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NASA SLS/Orion/Payloads

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1 minute ago, sh1pman said:

Probably a stupid question, but is it possible for SLS to launch with more than 2 side boosters?

My guess is no for a large number of reasons.

Not least of which is that they'd likely to reconfigure the VAB and MLP, and they've already said that those changes literally take years, and large sums.

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By my calculations, a maximum of 10 SRBs can be around an SLS core...

That would certainly be interesting to see! At that point, you would probably want to start looking into air starting some of the boosters to make the TWR not so ridiculously high.

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1 hour ago, Bill Phil said:

They have to redesign the core stage - otherwise they will suffer tremendous gravity losses on later variants. 

4 engines just doesn't cut it.

Perhaps. But not for EM-1/2. For future SLS’ (if they get that far- although I say SLS will fly and have a use, I also agree that once reliable competition arrives, it’ll be dropped like it’s on fire) they should improve the design to account for this. But scrapping the existing first stage hardware would be silly. Just use it for now and fix it as you go.

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20 minutes ago, ZooNamedGames said:

Perhaps. But not for EM-1/2. For future SLS’ (if they get that far- although I say SLS will fly and have a use, I also agree that once reliable competition arrives, it’ll be dropped like it’s on fire) they should improve the design to account for this. But scrapping the existing first stage hardware would be silly. Just use it for now and fix it as you go.

It shouls’ve been addressed years ago.

Too late now.

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59 minutes ago, Bill Phil said:

It shouls’ve been addressed years ago.

Too late now.

For EM-1/2 but for later missions we should address it now.

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1 hour ago, ZooNamedGames said:

For EM-1/2 but for later missions we should address it now.

The problem is that addressing issues with cost-plus contracting means spending huge sums, starting now. Remember, we're reusing SSMEs to save money. 16 RS-25s that cost 40 M$ new have now been refurbished, and upgraded... at a cost of 127 M$ each. To save money. Because that saves money in some alternate universe, I guess.

But they seriously bumped up the thrust of the SSME, which is great, but to put 4 upgraded SSMEs on the SLS core cost, 508 million dollars, and more thrust could have been had by simply using 5 instead of 4 at the old thrust level, obviating the need to spend over 3X what the engines cost new making them better.

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So the ascent stage is withing the realms of an SLS Block 1b comanifested payload (11 tons past Orion)---except that doesn't exist in the next 4 years. Also possible with Delta IV H. Alternately right now, it's in FH territory, easily. Note that the dv requirements are for the lunar aspect (LLO for the Ascent/Descent parts, from Gateway for the transfer vehicle). As a result, that's the delivered mass to either LLO or Gateway.

The descent element is also FH territory, though just barely I think (they claim 16+ tonnes to Mars, but it needs to do a LOI burn, not just TLI (Mars for them assumes direct entry).

The transfer vehicle? Also FH, maybe Delta IV H at the low end.

So the current architecture pretty much requires Orion on the Block 1 SLS, with the other 3 parts sent ahead on FH, and maybe ULA gets thrown a bone and sends the ascent stage with D IVH.

 

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2 hours ago, tater said:

The problem is that addressing issues with cost-plus contracting means spending huge sums, starting now. Remember, we're reusing SSMEs to save money. 16 RS-25s that cost 40 M$ new have now been refurbished, and upgraded... at a cost of 127 M$ each. To save money. Because that saves money in some alternate universe, I guess.

But they seriously bumped up the thrust of the SSME, which is great, but to put 4 upgraded SSMEs on the SLS core cost, 508 million dollars, and more thrust could have been had by simply using 5 instead of 4 at the old thrust level, obviating the need to spend over 3X what the engines cost new making them better.

Well they are also skimming their cost but altering the design, dropping components for reusability so they are trying to work on the cost. Plus it’ll drop more once it reaches economy of scale and they’re actually making new engines instead of refurbing the old which is an odd choice but using them, they know they’re starting with a working design. Rather than adjust and change a brand new engine. So I agree that refurbing isn’t the best choice but I can see their reasoning too.

10 minutes ago, tater said:
So the current architecture pretty much requires Orion on the Block 1 SLS, with the other 3 parts sent ahead on FH, and maybe ULA gets thrown a bone and sends the ascent stage with D IVH.

That’s probably what they have in mind. Using the SLS only when needed as the other two aren’t man rated.

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5 minutes ago, ZooNamedGames said:

Well they are also skimming their cost but altering the design, dropping components for reusability so they are trying to work on the cost. Plus it’ll drop more once it reaches economy of scale and they’re actually making new engines instead of refurbing the old which is an odd choice but using them, they know they’re starting with a working design. Rather than adjust and change a brand new engine. So I agree that refurbing isn’t the best choice but I can see their reasoning too.

The core stage has almost exactly the same thrust as a F9 (slightly less, actually). SRBs do the heavy lifting there.

Even at the old, brand new price of 40 M$ per engine, assuming the new ones cost the same---the core stage engines alone cost more than an entire FH---retail. The core in this case is getting Orion into a 2222km apogee orbit, whereas FH would have to use S2 for most all of the work of getting into any orbit at all. Still, it's an interesting cost comparison.

 

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10 minutes ago, tater said:

The core stage has almost exactly the same thrust as a F9 (slightly less, actually). SRBs do the heavy lifting there.

Even at the old, brand new price of 40 M$ per engine, assuming the new ones cost the same---the core stage engines alone cost more than an entire FH---retail. The core in this case is getting Orion into a 2222km apogee orbit, whereas FH would have to use S2 for most all of the work of getting into any orbit at all. Still, it's an interesting cost comparison.

 

Perhaps but the SLS is man rated and has plans to upgrade. Though only at ends with the FH now, eventually it’ll catch up.

Again though, by the time the B2 and the non Boeing EUS is ready for flight, I totally agree that by then, BFR/Vulcan and NG will be reliable and ready to take on SLS’ tasks. With NASA nearly entirely off loading missions onto them. But in the event they aren’t ready, then B2 will be the version of SLS we’ve wanted (well, wanted more than the current iteration).

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14 hours ago, sh1pman said:

Probably a stupid question, but is it possible for SLS to launch with more than 2 side boosters?

It seems unlikely unless the core stage tankage has been designed for more than two boosters from the outset. I’m no rocket engineer but I’d think those SRBs are putting a lot of force through whichever part of the tank they’re attached  to - welding a couple of extra decouplers on the side for the extra boosters and calling it done, will probably end badly. :) 

 

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Stage and a half to not-quite-orbit is such a bizarre architecture.

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18 minutes ago, RCgothic said:

Stage and a half to not-quite-orbit is such a bizarre architecture.

Indeed it is.

5 hours ago, KSK said:
19 hours ago, Ultimate Steve said:

By my calculations, a maximum of 10 SRBs can be around an SLS core...

That would certainly be interesting to see! At that point, you would probably want to start looking into air starting some of the boosters to make the TWR not so ridiculously high.

It seems unlikely unless the core stage tankage has been designed for more than two boosters from the outset. I’m no rocket engineer but I’d think those SRBs are putting a lot of force through whichever part of the tank they’re attached  to - welding a couple of extra decouplers on the side for the extra boosters and calling it done, will probably end badly. :) 

That's one of the big advantages of liquid boosters...they have no more thrust than the SRBs (actually lower thrust) but they burn for so much longer that they add a lot of dV. Lower thrust means the core doesn't have any more stresses than before so you don't have to redesign the core to accommodate them.

Adding more SRBs or more energetic SRBs means bigger loads going through the core, which means a redesign.

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So until just now, EM-2 was not even "all up."

EM-1 is boilerplate, but with a new heat shield. Yes, the SM will also be tested this time, but Orion itself is not complete.

EM-2 will be the first all-up SLS/Orion, and with people on top. AND, until the recent change of a docking port, was previously not really all-up, because EM-2 would have had no docking port.

Talk about mismanagement.

Assume SLS/Orion is awesome, and you have a bunch of money to build it (we did). Why did they chose the following:

Why ever build Block 1, with the ICPS, when this requires setting up the VAB and MLP for a rocket that was initially supposed to only ever fly once, then spend years, and hundreds of millions to then configure for Block 1b? Why not just build 1b from the start? Saves hundreds of millions (billions?), and it also results in EM-1 being an actual all-up test.

Grrrr.

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4 minutes ago, tater said:

So until just now, EM-2 was not even "all up."

EM-1 is boilerplate, but with a new heat shield. Yes, the SM will also be tested this time, but Orion itself is not complete.

EM-2 will be the first all-up SLS/Orion, and with people on top. AND, until the recent change of a docking port, was previously not really all-up, because EM-2 would have had no docking port.

Talk about mismanagement.

Assume SLS/Orion is awesome, and you have a bunch of money to build it (we did). Why did they chose the following:

Why ever build Block 1, with the ICPS, when this requires setting up the VAB and MLP for a rocket that was initially supposed to only ever fly once, then spend years, and hundreds of millions to then configure for Block 1b? Why not just build 1b from the start? Saves hundreds of millions (billions?), and it also results in EM-1 being an actual all-up test.

Grrrr.

Abfraccckinsurd.

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14 minutes ago, sevenperforce said:

Abfraccckinsurd.

I don't mean to constantly bash SLS/Orion... but they make it so easy...

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2 hours ago, tater said:

I don't mean to constantly bash SLS/Orion... but they make it so easy...

Yeah. Almost like it was never intended as a launcher for a comprehensive manned space exploration program...

3 hours ago, sevenperforce said:

Indeed it is.

That's one of the big advantages of liquid boosters...they have no more thrust than the SRBs (actually lower thrust) but they burn for so much longer that they add a lot of dV. Lower thrust means the core doesn't have any more stresses than before so you don't have to redesign the core to accommodate them.

Adding more SRBs or more energetic SRBs means bigger loads going through the core, which means a redesign.

Well the forces on the connectors might be very different, so a redesign might be required...

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10 minutes ago, Bill Phil said:

Yeah. Almost like it was never intended as a launcher for a comprehensive manned space exploration program...

Well the forces on the connectors might be very different, so a redesign might be required...

In theory, they wouldn't be. You'd have the same (or lower) force, just much longer burn time.

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SLS has a mission. The mission is to loft a vast payload to certain specific destinations.

Those destinations include the States of Alabama, Louisiana, and Washington---and the payload is cash.

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6 minutes ago, tater said:

and the payload is cash.

Astronomical sums.

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21 minutes ago, tater said:

SLS has a mission. The mission is to loft a vast payload to certain specific destinations.

Those destinations include the States of Alabama, Louisiana, and Washington---and the payload is cash.

Yeah.

It’s just that they can do both at the same time. That is they can have a rocket that’s actually usefup and effective and they can spread money around.

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5 minutes ago, Bill Phil said:

Yeah.

It’s just that they can do both at the same time. That is they can have a rocket that’s actually usefup and effective and they can spread money around.

True enough, and I'm fine with spending the money, but I would have preferred that they at least come up with a mission it can do other than delivering the money.

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2 hours ago, sevenperforce said:

In theory, they wouldn't be. You'd have the same (or lower) force, just much longer burn time.

Not exactly. If anything, I'm pretty sure higher Isp boosters (with nothing else changed) would produce less peak force on the coupling joints.

At launch, a pretty big fraction of the boosters' force is spent accelerating the boosters themselves. As propellant burns off, the fraction of thrust transmitted to the core increases as the boosters become a smaller fraction of the overall mass.

If your advanced boosters have the same thrust, dry mass, and full mass, and you change only specific impulse, you wind up extending burn time. With a later BECO, the core stage has burned off a bigger fraction of its mass, so at burnout, the booster/core mass ratio is higher.

That said, SLS definitely has a wonky configuration, with underpowered, undersized upper stages, SRBs that burn out too soon for a long-duration sustainer stage, and far too much of the dV pushed onto said underpowered sustainer stage. Realistically, if one had to use the RS-25s as sustainers, I'd probably go for large kerolox boosters, and see about reviving the J-2 as an upper stage engine.

Which, now that I think about it, basically describes an uprated Ares V rocket with Pyrios boosters instead of the old Shuttle SRBs. Maybe I have too much of a fascination with reviving Apollo-era hardware, but it's not like there's a lot of choice for SHLV-scale engines unless you go clean-sheet.

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Posted (edited)
6 hours ago, sevenperforce said:

Why ever build Block 1, with the ICPS, when this requires setting up the VAB and MLP for a rocket that was initially supposed to only ever fly once, then spend years, and hundreds of millions to then configure for Block 1b? Why not just build 1b from the start? Saves hundreds of millions (billions?), and it also results in EM-1 being an actual all-up test

It's no conspiracy. It's politics. Back when Obama was pushing ARM, NASA made the decision to basically do what you're saying: 'skip' Block I in favor of Block IB. Unfortunately, they were told to keep EM-1, so they compromised on doing one Block I mission then switching over (which IMO is the worst of both worlds, but whatever).

Five years later, and thanks to this new aggressive schedule, it looks like Block I is going to be the real workhorse of the fleet, and Block IB's future is uncertain. A complete reversal over just five years! Seems like a lot of time, but it's really not that long at all when you're dealing with literal rocket science.

This is why a lot of people bang on about having clearly-defined mission goals: because then you don't have to deal with a rocket constantly in flux. But the politics don't let you, because if you specifically build a moon rocket and the next guy doesn't want to go to the moon, welp, there goes your moon rocket. Thus NASA overbuilds generalist rockets that can be adapted to fit the politics, because it's the only way they can get anything built at all.

 

Edited by jadebenn

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