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Another application of satellites in formation is measure gravity fields: > That brings us to GRACE—a backronym for gravity recovery and climate experiment—a p

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-chase-to-measure-gravity-achieve-picometer-accuracy/ https://arstechnica.com/science/2019/07/satellites-play-chas... * https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO

_factor 3y ago
A space interferometer as well. Unfortunately, the planned SIM mission was shelved. https://en.wikipedia.org/wiki/Space_Interferometry_Mission?wprov=sfti1#Planet_hunting https://en.wikipedia.org/wiki/Space_Interferometry_Mission?w...
- perihelions 3y ago
  There's also https://en.wikipedia.org/wiki/LISA_Pathfinder 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 3y ago
    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 3y ago
TIL backronym.
- dylan604 3y ago
  US Congress is a fan of its use, even if they might not know there's a word for it
- verisimi 3y ago
  https://en.wikipedia.org/wiki/Backronym 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]
- sandworm101 3y ago
  "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."
  - HPsquared 3y ago
    That would be a good name for an artillery division.
- HankB99 3y ago
  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.

_factor 3y ago

A space interferometer as well. Unfortunately, the planned SIM mission was shelved. https://en.wikipedia.org/wiki/Space_Interferometry_Mission?wprov=sfti1#Planet_hunting https://en.wikipedia.org/wiki/Space_Interferometry_Mission?w...

perihelions 3y ago
There's also https://en.wikipedia.org/wiki/LISA_Pathfinder 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 3y ago
  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 3y ago

TIL backronym.

dylan604 3y ago
US Congress is a fan of its use, even if they might not know there's a word for it
verisimi 3y ago
https://en.wikipedia.org/wiki/Backronym 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]
sandworm101 3y ago
"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."
- HPsquared 3y ago
  That would be a good name for an artillery division.
HankB99 3y ago
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.