[HN Gopher] NASA Successfully Acquires GPS Signals on Moon
___________________________________________________________________
NASA Successfully Acquires GPS Signals on Moon
Author : sohkamyung
Score : 263 points
Date : 2025-03-05 11:29 UTC (11 hours ago)
(HTM) web link (www.nasa.gov)
(TXT) w3m dump (www.nasa.gov)
| tecleandor wrote:
| Oooooh. I guess that although the signal will be fainter, as
| they're ~21x further away than usual (240k miles vs 20k), they'll
| have the advantage of having less noise and practically no signal
| bouncing.
|
| What I don't know is: Even when receiving a good signal... how
| difficult would be calculating location when satellites are going
| to be all concentrated in a really small portion of the sky, and
| all of them in a proportionally small distance between them,
| compared to the distance of the receptor?
| TimorousBestie wrote:
| Geometric dilution of precision (GDOP, or just DOP) is used to
| evaluate the quality of a GPS satellite configuration; on the
| back of an envelope any moon-based solution is going to be
| quite a bit worse relative to terrestrial ones.
| gcanyon wrote:
| At any location on the moon that has a clear view of the Earth,
| you'll have access to >= half the GPS satellites -- so 15-16+.
| On Earth that number is as low as 4. The logic would be
| different (having to pick the farthest apart to get the
| clearest data to work with) but I can't imagine that it would
| be problematic for determining location.
| LVB wrote:
| I suspect the usable number is much lower and would be just
| those satellites mostly opposite the Earth but with some
| signal reaching the moon? I recall the beam width of GPS
| antennas being like 30 deg (?), so almost all of the signal
| is directed at Earth.
| BenjiWiebe wrote:
| Most receivers on earth aren't only using the GPS
| constellation. There's also Galileo, BeiDou, and GLONASS.
|
| Just pointing out that the typical "GPS" accuracy we're used
| to seeing isn't happening with only 4 satellites in view.
| nickcw wrote:
| The geometry will reduce the accuracy of the fix though as all
| the satellites will be in the same 8 degrees of the sky.
|
| I wish they had said in the article what the accuracy is!
| silverquiet wrote:
| Is 8 degrees the angular size of the Earth from the moon?
| Aren't GPS satellites in relatively high orbit, so it could
| potentially be a larger patch of sky.
| wanderingstan wrote:
| I hadn't realized it, but you are right.
|
| - Orbit height: 20,200 km
|
| - Earths diameter: 12,760 km
|
| https://www.gps.gov/systems/gps/space/
|
| https://science.nasa.gov/earth/facts/
| volemo wrote:
| It's the satellites' size.
|
| The satellites are 20 Mm high above the ground so their
| spread is 53 Mm, which is 4.4 times the diameter of the
| Earth (12 Mm). So yes, the angular size of the satellite
| cloud (7.896deg) is quite a bit larger than the Earth
| (1.785deg) from the moon PoV.
| mnw21cam wrote:
| Although since the GNSS satellites use directional
| antennae pointing at Earth, this experiment only picked
| up signals where the satellites are on the other side of
| Earth and close enough to its edge for some of that
| directional signal to leak past the edge of Earth and get
| to the Moon. So, the satellites that are nearly 4deg away
| from the centre of Earth cannot be detected because they
| are beaming their signal nowhere near the Moon, and the
| detectable angular size is much less than 7.896deg.
| bilsbie wrote:
| I suppose you also know where the moon is, how it's rotated and
| possibly your altitude on the moon.
|
| So you could treat that as a virtual satellite in the other
| direction.
| bobmcnamara wrote:
| How do you know those?
| maweki wrote:
| besides altitude: you'd just need to know the time which
| the GPS signals give you. From there it's just calculating
| rotations.
| sohkamyung wrote:
| While the headline says GPS, the article says signals were
| acquired from GPS and Galileo, which increases the number of GNSS
| satellites available to get a location fix.
| 7952 wrote:
| More details at https://www.gpsworld.com/lugre-receiver-captures-
| gnss-signal...
|
| "Despite the challenges of distance and velocity, the receiver
| achieved position accuracy within 1.5 km and velocity accuracy
| within 2 m/s. It successfully acquired signals from four GPS
| satellites (L1 and L5 frequencies) and one Galileo satellite
| (E1-E5 bands) during a one-hour observation window. Post-
| landing,"
| madaxe_again wrote:
| At that resolution the utility is somewhat questionable - I
| suppose the next inevitable step is LPS, and having a fleet of
| selenostationary satellites performing the same function
| locally.
| thatcherc wrote:
| A challenge there is that there are very few stable lunar
| orbits! High orbits are perturbed by Earth's gravity (3-body
| problem) and low lunar orbits are perturbed by the lumpy
| distribution of mass in the Moon's interior [0]. Lunar GNSS
| satellites with a little bit of onboard propulsion could
| probably correct for some of these perturbations but once
| they ran out of fuel they would have a limited orbital
| lifetime.
|
| [0] - https://en.wikipedia.org/wiki/Lunar_orbit#Perturbation_
| effec...
| adgjlsfhk1 wrote:
| could the legrange points work? dealing with the 3 body
| orbits would be a pain, but they would give you nice
| separation
| mkl wrote:
| You need signals from 3+ different locations to navigate,
| and the two stable Lagrange points, L4 and L5, are as far
| from the moon as Earth is:
| https://en.wikipedia.org/wiki/Lagrange_point.
| mlyle wrote:
| But-- GPS already produces an okayish fix. Improving it
| with another signal from somewhere else would make a big
| difference.
|
| > and the two stable Lagrange points, L4 and L5
|
| We have plenty of spacecraft hanging out around L1, etc.
| It's possible to orbit it without too much issue. Having
| one broadcast a navigation signal synchronized with GPS
| would not be too bad.
|
| > are as far from the moon as Earth is
|
| The issue isn't that they're far away-- it's that they're
| all in pretty much the same direction. There's very small
| uncertainties in orbits and measured path length, but if
| they're all in the same direction you get very poor
| lateral position.
|
| This is the same effect you can get if you can only see a
| little tiny bit of the sky with GPS. You might have
| enough satellites to navigate, but since they're all
| close to the same direction the navigation solution is
| much worse.
| ekianjo wrote:
| Is the 3 body problem mostly meaningful above a certain
| mass? If you had small satellites could you deal with it?
| xnorswap wrote:
| The mass of a satellite is already trivial compared to
| the mass of the moon.
| itishappy wrote:
| The restricted three-body problem deals with the case
| when the third mass is trivial and the orbits are
| circular. The new solutions in this case are the Lagrange
| points. That's helpful, but doesn't make finding dynamic
| solutions much easier on it's own.
| 0_____0 wrote:
| Oh wow, good reading in that link.
|
| I had no idea the moon was that lumpy. The wiki entry says
| that despite the mascons there are 4 known stable orbital
| inclinations?
| shagie wrote:
| That is correct. The NASA page link (now 404) has a bit
| more on the orbits and their history.
|
| https://web.archive.org/web/20210307002503/https://scienc
| e.n...
|
| And they're _very_ lumpy.
|
| > The mascons' gravitational anomaly is so great--half a
| percent--that it actually would be measurable to
| astronauts on the lunar surface. "If you were standing at
| the edge of one of the maria, a plumb bob would hang
| about a third of a degree off vertical, pointing toward
| the mascon," Konopliv says. Moreover, an astronaut in
| full spacesuit and life-support gear whose lunar weight
| was exactly 50 pounds at the edge of the mascon would
| weigh 50 pounds and 4 ounces when standing in the
| mascon's center.
| mmooss wrote:
| That is a great link. Do you know if any of it is
| outdated now?
| shagie wrote:
| It is still all completely correct. There may be some new
| findings, but the lunar prospector (
| https://en.wikipedia.org/wiki/Lunar_Prospector ) did all
| the work and this was written after that.
| BWStearns wrote:
| I wonder if lunar space elevators might be the fix here. If
| I understand correctly, such an elevator would not be as
| subject to the perturbations since the tension would keep
| it's orbit stable (is it still an orbit if it's tethered?).
|
| Another option might be a LORAN style system put up on
| towers. With lower gravity and no atmosphere I imagine we
| could stick transmitters up very high without super complex
| construction, maybe even just a giant carbon fiber tube
| with a transmitter at the top.
| kridsdale1 wrote:
| Let's put a high power laser on the end to send
| advertisements in Morse code to anyone looking towards
| the moon.
| datadrivenangel wrote:
| Raster-scan it to deliver persistence of vision ads!
| staplung wrote:
| Technically, satellite positioning only needs 1 satellite.
| GPS requires several but one of its forerunners was
| Transit[1] which I believe only needed a signal from a
| single satellite at a time. It worked by measuring the
| doppler shift of the signal coming from the satellite. Of
| course that only works if the orbit can eventually cover
| all (or much of) the surface and for all I know there is no
| such frozen orbit for the moon. Also, it would still
| presumably require extensive surface-based tracking and
| correction.
|
| [1] https://en.wikipedia.org/wiki/Transit_(satellite)
| mhb wrote:
| Wouldn't the next step be plopping some down on the moon?
| mannykannot wrote:
| I was wondering that too, and that led to the question
| whether, without an atmosphere, all radio communications at
| any wavelength would be strictly line-of-sight. It turns
| out, however, that the moon has something of an ionosphere,
| though I don't know whether it would support over-the-
| horizon radio (or, for that matter, whether it tends to
| interfere with the accuracy of GPS, as it does on Earth.)
|
| https://phys.org/news/2011-11-mystery-lunar-ionosphere.html
| t43562 wrote:
| Lunar Pathfinder.
|
| https://www.sstl.co.uk/what-we-do/lunar-mission-services
|
| QUOTE: A constellation of interconnected lunar orbiters will
| enable surface missions operating on the far side of the
| Moon, without direct to Earth line of sight, to keep constant
| contact with Earth. It will also provide lunar navigation
| signals to support critical mission phases such as precision
| landing of scientific equipment and the operation of rovers.
| In addition to communication services, the Lunar Pathfinder
| spacecraft has been selected by ESA and NASA to host a number
| of experimental payloads: An ESA GNSS
| receiver capable of detecting weak signals coming from the
| Earth GNSS infrastructure (GPS and Galileo), demonstrating
| its potential role into Lunar navigation A NASA
| retro-reflector to demonstrate laser ranging capabilities
| An ESA radiation monitor to study orbital radiation
| conditions Acting both as technology and service
| demonstrator, Lunar Pathfinder is the opportunity for
| scientific and commercial mission developers to support the
| development, test and standardisation of Lunar communication
| infrastructure, and for emerging off-planet telcos to acquire
| experience of lunar asset operations and off-planet service
| delivery. Lunar Pathfinder is due to operate in an
| Elliptical Lunar Frozen Orbit (ELFO) for an operational
| lifetime of 8 years. The spacecraft can operate 2
| simultaneous channels of communication with lunar assets: 1
| in S-band and 1 in UHF. Performance, such as coverage and
| data-rate, depend both on the relative position of the user
| asset to Pathfinder at the moment of the connection, as well
| as the capabilities of the communication module onboard the
| user asset. Once safely retrieved onboard Lunar Pathfinder,
| communications are relayed back to Earth ground stations in
| X-band.
| hammock wrote:
| 1.5km is not bad. Chris Columbus could resolve latitude to
| about 100-200km, and longitude only by dead reckoning.
|
| I do wonder though with computers and cameras and celestial
| navigation, why that is not used vs GPS on the moon
| patmorgan23 wrote:
| Are there any existing systems for that? Would you be able
| to resolve to a similar level of accuracy with computer
| vision looking at the stars?
|
| Ussally enhancing an existing technology that is widely
| deployed and understood to fit a new situation is better
| than inventing something wholly new (though not always)
| hammock wrote:
| What are GPS sats if not artificial stars used for
| celestial nav? (In a roundabout way, no pun intended)
| zokier wrote:
| GPS navigation is based on measuring the distance between
| observer and the satellites to triangulate position.
| Celestial navigation does not care about distance to
| stars at all, in many ways stars are considered to be
| infinitely far away.
| infinet wrote:
| https://en.wikipedia.org/wiki/Celestial_navigation
|
| > _Sextants can be read accurately to within 0.1
| arcminutes, so the observer 's position can be determined
| within (theoretically) 0.1 nautical miles (185.2 meters,
| or about 203 yards). Most ocean navigators, measuring
| from a moving platform under fair conditions, can achieve
| a practical accuracy of approximately 1.5 nautical miles
| (2.8 km)_
|
| Some napkin math, assuming using a Sextant to achieve
| similar accuracy of 0.1 arcminutes on the Moon, because
| Moon is about 3.7 times smaller than Earth, that 0.1
| arcminutes is around 50 meters on the Moon. One can
| expect extremely clear sky and certainly not riding waves
| on the Moon, so the practical accuracy should be close.
| teraflop wrote:
| Star trackers do exist and have been used on spacecraft
| for decades. But unfortunately, looking at the stars can
| only tell you your orientation in space, not your
| position. (At least, not to any remotely useful accuracy;
| you need to travel a huge distance to get a measurable
| parallax.)
|
| Celestial navigation works on the Earth's surface (or the
| Moon's surface), because being able to determine the
| orientation of the local horizon (or zenith) is
| equivalent to determining your latitude and longitude.
| But that doesn't work for a spacecraft that doesn't have
| a horizon reference.
|
| Of course, if you're orbiting the moon and you can
| accurately observe the directions to landmarks such as
| mountains and craters, you can fix your position relative
| to them. But that's not really what you'd call "celestial
| navigation".
| mlyle wrote:
| I'm curious what the assumptions are. Looking forward to
| reading the paper.
|
| a kilometer-or-so is about what you get on Earth without a
| lot of sophisticated corrections, averaging, and kinematics.
| So, if they're not doing all that stuff, they could be doing
| quite well. (on the other hand, one of the bigger correction
| terms-- the ionospheric delay -- they don't have to deal
| with-- but they have to deal with all of their measurements
| being in "one direction"). If e.g. they don't know about the
| moon's relative motion, that's a big disadvantage.
|
| If, on the other hand, they get the kilometer after a
| -loooot- of averaging, that's quite bad.
|
| I don't know how big of a fleet you need to make this
| worthwhile, though. Just one satellite in a different
| direction would collapse that big error ellipse to a much
| shorter arc.
| mmooss wrote:
| > I suppose the next inevitable step is LPS
|
| That has been planned for awhile as part of Artemis.
| throw0101d wrote:
| > 2 m/s
|
| 7.2 kph; 4.5 mph.
| jiehong wrote:
| > 7.2kph
|
| You mean 7.2 km/h.
|
| Thanks for the conversion, though!
| queuebert wrote:
| 7.2 km h^-1 if you want to be fully SI correct
| card_zero wrote:
| Why don't the ISO like writing km/h?
| jakeinspace wrote:
| Because if there are multiple inverted units, you'd need
| to add parentheses to put them all in the denominator.
| Tidily giving each a ^-1 is clearer (especially with
| superscript exponents).
| gattr wrote:
| You can use superscript Unicode characters on HN: km*h-1.
| jakeinspace wrote:
| Ah but you see, I am on my phone and very lazy.
| Evidlo wrote:
| What's wrong with a/b/c
| card_zero wrote:
| I guess they stick rigidly to things that are formally
| defined, in case somebody thinks that division is right-
| associative and it leads to the Challenger shuttle
| exploding again.
| ant6n wrote:
| > 7.2 km h^-1 if you want to be fully SI correct
|
| You mean 2 m/s.
| tempodox wrote:
| No, 2 m s-1.
| hunter2_ wrote:
| While kph is uncommon and ought not to have come about, the
| first sentence here [0] acknowledges it, so I don't think
| it's fair to say that people who use it don't mean what
| they say.
|
| [0] https://en.wikipedia.org/wiki/Kilometres_per_hour
| jiehong wrote:
| Thank you, I didn't realise kph is actually only used in
| English.
|
| In Europe, kph is non existent, and I felt that it's
| bizarre to convert like that.
| querbu wrote:
| More details: + 44dBm GPS transmit power
| -210dB path loss + 15dB rx antenna gain
|
| -151dBm received signal strength
|
| That's slightly worse (5dB) than signal strength of a handheld
| device/ phone (~15dB typical handheld loss, urban environment).
| There is still ~15dB margin. They are cheating a little with
| the 15dB narrow antenna gain, which requires accurate pointing.
| Nice result and there is room for improvement. Note: -210dB =
| 10^-21
| slow_typist wrote:
| That number doesn't tell much without knowing the background
| noise on the L-bands out there. It would also be interesting
| to know whether they achieved this with commercial Gnss
| receivers.
| querbu wrote:
| Since the high gain antenna is pointed at the entire earth,
| the noise temperature is similar earth temperature. Semi-
| custom gnss receiver, they collect mostly correlator
| outputs, and 2.5 seconds of raw IQ
| zokier wrote:
| > It would also be interesting to know whether they
| achieved this with commercial Gnss receivers
|
| They used Qascom QN400 receiver.
| H8crilA wrote:
| Are those reference numbers for L1 signals, or for L5
| signals? I remember that L5 uses much longer chip sequences,
| and thus can deliver much higher processing gains.
| querbu wrote:
| L5 can achieve 10-15 dB in ideal circumstances, with tuned
| loops. Not more. And those aren't ideal circumstances - the
| GPS signals are received mostly when satellites are grazing
| the earth (from the moon POV).
| JumpCrisscross wrote:
| > _They are cheating a little with the 15dB narrow antenna
| gain, which requires accurate pointing_
|
| Stars. Finding Earth is a necessarily solved problem for E-L
| communication.
| kridsdale1 wrote:
| Only for 2 weeks per month!
| JumpCrisscross wrote:
| > _Only for 2 weeks per month_
|
| Why?
| datadrivenangel wrote:
| Lunar night is 2 weeks, so you get earth visible 50% of
| the time from any point on the lunar surface... and earth
| will be the biggest thing in the sky
| querbu wrote:
| Er.... No. Earth is either visible 100% or 0% of the
| time, the Moon is tidally locked
| shagie wrote:
| The Moon is locked in rotation with its revolution. A
| location on the Moon that has the Earth above the horizon
| will _always_ have the Earth above the horizon.
|
| Lunar night means that the Sun has set - but the Earth
| remains in the sky in the same position.
| blebo wrote:
| Don't forget your phone on the Artemis mission so you can catch
| some sweet rare Pokemon!
| bayindirh wrote:
| I used to get excited for these kinds of news, and from a science
| perspective, this is very cool.
|
| On the other hand, as we get closer to colonize other planets, or
| at least try to plan for this end, I get depressed more and more.
|
| We're enough burden for a single planet, and definitely too much
| for a solar system.
|
| Honestly, no, I don't want more humans around.
| volemo wrote:
| I understand the premise that the humanity is a burden for the
| Earth (though I disagree -- we only make the conditions worse
| for ourselves, "The planet is fine; the people are fucked!"),
| but how could we possibly be a burden to a barren wasteland
| like Mars?
| palata wrote:
| > although I don't agree: we only make the conditions worse
| for ourselves, "The planet is fine; the people are fucked
|
| Except that we are measurably living in a mass extinction.
| Most species are dying, except for us (at the moment). So I
| disagree: we make the conditions worse for all species.
|
| The climate change that we are measuring now is happening a
| lot faster than the one that got the dinosaurs (and most big
| animals) extinct. 96% of animals on Earth are cattle, living
| in the conditions we know. I am not sure we can say "we don't
| have any impact on other species".
| volemo wrote:
| Sure we cause a mass extinction, I'm not saying "we don't
| have any impact on other species". My point still stands,
| the nature doesn't care, this isn't the first extinction
| and I bet won't be the last.
|
| However, you didn't address my main question: how can we be
| a burden to a red wasteland?
| bayindirh wrote:
| The nature doesn't care _yet_ , but it showed that it
| _might_ , and it will if we don't stop abusing the
| ecosystem.
|
| Ah, at worst, all humanity will go extinct. Which doesn't
| matter much at the grand scale. It'll be exciting for the
| next ones, if the planet is left in a state to allow
| another such evolution, or somebody else likes the colors
| and wants to visit for a couple of revolutions around the
| Sol.
|
| > how can we be a burden to a red wasteland?
|
| We are not sure that it's a red wasteland. We think that
| life has a single foundation and will evolve from that
| one.
|
| Maybe it had a similar ecosystem before, and tons of
| bacteria are in hiatus. Maybe there's something else
| underground. Maybe there are other living organisms which
| we can't detect.
|
| I don't think that Mars has worms which might eat us for
| snacks and giggles, but I'm not sure that it's devoid of
| life completely, either.
|
| Absence of evidence is not evidence of absence.
| palata wrote:
| > Ah, at worst, all humanity will go extinct.
|
| To be honest, I don't care so much about humanity going
| extinct in 500 years. But somehow I care about me or my
| children dying at an early age because we as a species
| don't manage to not screw up our lives.
| JumpCrisscross wrote:
| > _I care about me or my children dying at an early age
| because we as a species don 't manage to not screw up our
| lives_
|
| The only near-term total human extinction risks are
| cosmological. We don't have the ability to wipe ourselves
| out with even nukes, just wipe out modern civilisation.
| (And that would require someone going out of their way to
| nuke _e.g._ Oceania and South America.)
| palata wrote:
| Think about that: the dinosaurs did not die because of
| the impact of the asteroid, but because of the climate
| change that followed.
|
| Fun fact: that climate change was a lot slower than the
| one we are measuring now. _A lot._
| JumpCrisscross wrote:
| > _dinosaurs did not die because of the impact of the
| asteroid, but because of the climate change that
| followed_
|
| Dinosaurs couldn't construct shelter with A/C, harvest
| power from the sun and the earth's core or move around
| the planet in a day [1]. And even then, it took at least
| tens of thousands of years [2].
|
| It's about as unscientific to claim anthropogenic climate
| change is going to cause human extinction within even
| 10,000 years as it is to claim it doesn't exist.
|
| [1] _source needed_
|
| [2] https://www.reuters.com/article/lifestyle/science/ast
| eroid-m...
| palata wrote:
| > Dinosaurs couldn't construct shelter with A/C, harvest
| power from the sun and the earth's core or move around
| the planet in a day [1]
|
| Simple question: do you know what we humans eat? Can you
| grow that in your bunker _at scale_?
|
| And even if you could: if your project is to make the
| Earth look like mars and call it a success because _some
| humans survive_ when most species are extinct, then I don
| 't know what to say.
|
| > It's about as unscientific to claim anthropogenic
| climate change is going to cause human extinction within
| even 10,000 years as it is to claim it doesn't exist.
|
| This is called manipulation. I didn't say that. What I
| said is that _for what we know and measure_ , climate
| change _is likely_ to cause a global collapse, maybe
| human extinction.
|
| Claiming that climate change doesn't exist is just wrong.
| JumpCrisscross wrote:
| > _do you know what we humans eat? Can you grow that in
| your bunker?_
|
| Soil, artificial UV and nitrogen extraction from air are
| solved problems. And you would not need a bunker, just
| A/C (or filtration if we're going nuclear).
|
| > _because some humans survive when most species are
| extinct_
|
| If you're talking about climate change, it's some humans
| and some species are extinct. (Most cuddly wild mammals
| and birds we like.)
|
| > _for what we know and measure, climate change is likely
| to cause a global collapse, maybe human extinction_
|
| Right. This is false catastrophism. There isn't a "maybe"
| human extinction within known parameters. There isn't
| even an end to industrial civilisation without nukes.
|
| People say this crap and undermine the entire climate
| movement because when the lie in extinction risk is shown
| it brings into legitimate question the other claims.
| palata wrote:
| > There isn't a "maybe" human extinction within known
| parameters. There isn't even an end to industrial
| civilisation without nukes
|
| What the hell? Let's completely put climate change and
| mass extinction (which are huge problems on their own)
| aside for a moment.
|
| Do you know what threatens the collapse of the industrial
| civilisation? The end of fossil fuels. That's a very real
| problem right here right now. Without the climate change
| and mass extinction problems, that would still be a
| reason for our industrial civilisation to collapse
| _soon_.
|
| Luckily, the solution to all of those 3 problems is the
| same: cut down emissions, do less with less. A good
| introduction to the problem, I find, is here:
| https://www.amazon.com/World-Without-End-Illustrated-
| Climate...
| JumpCrisscross wrote:
| > _Do you know what threatens the collapse of the
| industrial civilisation? The end of fossil fuels_
|
| ...we have other power sources.
|
| No science supports your assertions. The single source
| you've put forward, _World Without End_ , doesn't support
| your assertions.
|
| We aren't going extinct because of climate change. We
| aren't losing industrial civilisation because of climate
| change or running out of fossil fuels.
|
| There are good reasons to act on climate change without
| lying. And by lying, you undermine the legitimate science
| around the damage and costs.
| palata wrote:
| > The single source you've put forward, World Without
| End, doesn't support your assertions.
|
| Clearly you haven't read it, have you?
| palata wrote:
| > how can we be a burden to a red wasteland?
|
| I couldn't care less about mars, to be honest. My problem
| is that some use it as (an absurd) justification to
| commoditise space. SpaceX is hurting the climate by
| making it cheap to send lots of rockets.
| volemo wrote:
| Ehm, do you claim space exploration cases a meaningful
| impact on the global climate in a world built on burning
| fossil fuel, refining iron ore, making almost everything
| out of mostly non recycled plastic, and eating cows and
| chickens? ._.
| palata wrote:
| Subsidising (with a whole lot of money) technologies that
| make the situation worse instead of subsidising changes
| that would make society more resilient most definitely
| has an impact.
|
| You want to say "oh, actually, we've seen that 99% of our
| emissions was due to our production of trackpads, so the
| solution is to stop using trackpads and all is well"? Let
| me tell you that the problem is _a lot harder_ than that.
| We need to work on everything everywhere.
| jeffhuys wrote:
| > we make the conditions worse for all species
|
| That's your deduction. We should correlate the "dying" to
| other times in the last millions/billions of years where
| the temperature rose tis "quickly".
|
| I really feel humans think they change way more than they
| do.
| palata wrote:
| > That's your deduction
|
| It's not.
|
| > I really feel humans think they change way more than
| they do.
|
| In 2025 this is either extremely uninformed or super
| dumb. Start reading, maybe.
| jeffhuys wrote:
| I wish we could discuss this in a more professional
| manner. I might be informed by sources that contradict
| the sources you read. That doesn't mean I'm wrong, or
| you're wrong, but it would be nice to just discuss this
| as humans.
|
| I do understand that this is a sensitive subject to some,
| so I apologize for any distress I seem to have caused.
| palata wrote:
| > That doesn't mean I'm wrong, or you're wrong
|
| There are things where the scientific consensus is so big
| that even if you "disagree" with it (whatever that
| means), you have to assume that you are wrong until you
| prove you aren't.
|
| Maybe gravity doesn't exist, maybe we live in the Matrix.
| But for all intents and purposes, gravity does exist. If
| you disagree, you're wrong unless you come with evidence
| that shakes the scientific consensus. I mean evidence,
| not a mere belief that maybe gravity doesn't exist
| because you've read it somewhere.
|
| If you don't believe that we humans are the cause of the
| biodiversity loss and climate change, today, you're
| wrong. And if you can't recognise that... well join a
| Flat Earther convention and have fun there, I don't have
| time for this here.
| subjectsigma wrote:
| Ah, the classic "Anyone smart thinks exactly like I do,
| so you must be dumb."
|
| I read his comment as an admission that nature is
| currently too wonderful and complicated for us to
| understand or control, not an assertion that global
| warming isn't real or whatever you think he said.
|
| Humans created global warming and mass extinctions and it
| seems like the best way to stop it is to get more smart
| and dedicated humans, which aren't rare but are uncommon.
| You better start hoping we pop out more people
| palata wrote:
| > Ah, the classic "Anyone smart thinks exactly like I do,
| so you must be dumb."
|
| Not at all, but that's the thing: it's very difficult to
| have a discussion with people who reason like you.
| Because you can believe something does not make it right.
| Saying "my sources are different" is just a way to
| justify your beliefs. "Well, I believe in some people,
| you believe in others, that makes us equal". That's how
| people like Trump get elected. He keeps saying everything
| and its contrary, and people just _believe_ in him. Where
| all the facts suggest that he is a dangerous (yet
| charismatic) moron.
|
| The scientific way to approach it is this: "There is a
| large consensus about X. I don't know much about X, so I
| could believe Y and Z. I want to get informed, so I need
| to read and understand X (not Y and Z, not yet). Once I
| do understand X, I can start to question it by reading
| about Y and Z". You'll find that usually, after you have
| some reasonable understanding of this large consensus, Y
| and Z usually are at least less consistent, usually
| vague, generally believed by people who don't have much
| knowledge about X.
|
| I am not saying that you need to have 3 postdocs in X to
| give an opinion. But you have to make the difference
| between scientific consensus and beliefs. And if you want
| to change the scientific consensus, you have to be pretty
| damn well informed, you can't just repeat Y and Z because
| you read it on some social network.
|
| Now I get your next answer: I'm just a nobody on the
| Internet, why would you believe me instead of Trump? But
| again, I don't need you to trust me. I need you to do
| your due diligence and read about the scientific
| consensus before you feel entitled to say "my opinion is
| worth just as much as yours". And now you say: "and why
| do you think you're right?". I studied environmental
| chemistry, and I can tell you that the consensus is
| goddamn consistent, whereas the climate denier claims are
| systematically uninformed.
| itishappy wrote:
| > Humans created global warming and mass extinctions and
| it seems like the best way to stop it is to get more
| smart and dedicated humans, which aren't rare but are
| uncommon. You better start hoping we pop out more people
|
| If humans created global warming, a very likely scenario
| is that more humans just means more warming. I'd argue
| that's a saner default assumption.
|
| Mass extinctions are not a human creation. They're
| natural events, like the plague.
| JumpCrisscross wrote:
| > _If humans created global warming, a very likely
| scenario is that more humans just means more warming_
|
| You're ignoring the energy intensity of GDP and lifestyle
| intensity per capita, _each_ of which varying within
| historic ranges flips your outcome across zero. Add to
| that the largest emitters facing _declining_ populations
| before immigration and I'm not sure what your point is.
| itishappy wrote:
| My point is that we have some evidence that humans don't
| always improve things, so "humans will improve things" is
| a dangerous assumption without further evidence. Nothing
| more, we're but one element of a chaotic system.
| itishappy wrote:
| > We should correlate the "dying" to other times in the
| last millions/billions of years where the temperature
| rose tis "quickly".
|
| We certainly would if we found evidence of any similar
| events in the past. Do you have contradictory info?
|
| > As the Earth moved out of ice ages over the past
| million years, the global temperature rose a total of 4
| to 7 degrees Celsius over about 5,000 years. In the past
| century alone, the temperature has climbed 0.7 degrees
| Celsius, roughly ten times faster than the average rate
| of ice-age-recovery warming.
|
| > Models predict that Earth will warm between 2 and 6
| degrees Celsius in the next century. When global warming
| has happened at various times in the past two million
| years, it has taken the planet about 5,000 years to warm
| 5 degrees. The predicted rate of warming for the next
| century is at least 20 times faster. This rate of change
| is extremely unusual.
|
| https://earthobservatory.nasa.gov/features/GlobalWarming/
| pag...
|
| > The findings also reveal that the Earth's current
| global temperature of 59 degrees Fahrenheit is cooler
| than Earth has been over much of the Phanerozoic. But
| greenhouse gas emissions from human-caused climate change
| are currently warming the planet at a much faster rate
| than even the fastest warming events of the Phanerozoic,
| the researchers say. That speed of warming puts species
| and ecosystems around the world at risk and is causing a
| rapid rise in sea level. Some other episodes of rapid
| climate change during the Phanerozoic have sparked mass
| extinctions.
|
| https://news.arizona.edu/news/study-over-nearly-half-
| billion...
|
| https://www.science.org/doi/10.1126/science.adk3705
| JumpCrisscross wrote:
| > _We should correlate the "dying" to other times in the
| last millions/billions of years where the temperature
| rose tis "quickly"_
|
| They're doing a bad job of arguing a good point. Let me
| try.
|
| We are objectively in a mass-extinction event [1].The
| sixth or seventh in our planet's billion-plus year
| history of life. Its most-intense phase lines up with
| industrialisation [2].
|
| That said, we obviously don't make life worse for _all_
| species. Cattle, cats, dogs, pigeons, rodents, roaches,
| influenza _et cetera_ are doing quite well with humans.
|
| [1] https://en.m.wikipedia.org/wiki/Holocene_extinction
|
| [2] https://en.m.wikipedia.org/wiki/Great_Acceleration
| palata wrote:
| I guess cattle is doing quite well if your metrics is the
| number of individuals. But you're right that we don't
| make life worse for _all_ species. Just _almost all_ of
| them.
| JumpCrisscross wrote:
| > _guess cattle is doing quite well if your metrics is
| the number of individuals_
|
| I live in ranch country. Cattle do fine. They're wild
| animals that live much like the bison, on the same land
| as the bison, except they get food and medicine and don't
| have to worry about predators tearing them apart alive.
| In exchange, we kill them relatively young (though not
| _that_ young risk adjusted), and that varies from place
| to place. (Dairies are more industrialised.)
| palata wrote:
| Sure, it's not bad everywhere.
| palata wrote:
| I also used to get excited, and this is very cool science.
|
| But same here: we have enough problems trying to survive on
| Earth, we should focus our great talents on that.
|
| > as we get closer to colonize other planets
|
| We won't colonise mars, and we definitely won't go further than
| the solar system. Just look at the distances, it's completely
| absurd.
| preciousoo wrote:
| "We" wont, until some generation figures it out
| lovelearning wrote:
| I genuinely feel getting off this planet is also one of the
| solutions to some problems just like getting away from one's
| country or kingdom has always been a solution.
|
| Why do you feel we can't colonize Mars? Or perhaps any of the
| asteroids? Perhaps not in this century but do you feel it'll
| never happen?
| palata wrote:
| > Why do you feel we can't colonize Mars?
|
| Depends on what you call "colonising". We may be able to
| send a few humans there, just for the sake of doing
| something super costly and completely useless. We as a
| species won't independently survive there.
|
| We, as a species, are on the verge of collapsing on Earth,
| which has all the conditions needed for life. We literally
| are failing to survive on Earth. Why the hell would we put
| resources into sending a few people to mars?
|
| > Perhaps not in this century but do you feel it'll never
| happen?
|
| The way we are going now, long before next century we will
| be in a place where a large portion of Earth (around the
| equator) is unlivable. As in, without life support we won't
| be able to survive outside. It's cute to think about
| colonising other planets, but at some point we should have
| priorities.
| krisoft wrote:
| > We, as a species, are on the verge of collapsing on
| Earth,
|
| Humanity is not on the verge of collapsing on Earth. Not
| even close. There is billions of us and our number is
| going up. Even with the worts climate change predictions
| the threat is not that we will all die, but that some of
| the places where we live now becomes uninhabitable and
| that our descendants will have a worse time living in the
| future.
|
| > We literally are failing to survive on Earth.
|
| That's literally not true.
| t43562 wrote:
| If we cannot achieve Mars colonisation now then in a
| "worse time" we won't be doing it either.
| palata wrote:
| > There is billions of us and our number is going up.
|
| You don't understand the meaning of "collapse", do you?
| t43562 wrote:
| We don't even know if we can live healthily in mars
| gravity. That's how clueless we are.
|
| The main reason, however, is that humans can't co-operate
| on a scale that would be needed to do it. World events show
| it clearly right now.
|
| This is not the age of colonial exploration where a small
| band of Europeans use their weapons to overpower the
| natives and grab their resources and take their fertile
| land. This is deciding to live in the middle of a frozen
| desert where there is nothing.
| jeffhuys wrote:
| We WILL colonise Mars. You might think it's absurd, I don't.
| As we both have no real arguments besides "just look at it",
| we're both just as correct.
| palata wrote:
| Well you're a climate denier (as you showed in another
| comment), I don't have anything more to tell you.
|
| BTW, "because I don't know means that I'm not wrong" is
| dumb, and dangerous.
| jeffhuys wrote:
| Climate denier is a bit harsh - I tend to ask questions
| people don't want answered, and then get thrown into that
| camp, true.
|
| Let me be clear: the climate IS changing, I just doubt
| that it's mostly caused, or potentially solved by, human
| behavior.
|
| It's a great way to sell some solar panels, though.
|
| EDIT: also, let me be clear (because I know how your
| brain works): I love that we're getting cleaner air. I
| love that we find alternative sources of energy. That's
| all amazing! But I predict there's never a "finish line".
| We'll never do good enough, and our kids will always die.
| Or our kids' kids. I'm not affected by that thought
| anymore.
| palata wrote:
| > I just doubt that it's mostly caused [...] by human
| behavior.
|
| Yep, climate denier. You put your belief before the
| scientific consensus. You may as well believe that the
| Earth is flat, it would not be less valid than your
| current position. Except that your kids won't die because
| of the Flat Earthers, probably.
|
| > It's a great way to sell some solar panels, though.
|
| Sure, many people try to sell their shit pretending it is
| "green". Tesla comes to mind (or Tesla before it became
| the nazi brand, I don't know nowadays).
|
| > We'll never do good enough, and our kids will always
| die.
|
| Well your kids will probably live in wars, global
| instability and die because of the climate change. Sure,
| they would eventually die anyway. Keep what you are
| saying now in mind, for when you'll have the discussion
| with your kids in a couple decades. Remember to tell them
| "we're living in a shit world, uh? Back in the days, I
| was one of those people who proudly didn't care. Enjoy
| now."
| weberer wrote:
| This post was written by a rogue AI
| trebligdivad wrote:
| I like this because it's such a neat unexpected idea to try.
| AnonHP wrote:
| It is not clear from the article, and these are noob questions:
| does it mean there were no other time dilation effects to take
| into account? In other words, is the adjustment done within the
| satellite clocks enough for the signal processing near or on the
| moon to get the position since the moon is so far off)?
| mandevil wrote:
| GPS has always had to account for relativistic time dilation,
| it's the first human scale issue where relativistic correction
| became necessary. (This would be general relativity,
| incidentally, not special: it's the effect of the Earth's
| gravity on the atomic clocks in orbit.) But that's because the
| whole system needs absurd levels of accuracy to be useful at
| all: at 8 km/s of orbital velocity every source of error
| creates enormous error bars on the ground.
|
| I also know that NASA has experimented for years with
| satellites (even all the way up in GSO) using GPS signals for
| position-finding, so this is further out but not unprecedented
| work.
| Qem wrote:
| So GPS a misnomer now, given not only "global" anymore. Perhaps
| better change it to CPS, Cislunar Positioning System.
| jiehong wrote:
| I like it!
|
| How about SPS: Satellite Positioning System
| ooterness wrote:
| Absolutely not. The GPS and Galileo spacecraft are all pointed
| at Earth. This demo is a special receiver that can piece
| together glimpses when that signal happens to slip past the
| edge of the Earth and reach the moon.
| queuebert wrote:
| Maybe someday it can be part of a Galactic Positioning System.
| JoeAltmaier wrote:
| So when do we put up GPS satellites around Mars? It makes sense.
| Or just put them on the moons I guess. They're pretty far from
| the surface - 9K and 14K compared to GPS of 12K so maybe not bad.
| And less atmosphere in the way. Also less radio noise?
| mandevil wrote:
| The issues would be A) that Mars upper atmosphere and internal
| mass distribution are not as well mapped as on Earth, so
| knowing your orbital accuracy is much more difficult (1)- and
| at 8km/s small orbital error bars become giant error bars on
| the surface and B) Putting a full constellation of 24-30
| satellites around Mars is going to be really expensive. That's
| more than the sum total of all satellites to successfully orbit
| Mars to this day (18).
|
| 1: On Earth we account for that by using ground stations to
| track the satellite locations, with the ground station
| locations determined very very precisely using non-GPS
| techniques (old school surveying techniques). On Mars, that's
| not going to be possible until we get a lot more done, probably
| a later human mission would be the first time that could be
| done.
| bluGill wrote:
| We don't need all of mars though. One GPS receiver on your
| lander will give you enough information for the area you can
| feasibly reach - and if not just old school survey some
| location to park another receiver to map things out.
| JoeAltmaier wrote:
| All good points. The solutions for Mars will necessarily be
| unique to that environment. Still, a combination of ground
| stations and satellites will be inevitably used for location-
| finding.
|
| And, the atmosphere? What atmosphere? It's negligible
| compared to Earth. Got to be down the list of important
| variables.
|
| We can send a mission to Mars and arrive within a few meters
| of desired orbit, but it's going to be hard to figure out
| where a satellite is? My doubt-meter is hitting the pin.
| mandevil wrote:
| Atmospheric drag on satellites- especially how it changes
| with solar output levels- is a hard thing to model
| accurately, and a major contributor to orbital uncertainty
| here on Earth. The Martian atmosphere is two orders of
| magnitude thinner, but it is far less than two orders of
| magnitude understood. And the level of our understanding
| matters for our ability to correct for it's perturbations.
|
| NASA is very good at sending spacecraft through regular
| space and hitting precise windows (MCO units issues aside),
| it's in orbit that things get more complicated, because now
| there are just a lot more potential interactions to deal
| with. We can use LOS on planetary occultations to give you
| some data, but it's still a lot of work to get from there
| to mascon maps, upper atmospheric data, etc.
| staplung wrote:
| > So when do we put up GPS satellites around Mars?
|
| A system like GPS? Probably never. It would be fantastically
| expensive and solve a problem that no one has. In any case, the
| moons would be a poor choice for signal transmitters: 1.
| landers are harder than satellites 2. two moons is not enough
| for a system like GPS 3. three-body problems mean that we can't
| really know the future configurations of the system with high
| precision on anything but the very short scale.
|
| In any case, it costs something like $700 million per year to
| operate the GPS system here on Earth.
| 7952 wrote:
| Navigation just seems comparatively easier than earth. You
| are much more likely to have a clear view of the terrain or
| sky. And the terrain is much less likely to change than the
| earth so computer vision should be easier.
| JoeAltmaier wrote:
| Already several orbiters around Mars now. To include a GPS
| radio in each would have been negligible further cost.
|
| And even three orbiters would give you a better fix than
| none.
|
| I think the naysayers are reaching, to argue against GPS
| transmitters around Mars. It seems inevitable.
| JumpCrisscross wrote:
| > _when do we put up GPS satellites around Mars? It makes
| sense_
|
| Once we have tens of Starships of annual transport between
| Earth and Mars such that putting about a dozen satellites in
| Mars orbits every decade or so [1] is cost effective.
|
| Using Elon math that's the 2030s. Ignoring his mortality-driven
| forecasts, probably the 2050s.
|
| They competition would be balloons, which can be made from
| indigenous polyethylene [2], floated above a settlement with a
| loud radio. You'd have range and direction home, which should
| be good enough for decades, potentially into the 2100s when, on
| a _very_ optimistic schedule, inter-settlement transfer begins
| to become common.
|
| [1] https://en.m.wikipedia.org/wiki/GPS_satellite_blocks
|
| [2] https://ntrs.nasa.gov/citations/20050157853
| schobi wrote:
| They tried on the moon, but there does not seem to be an
| assumption that this is limited to the moon? So one could obtain
| a position anywhere in earth's orbit, up to heights of 380.000km?
| 1.5km accuracy is impressive then.
|
| Apart from the attenuation from distance, I would expect that the
| navigation sallellites point their antennas mostly downwards to
| earth, but you might find some that radiate outwards. I don't
| think you can expect to receive from half the satellites though.
| rossjudson wrote:
| This is awesome. It means we will know where we aren't when we're
| on the moon.
| rossjudson wrote:
| ...then is immediately ordered to sell them to a private equity
| firm, payable in $TRUMP.
| codewritinfool wrote:
| I'm surprised that any useful accuracy can be obtained. Maybe an
| additional input to the solution would be to watch when various
| GPS satellites are occulted by the Earth.
| jlarocco wrote:
| I'm curious what coordinate system they're using and how the math
| worked a little more.
|
| I guess technically they could use latitude and longitude
| projected all the way out to the moon, but that would be pretty
| hard to use.
| lnauta wrote:
| Super cool! This only works on the side facing the GNSS
| constellation, right? There is no signal to use on the other
| side.
| 7e wrote:
| Use 1 km towers spaced every 100 km on the Moon's surface
| instead. No satellites needed.
| ant6n wrote:
| That'd be like 4000 towers
| mmooss wrote:
| If the comparison was 4000 towers on Earth compared with 32
| satellites in high orbits, and if we assume the same cost as
| standard radio towers (?), then I'd wonder which cost more -
| especially over a lifetime which includes servicing, etc.
|
| For the moon, it depends on many factors that differ from
| Earth. The radio towers' structures probably need less
| material, at least.
| andrewmcwatters wrote:
| Breaking: NASA discovers using Lunar GPS that taking a slingshot
| detour around the moon is still faster than commuting directly
| through I-10 during rush hour.
| qwertox wrote:
| Would this be used for location services or rather timestamping?
|
| Would it be possible to use celestial navigation to obtain a more
| precise location?
| JumpCrisscross wrote:
| Does this make the ESA's Pathfinder [1] redundant? Or are they
| measuring something materially different?
|
| [1]
| https://www.esa.int/ESA_Multimedia/Images/2023/06/Satnav_fro...
| mmooss wrote:
| My prior understanding was that the Artemis project included
| creating PNT (position, navigation, timing) in cislunar space,
| and that Earth's GNSS satellites wouldn't be sufficient. Is that
| plan now changed?
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