Solar sails fall into the category of "niche technologies" on the Frontier. That is, they are extremely useful but limited in their applications. The advantages of sails are that they are cheap and require no fuel; they are also fairly easy to maintain, and are the only drives potentially capable of more than 1 ADF that can be built at Class III Construction Centers. Their disadvantages, however, are equally great: they are only useful in the inner regions of solar systems, and they are easily detectable by radar. Thus, solar sails are common but only i a narrow range of applications - civilian freighters, passenger liners and research system ships. They will never be found as military, courier or pirate craft.
Knighthawks Performance Characteristics
A solar sail equipped ship's ADF is [1 x 1/(ship's distance from star in AU)squared]. Examples are given below of ADF's at typical system orbits:
Distance from Example
System's Star Planetary Orbits* ADF**
0.4 AU Mercury 7
0.5 AU Snowball (Mhemne homeworld) 4
0.7-0.8 Venus, Inner Reach, Gollywog (Clarion),
Liberty system's asteroid belt 2
1 AU Earth, Outer Reach / Dramune 1
1.5 AU Mars 1 / 3 turns (about 2 / hr)
2.2 AU Lost Reach / Dramune, White Light system's
asterod belt 1 / 5 turns (about 1 / 50 minutes)
5 AU Jupiter 1 / 25 turns (about 1/ 4 hrs 10 minutes)
10 AU Saturn 1 / 100 turns (about 1 / 16 hrs 40 minutes)
20 AU Uranus 1 / 400 turns (about 1 / 66 hours, 40 minutes)
30 AU Neptune 1 / 909 turns (about 1 / 151 hrs 30 minutes)
40 AU Pluto 1 / 1600 turns (about 1 / 267 hours)
* Sample orbits greater than 1 AU are rounded to the nearest AU for simplicity's sake; orbits less than 1 AU are rounded to the nearest 0.1 AU. 1 AU (Astronomical Unit) equals roughly 149.7 million km.
** ADF ratings are rounded to the next lowest number (ie. 2.5 ADF = 2)
No matter what the size of the ship, the size of the sail or the distance to the nearest star, a solar sail-propelled ship will always have a MR of 1; the MR is produced by altering the size and angle of the sail combined with high-efficiency chemical attitude jets.
Solar sails are too thin to generate power for the ship, which must carry an independent power supply (usually a small nuclear plant or a solar array. Since their power plants generate minimal energy emissions, solar sail equipped ships are invisible to energy sensors. Due to the huge area of the sails when they are deployed, a sail-driven ship can be detected by radar at twice the normal distance (600,000 km); if the sails are reeled in and stowed, the ship will be detected by radar at the normal range (300,000 km). Deploying and reeling in a sail requires 1 turn per 10,000 square meters of sail area.
Size and Cost of Solar Sails
The sizes and costs of solar sail drives are as follows:
Hull Size (Engine Class) Sail Size
HS 1-4 (Class A) 1000 square meters (1 square km) / HS point
HS 5-14 (Class B) 10,000 square meters (10 square km) / HS point
HS 15-20 (Class C) 100,000 square meters (100 square km) / HS point
NOTE: If a ship is equipped with a sail of the next higher engine class (ie. a HS 3 ship is equipped with a 30,000 square meter sail), the sail's ADF performance will increase by a factor of two; this is rarely done, especially on
larger ships, due to the prohibitively large sails required.
Hull Size (Engine Class) Class I Center Class II Center Class III Center
HS 1-4 (Class A) 10 Cr / square meter 12 Cr / square meter 15 Cr / square meter
HS 5-14 (Class B) 5 Cr / square meter 6 Cr / square meter 8 Cr / square meter
HS 15-20 (Class C) 1 Cr / square meter 1.2 Cr / square meter 2 Cr / square meter
Sail Construction, Mounting and Stowage
Solar sails are made possible by advanced materials technology, allowing for extremely thin and reflective films and superstrong support cables. Primitive sails were built using ultrathin thin mylar for the sails and high-strength copper alloys for the support cables. Modern sails are composed of heat-resistant boron only a few hundred atoms thick, manufactured under vaccuum conditions on orbital stations; the thin support cables are filaments of industrial diamond extruded in orbital factories.
Solar sails are the only drive that can be mounted in addition to traditional engines. Where traditional engines are mounted at the back of a ship's hull, sails are mounted at the front end, towing the ship along behind. It is not uncommon for a ship to mount a sail as a back-up to its regular engines for emergencies; this option is especially popular on deep space research vessels and on passenger liners.
Solar sails are composed of molecules-thick (in advanced sails, even atoms-thick) reflective materials ad thus add comparitively little mass to a ship. This allows them to be stowed in compartments mounted on the outer hull of a ship or in internal cargo bays. If sails are stowed internally, they occupy 2 HS points per Size Class of the sail; external stowage uses only 1 HS point per Size Class of the Sail.
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