How much it will cost to explore deep space with NASA’s planned heavy lift Space Launch System depends on who one asks and what is included in the costs. They range from a NASA estimate of about $500 million per launch according to Space.com to one by a space writer named John Strickland writing for the Space Review of as much as $14 billion per launch. A Saturday post in the blog Parabolic Arc sets every SLS mission at $2 billion.
Each estimate depends on what is included. NASA’s estimate seems to include just the cost of building and launching the rocket. The Parabolic Arc estimate claims that it throws in the other costs of launching a deep space mission, the Orion spacecraft, any other hardware such as a lunar lander or a deep space hab module, ground support, and other costs. The Strickland estimate, or so he claims, includes the development cost of the SLS over its lifetime of operation.
Just to complicate things further AL.com noted that the costs to launch an SLS largely depends on the flight rate. Because there are certain fixed costs for operating the heavy lift rocket, such as personnel and infrastructure, the cost of the SLS is more per launch the fewer times one launches it. Flight rate largely depends on the budget one allocates for deep space exploration.
In casting about for a cheaper alternative some have touted an internal NASA report that claims tremendous cost savings if smaller, commercially available or soon to be available rockets such as the SpaceX Falcon Heavy were to be used instead of the SLS. The idea is that several flights would launch fuel to an orbiting depot. Then more flights would be used to send the spacecraft used in a deep space mission to the depot to top off fuel before proceeding on to the moon or Mars. Thus the development costs of the SLS is saved.
There are some problems surrounding that approach. While using the SLS would likely mean one or two launches per mission to the moon or an asteroid, the study suggests that it would take six of the Falcon Heavy to do a lunar mission and nine to do an asteroid mission. A mission to Mars would require an uncounted number of such launches, clearly impossible in this scenario.
The more launches one requires to conduct a deep space mission the greater the possibility a launch failure will disrupt and delay the mission, perhaps indefinitely. The NASA study suggested that three asteroid missions or four lunar missions in a decade would be possible using commercial rockets and fuel depots. That is opposed to ten or more using the SLS in the same time frame.
Even if some magic way to cut launch costs to zero were found, every deep space mission would still cost a lot of money. Spacecraft, crew training, fuel and other supplies, and ground support would roughly remain the same whether one uses a heavy lift rocket or a Star Trek-style transporter. The bottom line is that you get what you pay for and all the arm waving in the world will not change that.