
Circular Shock Acoustic Waves in Ionosphere Triggered by Launch of Formosat‐5 - zdw
https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017SW001738
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eganist
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."

\---

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.

\---

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.

~~~
cwkoss
Is '~1 m' meters or miles?

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lopmotr
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.

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

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kdelok
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.

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m3kw9
Even plainer language:

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

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

~~~
Stratoscope
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/](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://en.wikipedia.org/wiki/Ionosphere)

[https://spaceplace.nasa.gov/ionosphere/en/](https://spaceplace.nasa.gov/ionosphere/en/)

[https://www.nasa.gov/mission_pages/sunearth/science/atmosphe...](https://www.nasa.gov/mission_pages/sunearth/science/atmosphere-
layers2.html)

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

[https://en.wikipedia.org/wiki/Stratoscope](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.)

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

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stanmancan
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!

~~~
lainga
_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.

~~~
wlesieutre
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?

~~~
marcosdumay
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.

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jessaustin
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?

~~~
ethbro
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.

~~~
drag0nballz
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.

~~~
ethbro
From what I heard, that extended to GPS spoofing.

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zaroth
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?

~~~
Tuna-Fish
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.

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lwhalen
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)?

~~~
pavon
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...](https://arstechnica.com/science/2018/03/spacex-launch-last-year-
punched-huge-temporary-hole-in-the-ionosphere/)

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SteveNuts
Can someone ELI5 how this would cause GPS errors?

~~~
lmm
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.

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lopmotr
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.

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

~~~
cbhl
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?

~~~
pbhjpbhj
The paper is on scihub.

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krick
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.

~~~
jazoom
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.

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

~~~
ethbro
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... ;)

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

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stonlyb
Related at all to the flight delays earlier today?

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bwang29
Plainer news headline style "SpaceX Falcon 9 launch might have interfered GPS
signal coverage in area three times larger than California"

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kodis
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?

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staplers
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 "

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

