Deadhead

Deadheading the name given to sublight interstellar travel. The art of flying from one solar system to another at the speed of light under the power of conventional engines.

It is commonly the only way for low TL empires to get to distant stars when the wormhole routes are nonexistent or too dangerous and they haven't discovered warp drive technology yet.

If a spacecraft without a avatar or officer on board tries to leave a system though, they will collide with dark matter.

Travel Time

Deadheading to a solar system can take anywhere from half an hour to several hours, depending on the distance to the destination and acceleration of the spacecraft.

Commonly it takes about 10 minutes to reach the speed of light, then 10 minutes per parsec, followed by another ~10 minutes of deceleration.

c = Lightspeed
a = Acceleration
t = Time
d = Distance

Acceleration to lightspeed in seconds
t = c / a

Distance traveled during acceleration
d = 0.5 * a * t ^ 2

Modified from dummies.com.