My next Q is: how do you navigate in deep space?
I know with Apollo they used earth based radar to confirm the spacecraft position. Amazingly this was usable even close to the moon. Obviously this won’t work much further out.
Many years ago someone involved in the satellite launching business told me they use DME distance, and knowing the orbital equations this is all they need to work out where it is. They get thousands of readings and end up with thousands of simultaneous equations which are solved and the 3D position pops out.
But how could a spacecraft do this autonomously?
“how do you navigate in deep space?”
Most of the times you don’t, you just have to trust free fall equations as by the time you reach deep space there is nothing left in power and things will go exactly as expected,
For trajectory tracking, we still rely on radio navigation with signal from the spaceship, these are received by earth ground stations (2 or 3 stations) then all gets processed on ground rather than onboard, while DME can handle max 100? aircrafts before saturation, I think “NASA DME” does 1 aircraft at a time ;)
Someone sent me this file_pdf which suggests you could use x-ray pulsars. It is heavy going maths-wise but there are many interesting snippets e.g. on page 7 that with appropriate corrections the timing can be as accurate as an atomic clock.
The report also states that the present Deep Space Network can determine a spacecraft position within 10km at a distace of 1 AU (the distance from the earth to the sun, roughly) which is pretty amazing.
Yes that is still radio nav based but you will need to have a bunch of large pulsars detectors and huge compute power onboard,
At the moment what we sent beyond earth/moon are small probes with GA aircraft size and 1KW max power, so they will still rely on ground-based navigation than having something onboard? But not sure if you can still use that for onboard position fix and send data (1kb/s) to earth for trajectory calculations?
