<P> The lightness number is also independent of distance from the Sun because both gravity and light pressure fall off as the inverse square of the distance from the Sun . Therefore, this number defines the types of orbit maneuvers that are possible for a given vessel . </P> <P> The table presents some example values . Payloads are not included . The first two are from the detailed design effort at JPL in the 1970s . The third, the lattice sailer, might represent about the best possible performance level . The dimensions for square and lattice sails are edges . The dimension for heliogyro is blade tip to blade tip . </P> <Table> <Tr> <Th> Type </Th> <Th> σ (g / m) </Th> <Th> a (mm / s) </Th> <Th> λ </Th> <Th> Size (km) </Th> </Tr> <Tr> <Td> Square sail </Td> <Td> 5.27 </Td> <Td> 1.56 </Td> <Td> 0.26 </Td> <Td> 0.820 </Td> </Tr> <Tr> <Td> Heliogyro </Td> <Td> 6.39 </Td> <Td> 1.29 </Td> <Td> 0.22 </Td> <Td> 15 </Td> </Tr> <Tr> <Td> Lattice sailer </Td> <Td> 0.07 </Td> <Td> 117 </Td> <Td> 20 </Td> <Td> 0.840 </Td> </Tr> </Table> <Tr> <Th> Type </Th> <Th> σ (g / m) </Th> <Th> a (mm / s) </Th> <Th> λ </Th> <Th> Size (km) </Th> </Tr>

How big would a solar sail have to be
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