| Space exploration is in a period of transition. The retirement of the Space Shuttle has left a void in heavy payload deployment that can be filled many ways. Private companies are getting more involved, while others in space agencies want to develop heavy-lift launch vehicles. One solution, which has attracted attention in recent years, is propellant depots. These depots would store cryogenic propellants in low Earth orbit for use by other spacecraft when needed. While propellant depots would be useful, the cost and time to develop them is prohibitively high.;An alternative proposed in this paper is the space tug highly elliptical rendezvous orbits (HERO) concept. In order to keep the development cost low and take advantage of flight proven hardware, the tugs can be made from the cryogenic upper stages of existing rockets like the Atlas V and Delta IV. Each tug boosts the payload into much higher elliptical orbits until the payload is ready to escape to its destination.;The studies included in this paper target Venus, Mars, and Jupiter as destinations for the payload. Venus and Jupiter were chosen because many missions use them for gravity assist trajectories to gain velocity. Mars is included because it is a site of heavy scientific interest, and a direct approach is very desirable.;With these three targets, the space tug HERO method can explore almost anywhere in the solar system. This paper will show that the proposed concept is more viable than propellant depots in many key areas including cryogenic propellant losses, maximum payload mass, and overall cost. |
