I love both Astrid and Nova - both really cool sounding.
I'm not really sure about 'strong but feminine' - very few girl's names sound masculine to me. I suppose names with consonant endings have a stronger sound to vowels? Things like:
Autumn, Brynn, Bronwen, Cerys, Charlotte, Clare, Devon, Dylan, Eirlys, Evelyn, Edith, Elise, Eve, Ellen, Elizabeth, Faith, Florence, Frances, Grace, Giselle, Gabrielle, Harriet, Hope, Isabel, Imogen, Iris, Juliet, Jasmine, Jade, Josephine, Kate, Katherine, Lois, Lauren, Madeleine, Merryn, Miriam, Nadine, Olive, Paige, Pearl, Quinn, Rachel, Ruth, Rhiannon, Rose, Saffron, Seren, Scarlett, Tegan, Taryn, Tess, Vivienne, Wren, Yasmin