You really should take a look at this NYTM "Ideas" issue...
Here's another one:
Solar Sailing
By BRYAN CURTIS Published: December 11, 2005
Solar sailing is a bit like a missing link between Carl Sagan and Patrick O'Brian. "Imagine hoisting a sail and being out there in space," says Louis Friedman, the project director of Cosmos 1, the world's first solar-sail spacecraft. "It's a beautiful idea, and it conjures up the idea of the great sailing ships and whole notion of exploration." On June 21, Friedman's team placed the unmanned Cosmos 1 inside an intercontinental ballistic missile and launched it skyward from a Russian submarine. The missile faltered, and Cosmos 1 crashed into the sea - a scene recalling great shipwrecks more than great discoveries.
But if, someday, it works, Friedman says that solar sailing could have many advantages over conventional space flight. For one thing, a solar-sailing vessel does not require fuel. Once in space, the Cosmos 1 would have unfurled eight 50-foot-long sails, which would have arrayed themselves around the ship like flower petals. Engineers built the sails from thin sheets of aluminum-coated Mylar that were designed to reflect photons from the sun's light and thus propel the craft forward. As with an earthbound ship, the angle of the sails was to be manipulated to control the direction of the craft.
At first, a solar-sailing vessel would accelerate very slowly. But its acceleration would be constant, so that in a little over a year's time the craft could be traveling at speeds in excess of conventional rockets. For this reason, Friedman sees solar sailing as the ideal method to visit other planets. It could, he predicts, shave a few years off a satellite's 10-year trip to Pluto.
I think Arthur C. Clarke beat Sagan to it... "The Wind From The Sun" is one of my favorite Clarke stories, and IIRC, it came out 30 years ago or more.
Misconception. Continuous does not equate with constant.
The density of the radiation/particles producing the propulsion attenuates with distance from the source. Good old inverse square law at work.
The farther from the source (Sol, sun) the less radiation per sq meter of sail, so the lower the force impinging on the sail.
Therefor, the acceleration RATE is continuously decreasing with increasing orbital radius, even as acceleration remain continuous, and velocity continuously increases.
This translates to "the acceleration would be continuous", not "constant".