Relativistic Weapon
A Relativistic Weapon is a mass-device such as an asteroid that is hurled at a planet, accelerating to relativistic, near-FTL speeds.
Description (Specifications)[edit]
Reactionless drives in theory allow unlimited acceleration times, so long as fuel and power are available. Given this fact, what's to stop someone using asteroids (or small craft such as lifeboats) as relativistic (i.e. near the speed of light) projectiles against unsuspecting worlds? Doesn't this capability give any spacecraft owner access to a weapon of unbelievable power?
In theory, yes. But there is little documented reference to this ever having happened, even though the physics clearly allow it. To find out why, we must look into what has historically prevented it.
History & Background (Dossier)[edit]
While it is not impossible for this to happen, and there have been a very few documented cases of it, there are several reasons that reduce the odds of this happening.
Doing this is not useful for any aim other than to exterminate whoever lives on the planet. Whatever infrastructure and population is at the impact site is destroyed. While there are a number of entities in Charted Space for whom destruction is occasionally the intent (such as K'kree against a world of unrepentant meat eaters), doing this throws up enough debris that it degrades living conditions across the world, lowering the world's value for any would-be conquerors. Mobile military assets typically have plenty of warning and are able to evacuate the impact sites - if there are enough impactors to target most of the military assets in the first place.
Which means that anyone setting up to do this, is advertising that they wish to commit mass murder. In almost any healthy starfaring society, even at the depths of the Long Night, advertising that one wishes to commit mass murder is an invitation for heroes (law enforcement if available, otherwise vigilantes) to prevent the scheme before it can start. There are no records of exactly how many groups filed a flight plan to do this, and were consequently detained without incident before they could take off. Although not filing such a flight plan might be obvious in hindsight, such groups were generally not gifted with foresight (if they had been, they would have chosen means other than relativistic weapons in the first place), nor did they get a chance to learn from experience.
It has probably been done, as a proof of concept, against worlds in uninhabited systems where there was no one, outside of the crew performing the feat, to witness and document it. Such one-off exercises are generally not widely recorded, as they are no more impressive than shoving a boulder around on a world's surface. Indeed, belters - especially ones working for belt mining corporations - will sometimes perform similar but low-velocity transfers of large numbers of planetoids for efficient mining and processing.
Generally, any target worth enough to do this against will be defended. A far more common trouble is for some small, poorly maintained starship to jump in, then its maneuver drive to fail en route to the world, turning it into an accidental version of this. Most starports that either contain or are next to significant value, have sufficient weaponry to either deflect such a ship or to render it into small pieces, especially where there is an atmosphere for the pieces to burn up in. Nearly all such starports also have sensors sufficient to surveil their entire solar systems, with sensors bigger and more distributed (and thus able to detect things at far longer ranges) than on any ship smaller than a World Class Ship (almost by definition), which will detect incoming planetoids - even ones moving at near-c, even ones that "go dark" (shut down all power-using systems) after getting up to speed - in time to fire upon them.
For any target without such protection, ortillery is far simpler and lower cost, to the point that has been preferred over relativistic weapons in nearly every recorded instance. A single 100-ton ship with a single laser turret is entirely capable of erasing an entire city - reducing it all the way down to a crater (possibly containing the most heavily armored parts such as bank vaults, depending on how armored they are and what sort of laser turret was used) - over time, if the city has no way to strike back.
Most systems with a planetoid belt have certain planetoids that may already be on course to impact the mainworld, without hostile parties giving them a push. This risk is known to most spacefaring civilizations even if they have yet to invent maneuver drive. As such, "look for incoming planetoids" is often among the first duties of a starport on a new colony. By the time the colony is large enough to be worth bombarding, this capability has been developed for decades if not centuries.
And then there are those worlds that fear military attack, and thus have deep site meson weapons and similar protections. While they may be scaled to annihilate mere capital ships, they are also sufficient to deflect larger planetoids.
It takes careful survey work to find a planetoid big enough, and cohesive enough, to serve as a projectile. Many planetoids suitable for mining are collections of gravel, which might fly apart if accelerated without caution - and if the target has a significant atmosphere, would disintegrate in the atmosphere without significantly impacting the planet's surface. Careful surveying can find a good planetoid, but anyone with the patience and equipment to do that can usually earn a good living as a belter, which tends to sap any motivation to annihilate planetary populations.
There are documented tales of would-be terrorist groups sitting around, complaining that they can not find anyone willing to do this work for them, with an unstated but obvious implication that they were unwilling to do this work themselves (perhaps finding it unthinkable that they should personally have to undergo weeks of labor in order to achieve their ends), which conversation was how law enforcement identified the would-be terrorists.
Aiming from far away is an issue. While it is known where a planet will be at a certain time in advance, small pebbles (which would be micrometeories were they to survive atmospheric entry) encountered on the way can inflict significant damage, or at least subtly alter the planetoid's course. The engines can generally correct early on, but the closer and the faster the planetoid is, the bigger the deflection. It is entirely possible for a debris cloud - or a few carefully-aimed torpedoes - to cause such a planetoid to simply miss. Slowing down and coming back around is often impractical if not impossible.
Even worse are attempts to accelerate from the next system over, at least a parsec away. Even at relativistic speeds, this takes over a year to set up and execute. Even if the target has no scouts or contacts in that next system to warn them, typical planetary sensors will detect the occlusion of light from the star and thereby detect the incoming object well before it reaches the target system. Correction for light lag (by the time the sensors detect the object, it is no longer at that location) is a simple extension of functions that have been part of standard fire control software for thousands of years. There are a variety of countermeasures that can be taken to deflect the object (not destroy it, as that would leave fragments moving at relativistic velocities), most simply constructing and launching another planetoid to intercept in deep space. More importantly, conditions may change over a year - and objects in the interstellar void have, collectively over the parsec or more between systems despite the lower density per unit volume, even more potential to deflect such a weapon.
In certain editions, maneuver drives can only achieve maximum effectiveness near a planet, meaning that accelerating through space away from a planet requires an excessively long time to set up such a bombardment (many thousands of years, enough to wipe out any possible cost savings and not serving any desire to wipe out the current inhabitants), and/or can only achieve a certain maximum speed (far slower than what is generally termed "relativistic").
Even without this limitation, most maneuver drives require a long time to accelerate to significant fractions of light speed. To achieve 0.9c at 1 G takes a bit over 27.5 million seconds, or nearly 319 days. Even at 10 Gs, it takes more than a month of constant acceleration to reach 0.9c. This is without taking time dilation into effect, which would make it take longer from an outside perspective (such as the target's).
References & Contributors (Sources)[edit]
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- INTERNAL LINK: Traveller Mailing List/FAQ
- Author & Contributor: Lord (Marquis) and Master of Sophontology Maksim-Smelchak of the Ministry of Science
- Author & Contributor: Adrian Tymes