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Forum designs new rocket to replace the SLS


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5 hours ago, zeta function said:

I think that an alternative to the sls would be not hydrolox fueled on the first stage, hydrogen just takes up tons of space and has relatively low efficiency at the surface of earth. Also, the ssme just costs to much.

The first stage is solid-fuelled in Block I and kerolox in Block II. Using Soviet terminology makes a lot more sense because otherwise the "first stage" very nearly makes it to orbit in many cases.

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Yeah, that is a problem. I wrote Step 1 wrong, really, because it sort of implies building large payloads just because.

If LV designs didn't require a program running in the background to support them, then it would not be a problem, but since the expensive program has to exist even if they only flew 1 every 10 years, it's a real issue.

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1 hour ago, tater said:

Yeah, that is a problem. I wrote Step 1 wrong, really, because it sort of implies building large payloads just because.

But it's also the central problem - nobody is going to fund, design, and build around a booster that may-or-may-not exist a decade hence.  SLS also faces an additional hurdle, the only probes worth it's performance are high end flagship ("battlestar") missions - a class of probe that's largely been deprecated and are extraordinarily unlikely to be funded.

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On 5/25/2017 at 4:21 PM, sevenperforce said:

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?

In RO I launched a 110 ton payload to a 380k by -12k orbit with just the core stage and boosters. With improved flying skills I could probably get it into an actual orbit.

But here is my suggestion. Have the regular core stage and boosters, but add a small upper stage with maybe 500 m/s Dv for circulization.

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1 minute ago, zeta function said:

In RO I launched a 110 ton payload to a 380k by -12k orbit with just the core stage and boosters. With improved flying skills I could probably get it into an actual orbit.

But here is my suggestion. Have the regular core stage and boosters, but add a small upper stage with maybe 500 m/s Dv for circulization.

I actually figured this out. The ICPS is considered to be part of the 70-tonne LEO payload.

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On 5/25/2017 at 3:21 PM, sevenperforce said:

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?

Because SLS is not a LEO launcher. SLS is designed to put payloads on high energy trajectories. Orion to the Moon, Europa Clipper to Europa, and so on. 

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13 minutes ago, Bill Phil said:

Because SLS is not a LEO launcher. SLS is designed to put payloads on high energy trajectories. Orion to the Moon, Europa Clipper to Europa, and so on. 

Surely, though, you'd think that large LEO launch capability for cheaper than a 'standard' SLS flight would be another nice talking point to sell to the more skeptical Congressmen and the like? LEO missions may not be the main purpose of SLS, but if this kind of configuration was feasible you'd think that we would hear about it.

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@Bill Phil, anything going elsewhere is first going to LEO. 70, 100, whatever tons in LEO doesn't mean it's staying there, or that the payload is 70, but that there is a 70 ton upper stage in LEO, and if it has a 5 ton payload, the bulk of the remaining 65 tons is an US engine, and propellant.

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Of course the poor dwell time of the hydrogen EUS means you won't be assembling anything in LEO, which limits SLS to small high energy payloads. It's basically useless for anything else.

Edited by RCgothic
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6 minutes ago, RCgothic said:

Of course the poor dwell time of the hydrogen EUS means you won't be assembling anything in LEO, which limits SLS to small high energy payloads. It's basically useless for anything else.

At least the fairing is large enough to send the DSG to cislunar orbit.

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1 hour ago, tater said:

@Bill Phil, anything going elsewhere is first going to LEO. 70, 100, whatever tons in LEO doesn't mean it's staying there, or that the payload is 70, but that there is a 70 ton upper stage in LEO, and if it has a 5 ton payload, the bulk of the remaining 65 tons is an US engine, and propellant.

Not in the case of SLS. The core injects the stack to a highly eccentric orbit. It's not going to LEO first.

And I was answering the question of why we'd add a second stage if it we don't need it. Because they want to put payloads into high energy trajectories, not in LEO. Or, in other words, without infrastructure in place (space tugs), we need a second stage for high energy trajectories, the current mission idea for SLS. 

Edited by Bill Phil
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11 hours ago, tater said:

Fair enough, but it depends on how the value was calculated. 70 tons in LEO is what in the nominal eccentric orbit, or would it be less in that, and more in LEO?

The SLS core+boosters have plenty of margin to take 70 tonnes to a circular LEO. But since the SLS core can't restart to deorbit itself, it's much more efficient to take the 70-tonne-stack of ICPS+Orion+SM into an eccentric orbit with a 0-km Pe; this way the core can burn to depletion without wasting anything on circularization and deorbit naturally. The ICPS can raise Pe from the high Ap.

I originally brought up the whole issue because I mistakenly thought the ICPS was going to be used for LEO payloads in addition to EM-1. This is, of course, incorrect; the ICPS is useless for LEO payloads because its TWR is so low.

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ICPS is useless, period. It will only ever fly on EM-1, and then they need to alter both the VAB catwalks/etc, and the pad for all further launches---which is slated to take 33 months. Seems idiotic.

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35 minutes ago, tater said:

ICPS is useless, period. It will only ever fly on EM-1, and then they need to alter both the VAB catwalks/etc, and the pad for all further launches---which is slated to take 33 months. Seems idiotic.

Because EUS isn't ready yet and would cause significant delays to EM-1. On the other hand, ICPS allows NASA to test the lower stages and Orion in a similar fashion as they will be used in EM-2. Without ICPS, EM-1 could probably only be launched in a similar timeframe as EM-2 is planned to happen, i.e. in 2023 instead of 2019.

Sure, ICPS costs money, but its derived from Delta IV's DCSS, which should reduce its costs. And 33 months for altering the VAB is a short time compared to the 4 years between EM-1 and EM-2.

Edited by Tullius
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37 minutes ago, Tullius said:

Because EUS isn't ready yet and would cause significant delays to EM-1. On the other hand, ICPS allows NASA to test the lower stages and Orion in a similar fashion as they will be used in EM-2. Without ICPS, EM-1 could probably only be launched in a similar timeframe as EM-2 is planned to happen, i.e. in 2023 instead of 2019.

Sure, ICPS costs money, but its derived from Delta IV's DCSS, which should reduce its costs. And 33 months for altering the VAB is a short time compared to the 4 years between EM-1 and EM-2.

I still think they should replace the square-arranged 4-engine stack on the EUS with a 1+3 arrangement that allows three engines to be dropped mid-burn, Atlas-style. It's not a ton of added complexity but it significantly increases payload capability.

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7 minutes ago, sevenperforce said:

I still think they should replace the square-arranged 4-engine stack on the EUS with a 1+3 arrangement that allows three engines to be dropped mid-burn, Atlas-style. It's not a ton of added complexity but it significantly increases payload capability.

I wouldn't recommend it. Red tape, bureaucracy, and so on and so on... They've likely already signed off on a lot of the important aspects of EUS. Getting everyone to commit to a redesign would just take... too much effort. Too much time. It's surprisingly hard, or rather, unsurprisingly so, to get anything approved or signed off. People have to be in the right place at the right time.

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2 minutes ago, Bill Phil said:

I wouldn't recommend it. Red tape, bureaucracy, and so on and so on... They've likely already signed off on a lot of the important aspects of EUS. Getting everyone to commit to a redesign would just take... too much effort. Too much time. It's surprisingly hard, or rather, unsurprisingly so, to get anything approved or signed off. People have to be in the right place at the right time.

Well, by "should" I meant from an engineering and rocket science perspective.

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3 hours ago, Bill Phil said:

Well, there is always the saying that the best system is the one that's not there...

It's not a saying, it's the summary of this thread.

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Im no rocket scientist, but a Space Shuttle launch vehicle (with the main engines, but without the shuttle) can get around 70 tons to LEO right? I think this has been mentioned on this thread before. I heard something like this was called Jupiter III, from the DIRECT program. Correct me if im wrong.

I might try building something moderately realistic in Realism Overhaul. I know making something in a game is not full on designing a revolutionary rocket, and im 100% sure NASA will not use a weird nerd kid's design for their new spacecraft, but it just sounds like fun to me.

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10 minutes ago, NSEP said:

Im no rocket scientist, but a Space Shuttle launch vehicle (with the main engines, but without the shuttle) can get around 70 tons to LEO right? I think this has been mentioned on this thread before. I heard something like this was called Jupiter III, from the DIRECT program. Correct me if im wrong.

I might try building something moderately realistic in Realism Overhaul. I know making something in a game is not full on designing a revolutionary rocket, and im 100% sure NASA will not use a weird nerd kid's design for their new spacecraft, but it just sounds like fun to me.

DIRECT was the brainchild of the NasaSpaceFlight forums, where a bunch of industry professionals got together and proposed a design to repurpose Shuttle-era hardware. This ultimately evolved into the SLS. Unfortunately, the SLS has evolved since then, to the point that it's no longer really useful for much of anything.

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Just now, sevenperforce said:

DIRECT was the brainchild of the NasaSpaceFlight forums, where a bunch of industry professionals got together and proposed a design to repurpose Shuttle-era hardware. This ultimately evolved into the SLS. Unfortunately, the SLS has evolved since then, to the point that it's no longer really useful for much of anything.

Interesting! Makes alot of sense, thanks!

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