Many different methods of propulsion exist: chemical rockets, ion engines, even nuclear propulsion.

None of these propulsion methods offer the capability of delivering a spacecraft to the focal region of the Sun in a reasonable amount of time. Think about it: For Voyager 1, it took nearly half a century to travel 150 astronomical units (AU, the distance from the Sun to the Earth.) The Focal region of the Sun is nearly 4 times as far; the useful part of the focal region begins at roughly 650 AU. For Voyager 1, it would take nearly two centuries to reach that distance. Clearly, something better is needed.

Presently, the only known, mature technology that can accelerate a spacecraft to a high enough speed to reach the focal region in 25-30 years is solar sails But even for solar sails, this is a tall order: to get enough of a kick from the Sun, a very light spacecraft is needed with a very large sail, flying very close to the Sun.

Still, it might just be doable using existing technologies and materials. The image below shows a sample (unoptimized) trajectory with a 10,000 m² sail accelerating a 50 kg spacecraft. Sail temperature is calcuated using the values of ρ=0.95 for sail reflectivity and ε=0.8 for infrared emissivity.

Units are in AU. Temperature (color) scale is in K.

The first image offers an overview of the first two years of the probe's cruise (its ultimate egress velocity is roughly 21 AU/year.) Markers along the path are in years.

The second image shows a close-up of the initial part of the journey; markers represent months.

Finally, the last image shows the closest solar approach (perihelion), with markers representing days.

The cruise »