A Treatise on the Plausibility of Hyperspace Ramming

Certainly not a visual metaphor for Star Wars fandom.

I haven't written for this blog in a while, so I thought I would start with something easy and uncontentious: the believability of hyperspace ramming in The Last Jedi, of course.

P.S. Spoilers for TLJ!

P.P.S. Usually I try to write about nerdy stuff in a way that is accessible to lay persons. A little more background knowledge is assumed here, since the people I am trying to persuade are mostly people who have higher-than-average familiarity with the Star Wars fictional universe.


Preamble

I was surprised by the intensity with which many Star Wars viewers disliked the hyperspace ramming sequence. Personally, I found it a great visual and emotional crescendo for the film. The scene is inscribed, awesomely, on my memory.

As I watched I also wondered to myself, briefly, “Does this make sense?” Pretty quickly, I thought of a few ways in which hyperspace collisions might be fit into Star Wars lore, and I moved on. I wasn't sure that in a protracted debate with an avid Star Wars nerd (I myself am a relatively casual Star Wars nerd) I could prove that this mechanic perfectly fit into the Star Wars universe, but I was able to generate a couple of explanations easily enough to maintain my suspension of disbelief.

So, my goal here isn't to prove that if this sequence did break your suspension of disbelief that you are wrong. What I do want to show is that people who enjoyed The Last Jedi, or indeed enjoyed this scene, are also not wrong to have enjoyed it. It is not necessary to turn one's brain off, or to have total disregard for the continuity of the Star Wars universe, to like The Last Jedi.

I could accept the criticism that Holdo’s ramming attack should have been prefigured earlier in the film, in the manner of Chekov’s gun, though I was not myself especially bothered by the lack of setup. But it is another thing to say that the scene absolutely and transparently violates Star Wars lore.

And I'm still not claiming that in protracted debate with someone who knows more about Star Wars lore than I do, I wouldn't be convinced that hyperspace ramming doesn't make sense. But I don't think that movies have to absolutely, irrefutably make sense in order to function as works of art or entertainment; they only have to make enough sense to feel so plausible as not to shatter the viewer's suspension of disbelief, and I do think that plausible reasons can be given to support the occurrence of a hyperspace collision in The Last Jedi.


Two Arguments

I take it that there are, broadly, two reasons why fans of Star Wars didn't find the ramming scene to be believable. (1) If hyperspace ramming worked, we would have seen a lot more of it in the previous Star Wars films, because it would have been a useful tactical technique. (2) Hyperspace ramming is not possible, because the mechanics of hyperspace do not permit collisions between spaceships. I'll tackle these in the order I just presented them. What I'll argue is that: (1) It is possible to think of reasons why we wouldn't have seen much hyperspace ramming previously; (2) There are some reasons to believe that hyperspace ramming is possible, given how hyperspace seems to works in Star Wars.


1. Why Didn't We See Hyperspace Ramming in the Previous Films?

(A) Off-Screen Action – The first point I'd like to make is that there could have been hyperspace collisions, deliberate or otherwise, occurring concurrent with the plots of the original trilogy and prequels, with that action simply happening off camera. This makes sense from a film-making perspective, because space battles generally focus on the actions of the protagonists, who are unlikely to commit kamikaze mid-film. It could also be relevant that depicting ships shooting at each other in the background of battles is probably easier than clearly depicting ships make hyperspace jumps into each other. If a ship in the background of the battle for Naboo had done what Holdo did with the Raddus in The Last Jedi it might have been hard to tell why several ships exploded. On the other hand, Stars Wars viewers are used to seeing ships shoot at each other and can easily apprehend what is happening. So, hyperspace ramming isn't generally something a protagonist does, while it also isn't the easiest thing to depict in the background of a space battle with ancillary characters.

Nothing forces us, then, to believe that hyperspace ramming didn't occur off-screen during the space battles shown in Star Wars. For that matter, entire strategic actions could have occurred centered around hyperspace-ramming that simply weren't part of the main plot. For all we know, the Rebel Alliance did hyper-jump a captured Lucrehulk into an Executor dreadnaught at some point. Just because something isn't explicitly mentioned or depicted in a narrative doesn't mean it never happens in that fictional universe.

However, there are further reasons to think, not just that ramming might have occurred without our seeing it, but that it would have been rare, perhaps to the point of negligibility, which further explains why it did not show up in the earlier movies.

(B) Poor Use of Resources – Obviously, hyperspace-ramming as depicted in The Last Jedi can be very effective. But you're paying for it not just in the cost of the spaceship sacrificed, but it in the cost of its replacement ships, or with all the future utility you lose if you do not replace it.

For the Empire, it would not normally have made sense to sacrifice a ship to achieve the destructive potential of hyperspace-ramming, since the Empire usually possessed overwhelming firepower anyway. Why pay the cost of a lost ship when you can just use the ship's normal combat-systems and keep the vessel to use again?

For the rebel alliance, it would be reasonable to assume that each ship was precious. Given that they were underfunded compared to their enemy, the Galactic Empire, paying to replace a ship would have cost them a greater percentage of their resources and would put them at a further disadvantage in the long run.

That's not to say that it would never happen, but under most circumstances it would be markedly more economical to use the ship in its intended combat capacity for many years than to spend its whole cost at once for short-term gains.

(C) Personnel Loss – An additional cost to FTL (faster-than-light) kamikaze is that, if it were used spontaneously during normal combat, the entire crew complement would be lost along with their ship. If the hyperspace ram were planned in advance, the crew could be evacuated, but if the decision were made mid-battle, it would result in the loss of the whole crew. Ramming might still be used if it became clear that the ship would be destroyed in combat regardless. However, there would probably be limited time between the direness of the situation becoming apparent and the ship's actual destruction, leaving limited opportunity to make the decision to sacrifice all of its personnel and hardware. The ship might well be lost more quickly than that decision could be finalized.

(D) People Don't Like to Die – It would be challenging to order somebody who doesn't want to sacrifice themself to perform a hyperspace ram, especially if they are left alone in a ship to do it (thereby minimizing personnel loss). After all, the normal purpose of a hyperdrive is to take the pilot instantly wherever they want to go. It would be easy for the pilot to warp away into the farthest reaches of space, rather than fulfill their mission. At the same time, threatening the pilot with death for dereliction would be hollow, given the nature of the command. A pilot could be threatened with torture or imprisonment if they are caught after going AWOL, but I suspect that many people would still take possible torture over certain death.

That's not to say it would be impossible to find volunteers, especially in organizations like the Rebel Alliance, whose participants are motivated more by ideology than by fear or material reward. However, the Alliance would also have strong countervailing reasons to make minimal use of hyperspace-ramming because of its relatively limited resources and personnel, as discussed above.

We might imagine that a fighter pilot in mortal danger would decide that if death were inevitable, they might as well go out on their own terms and do more damage to their enemy, rather than be shot down. I suspect, though, that in many cases it would be hard to convince somebody that there really is no way out of death. Most people, even in dire situations, seem hard-wired by evolution to keep searching for a way out until the very point of destruction, and a space battle is probably not the easiest place to have a philosophical discussion about the inevitability of death.

(E) Mass Ratios – Here I'm getting (more) speculative, but it makes sense that only certain rammer-rammee combinations would be strategically sensible. My assumption is that hyperspace-ramming doesn't work fundamentally differently from sub-light ramming. Basically, it involves the transfer of kinetic energy, just like a bullet or cannonball. In fact, I suspect this would be even more so with FTL ramming than normal ramming, because such a high percentage of the destructive energy of hyperspace-ramming would come from the velocity of the ramming vessel rather than the ignition of explosive materials stored on the ramming vessel.

Smaller objects, traveling at similar velocities, carry less kinetic energy. For example, if a cannonball and a bullet strike an object at the same velocity, the cannonball will do more damage. So, if you crashed an A-wing into the First Order's Supremacy at lightspeed, it would presumably do some damage, but not nearly as much as a large capital ship like the Raddus. You could crash a fleet of A-wings into it, and maybe do significant damage, but then you've lost a fleet of A-wings. This reinforces the above point that hyperspace-ramming is inefficient economically, since you either have to sacrifice a large ship, or a large number of small ships, in order to take down a sizable target.

Yet, the target has to be a powerful enough threat that it cannot be eliminated by the same large asset(s) using conventional means. For example, If you wanted to take out an Imperial-class star destroyer, you would only ram if your ship were sizable enough to transfer adequate kinetic energy through ramming, but not large or powerful enough to survive a conventional firefight.

So, hyperspace-ramming would usually make sense only when it involves a moderately smaller ship jumping into a moderately larger ship. You wouldn't see an X-wing hyper-ram the Death Star, because it wouldn't do enough damage to be worth the resources lost. You wouldn't see a Mon Calamari cruiser jump into a Star Destroyer, because the two are relatively evenly matched in conventional firepower. So, another reason we could expect hyperspace-ramming to be rare is that there is a limited range of ship-to-ship matchups where it really makes sense.

(F) Range and Vulnerability – It may be that hyperspace-ramming must be initiated from, cosmologically speaking, fairly short distances. The only time we see the maneuver being executed, by Holdo with the Raddus, the ship enters hyperspace within conventional turbo-laser range, and it strikes its target just as it is entering hyperspace.

This fits with other events in Star Wars; in The Force Awakens, it is regarded as risky for Han Solo to make a precise jump with the Millenium Falcon, exiting hyperspace between Starkiller's shields and its planetary surface. And this may not actually be a tiny target. If Rogue One is any indicator, planetary shields sit high above the surface, probably above the atmosphere. In fact, we could reasonably expect this to be the case, since it would be problematic to put a planet-wide force field in the middle of the atmosphere, where it could interfere with the planet's weather and ecology by blocking the passage of atmospheric particles.

So, if precise hyperspace exits are very difficult to pull off, this means that it would be difficult to aim a hyper-ramming ship from a great distance. It might be easier, on the other hand, to line up the shot so that the target is struck just as the rammer enters hyperspace. This means that ramming attacks would normally be initiated from a zone in which the target is able to fire on the rammer as it lines up its shot, or where the target's supporting fleet is able to do so. In fact, in The Last Jedi, it is explicitly a matter of the General Hux's arrogance that Holdo is able to enter hyperspace. Hux dismisses the threat of the Raddus, smirks, and tells his crew to ignore it. If Hux and his crew had responded properly, the threat posed by Holdo's ramming attack might have been neutralized before it began.

With that in mind, hyperspace ramming could have been very rare because it was easy for a competent crew to defend itself against this kind of assault. If ramming ships needed to be within range of conventional weapons, and if it would only be used against a target that conventionally outclassed the ramming vessel, then the target of the ramming maneuver would actually have a decent chance of destroying its attacker.

(G) The Death Star – We might wonder specifically why the Rebel Alliance didn't use a large ship, such as a Mon Calamari cruiser, to hyper-ram the Death Star when it threatened their base on Yavin. This seems like an ideal ramming scenario. Since the Rebel Alliance was facing extinction, sacrificing one capital ship, or even several capital ships, to protect itself doesn't seem unreasonable.

One possible explanation is that the Death Star was too massive to be destroyed by a Mon Calamari cruiser. The radius of the Death Star was approximately 114 times the length of the larger Mon Calamari cruisers. This is roughly the same scale of difference as between an X-wing and an Imperial II star destroyer.[1] But, in fact, because volume and mass increase exponentially with the dimensions of an object,[2] the difference in mass between an X-wing and an Imperial II would be far less than the difference between a Mon Calamari MC80 and the Death Star. If we made the assumption that the X-wing is too small to be used effectively as an FTL-rammer against a star destroyer, then it would certainly follow than an MC80 would be ineffective against the Death Star.

It's also worth mentioning that, if my speculation about the need to make a close approach for hyperspace-ramming turned out to be correct, the Death Star would have had an opportunity to destroy any approaching ship with its superlaser long before the rebels lined up their attack; this doesn't even take into account the support fleet of star destroyers around the battle station. This is another reason that hyper-ramming the Death Star might not have been the preferred tactic.

And, integrally to the plot of A New Hope, the Rebel Alliance did have another option...the one they successfully executed when Luke destroyed the Death Star by firing down its exhaust shaft. As far as we know, the alliance had a cadre of Mon Calamari cruisers lined up to make a Light Brigade-esque suicide run against the Death Star if the first plan failed. However, the protagonist was successful.

(H) The Raddus's Support Fleet – Maybe it's a little harder to explain why the smaller ships in the Resistance fleet, which accompanied the Raddus in The Last Jedi, and which were destroyed one by one, did not turn around and ram the Supremacy much earlier in the film. This seems like another optimal time to implement hyperspace ramming, since the captains of those vessels were certainly going to die anyway. Moreover, the destruction of the support ships was not sudden and would have allowed time to prepare materially and psychologically, and the size difference between the support frigates and the Supremacy might not have been so great as to prevent significant damage being done by a hyperspace ram.

I think there are a few reasonable possibilities. One is that the ships were not in fact massive enough to do serious damage. Another is that it was assumed they would fail, since the First Order would have had time to fire on them as they were preparing to jump to lightspeed; after all, it was only the arrogance and incompetence of the First Order commanders that allowed Holdo's ramming attack to be successful.

Still why not try? If the ships were going to be obliterated anyway, they might as well have attempted a ramming run, even with a very low chance of success. The last plausible reason I'll suggest is that nobody thought of it...because it was a very unusual maneuver for all of the reasons I've discussed above, and everyone involved was under great duress. I think we could even reasonably infer that Holdo didn't really know whether her attack would work; it was a last-ditch move, thought of under desperate circumstances.

(I) Forward and In Review – What I've argued so far is that hyperspace ramming could have occurred in the Star Wars universe previous to the destruction of the Raddus, but that it would not necessarily have occurred frequently enough to show up in the narratives of the previous films. This doesn't strike me as a particularly odd argument. Lots of things presumably happen in fictional universes that don't crop up during the associated narratives. Usually there are extra-fictional reasons why certain things don't show up in the narratives proper. Why don't we ever see the hobbits use the bathroom in The Lord of the Rings? The author decided it wasn't relevant to the plot. Why don't we see Darth Vader force-throw objects at Obi-Wan when they duel in A New Hope? Presumably because the filmmakers hadn't thought of that force power yet. Some of this can be retroactively explained; we might say that Obi-Wan would have been able to deflect thrown objects, while Luke lacked the skill to do so, and Vader knew it. But it just isn't that unusual for a series of books or films to gradually incorporate new in-universe mechanics and possibilities with the assumption that they did occur in-universe before, but did not occur on-page or on-screen.

The argument I'll be approaching in the next section concerns the possibility of hyperspace ramming. It could be argued, not just that hyperspace ramming is unprecedented in the Star Wars, but that it would be impossible given how FTL travel is supposed to work in that universe. I will try to reply to this kind of argument, showing that we could reasonably accept hyperspace ramming as possible in Star Wars.


2. Is Hyperspace Ramming Possible?

(A) Concerning Material from Non-Film Sources – In this half, I will be drawing more on information from Wookiepedia, which is itself drawn from sources other than the full-length movies. I think it's worth pointing out that in the novelization of The Last Jedi, Holdo's ramming attack is explained by the Raddus's special experimental shields. Most of the arguments for the impossibility of hyperspace ramming are likewise based on material outside of the Star Wars feature films. I could easily accept that the film The Last Jedi should not depend on its novelization for its plot to make sense, but then by the same standard, evidence from outside the films against the possibility of hyperspace ramming should not seriously be considered. That is, if we start arguing against the possibility of hyperspace ramming based on outside texts, the use of external texts is a two-way street, and we would also need to accept the relevance of The Last Jedi's novelization.

Still, although I'm not sure it is necessary to do this, I will try to show that hyperspace ramming makes sense canonically, in terms of information available outside of the films, even aside from the novelization.[3]

(B) Evidence for Hyperspace Collisions – The first piece of evidence, however, comes from A New Hope. It is quite clear that ships traveling through hyperspace can collide with other objects in space. During Luke and Kenobi's escape from Tatooine, Luke complains to Solo about how long it is taking to calculate their lightspeed route. Han replies, “Traveling through hyperspace ain't like dusting crops, boy. Without precise calculations, we'd fly right through a star, or bounce to close to a supernova, and that would end your trip real quick, wouldn't it?” (As seen in the escape from tatooine, 2:25-2:33)

If a ship in hyperspace can be acted on (can be destroyed) by a collision with other objects in normal space, we can reasonably assume that objects in normal space can also be acted on (destroyed) by ships traveling through hyperspace in the same collisions. To say otherwise, it seems to me, would violate the principle of conservation of momentum. Presumably, the Millenium Falcon has a lot more to worry about than a Supernova does, because a star or supernova is much more massive than the Falcon. So, although the effect of a hyperspace collision on a large celestial body would be negligible given the difference in mass, there would still be an effect however minor.

The possibility of hyperspace collisions, moreover, is backed up by the presence of hyperlanes in Star Wars lore. The Wookieepedia entry for hyperspace routes reads, “Those routes were regarded as safe, allowing starships to travel without colliding with a celestial body in realspace.” Given that hyperlanes are a major feature of Star Wars' extended lore, the possibility of collisions between objects in hyperspace and normal space is actually quite baked into the fictional universe.

And if there can be collisions between celestial bodies and ships in hyperspace, then in principle it should also be possible for a ship in hyperspace to collide with another ship in normal space. Of course, spaceships are much smaller targets than stars or planets, so it's likely that a collision of this kind would occur rarely. This jives well, however, with my earlier point that hyperspace ramming would have been rare because it would be difficult to aim at very small targets over great distances.

(C) Mass Shadows – It could be asked, though, how these collisions are possible at all? If hyperspace is not the same space as normal space, how can objects which do not share space collide? According to Wookieepedia, “A mass shadow was the gravitational signature of a large object in normal space. Since those shadows were potentially lethal to any starship traveling too near, it was necessary to avoid colliding with them.” How this affects the possibility of hyperspace ramming really depends on how we understand hyperspace shadows in the current canon, and there is relatively little information to go on.[4] If mass shadows are a byproduct emanated by massive bodies into hyperspace, like smoke from a volcano, then hyperspace ramming is not possible. If mass shadows are, instead, extensions of normal objects into hyperspace, like the sunken part of an iceberg, then it makes sense that a collision with the part of the entity in hyperspace would also affect the object in normal space.

I don't really think that this issue can be settled decisively; there is too little information available about a construct that is, at the end of the day, fictional. It would make some sense though, for there to be a two-way effect during a hyperspace collision. If the mass shadow, with which a ship would collide in hyperspace, is part of the gravitational field of the struck object, then the object itself could conceivably be affected by the violent modification of part of its gravitational field.[5] If earth, for instance, were suddenly subject to modified gravitational force, because of the disruption of its own gravity, different pieces of the planet could accelerate differentially, causing damage.

This is all rather disputable, but what I aim to show is not that hyperspace ramming would definitely work, but that an intelligent person could find it plausible enough that the presence of hyperspace ramming in The Last Jedi would not break the spell of the narrative.

A final possibility, to skirt the question of whether collisions in hyperspace could affect objects in normal space, is that Holdo hadn't actually entered hyperspace at the point of striking the Supremacy. Rather, she was still accelerating toward lightspeed at a relativistic speed, and that this was enough to destroy Snoke's dreadnaught. This is not really what is implied by the film, but it's at least worth considering that the film never explicitly states that the Raddus contacted the Supremacy at lightspeed.

(D) Interdiction Fields – Assuming that ramming at hyperspeed is generally possible, one might still object that it would be impossible in practice because starships in combat would raise interdiction fields to prevent other ships from traveling through hyperspace in proximity to them. According to Wookieepedia, “An interdiction field was an artificial gravity well capable of disrupting hyperspace maneuvers.” So, how could Holdo have rammed the Supremacy if it was capable of projecting an interdiction field?

Well, we don't really know how common interdiction fields were, we don't know if they were kept on by default, and we don't know how long it took to power them up. And, in the context of the film, the First Order had been allowing the Resistance ships to flee via hyperspace to make them waste fuel. So, even if the First Order possessed an interdiction field generator, it would fit acceptably with the events of the film if the field were not active.

But, that's not all! I think the existence of interdiction fields in Star Wars lore supports my argument in the first half of this essay, since it would provide another reason why hyperspace ramming did not appear in other Star Wars stories and would have been rare in that fictional universe.


3. Closing Thoughts

I've argued that hyperspace ramming can fit plausibly into Star Wars canon. Again, I'm not trying to convince anyone that they are objectively wrong if it didn't feel plausible, or if they thought of reasons while watching the film why it might not work and lost immersion. What I'm objecting to are the voices who took more extreme positions such as: (a) Hyperspace ramming is obviously and objectively impossible in Star Wars; (b) only an unthinking idiot could maintain suspension of disbelief; (c) the filmmakers must have been either stupid or apathetic to Star Wars lore.

Against these positions, I think I have made a reasonable case. It is evidently possible for an intelligent person, if I may be so bold about my own capacities, to think rather exhaustively about the possibility of hyperspace ramming and to come up in support of it. Perhaps there is some evidence I have not considered or some logical error I have committed, but it would be wrong to say that I went about this with no appreciation for Star Wars lore, or that I went about it idiotically. And so the same should be said for the filmmakers and other fans of The Last Jedi. While I don't think those who came to a different conclusion than I or who felt differently are idiots, I do think they are incorrect if they take the stronger stance that they are decisively right and that everyone else is stupid.

“But!” You may say, “But!”...If a movie requires a 5,000-word essay to explain howit makes sense, or to feel plausible, isn't that kind of a problem? Well, I would agree, and that's rather how I felt about Ridley Scott's Prometheus, for example. But I don't think that's really what's going on here.


When I first saw the ramming scene in The Last Jedi, I had the following set of thoughts:
– Oooooo! Pretty.
– Is hyperspace ramming possible, since it's in separate space, and we’ve never seen it before?
– Well, Han talks about hyperspace collisions in the first movie, so it should be possible.
– And it could be rare because it's wasteful and possibly hard to aim.

All this passed through my mind in a second or two. Then I went back to enjoying the movie. What I've attempted in the body of this essay was not to replicate the exact thoughts I had during the film. What I've done here, at some extended length, was to show that the brief thoughts I had during my viewing, which supported my suspension of disbelief, were neither obviously absurd nor in deep conflict with Star Wars lore. My feeling of the film's plausibility was maintained with a few brief reflections, which are after all reasonably consistent with a sincere interest in the intelligibility of the fictional universe that captured my imagination.


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1. The star destroyer is about 123 times longer than an X-wing, figures from Wookieepedia.
2. This is why a two foot long dog would actually be more than twice the weight of a one foot long dog.
3. Admittedly, I am choosing this approach in part because it seems that many readers did not find the explanation in the novelization very satisfying, and I can at least see why they would think that.
4. According to the Legends entry for mass shadows, the mass shadows are not collided with directly, but pull the ship out of hyperspace so that they collide with the celestial body in normal space. This would make it more obvious how hyperspace ramming works, since the ramming vessel would be pulled out of hyperspace and strike its target at a high relativistic speed.
5. And to reiterate – The mass shadow, at least, should be affected by the collision if momentum is properly conserved.