker and a copy of his original 1958 paper explaining the Sun’s solar wind.

The Parker Solar Probe orbiting the Sun. Credit: NASA/JHUAPL
The Parker Solar Probe orbiting the Sun. Credit: NASA/JHUAPL

I know we’re still more than a year away from liftoff, and several years away before the science data starts pouring in. But you’ll be hearing more and more about this mission shortly, and I’m pretty excited about what it’s going to accomplish. So stay tuned, and once the science comes in, I’m sure you’ll hear plenty more about it.

What Is The Interplanetary Transport Network?

What is the Interplanetary Transport Network?

It was with great fanfare that Elon Musk announced SpaceX’s plans to colonize Mars with the Interplanetary Transport System.

I really wish they’d stuck to their original name, the BFR, the Big Fabulous Rocket, or something like that.

The problem is that Interplanetary Transport System is way too close a name to another really cool idea, the Interplanetary Transport Network, which gives you an almost energy free way to travel across the entire Solar System. Assuming you’re not in any kind of rush.

When you imagine rockets blasting off for distant destinations, you probably envision pointing your rocket at your destination, firing the thrusters until you get there. Maybe turning around and slowing down again to land on the alien world. It’s how you might drive your car, or fly a plane to get from here to there.

But if you’ve played any Kerbal Space Program, you know that’s not how it works in space. Instead, it’s all about orbits and velocity. In order to get off planet Earth, you have be travelling about 8 km/s or 28,000 km/h sideways.

Artist's concept of a Bimodal Nuclear Thermal Rocket in Low Earth Orbit. Credit: NASA
Artist’s concept of a Bimodal Nuclear Thermal Rocket in Low Earth Orbit. Credit: NASA

So now, you’re orbiting the Earth, which is orbiting the Sun. If you want to get to Mars, you have raise your orbit so that it matches Mars. The absolute minimum energy needed to make that transfer is known as the Hohmann transfer orbit. To get to Mars, you need to fire your thrusters until you’re going about 11.3 km/s.

Then you escape the pull of Earth, follow a nice curved trajectory, and intercept the trajectory of Mars. Assuming you timed everything right, that means you intercept Mars and go into orbit, or land on its surface, or discover a portal to hell dug into a research station on Phobos.

If you want to expend more energy, go ahead, you’ll get there faster.

But it turns out there’s another way you can travel from planet to planet in the Solar System, using a fraction of the energy you would use with the traditional Hohmann transfer, and that’s using Lagrange points.

We did a whole article on Lagrange points, but here’s a quick refresher. The Lagrange points are places in the Solar System where the gravity between two objects balances out in five places. There are five Lagrange points relating to the Earth and the Sun, and there are five Lagrange points relating to the Earth and the Moon. And there are points between the Sun and Jupiter, etc.

Illustration of the Sun-Earth Lagrange Points. Credit: NASA
Illustration of the Sun-Earth Lagrange Points. Credit: NASA

Three of these points are unstable. Imagine a boulder at the top of a mountain. It doesn’t take much energy to keep it in place, but it’s easy to knock it out of balance so it comes rolling down.

Now, imagine the whole Solar System with all these Lagrange points for all the objects gravitationally interacting with each other. As planets go around the Sun, these Lagrange points get close to each other and even overlap.

And if you time things right, you can ride along in one gravitationally balanced point, and the roll down the gravity hill into the grasp of a different planet. Hang out there for a little bit and then jump orbits to another planet.

In fact, you can use this technique to traverse the entire Solar System, from Mercury to Pluto and beyond, relying only on the interacting gravity of all these worlds to provide you with the velocity you need to make the journey.

Welcome to the Interplanetary Transport Network, or Interplanetary Superhighway.

Unlike a normal highway, though, the actual shape and direction these pathways take changes all the time, depending on the current configuration of the Solar System.

800px-Interplanetary_Superhighway
A stylized example of one of the many, ever-changing routes along the ITN. Credit: NASA

If you think this sounds like science fiction, you’ll be glad to hear that space agencies have already used a version of this network to get some serious science done.

NASA greatly extended the mission of the International Sun/Earth Explorer 3, using these low energy transfers, it was able to perform its primary mission and then investigate a couple of comets.

The Japanese Hiten spacecraft was supposed to travel to the Moon, but its rocket failed to get enough velocity to put it into the right orbit. Researchers at NASA’s Jet Propulsion Laboratory calculated a trajectory that used the Lagrange points to help it move slowly and get to the Moon any way.

NASA’s Genesis Mission used the technique to capture particles from the solar wind and bring them back to the Earth.

There have been other missions to use the technique, and missions have been proposed that might exploit this technique to fully explore all the moons of Jupiter or Saturn, for example. Traveling from moon to moon when the gravity points line up.

It all sounds too good to be true, so here’s the downside. It’s slow. Really, painfully slow.

Like it can take years and even decades to move from world to world.

Imagine in the far future, there are space stations positioned at the major Lagrange points around the planets in the Solar System. Maybe they’re giant rotating space stations, like in 2001, or maybe they’re hollowed out asteroids or comets which have been maneuvered into place.

Exterior view of a Stanford torus. Bottom center is the non-rotating primary solar mirror, which reflects sunlight onto the angled ring of secondary mirrors around the hub. Painting by Donald E. Davis
Exterior view of a Stanford torus. Bottom center is the non-rotating primary solar mirror, which reflects sunlight onto the angled ring of secondary mirrors around the hub. Painting by Donald E. Davis

They hang out at the Lagrange points using minimal fuel for station keeping. If you want to travel from one planet to another, you dock your spacecraft at the space station, refuel, and then wait for one of these low-energy trajectories to open up.

Then you just kick away from the Lagrange point, fall into the gravity well of your destination, and you’re on your way.

In the far future, we could have space stations at all the Lagrange points, and slow ferries that move from world to world along low energy trajectories, bringing cargo from world to world. Or taking passengers who can’t afford the high velocity Hohmann transfer technique.

You could imagine the space stations equipped with powerful lasers that fill your ship’s solar sails with the photons it needs to take you to the next destination. But then, I’m a sailor, so maybe I’m overly romanticizing it.

Here’s another, even more mind-bending concept. Astronomers have observed these networks open up between interacting galaxies. Want to transfer from the Milky Way to Andromeda? Just get your spacecraft to the galactic Lagrange point in a few billion years as they pass through each other. With very little energy, you’ll be able to join the cool kids in Andromeda.

I love this idea that colonizing and traveling across the Solar System doesn’t actually need to take enormous amounts of energy. If you’re patient, you can just ride the gravitational currents from world to world. This might be one of the greatest gifts the Solar System has made available to us.

What Are The Lagrange Points?

Being stuck here on Earth, at the bottom of this enormous gravity well really sucks. The amount of energy it takes to escape into the black would make even Captain Reynolds curse up a gorram storm.

But gravity has a funny way of evening the score, giving and taking in equal measure.

There are special places in the Universe, where the forces of gravity nicely balance out. Places that a clever and ambitious Solar System spanning civilization could use to get a toehold on the exploration of the Universe.

The five Sun-Earth Lagrange points. Credit: NOAA
The five Sun-Earth Lagrange points. Credit: NOAA

These are known as the Lagrange Points, or Lagrangian Points, or libration points, or just L-Points. They’re named after the French mathematician Joseph-Louis Lagrange, who wrote an “Essay on the Three Body Problem” in 1772. He was actually extending the mathematics of Leonhard Euler.

Euler discovered the first three Lagrangian Points, even though they’re not named after him, and then Lagrange turned up the next two.

But what are they?

When you consider the gravitational interaction between two massive objects, like the Earth and the Sun, or the Earth and the Moon, or the Death Star and Alderaan. Actually, strike that last example…

As I was saying, when you’ve got two massive objects, their gravitational forces balance out perfectly in 5 places. In each of these 5 places you could position a relatively low mass satellite, and maintain its position with very little effort.

Sun-Earth Lagrange Points. Credit: Xander89/Wikimedia Commons
Sun-Earth Lagrange Points. Credit: Xander89/Wikimedia Commons

For example, you could park a space telescope or an orbital colony, and you’d need very little, or even zero energy to maintain its position.

The most famous and obvious of these is L1. This is the point that’s balanced between the gravitational pull of the two objects. For example, you could position a satellite a little above the surface of the Moon. The Earth’s gravity is pulling it towards the Moon, but the Moon’s gravity is counteracting the pull of the Earth, and the satellite doesn’t need to use much fuel to maintain position.

There’s an L1 point between the Earth and the Moon, and a different spot between the Earth and the Sun, and a different spot between the Sun and Jupiter, etc. There are L1 points everywhere.

L2 is located on the same line as the mass but on the far side. So, you’d get Sun, Earth, L2 point. At this point, you’re probably wondering why the combined gravity of the two massive objects doesn’t just pull that poor satellite down to Earth.

It’s important to think about orbital trajectories. The satellite at that L2 point will be in a higher orbit and would be expected to fall behind the Earth, as it’s moving more slowly around the Sun. But the gravitational pull of the Earth pulls it forward, helping to keep it in this stable position.

Animation showing the relationship between the five Lagrangian points (red) of a planet (blue) orbiting a star (yellow), and the gravitational potential in the plane containing the orbit (grey surface with purple contours of equal potential). Credit: cmglee (CC-SA 3.0)
Animation showing the relationship between the Lagrangian points (red) of a planet (blue) orbiting a star (yellow), and the gravitational potential in the plane containing the orbit (grey surface with purple contours of equal potential). Credit: cmglee (CC-SA 3.0)

You’ll want to play a lot of Kerbal Space Program to really wrap your head around it. Sadly, your No Man’s Sky time isn’t helping you at all, except to teach you that hyperdrives are notoriously finicky and you’ll never have enough inventory space.

L3 is located on the direct opposite side of the system. Again, the forces of gravity between the two masses balance out so that the third object maintains the same orbital velocity. For example, a satellite in the L3 point would always remain exactly hidden by the Sun.

Hold on, hold on, I know there are a million thoughts going through your brain right now, but bear with me.

There are two more points, the L4 and L5 points. These are located ahead and behind the lower mass object in orbit. You form an equilateral triangle between the two masses, and the third point of the triangle is the L4 point, flip the triangle upside down and there’s L5.

Now, it’s important to note that the first 3 Lagrange points are gravitationally unstable. Any satellite positioned there will eventually drift away from stability. So they need some kind of thrusters to maintain this position.

Imagine a tall smooth mountain, with a sharp peak. Put a bowling ball at the very top and you’re not going to need a lot of energy to keep it in that location. But the blowing wind will eventually knock it out of place, and down the mountain. That’s L1, L2 and L3, and it’s why we don’t see any natural objects located in those places.

But L4 and L5 are actually stable. It’s the opposite situation, a deep valley where a bowling ball will tend to fall down into. And we find asteroids in the natural L4 and L5 positions in the larger planets, like Jupiter. These are the Trojan asteroids, trapped in these natural gravity wells though the gravitational interaction of Jupiter and the Sun.

Artist's diagram of Jupiter and some Trojan asteroids nearby the gas giant. Credit: NASA/JPL-Caltech
Artist’s diagram of Jupiter and some Trojan asteroids nearby the gas giant. Credit: NASA/JPL-Caltech

So what can we use Lagrange points for? There are all kinds of space exploration applications, and there are already a handful of satellites in the various Earth-Sun and Earth-Moon points.

Sun-Earth L1 is a great place to station a solar telescope, where it’s a little closer to the Sun, but can always communicate with us back on Earth.

The James Webb Space Telescope is destined for Sun-Earth L2, located about 1.5 million km from Earth. From here, the bright Sun, Earth and Moon are huddled up in a tiny location in the sky, leaving the rest of the Universe free for observation.

Image: James Webb Space Telescope
NASA’s James Webb Telescope, shown in this artist’s conception, will provide more information about previously detected exoplanets. It will be at Sun-Earth L2.

Earth-Moon L1 is a perfect place to put a lunar refueling station, a place that can get to either the Earth or the Moon with minimal fuel.

Perhaps the most science fictiony idea is to put huge rotating O’Neill Cylinder space stations at the L4 and L5 points. They’d be perfectly stable in orbit, and relatively easy to get to. They’d be the perfect places to begin the colonization of the Solar System.

Thanks gravity. Thanks for interacting in all the strange ways that you do, and creating these stepping stones that we can use as we reach up and out from our planet to become a true Solar System spanning civilization.

Weekly Space Hangout – May 1, 2015: Prof. Coel Hellier, WASP & SuperWASP

Host: Fraser Cain (@fcain)
Special Guest: Prof. Coel Hellier, Professor of Astrophysics at Keele University, UK, to talk about WASP & SuperWASP.

Guests:
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Alessondra Springmann (@sondy)
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