Space sensors

ScumLord

Sci-fi would have us believe that finding things in space is pretty straight forward, fire up the sensors and they can tell you where something is, what it is and even if there' people alive on it.

A lot of our methods for understanding space seem to be based on light or radiation, we need to see it or radiation coming off it (often that radiation is measured as light as far as I know).

So say you have two identical space ships, a mile cubed and they're flying in tandem 10 miles apart, they're half way between our sun and the next nearest star. Would there be enough light coming from all the surrounding stars to even see the ship across from us. How bright is deep space once there's something there to reflect the light?

If the space ships didn't emit any light themselves would there be any way of actually knowing it's there?

Outside of light and maybe some way of measuring microgravity fields (can that be done) is there any other way of finding things in space?

If you could measure the micro gravity an object is creating by its mass, how up to date would that information be? Does gravity travel instantly is there a time delay? If I was just looking at a space ship using light I know that by the time I see that ship it's no longer where it was and I have to predict where it is currently. Is the same true for gravity measurements?

Would it basically be very easy for a ship to hide in space and would that ship go completely unnoticed if something wasn't actively looking for it?

riffmongous

ScumLord wrote: »

Sci-fi would have us believe that finding things in space is pretty straight forward, fire up the sensors and they can tell you where something is, what it is and even if there' people alive on it.

A lot of our methods for understanding space seem to be based on light or radiation, we need to see it or radiation coming off it (often that radiation is measured as light as far as I know).

So say you have two identical space ships, a mile cubed and they're flying in tandem 10 miles apart, they're half way between our sun and the next nearest star. Would there be enough light coming from all the surrounding stars to even see the ship across from us. How bright is deep space once there's something there to reflect the light?

If the space ships didn't emit any light themselves would there be any way of actually knowing it's there?

Outside of light and maybe some way of measuring microgravity fields (can that be done) is there any other way of finding things in space?

If you could measure the micro gravity an object is creating by its mass, how up to date would that information be? Does gravity travel instantly is there a time delay? If I was just looking at a space ship using light I know that by the time I see that ship it's no longer where it was and I have to predict where it is currently. Is the same true for gravity measurements?

Would it basically be very easy for a ship to hide in space and would that ship go completely unnoticed if something wasn't actively looking for it?

Well you could try sending out the radiation yourself if you have some sort of idea where something is, like radar. And the spaceship will probably give off it's own heat signature too, so you could just look for thermal radiation either. In short, use other wavelengths than visible light.

Rubecula

Radar would work

ScumLord

When would radar start to become ineffective? If the other ship was 10,000 km away how hard would it become to find?

If the ships are friendly and want to keep track of each other it would probably be straightforward enough, but how easy would it be for two ships with an entire solar system to hide in, to hide from each other? Or rather than an entire solar system, between the asteroid belt and the kuiper belt. ( I'm assuming the closer you get to the sun the easier it would get).

How likely is it that if a ship didn't announce itself that it would pop up on some sort of sensor, whether it just be visual tracking or radar?

riffmongous

ScumLord wrote: »

When would radar start to become ineffective? If the other ship was 10,000 km away how hard would it become to find?

If the ships are friendly and want to keep track of each other it would probably be straightforward enough, but how easy would it be for two ships with an entire solar system to hide in, to hide from each other? Or rather than an entire solar system, between the asteroid belt and the kuiper belt. ( I'm assuming the closer you get to the sun the easier it would get).

How likely is it that if a ship didn't announce itself that it would pop up on some sort of sensor, whether it just be visual tracking or radar?

Well there is the radar equation



It's a 4th root (if the transmitter and receiver are at the same place, otherwise its (R^4 = tx^2 * rx^2)) so the received power drops off very quickly with distance, but I don't know remember enough some of the other numbers to tell you too much...

Although, you could calculate it from one the max range example from this page
http://de.mathworks.com/help/phased/ug/radar-equation.html

adjusting it for the numbers from this astronomy radar, but who knows how radars will have developed by the time such large spaceships are possible.. http://www.naic.edu/~nolan/radar/radarstatus.html

A better option to track someone trying to hide would maybe be to monitor for radio signals using a dense solar system wide network of radio stations listening for signals, just like how you can get the rough location for a mobile phone..

Capt'n Midnight

You could also see it by occulation of background stars.

Perhaps by the way it blocks the microwave background radiation.

But these would only work close up. Since most of our tech is located on earth then it would be trivial to stay hidden upon approach until you get close.

Once upon a time the military wanted moon bases to launch missiles from. Forgetting that it would take several days for them to arrive on target.

Rubecula

Capt'n Midnight wrote: »

Once upon a time the military wanted moon bases to launch missiles from. Forgetting that it would take several days for them to arrive on target.

Depends on velocity

Capt'n Midnight

Rubecula wrote: »

Depends on velocity

Even so there'll be nothing quite as short as a four minute warning.

2 stroke

Rubecula wrote: »

Depends on velocity

Don't forget about misiles burning up on reentry.
Might make some sense now with lasar cannons.

Maximus Alexander

You'd have to be venting heat, which would probably mean IR radiation, otherwise your spacecraft would just keep getting hotter and hotter until everyone aboard died / it melted itself to slag.

Of course if you were actively trying to avoid detection there would probably be plenty of ways around this. You could probably store up heat and then switch on the radiators intermittently. You could direct it away from whoever was looking for you, if you knew where they were.

I'd love someone to do the numbers on how sensitive your detector would need to be to pick up reflected starlight in interstellar space, for say, a body with the albedo of the moon.

riffmongous

I suggested thermal earlier as well but after thinking about it a bit more, I thought of a potential problem, and it's a nice physics problem for anyone interested, what sort of resolution sensor (camera) would be needed to detect another spaceship of a certain size and at what minimum distance? Against a cold space background it will be easier I guess, but I wonder how much