Hi @romanst and welcome to the community 
Nice work! 
Here are a few improvements:
- The headers in the top row (Name, Mass, Diameter etc.) should be
<th scope="col">and not<td> - All the values and notes should have
<td>and not<th>. - The
scope,rowspanandcolspanattribute are all correct except for… - … three times where you used
colspan="row"which should bescope="row".
I hope that helps, 
Michael