Litmus test for the megarocket that will return humans to the Moon

The SLS is a giant. It belongs to the category of super heavy launchers, necessary to tackle titanic missions such as going to the Moon or Mars.


At 2:40 p.m. local time in Cape Canaveral, Florida, on Monday, June 20, (8:40 p.m. in Spain) the SLS rocket will pass, if all goes well, its last fire test. It will be on launch pad 39B, the one from which the mythical Saturn V departed in 1969 with Apollo 10, bound for our natural satellite. Now the Space Launch System takes its place. This test, the wet dress rehearsal , will be the last before the promising giant takes us back to the place we should never have left: the Moon.

What will be tested?

The wet dress rehearsal is a rehearsal of all the operations that are carried out prior to a launch. Fuel and oxidizer are cryogenic, so they cannot be stored in the rocket and must be charged before liftoff. The loading process, along with pre-operations up to T – 10 seconds, is what will be tested on June 20. If SLS passes them, everything will be ready for the first launch of the Artemis program , NASA’s ambitious goal of getting humans back on the Moon.

In the case of the SLS, about 2.6 million liters are loaded between oxygen and liquid hydrogen; the amount of propellants needed to go around the Moon and back (the Artemis I mission will not land). That amount would barely fit in a six-foot-deep Olympic pool.

A heavyweight to tackle titanic missions

The SLS is a giant. It belongs to the category of super heavy launchers, necessary to tackle titanic missions such as going to the Moon or Mars.

Launchers are usually classified by how many kilograms or tons they can put into Low Earth Orbit (LEO, up to about 1,500 km) and those that can put more than 50 tons into LEO are considered superheavy launchers.

This is more than the heaviest trailer you’ll see on the road filled to the brim. Accelerated to about 28,000 km/h and set to circle the Earth.

The SLS is even bigger. The first version, called Block-1, with its almost 100 meters high and 2,700 tons of total weight, will have a load capacity of 95t LEO. And there are still two more versions to come: the Block-1B (105t at LEO) and the Block-2 (130t at LEO), because 95t at LEO is not enough to fulfill NASA’s plans to return to the Moon.

It is planned to put humans on the Moon in 2025

The mass that can be sent towards the Moon (loading to TLI, Trans Lunar Injection ) is considerably less than what can be uploaded to LEO. In this case, the different versions of the SLS have a load capacity at TLI of approximately 27t, 40t and 45t and each kilo will be important for the ambitious plans to set foot on the Moon again, which involves previously establishing an orbital station around the itself, Gateway , from which to go down and go up to its surface. If all goes well this will happen in 2025 as part of the Artemis III mission.

The SLS is to the Artemis program what the Saturn V was to the Apollo program . And, although it might be thought that more than 50 years later the Saturn V should have been vastly surpassed, the reality is that it has not. In global terms, the load capacity of both launchers is very similar, both to LEO and TLI. That is if we talk about the Block-2 version of SLS, because the one that is currently on the launch pad is still a long way off.

SLS had to pass several litmus tests, and they were political

It may seem strange, but politics plays a fundamental role in these issues and the situation is completely different now than it was in the sixties of the last century. After Kennedy’s famous “We Choose to Go to the Moon” speech, America was a country with a common goal of national pride able to spend for the lunatic trip an amount equivalent today to about two-thirds of the annual general budgets of the United States. Spain. Today this impulse no longer exists. With the alternation of Democratic and Republican governments, space programs and launchers are mutually canceled by changing the political sign, and the total approved investment is about ten times less. Thus, until now, the path of the SLS has been bumpy.

A semi-recycled rocket

After the Columbia disaster , NASA had to reorganize its entire strategy. It needed an astronaut transportation system to the International Space Station ( ISS ) to replace the Shuttle and wanted to bolster its deep space program. The answer was the Constellation program , with the Ares I launchers for manned missions to LEO and Ares V for lunar and Martian missions.

After accumulating many cost overruns and delays, the program was canceled in 2009. But after pressure from the companies involved in the construction of the Ares, the Constellation program gave rise to the Space Launch System.

After the precedents, SLS had to be built in a short time and at a moderate cost, so it was decided to start from existing elements, fundamentally from the Space Shuttle . The remaining RS-25 engines of the Shuttle would be reused and its boosters (those lateral rockets that accompanied the mythical orange tank) would serve as the basis for the new ones.

First release planned for August 2022

The first launch is expected to be in August 2022, more than five years later than initially planned. It would not be unreasonable to think that one of the various factors that may have contributed to this is NASA’s contracting philosophy for this project, of the cost-plus contracting type , which translates into NASA assigning budgets to contractors, but it is also responsible for any additional costs that may be incurred.

In fact, cost overruns and delays have meant that the program has been close to running out of funds, and given the high price of each launch (difficult to estimate, but it is estimated that it is around two billion per launch), especially in comparison with other alternatives, it seems that the SLS may have little travel outside of Artemis. Even its iconic mission to the outer solar system, Europa Clipper , has been delegated to SpaceX’s Falcon Heavy. There are currently several initiatives to make it viable beyond the Artemis program, but to do so it would have to greatly reduce its costs per launch.

However, despite all the difficulties, the Artemis program is taking shape through this colossus and, if nothing prevents it, starting in August we will be able to begin to feel the emotion of seeing how it is being built again, through several missions, the path to the Moon.

It is possible to see the rocket live and the wet dress rehearsal scheduled for 8:40 p.m. in Spain on July 20.