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The Voyager 1 took one last photograph in 1990 and after that, the camera equipment was shut off for power saving. However, the estimates of where the photo was taken in space vary by many hundreds of thousand of miles - not an exact point in space. The Voyager probe is old, however, and I'm wondering, how well can we estimate a point in 3D space today? Would a spacecraft that was built today be able to say exactly where it was when it took a picture?

uhoh
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Takeru Nakajima
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  • here is some reading on the topic: https://www.scientificamerican.com/article/how-do-space-probes-navig/ and https://sbir.nasa.gov/printpdf/53085 and Trends in Space Navigation - IEEE Xplore Document ... best to move the question then. new equipment probably relies on visual correlation of the known sky map and planet positions, which are much more precise today, with an onboard celestial map, so that the equipment can adjust without waiting for days to send and recieve controls from control center. – bandybabboon Apr 29 '17 at 10:02
  • To take a recent example, the DSN deep space network located on earth can assess the satellite movement very well to mm/s and meters direction between two receivers. position is less precise. prior to Cassini mission, Saturns position error was 100km by ground telescopes. Cassini was navigated Relative to saturn with 1km uncertainty factor, and not relative to the solar system. Probes are programmed with a coordinate grid based on the star fixed position and the solar barycenter as origin. They used Cassini to reduce Saturn position from 100km precision in 2010 to 2 kilometers precision today. – bandybabboon Apr 29 '17 at 10:18
  • related? 'Pale Blue Dot' Images Turn 25 and 27 years ago today, Voyager 1 took its last photos ever. Turning its cameras inward toward the sun, it captured the only portrait of our solar system. Including the famous "Pale Blue Dot" and also https://en.wikipedia.org/wiki/Pale_Blue_Dot#Distance – uhoh May 02 '17 at 02:42
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    I think this question is really asking "...how well can we estimate a point in 3D space today?" and not primary asking about uncertainty of Voyager's position. – uhoh May 02 '17 at 02:46

2 Answers2

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The precision of position of the space probes depends mostly on the amount of money spent on the navigation sensors and the nav equipment.

Today at any distance of deep space we can invest in X ray pulsar based navigation, for which one test system has been launched on Neutron Star Interior Composition Explorer, NICER. it gives 5km precision using pulsar periods and requires lighter and smaller antenna to capture the x rays.

Other advanced equipments are self contained on-board nav systems made of sensors and celestial models that can self correct the course using optical measures and an onboard sky map of given precision. They are used together with a fixed space coordinate system with origin on the solar barycenter and fixed relative to the constellations.

Prior to 2017, Deep space position was imprecise, and fine control was done relative to the approached object with cameras, where the approached object is unkown to several km/ 100ds of km. it consists of 1/velocity 2/position 3/movement vector 4/space object map... all of those factors are being improved massively all the time, and the precision only depends on the nav equipment budget.

Radio Doppler measurement of the shifted radio signal gives very good precision of radial movement from the terrestrial receivers, to within 1 mm/s, and two radio receivers situated around the planet can determine the movement vector fairly well.

The position is more difficult, for example Cassini's position was known relative to Saturn by 1km and Saturn was know relative to earth by 100km. (after Cassini this was refined to 2km relative to us).

They are checking all kinds of new equipment to increase precision, for example Laser doppler between satellites using optical costas loops and helium-neon laser and other precise wavelengths. A test of optical doppler was done on a previous moon mission to improve positioning and data coms up to a distance of 250,000 miles (>earth-moon distance)

If voyager used a 30 megapixel camera and a very good zoom+moving camera, it could determine it's position many many times more finely than the 1970's version. The sky map is better too. the radio Doppler is still used today but is more precise, and the optical Doppler doesn't go that far. It's position relative to visited objects was much higher resolution than the position of the objects visited.

bandybabboon
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    on-board navigation can only determine attitude, not position within the solar system. – Hobbes May 01 '17 at 20:27
  • @Hobbes except for some very special cases e.g. if New Horizons had an ephemeris, it might be able to get a fairly good idea where it was after the Pluto flyby, at least for a while. (telescope+ephemeris+clock+flyby) – uhoh May 02 '17 at 02:51
  • @Hobbes why do you say that? Could an on-board navigation not be able to determine its position based on the apparent size of the sun/planets and their known positions? – Arthur Dent Jun 01 '17 at 16:27
  • See e.g. https://space.stackexchange.com/questions/5845/how-do-probes-locate-themselves/12138#12138 – Hobbes Jun 01 '17 at 17:58
  • on-board navigation, from one of the links that i posted, is said to be able to draw a static coordinate system based on the background stars, and can contain a map of the solar system. Perhaps you were thinking of comms satellites. I read 2 days ago that they are currently sending out new satellites to replace the deep space network, because it's a bit overloaded and imprecise. – bandybabboon Jun 02 '17 at 03:08
  • All of the options you mention have one thing in common: they are not in use on any current interplanetary mission. – Hobbes Jun 07 '17 at 13:56
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Current interplanetary spacecraft have no way to determine their own position. Their position is measured from Earth using e.g. the DSN. This gives a position that is very accurate on the Earth-spacecraft axis (~1 m resolution), but has less resolution in the other two axes.

Systems are being investigated to support autonomous positioning, but none of them are in operational use yet.

Hobbes
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