NASA was not alone in studying crewed lunar missions. Von Braun had always expressed an interest in this goal, and had been studying what would be required for a lunar mission for some time. ABMA's Project Horizon proposed using fifteen Saturn launches to carry up spacecraft components and fuel that would be assembled in orbit to build a single very large lunar craft. This Earth orbit rendezvous mission profile required the least amount of booster capacity "per launch", and was thus able to be carried out using the existing rocket design. This would be the first step towards a small crewed base on the moon, which would require several additional Saturn launches every month to supply it.