So, Earth has run afoul of an alien power. The aliens have a working FTL drive, but no one else (including us) does. They have used their technological superiority to create a far flung mercantile empire (think East India Company on steroids, that eventually co-opted the government).

It turns out that Negative Mass is the secret ingredient, and it is quite possibly the rarest thing in this section of space. The aliens found a supply centuries ago, and kept it to themselves. They guard their secret jealously, allowing no one else to even get a peek of how it works.

Then we humans stumble upon a supply of our own, and all hell breaks loose.

The aliens will stop at nothing to take it away from us, but unfortunately they are merchants, not warriors. However, there is a planet that has specialized in producing mercenaries. They have a working relationship with the merchants, since they are the only ones that can transport them from one system to another. So they hire the mercs, transport them to Sol space, and let them do their dirty work.

We humans know they're coming. We can see the FTL ship approaching. Our own fleet is armed and ready, guarding Earth and Luna (a smaller force is guarding Mars, which has been colonized. Sadly, the mining colonies on Ceres and Vesta are on their own). Their mission is simple...grab the Negative Mass from a base on Luna, bomb a handful of cities on Earth to make a point, and leave.

Now what?

I know, there's no such thing as stealth in space, but how can I give them a fair chance of success? Figure the humans are using destroyer sized vessels, while the mercenaries are equipped with smaller gunboat-type craft. The aliens have a slight edge on weapons, but having the smaller force that's something of a wash.

I don't need them to win, I just need them to realistically hold their own for awhile. Also, once they are dropped off by the merchants, they have no choice but to stay in Sol space until the contract is complete.

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    $\begingroup$ Have you read any military space opera? Something from the Honorverse, or maybe The Lost Fleet? In particular, David Weber (of the Honorverse) went to great lengths to define a reasonably coherent set of rules for the countless men-o'-war mercilessly slaughtered in his novels; his space battles are truly exciting, because the tactics make sense. And, if you have FTL, there just may be stealth in space; after all, stealth in space is at least within the realm of normal physics... $\endgroup$
    – AlexP
    Commented Apr 14, 2019 at 10:31
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    $\begingroup$ Sounds like an interesting story. How your humans manage to hold their own is an important part of that story. So, not something we can help you with. You've outlined the situation very well and it looks like luck and skill and helpful plot-wrangling is your answer. Good luck with it and please do post questions about Worldbuilding here. Also check out Writing.SE for any questions you might have that are writing specific (this question wouldn't be). $\endgroup$
    – Cyn
    Commented Apr 14, 2019 at 14:59
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    $\begingroup$ /We can see the FTL ship approaching./ that alone is no mean feat. $\endgroup$
    – Willk
    Commented Apr 14, 2019 at 15:04
  • $\begingroup$ Yeah as far as seeing an FTL ship approaching you're going to need to flesh that one out a tiny bit. I get that you're not writing hard scifi here, but we usually "see" things at the speed of EM waves and FTL quite literally means traveling faster than those waves. Maybe your humans are sensing a gravity wave bowshock that is a consequence of FTL travel? $\endgroup$
    – ben
    Commented Apr 14, 2019 at 17:26
  • $\begingroup$ The humans may have just gotten their hands on FTL, but the aliens have had time to perfect the technology, and weaponize it if they were so inclined. I don't know what exactly space-warping weaponry would look like, but I expect it might give the aliens an edge despite being a smaller force. Also, if the aliens are capable of procuring something as exotic as negative mass, it is plausible in comparison that they might be packing antimatter weapons. $\endgroup$ Commented Apr 15, 2019 at 6:24

9 Answers 9


The merchants control all FTL shipping, and they have deep pockets. They probably control a lot of in-system shipping too, wherever there isn't sufficient pressure from the government or powerful industries to keep them out. They can and should use this as a weapon, infiltrating troops, weapons, and even whole ships under the guise of legitimate business. Presumably - being merchants first, fighters second - they tried some kind of diplomatic overture to get their hands on the negative mass first, which gives them some time to set up in case they need to do things the hard way.

The mercenary fleet that we see approaching as they issue their ultimatum is a threat, but it's not really the main threat. Only when our forces are committed to engaging do they reveal their true strengths hidden among Earth's own shipping lanes.

Depending on how you want your story to play out, there are a couple of options from here. The hidden forces could try for a smash-and-grab while the defenders are busy with the diversion fleet. Or the hidden forces could fall on the defenders from behind, aiming to remove command and control and then engaging alongside their allies. Or they could try taking hostages ("surrender or we'll start bombing your cities").


I'd find it far more difficult to create a scenario where humanity has any chance to win.

Just imagine an FTL missile travelling through a human destroyer. Or, if that is not possible, just leaving a little bit of oxygen and phosphor in the fuel tanks, or a mine just in front of the most vulnerable part. One of their little ships will easily be able to destroy anything we have in space, including complete outposts not protected by an atmosphere.

Also, they are likely to have nuclear power. They don't even need to bring any fuel along - a lot of bodies in the solar system probably have enough fissionable and fusionable material to make enough nuclear bombs to throw evolution on Earth back by a few billion years.

They might respect the solar system as belonging to humanity while we are at peace and useful for trade. But when that stops, they will claim every asteroid, moon and planet which we didn't colonise yet. Which gives them enough of a production base to match anything humanity can produce to fight them off.

I'm afraid even if they sent only one small mothership (probably a trade freighter with some weapons and tools on board) with 2 or three small landing craft, they'd win even if they acted really clumsy and not very strategic.

The mercenaries would not even be needed for that. They might be useful as muscles to retrieve the loot from a dead lunar base.

Only if the traders were pacifists who refuse to kill anyone would there be a chance for humanity to hold them off. But even then: Zip by the loot at FTL, stun everyone, pack it up, leave at FTL. It's trivial with the FTL advantage, even if the aliens were only as advanced as humanity in all other areas.

I'm afraid you will have to give humans more to make this work in favor of them - like the traders only finding out about the 'negative mass' after humans started building FTL ships, too. But even then, the aliens only need to wait until humans get sloppy with securing their valuable resource, and then quickly grab it with an FTL ship as fast as the best human one, to win this. It's done in commando ops all the time, during war even sometimes successfully by the weaker power...

  • $\begingroup$ You seem like your'e assuming Star Trek like-FTL. If, however, the FTL is a jump point variety, that changes things. $\endgroup$ Commented Apr 15, 2019 at 1:39
  • $\begingroup$ True. The aliens would need to guard a portal somewhere in the solar system or such. However, this implies that the aliens managed to reach the Solar System conventionally, which would put them technologically even further ahead of humans. And it means they have something of a base the humans aren't able to crack in the solar system. So everything stays the same, except they have to be a little more clever with grabbing the loot. $\endgroup$ Commented Apr 15, 2019 at 21:04
  • $\begingroup$ Not exactly what I meant. Assume the aliens use the Standard SF Jump Point: they have to get to a certain location some distance from the star to make interstellar jumps, but in system, they're limited by more mundane physics. In that case, you don't get FTL missiles, you don't get ships racing in to snatch other ships, and so on. $\endgroup$ Commented Apr 15, 2019 at 22:39

I am guessing this is one of those lowscifi scenarios where FTL just means really fast, and that the planet destroying ramifications of the negative mass / Alcubierre drive are sidestepped. That is fine.

The best way to give your alien mercenaries a chance for success is to let them succeed. Somehow they have intelligence stating where the negative mass is. But they don't know us. Evacuate the base and play scared. When they come to the place, there will be some negative mass there. Let them take it. Maybe there is a bomb in it that goes off later, while they are moving FTL. Maybe it is a thin coating of negative mass around an evacuated plastic vessel full of fun prizes.

The way I would spin this is to meet the alien mercenaries with a show of strength and then offer to parley. Show the commander what we are about. Treat him (it?) with respect. Make clear that humans are not peaceful traders but bad of ass in our own right. Make clear that we are the natural allies of these warlike aliens because our peoples are like.

It is humiliating to these warriors to be dropped off by a bunch of cowards and then have to wait for a ride home. Give the mercenaries a gift of a FTL ship with its own supply of negative matter so they can go home by themselves. A selected crew can go with to help them fly and will collect intel on these aliens while they are with them.


We are fighting aliens, why can't they use alien technology?

Sure humans have the ability to adapt, but during a first hand encounter, it's pretty much a guessing game for humans.

This question tests how far the writer would go. You can make your alien ships invulnerable to any armament earth has because they have X element (where X is an element that is alien to us), then turns out they can be easily destroyed if you play Back Street Boys music for unknown reasons. Or maybe weapons that can destroy anything in its path but glass.

Even if your aliens may have the smaller force, as far as you use X element, and then tell the readers how this could be defeated after the first encounter, then I think your aliens have a pretty good chance on holding their own against humans, just use your imagination.



Secure a base of operations.

If Ceres and Vesta are not defended, the first step should be to take them. This will give you a base of operations and deny the enemy mineral resources at a time they would badly want those resources in order to build new hulls. The mining colonies not being defended would also be a thing that might be in a pre-war contingency plan so you can play up how the aliens have good spies.


Play up the politics.

Declare the mining colonies independent state under the protection of and allied to the aliens. The aliens are only here because the poor persecuted miners called for help to free them from the tyranny.

Hire some humans who look presentable on video to do your talking for you. The money is good and retirement package generous with relocation to another star system included so you'll have no issues finding people. For that matter, in many settings there really is genuine friction between the belters and the inner system so the belters might actually take you up on the independence.

Continue by promising to liberate Mars and Moon as well. While this might not make sense at face value, you are aliens so nobody expects you to actually know or care about human politics. And it does match well with your known actual goals of getting to the resources at the moon and cutting down human power so it is believable statement of intent.

The merchant aliens probably have the resources and connections to arrange some credence to these ambitions as well. Since they do not actually need to win election or arrange a genuine uprising just be visible in media, you'll probably be able to generate political movements in Mars and Luna for independence.

Again it does not matter if this makes actual sense. Majority of the things the brexiteers said during the referendum campaigning made no sense whatsoever and nobody really cared. People just don't. And this is not going to change any time soon. Politics is not about determining facts, it is about choosing sides. And "liberating the colonies" sounds much better casus belli than "securing our monopoly on a strategic resource for maximum profit". More importantly it also sounds much better than "breaking a monopoly on a strategic resource so that the elites back Earth can get more power and money".

Political support is a strategic resource just like metals from asteroid mines. Denying human governments the freedom to define the conflict as alien aggression that all humanity can unite against is an obvious thing to do. Since you are not interested in or capable of conquering anything there is really no reason to not dress up your war goals.

Nobody will believe it is the actual reason of course but it is believable that you will go away after achieving your goals and leave the colonies "liberated" and people won't really care about strategic resources enough for that to matter.


Target Mars.

Send a fleet that is significantly larger than best intelligence thought you have towards Mars on a fuel effective (slow) trajectory. Make clear that liberating Mars is on. Challenge the Earth government to the decisive battle to protect their colonial empire, if they have the guts. "We are even taking it slow so you won't have excuses for not making it to the fight."

Play up how the belters who volunteered to liberate Mars make up a significant portion of "the Fleet of Martian Liberation". Encourage all sympathizers on Mars to step up their actions "so that Mars can be liberated without actual fighting and collateral damage once the space battle is over". Discuss with Martian government how the planet cannot be defended once you control space and the details of transferring political power to "Free Mars" without unrest and disruption.

Assure the Martians that the fight is just a formality. They will be liberated for certain in the imminent future because while the brave soldiers of the human fleet do not lack in courage and ability their ships are unfortunately obsolete crap that will only perform well as targets for shooting practice. The responsible thing for the human government would be to just surrender but unfortunately politics requires that the innocent soldiers must die before surrender is an option.

Earth really must take this challenge. Mars is not something they can hand over to you and if they refuse to accept your challenge here people will with good reason ask what is the point of having this war at all. And since you cannot possible have another fleet in hiding with the fleet en route to Mars already exceeding what you were expected to have it will even be safe to send almost all ships defending the Earth to the decisive battle. This is going to be their best chance to take you on so they'll take it.


Lunar smash and grab

The reason the Martian fleet is bigger than your force was expected to be is not because reinforcements ferried to your bases on the belt. It is because it is entirely fake. It is just a bunch of painted metal on a ballistic "fuel efficient" trajectory towards Mars.

Add some EW systems, radars, radio transmitters to create "encrypted" chatter, and small maneuvering drives to avoid collisions. Should be fairly cheap to build and the ballistic trajectory with the EW systems should make it look real enough. Not having full powered space drives is not obvious if you do not use them.

Once the Earth fleet is far enough with enough momentum you'll send your actual fleet for the actual objective at Luna. Since the humans should have seen no reason to keep lots of ships back you should have comfortable superiority. And they should have gone for fast transfer option for Mars so they should not have the reaction mass to get back to Earth in time. You time it right and they'll need to stop to refuel at Mars.

You will still want to time this so that Mars is far from Earth and your bases at the belt and Earth and your bases close.

Interesting aspect of tricking your enemy to move in response to your actions is that you are essentially controlling their trajectories since the timing makes the best trajectory for them to take predictable years in advance. The only variable is their decision making delay. So depending on the technology it might be practical to have a mine field waiting for that Earth fleet on its route to Mars. And on its way back too.


Clean up.

You have either succeeded in taking your objective on Luna or been defeated. Mercenaries do not fight to the death and you have committed no atrocities that would make surrendering a no go. The Earthlings have no real reason to treat you as anything other than the professional you are.

If you have gotten the objective continuing the war is pointless. Contact Earth authorities, tell you have the loot and your ships are in position to do orbital bombardment on Earth. Isn't it time to end this nonsense? I am not getting paid per hour you know?

Suggest immediate cessation of hostilities and ask for recognition of the independence of your friends in the belt and referendums on independence for Mars and Luna.

Realistically almost all of the human shipyards should be in the Earth system and you would have destroyed them already as legitimate military targets after giving the personnel a chance to evacuate but if this is not the case you'll also want to ask for dismantling of military capability. Your customers will probably have something more specific in mind. They'd probably want a copy of all human research data on FTL for example on the off chance fresh eyes noticed new things.


If the humans weaponised the FTL tech somehow, or even just weaponised the negative mass in an innovative way these alien merchants never considered they may well have more than a chance. Humans are very good at weaponising and fighting, we have lots of hands on experience.

So that's the best angle of attack, fighting tactics are already known and practiced, a new weapon isn't a huge leap. We have huge budgets and teams of scientists for it right now.


The easiest way for the invading mercenaries to succeed would be to simply eliminate the human population of Earth from a distance. To do that they could simply accelerate a cloud of fairly small projectiles along a carefully planned trajectory to near relativistic speed. Due to low mass and large quantity those projectiles would be difficult to spot and divert, but upon contact with earth atmosphere they would deliver a lot of energy potentially flash - boiling every living thing on Earth.

Multiple clouds of small, fast moving projectiles converging at the same time around the Moon should also take care of the human defense fleet, or at least cause enough chaos for mercenaries to land and take control of the facility.


Sabotage The merchants use their wealth to bribe a bunch of humans to disable parts of the defenses.

Civil War The negative mass is probably not owned by all humans. A government or corporation is probably in charge of it and the other governments/corporations are probably jealous as all hell. If the merchants can play off these tensions they might be able to go beyond sabotage in to an all out civil war. Just promise the winners extra steep discounts or minor access to negative mass tech or just play off of resentment.


A ship that is both faster and has longer ranged weapons than an opponent is pretty much guaranteed to win a fight in space. Their ships could match speed with the human destroyers and pummel us at a range while dodging 95% of what we throw back at them. People familiar with MMOs know this strategy as kiting.

The merchants have been space faring much longer than us, so their ships are likely much faster than ours, and even if their weapons aren't strong, their computers and aiming mechanisms are probably quite advanced just in keeping with the age of their civilization. The mercenaries are experienced enough to know this advantage and to try to exploit it.

Human ships would be at a huge and frustrating disadvantage at the outset of the battle, but we could manage to adapt using bait and flank tactics or micro warp jumps to encircle the alien ships (which we know as counters to kiting thanks to our culture of violent video games). Our come-back would be unexpected and devastating forcing the remaining alien ships to either dart for the moon's surface or retreat. The remaining alien ships would still be fast enough to run the blockade to pick their people up when it is time, but they would have suffered too many losses for another all-out attack.

I think this should create the hold their own, but only for a while scenario you are talking about.


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