13

In an aircraft, can you look at the sky to get your bearing and position like sailors do?

Rodrigo de Azevedo
  • 1
  • 1
  • 9
  • 28
Alex Jasmin
  • 231
  • 2
  • 6
  • 3
    The Zeppelins used a sextant quite often. In the times before radionavigation that was the best they could do when ground was obscured or of no help (like over deserts or open water). – Peter Kämpf Mar 12 '20 at 12:27
  • 3
    In Canada knowledge of how to get a fix with a sextant was included in the Airline Transport exam until the 80s. – John K Mar 12 '20 at 13:03
  • 2
    Yes, but for most of us, it's far more useful to look at the ground. E.g. IFR = I Follow Roads :-) – jamesqf Mar 12 '20 at 16:40
  • 1
    Related: https://aviation.stackexchange.com/questions/25096/what-is-the-purpose-of-eyebrow-windows – AndreKR Mar 13 '20 at 09:58

3 Answers3

27

You sure can! It's not really done all too much any more in the days of GPS but it was done quite a bit in the early days of aviation. Historically, this was done by the "flight navigator" a position that no longer really exists. Some aircraft even had mounted sextants.

enter image description here

(source)

Here is a video of it being done in practice (fanta optional)

This was even automated on the SR-71's Inertial Astro-Navigation system which used the stars to align itself.

Dave
  • 101,073
  • 5
  • 220
  • 364
  • 2
    The SR-71 operated in the 1960s and 1970s, long before high-resolution light-sensors (i.e. CCD/CMOS sensors) and computer-systems powerful enough to process a raster graphics of the night-sky existed (let alone a frame-buffer big enough) - so on what basis did the SR-71's NAS-14V2 operate? Surely there's too many bright stars visible in the sky for a computer system back then to reliably know which star it's looking at from what I assume was a 1960s-era vidicon tube output signal? – Dai Mar 13 '20 at 05:44
  • 4
    @Dai You don't need a computer to process raster graphics. The Russians sent back images of the moon in 1959. They scanned an analog TV camera and converted it to a fax signal. The format of the images was basically fax. You can do something similar to process star locations - point an analog TV camera at the sky and process the signal in analog. Of course, a standard analog TV signal is essentially 320x240 but a custom camera can be any resolution you're willing to process – slebetman Mar 13 '20 at 08:44
  • 3
    @Dai you're assuming that a general-purpose digital computer is required. Dedicated analog computers can sometimes achieve performance levels that general-purpose computers can't. – barbecue Mar 13 '20 at 16:35
  • 3
    @Dai if you are curious the full POH has been declassified, containing operational instructions. There is not all that much out there on how it worked but if you watch some of the -71 interviews they talk about it tacking certain bright stars. – Dave Mar 13 '20 at 18:21
  • 3
    @Dai here is another copy of the manual that discusses a bit more in depth how the unit works – Dave Mar 13 '20 at 18:24
  • @Dai: While I know nothing about the SR-71's system, it was quite common for space probes to orient themselves by tracking bright stars. Apparently it was also used for missiles, so there would seem to be no reason such a system couldn't be used on a manned aircraft: https://en.wikipedia.org/wiki/Star_tracker – jamesqf Mar 13 '20 at 23:54
  • 1
    Basically the trick to doing astronavigation with limited computing power is not to attempt to process a raster image. Instead there is a small telescope with a narrow field of view, focusing onto a quadrant photodetector which you could think of as being similar to a CCD with just 4 pixels. This telescope is initially aimed either manually or automatically (based on an existing INS alignment) at a star selected from a small catalog. The relative intensities of the 4 pixels provide a correction signal that indicates how far and in what direction the star is from the center of the viewfield. .. – pericynthion Mar 14 '20 at 03:52
  • 1
    ... and the computer then steers the telescope so as to null out this correction signal (all 4 quadrants at equal brightness). This condition is maintained continuously, "tracking the star" as the aircraft attitude and position changes. The gimbal angles necessary to do this provide a measurement of the line-of-sight vector to the star, which is used in the navigation solution. – pericynthion Mar 14 '20 at 03:55
  • @pericynthion In a dogfighting situation - or anything with short, sharp maneuvers - I don't see the gimbal being able to react fast enough to track the star like that. Was astronavigation only available when flying in a straight-line? – Dai Nov 29 '20 at 00:54
  • @Dai I doubt any automated astronavigation systems would have been installed on aircraft that engaged in dogfights. – pericynthion Nov 29 '20 at 00:59
8

It has in the past. Though the process for both pilots and sailors is a little more complex than just looking at the stars. See a previous AviationStackExchange question.

Do pilots need to know how to use a sextant?

Modern aviation has so many other navigation tools:
GPS
Radio NavAids
Inertial Navigation Systems

They make Celestial navigation obsolete. Although, it is not required pilot training. And you won’t see it used in GA aircraft. It is still in use by the military. Especially in ICBMs. My understanding is that the automated celestial navigation system used by the military was too expensive for widespread use.

Chapters 8-13 of the FAA Flight Navigator Handbook are dedicated to the subject. Sadly, the position of a Flight Navigator is also all but obsolete.

Mike Sowsun
  • 37,747
  • 4
  • 122
  • 156
Dean F.
  • 16,507
  • 1
  • 30
  • 70
  • FWIW, I spoke with a chief engineer about how often all navigation sources you listed simultaneously fail, and the answer was that you might never see it happen over an entire fleet's lifetime. The only cases I've seen in ASRS of total position loss are for AHRS planes. – Cody P Mar 13 '20 at 17:31
3

Of course it can be done, and astronavigation was often used in long-range flights, and transatlantic passenger liners such as the Super Constellation were fitted with a plexiglas astro-dome so that the navigator might 'take' the stars with a bubble sextant.

xxavier
  • 11,071
  • 3
  • 29
  • 72