You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Space_Race

Context:
The American professor Robert H. Goddard had worked on developing solid-fuel rockets since 1914, and demonstrated a light battlefield rocket to the US Army Signal Corps only five days before the signing of the armistice that ended World War I. He also started developing liquid-fueled rockets in 1921; yet he had not been taken seriously by the public, and was not sponsored by the government as part of the post-WW II rocket development effort. Von Braun, himself inspired by Goddard's work, was bemused by this when debriefed by his American handlers, asking them, "Why didn't you just ask Dr. Goddard?"[citation needed]

Question:
What professor began working on solid-fuel rockets since 1914?

Robert H. Goddard