Proposals have been made to ?sail? spacecraft to the outer solar system using the pressure of sunlight, or even to propel interstellar spacecraft with high-powered, Earth-based lasers. Sailing spacecraft would need no fuel a great advantage because fuel constitutes much of the initial weight of any space mission. NASA?s Sunjammer, launched in 2015, is the first sailing spacecraft deployed beyond Earth orbit. Figure 29.15 shows what a similar solar sail might look like in space.

If a sunlight-powered sailing spacecraft accelerated at 1m/s 2 in the vicinity of Earth?s orbit, what would be its acceleration at Mars, about 1.5 times as far from the Sun as Earth?a. about 0.25 m/s²b. a little less than 0.5 m/ s²c. a little more than 0.5 m/ s²d. about 0.66 m/ s²