The discovery that allowed the members of the four races to expand beyond their home worlds and enter the Frontier was purely accidental. It occurred when spaceships were developed that could accelerate to a speed of about 12 million km per hour (1% of the speed of light). At this speed, a unique reality of space becomes apparent; in defiance of all previously accepted laws of physics. a ship will disappear from the space known as the universe and enter a region called “the Void."
Time is very distorted in the Void, and space does not seem to exist at all. If a ship decelerates slightly while in the Void, it will emerge into the "real" universe at some point far distant from where it left the universe. By carefully coordinating the ship's direction with the length of time the ship spends in the Void (usually 3 to 15 seconds), a navigator can "jump" his ship into the vicinity of another star.
Although this process of jumping through the Void allows ships to cover immense distances in very short times, jumping still takes several days. Most of this time is spent accelerating to jump speed and then decelerating at the other end. [CB, p. 3]
Some initial points: Mostly this feels like a dodge on the part of the designer Doug Niles, trying to avoid any real description or argument over fictional faster-than-light travel, but the cure may be worse than the disease. Unlike most conventional science fiction (space opera), Star Frontiers ships don't have any kind of special technology or sci-fi engine to enable crossing interstellar distances. It is just, well, an accident. (I suppose that when Niles was writing, we didn't have concrete examples of macroscopic bodies in the universe traveling faster than 1% light speed, but now we do know about hypervelocity planets and the like.)
What Star Frontiers ships do have is 20th-century technology for engines (chemical, ion, or atomic), and when they happen to accelerate to the magic speed of 12 million km/hr, then they enter the "Void" and cross interstellar distances in a few seconds. Note that this works out to a tactical game speed of 200 hexes/turn, so in principle this could serve as a maximum velocity for ships in the boardgame (and perhaps intentionally or unintentionally triggering a Void jump). Why Niles called this easily-recognizable space the Void (instead of more the customary "hyperspace"), and why he didn't include one of the common gamut of specialized sci-fi engines (jump drive, hyperdrive, warp drive), is unclear.
Now, in the original Star Frontiers RPG ("Alpha Dawn"), interstellar travel was said to simply be at a rate of 1 light-year per day (SFAD p. 49), and the campaign setting shows routes between systems anywhere from 4 to 14 light-years distant (days travel time). Most of the routes are on the lower end of that range (median 7, mean 7.7, stdev 2.5; about 2/3 are in the range 5-8, i.e., 13/20 = 65%). But this conflicts with the core information above, that jumping need only vary from "3 to 15 seconds" to travel a desired distance between stars. The Star Frontiers: Knight Hawks Campaign Book includes not one, but two distinct systems intending to resolve this situation, seemingly in isolation from one another, and each with their own kinks and problems. I'll describe each separately below.
Acceleration to Void Speed
The first explanation for the standard travel time between stars is the idea that several days must be spent accelerating to the magic "Void speed" (and this is included in the initial description above: "Most of this time is spent accelerating to jump speed and then decelerating at the other end"). Now, the first and most significant problem here is that since Void speed is a fixed number, the travel time will be identical between any two star systems, differing at most by the 3-15 seconds mentioned above (not a difference of days). A second problem pops up around how Niles mangled the conversion between ADF and g-values (boardgame acceleration and standard gravity factors); if ships normally accelerate at 1 ADF, then it would take a fixed 2×200 turns ~ 67 hours ~ 3 days for a one-way trip, but if ships accelerate at 1 g, then it takes 6×200 turns ~ 200 hours ~ 10 days on every trip (they're not the same, despite the book saying that they are: CB p. 33).
"Risk Jumping" in the campaign game (Second Sathar War) is based on increasing the acceleration value when needed (something like a forced march). If desired, military ships or task forces can choose to increase their acceleration to Void speed, shortening the amount of time they spend traveling between systems, in exchange for a percent-chance that they misjump entirely out of the game (see CB p. 58). Presumably the crew and equipment will be suffering from the increased gravitational pressure throughout the several days of this maneuver (either 2-3g or 6-9g depending on your preferred conversion).
Plotting Interstellar JumpsMeanwhile, in the Campaign Book's section on Spaceship Skills, we get our second rationale for why jumping takes a variable number of days. Every starship must carry a character with Astrogation skill, and they are tasked with computing the complicated flight path between star systems:
A ship that makes an interstellar jump must carry an astrogator, or the pilot will not be able to predict where the ship will exit the Void. The time needed to make course calculations increases for long jumps, because even small errors become very serious as the distance increases.Note that 10 hours is exactly the normal workday in the Frontier (half a day), so the 10 hours/light-year perfectly recreates the 1 day/light-year travel time mentioned in the original RPG. This kind of restriction is also very familiar from lots of traditional sci-fi, from Asimov's Foundation series to Star Wars ("Without precise calculations we could fly right through a star", and all that). But in some ways it raises more questions than it answers -- How far in advance of the trip can calculations be made? Can they be done at a spaceport before the ship ever leaves (and then just take 3 days of travel, per the prior section)? Or is there some reason that the ship must actually be in motion while plotting takes place? If a ship delays jumping for some reason, can they hold onto the flight plan indefinitely? Can precalculated routes be stored, copied, sold commercially? Doesn't this imply that almost all of the "delay" time is on the departure side of the trip, with no computing needed on the destination side after the jump (in contradiction to the campaign game travel box display)? And worse...
Normal plotting time for a jump is 10 hours for each light-year that will be jumped. For example, an astrogator plotting an 8 light-year jump must spend 80 hours performing calculations before the ship could accelerate to jump speed.... [CB p. 25]
"Risk Jumping" has an entirely different meaning and mechanic in this section of the rules. Here, it means that the astrogator is reducing the amount of time that they'll spend working on the calculations for the flight path (CB p. 25; compare to usage of the same term in the section above, or CB p. 58). In this case, the chance for success is a ratio of time spent to optimal time, with a bonus for the astrogator's skill level. Interesting added detail -- even on a misjump, starships automatically re-appear in the vicinity of some star system (possibly a random or uninhabited one: see CB p. 31). This tidbit could possibly be extrapolated into a broader description of Void-jumping physics, although it was glitched up/overlooked in certain later adventures and supplements (like the execrable Zebulon's Guide).
So, in summary: Star Frontiers: Knight Hawks goes out of its way to avoid conventional sci-fi explanations for interstellar travel, and seems to create more problems for its trouble. It has two separate explanations for the core 1 day/light-year travel schedule, neither of which is completely satisfying, each with its own problems, and they even manage to bonk heads together with two contradictory meanings of "Risk Jumping". To say nothing of how the two mechanics interact: Does one imply the other? Can you choose to implement (wholly or partially) some of each version of "risk jumping"? Was Doug Niles aware of the conflict between these two separate sections of rules -- and why did he radically depart from traditional sci-fi with the "Void" idea (a fixed real speed, no special engines), for little or no apparent benefit?