the spacecraft doesn’t immediately lose all the celestial relative velocity just by going into space, it’s still moving extremely fast:

• with the sun and earth through the galaxy
• with the Earth around the sun
• and is still affected by Earth’s gravity, just now it’s able to counter Earth’s pull with a faster motion pulling it outward, so it balances out to appear weightless

Think of how the moon gets dragged along with the Earth around the sun and the sun drags the Earth and moon along through the galaxy.