sevenperforce

Anything the ICPS can do, the core can do on direct ascent. The only thing the core can't do is restart. Launch TWR with a 70-tonne payload is 1.59 with the ICPS, 1.61 without. So it's hardly even a significant difference in initial ascent profile. Does anyone have a more detailed/exhaustive launch performance calculator than the one I linked to above? I want to double-check these numbers.

Because the SSMEs are not restartable. For EM-1, the payload will be fairly low (roughly 25.8 tonnes including Orion, the Service Module, and the SM's propellant), so the SLS Core will be able to carry the ICPS and Orion almost all the way to orbit. The ICPS will ignite once to circularize, followed by time in LEO, then ignite a second time for the TLI burn. This is similar to what the Saturn V's third stage did for Apollo 8-17. But if the SLS can take up to 70 tonnes to LEO, then yeah -- why bother with the ICPS at all? Just add more propellant to the Orion's Service Module and be done with it. The SM's main engine, an old Shuttle OMS engine, has 316 seconds of vacuum isp and it currently flies with 9.3 tonnes of propellant. If you can put 70 tonnes in LEO with the Core and boosters alone, you can add up to 44 tonnes of propellant to the Service Module (probably using drop tanks), giving Orion almost 4.5 km/s of delta-V. Hold on, the wikipedia page for the SLS says the first stage thrust is 7,440kN. The RS-25s develop 1,860 kN of thrust at sea level, giving the SLS first stage a liftoff thrust of 7,440 kN (1,860 x 4). The RS-25s go up to 2,279 kN of vacuum thrust, so I took average thrust as (2279 + 1860)/2. Honestly, I'm not even sure that the ICPS actually increases LEO payload at all. Think about it. The Shuttle, with 4-segment boosters and three RS-25s, could lift 27.5 tonnes to LEO, inside the 69-tonne orbiter. It also carried the 27-tonne external tank to the very edge of space; if the OMS engines and fuel had been removed, the SSMEs could have carried the tank all the way through orbital insertion. That's a gross total of roughly 123.5 tonnes to LEO. With the five-segment boosters of the SLS and its four RS-25s with its 73-tonne tank, we are looking at a gross total of 155 tonnes to LEO without any upper stage at all. A second stage doesn't really make much sense.

The ICPS does have restart capability, yes. But for 70-tonne LEO payloads, it is completely expended during the circularization burn. The SSMEs are very altitude-sensitive; as you'll recall, they were designed to function from SL through to outer space. Apparently, the added mass of the ICPS keeps them low in the atmosphere for longer, making them so much less efficient that separation occurs roughly 1.4 km/s below orbital velocity. Without the ICPS, they would ascend so much more quickly that their increased efficiency would allow them to carry the exact same payload all the way to orbit.

Whoa, guys (and gals). I just realized something really, really crazy. The current SLS Block 1 comprises: Two five-segment SRBs (each with dry mass 102 tonnes, propellant 623 tonnes, isp 269 sec, thrust 16,000 kN) ET-derived core stage with four RS-25s (dry mass 85.3 tonnes, propellant 894 tonnes, avg isp 430 sec, avg thrust 2070 kN) Interim Cryogenic Propulsion Stage with one RL10 (dry mass 3.5 tonnes, propellant 27.2 tonnes, vac isp 462 sec, vac thrust 110 kN) It is projected to be able to put 70 tonnes of payload in LEO. My estimate using this calculator and the numbers above gives 73 tonnes to LEO (185 x 185 km, 28.5 degrees inclination, Cape launch). Here's the thing, though. If I remove the Interim Cryogenic Propulsion Stage completely, launching only the two SRBs and the core, I get 71 tonnes to LEO. And that's not even taking into account that the higher TWR would make the thrust and specific impulse of the RS-25s come up faster, meaning that the addition of the ICPS could actually decrease the payload. Why on Earth would we add a whole second stage if we don't actually need it?

The SLS Core Main Tank is so large that 4-5 RS25s isn't enough to get it off the ground, so Core + Upper won't work; you need at least six RS-25s or you need SRBs. That's why I propose the engine skirt. With that route, you have a modular capability the current SLS just doesn't have. You can use Core + Skirt for smaller payloads, SRBs + Core for larger payloads, and SRBs + Core + Skirt for the largest payloads. These can be swapped in and out based on mission requirements, whereas the current SLS will depend on block upgrades to improve its overall performance. I'm still doing the math to determine whether an upper stage makes sense.

Shyung was proposing the addition of liquid boosters or SRBs, but the 4+2 Super Atlas configuration has sufficient TWR on its own. You could add SRBs as a way to increase payload or add an upper stage.

Soyuz is kerolox. Hydrolox strap-on liquid boosters are ridiculously inefficient; just look at Delta IV Heavy. A hydrolox core stage really only makes sense if you're sending it all the way (or almost all the way) to orbit, as with the Shuttle, the DIRECT's Jupiter family, and my proposal. Another advantage is that the SLS core stage size and the use of the SSMEs is already established and tested by the Shuttle program. If we wanted to do liquid boosters, it would be better to go with the Pyrios approach and use one or two F-1As on each kerolox booster. But then you have to plumb the pad for LOX, LH2, and RP-1, which is unpleasant. EDIT: Delta IV heavy uses an 82-tonne (dry mass) vehicle to place 29 tonnes into orbit; Falcon Heavy uses a 70.6-tonne vehicle to place more than twice as much mass into orbit. That's what I mean about low efficiency of hydrolox strap-on boosters.

Note that the use of the SSMEs and ET-derived common core tank as the orbital insertion vehicle is what was proposed by DIRECT for the Jupiter launch family, the "original" SLS that our buddies over at NSF lobbied for. Payload masses up to 70 tonnes would send the core tank all the way to orbit; payload masses over 70 tonnes would use an upper stage. As I've shown above, the use of 5-segment SRBs and a super-Atlas skirt configuration increases this capability to 100 tonnes, all without any upper stage: DIRECT's Jupiter launch family was a far better idea than the current SLS system; adding the super-Atlas configuration makes it even better.

Very little unless it launches with the payload or can rendezvous with it very shortly thereafter. Immediate rendezvous would be the plan, yes.

Admittedly, I was thinking of spending the five billion dollars repurposing the SLS systems rather than coming up with something completely new. And the goal is not an LEO propellant cache/depot, but a single-use LEO propulsion bus to enable BLEO missions. Want a moon mission? Design the lander and send it up on Falcon Heavy or New Glenn, launch a propulsion bus on SLS, and then send the crew up on Falcon 9. Want a Mars mission? Do the same thing, but use multiple propulsion buses in parallel (thus the need for RCS, propellant transfer tech, and side docking ports). This is the closest thing we can get to going kerbal. If propellant transfer is a nonstarter, that's fine; we'd still want side docking ports to enable parallel coupling for injection burns. The only thing hydrolox is really good for is high-energy upper stages for large BLEO missions. So if you are desperate to reuse mothballed SSMEs, it does make a bit of sense to use a modified SLS stack to send up propulsion buses. The Shuttle SRBs held 498.7 tonnes of propellant each, so the planned five-segment SRBs will hold around 623 tonnes, with a GLOW of 726 tonnes, a vacuum isp of 269 seconds, and an estimated vacuum thrust of 18,176 kN. With this in mind, here are the LEO payloads (185 km x 185 km, Cape launch) for the first three configurations: Skirt + Core (see above): 39.6 tonnes, skirt jettisoned at 87.5% fuel expenditure Core + SRBs: 88.3 tonnes Skirt + Core + SRBs: 100.5 tonnes, skirt jettisoned at 91.5% fuel expenditure Just imagine what sorts of missions would be possible with the ability to drop a 100-tonne hydrolox propulsion bus into LEO. Liftoff TWR for the skirt+core+SRB stack is 1.8, so we could add an upper stage easily enough. I'll see what numbers I can run up.

Adding tanks for the skirt engines would make TWR worse, not better. But yeah, adding SRBs is one way to fix it. I could envision four configurations: Core + Skirt, Core + Boosters, Core + Skirt + Boosters, and Core + Skirt + Boosters + Upper Stage. SRBs are one option, but advanced liquid boosters powered by F-1As is preferable, I think.

Running some numbers to see what an Atlas-configured ET-and-SSME-derived launch family would be able to send to orbit. Launch TWR is somewhat of an issue; the RS-25s provide 1,860 kN each at sea level, so five of them would have a max takeoff thrust of 948 tonnes thrust. However, the SLS core masses 967 tonnes not including engines. If the RS-25 had its vacuum thrust at launch, a super-Atlas configuration could put 36 tonnes into LEO. If we up the ante and place six engines on the base (two at the center, four on the skirt), things get a little better. We have 1,138 tonnes thrust to play with, which gives us breathing room. With four engines on the skirt and two on the core, dropping the skirt when just over 87% of the fuel is expended, you could put 39.6 tonnes into a 185x185 km orbit from the Cape. Launch TWR is 1.11:1. Probably not possible to put a second stage on this, but parallel boosters would make it quite impressive.

At least I've still got the altitude record!

That's what I did. EDIT: Ah, I see the problem. i needed to drop the ModuleManager dll into the GameData folder too.

I've always played vanilla, but I wanted to add Tweakscale, so I did. Downloaded the mod, unzipped it, and dropped it into my "GameData" directory. Then I opened KSP, made a new sandbox game, went to the VAB, added a part, right-clicked, and...nothing. I feel stupid. What step am I missing?

Was just thinking... If NASA really is determined to throw their mothballed SSMEs into the Atlantic, there's a particularly efficient way to do it: Super-Atlas. No parallel boosters. Redesign the four-engine thrust platform to make it open; put a fifth RS-25 at the center. All five engines fire at launch, but the thrust platform with the four RS-25s drops away part of the way through the first-stage burn, leaving the center sustainer engine to run through to MECO. An RS-25-based Super Atlas. Then, repeat the exact same arrangement with the RL-10s on the upper stage. This way, the upper stage finishes with just a single engine, meaning it can be its own payload if equipped with the previously-described persistent modular propulsion system components. Or it can fly without those components and merely be used to lift very heavy payloads. I'll run some numbers tomorrow but I think it would be pretty badass. EDIT: Of course, SRBs or Advanced Liquid Boosters could be used optionally. One really nice thing is that the sub-staging point (dropping the engine ring) can be varied based on payload and ascent profile, whereas traditional serial staging is pretty much noncustomizable. EDIT 2: Those familiar with the history of the Saturn program may note the similarity to the S-1D proposal. EDIT 3 (because apparently I cannae stop editing): In theory, an entire launch family (like Atlas V) could be assembled around the same ET-derived hydrolox single-SSME core. You could have a near-SSTO with two auxiliary engines on the thrust ring (a la Atlas D Mercury), a 4+1 variant (a la Saturn S-1D) with or without a second stage, or various parallel-boosted configurations.

Ran some quick numbers. Replacing the SLS boosters with Pyrios boosters (2 x F-1B, 1,054 tonnes gross launch mass each) and using a 145-tonne second stage powered by four RL10s allows you to put 145 tonnes into a 185x185 km orbit matching the inclination of the ISS, launching from Kennedy. This means the "payload" can be the same size and weight as the second stage, so you have common manufacturing between the tank on the upper stage and the tank on the Persistent Modular Propulsion System. The PMPS would then be able to notionally place up to 77 tonnes in lunar orbit, or it could send itself to lunar orbit to act as a propellant depot with 45 tonnes of propellant remaining. Multiple PMPSs would be able to dock to each other lengthwise for propellant transfer or for asparagus-staged transfer burns. With that kind of system, you can literally send ANYTHING to ANYWHERE. Of course, you'd need to devote some funding to actual mission architectures. Establish a lunar base, retrieve an asteroid, head to Mars, that sort of thing.

Inductive ignition is nice but catalytic ignition is faster and more reliable. Though H2O2 is not terribly pleasant to handle.

My preferred SLS replacement: Persistent Modular Propulsion System Stretched ACES-derived hydrolox upper stage with a single powerplant derived from the RL10 and spark-based ignition system Solar-based autogenous coolant system for propellant persistence Hydrolox RCS thrusters for independent orbital maneuvering Side-mounted docking system with magnetic structural linkage and propellant transfer capacity Forward docking system for orbital payload coupling High Energy Upper Stage (similar to EUS) Uses the same tank and engine as the Persistent Modular Propulsion System No thrusters, coolant system, or docking system Additional thrust structure that allows four engines rather than one Core Booster (same as current SLS) Core tank and thrust structure assembled at Michoud Four RS-25s Advanced Liquid Parallel Boosters Pyrios-derived kerolox boosters Two F-1B engines per booster That's all. Launches either send a full PMPS into orbit to couple with a BLEO payload, or they send very large BLEO payload components into orbit for assembly. Contract with commercial providers for smaller payload components and crew launches. Orion is fine, just launch it unmanned on a Delta IV Heavy or something.

I would much rather spend the SLS money on helping to fund commercial lift vehicles and developing BLEO missions and stages. I agree. Though honestly Ares 1 can be dropped altogether. Let the commercial crew program handle man-rating and stick to getting large payloads into orbit for actual missions.

With a bunch of Separatrons, I can boost my acceleration up to 1,270.1 m/s2; with artful use of 4x warp, this will get me to c in about 16.4 hours. Ignore the "max acceleration" shown; that is adding its spin rate, which is rather prodigious at this point.

Here's the LV. Infinite electricity, infinite prop, no heating damage: Toasty on ascent: Even toastier in space. Solar escape was reached within the first 2 minutes. This is after I let it run a bit longer. Looks like the maximum acceleration is 266.3 m/s2, so I'd need to run it for just over 32 days. EDIT: Actually, upon review, an empty Separatron has a far higher TWR than a Mammoth, so lemme rebuild it real quick.

Not sure if it's considered a glitch, but if you DO get enough speed going, you can always get a nice multiplier by smashing into Jool just right. In reality, there is a maximum gravity assist you can get, but I don't think the game simulates slingshots properly at high speeds. The Mammoth has the highest vacuum TWR of any engine now. I used two of them and turned on infinite propellant and infinite electricity -- lemme see how fast I get to c.

You need an effective fuel fraction of 1:1.193e3161. No, that's not a typo. 1.193x103161. That's 11,930 thousand million billion trillion quadrillion quintillion sextillion sextillion septillion octillion nonillion decillion undecillion duodecillion tredecillion quattuordecillion quindecillion centillion centillion centillion centillion centillion centillion centillion centillion centillion times more fuel than payload. Given that the mass of the Dawn ion engine is a quarter-tonne, you'd need 3e3160 metric tonnes of xenon, not counting the mass of the tanks. To put this in perspective, the mass of the observable universe is roughly 6e49 metric tonnes. If every particle in the observable universe was a massless Dawn ion engine that could consume one trillion universes every nanosecond, and you ran these engines from the Big Bang until the heat death of the universe, you would still need to repeat this process 10493 times before you'd burn through that much xenon.

Not really, I don't think. Compared to a modern fighter, a glide-down shuttle has a very limited range of conditions. There's virtually no variation in descent profile; the only variables are weight (in case you're bringing downmass home) and crossrange path. Why would you go for a separate OMS system at all? The only reason the Shuttle used OMS was to avoid having to crossfeed the SSMEs from the ET and from an internal tank. If you're already carrying your tank internally, this advantage goes away. Catalyzed H2O2/RP-1 is a better combo, imho. High TWR, great throttle range, room-temp, decent ISP, etc.; and storable for reasonably long enough. You can even use the peroxide as the restartable ignition system for a kerolox engine (booster or otherwise).