The crux of the argument about near-c rocks as weapon in regards to sensing them isn't the sensitivity of the sensors, it how light behaves around a near-c object. I don't know the math well enough to explain it in detail, but let me try an explanation. Assume the speed of light is 1000 (in whatever units of velocity). A ship moving at 90% of light speed would be moving at 900 (units). Any light coming off of the object is moving at a velocity (relative) of 100 (units). So the issue becomes the wave of light signals that say there is a dangerous object moving toward you is very close to the object itself. So regardless of how good your sensors are, the signal is at most a few hours ahead of the object. And more likely minutes ahead of the object. Especially if the object keeps acceleration. So there would be this massive way of reflected and emitted light showing something was coming and, with no time to react, the object itself. You are correct, that there is no stealth, the object will have a great deal of reflected light, emitted heat blue-shifted into the visible spectrum, and radiation from impacts as it comes toward your unsuspecting planet. The warning arrives too late to do anything (much) about stopping the ship. On the other hand, just blowing up the ship doesn't stop the damage. The kinetic energy of the system still exists. You have a large mass moving very fast. It doesn't matter if the mass is a solid object or just a close set of particles. All that energy is going to be dumped into the target. In fact, for calculation purposes the binding energy of the atoms in the object are largely irrelevant. For damage calculations you will be treating it like a large blob of plasma moving at relativistic velocities. If the weapon has enough mass/velocity to crack a planet, the only thing that will stop that is... another planet. On Sat, Mar 15, 2025 at 11:33 PM Jim Vassilakos - jim.vassilakos at gmail.com (via tml list) <xxxxxx@simplelists.com> wrote: > > Obviously, I am posting this with some measure of trepidation, as I am aware that this topic (near-c rocks) incited at least one flamewar at some point in the TML's history. Granted, we were all a bit younger then. And I'll have you know I didn't partake. Indeed, I barely observed. I was aware of people yelling at each other, lots of all-caps and exclamation points, but the math was too much for me to bear. Nonetheless, it underscored for me yet another aspect of Traveller that seemed broken. > > The argument goes like this. Near-c objects of any kind (rocks, missiles, starships, etc) are easily the most destructive of WMDs, and starships in Traveller, by the very nature of how maneuver drives work, are all capable of delivering a payload of such objects to any planet they'd like to convert into an asteroid field. It would take a little bit of time and effort, granted, but the upside is that after all is said it done, it would be very hard to figure out who initiated the attack, and if you don't care about anonymity, it's also a great way to begin a war. > > The crux is that in Traveller, you don't need a Deathstar. Even small ships could perform this attack. Indeed, it could probably be performed sans crew. Just jump to some location well outside the starsystem and before you disembark to your getaway craft, tell the computer to accelerate toward Alderan and not to let up on the gas. It will take a long time for the ship to reach relativistic velocities, but there's nothing stopping it from doing so. > > However, there's one potential problem, and it has to do with stealth or rather the lack thereof, as this attack (in my uninformed opinion) requires the element of surprise. I'm no physicist, but I'm guessing that any object accelerating to a relativistic velocity will unavoidably collide with the interstellar medium, a very thin fog of hydrogen atoms. The current best guess is that there's about one atom per cubic centimeter, or about a million per cubic meter. Any object colliding with them will likely tear away electrons and perhaps generate some radiation in the process, perhaps enough to give the target planet some advance warning, assuming they're got any astronomers worth their salt. I'm imagining there would be some sort of detectable emission, and so if the planet has detectors in orbit watching for this sort of thing.... Obviously, it all boils down to the sensitivity of the detectors and how much radiation would likely be emitted. > > I've looked for information on the sensitivity of sensors in Traveller, and I haven't found very much. My guess is that the best version (the set with the highest correspondence to reality) are the rules outlined in the T4 version of Fire, Fusion, and Steel, pgs. 72-73, where it says that for Passive EMS, detection probability can be derived from the signal strength (Table 195 on page 109), which is itself computed using this formula: signal signature + sensor sensitivity (Table 198 on page 110) – range (Table 194 on page 109). But what would those values be for this specific scenario? > > Assuming the planet gets advanced warning, its SDBs can move to intercept. If they can hit the near-c object before it reaches the target, the explosion will, I'm guessing, vaporize the incoming threat. Actually, any impact, even a small one, would (again I'm guessing) turn the incoming payload into a white hot plasma. It would be very tricky, because due to the relative speeds, they'd only get one shot, but if they could connect with it, I'm thinking it would be like a nuclear explosion in space, one that spreads from the point of impact like a cone, so only a small fraction of the initial payload would ever hit its target, although even this might still be enough to disrupt the target planet's magnetic field, assuming it has one. > > If this analysis is true, then this solves the question of why this sort of attack isn't perpetrated by invading militaries or terrorist organizations. Otherwise, it seems like a big, gaping vulnerability. But I'm not sure about passive sensors detecting the incoming threat from so far away. Is this realistic? Is it permissible under Traveller's sensor rules? > > ----- > The Traveller Mailing List > Archives at http://archives.simplelists.com/tml > Report problems to xxxxxx@simplelists.com > To unsubscribe from this list please go to > https://www.simplelists.com/subs/ -- Thomas Jones-Low xxxxxx@gmail.com
