Jump Drives

Jump Drives are the only known means of faster than light travel. They allow spacecraft to travel through a wormhole that follows a “jump chord” between two nearby stars. Jump-1 chords connect stars up to 1 parsec apart. the chord has a well defined start and end point, usually within the inner system of its star.

The spacecraft travels in normal space to the local chord endpoint. It then engages its jump drive, and disappears from normal space. Approximately 5 days later the ship It instantly emerges from jump at the chord’s other endpoint, near to the destination star.

Travelling to and from the jump point in normal space is often the longest part of a journey. Even with the best commonly available space drive (antimatter-catalysed fusion direct drive, capable of 1G continuous thrust) it can take several days to travel between the jump point and a world in the habitable zone. Travel to the outer system often takes weeks or months.

Note: I’ve removed the traditional Traveller “5 days in jump”. Passing through the jump wormhole is now instantaneous, from the perspective of the traveller. Ad Astra jump drive is now identical to the Alderson drive. Getting to and from the jump point takes quite long enough – having another delay during jump just seems unnecessary.

Jump Sickness

The extra-dimensional wrenching of jump space can cause mental and physical problems. The more jumps you make, the more you are exposed to jump sickness. The symptoms start out as mild headaches and trembling, but can rapidly progress to serious mental problems, physical weakness, and even death. Travellers have to ensure that they spend sufficient time in normal space, to allow the effects of jump sickness to dissipate.

Earth is located in the “Core Worlds” – a large island cluster, isolated from the Main.


Light blue: J1 routes. Dark blue: J2 routes.

Jump drives are invented on the “Dimensional Engineering” tech level track.

Tech Level 9

Although the simplest jump drives are invented at TL=10, it’s possible to construct them TL=9, as long as detailed schematics are available.

Tech Level 10 (Jump-1 drives)

Tech level 10 is the highest generally available to civilization on the Main. Jump-1 ships are required to have spherical hulls.

Jump-1 drives cannot utilise jump-chords longer than about 1 parsec, even though such chords are theorised to exist. This places many stars completely out of range – such inaccessible systems are called “islands”. Travel even to accessible systems might require highly convoluted multi-jump journeys. The sequence of connected systems, accessible to Jump-1 equipped starships is called the “Main”.

For example (see map), in order to travel from Earth to Epsilon Eridani, a jump-1 ship would need to go via Wolf-359, Procyon, and Sirius, even though the distance is only 2 parsecs.

Since all J1 ships must enter & leave each jump chord at the singular end point, these end points have become popular locations for refuelling stations, customs inspections, naval blockades, and pirate ambushes.

Tech Level 11 (Jump-1+ drives)

The Jump-1+ drive is a development of the Jump-1 drive, with two key advantages:

  1. Increasingly sophisticated manipulation of the jump field allows J1+ ships to introduce a “bias” which can open the jump portal, even when the ship is some distance away from the chord end point. A skilled astronavigator can also influence the destination point of the ship. Not only does this enable a ship to avoid the possible dangers & inconveniences of the jump point, it can also shave vital days off the normal space travel time to the destination world.

    J1+ drives can enter & leave the jump chord anywhere up to 1 half an AU from the jump point, although more refined jumps get increasingly difficult and use more fuel.

    In order to introduce the critical “bias” into the jump field, J1+ ships must not have spherical hulls. Cones, oblate spheres and even wedge shaped designs are all used.

  2. J1+ drives can access higher level (J1) harmonics, in J2 chords. This enables them to travel along a 2-parsec long jump chord, in two five-day jumps. The first jump gets the ship into deep space, half way between the two stars, and the second jump completes the journey.

    In order to perform this feat, the J2 chord must be completely and accurately mapped. In practice, the J2 chord can only be used if both ends are accessible by ordinary J1. So, although J1+ allows for much more convenient routes, it does not allow ships to access island worlds.

    Such jumps into deep space are highly dangerous, and must be attempted only from the precise location of the jump-2 point.

Both Earth and the Esperanzan Commonwealth routinely use J1+ drives. This innovation has given them a critical advantage over the civilizations of the Main. The Xa Imperium, which controlled humanity’s access to the Main for centuries has been completely bypassed in the century since the invention of J1+.

Jump-1+ drives produce much stronger jump sicknesses than normal J1 drives.

Tech level 12 (Jump-2 drives)

Finally at TL=12 the jump-2 chords can be used directly. These drives can complete the 2 parsec journey in only a week one jump, and can do so safely even without a detailed survey of both end points. Island systems are trivially accessible. This opens up whole new worlds to exploration.

Procyon’s various megacorporations have been researching the J2 drive for decades. The recent arrival of many talented refugees from Earth, including some brilliant uploaded minds, has enabled them to finally unlock the secret…

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  1. alex said,

    15 December, 2014 @ 18:10

    Facebook comments:

    Tony Jones Sounds very much like a version of the Anderson Drive.

    Alexander Tingle Thanks. I didn’t realise that the star drive from Mote in God’s Eye had a name, although I was aware of the similarities. Most of my inspiration came from this article on the Traveller wiki: http://wiki.travellerrpg.com/Jump_Drive_History

    My goal has been to try and shave off some of the things that annoy me about “traditional” Traveller jump drives. To me, the intention always seemed to be something like this. Deep space jumps were never really mentioned in the basic rules, but I think the game designers never intended them to be possible… exhibit A: the history of the Vilani Imperium being “trapped” on its J1 main. In the “Imperium” board game, deep space jumps are explicitly forbidden – in fact the “jump chords” are actually drawn onto the game board!

    I’ve essentially made deep space jumps into an extra level of the technology. In my scheme, J1 drives operate like the Alderson drive, and at the next TL J1+ drives operate pretty much like “normal” Traveller jump drives. I introduced the need for both endpoints to be fully surveyed, in order to prevent J1+ drives from getting to island worlds.

    Alexander Tingle “Jump sickness” is basically “space scurvy”. Early East Indiamen suffered massive casualties from scurvy on their epic voyages.

    Matt Fitzgerald For stars with multiple jump chords, are the jump points distinct (e.g. is the Sol-Centauri jump point in a different place to the Sol-Barnard jump point ?) Are they clustered ? i.e. close enough that a single fleet can cover all jump points ? Intuitively I would guess each jump chord runs along the line between the centres of mass of the stars involved, so the answer to both questions would be ‘not unless you can survive in the heart of a star’

    Matt Fitzgerald How does jumping interface with Newtonian momentum ? Do you have to be stationary in the star’s rest frame relative to the jump point ? Moving ‘into’ the jump point in the direction of the chord ? Do you carry momentum out of the jump (e.g. along your original vector toward the destination star, or in an effectively random direction ?)

    Personally I like the ‘along the chord between star centres’ idea – it gives the option of ‘running hot’ through the jump to speed past waiting pickets at the risk of a fiery death if your drive cuts out, and gives defenders less of an overwhelming advantage.

    Matt Fitzgerald Why have deep space emergence for J1+? That involves ‘breaking back into’ a jump chord from somewhere other than the jump point, and thus potentially bypassing jump points altogether.

    Instead you could have the ship running out of jump momentum in hyperspace and needing to fire the jump drive a second time to reach the destination. I’d make jump sickness exponentially worse for this second boost, thus dealing with the ‘why can’t we use J1+ to do multiple hops to any known destination?’ problem.

    Also allows the possibility of ‘ghost ships’ trapped in hyperspace by a drive failure half way into their trip.

    Oh, ‘Islands’ would be accessible via J1+. Somebody just has to take a survey ship in via sublight drive to open up the route.

    Alexander Tingle All good questions. Answers:

    Jump points typically lie about 1AU from each star, roughly on the straight line between them. Tony’s suggestion of the Alderson drive has made me realise that this might put the jump point actually inside large stars. I’m not sure how I feel about that.

    The ship emerges at rest wrt the destination star. That means it needs to start accelerating or it’s going to fall to a fiery fate. That should be relatively convenient, because it enables a slingshot around the star to “easily” get to a variety of possible destinations in system. Ships can enter a jump point with any velocity – perhaps higher entry velocities will require more jump fuel, or a harder roll?

    J1+ drives are pretty much like “standard” traveller jump drives. You only need to be within 1AU of a jump point, in order to use it. This ability to bypass blockades on jump points is a key advantage.

    The way I see the deep space jumps is that the “second harmonic” of a J2 chord looks like two J1 chords laid end-to-end. Like the first two lines in this picture:

    Yes, islands can be reached by sub-light. That’s how Earth finally managed to escape from its island. However, the survey data gets rapidly out-of-date. So if you send a simple sublight probe two parsecs away, its survey data will be 7 years out of date by the time it reaches you, by which time, it’s all but useless. If you perform a massive, highly detailed survey of both ends, with several years worth of data-gathering, then your gigantic supercomputer might be able to successfully predict how the survey results will develop over time, and thereby get across to the island. That’s how Earth+Esperanza finally managed it – there were huge observational resources at both ends.

    If you can take a quick survey and then nip back round the long way with jump drives, then simple surveys will suffice. So Earth was trivially able to start using deep space jumps to reach Eridani.

    Matt Fitzgerald OK, makes sense. So, if you can hold both end points and the centre of a J1+ line for long enough it effectively becomes impassable to anyone you don’t choose to share the survey data with (so the ‘New Men’ could stand down most of their Sol-Esperanza jump point defences and devote the resources to the blockade of Procyon).

    Or interdict the mid point for long enough and render the chord unusable to both endpoint systems until they can resurvey (Procyon Freedom Commandos, attack !)

    Alexander Tingle Survey data is irrelevant to Procyon. They just invented Jump-2.

    Matt Fitzgerald Indeed. But it’s not irrelevant to the Esperanzans, so interdicting the mid point of their Esperanza-Sol route would be highly effective.

    And a very nasty surprise if the Esperanzans don’t yet know about the J2 drive.

    Alexander Tingle Ah, I see what you mean. Yes, that would be quite effective.

    Tony Jones I had a few thoughts on jump drives that might interest you…Traveller: Jump Drive Thoughts and Ideas

    Note that most of the ideas on this page are only available at much higher levels of technology than the normal Traveller maximums, and some of them have the potential to change the nature of Jump Drives within a setting in which they appear. As such, they should be used with care!

    Matt Fitzgerald With the very precisely located jump points in Ad Astra, and hence very predictable arrival locations, Megacorporations could implement a very high efficiency combination of ‘jump frames’ (an absolutely minimalist starship containing just the jump net, cargo hold and minimal crew quarters), ‘Jump stations’ (fuel bladders and the drive mechanisms to charge the jump nets on the frames) and ‘Tugs’ (maneuver drive units for shipping cargo to and from the local world, and/or maneuvering frames and cargo around the jump point).

    For non time critical cargos, mass driver stations might also be an economical option.

    The equivalent of supertankers and container ships.

    Alexander Tingle Ad Astra jump drives don’t permit drop tanks. The dimensional portal begins to open as soon as the drive begins to operate.

    Tony Jones Some more jump drive thoughts.

    At what point in the star formation process do tramlines linking it to other stars appear? Is there some critical gravitational gradient or energy density or mass density that a star crosses but a planet does not which triggers tramline formation? If so, where is the cut-off. Do brown dwarf objects generate tramlines? Or are they the border with smaller brown dwarves not and larger ones yes.

    It also occurs to me that the tramlines linking stars must be dynamic, and vary over astronomical time as stars move relative to one another. Otherwise the Sun (for example) would be linked to the stars that were its neighbours when it formed, which are probably scattered across the galaxy by now, not the ones that are its neighbours now. So tramline links would be constantly breaking and forming as stars move around the centre of the galaxy. What might be the symptoms of a tramline being about to break, or a new one about to form? What plots could come out of this?

    Perhaps stars are alive, and tramlines are how they mate, like bacteria conjugating, changing partners as they move relative to each other?


    Or might some older tramline links survive to/from some stars? This could give you the long-range links you were talking about in an earlier post.

    If not is there any way you could ever have a tramline linking to a star (for example) deep in intergalactic space?

    There are some stories I’m reading on a forum where interstellar travel uses tramlines similar to those you describe. In that universe they come in different strengths, so at one TL you can only use the stronger ones, while at higher TLs weaker ones become available; they don’t necessarily go further but they do give you access to a bigger tramline network, which obviously has advantages…

    Is there any dependence of tramline properties (stability, length etc.) on the types/sizes of the stars at each end?

    Do things happening to a star (e.g. solar flares, it being a variable star etc.) affect any tramlines linking to/from it?

    Alexander Tingle I actually touch on brown dwarfs in some of my material. Here’s what I wrote: “Brown dwarf stars are not usually large enough to create jump chords, but just breaks that limit. Its jump points are tiny, and only possible to find with highly accurate astogation data.”

    The jump chords definitely do change over time. Kapteyn’s star has sufficient proper motion that Earth would not have been in a jump island 5,000 years ago. There is an alien race called the Khigrish who claim to be part of a vast interstellar empire, but that they were cut off from the main part of it thousands of years ago.

    “at one TL you can only use the stronger ones, while at higher TLs weaker ones become available” – that sounds exactly the same as this scheme.

    As you can tell from the little passage about brown dwarfs, the jump points are more stable and easier to find, the larger the stars at both ends. BTW, it’s possible to use J1 drives to travel between stars in a multi-star system.

    M J Harvey Is the vessel’s momentum conserved during a jump?

    Matt Fitzgerald The ship arrives at rest wrt to the destination star from Alex’s earlier comment. We may be geeking out just a bit, or passing the comment event horizon, with a few…err most…of these threads

    Tony Jones Us? Geeking out?! That would never happen, surely!

    Alexander Tingle If the vessel’s momentum were conserved, then in many cases you would arrive at many times the solar escape velocity in the destination system. if I were writing a novel, that’s the way I’d do it, but for space opera, it would be tedious. Also, I don’t want to have to catalogue the relative velocities of hundreds of stars.

    Alexander Tingle I’m enjoying these threads immensely. Tomorrow’s is the last I have scheduled – The Long Republic. It is supposed to be rainy tomorrow though…

    M J Harvey Sorry, I’m joining in late. Is the 5 days’ travel time the subjective experience for the vessel and also that for an observer at rest in the departure system? (so ten days elapse there while waiting for a there-and-back trip). What’s in jumpspace? Can vessels there interact? Can radiation be sent via jumpspace, or do all communications have to go by messenger packet? What’s the cost of building J1 jumpdrives -where are they on the disposable-to-hen’s teeth spectrum for each TL?

    Alexander Tingle M J – The standard Traveller jump drives are described here: http://wiki.travellerrpg.com/Jump_drive Most of your questions relate to aspects that I’ve not changed. In brief, yes jump drives completely ignore general relativity, it’s 5 days to all observers. You can’t interact with jump space, and only ships can use it, so there’s no FTL comms. Jump drives roughly double the cost of a space ship – that’s the order of magnitude.

    Matt Fitzgerald Is there any way to archive these threads so that they don’t get lost in the mists of random Facebook reshuffles ?

    Alexander Tingle I’ll copy them and post them to my blog. You might want to check out the “Fsearch” FB app.

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