SLS Block II Booster

[fredinno]

Regarding the SLS Block II, why did NASA decide to create an entirely new set of boosters for it, rather than add another set of (Block I) boosters, for example? I do realize that SLS Block I/IB boosters need to be replaced, as the Shuttle SRBs are no longer in production, but wouldn't it cost more to create an entirely new set of boosters for different blocks of the SLS instead of just working with one type of them?

[sgt_flyer]

At first, 5 segment SRBs were already thought to be used for the space shuttle - would have allowed 9 tons of additional payload with minimal changes (adding 2 additional SRBs to the ET would require a lot of rework on the ET structure - and severe modifications on the VAB.

It would also require severe reinforcement of the crawler transporters (& maybe the crawlerways too) (which were already modified to carry the shuttle's weight - SRBs are mounted with all their solid fuel already casted after all (1 4 segment shuttle SRB alone is 590 tons - more than two times heavier than an unfueled saturn V - per shuttle booster ! so imagine an unfueled 4 booster SLS - that would be a bit more than 2400 tons to transport (not counting an umbilical tower if they add one) the 'empty' shuttle + the loaded SRBs weighted around 1300 tons, on the 3700 tons mobile platform. (All that carried by a 3000 tons crawler)

SLS is already costly enough like that all the new ground works and support equipment it would require would cost a lot of money. for a rocket with lots of planned launches, it's not a big deal to spend this kind of money on infrastructures do it for a rocket that'll only fly a few times, and that adds significantly to the rocket's price tag

Edited June 21, 2015 by sgt_flyer

[Bill Phil]

Because another booster can be bigger. Maybe it would allow for more payload.

Although, if they wanted to use a large cluster of SRBs on SLS, they could have designed the core to do so. But they didn't...

[fredinno]

At first, 5 segment SRBs were already thought to be used for the space shuttle - would have allowed 9 tons of additional payload with minimal changes (adding 2 additional SRBs to the ET would require a lot of rework on the ET structure - and severe modifications on the VAB.

It would also require severe reinforcement of the crawler transporters (& maybe the crawlerways too) (which were already modified to carry the shuttle's weight - SRBs are mounted with all their solid fuel already casted after all (1 4 segment shuttle SRB alone is 590 tons - more than two times heavier than an unfueled saturn V - per shuttle booster ! so imagine an unfueled 4 booster SLS - that would be a bit more than 2400 tons to transport (not counting an umbilical tower if they add one) the 'empty' shuttle + the loaded SRBs weighted around 1300 tons, on the 3700 tons mobile platform. (All that carried by a 3000 tons crawler)

SLS is already costly enough like that all the new ground works and support equipment it would require would cost a lot of money. for a rocket with lots of planned launches, it's not a big deal to spend this kind of money on infrastructures do it for a rocket that'll only fly a few times, and that adds significantly to the rocket's price tag

So basically, since SLS was designed to use shuttle infrastructure to a large extent (as far as I know) adding additional SRBs would require significant modifications to the facilities using it, that it would be more worth it to design an entirely new set of boosters?

[Kryten]

Also it would take about as much effort to put the original boosters back into production as it would be to set up a new design with modern manufacturing techniques. Winding composites is a lot easier than machining steel to that level of precision, and gets you a nice performance boost.

[fredinno]

Also it would take about as much effort to put the original boosters back into production as it would be to set up a new design with modern manufacturing techniques. Winding composites is a lot easier than machining steel to that level of precision, and gets you a nice performance boost.

I know that, I was wondering why they were going to make 2 versions of the "Dark Knight" Composite boosters for the different blocks of the SLS, rather than just adding another set of the smaller composite boosters designed for the Block I/IB for the Block II.

[Kryten]

The composite boosters are for Block II, Block I and IB are both intended to use the existing SRBs.

[fredinno]

What happens when they run out of Shuttle SRB segments for the Block I/IB then?

[andrewas]

They make more. The casings are just steel, manufacturing new segments would not be hugely expensive compared to the rest of the rocket. If they somehow fly enough SLS to use up all the existing boosters, its not a big problem.

[Kryten]

What happens when they run out of Shuttle SRB segments for the Block I/IB then?

Then they're to be retired. The variants are an upgrade path, they aren't intended to be used concurrently.

[fredinno]

Then they're to be retired. The variants are an upgrade path, they aren't intended to be used concurrently.

<Citation Needed>

[Kryten]

<Citation Needed>

The SLS manifest i have isn't publicly available, but do you really need a citation for that? The other option is NASA pumping tons of money into rebuilding the infrastructure just so they can keep building variants that are less powerful.

[SciMan]

I think the Block II boosters are likely to be some variant of the ASRB. IIRC there have been test articles produced for that, and they are currently on display as the SRBs for the Enterprise shuttle (also a test article).

If it's not an ASRB with an additional "segment", then it's likely the FWSRB proposal. Carbon fiber filiment wound SRM casings have been used for years on the Delta-II as the GEM series, the FWSRB is just be a Shuttle sized version.

Both of these were proposed as improvements to the Shuttle SRBs that would be safer and improve payload-to-orbit capacity of the Shuttle.

In other words, they're anything but a "clean sheet" design.

Also, they were proposed sometime after the Challenger disaster but before the Columbia disaster, so it's not even a new idea, and is still (kinda) Shuttle-derived.

If it's not one of those, then it probably at least is heavily derived from them, unless they go back on their decision to not use the Pyrios LFBs.

Edited June 22, 2015 by SciMan

[fredinno]

The SLS manifest i have isn't publicly available, but do you really need a citation for that? The other option is NASA pumping tons of money into rebuilding the infrastructure just so they can keep building variants that are less powerful.

Or create a thinner version of the SLS advanced boosters?

I think the Block II boosters are likely to be some variant of the ASRB. IIRC there have been test articles produced for that, and they are currently on display as the SRBs for the Enterprise shuttle (also a test article).

If it's not an ASRB with an additional "segment", then it's likely the FWSRB proposal. Carbon fiber filiment wound SRM casings have been used for years on the Delta-II as the GEM series, the FWSRB is just be a Shuttle sized version.

Both of these were proposed as improvements to the Shuttle SRBs that would be safer and improve payload-to-orbit capacity of the Shuttle.

In other words, they're anything but a "clean sheet" design.

Also, they were proposed sometime after the Challenger disaster but before the Columbia disaster, so it's not even a new idea, and is still (kinda) Shuttle-derived.

If it's not one of those, then it probably at least is heavily derived from them, unless they go back on their decision to not use the Pyrios LFBs.

No, it's neither. There were 2 main proposals to the SLS Advanced Boosters. One was Dynetics, which would have used 2 RP-1/ LOX boosters to power the rocket.

The other, which was chosen, was a Carbon-Fiber SRB called "Dark Knight", but used a different, higher ISP SRB fuel than the Shuttle SRBs (They needed more power; the Block II requirements pushed the limits of SRB Tech). This is similar to the FWSRB proposal. (The new boosters also look pretty badass: