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

Just by going into orbit and counterbalancing the Earth's gravity with rotational velocity doesn't mean it's not still moving extremely fast relative to the stars