NASA plans to launch the most powerful rocket sometime in the next few years. The rocket experienced delays and cost overruns which keeps NASA pushing the debut out. The goal is still, bring America along with allies into deep space for longer and farther than ever before. The launch might not happen in 2021 but the first rocket slowly is getting closer to being real. Even though the rocket has not flown yet, NASA already inked deals for more SLS mega rockets engines.
Many people want the SLS rocket to go away and redirect funds to new space companies under commercial launch contracts. Why? Some view the already working SpaceX Falcon heavy as a practical, less costly option. Some think Blue Origin’s New Glenn also offers access at a lower cost. Both the Falcon Heavy and New Glenn need multiple launches to equate to the SLS lifting power. Others feel SpaceX will bring the SLS usefulness to an end rather abruptly once Starship and booster successfully launch. But what is going on with this procurement?
NASA doubled down on SLS, again.
NASA appears a big supporter of the SLS and remains optimistic about the long-term usefulness. NASA awarded a follow-on contract to Aerojet Rocketdyne of Sacramento, California, to manufacture 18 more Space Launch System (SLS) RS-25 rocket engines to support Artemis missions to the Moon. Without the billions of dollars invested in SLS, NASA would need to approach going to deep space differently.
“This contract allows NASA to work with Aerojet Rocketdyne to build the rocket engines needed for future missions. The same reliable engines that launched more than 100 space shuttle missions have been modified to be even more powerful to launch the next astronauts who will set foot on the lunar surface during the Artemis missions.”
John Honeycutt, the SLS program manager at NASA’s Marshall Space Flight Center in Huntsville, Alabama.
The engines for the Artemis I mission to the Moon already began Green run testing after being assembled to the core stage. The term “green” refers to the new hardware that will work together to power the stage, and “run” refers to operating all the components together simultaneously for the first time. Green Runs are used for risk reduction.
Why need more engines? Isn’t it the same as the Space Shuttle?
The 212-foot-tall SLS core stage leverages four RS-25 rocket engines mounted at the base. The Space Shuttle only used three. The SLS core stage holds more than 700,000 gallons of propellant necessary for the brief existence of the rocket. That is the problem. The rocket’s first stage falls back to Earth and is not used again. The engines attached also are expendable. NASA’s design approach wasn’t targeting reusability, but to maximize mass to orbit and beyond.
The SLS uses an upgraded version of the shuttle main engine also known as RS-25. The RS-25 ranks as a high-performance rocket engine with a design dating back to the original shuttle program in the 1970s. The first 16 RS-25 engines slatted for the first 4 SLS launches come from the space shuttle program.
These leftover rocket engines got an overhaul. The upgrade to the controllers implemented further improvements over the original SSME’s already impressive performance. The higher performance level necessary to launch the larger SLS required the upgraded and tested engine performance. Once again, NASA went for higher performance over reusability.
That’s great news, right? NASA using leftover stuff to save money. So what’s the Catch? The engines are used only once. Unlike the shuttle, the engines came back with the orbiter and were used again.
A quick look at RS-25 Engine cost.
Okay – but things can’t be too bad, right? These engines have been used before. Don’t get ahead of yourself.
The newly announced follow-on contract increased the procured value by $1.79 billion. The contract includes labor to build and test the engines, produce tooling, and support SLS flights powered by the engines. The contract extension adds on to the first contract awarded in November 2015 to rectify and produce six new RS-25 engines. The new total contract total tallies up to almost $3.5 billion. The procurement of engines does clarify NASA’s intention on launching with a period of performance through Sept. 30, 2029. A total of 24 engines to support as many as six more SLS flights.
The contract is good news for the Aerojet Rocketdyne’s factory in Canoga Park, California. Though the price is high, NASA shared Aerojet’s commitment to carry out a cost optimization plan targeting cost reductions by as much as 30%. The reduction takes advantage of more advanced manufacturing techniques to change some of the rocket components. Even with a 30% cost reduction, the SLS will still be underpriced by commercial rockets.
Okay – here is the RS-25 math…
Each SLS rocket uses four RS-25 engines, providing a total of 2 million pounds of thrust to send SLS to space. The SLS rocket leverages the assets, capabilities, and leftovers of NASA’s Space Shuttle Program, using 16 existing surplus RS-25 shuttle engines for the first four SLS missions. Great.
A total of 46 engines throughout the shuttle program cost about 1.8 billion dollars. 16 remaining upgraded engines now include one last flight each. The Shuttle engines flew multiple times each. The SLS rocket and drops the engines into the ocean like the Apollo approach. Even ULA realized the issue with throwing away hundreds of millions of dollars each time a rocket launches.
| Qty | Approximate Cost per engine (M USD) | Total cost | |
| SSME | 40 | 46 | 1840 |
| SLS RL-25 | 18 | 100 | 1790 |
The cost is huge. The cost of the one engine is more than the entire Falcon 9 rocket. The RS-25 is an amazing engine, but the price tag might not line up with the results. The engine is a major contributor to the overall cost of a rocket system.
In an unrelated discussion, ULA’s Tory Bruno shared his rule of thumb recently on Twitter. Use his rule of thumb we can back-calculate the cost, give or take, of the SLS. Based on Tory’s rule of thumb, the cost per SLS launch should be about 2.4 Billion dollars. Interestingly, the cost rule of thumb likely will be very close to reality. The SLS mega-rocket has a mega price tag. Keep in mind, this is a really rough estimate.
| Rule of thumb cost | Qty | Per each | ||
| Total cost to provide Launch Service | Launch Service | 2400 | 1 | 2400 |
| 50% is the rocket | Rocket | 1200 | 1 | 1200 |
| 50% of Rocket is 1st stage | 1st stage | 600 | 1 | 600 |
| Engines are about 2/3 of 1st stage | engines | 400 | 4 | 100 |
With a cost per launch of 2.4 billion dollars, many people argue using two Falcon Heavy rockets at a fraction of the cost should be considered. With a cost of 2.4 billion dollars per launch, the SLS delivering 130 tons to Low Earth Orbit would cost about 18,500 per lb. The Falcon heavy estimates for per lb launch come in at about 1/10th of SLS. In comparison, a series of Vulcan Rockets would also be cheaper than SLS and could potentially accomplish the same thing. Though it would take more than 4 launches to accomplish the same mass to orbit and still be less than half of the cost.
With that kind of cost difference, the Artemis program might do better to use commercial launch providers and make some adjustments to the mission profile. NASA might take a page from Tory Bruno’s playbook and try to recover the RS-25 engines for reuse. Even Rocket Lab is working on recovering the first stage booster of their Electron rocket. Reusability or partial reusability appears to be the right direction for the space industry. Unfortunately, the SLS is not reusable.
For space mission design, doing in orbit assembly is a costly and time-consuming activity. NASA strongly emphasizes the critical necessity of the SLS regarding the next step in human space exploration. SLS will be a strong addition of capabilities for NASA, but the cost might be limiting the usefulness.
The good news still is NASA is on it’s way back into Deep Space after being stranded in Low Earth Orbit for fifty years.
About The Author
Bill D’Zio
Co-Founder at WestEastSpace.com
Bill founded WestEastSpace.com after returning to China in 2019 to be supportive of his wife’s career. Moving to China meant leaving the US rocket/launch industry behind, as the USA and China don’t see eye to eye on cooperation in space. Bill has an engineering degree and is an experienced leader of international cross-functional teams with experience in evaluating, optimizing and awarding sub-contracts for complex systems. Bill has worked with ASME Components, Instrumentation and Controls (I&C) for use in launch vehicles, satellites, aerospace nuclear, and industrial applications.
Bill provides consulting services for engineering, supply chain, and project management.
