|
School of Aerospace 宇航学院 |
|
Tsinghua Space Center 宇航中心 |
|
Space Propulsion 空间推进 |
|
Solar Sail 中文
Solar sails reflect photons of sunlight, thus harnessing their momentum. A flat surface of reflective material is used in solar sail to create a thrust. Since no propellant is necessary for their operation they may be referred as propellantless propulsion Solar-light pressure can be calculated as:
where p – light pressure, Pa R – sail reflectivity FE = 1373 W/m2 – solar-light flux at Earth’ orbit c = 3×108 m/s – light speed rE = 1.496×1011 m – Earth’s orbit radius r – distance from the Sun, m Whence, light pressure reaches maximum when R = 1, i.e. the sail surfaces must be tremendously reflective to maximize the propulsive force from the particles of sunlight. Reflectivity of modern mirrors 0.95-0.97. Reflectivity of advanced materials multi-layer films using diffraction can reach 0.9997.
Figure 1. Solar-light pressure as a function of distance from the Sun (R =1). (A.U.— Astronomical Unit)
A solar sail uses no propellant, however, the thrust-to-weight (T/W) ratio is very low, 10-3 to 10-5 (Figure 1 shows the 9 N/km2 solar pressure at Earth's distance from the Sun), resulting in long trip times. Simulations of solar sail propulsion missions done at Tsinghua Space Center demonstrate that: · Traveling time to Martian orbit would take more than 5 years (Figure 2)
Figure 2. Solar sail mission to Martian orbit
· Traveling time to Venus’ orbit would take about 3 years (Figure 3)
Figure 3. Solar sail mission to Venus’ orbit The simulations were done assuming 40kg spacecraft (s/c) equipped with 400m2 solar sail.
Figure 4. 3-D solar sail mission to Venus’ orbit
Phone: +86-10-627-94446 Home Updated Jan. 2006 |
