Starship as an Enabling Option for a Uranus Flagship Mission

Abstract

In 2022, the National Academy of Sciences Planetary Science Decadal Survey recommended exploration of Uranus as its highest priority Flagship mission for the 2030s. The Decadal recommendation relied on the Uranus Orbiter and Probe (UOP) concept as its baseline for the mission. UOP assumed a launch in 2031 on a Falcon Heavy Expendable rocket and an intermediate Jupiter flyby, allowing it to arrive at Uranus before 2050. At present, it is likely that the original UOP launch will be postponed, which will cause a Jupiter gravity assist to become unavailable and could delay the arrival at Uranus. However, a later launch date allows us to consider launch vehicles currently under development such as SpaceX's Starship, a two-stage heavy-lift launch vehicle that is intended to be refuelable on-orbit. Although Starship's performance capabilities have yet to be demonstrated, current development timelines suggest they will be known before selecting a launch vehicle for a Uranus mission. This study investigates the possibility of leveraging the anticipated capabilities of Starship to support a Flagship mission to Uranus. The results show that with on-orbit refueling, Starship will be capable of performing direct transfer to Uranus without the need for intermediate planetary flybys. Direct transfer with Starship orbit insertion allows nearly five metric tonnes of mass to be deployed to Uranus orbit using nine refueling launches in ten years, compared to more than thirteen years for UOP. If the spacecraft is used to perform the orbit insertion maneuver, five tonnes of mass can be deployed in less than nine years with seven refueling trips. Larger payload masses and shorter times of flight can be achieved by using Starship to perform aerocapture. As a mid- to high-lift to drag ratio vehicle, Starship can succesfully perform aerocapture while maintaining deceleration and heating values that are not more severe than those observed by aerocapture studies for other vehicles. With seven refueling launches and a seven-year transfer time of flight, Starship can deliver nearly six tonnes of payload mass to Uranus using aerocapture. With a longer time of flight and additional refueling launches, mission masses greater than fifty tonnes can be delivered to Uranus orbit. By using Starship to deploy a spacecraft and probe of a similar design as UOP, the reduced transfer times can facilitate an arrival at Uranus well before equinox, and can enable science phases of up to ten years. Performing the insertion burn with Starship also increases the Δv available for the science tour. Using the UOP architecture would make the mission compatible with both Falcon Heavy and Starship, thereby reducing risk. Alternatively, the additional payload mass that can be deployed to Uranus with Starship can enhance the orbiter and probe architecture beyond the current design, potentially allowing for a larger instrument suite, additional probes, and even a secondary spacecraft. To this end, a Uranus Flagship mission using Starship presents a higher-risk, yet potentially greater-science-return option that could become viable if financial conditions permit.