[HN Gopher] Three hours to save Integral spacecraft
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Three hours to save Integral spacecraft
Author : jensgk
Score : 351 points
Date : 2021-10-19 09:08 UTC (13 hours ago)
(HTM) web link (www.esa.int)
(TXT) w3m dump (www.esa.int)
| sharmin123 wrote:
| How to Protect Your Privacy And Personal Data from Hackers?:
| https://www.hackerslist.co/how-to-protect-your-privacy-and-p...
| xioxox wrote:
| One of the interesting things about the telescope on Integral [1]
| is that it uses a coded aperture mask [2] to image the sky in
| high energy X-rays to gamma rays, rather than a focusing optic.
|
| [1] https://en.wikipedia.org/wiki/INTEGRAL [2]
| https://en.wikipedia.org/wiki/Coded_aperture
| moralestapia wrote:
| Wow, thank you for this! I had no idea such thing was possible,
| now I'm reading a lot on it.
| m4rtink wrote:
| AFAIK thats because we dont have any usable material for X-ray
| lenses, right ?
| ncmncm wrote:
| Used to be, they would loft a whole bunch of concentric
| cylinders, and rely on total internal reflection off their
| surfaces, which works even with X-rays.
|
| If I understand correctly what they do now, they treat the
| diffraction pattern from X-rays going through a mask as a
| sort of 2-D Fourier transform, and transform it to an image
| with the inverse transform based on the known mask. Which is
| very clever. I don't doubt that this description glosses over
| the actually interesting bits.
| KingOfCoders wrote:
| "Flash, I Love You! But We Only Have Fourteen Hours Left to Save
| the Earth!"
| fouc wrote:
| Did anyone notice the amazing cookie banner?
|
| 1. It offers a 'accept essential cookies' button 2. It doesn't
| take up as much space as many other cookie banners do.
| colejohnson66 wrote:
| Re #2: Are you on a desktop/laptop? It took up a third of my
| screen on my phone. That's not much better than others.
| xboxnolifes wrote:
| I like the accept essential cookie button, but it doesn't much
| smaller than most banners I come across.
| perihelions wrote:
| After checking uBlock's debug log, yes, I did notice it! It is
| ##.cc-cookies from the rulesets "Fanboy's Annoyance" and
| "AdGuard Annoyances".
|
| (To anyone unfamiliar: these "extra" rulesets ship with uBlock
| Origin, are disabled by default, and can be toggled in the
| "Filter lists" tab of Settings).
|
| https://github.com/gorhill/uBlock/wiki/Dashboard:-Filter-lis...
| jimmaswell wrote:
| I thought "essential" cookies didn't even need consent? Either
| way, cookie consent nonsense and the banners caused by it are a
| blight whose benefits ("solving" the absolute non-problem of
| advertisement tracking) pale in comparison to the enormous
| collective inconvenience and wasted developer hours they've
| caused us all. It's sad that we look at a banner that's not as
| bad as it can be and appreciate it, like someone saying their
| spouse only hit them three times today instead of ten.
| fouc wrote:
| Yeah, it's unfortunate that the bar is so low
| greenail wrote:
| These reaction wheels have such a high failure rate. Is it a
| fundamental Tribology problem? _edit_ I see they think it was a
| software issue but I still wonder about reaction wheel failure
| rates.
| opwieurposiu wrote:
| One failure mode is static electricity build up leading to arc
| discharge and pitting the bearing races. Also, the vacuum tends
| to make the bearing grease evaporate. Back in the 60's they
| used spermaceti, maybe we should go back to that?
|
| https://est-aegis.info/2018/08/in-space-no-one-can-hear-your...
| nitrogen wrote:
| I'd wager that modern synthetic oils could beat whale oil,
| but now I'm curious what the state of the art is.
| outworlder wrote:
| High failure rate? This particular spacecraft is 19 year old.
|
| There was a string of reaction wheel failures in the past that
| were tracked to a single supplier (forgot exactly what the
| issue was, but I think it was some contaminant).
|
| Regardless, it's a device that has to continuously spin at high
| speeds, in space. It's actually remarkable that they survive
| for as long as they do.
| xtiansimon wrote:
| > "Most of the Control Team were working from home at this point
| - I was following operations from the train!"
|
| The future is here!
| [deleted]
| thriftwy wrote:
| I wonder why did they call it so. Either they did not know of
| prior art[1], or knew it all too well and embraced it.
|
| 1. https://en.wikipedia.org/wiki/We_(novel)
| [deleted]
| bjackman wrote:
| Cool story! I wonder if the mission engineers do a lot of
| operational training for incidents like this: for example the
| SREs at Google do "tabletop" role-playing exercise to practice
| incident response. Would be cool to hear similarities/differences
| with ESA folks.
| marsokod wrote:
| There are many simulations like that when sadistic engineers
| (sorry, simulation engineers) will inject errors in the
| simulator and see how the operators react. Then the operators
| have to find a way out. This is also used to make sure that
| monitorings and procedures cover all the errors.
| milgrim wrote:
| I am surprised to read that Safe Mode did not automatically
| disable all non essential systems. That seems to be very risky
| behavior.
| perihelions wrote:
| This one regained spin control too late,
|
| https://en.wikipedia.org/wiki/Wide_Field_Infrared_Explorer#W...
| (1999)
| trenning wrote:
| Did the reaction wheel recover from this or is it dead? Article
| started by saying they used 3 so now only 2 are operational? Can
| they sustain the satellite with 2?
| moffkalast wrote:
| From what I gather it was just a radiation caused software
| glitch that momentarily shut it down.
|
| > Integral has since remained under control, and from 27
| September all systems are back online. Since 1 October, after
| an extended checkout, its instruments are back observing the
| high energy Universe.
|
| Seems like they're back in shape.
|
| As a comparison the Kepler telescope had 4 wheels, of which 2
| eventually completely failed and they managed to get it into a
| neutrally stable orientation that could be managed with just
| the two and some thruster assistance. Until RCS ran out that
| is. 3 are generally the minimum you'd need to orient yourself
| in 3 axis, as one might expect.
| ericpauley wrote:
| The article briefly mentions dumping energy at regular periods
| without using thrusters. Does anyone know what mechanism they're
| using to do this? At first glance I'd assume it would look like
| rotating/configuring the satellite so the solar wind imparts
| angular momentum.
| jakewins wrote:
| https://en.m.wikipedia.org/wiki/Control_moment_gyroscope
|
| Perhaps? The ISS uses these.
| [deleted]
| Gravityloss wrote:
| Excellent question and it turns out there's a whole article
| about the solution!
| https://www.esa.int/Enabling_Support/Operations/Rescuing_Int...
|
| > By using a specially designed sequence of manoeuvres, the
| control team realised they could redistribute the angular
| momentum stored onboard the satellite using two different
| reaction wheels spinning in opposing directions, causing the
| spacecraft to flip.
|
| > "So at this point we knew we could control the build up of
| energy absorbed from the Sun, and christened this new manoeuvre
| the z-flip".
| techdragon wrote:
| There's actually several small to medium effects on any
| spacecraft in orbit around earth. There will be tiny
| perturbations from the interaction of earths electromagnetic
| field as it moves through it slowly, there's atmospheric drag
| on solar panels and the spacecraft body that can create
| "aerodynamic" torques related to what the normal orientation is
| relative to the earth. There's even smaller perturbation from
| the solar wind... some spacecraft have a thing (or can fudge
| one using some part of the electrical subsystems) called a
| "magneto-torquer" which is basically a solenoid/electromagnet
| designed to tug on the earth's magnetic field so they can trade
| electrical power for physical force.
|
| It's a pretty cool thing that seems to be happening more and
| more frequently with spacecraft flight dynamics teams
| developing such a detailed model of all these forces that they
| can invent new "stable modes" like the one they used in this
| article, or the Kepler missions K2 mode where they found
| another useful mode instead of just ending the mission. It's
| not as dramatic as something like a solar sailing mission, but
| I think it's a pretty awesome technical achievement, like
| watching a trained stuntman drive a car on two wheels through a
| slalom course, like a form of highly skilled, kinetic, robot
| based gymnastics.
| baybal2 wrote:
| https://en.wikipedia.org/wiki/Tennis_racket_theorem
|
| Just turn it 180 every few days this way, so the torque from
| external influences is cancelled out.
| finnh wrote:
| The NASA video on that page is mesmerizing.
| frayesto wrote:
| I think what they are referring to is "angular momentum dumps".
| The reaction wheels have a fixed maximum amount of angular
| momentum. This is a function of the speed of the wheels
| themselves since the mass/moment of inertia is fixed.
|
| Over time external forces continue to add momentum to the
| system (from drag/solar radiation pressure). In order to
| maintain a desired pointing direction this means the wheels
| must increase in velocity to "absorb" this momentum.
|
| Eventually you need to "dump" the momentum using another
| external force, such as thrusters, or in this case the same
| solar radiation pressure.
|
| Goal is to orient spacecraft such that external forces can be
| used to spin down the various reaction wheels, thereby
| "dumping" momentum out of the wheels.
|
| This is pretty common on all spacecraft, but gets
| complicated/innovative when you have to do it in an emergency
| or if you don't have a full set of reaction wheels.
| jcims wrote:
| Just adding it because I think it's a cool use of the word.
| When reaction wheels are operating at maximum speed and can
| no longer exchange momentum with the spacecraft in both
| directions, they are considered 'saturated'.
| taneq wrote:
| 'Saturated' is used in control systems engineering for any
| value (sensor input, drive output etc.) that has reached
| maximum or minimum value and can't be further
| increased/decreased. It's the same sense of the word as
| used in the HSV colour space in computer graphics.
| amundsentb wrote:
| "using its highly sensitive reaction wheels"
| mcherm wrote:
| Yes, the article uses those words. But an understanding of
| elementary physics tells us that momentum is conserved in an
| isolated system. Spending the reaction wheels can cause the
| outer frame of the satellite to rotate in a certain fashion
| but it cannot possibly alter the overall momentum or angular
| momentum of the entire satellite unless it somehow interacts
| with an external force.
| snovv_crash wrote:
| I guess the motors are lossy and some of it gets converted
| to heat if they speed the wheels up and down
| WJW wrote:
| That won't solve the conservation of momentum problems
| though, it'll just use more energy to get to the same
| state. If you could demonstrate controlling the rotation
| of a spacecraft just by using more inefficient motors you
| would upend a large portion of modern physics and could
| probably go and collect your Nobel prize within the week.
| snovv_crash wrote:
| Ok, read TFA now. It sounds like they need to dump energy
| from the reaction wheels. Maybe they can do this by
| inducing a spin, rotating 180 on a different axis then
| cancelling the spin?
| FeepingCreature wrote:
| You can't cheat conservation of momentum, no matter how
| cleverly you move your spacecraft. That's why all the
| solutions involve expelling reaction mass. (Or, in the
| case of solar wind, interacting with an external force.)
| [deleted]
| misnome wrote:
| Right, the reaction wheels help if you want to maintain
| orientation of the satellite under external forces that
| want to (gently!) rotate it. And eventually your reaction
| wheel saturates and you can't get more useful rotation out
| of it.
|
| This is where thrusters are useful, because you can use the
| thrusters to give you a "source of force" while you spin
| the reaction wheels back down. I believe this is where the
| original parent's question is coming from - if you have no
| thrusters, how do you avoid saturation?
|
| Presumably, they've worked out a way to accurately predict
| the external forces and gently operate against them while
| spinning the wheels down in a way that doesn't make the
| satellite spin faster.
| [deleted]
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(page generated 2021-10-19 23:01 UTC)