What Anton did not want the vampire to realize was that because Kostya was an Other (an Other without classification to boot), he would not be able to perform any magic in the vast emptiness of space. There would be no energy there from which he could draw on, in space he was separated from the source of all Others' energy. Kostya, assuming the shield was put up because Anton was afraid and wanted to protect himself from harm, expressed his surprise at such an act of cowardice and opened the portal. Only when the vampire stepped through it did Anton relax - the threat was over. It takes thousands of calculations to put a rocket into orbit. He knew that Kostya could not possibly calculate the exact position of the station. The portal deposited Kostya into orbit, leaving him to float in his spacesuit, unable to perform any magic. He could not make a corrective teleport into the space station - he could not open a portal back to the planet. He could only remain in orbit as that orbit decayed and he ended up burning up in the atmosphere upon re-entry, along with the book.