It has been over fifty years since Eugene Cernan, the last man to walk on the moon, climbed up the ladder back into Apollo 17’s lunar module Challenger, ending an era of lunar exploration. Even though the hype of the 1960s Apollo program has long since passed, NASA is planning to return humans to the moon within our generation.
After the end of the Space Shuttle era in 2011, NASA had a stock of unused technology in various warehouses, including parts of the solid rocket motors and the RS-25 engines mounted on each shuttle. In an effort to cut development costs, NASA opted to adapt these pieces of equipment for their new lunar program. Even though said costs were reduced by this measure, the SLS differed vastly from the Shuttle in many aspects. For example, the Space Shuttle used three RS-25 main engines, while the SLS uses four. Additionally, the pair of solid rocket motors used on the Shuttle each have an additional fifth segment to augment thrust and support the extra weight of the craft.
In addition to the lower development costs of the SLS, the rocket has a modular design, meaning that payload and upper stages of the rocket can be swapped out and other technology on the booster can be upgraded with minimal change to the main design, allowing for a more flexible flight schedule. Outside of the spaceflight regime, the Artemis program, including SLS, “has generated $14 billion and supported 70,000 jobs across the U.S,” according to Space.com.
Even though the SLS may seem undefeatable due to its flight-proven technology, it also has its critics and issues. For instance, like many NASA megaprojects are, the Artemis program has gone significantly over-budget and is several years behind schedule; the first flight, originally planned to fly in December 2017, was nearly five years overdue, launching in November 2022. Furthermore, companies such as SpaceX, Astra, and Northrop Grumman have begun to develop their own launch vehicles to take payloads to space, most notably the recent developments in SpaceX’s Starship super-heavy-lift launch system, which quickly is becoming a competitor to the SLS, rendering the SLS potentially obsolete.
An alternative approach to replace the SLS was to construct propellant depots (similar to gas stations in space) to refuel smaller spacecraft headed for deep-space destinations, including the moon. As reported by SpaceRef, internal NASA studies conducted in the early 2000s postulated that propellant depots would allow for billions of dollars saved, frequent launches due to smaller and cheaper rockets, more competition to lower costs, and a lower-risk option for international collaboration. However, Boeing, the prime contractor for SLS, has repeatedly rebuffed such proposals as it would pose a threat to the SLS’ development, one of the main sources of profit for the company. Physicist George Sowers, a former employee of the United Launch Alliance (ULA), a spaceflight company formed by Boeing and Lockheed Martin, tweeted that “[ULA] had released a series of papers showing how a depot/refueling architecture would enable a human exploration program using existing (at the time) commercial rockets…Boeing became furious and tried to get me fired. Kudos to my CEO for protecting me. But we were banned from even saying the ‘d’ word [depot] out loud. Sad part is that ULA did a lot of pathfinding work in that area and could have owned the refueling/depot market, enriching Boeing (and Lockheed) in the process. But it was shut down because it threatened SLS.”
However, perhaps the most controversial aspect about the SLS does not come from its funding or schedule, but from the expenditure of the four RS-25D engines on the first stage of the rocket. NASA has currently planned four SLS flights, thus using up its sixteen RS-25D engines from the Space Shuttle. These engines each cost over $40 million to manufacture and are the most complex pieces of technology ever built. As Scott Manley said in his video Four Old Space Shuttle Engines Team Up For One Last Rocket Launch, “It is kind of sad because these are the first really [sic] reusable engines and they are [going to] be expended, and also because all the Block 2 (RS-25D) engines are essentially [going to] go into the ocean we’re not gonna have a museum with a flight-flown Block 2 engine.” This means that no fully-functioning RS-25D engines will make it to museums for the public to see – in other words, the RS-25D will only leave a legacy through images and videos, not as a live artifact of the Shuttle program. NASA has already contracted Aerojet Rocketdyne to develop new iterations of the RS-25, namely the E and F variants, which utilize modern manufacturing technologies to cut costs, optimizing for an expendable configuration for future launches beyond Artemis 4. In fact, several RS-25E test articles have been produced and are performing as expected, meaning that they could be flight ready very soon, allowing the older RS-25D’s to be retired.
Yet another hit to the SLS program is the rapid advancement of commercial agencies like SpaceX: Starship’s development is rapidly nearing completion, with its first orbital launch scheduled within the next three months. Consequently, the SLS may already be obsolete in terms of both cost and capability, despite reaching operational status before the Starship does. As the Space Launch System is an expendable launch vehicle where all parts of the rocket only fly once, the cost for each launch is approximately $2 billion, nearly twice that of the Apollo-era Saturn V, which cost $1.12 billion per launch. Meanwhile, the Starship may cost about $2 million to fly, according to the website Inverse, particularly due to its reusable nature, thus requiring only refuels. This means that the Starship may be up to one thousand times cheaper than the SLS, in addition to its payload capability.
Furthermore, the SLS is merely a launcher, not a full rocket and spacecraft assembly, meaning that more funds will have to be spent on spacecraft and payload, such as the $300 million Orion spacecraft sent on its first mission, Artemis 1. Meanwhile, the Starship is a launcher-spacecraft pair, with optional modifications for extraplanetary landing, such as the HLS (Human Landing System) for NASA’s future Artemis III mission, which will utilize an SLS to carry the crew to the moon, dock with the Starship HLS, and land on the surface.
With recent political developments such as the appointment of SpaceX founder Elon Musk as leader of the Department of Government Efficiency, the state of NASA is more dire than ever. Perhaps it is time for society to re-evaluate the contributions this once-great national organization has made for us in the past, and take action to keep it alive as humans continue to explore the cosmos.