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The SR-71 Blackbird Astro-Nav System worked by tracking the stars

theaviationgeekclub.com

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Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#311

Post by grotorea »

jacurtis wrote: post #32

> 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 ear…

> 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.

From what I understand of the manual[0], the system doesn't get completely lost if the crew decides to abort and fly away or something. The preprogramming is mainly so the sensors and camera automatically engage at the predefined points in the planned flight.

[0] https://airandspace.si.edu/webimages/collections/full/NAS-14...

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#312

Post by tester756 »

drt5b7j wrote: post #274
jacquesm wrote: post #143

Earlier quoted context omitted.

It's not just analog tech: it's actual engineering. The hardware we have is amazing, most of our software royally sucks. But software done right is also most impressive.

Do you think the "software engineering" people are giving engineering a bad name? "Christian scientists" are Christians who attach themselves to the word science because science has such a powerful reputation. In their case I'm not worried about their trickery because everyone recognizes this. Everyone knows that Christian scientists are not scientists. With software engineering it's not as clear. It's possible to cr…

Software is engineering.

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#313

Post by Gravityloss »

The early North American SM-64 Navaho supersonic cruise missile that was cancelled developed some technologies that were later used in other projects. (Same for Lockheed Suntan.) If you fly high and fast enough, there's considerable overlap with spacecraft navigation technologies. You can navigate in space with sextant too. No trouble with clouds!

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#314

Post by jcpham2 »

jaybo_nomad wrote: post #195

Semi-related tangent: During the early 1990's I developed a star chart and ephemeris for the (momentarily) fashionable Windows Mobile platform called "Pocket Stars" that calculated one's geographical position from three or more sextant observations, mainly as backup for offshore sailors should their GPS system fail. For reasons I still can't fathom, a contractor for the Israeli military purchased many copies, apparen…

I used Pocket Stars on Windows Mobile during it's brief tenure of existence on this planet; thanks.

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#315

Post by xjlin0 »

tgsovlerkhgsel wrote: post #45

How complicated/expensive would it be to build an open source star tracker nowadays? How accurate of a fix could you get just by pointing a phone at a sky? Or a DSLR on a commercial gimbal?

Too bad the star tracker on my phone still relies on GPS instead of electro-opitical geolocation.

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#316

Post by tekla »

2rsf wrote: post #306
robbs wrote: post #295

Earlier quoted context omitted.

It doesn't have to be a small team. See "They Write The Right Stuff".

And even they make mistakes, software contains much more moving parts than hardware. https://space.stackexchange.com/questions/37110/what-was-the...

Wow, thats a hell of a HN thing to say.

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#317

Post by frud »

ezconnect wrote: post #135
TheRealPomax wrote: post #119

[it] was so powerful that it could see the stars even in daylight That's a very odd thing to say: when you're at 85,000 feet (as noted, the SR-71's cruising altitude), the concept of a blue "daylight" that blocks the view of space only exists below you, not above you [1]. There is not enough Rayleigh scattering at that height to get in the way of a camera looking for stars to map to a star chart. It's pretty much why…

They also need an initial fix before take off and that could be day or night depending on the mission.

I think that in order to calculate your latitude and longitude position using what amount to high-tech sextant readings you have to know your local down vector to a high degree of accuracy. That is, the system judges the position of the Blackbird by comparing its local down vector with the angles to the star sightings. If the down vector measurement is off by an arcsecond, the measured latitude and longitude position on the earth will also be off by an arcsecond (at sea level, about 600 feet).

It seems to me that there's an interesting problem that the Blackbird goes so fast that its down vector changes dramatically over the course of a typical flight, so I'm wondering how it accurately updates its down vector reference. Jets can go through arbitrary and wobbly 3-d trajectories, accelerating in any direction, so it can't be a simple measurement of gravity. It would have to be a accelerometer combined with inertial and gyro and elevation readings all summed up.

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#318

Post by nojvek »

bookofjoe wrote: post #283
sonthonax wrote: post #252

Earlier quoted context omitted.

> Why would anyone trade an EMP for all their cities? ICMBs were a theoretical threat. Cold War doctrine had a more realistic (and less apocalyptic) WWIII that would be fought by tactical nukes and tanks through Europe.

>I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones." ― Albert Einstein

We will have countries against each other fighting for their borders but world war is v unlikely in our lifetime.

We love our cheap goods, cheap-ish energy and ability to change presidents and prime ministers.

Yes China, North Korea and Russia banding against the rest of the world is a real threat but China has shown it is selfish too and cares more about its economy.

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#319

Post by umeshunni »

frud wrote: post #317
ezconnect wrote: post #135

Earlier quoted context omitted.

They also need an initial fix before take off and that could be day or night depending on the mission.

I think that in order to calculate your latitude and longitude position using what amount to high-tech sextant readings you have to know your local down vector to a high degree of accuracy. That is, the system judges the position of the Blackbird by comparing its local down vector with the angles to the star sightings. If the down vector measurement is off by an arcsecond, the measured latitude and longitude position…

What does 'down vector' mean in this context?

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#320

Post by frud »

umeshunni wrote: post #319
frud wrote: post #317

Earlier quoted context omitted.

I think that in order to calculate your latitude and longitude position using what amount to high-tech sextant readings you have to know your local down vector to a high degree of accuracy. That is, the system judges the position of the Blackbird by comparing its local down vector with the angles to the star sightings. If the down vector measurement is off by an arcsecond, the measured latitude and longitude position…

What does 'down vector' mean in this context?

A very precise estimation of which direction gravity is pulling down towards. Which is almost, but not exactly, the vector towards the center of the earth. And it also needs to be disentangled from the suborbital centrifugal/centripetal forces experienced by the movement of the Blackbird.
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