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NASA completes assembly of SLS’s first two solid rocket boosters

The stacking and assembly of the first two solid rocket boosters for the first launch of SLS has been completed at Cape Canaveral.

The boosters, built by Northrop Grumman, now only wait for the arrival of Boeing’s core stage, which is still awaiting the successful completion of its final static test, now tentatively set for sometime in the next week or so.

Stacking of the boosters began in November 2020, which means that the first SLS launch must happen by November ’21 because the boosters have a limited life span of about a year. To make that November launch happen on time however is becoming increasingly difficult. Assuming the mid-March core static static fire test in Mississippi is successful, NASA will have to then ship the stage to Florida and get it assembled with those two boosters. NASA has previously said it will take about six months to do this. Their margin between now and November is thus getting quite tight.

Conscious Choice cover

Now available in hardback and paperback as well as ebook!


From the press release: In this ground-breaking new history of early America, historian Robert Zimmerman not only exposes the lie behind The New York Times 1619 Project that falsely claims slavery is central to the history of the United States, he also provides profound lessons about the nature of human societies, lessons important for Americans today as well as for all future settlers on Mars and elsewhere in space.

Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space, is a riveting page-turning story that documents how slavery slowly became pervasive in the southern British colonies of North America, colonies founded by a people and culture that not only did not allow slavery but in every way were hostile to the practice.  
Conscious Choice does more however. In telling the tragic history of the Virginia colony and the rise of slavery there, Zimmerman lays out the proper path for creating healthy societies in places like the Moon and Mars.


“Zimmerman’s ground-breaking history provides every future generation the basic framework for establishing new societies on other worlds. We would be wise to heed what he says.” —Robert Zubrin, founder of founder of the Mars Society.


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  • David

    From what I’ve been seeing elsewhere, that one year limit on the stacked boosters is predicated on the whole booster being stacked in more or less one go. They delayed the process, adding additional stacks over time, so that the bottom segments haven’t had as much downward pressure on them so far as if they’d been completely stacked all along. Just how much time this gains them is not something I’ve heard, but presumably it’s enough to get to them to the currently projected launch date in 2022 Q1. Of course, if it slips again…

  • mkent

    I believe the operative limit on the boosters is now January 2022, not November 2021. This is still problematic, as I’m hearing that internal NASA schedules showed a February 2022 launch date even before the recent delay in the static fire. I’m also hearing that Boeing believes SLS can still be launched by the end of the year even after the recently delay. Presumably that’s if everything goes perfectly from here on out. What are NASA’s plans if everything doesn’t go perfectly? I have no idea.

  • Andi

    Wondering why they stacked the boosters so early? If they started in November and just finished, then it takes about four months to complete. So why not wait until let’s say five months before scheduled launch to start the process?

  • Andi: Now that is a great question. It also illustrates the inefficient nature of how NASA operates.

  • Chris Lopes

    My guess is they stacked them early to show “progress”.

  • Jeff Wright

    At least we will likely get a payload per every SLS. Starship is expendable as well at this point. A production Starship/Super-Heavy stack might well also be a billion a pop by the end-with a higher part count. SLS is a pretty conservative stage-and-a-half-to-orbit design which should be cheaper. Boeing wanted to sell scores of D-IVs originally-so that recalcitrance worries me. Must keep doing my breathing exercises :-/

  • john hare

    SLS should been have been cheaper per unit, except that the inherent low flight rate reverses the should. And a production Starship will be reusable as opposed to the expendable test articles. So at a billion a pop, how much per flight at a hundred flights per airframe? And at a thousand?

    Not including the difference in development cost and time.

  • Jeff Wright

    SLS isn’t trying to be a spacecraft though. Now, we hope Starship works. I at least want to see Exploration upper stages atop Super-Heavy…maybe even allowing solids if he gets more infrastructure.

  • Edward

    Jeff Wright wrote: “At least we will likely get a payload per every SLS. Starship is expendable as well at this point.

    I love how people keep conflating flight units and development test items. NASA and Boeing are now verifying their first space flight unit, their final design, but SpaceX is still figuring out how to build and operate future development test item designs.

    As for expense, I agree. SpaceX is spending a whopping $2 billion for a radically new design and methods, a new alloy, a dozen test items, new manufacturing facilities and methods, and new test facilities and launch pads. Meanwhile, Boeing is able to reconfigure STS into SLS for a mere $20 billion. We can see which one is focused on cost efficiency and cost effectiveness.

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