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-   -   Space Logistics: Space Distances and Comms (http://forums.sjgames.com/showthread.php?t=179121)

Logrus 04-05-2022 12:30 PM

Space Logistics: Space Distances and Comms
 
I've recently dusted off my Transhuman Space books to run a small campaign, and I've run into a couple minor snarls. The plot I'm working on relies on the timing of information and travel times from various places, but I realized that I don't have a solid way of determining relative distances between objects in the solar system at an arbitrary time... and further, that travel is typically an intercept with an orbiting object, which requires another calculation. The default action will be rolling my own calculations for the relevant celestial objects (including but not limited to Titan, Ceres, and some of the Trojans) using R and some orbital physics stuff grabbed from wikis and educational websites, but if there's a solution in a box I'd rather just open the box. Ideally, I'm looking for something where I can punch in an arbitrary date and get the positions of every major object in the solar system at that date, and then a program for calculating travel time for intercepts.

I just bought GURPS Spaceships for use with the Transhuman Spacecraft supplement if that's of any help on the second question.

Also: In regards to TS communications technology, the most powerful communications laser listed in the book has a stated range of 2000 miles, with 10x for vacuum for a total distance of 20,000 miles effective range. The strongest mentioned radio has a pretty small effective distance as well. Is it just assumed that ship and large, institutional comm lasers and radios have much higher effective ranges? In 2013 NASA used a laser to transmit information at around 239,000 miles, and of course people on Earth communicate with the rover on Mars via a combination of radio and xband. Also, are there any good rules for using a comms laser as an improvised weapon?

TGLS 04-06-2022 11:06 AM

Re: Space Logistics: Space Distances and Comms
 
Quote:

Originally Posted by Logrus (Post 2423055)
Ideally, I'm looking for something where I can punch in an arbitrary date and get the positions of every major object in the solar system at that date, and then a program for calculating travel time for intercepts.

Well I suppose the first thing to mention is that the equations in spaceships are lazy and ignore the movement of the planets, gravity assists and so on. So here are some fudges:

A) It takes no more than the shorter orbital period of where you are and where you want to go to get around. The optimal launch window can always be achieved within no more than the shorter orbital period, so assume that you get close enough in just under that. Saturn isn't so far out that travel time will likely be an issue.

B) Pick an arbitrary day in the 20th century. Declare all orbits are circular and that all relevant planets were aligned that day. Then just calculate where the planets are based on that. Here's an example that shows the relative locations of Earth, Jupiter and the Greek & Trojan camps.

C) Roll whenever the PCs want to travel. If you roll well, the target is close to the minimum distance. If you roll badly, then the target is close to the maximum distance.

thrash 04-06-2022 12:36 PM

Re: Space Logistics: Space Distances and Comms
 
Travel time depends on a host of variables. I'm not aware of any pre-packaged system that will calculate it for you. For positions, however:

Go to the JPL Horizon's web interface ( https://ssd.jpl.nasa.gov/horizons/app.html#/ ).

Set the ephemeris type to "vector table."
Set the target body to whatever object you're looking for. The system is smart enough to understand common names, and numbers for asteroids.
Set the coordinate center as "solar system barycenter" or "500@0."
Enter the date or range of dates of interest.
Edit the output units under table settings to "au and days."

Hit "Generate Ephemeris." The output tables are underneath all the header data and a key.

This will give you an accurate location for any solar system body (and a few human artifacts), in Cartesian (x, y, z) coordinates. The only drawbacks are (a) you have to request one body at a time, and (b) if you want polar coordinates, you have to convert by hand.

You can get positions relative to a different body (e.g., Jupiter for its moons) by changing the coordinate center.

The system is extremely flexible, especially if you use one of the other interfaces, but how useful that is depends on how comfortable you are with astrometrical data.

Celjabba 04-06-2022 01:23 PM

Re: Space Logistics: Space Distances and Comms
 
You can use Stellarium (https://stellarium.org/) to easily find the distance between two bodies and their positions at a specific date/time.

Set the date with F5
Select your observation location with F6 (planet, moon, ...)
Hide the ground with G
Find and select another location with F3.
Among the data show on the left will be the distance from the observer to the target (in AU and km).

By selecting the observer location as observer of solar system, centering the view on the sun, and adding the orbits, you will get a nice planet location map for any given date/time

You can much more, obviously, it is an amazing tool.

Edit : even easier, there is a distance tool between 2 items (using F10)

Anthony 04-06-2022 05:00 PM

Re: Space Logistics: Space Distances and Comms
 
There's two basic things you want to work out transits: actual tables for where things are, and a porkchop plot generator to get true time and delta-V requirements. Last I looked at this there were various digital orrery programs that would help with the first, but not much for the second, but current searching did find me http://sdg.aero.upm.es/index.php/onl.../porkchop-plot.

Daigoro 04-10-2022 10:02 AM

Re: Space Logistics: Space Distances and Comms
 
There was a Pyramid article, Halfway to Anywhere (in 3/79), which had an included spreadsheet, for working out flight times and delta-V's of various kinds of trajectory.

the-red-scare 04-22-2022 01:34 PM

Re: Space Logistics: Space Distances and Comms
 
Wolfram Alpha will also give you distance between solar system bodies at any date. Just go to wolframalpha.com and type “distance from Earth to Neptune on 8/17/2100” or whatever. It’ll give you a whole bunch of other possibly useful info in the same result screen.

It’s 31.15 AU, incidentally.


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