Imagine there was another Earthlike planet in our system

[Derren]

I was under the impression that detection of ballistics was not a sure thing. Would a stealthed rock on an odd approach be easy or hard to detect?

The cold war made sure that we are quite good in detecting launches.
The real problem is heat. Detecting a cold rock in space is hard (and we can still do it), detecting something that is emitting heat is very easy .

 

[jonesy]

Response is to "You can't attack by surprise."

I was under the impression that detection of ballistics was not a sure thing. Would a stealthed rock on an odd approach be easy or hard to detect?

Stealth in space is impossible. Any measure to hide yourself results in another way that you can be seen (of course I'm assuming here that we'd have the detection network ready. At the moment we are only looking at a portion of the sky). Ballistics are difficult to see when they go through an atmosphere. The hardest to detech things in space are the really small and the really fast. And like I inferred earlier, the moment that the speed of the projectiles becomes faster than the ability to see them the whole concept of starting a war becomes crazy, because at that point we are talking about planet busting weapons and then the war options are cold war or xenocide.

 

[Umbran]

The cold war made sure that we are quite good in detecting launches.

We are good at detecting launches from Earth. There's lots and lots of cameras pointed downwards, and lots of radar dishes scanning the atmosphere.

Stealth in space is impossible.

Yes... and no. As the man said - Space... is big. Really big. You just won't believe how vastly hugely mindbogglingly big it is.... So, "stealth" may be difficult. But, on the other hand, we cannot actively probe the entire sky with radar. We cannot yet even manage to actively *watch* the entire sky at once. Smallish, dark objects that aren't under active thrust may well go unnoticed until it is too late to do anything about them.

 

[Dannyalcatraz]

Smallish, dark objects that aren't under active thrust may well go unnoticed until it is too late to do anything about them.

Pygmy Space Jump Commandoes?

 

[jonesy]

Pygmy Space Jump Commandoes?

Hmm. Self Replicable Robot Pygmy Space Jump Commandoes?

 

[Derren]

We are good at detecting launches from Earth. There's lots and lots of cameras pointed downwards, and lots of radar dishes scanning the atmosphere.

And the instant we know that there is intelligent and technologically equal (which means that they can launch weapons towards us) those dishes will point up.

we cannot actively probe the entire sky with radar.

IR is the way to go. All man (+ alien) made objects with their own propulsion will emit heat.

 

[Umbran]

And the instant we know that there is intelligent and technologically equal (which means that they can launch weapons towards us) those dishes will point up.

And be useless. They're all short-range. We don't have the capability to blanket the entire solar system from, say, Jupiter inwards with active radar. The power requirements alone would be absurd.

IR is the way to go. All man (+ alien) made objects with their own propulsion will emit heat.

Pretty much everything that the sun shines on emits heat. If it is using something a bit more passive, like a solar sail, it may appear just like a large rock in IR.

 

[dark2112]

No trader traveled on the whole silk road. Goods were transferred from one outpost on the road to the next where someone else would buy it and continue to the next outpost. And emissaries and pilgrims whos destination was on the other end had plenty of time and could rest along the way.

People of that time were very certain that India existed (thats what they were looking for)

http://en.wikipedia.org/wiki/Marco_Polo
http://en.wikipedia.org/wiki/Giovanni_da_Pian_del_Carpine

You could argue that Marco Polo was an explorer, not a merchant, at that stage of his life, and Giovanni was technically a courier, but 20 seconds of research discovered two people who had traveled the silk road. I'm sure there were more, although certainly not a majority. It was more common, as you said, for a merchant to travel a small section, trading goods between outposts.

As for India, he was technically aiming for the orient, and insisted that the lands he discovered were in fact part of Asia. I suppose I could have worded my sentence a bit better, as it was largely popular sentiment at the time that the world ended, and not the opinion of the educated elite, but even they doubted that a western passage to Asia would be feasible, and if I recall correctly, the distance he initially proposed was somewhere around half what he actually traveled to reach Cuba, with no re-supply.

 

[Morrus]

And be useless. They're all short-range. We don't have the capability to blanket the entire solar system from, say, Jupiter inwards with active radar. The power requirements alone would be absurd..

Or, indeed, more than a few percent of the sky at any one time.

 

[Morrus]

as it was largely popular sentiment at the time that the world ended, and not the opinion of the educated elite

That's a myth invented by popular fiction. The flat earth was never a popular opinion. Even uneducated medieval folk could see that was ludicrus; there's no shred of evidence to suggest that such a thing was a widespread opinon at any time.