Travel times for system ships

KRingway's picture
KRingway
September 10, 2019 - 5:26am
For the life of me I can't remember if there are any distinct rules for the time needed for a system ship to travel X amount of distance. I'd like to think that this type of ship is faster in SF than in it is in our current time, but I don't know if that's possible. KH states that these ships have chemical drives, but I was wondering if they could have an ion drive instead - possibly if it made them faster.

I ask as I have an adventure in development where I want the players to travel in a CDC system ship to an asteroid belt at the edge of a system. I wasn't sure how long this would take, but was imagining an HS:4 ship that either has chemical or an ion drives.
Comments:

KRingway's picture
KRingway
September 11, 2019 - 6:06am
So, judging by a discussion about this over at the MeWe SF group, there aren't any rules dictating how fast ships travel within a system. KH doesn't cover this, as it's only interested in interstallar travel, not intrasystem. So there's a gap there in our picture. It seems speed is only relevant really WRT combat and, although that's possibly within a system, it doesn't give a hint about how fast a ship can travel generally when not in combat or to and from a jump.

I do wonder if it's possible to generate some numbers and speeds based on a ships ADF, but I don't know how feasible that is...

Any ideas?

jedion357's picture
jedion357
September 11, 2019 - 5:35pm
I would say that the CDC would just spring for the expense of an ION drive and be done with it. Ssytem ships are just slow. and corporation would just dispense with them and employ ion drives as system ships for the speed and flexibility they offer.
I might not be a dralasite, vrusk or yazirian but I do play one in Star Frontiers!

KRingway's picture
KRingway
September 11, 2019 - 9:35pm
There's still a gap in the way things work though. If a ion drive is 'slow' (ADF 1) what exactly does that mean in terms of how long it takes to get from A to B in a system? It also suggests that atomic drives are faster, possibly also chemical drives, but we're not told by how much. There's mention of chemical drives being able to travel at 10,000 kph so that they can make a round trip on one fuel load, but that's extremely slow and the time/distance of a round trip is not given.

Anyway, it might be a fun exercise to design this system ship for a Frontier Explorer article. I think I'll just have to say that the ship takes 'a few days' to get to the asteroid belt. It's going there to find an NPC ship. I've also worked up a quick doodle of this:


iggy's picture
iggy
September 11, 2019 - 10:59pm
Terlobar and I have done the math before that converts ADF to metric units and then the travel times can be done.  There are a few threads on this site with good write ups by Terlobar.  This may also be on his website as an article too.

Tell me how far you want to go and the acceleration you want to have the players endure and I can calculate it for you.  If I remember one ADF is more than 1G of acceleration and hard to endure for long durations.
-iggy

iggy's picture
iggy
September 11, 2019 - 10:59pm
I like your ship drawing.
-iggy

KRingway's picture
KRingway
September 12, 2019 - 1:05am
I want to keep things simple, so possibly it's a straight run to the asteroid at 1G. I've invented an asteroid belt within the Madderley's Star system, as the adventure starts on Kdikit. I've no idea what the distance would be.

JCab747's picture
JCab747
September 13, 2019 - 12:39pm
Interesting topic. I would think a chem drive ship just accelerates to the equivalent of 1 hex a turn and then just coasts, using fuel for various course corrections and then decelerating. Now, hopefully it has enough fuel for a return trip to its destination!
Joe Cabadas

Stormcrow's picture
Stormcrow
September 13, 2019 - 5:37pm
Yes, a system ship certainly can't accelerate its entire journey, or else it would have enough fuel to jump into the Void.

They probably didn't include system travel times because calculating those is really hairy. What are the orbital velocities of your start and destination? It's supposed to use one load of fuel to make one trip; how much delta-V can a chemical drive produce?

Fortunately, this sort of thing can be hand-waved by the referee. "The trip will take four months." "Four months! But last time it only took two weeks!" "That was three months ago. Inner Reach is on the other side of Dramune now."

I would tend to err on the side of shorter travel times, assuming Frontier chemical engines are much better than anything we have.

KRingway's picture
KRingway
September 14, 2019 - 12:15am
Going by the discussion over at MeWe, chem drives aren't very practical just becaue of the amount of fuel that has to be taken with them to get any distance. Ion drives seem like a better option, as they can carry a lot of fuel. So I may go with that option - possibly there's a chance for a slightly new ion engine design, that has a limiter so that it can't reach the speeds needed for a jump.

But maybe that's just too much detail. I think I'l just say that there's an asteroid belt in the system (Madderleys Star) and it takes 2 days to get via system to ship from Kdikit.

In the meantime, here's some more quick doodles - the second image is the NPC ship that the players will be looking for, a dralasite design:



JCab747's picture
JCab747
September 14, 2019 - 9:32am
Slap me upside the head! I believe the 2001 and 2010 Space Odyssey modules provide a few rudimentary rules for, shall we say, primative system ships.

The 2001 module provides the new Star Frontiers skill of Astronomy (hmm, sounds a bid Zebs like), and system navigation for plotting courses within a system.

On a star map, "the Leonov can move into any adjacent hex on map 8 every 6 hours. After the Discovery is repaired in chapter 3, it too, can move into any adjacent hex every 6 hours..."

The scale on map six is one hex = 100,000 kilometers... Isn't that 10 times the size of a Knight Hawks hex? 

The rules also provide info on aerobraking in Jupiter's atmosphere and using Jupiter's gravity to slingshot back toward Earth.

Again, one could view these as rules for very out of date system ships, but they provide a few ideas.



Joe Cabadas

JCab747's picture
JCab747
September 14, 2019 - 10:42am
but, I would agree that chem drives seem particularly slow for interplanetary travel except for those who can't afford a better ship.
Joe Cabadas

KRingway's picture
KRingway
September 14, 2019 - 12:03pm
Hehe - I avoided the 2001/2010 adventures like a bad smell as I didn't like the movies (and still don't). But it sounds like they may have their uses. Then again, even if chem drives in SF are waaaaaaay better than anything we know of here on Earth, and maybe also with some super-fuel that we don't have, maybe they're useable in some way as system ships with people inside who don't want to spend their whole lifetime getting from one place to the next...

JCab747's picture
JCab747
September 14, 2019 - 12:50pm
KRingway wrote:
Hehe - I avoided the 2001/2010 adventures like a bad smell as I didn't like the movies (and still don't). But it sounds like they may have their uses. Then again, even if chem drives in SF are waaaaaaay better than anything we know of here on Earth, and maybe also with some super-fuel that we don't have, maybe they're useable in some way as system ships with people inside who don't want to spend their whole lifetime getting from one place to the next...
 

Understood, but, yess the modules have some interesting things that can be incorporated into the game such as a luner exploration vehicle and the like. I used to own the modules (along with all the rest of the pieces of the original game), though I never had a chance to use them... The 2001 module has a place where you can play ape men... I think I would have avoided that. 
Joe Cabadas

JCab747's picture
JCab747
September 14, 2019 - 12:53pm
I would say, chem drives for surface to space, space to surface takeoffs and landings and an ion drive for system travel. The Knight Hawks rules don't exactly prohibit a ship from having two types of drives, do they? Of course, they don't explain how tugs can be used or the particulars of Ag ships that seem to violate the construction rules either.
Joe Cabadas

KRingway's picture
KRingway
September 14, 2019 - 2:22pm
Yep, one idea would be that ships with ion drives carry a bolt-on chem drive to get them to and from a planet's surface, if their HS is small enough. Possibly these could use the same fuel rate rules as shuttles, plus some tweaking to take into account the size difference - i.e. a modifier based on HS. If a ship doesn't have one installed, perhaps a kit can be rented - it's bolted on in orbit once the ship arrives, is replenished on the ground, and then after the surface to orbit trip back out the kit is discarded for reuse by the rental company. This of course only works in there's suitable facilities for this in orbit and on the surface.

JCab747's picture
JCab747
September 14, 2019 - 4:14pm
I like the bolt on chem drive!
Joe Cabadas

KRingway's picture
KRingway
September 14, 2019 - 11:02pm
It's still a bit handwavey, but so is quite a lot of things in SF.

TerlObar's picture
TerlObar
September 15, 2019 - 7:52pm
Late to this discussion but here are some numbers you can work with.  As someone said, this is really tricky because it really depends on the positions of the objects and their orbits.  Also, this assumes you have ion drives on your ships.  Chem drives work around a planet and it's moons but if you really want to get anywhere on a timescale less than months or years inside a star system, you need ion or atomic drives to sustain constant thrust.  Anyway, here are some rough numbers.

Accelerating at 1g (which I set to 10m/s/s for SF), it takes just over 83 hours to get up to Void speed (3,000 km/s).  In that time you cover 3 AU and you are traveling at a speed of just over 1 AU every 13.8 hours.  So let's assume you stop just before jump speed and reach a maxium velocity of 1 AU every 14 hours.  And it would take another 3 AU and 83 hours to slow down at your destination.

For a trip over 6 AU, the travel time is just 166 hours plus the distance over 6 AU times 14 hours.  So getting from Earth to Neptune, a distance of 30 +/- 1 AU depending on the relative positions of the planets, would be 166 hours under acceleration at the start and end, and 24x14=336 hours coasting +/- 14 hours.  So going with the average, it would take 502 hours or just over 25 days to make the trip.

For trips under 6 AU the travel time will be under 166 hours (8.3 days) and will depend on the distance traveled.  You spend the first half of the trip speeding up, then flip over and spend the second half of the trip slowing down.  Here's a table you can extrapolate between:

1 AU - 68 hours
2 AU - 96 hours
3 AU - 118 hours
4 AU - 136 hours
5 AU - 152 hours
6 AU - 166 hours

It's not linear since you don't get up to as high a speed on the shorter trips.

You just have to decide how far it is from your starting point to the ending point and then you can estimate the travel time.  When traveling in the inner system, it's going to depend a lot on the relative positions of the planets.  For example, traveling from Earth to Venus could be as little as 0.3 AU if they are at their closest point (inferior conjunction), a travel time of only 37 hours, or as much as 1.7 AU if they are at their farthest distance (superior conjuction), a travel time of 89 hours (plus a little bit as you have to dodge the sun).  For going to the outer planets (beyond Jupiter) from the inner ones, it's just the time based on the orbital distance of the destination +/- 14 hours per AU for the orbital distance of the origin.

Hopefully that helps.
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KRingway's picture
KRingway
September 15, 2019 - 10:33pm
Very interesting - thanks!

For the plot, I think I'll just have to work on the assumption that there's an asteroid belt two days out by ion engine from Kdikit. Hopefully it's not really important to anyone exactly how far away that is in terms of outright distance.

JCab747's picture
JCab747
September 16, 2019 - 8:29am
TerlObar wrote:
Late to this discussion but here are some numbers you can work with.  As someone said, this is really tricky because it really depends on the positions of the objects and their orbits.  Also, this assumes you have ion drives on your ships.  Chem drives work around a planet and it's moons but if you really want to get anywhere on a timescale less than months or years inside a star system, you need ion or atomic drives to sustain constant thrust.  Anyway, here are some rough numbers.

Accelerating at 1g (which I set to 10m/s/s for SF), it takes just over 83 hours to get up to Void speed (3,000 km/s).  In that time you cover 3 AU and you are traveling at a speed of just over 1 AU every 13.8 hours.  So let's assume you stop just before jump speed and reach a maxium velocity of 1 AU every 14 hours.  And it would take another 3 AU and 83 hours to slow down at your destination.

For a trip over 6 AU, the travel time is just 166 hours plus the distance over 6 AU times 14 hours.  So getting from Earth to Neptune, a distance of 30 +/- 1 AU depending on the relative positions of the planets, would be 166 hours under acceleration at the start and end, and 24x14=336 hours coasting +/- 14 hours.  So going with the average, it would take 502 hours or just over 25 days to make the trip.

For trips under 6 AU the travel time will be under 166 hours (8.3 days) and will depend on the distance traveled.  You spend the first half of the trip speeding up, then flip over and spend the second half of the trip slowing down.  Here's a table you can extrapolate between:

1 AU - 68 hours
2 AU - 96 hours
3 AU - 118 hours
4 AU - 136 hours
5 AU - 152 hours
6 AU - 166 hours

It's not linear since you don't get up to as high a speed on the shorter trips.

You just have to decide how far it is from your starting point to the ending point and then you can estimate the travel time.  When traveling in the inner system, it's going to depend a lot on the relative positions of the planets.  For example, traveling from Earth to Venus could be as little as 0.3 AU if they are at their closest point (inferior conjunction), a travel time of only 37 hours, or as much as 1.7 AU if they are at their farthest distance (superior conjuction), a travel time of 89 hours (plus a little bit as you have to dodge the sun).  For going to the outer planets (beyond Jupiter) from the inner ones, it's just the time based on the orbital distance of the destination +/- 14 hours per AU for the orbital distance of the origin.

Hopefully that helps.
 

Great stuff! You should put it in an article for the magazine. It's a clear help to the mathematically challenged here... like myself.
Joe Cabadas

Shadow Shack's picture
Shadow Shack
September 16, 2019 - 1:33pm
KH has very limited rules pertaining to chemical drives. ADF is always one and a load of fuel is 250Cr/doubled if taking off from a planet, and that load gets used over the course of the journey. That's pretty much it.

I did an expansion when I was drumming up my Historical Adventures pf:100 project, it can be found here: http://starfrontiers.us/node/3691



KRingway wrote:
If a ion drive is 'slow' (ADF 1) 

There are also KH references to ion drives being "powerful". Yep, they're powerfully slow, just as powerfully slow as a chemical drive.

See? I don't reserve my critcizing solely for Zeb's. Wink
I'm not overly fond of Zeb's Guide...nor do I have any qualms stating why. Tongue out

My SF website

iggy's picture
iggy
September 16, 2019 - 5:52pm
Ion drives are powerful when you think to measure them as constant power over the full duration of the flight.  Chem drives expend all their power in quick bursts and then the engine is off and you coast.  So, when you add up the power availble and used over the entire duration of the trip then ion drives are more powerfull.
-iggy

iggy's picture
iggy
September 16, 2019 - 5:55pm
@KRingway, I love your ship art.  How long does it take you to draw up one of these?
-iggy

KRingway's picture
KRingway
September 16, 2019 - 6:16pm
Thanks! They're pretty much loose sketches, so maybe each one takes about 30 minutes or so. The dralasite ship took an hour or so as it's a bit more polished, took several redraws and evolved out of thin air. It started out as more like a saucer - if you rotate the image 90 degrees clockwise, that should give you some idea Smile I had less of a mental image of it when I started drawing, whereas with the system ship I wanted something a bit like a cross between the Palomino and some other shapes.

jedion357's picture
jedion357
September 17, 2019 - 3:24pm
Side Note- Stars Without Number rules handles things this way, or at least as I remember.

within a zone like planet to moon- 1 dice something hours

leaving a zone inner system to mid system 1 dice days

multiple zones inner system to outer system 1 dice weeks.
I might not be a dralasite, vrusk or yazirian but I do play one in Star Frontiers!

Shadow Shack's picture
Shadow Shack
September 17, 2019 - 3:58pm
iggy wrote:
Ion drives are powerful when you think to measure them as constant power over the full duration of the flight.  Chem drives expend all their power in quick bursts and then the engine is off and you coast.  So, when you add up the power availble and used over the entire duration of the trip then ion drives are more powerfull.

Which begs the inevitable question: what if a chem-drive ship has sufficient fuel tankage and simply installs a jump-governor to prevent it from entering the void? An ion drive holds 10,000 units of fuel regardless of ship size, so why couldn't a system ship hold a slew of fuel too? Not so powerful anymore...

Seriously though, it's like comparing gas driven automobiles to electric vehicles. Both perform similarily on the road but the electric has a much more limited range due to charging time and battery "life" per charge. To say the gas engine is more powerful because it goes further is the same argument.

So one is not more powerful than the other, rather one simply has a greater range.
I'm not overly fond of Zeb's Guide...nor do I have any qualms stating why. Tongue out

My SF website

JCab747's picture
JCab747
September 17, 2019 - 4:05pm
I'm more for the idea that you need something besides accelerating to one-tenth light speed to enter the Void.
Joe Cabadas

Shadow Shack's picture
Shadow Shack
September 20, 2019 - 2:16am
JCab747 wrote:
I'm more for the idea that you need something besides accelerating to one-tenth light speed to enter the Void.

At one-tenth you're already halfway to an alternative. SF only requires you to accelerate to 1/100 light speed.  Foot in mouth
I'm not overly fond of Zeb's Guide...nor do I have any qualms stating why. Tongue out

My SF website

KRingway's picture
KRingway
September 20, 2019 - 5:06am
JCab747 wrote:
I'm more for the idea that you need something besides accelerating to one-tenth light speed to enter the Void.

There's my ruleset for the Void Drive...

JCab747's picture
JCab747
September 20, 2019 - 10:31am
KRingway wrote:
JCab747 wrote:
I'm more for the idea that you need something besides accelerating to one-tenth light speed to enter the Void.

There's my ruleset for the Void Drive...
 

thanks
Joe Cabadas