By the time radar gets reading back the enemy not only will be in different place, he will be twice as much further. I don't need IFF to know how, let's say, MiG-29 looks like.
Right. But what does a Mig-29 look like three hundred thousand kilometers away?
It looks like nothing, because you can't see it.
There is plenty of telescopes, not only optical ones and being passive sensor they cut the time of data gathering by half.
There are plenty of types of image recognition software as well, but if we're not allowing far-future technology (not that accurate image recognition is particularly far future), then we're stuck with the telescopes we have, not hypothetical wonder-telescopes which can somehow scan the whole sky, form a perfect image of such amazing resolution that it can identify the features of objects hundreds of thousands of kilometers away and somehow convey all this to a human pilot. In this case, it doesn't really matter what part of the electromagnetic spectrum you use, it's about the resolution. If you want to cover the whole sky, then the amount of radiation directed at any given point in the sky will be smaller, which hurts the quality of the image.
Also, part of an active sensor which receives the reflected radiation is also a passive sensor.
Remember that if you send artificial signal, be it for IFF or radar, you pretty much give away your position.
No you don't, because the signal takes time to arrive at its destination, and in the intervening time you would probably want to change velocity.
This is the major challenge of any kind of space warfare. The distances involved are so large that in the time it takes light to cross those distances the object itself will always have a chance to change velocity. Therefore, predicting the trajectory of an object becomes increasingly difficult the further away that object is. Thus, the position of combatants in a space battle is always uncertain. However, if you were thinking of trying to hide and be stealthy, then carrying a human crew is a pretty poor idea because humans need a nice warm atmosphere to live in, and the background of space is very cold.
And limited fuel won't let you manoeuvre indefinitely.
Which is why ideally you want to reduce the payload mass of your spacecraft as much as possible. One way to do this would be not carrying several tons of life support equipment.
Space won't give you that much interference but it doesn't mean there won't be any.
In which case, the same would be more true of trying to passively scan for visual images. The only difference between pinging actively and scanning passively is that pinging actively creates a signal which can then be reflected back onto the reciver, making it more likely something will show up. Without that, you're just pointing the receiver at things and hoping they are emitting enough radiation.
Also enemy may wish to deploy countermeasures and, in your example, there will be no one onboard to know better.
What kind of countermeasures, and how would a human be able to identify them? Remember, the human can't see anything.
No, space is not really, really, really empty. There are stuff in it, planets, black holes and all that.
http://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html
As I've said, the scale of space is not something we are really neurologically equipped to imagine. This little diagram may help to give a vague sense, however, of just how utterly vast the spaces between the various objects in space actually are, and just how utterly insignificant they are in size relative to the emptiness between them. There really is almost nothing out there. It is nothing like earth's oceans. It is nothing like earth's atmosphere. It is a whole different, completely alien environment with a completely different scale to anything we have previously attempted to conceive of or understand. No theoretical knowledge about naval warfare is going to apply. No theoretical knowledge about atmospheric aircraft is going to matter. Realistically, anyone wishing to engage in space warfare must start from the premise that they are fighting in space, and design vehicles which are best suited to the particular features of space itself.. i.e. that space is very big, very empty and very hostile to living things.
As I keep saying, there's nothing wrong with imagination and fiction, but they are just that.
