Chris Gebhardt wrote a fantastic piece over on NASASpaceflight.com on SLS, Europa Clipper, EM-2, and its Mobile Launcher(s?). The Mobile Launcher is being finalized in its SLS Block 1 configuration for EM-1, after which it will need to be converted for SLS Block 1B—a 33-month process.
NASA’s Aerospace Safety Advisory Panel has some concerns regarding the safety of NASA’s plans beyond EM-1, but not because of the duration of the conversion of the existing Mobile Launcher, but, per NASASpaceflight.com, because of its total weight:
At present, the SLS Block 1 ML will end up being roughly 200,000 lbs overweight.
The recently upgraded Super Crawler, CT-2, was built to carry 18.5 million lbs, but the combined weight of the SLS Block 1 and ML at rollout will now be at least 18.7 million lbs.
That in itself is not an issue, as all NASA products have a safety factor of four. Thus, CT-2 is more than capable of carrying an 18.7 million pound ML/SLS Block 1 to Pad-B.
The bigger safety issue is post-EM-1 and all of the modifications needed to the ML for the SLS Block 1B – modifications that will bring the ML to 1-1.2 million lbs overweight – with a total SLS Block 1B/ML combined rollout weight of 19.5 to 19.7 million lbs.
That creates a lower than desired safety factor of 3.78 to 3.74.
So the debate is whether or not NASA should build a new Mobile Launcher for crewed Block 1B missions and convert the existing launcher for uncrewed cargo missions. But so far, there’s no money for that in the budget.
Furthermore, there’s the long-known-about safety issue surrounding the first flight of SLS Block 1B:
In the larger certification plan for SLS Block 1B, Europa Clipper is highly desired to fly before EM-2 – the first SLS mission to carry crew aboard Orion.
It has been noted by the ASAP, the NASA Advisory Council, and the Astronaut Office that the Astronaut Office is against any plan to fly crew on any SLS – or any rocket, for that matter – that has not flown at least once in its crew launch configuration.
Since EM-1 will use the ICPS Block 1 and EM-2 will use the EUS Block 1B, the Block 1B variant needs to fly at least once before EM-2 for NASA to adhere to its own stated safety guidelines.
If it were me, I’d take the risk of a Mobile Launcher with only a 3.74 safety factor over flying on a new upper stage. To each their own.
To review: the slip-prone EM-1 mission has to fly before the Mobile Launcher can undergo a 33-month-long conversion to fly SLS Block 1B, which needs to launch an uncrewed mission first, which would be Europa Clipper since it was mandated by Congress that Europa Clipper will fly on SLS, but that mission has two defined launch windows (June 2022 and a 2023 backup) which are tough to hit given how much work has to happen on the launcher and also given the fact that EM-1 doesn’t have a set launch date yet. Oh, and also, NASA will probably be pretty eager to get EM-2 up, since that’ll be carrying the first module for the Deep Space Gateway.
What a complicated mess.
Be sure to read the whole article for Chris’ insight into this tricky situation. According to Chris, a new Mobile Launcher wouldn’t be ready in time for Europa Clipper and doesn’t solve anything other than providing that 0.26 safety factor increase for crewed SLS Block 1B flights.
Now would be a really good time for ULA, SpaceX, and Blue Origin to start talking up how much mass they could throw towards Jupiter with Vulcan, Falcon Heavy, and New Glenn.1
Given that SLS was a Congressionally-mandated launch vehicle and not a decision based on technical requirements, I’m not totally sure Europa Clipper needs the giant fairing that SLS offers. NASA has said in the past that alternative launch vehicle plans are being maintained, which I’m pretty sure means it could fit in the standard 5-meter fairings found on Vulcan and Falcon Heavy. ↩︎