Circular Shock Acoustic Waves in Ionosphere Triggered by Launch of Formosat‐5 | Hacker News Reader

Circular Shock Acoustic Waves in Ionosphere Triggered by Launch of Formosat‐5

agupubs.onlinelibrary.wiley.com

313 pointszdw83 comments

I'm taking the liberty of reworking their "plain language summary." I aimed for maintaining accuracy with relaxed precision, but please correct me if I've lost too much of either in the process.

I corrected a specific bit of imprecision in language in the source's plaintext summary not clearly distinguishing between vertical/y v. vertical/z, something the technical abstract clarified by stating "vertical altitude."

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In plainest language, the rocket was lobbed up, not hurled forward, and this resulted in a shock wave that was followed some interesting reactions in the ionosphere between the rocket exhaust plume and the plasma in the ionosphere, all of which need further study because of potential risks to things like how accurate your GPS might be in the area around the "hole" caused by these reactions.

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Plain(er) Language Summary

On 24 August 2017, a SpaceX Falcon 9 rocket took off from Vandenberg Air Force Base in California, carrying Taiwan's FORMOSAT‐5 Earth observation satellite into orbit. The lightly weighted solo payload lets the rocket fly a path higher than the bare minimum to insert the payload directly where it needs to operate (the mission altitude), at 720 km. This unique nearly vertical path away from the ground is different from the usual satellite launches where rockets fly over horizontal paths more closely to the ground and insert satellites at 200 km above Earth and rely on orbit maneuvers to reach mission altitudes. Because of this lofty (more vertical) launch path, the rocket launch generated a gigantic circular shock wave in the ionosphere covering a wide area four times greater than California. It is followed by an ionospheric hole (plasma depletions) due to rapid chemical reactions of rocket exhaust plumes and ionospheric plasma. Large spatial gradients caused by these reactions and the resulting hole could lead to ~1 m range errors into GPS navigation and positioning system. Understanding how the rocket launches affect our upper atmosphere and space environment is important as these human-caused space weather events are expected to increase at an enormous rate in the near future.

hmm, I put your "plainest" language answer into XKCD simple writer, and there was some complexity in there.

In most simple language, the space truck was thrown up, not tossed forward, and this caused a sound wave that was followed with some interesting events in one of the high bits of the sky, between the space truck refuse air and the hotter-than-air stuff in the high sky, all of which need further study because of possible bad things like how true your sky-computer computer-map might be in the area around the "hole" caused by these waves.

I'm actually really impressed by this, not bad

Now it is perfectly clear to me, thank you! :-)

We sure need to study the ability to affect the ionosphere. And then people will build weapons capable of doing it in suitable ways. Unless they already have those.

You mean, like HAARP? Not saying it is a weapon. But it certainly has the pedigree to perceived that way, from a program & pop-culture standpoint:

https://www.popsci.com/military-aviation-space/article/2008-...

* Note: University of Alaska fairbanks appears to have taken over HAARP and converted it to a "Fee based" research center -- much like a radiotelescope at other academic institutions I assume?

Looks like HAARP is rather limited in comparison, I don't think it can affect the ionosphere so drastically. But yeah the same kind of device, just less potent.

Is '~1 m' meters or miles?

This is science!, therefore, metric system. Also GPS navigation errors of 1 mile would have been something you would have noticed.

m is standard for meters

mi is standard for miles

Good ask.

"Ask" is bad enough as a synonym for "request." I really hope we can avoid "ask" also becoming accepted as a synonym for "question."

Why? Decreasing language complexity sounds like a good idea. It's not like "question" or "request" are going away, it's just adding a simple context-specific word that is already used in similar situations.

Where have you ever seen 'm' used for miles? Wherever that is, go there and scribble it out! Also tell off the person who wrote it.

mph is the only acronym I've seen it used without mi.

It's used that way on highway signs in England, where it's very confusing.

’orrifying.

I'm not sure it's very confusing. Context suggests that you're not going to be told how many metres you are away from London.

Now, can this launch profile tell us anything about the mission?

Not anything that we didn't already know from its (publicly-available) destination orbit.

~1m range errors in the pseudorange from just the satellites which are on the other side of this hole, is a relatively small error, and certainly within or close to normal ionosphere and troposphere fluctuation impact on GNSS performance.

This would not be noticeable at all on a standard GNSS like the one in your phone.

Survey receivers use (at least) two frequencies which allows a simple calculation to determine pretty much exactly the delay due to the ionosphere, so they aren't affected by this at all.

This is an interesting anomaly, but GNSS is built to cope with this under normal usage, so it's inconsequential as far as I can tell.

If anyone has time and wants to see for yourself, 'CORS' - continuously operating reference stations, are available all over the place around where this happened, and the raw receiver data is freely available. You can download it and because you know the exact position of each receiver, you will be able to see the exact impact of this event at which ever location you would like to analyze.

Various open source tools are out there to process the data such as gLab and RTKLIB.

If anyone has the time to give it a crack and needs a hand or guidance feel free to ping me here.

Even plainer language:

Rocket exhaust can have impact with atmosphere, we need to study it more on short and long term effects.

This is ELI5 territory, which is cool because we probably need one of these as well.

I call it EOD explanation.

EOD?

I'm assuming "End Of Day."

As in, after a full day, my brain is fatigued from overly-complex discussions and just needs the most direct, un-fussy information possible.

That sound right, mk3w9?

Explosive Ordnance Disposal

Esoteric Order of Dagon

Yes, the - at the “End of the Day” EOD

The rocket made the air go funny which meant your phone got confused about where it was.

Spot on!

The really fast up goer made the air go funny which meant your phone got confused about where it was.

https://xkcd.com/1133/

The ionosphere is not the same thing as the atmosphere. The ionosphere is a shell of super hot gas outside of the atmosphere.

The ionosphere is not outside the atmosphere, it's part of the atmosphere.

The atmosphere consists of many layers. From the ground up, these are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

You may be thinking of the thermosphere, which is indeed very hot (thus the name), albeit with such low density that it wouldn't transfer much heat to your spacesuit or spacecraft. But the thermosphere is part of the atmosphere too.

https://spaceplace.nasa.gov/thermosphere/en/

The ISS and other low earth orbit satellites are orbiting inside the thermosphere. Yes, the ISS is in the atmosphere and suffers from a small amount of atmospheric drag, so it requires occasional reboosts to maintain altitude.

The ionosphere isn't exactly a separate "layer" from these. It's a very tall region of ionized gas that starts near the top of the stratosphere and overlaps parts of the layers above. Its exact limits vary with solar conditions.

The ionosphere is actually made up of several layers of its own, defined by the solar energy wavelength that causes ionization in each layer. These are the D, E, and F layers, and occasional sub-layers within those. Hams and other shortwave radio operators are familiar with these ionospheric layers because of their different effects on radio propagation.

https://en.wikipedia.org/wiki/Ionosphere

https://spaceplace.nasa.gov/ionosphere/en/

https://www.nasa.gov/mission_pages/sunearth/science/atmosphe...

And I finally get to say about one of my own comments: "Username checks out."

https://en.wikipedia.org/wiki/Stratoscope

(I'm actually named after the Truetone Stratoscope radio antennas, not the balloon, but sometimes people do say I'm full of hot air.)

that nasa site was actually interesting. but i think like i'm 5.

But, it is outside the environment?

>Rocket exhaust can have impact with atmosphere, we need to study it more on short and long term effects.

Wasn't this already known? We have been sending rockets to space for a while now, right?

EDIT: Found something from 2014, https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014...

Spare me your rocketry mumbo jumbo!

That's what I a call a content free sentence.

Saying "can" also implies "might not".

"Need" needs to come with "in order to do X". I don't need to breathe, but if I want to stay alive I do. So do I need to breather or not? It's either.

Can this cause any other issues other than GPS errors? Lines like

It is followed by ionospheric hole (plasma depletions) due to rapid chemical reactions of rocket exhaust plumes and ionospheric plasma.

sound concerning but that's most likely because I only understand half the words, and have even less of an understanding when they're strung together in that manner!

It is followed by ionospheric hole (should be It was... holes)

A ~900km wide patch of the ion blanket around the earth became thinner. Probably in the density sense, not the size sense: there was less plasma there than normal. (The abstract measures this in terms of how many electrons they counted in that area.)

due to rapid chemical reactions of rocket exhaust plumes and ionospheric plasma.

They think the thin patch was caused because the Falcon's exhaust reacted with the ion blanket. I'm not sure how.

I'm curious about this too. The Falcon burns RP-1, essentially a very refined kerosene, with liquid oxygen. Exhaust should be water, carbon dioxide, and a bit of carbon monoxide.

Not typically the most reactive things, but perhaps there are different interactions with plasma?

This other paper [0] seems to indicate that TEC (total electron count) fluctuations are caused by shock waves, not rapid chemical reactions, and can arise from ground explosions as well. IANA ionosphere scientist, so I don't know if the parent paper made a mistake.

[0] https://arxiv.org/pdf/physics/0007043.pdf

Anything is reactive when interacting with plasma.

There should be little of those gases naturally up there (mostly so for water), and even throwing a large mass of gases up there may be enough to disturb everything.

I wonder if in the future this means large rockets may have to throttle back while transitioning through the ionosphere to reduce side effects?

Is the altitude stable enough to predict it accurately for a given launch?

It might affect short wave propagation and things like atmospheric electricity.

The worst such event on record caused errors of ~1 meter. I didn't think civilian GPS was that precise anyway, and that's why various schemes are used in conjunction with GPS for greater accuracy? Presumably, military GPS has similar schemes to deal with this sort of event?

US currently claims 4m RMS (7.8m 95% Confidence Interval) horizontal accuracy for civilian (SPS) GPS. Some devices/locations reliably (95% of the time or better) can get 3m accuracy.

Yes, my expectation is that standard consumer-grade devices with GPS capability (even using tiny chip antennas) can achieve ~2.5M horizontal on L1 when using WAAS/SBAS augmentation.

Military GPSs use multiple frequencies which helps them mitigate errors from the ionosphere. NOAA publishes enough space weather data to let commercial receivers make their own corrections, but I don't know if any actually do.

In the relatively near future, GPS satellites will broadcast multiple frequencies for civilian use, once commercial receivers catch up everyone should be able to reduce the error due to atmospheric conditions

Civilian devices can use two frequencies as well, they just don't for cost and complexity reasons. The new L5 frequency has been available for some time and new devices supporting it are coming out this year. There are also multiple augmentations users can use to increase their accuracy to even greater levels than military users: https://www.gps.gov/systems/augmentations/

I don't have firsthand knowledge, but I'd be surprised if mission critical military gear uses GPS for more than a secondary / corrective role.

I can't imagine the signals play that well in a heavily-jammed environment.

High probability rough GPS fix + radar / optical terrain comparison & dead reckoning for terminal guidance seems more likely.

I'm not sure if you consider this "mission critical" but US military drones use GPS for navigation. There have been several cases of them being captured via GPS jamming.

From what I heard, that extended to GPS spoofing.

Military GPS devices have access to more frequencies and channels that consumer devices don't have. These frequencies use anti-jamming techniques (frequency hopping using pseudo-random patterns, etc). They also have much better accuracy available to them than the consumer devices. Typical dumb jamming systems aren't really going to do much against military anti-jamming techniques and if it really is hurting comms they can send in an anti-radiation missile and blow up the jammer, no GPS needed.

Do you have a source for the better accuracy claim?

I know they turned off Selective Availability ( https://en.m.wikipedia.org/wiki/Error_analysis_for_the_Globa... ) in 2000, so not sure if it's been true since then.

From what I was reading, it seems like semi-codeless approaches to the P(y) (aka military) signal offer approximately similar accuracy to actually being in possession of the key.

Furthermore, the P(y) signal uses the same L1 and L2 frequencies as civilian devices. Which makes sense when you're designing a system with 1970s broadcast technology.

From Wikipedia, it seems like the soon-to-be-launched Block IIIA satellites are the first that will incorporate the ability to spot-beam at higher power ( https://en.m.wikipedia.org/wiki/GPS_Block_IIIA#New_navigatio... ).

A non-insignificant portion of what GP said is mumbo jumbo. The reason military usage of GPS is more accurate is most significantly due to usage of multiple frequencies (which is now available to civilian too). What you’ve stated indicates you have good sources, so I recommend trusting those and asking questions if there’s gaps rather than trusting random folks commenters (yes, guess this includes me).

Many commercial GPS systems can get to within 2cm (< 1 inch). They all rely on complex antenna schemes and timing analysis combined with correction signals from another GPS at a known fixed point not far away. Search for differential GPS if you want more information.

I don't know if the correction GPS will see the same error and thus give the correct correction factor or not.

By "another GPS" do you mean a different satellite in the same network, or a different GNSS?

It's another receiver at a known location.

Atmospheric conditions cause errors that are in some cases hard to predict.

If you have a GPS receiver at a known nearby location, you can subtract the difference from what you receive and what you would expect to receive at your actual location, and then add that in to your GPS receiver at the unknown location.

It needs to be nearby because you want the atmospheric conditions between your fixed receiver and your moving receiver to be as similar as possible.

See https://en.wikipedia.org/wiki/Differential_GPS for more information

Also https://en.wikipedia.org/wiki/Real_Time_Kinematic is what's used to get ~1cm accuracy, but RTK would not be useful because while RTK increases precision of the measurements it does not (by itself) eliminate errors introduced by the atmosphere, which are already larger than what can be obtained without taking carrier phase into account.

I thought orbiting was all about horizontal velocity, otherwise what comes up must come down!

Did the rocket just turn sideways to accumulate the necessary horizontal velocity to actually maintain an orbit at a much later phase in its flight?

Yes, absolutely. The total sideways velocity required is fixed, going on a steeper trajectory requires more fuel for the same target orbit.

The reason Falcon 9 still does that sometimes is that a more vertical trajectory makes the return flight back to the launchpad easier. So if the payload is light enough that there is enough free delta-v, they want to do that. If there isn't, they land on the barge or fly expendable.

It is almost, but not quite, entirely about horizontal velocity. You also need sufficient altitude to be outside the atmosphere, as orbits with altitudes of under 100km are very short lived.

Additionally, it's generally not great to try to spend a lot of time accelerating through the atmosphere. For this reason rockets tend to fly upwards and then once they are out of the bulk of the atmosphere they fly mostly sideways.

I'd be curious to know roughly how long the disturbance lasted. Did it dissipate/recover in minutes, or did it stick around for the better part of a day (or two, or three)?

According to arstechnica's reporting on the paper (I don't have access to full text):

"In the case of this Falcon 9 launch, it induced a plasma hole that lasted for two to three hours, which a magnitude comparable to a magnetic storm"

https://arstechnica.com/science/2018/03/spacex-launch-last-y...

Can someone ELI5 how this would cause GPS errors?

Ionosphere's charge density introduces change in speed of the radio waves passing through it. This messes up with the GPS' calculations which assumes that ionosphere's density doesn't changes rapidly.

GPS works by computing your distance from satellites by measuring how long it takes radio signals from those satellite to reach you. As an electromagnetic wave, radio moves at a different speed through plasma (which is full of charged particles) than through holes in that plasma, so this will change how long those radio signals take to reach you, which will change how far away from the satellite you think you are.

SAW also means Surface Acoustic Wave which is a different type of wave like what travels along the ground in an earthquake. That's a terrible double use of an acronym! I think the author of this story might have just made it up and not seen the existing meaning.

Did anyone try downloading the actual paper? My browser opened and then closed a tab. Kind of odd.

The paper is behind a paywall. It probably went back to the abstract page because the login / buy panel is on the right side of that page.

Maybe see if your local library or university has an institutional subscription you can use to access the paper?

The paper is on scihub.

Every time somebody else burns a hole in the ozone layer I wonder if they did it over their home or over mine. Somehow I don't expect to be pleased by the answer.

As an Australian this is what we've had to deal with for decades. We don't produce much pollution but the hole is largely over us and giving us skin cancer.

Could major GPS issues become a nonstarter for the BFR intercontinental transport vision?

Maybe that's why the BFR interplanetary version is the focus. Screwing up GPS is less of a deal when you're leaving the planet for good... ;)

Are there any noted events in history that have exploited such ionosphere disturbances?

Related at all to the flight delays earlier today?

Plainer news headline style "SpaceX Falcon 9 launch might have interfered GPS signal coverage in area three times larger than California"

I wonder why a SpaceX Falcon-9 was singled out. Wouldn't any sufficiently large rocket have the same effect? And if so, wouldn't the Falcon heavy cause an even more dramatic effect?

A sufficiently large rocket with a similar payload being launched to reach a similar orbit. Apparently that combination is not very common.

Read the article before asking questions.

"This unique nearly vertical trajectory is different from the usual satellite launches that the rockets fly over horizontal trajectory "

To add to that, also from the article: "This is the largest rocket‐induced circular SAWs on record."

I would but the site's not responding for me.

Reply on news.ycombinator.com