Author Topic: SLS General Discussion Thread 2  (Read 160025 times)

Offline TakeOff

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Re: SLS General Discussion Thread 2
« Reply #940 on: 05/18/2017 01:14 PM »
Is the fully fueled upper stage (ICPS) considered "payload"? Isn't that an unconventional definition?

While SLS is planned to launch Orion to Lunar orbit, I think that all SLS based crewed Mars missions I've heard of actually do suggest launches to LEO in order to assemble multiple SLS payloads, and the separately launched crew, into a Mars capable spacecraft. Is SLS unsuitable by design to do that?
Why does the SLS have lower mass capacity to LEO than the Shuttle's launch stack did?

The forum is full of multiple hundreds of posts re. this. Suggest you dig into the archives and do some reading.
This is a recurring problem. I've gotten used to more advance search functions, like Stack Exchange that has tags and headline searches. Here one has to fiddle quite a bit in order to get relevant results. Which is a bit hard when one is asking about something one doesn't know much about. But I'll improve on searching. I've found some interesting threads on it now. (It's hard to come up with anything new here).
« Last Edit: 05/18/2017 01:17 PM by TakeOff »

Offline envy887

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Re: SLS General Discussion Thread 2
« Reply #941 on: 05/18/2017 01:59 PM »
Is the fully fueled upper stage (ICPS) considered "payload"? Isn't that an unconventional definition?

While SLS is planned to launch Orion to Lunar orbit, I think that all SLS based crewed Mars missions I've heard of actually do suggest launches to LEO in order to assemble multiple SLS payloads, and the separately launched crew, into a Mars capable spacecraft. Is SLS unsuitable by design to do that?
Why does the SLS have lower mass capacity to LEO than the Shuttle's launch stack did?

The forum is full of multiple hundreds of posts re. this. Suggest you dig into the archives and do some reading.
This is a recurring problem. I've gotten used to more advance search functions, like Stack Exchange that has tags and headline searches. Here one has to fiddle quite a bit in order to get relevant results. Which is a bit hard when one is asking about something one doesn't know much about. But I'll improve on searching. I've found some interesting threads on it now. (It's hard to come up with anything new here).

Try Google:
https://www.google.com/search?q=site%3Aforum.nasaspaceflight.com+SLS+payload+shuttle

Payload definitions depend on which vehicle you're looking at. For SLS Block 1, the payload is everything above the core stage. Since all of this is actually delivered into orbit (including the core stage), counting the ICPS as payload is sensible.

Online Lars-J

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SLS General Discussion Thread 2
« Reply #942 on: 05/18/2017 03:23 PM »
Is the fully fueled upper stage (ICPS) considered "payload"? Isn't that an unconventional definition?

While SLS is planned to launch Orion to Lunar orbit, I think that all SLS based crewed Mars missions I've heard of actually do suggest launches to LEO in order to assemble multiple SLS payloads, and the separately launched crew, into a Mars capable spacecraft. Is SLS unsuitable by design to do that?
Why does the SLS have lower mass capacity to LEO than the Shuttle's launch stack did?

The forum is full of multiple hundreds of posts re. this. Suggest you dig into the archives and do some reading.
This is a recurring problem. I've gotten used to more advance search functions, like Stack Exchange that has tags and headline searches. Here one has to fiddle quite a bit in order to get relevant results. Which is a bit hard when one is asking about something one doesn't know much about. But I'll improve on searching. I've found some interesting threads on it now. (It's hard to come up with anything new here).

Try Google:
https://www.google.com/search?q=site%3Aforum.nasaspaceflight.com+SLS+payload+shuttle

Payload definitions depend on which vehicle you're looking at. For SLS Block 1, the payload is everything above the core stage. Since all of this is actually delivered into orbit (including the core stage), counting the ICPS as payload is sensible.

Since when does the SLS core stage go into orbit???
« Last Edit: 05/18/2017 03:23 PM by Lars-J »

Online okan170

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Re: SLS General Discussion Thread 2
« Reply #943 on: 05/18/2017 03:36 PM »
Since when does the SLS core stage go into orbit???

In NSF's EM-1 article, it was noted that after core burnout, the orbit is 975 x 22 nautical miles, in order to ensure the core is disposed of safely, and then a 45+ minute coast to apogee which would be the first time the upper stage lights to just lift the perigee out of the atmosphere.  The way I understand it is that its similar to the Shuttle in that the ET could theoretically have been carried all the way to orbit, but was placed in a disposal trajectory.  In this case, the extra performance seems to be being used to help the subsequent TLI burn via the Oberth effect.

Online Lars-J

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Re: SLS General Discussion Thread 2
« Reply #944 on: 05/18/2017 04:45 PM »
Since when does the SLS core stage go into orbit???

In NSF's EM-1 article, it was noted that after core burnout, the orbit is 975 x 22 nautical miles, in order to ensure the core is disposed of safely, and then a 45+ minute coast to apogee which would be the first time the upper stage lights to just lift the perigee out of the atmosphere.  The way I understand it is that its similar to the Shuttle in that the ET could theoretically have been carried all the way to orbit, but was placed in a disposal trajectory.  In this case, the extra performance seems to be being used to help the subsequent TLI burn via the Oberth effect.

Ok, for all missions the core stage is almost left in orbit (like STS), but I guess I never realized that the apogee would be that high for that mission.

Offline envy887

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Re: SLS General Discussion Thread 2
« Reply #945 on: 05/18/2017 06:03 PM »
Since when does the SLS core stage go into orbit???

In NSF's EM-1 article, it was noted that after core burnout, the orbit is 975 x 22 nautical miles, in order to ensure the core is disposed of safely, and then a 45+ minute coast to apogee which would be the first time the upper stage lights to just lift the perigee out of the atmosphere.  The way I understand it is that its similar to the Shuttle in that the ET could theoretically have been carried all the way to orbit, but was placed in a disposal trajectory.  In this case, the extra performance seems to be being used to help the subsequent TLI burn via the Oberth effect.

Ok, for all missions the core stage is almost left in orbit (like STS), but I guess I never realized that the apogee would be that high for that mission.

No, just for the Block 1 mission. Block 1B drops the core stage well before reaching a positive perigee. Block 1B brings less mass to orbit than Block 1 or STS (~120t vs ~165t and ~145t, respectively), but far more of it is useful mass.

Offline A_M_Swallow

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Re: SLS General Discussion Thread 2
« Reply #946 on: 05/22/2017 06:44 PM »

In the case of SLS Block 1, the "second stage" is the core stage, which is 85 tonnes at burnout.

If the payload performs the circularization burn does this mean that the SLS block 1 alpha is a 85 tonne payload SSTO? A significant cost saving for launching medium heavy payloads.

Offline envy887

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Re: SLS General Discussion Thread 2
« Reply #947 on: 05/22/2017 07:46 PM »

In the case of SLS Block 1, the "second stage" is the core stage, which is 85 tonnes at burnout.

If the payload performs the circularization burn does this mean that the SLS block 1 alpha is a 85 tonne payload SSTO? A significant cost saving for launching medium heavy payloads.

It's no SSTO but 1.5 stage to orbit, just like STS. In the case of STS, the "payload" (orbiter) did do the circularization burn.

Offline hkultala

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Re: SLS General Discussion Thread 2
« Reply #948 on: 05/22/2017 07:58 PM »

In the case of SLS Block 1, the "second stage" is the core stage, which is 85 tonnes at burnout.

If the payload performs the circularization burn does this mean that the SLS block 1 alpha is a 85 tonne payload SSTO? A significant cost saving for launching medium heavy payloads.

SSTO == Single Stage To Orbit.

What you are talking is neither single stage nor to orbit.

Offline envy887

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Re: SLS General Discussion Thread 2
« Reply #949 on: 05/22/2017 08:06 PM »
Even if SLS was a SSTO (it's not even close) it's not remotely close to a significant cost savings. SSTO is only useful if it's rapidly reuseable. Or at least reuseable. Or even recoverable for refurbishment. SLS is none of the above. It's a step backwards from the Shuttle in just about every capability.

Offline oldAtlas_Eguy

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Re: SLS General Discussion Thread 2
« Reply #950 on: 05/22/2017 08:25 PM »
The two exceptions to your statement is payload mass and orbit achievable from that of Shuttle.

Offline envy887

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Re: SLS General Discussion Thread 2
« Reply #951 on: 05/22/2017 08:41 PM »
The two exceptions to your statement is payload mass and orbit achievable from that of Shuttle.

Only payload mass & diameter. Shuttle with IUS reached high energy orbits with lighter payloads up to 5 m diameter.

Offline envy887

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Re: SLS General Discussion Thread 2
« Reply #952 on: 05/22/2017 08:46 PM »
SSTO == Single Stage To Orbit.

What you are talking is neither single stage nor to orbit.

It is certainly "to orbit". It's only stable for one revolution due to atmospheric drag at perigee, but it is an orbit.

Quote from: Philip Sloss
After Core Stage separation, both the spent stage and the mated Orion-ICPS stack will be in an elliptical Earth orbit with an apogee of about 975 nautical miles and a perigee of about 22 nautical miles.

At the first apogee, around forty-five to fifty minutes after liftoff, the ICPS will make its first burn to bring the perigee of the orbit up to 100 nautical miles.
https://www.nasaspaceflight.com/2016/07/mission-trajectory-sarafin-outlines-ride-uphill-em-1/
« Last Edit: 05/22/2017 08:47 PM by envy887 »

Offline A_M_Swallow

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Re: SLS General Discussion Thread 2
« Reply #953 on: 05/22/2017 10:36 PM »
The cost saving on the first stage only SLS is not having to buy an ICPS. I have a feeling that they will be very expensive.

Offline envy887

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Re: SLS General Discussion Thread 2
« Reply #954 on: 05/22/2017 10:57 PM »
There will be only one ICPS. And it's probably adding $2 billion to the program between man rating and infrastructure costs. But I'm not sure that flying without it is much cheaper... Besides, what weighs 80 tonnes and needs to go to LEO in one launch?
« Last Edit: 05/22/2017 10:58 PM by envy887 »

Offline Proponent

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Re: SLS General Discussion Thread 2
« Reply #955 on: 05/22/2017 11:42 PM »
The cost saving on the first stage only SLS is not having to buy an ICPS. I have a feeling that they will be very expensive.

I wouldn't think so.  The ICPS is small has commonality with the Delta IV upper stage and uses engines used by other vehicles.  The core stage and SRBs, on the other hand, are big and have nothing in common with anything.

Online rst

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Re: SLS General Discussion Thread 2
« Reply #956 on: 05/23/2017 01:44 AM »
There will be only one ICPS. And it's probably adding $2 billion to the program between man rating and infrastructure costs. But I'm not sure that flying without it is much cheaper... Besides, what weighs 80 tonnes and needs to go to LEO in one launch?

The crewed EM-1 proposal seems to be off the table for the moment.  Does the ICPS need to be man-rated if it's only going to be used on an uncrewed EM-1?

Offline TomH

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Re: SLS General Discussion Thread 2
« Reply #957 on: 05/23/2017 02:31 AM »
If all the political inertia could be shaken free, and if they are determined to continue putting money into it, and if they want to get a better ROI, and if they would actually fly it frequently, a more effective way to employ this LV would be to put as many of those reusable RS-25Ds as will fit on the core with an RL-10 (or something with appropriate thrust) in the center to use as a landing engine, put RTLS reusable liquid boosters on the sides, and develop an 8.6m multiple J-2X powered LUS. Then the three lower cores could be reused and only the LUS would have to be replaced on every launch. Core prop would need to be be expended early enough to survive reentry. After a fleet of cores and boosters are built, the line only builds more of the LUS and J-2X could go into production fairly easily. Then payload capacity would increase and cost per launch decrease. A time is coming in the not so distant future when all boosters and S1 cores are landable and reusable. This one either gets needed changes, or it gets cancelled as cheaper and equally capable other LVs come online. But I'm not holding my breath.
« Last Edit: 05/23/2017 02:39 AM by TomH »

Online okan170

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Re: SLS General Discussion Thread 2
« Reply #958 on: 05/23/2017 03:05 AM »
There will be only one ICPS. And it's probably adding $2 billion to the program between man rating and infrastructure costs. But I'm not sure that flying without it is much cheaper... Besides, what weighs 80 tonnes and needs to go to LEO in one launch?

The crewed EM-1 proposal seems to be off the table for the moment.  Does the ICPS need to be man-rated if it's only going to be used on an uncrewed EM-1?

It does if its going to be used in an argument against the whole program!  (nothing is off the table in that case  ::) )  But thats really what this thread is now, people posting how much they hate everything and how it needs to be cancelled etc.  Repeat for 5+ years and probably through the missions too.

Offline Steven Pietrobon

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Re: SLS General Discussion Thread 2
« Reply #959 on: 05/23/2017 06:51 AM »
For the record, SLS Block I is capable of putting 70 t of payload into a 185 x 1806 km orbit. Block IB is 93.1 t of payload into a 241 km circular orbit. The 105 t value that is often used for Block IB is the initial mass in low Earth orbit (IMLEO), which includes the dry mass of EUS. Data from

B. Donahue and S. Sigmon, "The Space Launch System capabilities with a new large upper stage," AIAA Space 2013.

Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

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