Outer space scanning

[Ivan Tuzikov]

In which ranges of the E.M. spectrum was the Geospace and interplanetary space scanned? And to which distance? And to which distance was the outer space scanned by radars in order to avoid obstacles for unmanned interplanetary flights?

[pavelcherepan]

First of all, the space is big, like really-really big and it's so much harder to hit something than not to. Even within the main asteroid belt distances between objects large enough to be spotted by current technologies (several meters) can be in the range of a million kilometers or more. So with that in mind there's not much danger at all that you're going to crash into stuff.

 

At the same time asteroids do get routinely observed mostly using either visible or infra-red part of spectrum. Radars are not very useful for this purpose because of their wave length. You can only use radars to locate larger objects, but then you can use visible light and get more precision.

Edited January 5, 2016 by pavelcherepan

[Ivan Tuzikov]

And what about monitoring spacecrafts of different countries? Which methods are used besides visual monitoring through telescopes? And to which distance?

[EdEarl]

And what about monitoring spacecrafts of different countries? Which methods are used besides visual monitoring through telescopes? And to which distance?

Spacecraft usually transmit data, so they can be tracked without radar.

 

Arecibo can be used as a radar and can track Saturn and has imaged the asteroid 4769 Castalia which is about 1km size.

[Ivan Tuzikov]

Spacecraft usually transmit data, so they can be tracked without radar.

 

Arecibo can be used as a radar and can track Saturn and has imaged the asteroid 4769 Castalia which is about 1km size.

Thank you, everything is clear.

[Enthalpy]

Collisions were a concern very early in space exploration, say before Pioneers were launched. These told not to worry. Meanwhile, spacecraft have passed through the rings of Saturn without noticing anything, because even these are essentially void.

 

Intercontinental ballistic missiles are tracked by several ground-based radars. Norad has some in northern America, Russia has (or at least the Soviet Union had) one in Krasnoyarsk and elsewhere. The aim was to shelter the populations and start a retaliation strike. Meanwhile it may help trying to intercept the missile.

 

Consequently, people launching a rocket or satellite tell it in advance to the world to avoid misunderstandings and undesireable consequences. Essentially, international organisms attribute a number to every new orbital object. There might be objects that were not declared, but very, very few.

 

Said radars follow every object in low-Earth orbit down to a non-disclosed size that may be like 0.2m, even passive ones. A concern is that they can't detect smaller debris from past collisions. In geosynchronous orbit, they detect every object but bigger, possibly 0.5m.

 

Then, you have just telescopes. Satellites are very visible when they get sunlight but the observer stays in the night and are an annoyance to astronomers. I saw once with naked eyes at ~800km distance a Progress (20m²?) following Mir, so a D=1m telescope instead of a D=1cm eye must see 20cm² objects at that distance. Small amateur telescope see geosynchronous (36.000km) easily, bigger telescopes and special software see smaller ones.

 

A Lidar must be better, especially if based in space.

[EdEarl]

Radars see microwaves (EMF) and people see light (EMF). We see things that are bright enough and cannot see things that are not. A radar is similar, they can see things that are bright enough. Object brightness depends on size, distance physical properties.

 

Physical properties of EMF and objects are related in complex ways. Both microwaves and light can be emitted or reflected by an object. Reflections are brighter for mirror like objects and dimmer for dark or black colored objects; although, a mirror for light may not be a mirror for microwaves and an absorber of light may not be a absorber of microwaves. Generally objects emit, reflect and absorb various wavelengths EMF in various amounts, continually.

 

Large telescopes and large antennas serve the same purpose, to capture more EMF to make objects brighter and clearer (better resolution).

 

Two objects of equal brightness may vary in size, distance and physical properties. Thus, some very distant, bright objects appear the same as very small, bright objects, whether radar or light.