The current rules (and, possibly, on reading back, the old rules) have some oddities than need to be changed or fixed. Like an 8000 miles air envelope around an earth sized planet. The fastest ship in the AA book would need 40 days to get off that planet.

So...here are my fixes.
This message was last edited by the GM at 21:04, Sat 29 July 2023.

I checked, and the book specifically states that even a planet's atmosphere extends outward the same distance as the planet diameter.

That would be 8000 miles for Earth, or about 41 days to get out of it in the fastest Spelljamming ship. Someone at WoTC didn't do the math.

Even using real world distances (60 miles) that's 20 hours for the slowest ships and almost 8 for the fastest. A lot for one helmsman, and changing helmsman would be....risky, what with the period you'd be falling and all.

I've used the size categories from the previous edition, and Earth's actual atmosphere size as a guideline to come up with atmosphere envelopes for planets:
Size A: not planets. less than 10 miles across envelope is quite large, gravity plane is flat
Size B:  10-100 miles across, 15 miles
Size C:  100-1k miles across, 30 miles
Size D:  1k-4k miles across, 45 miles
Size E:  4k-10k miles across, 60 miles (Earth)
Size F:  10k-40k miles across, 75 miles
Size G:  100k-1000k miles across, 90 miles (Jupiter, all atmosphere in reality)

There may well be exceptions, of course: a planet that is a ball of water may have very little air around it. And a planet that is all air is going to be thousands of miles of nowhere to land.

Encounter distance in 5e is DM choice from 3 given basic ranges: Close, Medium, and Long. It affects time to missile range, chase times, etc.

In my playtest of the rules I used a flat d20 rounds of distance (based on players' ship speed). If both ships approached each other it would be much quicker, in fact. This is backwards to Reality, as it has faster ships slowing down faster than slower ships.

Going forward I'll be using a flat distance of 1d20x100'. Fast ships will have an average of 14 rounds (slower ships up to 3x that) to prepare crew and weapons. Less if the encountered ship/beast moves towards you at the same time.

And, yes, with low rolls, you could come to encounter speed with overlapping envelopes. But then, with two large enough ships, the closer choice from the book could, also. And you might STILL be out of range for ballista.

Note that you CAN load a weapon before you reach that weapon's long range, but you can't aim or fire it until long range is reached. Still, loading it early saves time on an undermanned weapon.
This message was last edited by the GM at 19:08, Thu 12 Jan 2023.

Each of these may have the skill replaced with Vehicle(Space) to reflect spacer training. DCs will likely be low, most times:

-Swapping orientation passing through a gravity plane would be Dex(Acrobatics) as movement if time is short. Otherwise you're getting up from prone, literally. And that's assuming a floor is handy. Other times a fall has turned into a climb, such as barnacle scrapping duty. DC 5 most times, after some experience at it, DC 10 the first time or two, until you've rolled 3 successes (which may be over multiple instances).

-Boarding in combat is a Strength(Athletics) roll. You're jumping a gap that may be up to 5' per the rules given. See jump notes in another post

-Semaphore codes are universal (except when they aren't, for some reason) in space. They likely won't be the same as water ships use. See Semaphore notes in another post.

-Most sailor jobs (Vehicles(water)) will have an equivalent Spacer job (vehicles(space)), of course, but as other specialty tasks come up, I will add them to this list.

The boarding rules in AA almost follow all the typical jumping rules. Boarding is usually a 5' standing long jump with a DC 10 to clear an obstacle of up to 1.25 feet.

Typically a standing long jump of 5 or less is automatic for a Strength of 10 or more. However for a strength of 8 or 9, which can't clear the gap, more is needed. For a 1' I'll allow a Strength (Athletic) roll.

Of course, both ships have guard rails that need to be cleared. Standing on yours to remove the DC 10 is another Acrobatics check. If boarding is a frequent activity, place crates along your guard rails to stand on. Even then you still need to hope their guardrail isn't higher (BTW, 3' is typical for a guardrail, you can only clear 16 inches, even with a roll).

So, in an effort to assume AA isn't just poorly playtested, let's assume a trained spacer (one with Vehicle(Spacer) proficiency) can clear a guardrail(only) of 3' or less with a  standing broad jump...if he or she has a strength of 10 or higher. Everyone else needs prior planning and/or a die roll or two.
This message was last edited by the GM at 21:11, Sat 29 July 2023.

Semaphore signals in Space are pretty universal, except when they are not, usually due to isolation of one party for the recorded past.

Basically, you can wave signals to other ships and understand replies unless, for some reason, they are determined to not to use the same code patterns.

One of those reasons might be that they are using a planetary signal protocol, implying they are new to space.

While Vehicle(space) shares one flag language, Vehicle(water) doesn't. Each planet has their own, and oceans far enough apart not to have contact (Such as Medieval Atlantic and Pacific) might have different flag languages.
This message was last edited by the GM at 21:12, Sat 29 July 2023.

Ok, officially you can see stars from the space station, even with the sun up, due to a lack of atmosphere to diffuse sunlight.

Same with the lunar landers, although they saw more standing in the lander's shadow.

How much atmosphere is necessary to block the view is the question, because you certainly have some on a spelljammer.

I'm sure someone somewhere could work it out, but that someone isn't me. Obviously light intensity is going to affect diffusion and even iris dilation (brighter light means eyes adjusting to compensate, so less able to see dimmer lights).

As I have already ruled "no" at earth light intensity, that will be the cut off. You can enjoy the stars heading out, and will barely notice the Sun when you hit the asteroids (about 11% Earth intensity and Dim in direct Sunlight).
This message was lightly edited by the GM at 18:49, Sat 14 Jan 2023.

Ok, folks, as I was already down the "Light in Space" rabbit hole, a fact about Ceres light:

It is 11% Earth normal. A Full moon on Earth, by contrast, is .1% daytime normal.

Jupiter gets 4%. That's 40x a full moon.

A full moon MIGHT count as Dim light per the PHB, so I'll set THAT cutoff at 1% Earthlight

Of course, this is direct sunlight. the tiniest shadow sets you in Dark conditions.
This message had punctuation tweaked by the GM at 21:14, Sat 29 July 2023.

Encounter distance in 5e is DM choice from 3 given basic ranges: Close, Medium, and Long. It affects time to missile range, chase times, etc.

In my playtest of the rules I used a flat d20 rounds of distance (based on players' ship speed). If both ships approached each other it would be much quicker, in fact. This is backwards to Reality, as it has faster ships slowing down faster than slower ships.

Going forward I'll be using a flat distance of 1d20x100'. Fast ships will have an average of 14 rounds (slower ships up to 3x that) to prepare crew and weapons. Less if the encountered ship/beast moves towards you at the same time.

A thought occurred:

Astral Space has no biological activity: Characters don't age, food doesn't spoil, even sleep in unnecessary (although rest is needed for spell recovery). Astral elves and Githyanki need bases in the Prime to raise children (and, presumably, to conceive them).

This means healing in the Astral wouldn't happen, either. All Astral healing would have to be by magic.

On the plus side, poison and disease would need some hefty magic to affect you while Astral, although unknown poisonings and disease exposures could manifest as soon as you return to the Prime.

This makes healing during Short Rests impossible, as well, although there may be other Short Rest benefits based on class, feat, or skill.

I'm not sure if this is House Rule, strict RAW, or overlooked ramification of RAW that seems to crop up in the new SJ rules a fair bit.
This message was last edited by the GM at 21:16, Sat 29 July 2023.

Items tend to recharge at dawn. What if there is no dawn?

Well, technically, you could take the ship in a barrel roll and make it dawn...or say that nothing ever recharges in the Astral.

So I'm going to start the clock at 24 hours, exactly, after the first charge is used, and every 24 hours going forward until the item is fully recharged. Then the clock will start anew on the next usage.

This probably won't come up much with days passing between random encounters, but you never know.