The first three missions of NASA’s next big rocket will have to settle for a less-powerful ride

The first three missions of NASA's next-generation rocket, the Space Launch System, will fly with the less powerful version of the vehicle that the space agency plans to build. NASA is moving forward with its plan to use a degraded version of the SLS for its second and third flight, according to a memo from NASA headquarters obtained by The Verge . The original plan was to fly those two flights in a much more powerful update of the rocket, but now, it seems that the version will not be released until at least 2024.

The SLS, destined to take humans to deep space, has been in development for the last decade, with its first three missions mostly in stone. For its debut flight, called EM-1 and scheduled for 2020, the rocket will send an empty crew capsule called Orion on a three-week trip around the Moon. Then, a few years later, NASA plans to put a team on board: a second mission, called EM-2, will send two astronauts on a three-week trip around the Moon. Around that same time, NASA plans to use the SLS to launch a robotic spacecraft to fly across the icy moon of Jupiter Europe, called the Europa Clipper mission.

these three missions were not supposed to fly in the same version of the SLS. NASA plans to make two main variants of the vehicle: Block 1 and Block 1B. Block 1 is the least powerful form of the rocket, capable of carrying 150,000 pounds (70 metric tons) to low Earth orbit. Block 1B is designed with a much more powerful upper stage, which allows it to carry more than twice that weight. NASA's plan was to fly Block 1 only once for the first SLS flight, and then fly Block 1B. But now NASA will fly the three missions, EM-1, EM-2 and Europa Clipper, in Block 1. The note, signed by Bill Hill, associate administrator of NASA for the development of exploration systems, instructs the contractors of the space agency to begin to plan the change A spokesman of the NASA confirmed this change to The Verge .

In April, former NASA administrator Robert Lightfoot said that NASA could make this change, thanks to an unexpected influx of cash received from Congress in March. The bill finalized for fiscal year 2018 gave NASA an additional $ 350 million to build a second launch platform for the SLS. And that gave NASA more options on how to move forward with the first SLS flights.

The different planned versions of the SLS
Image: NASA

At this time, NASA has only one mobile launch platform: a slow moving structure designed to take the rocket to the launch pad where it will then take off. However, this single platform can only support flights from the SLS of Block 1 at this time. The platform would need significant updates to support the largest and heaviest block 1B. And all that remodeling would take time, at least 33 months to complete. During that time, nothing can take off from the platform. Then, according to the original plan, NASA would first launch SLS's inaugural mission in a block 1 and then suspend all rocket flights for almost three years, while improving the mobile launch platform to support block 1B. That meant that the second flight of the SLS would be retained for the duration of those improvements.

To avoid this mess, Congress decided to give NASA the money to build another mobile launch platform, one specifically designed to fly the most bulky and powerful 1B block. In this way, NASA could begin to build the new platform now, to have it ready for the second flight of the SLS. But ironically, NASA is using this new money to shake its rockets. Now the space agency is going to build the second and most solid platform while will launch multiple blocks 1 on the existing platform in the meantime. According to the memorandum, NASA will aim to have the second platform ready for a launch of Block 1B in early 2024.

What is not yet decided is which mission will fly first: the Europa Clipper mission or the first flight with crew of Orion. Both are planned to happen at the same time, but Europe Clipper could fly before EM-2. It all depends on which one is ready to be first, according to the NASA memos obtained by The Verge . NASA has set the date for this second flight to occur by mid-2022.

The decision to fly multiple Blocks 1 may have which has to do with the fact that the powerful upper stage needed for Block 1B, called the Upper Scan Stage, will cost much more than originally planned, according to Ars Technica . In addition, the new stage is being designed from scratch, so it is likely to take many years to have the hardware ready for a 1B block flight. Meanwhile, the first flight of Block 1 is scheduled for the year 2020. If by then you have already demonstrated your skills, it will be easier and faster to simply launch more Rockets from Block 1 over and over again. So, this decision could mean that the SLS will fly faster in the future, instead of NASA waiting many years for Block 1B to materialize.

Flying in these less powerful of Block 1 will change the mission profile of at least the manned flight the SLS. It will not be able to carry additional charges as NASA had originally planned, but it will still have the astronauts around the Moon. It is not clear exactly how the Europa Clipper mission will change; however, Block 1 is still capable of sending the spacecraft on a direct route to Jupiter. NASA says that Europe Clipper has the opportunity to launch each year between 2022 and 2025. Other similar rockets, such as Falcon Heavy from SpaceX, do not have much energy to make a direct shot and would need a gravity boost from another planet, according to Barry Goldstein, the project manager of Europa Clipper, as Space News reported.

Still, the fact that we do not see Block 1B for a while does not bode well for the SLS program. Critics of the rocket say it's too expensive to build and fly, especially when there are comparable vehicles like Falcon Heavy, which can place almost the same amount of weight in low Earth orbit and is more economical to launch. NASA and Boeing, the manufacturer of the SLS, claim that the space agency needs the SLS because it is much more powerful than anything else on the market. But the longer it takes for Block 1B to build, the harder it will be to argue.

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