In 1923, Sander purchased the H. G. Cordes company in Bremerhaven, which had been manufacturing black powder charges to power whaling harpoons since the mid nineteenth century. Sander soon expanded the factory's products to include signal rockets. In 1928, he was approached by Max Valier, on behalf of Fritz von Opel to provide rockets to propel cars and aircraft as a means of promoting the Opel company. Their joint projects involved the creation of the world's first rocket car, the Opel RAK.1 and the first rocket plane, the Ente.
From 1930, Sander (with other pyrotechnics factories) began secretly manufacturing rockets for military purposes, at the direction of Walter Dornberger. In 1936 he signed a contract for the sale of some of these weapons to Italy but was denounced as a traitor by the Nazis and imprisoned. During this time, the company was bankrupted, but upon his release later the same year, Sander founded a new company, Comet GmbH with the assistance of some of his previous suppliers. In 1938, the firm was nationalised and Sander, again imprisoned, was forced to sell his interests in it to the Nazi Party. He died while in custody.