Date: Fri, 31 Jan 97 17:52:46 -0500 From: Derek Wildstar Subject: [Traveller Answer] Stellar Radii Douglas E. Berry asked: > What is a solar radii? Is this refering to the radius of the sun > or the radius of the solar system? SSDS refer's to this when talking > about Thruster Plates. It should probably be "stellar radii" (the radius of a star; "solar radii" means the radius of the Sun). No matter what you call it, it's referring to the useful distance for thruster plates. Thruster plates are gravitic technology, and require a gravity field to "push against" (that's a poor analogy, but it works for our purposes). As a rule of thumb, the gravity field is strong enough out to about 1000 diameters (2000 radii, since radius is half of diameter). Ususally the central star is the biggest object around; anywhere within 2000 radii of the system's star, the thrust plate drives will work. They'll also work within 1000 diameters of anything else, but for interplanetary travel amoung the outer planets of a system, thrust-plates are pretty useless. Dave Strebe asked: > So then what is the limit in AU's or Light Seconds of thruster plates? > 2000 solar radii=? Here's some tables to help you out: This first table lists the diameter of a star (in light-seconds) by the star's spectral class and luminosity. For example, Sol (our Sun) is a a main-sequence (Luminosity class V) G-type star. The diameter of a G5 V star is 4.2 light-seconds; the thrust-plate limit is 4200 light-seconds. Stellar Diameters in Light-Seconds Spect Luminosity Class Ia Ib II III IV V VI B0 243 140 103 75 61 47 -- B5 350 163 93 47 25 21 -- A0 630 233 84 29 21 15 -- A5 696 257 65 21 13 8.4 -- F0 813 276 75 22 13 7.9 -- F5 953 280 84 24 12 6.3 5.3 G0 1392 392 117 33 12 4.8 4.8 G5 2120 598 173 51 13 4.2 2.6 K0 3054 1009 252 75 15 4.2 1.9 K5 4716 1831 579 196 -- 2.6 1.4 M0 6837 4002 1107 294 -- 2.6 1.2 M5 14103 9680 3325 1065 -- 1.7 0.49 M9 16339 13430 4346 1681 -- 0.94 0.25 Dwarf Stars DB 0.084 DA 0.079 DF 0.061 DG 0.056 DK 0.042 DM 0.028 The limit for thrust plate drives is 1000 diameters (2000 radii). Multiply these values by 1000 to determine the distance in light-seconds. If you want to convert to AU, divide by 500 (500 light-seconds is 1 AU). Here are the "standard" orbits, in AU, millions of kilometers, and light-seconds. To use this table, look up the limit value in light seconds, to find the orbit numbers that are inside and outside the limit. For example, Sol's limit is 4200 light-seconds. This falls between orbits 6 and 7; therefore, in our solar system Jupiter is inside the limit, and Saturn is outside it. Orbital Radii in Light-Seconds Orbit AUs MKm L-S 0 0.2 29.9 99.7 1 0.4 59.8 199 2 0.7 104.7 349 3 1.0 149.6 499 4 1.6 239.3 798 5 2.8 418.9 1397 6 5.2 777.9 2595 7 10.0 1495.9 4990 8 19.6 2932 9780 9 38.8 5804 19360 10 77.2 11548 38520 11 154.0 23038 76846 12 307.6 46016 153493 13 614.8 91972 306786 14 1229.2 183885 613374 15 2458.0 367711 1226552 16 4915.6 735363 2452907 17 9830.8 1470666 4905613 18 19661.2 2941274 9811033 19 39322.0 5882488 19621865 Planets The limit also applies to planets, so it is sometimes useful to know what it is. I've pre-computed the limit, in light-seconds, for each size world. World Size and Distance Table Size Diameter (Km) Avg Diameter T/P Limit Code Min Max Km L-S Light-Sec R 0 <1 0 0.0 0.0 0 1 199 100 0.0 0.3 S 200 799 400 0.0 1.3 1 800 2399 1600 0.0 5.0 2 2400 3999 3200 0.01 11.0 3 4000 5599 4800 0.02 16.0 4 5600 7199 6400 0.02 21.0 5 7200 8799 8000 0.03 27.0 6 8800 10399 9600 0.03 32.0 7 10400 11999 11200 0.04 37.0 8 12000 13599 12800 0.04 43.0 9 13600 15199 14400 0.05 48.0 A 15200 16799 16000 0.05 53.0 SGG 20000 59999 40000 0.13 133.0 LGG 60000 119999 90000 0.30 300.0 Note: The average sizes given for small and large gas giants may vary slightly from that assumed by the Traveller rulebook. The averages above are the middle of the size range, and are generally larger than corresponding worlds in Earth's solar system. starwolf@sn.no (StarWolf) observed: > As the thruster plates push against a gravity well, it would imply > that the thrusters also would work outside the stellar radii limit, > but close to a planet. Right. 1000 diameters will do as a rule of thumb. Guy "wildstar" Garnett Traveller Answer Team wildstar@qrc.com - ------------------------------------------------------------------------------ Science-Fiction Adventure In the Far Future ------------------------------