A Tour Of The Lagrange Points. Part 3 – Trojans and Space Colonies at L4/L5

A Tour Of The Lagrange Points. Part 3 – Trojans and Space Colonies at L4/L5


We’ve reached the third part of our series
on Lagrange Points, those stable spots in the Solar System, where you can sort of hover
with the minimum amount of fuel. This episode we’re going to look at the
L4 and L5 points which share the orbit with a more massive object. Again, this is the third part of a series,
so if you need an overall explainer on what the Lagrange points are, I suggest you go
back to the beginning and watch episode 1. All right, let’s talk about L4 and L5. While the previous L1, L2 and L3 points are
located along a line that connects the two masses, L4 and L5 orbit with the less massive
object, maintaining a position 60 degrees ahead and behind. And unlike the previous points we talked about,
L4 and L5 are meta-stable. Which means that a spacecraft can loiter in
this area without needing to use any fuel at all. In fact, it’s a gravity well that a spacecraft
would need to fight to escape if it wanted to. As with the previous points, it’s important
to remember that any object in L4 and L5 needs to have insignificant mass compared to the
two massive objects. Astronomers call natural objects hanging out
in these regions: Trojans. So, in the case of the Sun and Jupiter, you
can have a pretty hefty asteroid hanging out in these points. In fact, the most massive Trojan asteroid
discovered so far is 624 Hektor, measuring about 225 kilometers across and has a mass
of 9 quintillion kilograms. Many other smaller asteroids have been detected
in this region as well. For the longest time, astronomers knew that
the Earth had trapped dust in its L4/L5 points. But in 2010, NASA’s Wide-field Infrared
Survey Explorer, or WISE discovered the first actual Trojan asteroid lurking in this region. Designated as 2010 TK7, the object measures
about 300 meters across, and traces an unusual orbit that moves above and below the Earth’s
orbital plane. In fact, WISE was able to discover the trojan
in the first place because it has such an unusual orbit that carries it quite far afield
from the L4 point. Normally the Sun obscures our view into this
region. Astronomers have also discovered dust in the
Earth-Moon L4 and L5 points, known as Kordylewski clouds, but so far, no actual asteroids. Astronomers have found Trojan asteroids sharing
Neptune’s orbit, Uranus, and even Mars has its share of Trojans, which astronomers think
might have formed out of ejected material from an ancient collision with Mars. Astronomers think that the largest Mars Trojan,
5261 Eureka, was blasted out of Mars more than a billion years ago, and then it was
spun up over eons to the point that fragments were ejected into new, but similar orbits. So, clearly Nature has figured out how to
use the L4 and L5 points, but what about spacecraft missions? Actually, so far, no mission has ever been
sent to these regions. No Sun-Earth L4 missions, nothing to Jupiter
or Mars. There, the history portion is over. So, what about the future? Are there any clever ideas to use them? You bet. At the 46th Lunar and Planetary Science Conference,
astronomers proposed that a Cubesat mission be sent to one of the Sun-Earth L4/L5 regions
to search for additional Trojan asteroids beyond 2010 TK7. Equipped with an infrared camera, this Cubesat
mission would be able to perform a comprehensive survey of the region, tracking down many of
the larger Trojan objects. From this, astronomers would be able to identify
potential candidates for future robotic orbiters and landers. Depending on their inclination to the Earth’s
orbit, they would require very little change in velocity to reach from Earth, which means
they’d be inexpensive energy wise. We could get a lot of science done with not
a lot of spacecraft. Another mission that’s coming together is
NASA’s Lucy Mission. Due to launch in 2021, Lucy will spend 12
years visiting seven different asteroids; one in the main asteroid belt and then 6 in
Jupiter’s Trojan regions. Its flight path will carry it on several slingshot
maneuvers past Earth to gain speed, and then it’ll fly out to Jupiter’s L4 region in
2025, visiting 4 asteroids, including a double asteroid. Then it’ll fly back to Earth, slingshot
out to the L5 region and visit another asteroid in 2033, and then fall back down into the
inner Solar System again. Of course, Lucy will be equipped with the
standard array of remote sensing instruments to study the geology, surface composition
and physical properties of all the asteroids it flies past. In the last episode, I mentioned that there’s
no good use for the Sun-Earth L3 point, but there’s actually one idea that might use
L3, L4 and L5 to build a gigantic gravitational wave interferometer called the Astrodynamical
Space Test of Relativity using Optical Devices, or ASTROD. Astronomers are already planning the LISA
observatory to fly in the 2030s, which will consist of three spacecraft flying in an equilateral
triangle formation 2.5 million kilometers apart from each other to detect gravitational
waves with more sensitivity than the best Earth-based instruments. The ASTROD plan would take this to the next
level, building a gigantic equilateral triangle by positioning a spacecraft at L3, L4 and
L5. Each arm of the instrument would measure 260
million kilometers across, and by timing their movements, they could remain within about
20,000 kilometers of this distance at all times. A gravitational wave laser interferometer
this big would be 260 times more sensitive than LISA, able to detect collisions between
supermassive black holes, intermediate mass black holes, compact binaries, and even the
gravitational wave vibrations left over from the Big Bang; a time that we can’t see with
optical wavelengths. A laser interferometer the size of the Earth’s
orbit. That would be pretty cool. Those are some missions to explore the L4
and L5 regions, but I know what you want to hear. You want to know about massive rotating space
colonies proposed by Gerard O’Neill in the 1970s. Okay fine, we’ll get to that in a second,
but first I’d like to thank: Timothy Pifer
Bill Munn Rajesh And the rest of our 801 patrons for their
generous support. Educational content should be freely available
to anyone in the world. The Patrons make this possible. Join our community at patreon.com/universetoday
and get in on the action. The most science fiction use of the Earth-Moon
L4 and L5 Lagrange Points has got to be the O’Neill Cylinder Space Settlements proposed
by Princeton physicist Gerard O’Neill in the 1970s. The concept came out of a 10-week program
in engineering systems design at Stanford and Ames Research Center in 1975. More than two dozen scientists, students and
professors came together for ten weeks to design how a future space colony might work,
allowing people to survive and even thrive in the harsh environment of space. The O’Neill Cylinder would be a giant, rotating
space station measuring 1,800 meters across, and be a home for 10,000 people. And to keep it in a stable location, they
proposed putting the station at Earth-Moon L5. People would live in the outer ring, connected
to the central docking area by 6 giant spokes. The centripetal force from the rotation of
the space station would give the inhabitants artificial gravity, allowing them to carry
on regular lives as if they were under Earth’s gravity. Because it’s located out beyond the protection
of the Earth’s magnetosphere, the space station needs to protect the inhabitants from
cosmic radiation. Back in the 1970s, the design team decided
that an active magnetic shield would be too complicated and energy intensive. Actually, it still is today, we’ve done
a whole episode on this. Instead, they proposed mining thousands of
tonnes of rock from the surface of the Moon and surrounding the outer shell of the habitats
with protective bricks. If you want to prevent cosmic radiation, all
you need is mass. A lot of mass. It would be too expensive to bring it up from
Earth, but electromagnetic railguns on the Moon could be constantly throwing material
into space that could be added to the station. Giant mirrors would reflect sunlight into
the station, at an angle that prevents cosmic rays from coming in too. Variations on the O’Neill Cylinder were
proposed over the next few years, like the Stanford Torus and the McKendree Cylinder
but they all suffered from the problem that they’re inherently unstable. If you have a long tube rotating in space,
it has two axis of rotation. Whichever is the longer axis is the preferred
direction of rotation. Which means that you have to fight against
your space station wanting to tumble end over end. O’Neill and other’s solutions was to build
their stations in pairs which rotate in opposite directions from each other, balancing out
the forces. The amount of raw materials that will need
to go into a space station of this size will help you understand why we’ve never built
one yet. The largest version of the O’Neill Cylinder
would require 4.5 billion tonnes of rock, steel, machinery, shielding and other components. Even if the SpaceX Starship could bring launch
costs down to $100 per kilogram, that would still cost about $450 trillion. That would require about 45,000 Starship launches
to build one in Low Earth Orbit, not to mention getting it up to L5. That’s why it’s so important for us to
develop space-based mining and manufacturing before we have any chance of living in our
rotating space stations. I hope you enjoyed this tour through the Solar
System’s Lagrange Points. We’ve already take advantage of them with
our missions and space telescopes, and I’m sure this is only the beginning. I can’t wait to see what happens next. What do you think? Are you aware of any other ideas to use the
L4 and L5 points in the Solar System? Let me know your thoughts in the comments. Here are the names of the Patrons who support
us at the $10 level and more. Want to see your name here and support the
work we do? Go to patreon.com/universetoday Once a week I gather up all my space news
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up. Did you know that all of my videos are also
available in a handy audio podcast format, so you can have the latest episodes as well
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Universe Today on iTunes, Spotify or wherever you get your podcasts. I’ll put a link in the shownotes. Here’s a link to the next episode in the
series.

100 thoughts on “A Tour Of The Lagrange Points. Part 3 – Trojans and Space Colonies at L4/L5

  1. If the L4 and L5 Lagrange points are stable and asteroids naturally pool there, then what would the benefit be to searching for additional trojan asteroids? If they pool there they aren't dangerous to Earth, but is there a specific reason or something else I'm missing? Are these asteroids naturally more "special" than the others?

  2. Hey.
    Q:
    Can we bounce a probe of a gass Giants atmosphere to bring back a sample? What speed does a theoreticall probe need? Can it survive?
    Love what you do keep it up!

  3. Hey Fraser, ever consider posting on Bitchute.com? It's a free speech alternative to Youtube that would be enriched by great science centered content creators like yourself.

    Considering whistle-blowers pointed to google has proven to be socially engineering and politically censor the public's discourse. I plead that people that are even a bit principled on freedom of speech to play a part, thanks.

    https://www.bitchute.com/video/re9Xp6cdkro/

    https://www.bitchute.com/video/g1VeElBAeas/

  4. A trojan, there is, at least the first, shielding mass and construction material. Going to be an exciting time. Seems like an equilateral arrangement would have some great observational applications. The far side of the sun would have very little earth based QRM and, given an L4 or L5 relay, would also be a great long term solar observatory. Three cube sats?

  5. can you, please, make a video about the Gateway Foundation? they have impressive animations about awesome space stations (recent videos, too), but mankind cannot even produce the space plane shown there, let alone the entire station. So they seem to be a little off to me.
    thanks

  6. Are L4 and L5 points in Earth-Moon system stable? Is it a good idea to put a space-station there, instead of L4 and L5 in Sun-Earth system? They much closer to us after all.

  7. Hey Fraser! Just a thought, but could you negate the cost of an O’Neil Cylinder by building in an existing asteroid? If you voted out the middle of one and used the materials to build it wouldn’t that change the cost aspect by a large degree? Trojan asteroid mining and building company anyone?

  8. Would it be possible to design space craft that could capture some of the material that’s trapped at the Lagrange points close to earth and bring it to LEO to kick start industrialisation in Space? Or is it that material spread too far to make that feasible regarding fuel usage?

  9. How does the gravity wave observatory proposed (or existing ones) detect tiny changes in lengths if tidal forces are causing much larger changes? Do they adjust their light path to remain constant, record the adjustments required to do so, and subtract out the low frequency components mathematically?

  10. I think Bezos's idea is more like filling the solar system with O'Neill cylinders, not just Lagrange points, including orbits outside the plane of the ecliptic. It's basically a realistic Kardashev II solar system.

  11. What angle would prevent cosmic rays from entering the cylinder? Don’t they come from everywhere?
    Also regarding the question in the live q+a about gravitational waves moving slower in different mediums:
    Wouldn’t we be able to see shadows, scattering or distortions from all the stuff they passed through. I mean they came from really far away (log ago) and must have encountered a lot of massive galaxies and other black holes

  12. uhmm i think you've already done a video on the Interplanetary Transport Network, but seems like a reboot is in order as part four of this series.

  13. Hi Frasier, with your passion for space colonies I was wondering if you have seen any of the mobile suit Gundam anime , I think you would get a kick out of its depiction of the concept of humanity living in space.

  14. Could L3-5 also be used for radio interferometry? Like a super-massive upgrade of the Event Horizon Telescope? If so, what could that resolve?

  15. It should be obvious to start mining any asteroids already in Earth-Sun L4 and L5.
    And bring captured asteroids there for same reason.
    We have to get started mining asteroids very soon, to ease of pressure on Earth's resources.

    Thanks for yet another great video, Fraser. 👍

  16. Earthlings, those Lagrange points are within the territory of the Solar System Empire!

    But you can visit them, and maybe buy some souvenirs!

    SSE Bucket Hat
    Available with either English or Russian text embroidery.
    https://ic.pics.livejournal.com/jenab6/14257799/112230/112230_900.jpg

    SSE Tee Shirt
    Formerly available only to Empire citizens employed by the ICP.
    https://ic.pics.livejournal.com/jenab6/14257799/113778/113778_900.jpg

    SSE Shopping Bag
    So you can carry your other purchases comfortably.
    https://ic.pics.livejournal.com/jenab6/14257799/113514/113514_900.jpg

    (Note to Fraser: this is a spoof. I'm really not selling anything.)

  17. Talking about using moon rock to shield against cosmic radiation reminded me of the ship in Neal Stephenson's Anathem, which used rock shielding for much the same reason.

  18. … gravity wells… what are their escape velocities? Could we store junk there? Further question… are there "points" outside the elliptical plane of a similar nature?

  19. Somewhat-related question: Could an advanced solar shield potentially protect Earth from a GRB? I'm thinking about WR104

  20. Hi Fraser. Thanks for another great video. I thought I'd ask you something I'm curious about. Why is Charon not classified as a dwarf planet like Pluto? Why is it called a moon of Pluto if they orbit each other? Is it possible that it will be reclassified at some time? Do you think it should be? Thank you! 🙂

  21. Could you do a video on the capabilities of two Hubble 2.0 telescopes working together as a array in the L4 and L5, and maybe a third on in the L3. Wouldn’t that be like the telescope array used to image the black hole but with a relative diameter of over 200,000 kilometers?

  22. Another great video. Have you ever discussed how gravitational slingshot work. I mean, how do satellites use planets to speed up, doesn't the gravity of a planet slow things down by pulling them inward?

  23. L4, L5 seem more likely to be a future Detroit city as far as space manufacturing go, wouldn't want any planet killer size factory facility hanging above are head's here on earth. Maybe even a place fit out an astro for human habitation?

  24. L4 & L5 should be used for communication relays between Earth, other Planets and deep space. Not only can they act as a backup communication path, but they can also provide coverage to missions and outposts that happen to be in conjunction with the sun & blocking transmissions. A relay may also increase data transmission speed due to it being physically closer to the off world communication object because farther objects have weak signals and thus slow bitrates for reliable communication. (example Voyager spacecraft near Jupiter bitrate of 115,000bps but now it's 160bps due to it being so much farther) The stable Lagrange points could let us park and use a solar powered comm relay for a very long time due to not needing to expend propellant for station-keeping.

  25. As I sayd in the first vid of this series: Push the asteroids, that cross the earth orbit slowly towards one sun earth L4 or L5. Also build a faktory there for astoroid mining.

  26. Why dont we use L4 and L5 points to build there a planet. Earth 2 and Earth 3. They are in the perfect distance from the Sun

  27. 7:00 – Jeez all this speculation based on a 10 week workshop?
    We've learned a lot in the last 50 years. It's time for an update!

  28. Thanks Fraser. You say there have been no L4/L5 missions but my understanding is that they have each been scanned closely by OSIRIS REx and Hayabusa, with one earth Trojan detected only (so far).

  29. Why do we call the asteroids at lagrange points Trojans? I had sort of assumed they were named for the Trojan horse, but since that was a Greek ploy, it seems sort of weird that they have names like "Hector"

  30. Your explanation was great about Lagrange points.
    Could there be Galactic Lagrange points, where rogue Stars and planets could lurk around in the dark abyss, just like those trojan asteroids in L4&L5 points of Sun and Jupiter.

  31. I hope Elon Musk sends some lightly modified Starlink sats out to Earth's L4 and L5. Seems like some basic sats out there is really all we need to get some MAJOR science. Maybe even space minning, ISRU and station points.

  32. why put an interferometre at earth lagrange points, jeeze with all that work put it at jupiter lagrange points or even neptune ones the longer the better right?

  33. Future ideas for L4 and L5 point? I've got one! You mentioned there might be Martian material at the Sun-Mars L4 and L5 point. Could we fly a spacecraft there and scoop up some dust or perhaps even a small chunk of ancient mars to bring it home and not have to do a sample return mission directly from mars?

  34. Could use the Lagrange points L4 and L5 and maybe L3 to position satellites around the sun to monitor the sun's weather and thus give better and more advanced weather predictions for the earth. That is, a weather station/satellite positioned 60 degrees ahead of the Earth could predict solar events 2 months ahead of time before they are visible to the Earth.

  35. Hi Fraser, I tried to go to Universetoday.com/audio and received this error message: This XML file does not appear to have any style information associated with it. The document tree is shown below.

  36. Can you make a series of astronomy and orbital mechanics and rockets working videos like #crashcourseastronomy ??? 🤔🤔🤔

  37. could you use lagrange points to do gravity assist slingshots? some of the lagrange points are things that you have to use thrusters to keep in place and others are fixed points in space, could you use those fixed points that don't require station keeping as gravity assist?

  38. We gathered too much info about moon what we do about it? Nothing. Why not spend that money colonizing moon first because launching probs from moon is very very cheap

  39. No rail guns. Rail Guns are weapons. O'Neill proposed mass drivers to send bucket of stuff. With Good Engineering, it can arrive at the destination slowly and peaceful for capture.

  40. Uhh… To state the obvious; if there's an asteroid at a Trojan point then why not use that for as much of the mass as possible. I can't thank you enough for this info. We now have a new destination for a manned landing that doesn't really need a lander. Are you listening NASA? We could build a space colony more easily than O'Neil could have imagined! If he'd only known…

  41. I enjoyed that series a lot… I have heard the term before but never understood its true meaning, and now I know there are a couple of those Lagrange points! thanks for the videos :)))

  42. I'm wondering that !!!

    is there ever any space craft collided with any space stone or Asteroid or meteoroid (especially out of earth orbit) ????????

    becuz there were many space craft launched but i have never heard of collision

    like Voyager 1,2 . its probably floating in space around 40 years. how lucky it can be that not a single debris hit that craft

    EVEN IF THE ANSWER IS NO.

    But why IS IT SO!!!!!!

  43. Frasier, it's a somewhat easy concept for me to grasp orbiting around unstable LaGrange. How does this work with stable LaGrange points. If it's an automatic process being pulled into a well, how do you keep from hitting the other objects at, or coming in to the area?

  44. How do the sizes of these regions compare with one another? Are they all about the same size relative to astronomical objects?

  45. When the picture of the black hole was published I thought that it would have been better if we had had 3 of the ALMA telescopes in Earth-Moon L3, 4 and 5. Well, one could dream 🙂

  46. When gb00234 makes its closest approach to the sun, is there any chance that is could be a naked eye comet? Or even be visible with a telescope? I’ve seen people saying it might be quite large.

  47. Any O'Neal cylinders will have to be built from material mined in space. We should never launch that much of our earth into space,

  48. Looking towards Kardashev Type II megastructures are a bit demoralizing at our current tech level. I think humans should put away currently unreachable goals and non-sci fi fantasy tropes from years back like magical emitting artificial gravity fields and warp drives. True spaceships will not look like airplanes, submarines, naval ships, weird crescents, saucers, or other transient shuttles. They will be orbs. Orbs with radiation shielding, deflective curvature, and jack shaped skeleton trusses with suspended counter rotating compact pinion shafted O'neills inside them. A six configuration config is a gyro, a 14 config will fill up the diagonals. 14 centrifuges also means 7 trusses making the entire shell rigid. And each centrifuge should have a floor to pinion shaft height minimum of 25 meters. This is for anti-nausea. Plus you're gonna have comfort ceilings so you don't see any rotation. All in all we're talking a 150ish meter diameter spaceship. Bigger ships and you'll start seeing concentric multi-floored centrifuges. And the disparity of centripetal artificial gravity between the floors will be remedied by sliding topical surfaces.

  49. I love your videos and this series on the L points is really helpful!

    While watching a video by TMRO, I had an idea, and thought you might be able to make a video about it or include it in Q&A. I posted it there and I'll put the same post below.

    The topic is space debris, with the context being the recent Starlink incident of not maneuvering to avoid ESA's satellite. Post starts here:

    I have an idea for directing who needs to make corrective maneuvers in space: each satellite gets listed under a different classification (priority) depending on certain criteria. A cubesat or other immobile spacecraft would have right of way (they can't move). Then crewed spacecraft. Those certainly have to be first. Then we have the real classes (priorities): one-off, expensive satellites (like the science satellites from NASA, ESA, and other global space agencies) would pay to have a higher priority. That price could be determined by certain factors like how difficult it is to perform a maneuver (i.e. thrusters only meant for de-orbit). Few satellites on lower budgets would purchase lower priorities. Large constellations would get low priorities (or pay a higher premium). Ideally, in my humble opinion, large constellations like Starlink would make the majority of maneuvers themselves, regardless of which craft was there first. Especially for large, commercial constellations, purchasing a higher priority for each satellite wouldn't likely be worth it.

    Ok, but to purchase something requires a seller. These funds would have to go to an international organization (we know we will need one eventually) which will use the funds to help with cleaning up space debris.

    I know that the majority of debris is not from active satellites, but this is one way to address the active satellite part of the equation.

    What do you guys think? Did anyone actually read this post?

    One loophole I see is that non-mobile spacecraft have preferance, and therefore may be preferred by designers. Maybe all spacecraft above a certain mass would need to be able to do obstacle avoidance (with exception), or pay a higher fee. And of course, spacecraft should always have a way to deorbit, whether passive or active.

    P.S. What about spacecraft with the same registered priority? Here we could refer to the spacecraft in orbit longest and/or consider the unique circumstances and/or ask the companies to figure it out (large fine if they choose to not move but collide? And/or heavily restricted access to space for those companies) Ideally, the decision of who maneuvers would be autonomous and indisputable.

  50. dont get me wrong, i love astronomy but the size of this project wont happen in the next 1000 years, by that time earth will be gone (doomsday)

  51. What are the chances that the object that created the Chicxulub crater, was of extra Solar origins.
    They seem to be looking like they are quite common and travel relatively fast, so can do a lot of damage.?

  52. One of the first SF stories I read was Niven’s “Flatlander”. In it one of the characters remarks that a mistake was made in launching a spacecraft on a course that took it through one of the Earth’s Trojan points, the problem being that Trojan points are dust collectors and sending a spacecraft at speed though a concentrated dust field would not be good for it.

    I haven’t seen this issue mentioned in any recent discussion on spacecraft at L4 or L5. Was Niven exaggerating the danger?

  53. A stimulating three videos. But what about the Lagrange points of the other solar system planets? Wouldn't these be even MORE useful, particularly for astronomical purposes?

  54. If it is so easy fuel-wise to get to L4 or L5 then surely it is also easy to get back to Earth. And if there is a 220 km diameter asteroid at one of these points, what is to stop it too from ultimately coming our way? That is pretty frightening because a collision with such a beast would wipe out all life on Earth, boil the oceans, etc.

  55. No, I don't want to her about the giant multi trillion dollar space habitats that will; never happen! The US is over $22 Trillion in debt and will be much more at the end of this administration! Even the initial Gateway Foundation's concept of Von Braun is way too grandiose, and will cost trillions, let along the full size one!
    Instead of jumping to science fiction, how about we deal with science fact when it come to space habitats!instead of day dreaming of multi trillion dollar habitaes that will never happen?

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