regina in-system travel

[grymlocke]

Situation: Players need to travel from regina starport to the gas giant (Elazair) around Darida and have at up to 6g at their disposal.

anyone have an idea how long it would take?
canon regina system:
Lusor
0 clement
1 ausun
2 burgund
*3 cent
*7 thermidor
3 olybrius
*25 alise
4 assiniboia
*3 redes
*6 pritemps
*7 brumaire
*30 hardourt
*55 regina
companion darida
0 augur
1 kirunda
*8 irkirka
*11 arkurer
*13 irgurkar
2 elazair
*3 lashir
*8 diuur imar
*9 shamardae
*20 arapan
*50 edaku
*125 garamshir

 

[RandyT0001]

According to the Classic Traveller Scouts Book Darida is 5000AU's from Lusor, Regina's primary star. (LBB6 p.55) According to MegaTraveller's Referee's Companion p.21 a normal space journey of 5000 AU's at 6G would take 81 days, 19 hours, and 12 minutes. It would be quicker to use jump drives to travel there in a week then refuel at the gas giant.

Hope this helps.

 

[klingsor]

Just to add to the fun the planets move relative to each other as they orbit so the distance will vary considerably - they might be relatively close or they might be on opposite sides of the sun to each other.

 

[RandyT0001]

Just to add to the fun the planets move relative to each other as they orbit so the distance will vary considerably - they might be relatively close or they might be on opposite sides of the sun to each other.

That will depend upon the orientation of each star's orbital plane to the other. There could be very little change (very rare since the planes in effect have to have their axis pointing at each other) to high (when the planes' axes are effectively parallel to each other). IMO the variation probably would fall within a 100 AU range, possibly adding a day or two (at most) to the overall travel time. I think his biggest worry will be if the ship reaches/approaches lightspeed since it is accelerating at 6G's for about month and a half then flipping around for the decceleration and the relativistic effects.

 

[alex_greene]

They wouldn't get that far. Interplanetary dust particles would have become a hazard to navigation long before then.

 

[EDG]

A little related to the topic, I posted a more realistic system layout for Regina on the Avenger boards a while back. Unfortunately most of the derivation of it got lost when they last reorganised their forums, but I did rescue some of it from the google cache and posted it here:

http://www.traveller.comstar-games.com/viewtopic.php?f=31&t=1471

Primary: Lusor (Solo F7 V, 3 Ga old, 1.25 solar masses, 3.17 Sol luminosity)
Close Orbit (0.05 AU): Speck (Hot Jupiter, 1.7 Jupiter Masses)

0 Clement (Terrestrial world)

1 Ausun Belt (Planetoid Belt)

2 Burgund (Superjovian, 4.2 Jupiter masses)
• 8 Cent
• 17 Thermidor

3 (Empty Orbit)

4 Regina (Terrestrial World)
• 40 Printemps

5 (Empty Orbit)

6 Assiniboia (Superjovian, 7.941 Jupiter masses)
• 7 Redes
• 11 Brumaire
• 30 Harcourt

 

[alex_greene]

Have you checked the writeup of the Regina system in Mongoose' The Spinward Marches, by the way?

 

[RandyT0001]

Have you checked the writeup of the Regina system in Mongoose' The Spinward Marches, by the way?

Yep (p.66), and there is no mention on the distance between the systems, hence my reference to the CT source.

 

[EDG]

5000 AU is 750,000,000,000,000 m - assume 6g (60 m/s²) acceleration and a standard accelerate-turnaround-decelerate procedure.

Travel time = SQRT(2s/a), where s = distance/m, a = acceleration. But since you're accelerating to the halfway point you use half the distance in the equation, and then multiply the result by two to get the total travel time.

So it should take 982.09 hours (about 41 days) to get to the halfway point - given that it'll take the same amount of time to decelerate from that, you have a total travel time of around 82 days.

So Randy's answer from the book was correct .

 

[alex_greene]

More than that.

According to Mongoose' Spinward Marches, Regina is now a moon of Assiniboia.

 

[RandyT0001]

More than that.

According to Mongoose' Spinward Marches, Regina is now a moon of Assiniboia.

Regina is listed as a moon of Assiniboia in the Classic Traveller Scouts Book also.

 

[RandyT0001]

5000 AU is 750,000,000,000,000 m - assume 6g (60 m/s²) acceleration and a standard accelerate-turnaround-decelerate procedure.

Travel time = SQRT(2s/a), where s = distance/m, a = acceleration. But since you're accelerating to the halfway point you use half the distance in the equation, and then multiply the result by two to get the total travel time.

So it should take 982.09 hours (about 41 days) to get to the halfway point -

But what is the speed at that time, is it faster than light or close enough to it to cause significant relativistic effects?

So Randy's answer from the book was correct .

Just hoping to prove I'm smart enough to get into your planetary science / astrophysics classes online. 8) :wink:

 

[EDG]

According to Mongoose' Spinward Marches, Regina is now a moon of Assiniboia.

It always was in CT. My realistic version makes it a planet in its own right because in all likelihood it should lose its atmosphere as a result of being in Assiniboia's magnetic field. Also, it'd be tidelocked to Assiniboia which means it would have a very long day (too long to be habitable).

 

[EDG]

So it should take 982.09 hours (about 41 days) to get to the halfway point -

But what is the speed at that time, is it faster than light or close enough to it to cause significant relativistic effects?

212,132 km/s at turnaround. So yes, it'd be a bit silly (over 2/3rds the speed of light). Dunno if you'd have strong relativistic effects - I think you'd only see significant time dilation closer to 0.9c - but you don't want to be hitting dust particles at that speed.

 

[alex_greene]

I do find myself wondering how Regina could get away with being a moon of a large gas giant.

I mean, it must have some wicked winters, and several of them in each orbit as it goes behind Assiniboia's shadow and gets cut off from Lusor every time.

 

[EDG]

I do find myself wondering how Regina could get away with being a moon of a large gas giant.

It can't - which is why I made the system more realistic.

At an orbital distance of 55 radii, it'd take 18.87 days to orbit Assiniboia (assuming 7.941 Jupiter masses, which is about as small as it'd have to be to have a satellite that big). Since it'd be tidelocked to the gas giant at that distance, that means its day would also be that long. That wouldn't make it anywhere near as habitable as it's supposed to be.

Also, the time it spends in eclipse is very short compared to the long night length (9.435 days), so it wouldn't make any significant difference.

 

[RandyT0001]

I do find myself wondering how Regina could get away with being a moon of a large gas giant.

I mean, it must have some wicked winters, and several of them in each orbit as it goes behind Assiniboia's shadow and gets cut off from Lusor every time.

If we were to use Saturn, the smallest a Large Gas Giant (LGG) can be at about 60,000km radius, as a baseline for Assiniboia we find that Regina is 3,355,000km from Assiniboia or about 8.3875 Earth-Moon distances. Saturn (and Assiniboia) is about 95.2 masses of Earth and Regina is almost the size of Earth we can roughly calculate the orbital period, in Lunar months (28 days), of Regina around Assiniboia using the 96 Earth mass equivelants in the following equation from LBB6.

P=sqrt(D^3/M) where D=8.3875 and M=96
P=69.4 days

So for Regina to cross the shadow of Assiniboia it will take a little less than five hours (I think).

I might not have the calculations right though.

 

[EDG]

I might not have the calculations right though.

Well there's the fact that Assiniboia's mass has to be nearly 8 Jupiter masses for it to even have Regina formed in orbit around it (radius is 74,120 km, density 8839 kg/m³)...

And the fact that I already calculated the orbital period in the previous post

EDIT Also, this could probably be adapted to figure out the length of an eclipse of a satellite around a gas giant...
http://www.eso.org/public/outreach/eduoff/aol/market/experiments/middle/skills202.html

 

[Gee4orce]

Most worlds (and their satellites) are inclined with respect to their orbital plane. This means that passing through the shadow of it's parent world is probably a fairly uncommon event for Regina, and not something that happens every orbit. This is the equivalent of 'lunar eclipses' here on earth, which only seem to happen every couple of years - plus Regina's orbit is 3 times longer than Lunas - so you could handwave that it's something that only happens a couple of times a decade.

I don't think the presence of a significant atmosphere is a problem for a moon of a gas giant - witness Titan.

As EDG points out, the big problem is being tidally locked. It's possible that Regina has been recently captured by Assiniboia which would give a reason that its not locked, but that wouldn't help it's habitability any, as I doubt being yanked out of your original orbit does much for your habitability.

There may be 2 solutions:

move it closer to assiniboia, so that it's tidally locked but it's day lengths are more reasonable. You'd probably then run into problems with hard radiation from Assi, and atmosphere stripping.

move it further away, which I think would reduce the tidal forces and make it less likely to be tidally locked.

 

[Kilgs]

I use the Interactive Atlas. Click on the Systems Detail in a system and there is a map that plots travel times and orbits based on the calendar.

http://www.utzig.com/cgi-bin/iai/map_top.pl