In-space refueling vs heavy lift? NASA and SpaceX choose both

Recently, NASA announced several technological development projects designed to advance the art and science of deep space travel. In one of these projects SpaceX will practice transferring fuel in space using the Starship deep space vehicle now being developed.

The argument over whether to use heavy-lift or in-space refueling has raged across the space community since the George W. Bush-era Constellation project to return to the moon. NASA’s traditional fueling method has been to use a big, heavy-lift rocket such as the Saturn V or the more modern Space Launch System. However, an alternate architecture has been proposed, which uses smaller, commercial rockets with a refueling depot to send people and cargo back to the moon.

A 2011 NASA study of a lunar travel plan using a refueling depot suggested that a fuel depot would be deployed in low Earth orbit, taking six launches of the Falcon Heavy and one of the Falcon 9 before the first lunar mission. Then another 24 launches (20 of the Falcon Heavies, most of which would top off the depot with liquid oxygen and liquid hydrogen, and 4 launches of the Falcon 9 which would launch crew to Earth orbit) would result in a lunar mission taking place once every two years for a total of four more trips to and from the lunar surface. (The Falcon Heavy today has improved its performance by 20 percent and the Falcon 9 has improved even more since this 2011 NASA study, so the system would be even better today.)  A similar NASA plan using the Delta IV Heavy would involve 36 launches for four missions to the Moon (or nine launches per mission) over a similar period of time after the deployment of the fuel depot.

NASA would avoid the cost of developing a heavy-lift launcher such as the Constellation-era Ares V or its successor Space Launch System. The flaw in the approach involved a very ambitious flight rate for either the Falcon Heavy or the Delta IV Heavy. NASA could only launch a lunar mission once every two years if the flight rate could be achieved,

Also, relying on in-space refueling and not developing a heavy-lift vehicle proved to be politically unacceptable. Indeed, as Ars Technica reports, Senate Appropriations Committee Chairman Sen. Richard Shelby (R-Ala.) vetoed any thought of an alternate architecture using space-based refueling, since it would compete with the heavy-lift SLS, then as now under development in his home state. NASA at the time did not consider the Falcon Heavy a “real” rocket. Taking direction from its congressional masters, the space agency abandoned any thought of reusing the refueling approach.

Fast forward to 2019. SpaceX has pioneered the use of reusable first stages, both for the Falcon 9 and the Falcon Heavy. The Starship is not only a heavy-lift rocket — it also is designed to be reusable. The heavy-lift vehicle is also designed to be topped off with fuel before proceeding to deep space destinations such as the moon and Mars.

Meanwhile, the Space Launch System is many billions of dollars over budget and years behind schedule. The latest date for its first flight is sometime in 2021.

NASA first acknowledged the Starship’s existence when an official of the space agency suggested that it would partner with SpaceX if it landed a Starship on the lunar surface. The latest announcement of several partnerships with industry included a project to study in-space refueling using the SpaceX Starship. The Starship, designed to be both reusable and to have a frequent flight rate, would benefit from such an approach, in effect combining the power of a heavy-lift rocket with the reduced expense of in-space refueling.

Why is NASA jumping back into the in-space refueling game after nearly a decade? One factor is that the Trump administration, unlike President Obama’s, is quite serious about sending American astronauts back to the moon. Vice President Mike Pence has been pushing NASA to try innovative approaches to accomplish the goal of sending people back to the moon and on to Mars.

Also, while NASA Administrator Jim Bridenstine has sworn solemnly that the “first woman and the next man” will fly to the lunar surface using the Space Launch System, the expendable, heavy-lift launcher championed by Shelby, the powerful appropriations chairman is 85 years old and is not getting any younger. Shelby is up for reelection in 2022 and may not choose to run because of his advanced age. With Shelby gone, the main champion of the SLS also goes away. Thus, the era of the expendable launcher will come to an end, and reusable rockets such as the Starship will fly unimpeded. 

Mark Whittington is the author of space exploration studies “Why is It So Hard to Go Back to the Moon? as well as “The Moon, Mars and Beyond.” 

This piece has been updated.