Navigating by GPS is pretty accurate for anything on the ground or in the air, but if you provided the appropriate software could you navigate in orbit?
I can’t see that being too difficult, but how about above the orbit of the GPS satellites? Say to help navigate a spacecraft to the Moon?

You only need 4 points to accurately map in 3D and it shouldn’t matter whether you’re on the inside or the outside of the network.

OCDC said:

You only need 4 points to accurately map in 3D and it shouldn’t matter whether you’re on the inside or the outside of the network.

Yeah that’s what I reckon as well. But of course the more satellites the better. And there’s little chance of a mountain or even a tall building getting in the way.

Spiny Norman said:

OCDC said:

You only need 4 points to accurately map in 3D and it shouldn’t matter whether you’re on the inside or the outside of the network.

Yeah that’s what I reckon as well. But of course the more satellites the better. And there’s little chance of a mountain or even a tall building getting in the way.

It’s not reckoning – it’s simultaneous equations. But the thing in the way point is good, happens often enough just with the weather radar.

OCDC said:

You only need 4 points to accurately map in 3D and it shouldn’t matter whether you’re on the inside or the outside of the network.

So long as you can get the signal then it doesn’t matter where you are, as long as the software knows that you can be inside or outside the shell of satellites ( quick acquisition system use the premise that you are likely to be in a certain area, the surface of the earth). As you get a long way higher than the satellites you will lose accuracy as the signals will get closer and closer in time to each other.

Stealth said:

OCDC said:

You only need 4 points to accurately map in 3D and it shouldn’t matter whether you’re on the inside or the outside of the network.

So long as you can get the signal then it doesn’t matter where you are, as long as the software knows that you can be inside or outside the shell of satellites ( quick acquisition system use the premise that you are likely to be in a certain area, the surface of the earth). As you get a long way higher than the satellites you will lose accuracy as the signals will get closer and closer in time to each other.

Yep, I just wonder how far out it would be of use.

I don’t think that gps systems are Omni directional , they are roughly directional. they won’t be pointing at the moon

you’d be needing an onboard inertial measurement system and something looking at the stars, the yanks used a system where they looked at the stars and then by using three elipses and mathematical cone sections created a zone of probability of where the spaceship was.

the other option is this

you have your own transmitters based on earth at known points as referenced by a GPS position (surveyors GPS systems haven’t been interfered with to create false results)

you then broadcast from these known positions with your own signal that your spacecraft picks up.

you could have one transmitter in Alaska and another in the tip of argentina and another in Australia you could triangulate I guess or use the same system as the satellite system except broadcast upwards instead of downwards.

the transmitter would need to roughly track the rough position of the spacecraft to make sure signal strength didn’t diminish

Surveyors GPS receivers are accurate to within millimeters. The further away from the GPS’s orbit you are, the less accurate your GPS location will be. My guess is that at the distance of the moons surface, your location would be accurate to within a meter or so. If you included a few “local” pulsars signals in your receiver, you could narrow it down even further.

Maybe soon a few GPS satellites will be sent out of Earths orbit and into an escape orbit so that the further away they get, the more accurate any trans solar system objects can be tracked.

Maybe soon a few GPS satellites will be sent out of Earths orbit and into an escape orbit so that the further away they get, the more accurate any trans solar system objects can be tracked.

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I can’t imagine that they designed them to be able to do that.

Stealth said:

Maybe soon a few GPS satellites will be sent out of Earths orbit and into an escape orbit so that the further away they get, the more accurate any trans solar system objects can be tracked.

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I can’t imagine that they designed them to be able to do that.

I’m pretty sure that they are just a transmitter that sends out a perfectly timed signal which includes the time that it was sent.

Therefore no problem if you just hurled one out into the solar system.

Kingy said:

Surveyors GPS receivers are accurate to within millimeters. The further away from the GPS’s orbit you are, the less accurate your GPS location will be. My guess is that at the distance of the moons surface, your location would be accurate to within a meter or so. If you included a few “local” pulsars signals in your receiver, you could narrow it down even further.

Maybe soon a few GPS satellites will be sent out of Earths orbit and into an escape orbit so that the further away they get, the more accurate any trans solar system objects can be tracked.

what i’m saying is that you set up broadcast at a known place as placed by surveyors equipment, you are using the transmitters on the earth to act as a lunar GPS system possibly by the spacecraft finding the strongest signal from those set places and using triangulation.

wookiemeister said:

Kingy said:

Surveyors GPS receivers are accurate to within millimeters. The further away from the GPS’s orbit you are, the less accurate your GPS location will be. My guess is that at the distance of the moons surface, your location would be accurate to within a meter or so. If you included a few “local” pulsars signals in your receiver, you could narrow it down even further.

Maybe soon a few GPS satellites will be sent out of Earths orbit and into an escape orbit so that the further away they get, the more accurate any trans solar system objects can be tracked.

what i’m saying is that you set up broadcast at a known place as placed by surveyors equipment, you are using the transmitters on the earth to act as a lunar GPS system possibly by the spacecraft finding the strongest signal from those set places and using triangulation.

if you were hardcore you could use lasers to point at the rough location of the spacecraft and follow it all the way to the moon

you could have a reflector on the spacecraft the laser is fired at it at a known angle and time, the reflect signal then comes back, you do this with three or four other lasers

based on the angles of the laser and the time of reflection the spacecraft location is ascertained and then broadcast to the spacecraft, the spacecraft and lasers have synched time and the spacecraft is told at X time the spacecraft was calculated to be at Y position in space travelling at Z velocity (velocity implies the direction of travel is known)

Kingy said:

Stealth said:

Maybe soon a few GPS satellites will be sent out of Earths orbit and into an escape orbit so that the further away they get, the more accurate any trans solar system objects can be tracked.

—————————-
I can’t imagine that they designed them to be able to do that.

I’m pretty sure that they are just a transmitter that sends out a perfectly timed signal which includes the time that it was sent.

Therefore no problem if you just hurled one out into the solar system.

Thje problem I foresaw, was the ‘hurling out into the solar system’

wookiemeister said:

wookiemeister said:

Kingy said:

Surveyors GPS receivers are accurate to within millimeters. The further away from the GPS’s orbit you are, the less accurate your GPS location will be. My guess is that at the distance of the moons surface, your location would be accurate to within a meter or so. If you included a few “local” pulsars signals in your receiver, you could narrow it down even further.

Maybe soon a few GPS satellites will be sent out of Earths orbit and into an escape orbit so that the further away they get, the more accurate any trans solar system objects can be tracked.

what i’m saying is that you set up broadcast at a known place as placed by surveyors equipment, you are using the transmitters on the earth to act as a lunar GPS system possibly by the spacecraft finding the strongest signal from those set places and using triangulation.

if you were hardcore you could use lasers to point at the rough location of the spacecraft and follow it all the way to the moon

you could have a reflector on the spacecraft the laser is fired at it at a known angle and time, the reflect signal then comes back, you do this with three or four other lasers

based on the angles of the laser and the time of reflection the spacecraft location is ascertained and then broadcast to the spacecraft, the spacecraft and lasers have synched time and the spacecraft is told at X time the spacecraft was calculated to be at Y position in space travelling at Z velocity (velocity implies the direction of travel is known)

you’d need to have the lasers controlled in a manner to track the spacecraft as the earth turns

as the stations will be spread across the earth contact would never be lost

wookiemeister said:

wookiemeister said:

Kingy said:

Surveyors GPS receivers are accurate to within millimeters. The further away from the GPS’s orbit you are, the less accurate your GPS location will be. My guess is that at the distance of the moons surface, your location would be accurate to within a meter or so. If you included a few “local” pulsars signals in your receiver, you could narrow it down even further.

Maybe soon a few GPS satellites will be sent out of Earths orbit and into an escape orbit so that the further away they get, the more accurate any trans solar system objects can be tracked.

what i’m saying is that you set up broadcast at a known place as placed by surveyors equipment, you are using the transmitters on the earth to act as a lunar GPS system possibly by the spacecraft finding the strongest signal from those set places and using triangulation.

if you were hardcore you could use lasers to point at the rough location of the spacecraft and follow it all the way to the moon

you could have a reflector on the spacecraft the laser is fired at it at a known angle and time, the reflect signal then comes back, you do this with three or four other lasers

based on the angles of the laser and the time of reflection the spacecraft location is ascertained and then broadcast to the spacecraft, the spacecraft and lasers have synched time and the spacecraft is told at X time the spacecraft was calculated to be at Y position in space travelling at Z velocity (velocity implies the direction of travel is known)

you’d need to have the lasers controlled in a manner to track the spacecraft as the earth turns

as the stations will be spread across the earth contact would never be lost

I probably agree with Wookie here. The antennas on a satellite are not going to be omni-directional. Be on the wrong side of the satellite, ie above it, and it may be difficult to relieve a signal.

sibeen said:

I probably agree with Wookie here. The antennas on a satellite are not going to be omni-directional. Be on the wrong side of the satellite, ie above it, and it may be difficult to relieve a signal.

falls over

sibeen said:

I probably agree with Wookie here. The antennas on a satellite are not going to be omni-directional. Be on the wrong side of the satellite, ie above it, and it may be difficult to relieve a signal.

There is quite a few on the “other” side on the Earth that are transmitting “downwards”, and missing the planet that you would be able to pick up easily.

Kingy said:

sibeen said:

I probably agree with Wookie here. The antennas on a satellite are not going to be omni-directional. Be on the wrong side of the satellite, ie above it, and it may be difficult to relieve a signal.

There is quite a few on the “other” side on the Earth that are transmitting “downwards”, and missing the planet that you would be able to pick up easily.

if the signal is relatively directional I reckon it wouldn’t be reliable

Speaking from a point of ignorance…

I would not expect off-the-shelf GPS gear to work for the task you describe but I would expect that you could write software to handle it, albeit with less positional precision.

dv said:

Speaking from a point of ignorance…

I would not expect off-the-shelf GPS gear to work for the task you describe but I would expect that you could write software to handle it, albeit with less positional precision.

you’re right

to be honest I would favour my own transmitters/ lasers at known earth based gps co ordinates and triangulate

Why lasers?

dv said:

Why lasers?

you are bouncing a signal off the reflector on the spacecraft (as opposed to the moon laser experiment) , the reflector guarantees return, the lasers give a relatively tight field of fire.

see my previous thoughts

wookiemeister said:

dv said:

Why lasers?

you are bouncing a signal off the reflector on the spacecraft (as opposed to the moon laser experiment) , the reflector guarantees return, the lasers give a relatively tight field of fire.

see my previous thoughts

its the poor mans space radar

dv said:

Why lasers?

Have you seen what lasers can do?

wookiemeister said:

wookiemeister said:

dv said:

Why lasers?

you are bouncing a signal off the reflector on the spacecraft (as opposed to the moon laser experiment) , the reflector guarantees return, the lasers give a relatively tight field of fire.

see my previous thoughts

its the poor mans space radar

Lasers are improving with technology

How difficult could it be to navigate to the Moon?

I mean, seriously… Point nose at moon and press throttle.

Sheeesh…

Rule 303 said:

How difficult could it be to navigate to the Moon?

I mean, seriously… Point nose at moon and press throttle.

Sheeesh…

Not quite. But I agree that knowing the geocentric latitude & longitude of a spacecraft on a lunar trajectory is of limited usefulness.

See Trans-lunar injection

PM 2Ring said:

Rule 303 said:

How difficult could it be to navigate to the Moon?

I mean, seriously… Point nose at moon and press throttle.

Sheeesh…

Not quite. But I agree that knowing the geocentric latitude & longitude of a spacecraft on a lunar trajectory is of limited usefulness.

See Trans-lunar injection

you’d need to know if you were on the right trajectory

wookiemeister said:

PM 2Ring said:

Rule 303 said:

How difficult could it be to navigate to the Moon?

I mean, seriously… Point nose at moon and press throttle.

Sheeesh…

Not quite. But I agree that knowing the geocentric latitude & longitude of a spacecraft on a lunar trajectory is of limited usefulness.

See Trans-lunar injection

you’d need to know if you were on the right trajectory

The advantage of orbital navigation is that if you get it wrong first time around, you can just wait a while and have another go on the next lap.

Stealth said:

wookiemeister said:

PM 2Ring said:

Not quite. But I agree that knowing the geocentric latitude & longitude of a spacecraft on a lunar trajectory is of limited usefulness.

See Trans-lunar injection

you’d need to know if you were on the right trajectory

The advantage of orbital navigation is that if you get it wrong first time around, you can just wait a while and have another go on the next lap.

you might not have enough fuel to do that

the yanks had to make sure they had got things right before they went for TLI, they then checked if they were on the right path throughout the mission by eyeballing the stars and comparing the result with the accelerometers onboard. I think they were also bouncing radar off them to see where they were.

the Russians were also watching carefully, this is why the conspiracy story about the moon doesn’t add up. if the americans had pulled a fast one the first ones to know would have been the russians

The advantage of orbital navigation is that if you get it wrong first time around, you can just wait a while and have another go on the next lap.

depends on initial conditions. one plan for a mars mission is what is termed a free return trajectory it is also applicable to any two body mission though.

http://en.wikipedia.org/wiki/Free_return_trajectory