Answering a question from Shuttle Mission Control veteran Wayne Hale, NASA’s Human Spaceflight head honcho Bill Gerstenmaier said SpaceX's Falcon was not an option for Uncle Sam's space agency since it simply could not lob enough metal into the heavens in one go:
Wayne Hale asks why not buy some Falcon Heavy launches in lieu of SLS, given FH’s lower costs.— Jeff Foust (@jeff_foust) March 26, 2018
Gerstenmaier: FH capacity still a lot smaller than any SLS version; we’ll need that for large volume, monolithic pieces.
The question was asked during a scheduled meeting of the NASA Advisory Council this week, following the successful demonstration launch of Falcon Heavy earlier in the year.
With the SLS snaffling the best part of a $2bn per year funding pot, and SpaceX supremo Elon Musk estimating that a Falcon Heavy would cost $150m “at most,” it doesn’t take NASA-level genius to work out that one SLS equals, er, a lot of Falcon Heavy fire sticks. On the other hand, NASA reckons SLS is more bang for its bucks.
The performance numbers in this database are not accurate. In process of being fixed. Even if they were, a fully expendable Falcon Heavy, which far exceeds the performance of a Delta IV Heavy, is $150M, compared to over $400M for Delta IV Heavy.— Elon Musk (@elonmusk) February 12, 2018
While the first iteration of SLS will loft a payload only slightly heavier that a Falcon Heavy can carry, forthcoming versions will be able to dump considerably heavier gear [PDF] onto a trans-lunar injection trajectory to the Moon, with the final version able to loft 45,000 kg, compared to the 16,800 kg SpaceX reckons its launcher can send to Mars.
A cynic might suggest that just three launches of a Falcon Heavy would do the job of the most powerful version of the SLS, but NASA has an answer for this. The Lunar Orbital Platform Gateway will have modules so large that nothing but a SLS will do.
There are a few problems with this statement.
The first is that the Lunar Orbital Platform Gateway is still very much on the drawing board, so there is no reason why it could not be designed to be launched in smaller pieces.
The second is that former astronaut Richard Mastracchio (now Senior Director of Operations for Commercial Resupply Services at Orbital ATK) remarked at a lecture given in the UK at the weekend that Lunar Orbital Platform Gateway would likely be constructed from Space Station-derived modules.
The heaviest module on the Space Station is the Japanese Kibo lab, weighing in at 15,900 kg.
The third is that NASA moved away from single Skylab-style launches some time ago, and now has far more experience with the modular building techniques used for the Space Station.
Skylab was, of course, nearly lost during launch as unexpected airflow tore off a meteoroid shield and one of the solar panels.
Gerstenmaier finished on more conciliatory tone, restating NASA’s position that it was not a case of ‘Or’, but ‘And’, with there being plenty of room for Musk’s trio of thrust tubes as well as the wares of Jeff Bezos and the other commercial launch vendors.
Until the SLS finally launches and demonstrates its value, this question is unlikely to be going away any time soon. ®