[HN Gopher] ESA satellites to test razor-sharp formation flying
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ESA satellites to test razor-sharp formation flying
Author : rbanffy
Score : 132 points
Date : 2024-04-11 10:05 UTC (12 hours ago)
(HTM) web link (spectrum.ieee.org)
(TXT) w3m dump (spectrum.ieee.org)
| throw0101c wrote:
| Another application of satellites in formation is measure gravity
| fields:
|
| > _That brings us to GRACE--a backronym for gravity recovery and
| climate experiment--a pair of satellites that orbited the Earth
| at a fixed distance from each other. Or they would be fixed if
| the Earth's gravity didn't change in time and space. GRACE used a
| radar system to measure the distance between the two satellites
| to track those changes, providing information about the
| gravitational field it was traveling through._
|
| * https://arstechnica.com/science/2019/07/satellites-play-chas...
|
| * https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO
| _factor wrote:
| A space interferometer as well. Unfortunately, the planned SIM
| mission was shelved.
|
| https://en.wikipedia.org/wiki/Space_Interferometry_Mission?w...
| perihelions wrote:
| There's also
|
| https://en.wikipedia.org/wiki/LISA_Pathfinder ( _" LISA
| Pathfinder"_)
|
| I wonder how precisely they can control the relative
| separation of those interferometer spacecraft? (They
| advertise they can _measure_ the separation to <0.01
| nanometers--but that's not quite the same thing).
| dotnet00 wrote:
| I think with those the idea is to make the arms so long
| that the precision of the relative separation matters less,
| especially since LISA is trying to listen for much longer
| wavelengths than LIGO. On top of that, they likely just
| need to get the unpredictable component of the relative
| acceleration to vary (unpredictable component of the
| relative jerk?) slower than the time taken for a
| gravitational wave to pass through.
|
| Probably more a matter of precisely measuring the
| gravitational fields and accounting for those than of
| controlling their relative position extremely precisely
| (besides of course the precision needed to target the
| lasers across such a large distance).
| 27theo wrote:
| TIL backronym.
| verisimi wrote:
| https://en.wikipedia.org/wiki/Backronym
|
| > A backronym is an acronym formed from an already existing
| word by expanding its letters into the words of a phrase.
| Backronyms may be invented with either serious or humorous
| intent, or they may be a type of false etymology or folk
| etymology. The word is a portmanteau of back and acronym.[1]
|
| > A normal acronym is a word derived from the initial letters
| of the words of a phrase,[2] such as radar from "radio
| detection and ranging".[3] By contrast, a backronym is "an
| acronym deliberately formed from a phrase whose initial
| letters spell out a particular word or words, either to
| create a memorable name or as a fanciful explanation of a
| word's origin."[1] Many fictional espionage organizations are
| backronyms, such as SPECTRE (special executive for
| counterintelligence, terrorism, revenge and extortion) from
| the James Bond franchise.
|
| > For example, the Amber Alert missing-child program was
| named after Amber Hagerman, a nine-year-old girl who was
| abducted and murdered in 1996.[4] Officials later publicized
| the backronym "America's Missing: Broadcast Emergency
| Response".[5]
| dylan604 wrote:
| US Congress is a fan of its use, even if they might not know
| there's a word for it
| sandworm101 wrote:
| "Strategic Homeland Enforcement and Logistics Division."
|
| "And what does that mean to you?"
|
| "It means someone really wanted our initials to spell out
| "S.H.I.E.L.D."
| HankB99 wrote:
| I graduated from Purdue University Calumet Campus in
| northwest Indiana (PUCC.) At one point they considered
| renaming as the South Hammond Institute of Technology.
|
| Ba-dump-tish.
| sandworm101 wrote:
| Lookup the World Taekwondo Federation, recently shortened
| to World Taekwondo. I pity the poor soul who had to explain
| the need to elders of the sport, many of which did not
| speak english.
| jdiez17 wrote:
| Very cool! We're actually doing something quite similar (although
| on a much smaller scale) at the TU Berlin:
| https://www.tu.berlin/en/about/profile/press-releases-news/n...
|
| Just recently, we completed a series of correction burns to match
| the semi-major axis of the orbit of both satellites to stop them
| drifting away from each other. In a few weeks/months we'll bring
| them back together and send a software update that will allow
| them to autonomously maintain formation flight.
|
| Also, we will be doing live satellite operations at the Lange
| Nacht der Wissenschaften (22. June 2024) :)
| consumer451 wrote:
| Is this your first work in orbit?
|
| Does it feel as cool as one would imagine?
| jdiez17 wrote:
| It is and it does feel about as awesome as you can imagine.
| In our case we also had a tough integration and testing
| campaign where we were changing software and running into
| hardware issues, etc. so I was personally quite tense until
| we got first contact :) and since then, the satellites are
| surprising us every day with how well they work! (although we
| still have lots of things we want to improve)
| consumer451 wrote:
| Congratulations and major respect!
| mlyle wrote:
| I'm mentoring a group of high school students who were just
| selected by the CubeSat Launch Initiative to put a smallsat
| up.
|
| It's not quite my first rodeo with this stuff, but it's still
| incredible to be a part of and see.
|
| [It's incredible to be a part of, but it's also just a whole
| lot of attention to detail, paperwork, and paranoia]
|
| People don't tend to let HS students do much, so it's pretty
| stirring when they get an email that said approximately "We
| appreciate your... dedication to furthering humanity's
| presence in space and knowledge of the cosmos."
| consumer451 wrote:
| That is so cool! My biggest wide impact was creating the UI
| for first, or second, airline touchscreen check-in system
| ever deployed. The feeling of ownership/creation that I had
| knowing that my code was all around the West Coast was
| awesome.
|
| I can only imagine how cool it must feel to be part of a
| project that has escaped the Earth's atmosphere, and zips
| by at orbital speeds. I would think that those high school
| kids will benefit from this project a lot. A truly mind-
| expanding experience.
| rrr_oh_man wrote:
| Wait, what? They'll create artificial solar eclipses?
| zith wrote:
| They'll use one spacecraft to block the sun shining on the
| other spacecraft,yes.
| rcxdude wrote:
| Only for each other: it's more like holding up a plate to cover
| the sun, not making an eclipse for a large portion of the
| earth.
| mackman wrote:
| Damn, this would have been a great way to combat global
| warming. We just need much bigger plates.
| bee_rider wrote:
| The idea of a solar shade to manage the amount of sunlight
| we get has been around for a while.
|
| https://en.m.wikipedia.org/wiki/Space_sunshade
| frederikvs wrote:
| I work at the company building these satellites, I've seen them
| sitting in our clean room.
|
| If there's any questions, I might be able to give some answers.
| However, I'm not involved with Proba-3 directly, so no
| guarantees.
| _hl_ wrote:
| I understand that part of the objective is to demonstrate
| precise autonomous navigation and choreography, but for the
| "main" scientific objective re. observing the solar corona, why
| not just stick a big stick with a disk on the observing
| satellite?
| frederikvs wrote:
| That's what's been done so far [0], both on the ground and in
| space. As I understand it, the further your disk is from your
| telescope, the better. But your stick needs to be rigid
| enough to keep the disk exactly in its place. And a rigid
| stick has weight.
|
| For Proba-3 the goal is to have the two satellites more than
| 100m apart. If you want to do that with a stick, your stick
| has to be longer than the ISS. That should tell you a thing
| or two about the complexity and cost of building and
| launching that stick.
|
| I do have to admit I'm not exactly sure what the advantages
| are of having the disk further away from the telescope. I
| suspect it's to do with the interaction between the light and
| the edge of the disk, but I'm not sure.
|
| [0] https://en.wikipedia.org/wiki/Coronagraph
| _hl_ wrote:
| Huh, very interesting- and counterintuitive that distance
| matters. If anyone here knows why I'd love to learn more!!
|
| EDIT: maybe not so counterintuitive after all: if you scale
| everything up, you get a higher fidelity sensor and more
| signal to noise. Same reason telescopes want to be big: to
| collect more light especially from dim signals. Distance of
| the occulter then reduces perspective distortion that would
| eclipse the inner parts of the sensor more than the outer
| ones. Just my speculation though.
| dr_orpheus wrote:
| The even more extreme version of this JPL has been working
| on with their Starshade program. Not specifically a
| cornograph, but same concept of blocking light from a star
| to look for something more dim, in this case its looking
| for exoplanets. But it is a much larger scale. A 25 m
| deployable shade in formation 100 km away with the same
| level of mm precision.
|
| https://www.jpl.nasa.gov/news/starshade-would-take-
| formation...
|
| Edit: Just to be clear on status of this, Starshade is
| still in early technology demonstration phase that they can
| actually build the shade and do the formation maintenance.
| This is not in full build or slated to launch any time
| soon.
| jsemrau wrote:
| Why did you use cold gas thrusters?
| frederikvs wrote:
| I'm not familiar enough with the project to answer why
| specifically cold gas thrusters were chosen. What I can say :
| if old, proven technology will get the job done, there's a
| strong preference to use that.
|
| When needed to achieve the mission, new technology will be
| developed - sometimes the whole point of a mission is
| specifically to develop new technology. In this case, one of
| the major goals of the mission is to develop formation flying
| technology. Learn what the pitfalls and the tricky bits are,
| and make the technology available for future missions.
|
| But when the mission can be achieved with old technology -
| technology with a long record of being used in space, where
| the problems are known and understood, where we know what
| works and what causes problems - then the mission will use
| old technology.
|
| If you use newer technology, there's always a risk that
| you'll hit a new issue, previously unknown. Maybe you can
| work around it, maybe you can't. But this isn't web
| development where you can refactor, switch to a new framework
| and continuous deploy your way out of it. For the hardware,
| you get one launch and that's it. Why run the risk if you can
| avoid it? It'd be a shame if the mission can't achieve its
| primary objective (learning about formation flying) because
| it chose some new type of thruster, and encountered some new
| issue with it.
| nuccy wrote:
| Cold gas thrusters are as reliable (because of simplicity -
| basically just container of pressurised gas and a valve
| [1]) and as precise in their thrust pulses execution as it
| can get. Better precision in thrust execution probably only
| ion engines have but just because of extremely low thrust
| levels in general (milli-newtons).
|
| 1. https://en.m.wikipedia.org/wiki/Cold_gas_thruster
| dr_orpheus wrote:
| They need the milli-newton level of thrust control and so
| need tiny thrusters. Generally the simplicity of the cold gas
| thrusters in a small package is easy. Yes it is not as
| efficient, but moving up in efficiency and complexity to
| catalyzed monopropellant (generally hydrazine) thrusters the
| thrust ranges are usually > 1N. Same story with any bi-prop
| thrusters. Certainly electric propulsion has the levels of
| thrust needed, but then you would need a lot of power for it.
| And since they are not doing large delta V maneuvers there is
| less concern about the actual amount of propellant that you
| need to take with you.
| jsemrau wrote:
| Interesting that they still use cold gas thrusters. Electric
| propulsion (FEEP) is much more efficient for this kind of
| maneuver.
| ooterness wrote:
| Everything has tradeoffs, and everything depends on use case.
|
| The FEEP thrusters I've seen had a hefty power penalty to keep
| it on standby, and a long warmup time. Cold gas uses more
| propellant mass per unit impulse, but it can still come out
| ahead in total size/weight/power.
| jsemrau wrote:
| Is the power penalty really such a big issue anymore? The
| Enpulsion Nano for example uses 10-15 Watt only on hot
| standby.
| frederikvs wrote:
| From the article, Proba-3 has 10 thrusters, so that would
| bring the total to 150 Watt.
|
| I don't know the power budget for the satellite, but we can
| make an educated guess : the occulter is 1.4 meter
| diameter, or a surface area of 1.54 square meter. That's an
| upper bound for the surface area of the solar panels -
| there's nothing sticking out beyond the disk, that would
| interfere with observations.
|
| Solar power at earth is about 1.3kW/sqm, solar panels are
| maybe 20% to 30% efficient. That puts you in the ballpark
| of 400 to 600W.
|
| 150W on standby would be a pretty big bite out of your
| power budget.
| dr_orpheus wrote:
| Yep, definitely power is an issue and a trade-off even with
| low levels of power. The other item is cost. Cold gas
| thrusters are super cheap and reliable. So the savings in
| amount of propellant in going to an electric propulsion
| system is not going to be worth it in the overall program.
| This is also because the total amount of maneuvering they are
| doing (in terms of deltaV) is probably not very large. Lots
| of little maneuvers. This is compared to something where you
| have large delta V for big maneuvers or continuously
| overcoming drag in low LEO orbits where the amount of
| propellant will become a huge design driver.
| frederikvs wrote:
| From what I can see on wikipedia [0] the first FEEP to be used
| in space was in 2018. Proba-3's implementation phase started in
| 2014 [1]. The choice of thruster technology was probably made
| well before that. They wouldn't use a technology that hasn't
| flown yet, unless it was crucial for the mission.
|
| [0] https://en.wikipedia.org/wiki/Field-
| emission_electric_propul... [1]
| https://www.esa.int/Enabling_Support/Space_Engineering_Techn...
| jsemrau wrote:
| That explains a lot actually
| brutusborn wrote:
| Does anyone else read "formation flying" and instantly think
| "Kessler syndrome"
| psunavy03 wrote:
| No because it's exactly the opposite. Kessler syndrome results
| from satellites smashing into each other with high relative
| velocities. The entire point of formation flying is zeroing out
| relative velocity. That's how you stay in formation with
| something.
| brutusborn wrote:
| I was imagining them flying close-by, so any failure would
| have a higher chance of causing a cascade. I couldn't find
| any info on how close they are, but I imagine it's too far
| for this to be an issue.
| frederikvs wrote:
| The goal is to have them a bit more than 100m apart. During
| observations they aim to maintain millimeter precision.
|
| I'm pretty sure the risk of collision has been analysed to
| death. I would expect they've analysed what would happen if
| one or both devices suddenly stop listening to commands,
| and that even then there's essentially no risk.
| dotnet00 wrote:
| The article says they're going to be 144 meters apart. A
| collision of things that are in basically the exact same
| orbit is also not going to be much of a risk, as the
| collision would be at a low relative velocity. Collisions
| between satellites are a kessler syndrome risk because due
| to differing orbits, the collision velocities can be in
| km/s, which can spread debris into a wide range of orbits,
| thus causing the heightened risk of cascading failures.
| jauntywundrkind wrote:
| Speaking of razor-sharp formation flying satellites, reminder
| Interferometer Space Antenna (LISA) got the go ahead this year.
| Incredibly ambitious & cool attempt to build a much much much
| bigger space based version of the already 4km long Laser
| Interferometer Gravitational-Wave Observatory (LIGO). Requires
| absurdly stupensously precise formation of three satellites.
|
| https://www.esa.int/Science_Exploration/Space_Science/Captur...
| panick21_ wrote:
| Yes. Super cool project. The free flying cores that get
| manipulated with magnets are crazy. Will allow gravitational
| wave observation in a totally different domain.
| visviva wrote:
| The combination of mm-level precision and a highly elliptical
| orbit with a very high apogee (60+ kkm) is really impressive.
| bgnn wrote:
| Maybe I'm dumb, but couldn't they just use an umbrella instead of
| a separate sattelite?
| frederikvs wrote:
| Many observations of the sun's corona just use a disk attached
| to the telescope, as you're suggesting [0]. However, for
| Proba-3 they want the disk to be over 100m away from the
| telescope, which isn't practical. Also, one of the goals of
| Proba-3 is to develop formation flying technology, because it
| will be useful for many other missions in the future.
|
| [0] https://en.wikipedia.org/wiki/Coronagraph
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