# How to catch those beating red light in space?

In the year 2155 C.E. humans colonized the solar system and eventually settled on the ninth planet, interplanetary travel is very common and the authority wants to monitor every space vessel for contraband materials. To make matters worse, there are private companies building ships that travel really fast -- so fast indeed, that the ship itself becomes invisible to the traffic light cameras, as the light reflected from the ship chassis is being shifted outside the camera spec range. (their minimum speed is at 0.6c -- also note no FTL!)

Speed limit set at 1c in vacuum, food for thought.

How can we catch those spacecraft that beat traffic light cameras?

• Doesn't one c = the speed of light? Or am I just confused? – Xandar The Zenon Mar 20 '16 at 5:14
• @XandarTheZenon: do not be concern with the constant at the moment, it's a trap meant for those physics-challenged reader! I'm trying to catch people who don't stop at red light not those that break laws of physics😁 – user6760 Mar 20 '16 at 5:26
• I hoe you realize just how impossible this is. Space is so huge and empty there isn't a whole lot of danger of hitting another spaceship, or really very much of anything until you get close to a planet. So it would make more sense to have police around the planets themselves. – Xandar The Zenon Mar 20 '16 at 13:58

## 4 Answers

No problem. Initially ultraviolet light will be shifted in to the visible range. Or, use a more suitable (IR) camera for the purpose.

The whole thing is silly anyway, so I don't think you want real amswers.

Hmm, it's the 22nd century and we're still using traffic lights and optical cameras in outer space? Well, if the government wants to start monitoring vessels for smuggling at such a late time in mankind's development in space, they must have had a pretty stable economy so far to not care about the losses in trade revenue. Get your engineers to start setting up new detection systems -- radar, heat detection, there's loads of options. Anything that can detect a passing body and then realize that it hasn't stayed there for the allotted amount of time.

Your best weapon would be intelligence.

You could use tachograph-equivalents that would record speed, position, resting times, etc. These are found on trucks, buses and other large vehicles to make sure drivers respect speed limits and stop to rest. Say, if you ever caught a ship with a falsified tachograph (or lack thereof), they'd be in trouble.

However, the tachograph would only serve to prove wrongdoing, not help catch the wrongdoer. So your first bet at catching them would be random controls. Also controls directed at companies known to play with the limits of legality. In other words, standard police work.

Second way, assuming there's some of traffic control in and out of planets like there are in naval/air ports, you would know which ships leave planet A and which arrive at planet B. If planets A and B exchange the relevant information, you could know if a ship travelled way over the limit, and maybe if they stopped on route for a suspicious amount of time. If it's a day's travel and it took them two, maybe you can start asking questions.

Another solution would be to monitor their navigational computers. I would assume a spaceship would require a space-GPS of some sort. So, much like intelligence agencies can track you based on your smartphone GPS, you could have your agencies track ships based on their onboard space-GPS. Tracking one precise ship should be fairly easy, though tracking all the ships to catch suspicious behaviours would require a little big more.

First, GPS-listening stations/satellites all over. Depending on the political structure of your world, cooperation between foreign agencies could be required. Then you'd need a way to compute all the data you gathered across the whole solar system.

Depending on the computing power at your disposal and your communication infrastructure, you may only have a daily list of suspicious activities as opposed to real-time tracking. It depends on how effective and up-to-date you want it to be.

These solutions aren't mutually exclusive. Obviously, this only works if your justice system can inflict dissuasive penalties on any offender.

• "I would assume a spaceship would require a space-GPS of some sort." You assume wrong. (Keep in mind that velocity is just distance divided by time, so if you have two 3D positions and a time between them, you can trivially calculate your average velocity between those points. Integrate as needed.) – user Apr 25 '16 at 14:32

The offending ships, of course, would respond by throwing out their beer cans. An empty beer can weighs about 14 grams. At 0.6 c, ignoring relativistic effects, the impact of a beer can will release about $$E = \frac{mv^2}{2} = \frac{(0.014)(1.8\times 10^8)^2}{2} = 2.3\times10^{14}\text{ J} = 575\text{ kT}$$ of energy. So retrieving the film may be a problem. It's really hard to make a cheap traffic cam which will take a half-megaton blast.

• ??? I'm not sure I see your answer... And don't worry I didn't down vote you. – Aarthew III Mar 21 '16 at 5:24