A blog called “Innerspace” uploaded on March 12, 2014 what it called a detailed analysis of the NASA FY2015 budget request but was really a lament for that budget’s downgrading of an in orbit demonstration of cryogenic fuel depots to a ground based experiment in support of the Space Launch System.
A faction exists among space advocates that maintains building a heavy lift rocket such as the Space Launch System is unnecessary. Instead NASA should develop a concept that involves multiple launches of currently or soon to be available rockets to lift fuel to a depot in low Earth orbit. While this would involved extensive research and development of technology that would allow the long term storage of liquid hydrogen and liquid oxygen in space, currently subject to a phenomenon known as “boil off,” a NASA study suggested that there would be cost savings by using fuel depots rather than developing a heavy lift rocket.
Curiously, the blog post cherry picks a part of the most recent Augustine Commission report to buttress the point.
“In the absence of in-space refueling, the U.S. human spaceflight program will require a heavy-lift launcher of significantly greater than 25 mt capability to launch the EDS and its fuel. However the picture changes significantly if in-space refueling is used.” Furthermore “Studies commissioned by the Committee found that in-space refueling could increase by at least two to three times the injection capability from low-Earth orbit of a launcher system, and in some cases more. Thus, an in-space refueling capability would make larger super-heavy lift vehicles even more capable, and would enable smaller ones to inject from low-Earth orbit a mass comparable to what larger launchers can do without in space refueling.”
However the entire section on the utility of using fuel depots suggests a different conclusion. It suggests that relying on fuel depots alone would create unacceptable risks, would eat up most of the production capacity of current commercial rockets, and would be an expensive alternative in any case. The commission concluded that heavy lift is vital for any space exploration,, though it would later benefit from the addition of fuel depots when the technology is thoroughly matured and tested.
“The Committee finds that exploration would benefit from the development of a heavy-lift capability to enable voyages beyond low-Earth orbit. This might be supplemented by the development of an in-space refueling capability. In-space refueling has great potential benefits, but needs development and demonstration before being incorporated into a baseline design. Using a launch system with more than three critical launches begins to cause unacceptably low mission launch reliability. Therefore a prudent strategy would be to use launch vehicles that allow the completion of a lunar mission with no more than three launches without refueling. This would imply a launch mass to low-Earth orbit of at least 65 to 70 mt based on current NASA lunar plans. Vehicles in the range up to about 100 mt will require in-space refueling for more demanding missions. Vehicle above this launch capability will be enhanced by in-space refueling, but will not require it. When in-space refueling is developed, any of those launchers will become more capable.”
It other words it suggests that marrying in orbit fuel depots to the Space Launch System is actually compliant to the option suggested by the Augustine Report.
By the way, the NASA study suggested that using fuel depots to go to the moon would take six launches of the SpaceX Falcon Heavy and visiting an Earth approaching asteroid would take nine launches, far beyond the three critical launches limit that the Augustine Commission cites.