[HN Gopher] The SR-71 Blackbird Astro-Nav System worked by track...
___________________________________________________________________
The SR-71 Blackbird Astro-Nav System worked by tracking the stars
Author : bookofjoe
Score : 57 points
Date : 2023-09-25 21:47 UTC (1 hours ago)
(HTM) web link (theaviationgeekclub.com)
(TXT) w3m dump (theaviationgeekclub.com)
| hangonhn wrote:
| Anyone know if modern military aircraft have something similar? I
| imagine it would be even cheaper and easier to do these days
| given the processors and cameras we now have. Seems like a good
| backup to have.
| aidenn0 wrote:
| Astronomically corrected INS[1] is definitely still a thing in
| aerospace in general. I have no knowledge of whether or not
| they are in modern military aircraft though.
|
| 1: https://en.wikipedia.org/wiki/Inertial_navigation_system
| colechristensen wrote:
| Still used in spacecraft, a vendor:
| https://www.ball.com/aerospace/capabilities/technologies-com...
|
| What's actually on aircraft tends to be classified.
| [deleted]
| nvy wrote:
| Former military aerospace engineer here. In my opinion it would
| only be worth it on long range strategic bombers such as the
| B-52.
|
| Fighters don't have the legs to fly far enough that celestial
| navigation becomes worth the added complexity.
|
| For other air mobility platforms like the C-130 or C-17 in my
| experience they do not include these features, as GPS, INS, and
| regular old "ask ATC for a vector" are usually good enough.
|
| There are ongoing experiments with magnetic and other forms of
| navigation, some of which are classified, but I'm a civilian
| now so I don't know any specifics.
| malfist wrote:
| When I first heard of astro-nav (for missiles) I thought it was
| so future sounding, like star trek.
|
| But now that I do astrophotography regularly it's just another
| tool that I use. It's super simple to do, I can take a photo of
| the night sky, and if I know the focal length and pixel size of
| my camera I can figure out exactly where my telescope is pointed
| in seconds, with an accuracy 2.5 arcseconds.
|
| You can even do it blind (without knowing any details about the
| telescope/camera) though that takes a couple of minutes.
| Ductapemaster wrote:
| What software do you use to accomplish this?
| blackhaz wrote:
| OK. Now please do the same with a Z-80 class CPU.
| [deleted]
| thsksbd wrote:
| The hardest part would be doing the image recognition, but
| that wouldn't be that bad since the position (and therefore
| expected picture) is already known, a priori, to a good
| accuracy.
| mat_epice wrote:
| ICBMs have used celestial guidance since the 50s.
| https://airandspace.si.edu/collection-objects/snark-guidance...
| dboreham wrote:
| Also B-58
| perihelions wrote:
| There's a sad poetry that the simplest ICBM guidance is a camera
| that simply watches the stars.
| kderbyma wrote:
| I float through the atmosphere gazing up upon the lights
| mapping my way, I see a bear crossing with it cub, what glory
| doth orion project, and soon onwards towards my destination
| does my heavy soul carry forth a atomic bluster and putrid
| death, but at in these last few moments I ponder my place among
| the stars.
| jacurtis wrote:
| > the flight plan was recorded on a punched tape that told the
| aircraft where to go, when to turn, and when to turn the sensors
| on and off.
|
| This is equally fascinating to me. Before each flight, someone
| had to generate a flight plan and punch it onto a physical tape,
| then load it into the plan. T
|
| No mid-flight "re-calculating route" if stuff goes wrong.
|
| One of the most interesting and under-appreciated aspects of
| early aviation that is routinely forgotten by history is the fact
| that navigation was extremely difficult in a world before GPS.
| For example in WWII, pilots getting lost was a huge problem,
| especially for the Navy pilots. Imagine taking off of an aircraft
| carrier and flying hundreds of miles away from it, completing a
| mission and then trying to retrace your steps and find the 100
| yard long dot in the wide open ocean again while flying at
| 10,000+ feet altitude. Pilots navigated with simple directions
| of, "heading 310 for 50 knots, heading 120 for 80 knots" and they
| would follow a handwritten piece of scrap paper and then try to
| come back. There were no landmarks to follow. To make things even
| more complicated, we didn't exactly know distances very well. In
| a world like the ocean with no landmarks, you rely purely on
| compass and distances and time for directions. But if there is a
| tailwind vs a headwind then you could travel 80 knots in 30 mins
| instead of 45 minutes. This could put you wildly off course when
| you go to turn. It was incredibly scary to get into a cockpit and
| sail off into the ocean with no landmarks and hope to find a
| target and return back to the carrier (which itself is also
| moving). This is also why bombers and even long-range fighters
| actually had dedicated "Navigators" on board who's sole job was
| navigation during flight.
|
| As an example, The Battle of Midway was almost a complete failure
| for the USA because the main bomber squadron actually got lost
| trying to find the ships that they were meant to bomb. Iirc they
| had meandered around the destination area for almost an hour and
| were bingo on fuel. The squad commander had actually given the
| order to turn around and as the planes were turning around, one
| of the pilots spotted the Japanese carriers in the distance. The
| battle of midway up to this point was a complete failure and had
| overexposed the Navy. The first dive bomb attack had lost all but
| 3 dive bombers (one of which only survived because he got
| separated and lost). The Japanese were getting ready to counter
| strike on the remaining US Navy which were congregated (against
| the will of most admirals and generals) just a hundred miles
| away. The fighter wing had shown up before the second primary
| bomber wing (which had gotten lost) and had alerted the Japanese
| to the surprise attack, in addition to devestating losses (about
| 2/3) for the fighters. If these lost bombers had returned back
| without completing their successful bombing raid, it is safe to
| say that history would be re-written. Japan would have destroyed
| the US Navy and eventually consumed the USA. This would have
| distracted the US from aiding Europe and Europe would have likely
| been lost to Germany. All because of how difficult it was to
| navigate before GPS.
|
| I just find early aviation so fascinating with how they
| accomplished so much with so little. We often look back and
| forget so many simple things about aviation like navigation
| because we take it for granted today. Hell, my watch can pinpoint
| my location anywhere on earth to within a few feet. Yet location
| in the 40s and 50s was usually determined by drawing circles on a
| map that cover 50 mile diameters and saying "we think we are
| somewhere in here".
|
| A prime example is the original story. In a world before GPS,
| where we need precise long-range navigation, what are you going
| to do? You have to work with what you have. We didnt have
| satellites yet (well at least not ones like we needed), you are
| too high for anything visual on the ground, too fast to reliably
| navigate manually, so what's left? The stars. I'm sure someone in
| that brainstorming meeting said it was impossible, but there were
| no other choices, so they figured it out. And it's incredible!
| darth_avocado wrote:
| Interesting that it's not confirmed if the SR-71 flew in the
| Southern Hemisphere. Would be a very bold design if it didn't and
| the system wasn't designed for it.
| eastbound wrote:
| Is it true that military branches (navy, airforce) from around
| equator use a grid-square reference system for radars and have
| issues when going further north, while triangle-based reference
| systems are a really good model in polar countries that doesn't
| scale well when going South?
|
| It's a problem so predictable that I can't believe I have been
| told the truth, and it's impossible to find the right keywords
| to search that on Google ;)
| chipsa wrote:
| The military does use a grid square reference system,
| Military Grid Reference System (MGRS), and to resolve the
| issues when sufficiently far north, the grid squares stop
| being aligned with the latitudes and longitudes, but rather
| just sit lined up with the 0/90/270/180 longitudes, as a sort
| of circular cap cut out of grid paper. (Properly speaking,
| it's Universal Transverse Mercator (which is a series of 60
| Mercator projections) between 80S and 84N, and Universal
| Polar Stereographic near the poles).
| fidotron wrote:
| The F22 had an unintentional problem of being unable to cross
| the international date line, which was discovered when
| attempting to fly from Hawaii to Japan.
|
| Given that it may very well be better to assume that anything
| untested doesn't work at all and to live within those
| restrictions.
| omginternets wrote:
| Something about non-monotonic software clocks?
| _moof wrote:
| The International Date Line and the 180-degree line of
| longitude have bitten a _lot_ of folks who don't think to
| test at the boundaries.
| tlrobinson wrote:
| "Unable"? How did this manifest?!
|
| > Given that it may very well be better to assume that
| anything untested doesn't work at all and to live within
| those restrictions.
|
| There are an infinite number of untested cases though.
| Figuring out the important ones is the hard part, otherwise
| they likely would have been identified and fixed in
| development.
| sampo wrote:
| > "Unable"? How did this manifest?!
|
| https://news.ycombinator.com/item?id=4541501
| eastbound wrote:
| Would it invert North and South after crossing the line?
| No, that's the story of the Soviet bomber that took off the
| wrong way from the airstrip in a secret night mission, and
| ended up 180deg in Iran. Fortunately the two iranian
| jetfighters supposed to down it, ended up chasing each
| other. Real world is hilarious.
| https://youtu.be/i-bdJF6TUFs
| stevenwoo wrote:
| It says they did have capability to navigate in Southern
| hemisphere though it might be implied one had to use two stars
| only visible in southern hemisphere.
| comandillos wrote:
| Simply amazed by the fact that something similar to "star
| trackers" as we know them today goes back to the 60s...
| dylan604 wrote:
| um, doesn't the sextant go back much much further than the 60s?
| BHSPitMonkey wrote:
| I think GP finds it impressive that the technology enabling a
| device to _automatically_ resolve its position (simply by
| looking up at the sky) goes back this far. It impresses me,
| at least.
| fragmede wrote:
| Actually, '94.
|
| 994, that is.
| camel_gopher wrote:
| Insert story about shaming a Hornet driver over ATC, and showing
| the bugsmashers who the king of speed was.
| cushychicken wrote:
| You can see one of these up close - both the device, and the
| airplane! - at the Evergreen Aerospace Museum in McMinnville, OR.
|
| They also have on display another Blackbird payload labeled
| DEF-H. It's a nondescript white box which you are allowed to look
| at, but not allowed to know what it does. XD
| cmiller1 wrote:
| I got to see an SR-71 on display in New York several years ago.
| What really struck me was how BIG it was, seeing pictures of it
| doesn't really give you sense of scale, it was a massive plane.
| dboreham wrote:
| Even more impressive seeing it sweat fuel onto the apron in
| the afternoon sun for a few hours then engine ignition with
| Chevy V8 start cart, takeoff followed by low level transonic
| flyby.
|
| Fairford IAT 1989.
| [deleted]
| ceocoder wrote:
| Per this[0] it seems like a radar jammer, however details, like
| you mention, are classified.
|
| [0] http://www.sr71.us/sr_sensors_pg3.htm
| singleshot_ wrote:
| [flagged]
| davidw wrote:
| I'm not much into planes, in particular, but that museum is
| really cool.
| porphyra wrote:
| How does it see the stars? Even modern CMOS image sensors cannot
| see the stars during the day.
___________________________________________________________________
(page generated 2023-09-25 23:00 UTC)