Update : Nose gear is missing and I wanted to know how to make my own instead of buying one. Any answers?

As far as private airplanes, only call sign approved is the aircraft registry -
G-ABCD in full, abbreviated to Charlie Delta after first call -
In USA, the registry is often known as the "tail number" -

Airlines have call signs approved by ICAO, if not they use registry -
Either the regular airline name, such as Argentina 1234 -
Or the "airline call sign" - British Airways has "Speedbird" approved -

It was built to do specific research on high speed, high altitude flight, once they had all the information they could get from it, there was no point in continuing to fly an expensive and rather risky experimental aircraft.

Have to agree though, it was one hell of a machine!

It depends a lot on the jet and where it is and the conditions it is landing in, bearing in mind that it probably needs to be able to take off again.

As an example, some good few years ago I used to fly a DH125 (better known now as the Hawker 800 XP) around Australia

There were many 4-5000 ft runways in the lower and cooler parts of Australia that we could use with ease.

But Alice Springs, for instance, in the centre of Australia at about 1750 feet altitude, had 8000 ft of runway and was really too short to be safe in anything much over 30 degrees C, which was a cool day in Alice.

Not so much for landing, but if you wanted to get away before it got dark, you were pushing your luck. It needed to cool down considerably first.

It is less of a problem with today's more powerful aircraft, but you will generally always be able to land small jets on runways you can't take off from, so the question of landing distance is secondary.