Author Topic: SLS General Discussion Thread 3  (Read 97267 times)

Online ugordan

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Re: SLS General Discussion Thread 3
« Reply #520 on: 03/14/2019 07:51 pm »
EM-1 is baselined with lunar orbit insertion. FH+DIVH, FH+AV551, and possibly DIVH+AV551 all offer the performance to keep the lunar orbit part of the mission.

How do you envision an Atlas V offering enough performance for a lunar orbit combined mission? It can neither launch the Orion/SM stack into LEO nor can it lift a big enough upper stage to propel it to TLI. Even a fully fueled Centaur in LEO would not have enough oomph to do that.

Online envy887

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Re: SLS General Discussion Thread 3
« Reply #521 on: 03/14/2019 07:58 pm »
EM-1 is baselined with lunar orbit insertion. FH+DIVH, FH+AV551, and possibly DIVH+AV551 all offer the performance to keep the lunar orbit part of the mission.

How do you envision an Atlas V offering enough performance for a lunar orbit combined mission? It can neither launch the Orion/SM stack into LEO nor can it lift a big enough upper stage to propel it to TLI. Even a fully fueled Centaur in LEO would not have enough oomph to do that.

See the rest of my post. FH can lift Orion much higher than LEO. Rendezvous with Centaur in an elliptical orbit, Centaur finishes TLI at the next perigee. You'd want to pick an orbit with a low enough period that Centaur can coast back to perigee, probably about 1000 to 6000 km apogee and 2 to 6 hour period.

Orion also has the SM with enough performance to finish the last few m/s of TLI and also do LOI/TEI. I believe this was baselined for EM-1. So Centaur doesn't necessarily need to get it all the way there.

Offline Proponent

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Re: SLS General Discussion Thread 3
« Reply #522 on: 03/14/2019 08:05 pm »
"2.   Docking crewed vehicles in Earth orbit to get to the Moon adds complexity and risk that is undesirable."

NASA has a lot of experience in assembling modules in space. If a rocket launch failure is considered a credible risk, is it safer to use two rockets or one? If SLS fails, everything is lost, if one of the heavy lift rockets fail only half the equipment is lost.

Unless you're able to launch a duplicate of the lost payload quickly, the whole thing will effectively be lost.  There definitely is a downside to relying on multiple launches.  It think the point is that the pluses and minuses should be weighed comprehensively by competent engineers.  In contrast, to date it's principally been politicians and us Internet experts weighing in.

Offline Patchouli

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Re: SLS General Discussion Thread 3
« Reply #523 on: 03/14/2019 09:08 pm »

See the rest of my post. FH can lift Orion much higher than LEO. Rendezvous with Centaur in an elliptical orbit, Centaur finishes TLI at the next perigee. You'd want to pick an orbit with a low enough period that Centaur can coast back to perigee, probably about 1000 to 6000 km apogee and 2 to 6 hour period.

Orion also has the SM with enough performance to finish the last few m/s of TLI and also do LOI/TEI. I believe this was baselined for EM-1. So Centaur doesn't necessarily need to get it all the way there.

Could be a chance to test the docking hardware for Ixion on the Centaur stage.
I think getting Orion on Delta IV-H might be quicker than adapting FH simply because of EFT-1 though the latter is cheaper and more capable in expendable mode.

Though the question remains could all this be ready sooner then finding funding for the EM-1 SLS?
« Last Edit: 03/14/2019 09:12 pm by Patchouli »

Offline Proponent

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Re: SLS General Discussion Thread 3
« Reply #524 on: 03/14/2019 09:28 pm »
Mentioning the dual-launch approach of Constellation is unfair and comparing apples to oranges, and you know it.  Constellation called for launching a fully capable, fully fueled six-person spacecraft with (some) supplies and the second launch a long duration habitat and propulsion module.

The trade-offs between dual- and single-launch architectures will certainly be different for Orion than they were for Constellation, but that does not change the fact that NASA's most recent architecture study found that dual-launch architectures were not ipso facto unsustainable.  That conclusion may have been wrong, but Bridenstine's claim is as yet unsupported.  The sustainability of any launch vehicle that might fly once per year is obviously open to question.

Quote
What is currently envisioned in this dual launch is a bare bones uncrewed four person spacecraft and then what amounts to a propulsion module to get it around the moon (not even lunar orbit).

That's not relevant, because the dual-launch architecture is presently proposed only for a single uncrewed test.  Whether the same architecture would be suitable for crewed Orion missions to a lunar Gateway has not been raised, and I very much doubt it will be in the report now underway.

Quote
Look, when it was decided to go with a LV based around 5 segment SRBs, it was evident the LV would be constrained to under-performance without the EUS (and even then with 4x RL10 it is barely passable...).  As stated, I am really disappointed the program now calls for four missions using ICPS--that's why I had such a negative, catty post a page or two ago...

I feel your pain.  I had my first nightmare about the lack of emphasis on a proper upper stage almost a decade ago.  That nightmare has now become reality.
« Last Edit: 03/14/2019 09:32 pm by Proponent »

Offline Proponent

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Re: SLS General Discussion Thread 3
« Reply #525 on: 03/14/2019 09:33 pm »
Though the question remains could all this be ready sooner then finding funding for the EM-1 SLS?

Do we know that even more money would solve the problem?  SLS has been well funded for many years now, yet it has slipped and slipped.

Offline Patchouli

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Re: SLS General Discussion Thread 3
« Reply #526 on: 03/14/2019 09:52 pm »
I feel your pain.  I had my first nightmare about the lack of emphasis on a proper upper stage almost a decade ago.  That nightmare has now become reality.

I really don't know why the didn't just reuse the Ares I upper stage on SLS since the J-2X engine was finished?
Most of the issues with the upper stage were related to the stick design and were no longer present on SLS.
« Last Edit: 03/14/2019 09:53 pm by Patchouli »

Offline Proponent

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Re: SLS General Discussion Thread 3
« Reply #527 on: 03/14/2019 10:14 pm »
IIRC, J-2X-powered upper stages were better for hauling heavy loads to LEO but inferior for lunar and planetary missions.  More thrust but lower Isp.  No doubt a much higher cost per unit too, since nobody else would have used the J-2X.

And the major stumbling block is getting the stage developed in the first place:  I don't think J-2X would have helped with that.
« Last Edit: 03/14/2019 10:16 pm by Proponent »

Online Slarty1080

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Re: SLS General Discussion Thread 3
« Reply #528 on: 03/14/2019 11:21 pm »
What is currently envisioned in this dual launch is a bare bones uncrewed four person spacecraft and then what amounts to a propulsion module to get it around the moon (not even lunar orbit).

I don't think that is accurate.

EM-1 is baselined with lunar orbit insertion. FH+DIVH, FH+AV551, and possibly DIVH+AV551 all offer the performance to keep the lunar orbit part of the mission.

If a free-return is planned, FH can do that without a second launch, since it only has to get Orion high enough for the SM to finish TLI. SpaceX advertises 26,700 kg to GTO-1800, which is more than the mass of Orion and more than high enough for the SM to get it to a free-return.
Can the Delta Heavy achieve the same thing? Could a stretched FH complete the whole mission with Lunar orbit? (yeah I know that won't happen).
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Offline PM3

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Re: SLS General Discussion Thread 3
« Reply #529 on: 03/14/2019 11:24 pm »
https://twitter.com/SciGuySpace/status/1106337152177180675

Quote from: Eric Berger
Am hearing varying ranges as NASA assesses new dates for first SLS flight. Median is around November, 2021. Supposed to be announced later this spring.

Offline Joseph Peterson

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Re: SLS General Discussion Thread 3
« Reply #530 on: 03/14/2019 11:36 pm »
November 2021?

Granted I've been expecting periodic slips to a first launch in 2022 but I wasn't expecting the slip to Q4 2021 this soon.  If Shelby has anything to say about it that schedule date will shift left(not that moving the schedule around will change when SLS finally launches).
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Re: SLS General Discussion Thread 3
« Reply #531 on: 03/15/2019 01:09 am »
Though the question remains could all this be ready sooner then finding funding for the EM-1 SLS?

Do we know that even more money would solve the problem?  SLS has been well funded for many years now, yet it has slipped and slipped.

According to Eric Berger, Pence asked if more money would let them make the schedule.  The answer was no, and might be what precipitated this whole business.

Offline ncb1397

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Re: SLS General Discussion Thread 3
« Reply #532 on: 03/15/2019 01:21 am »
November 2021?

Granted I've been expecting periodic slips to a first launch in 2022 but I wasn't expecting the slip to Q4 2021 this soon.  If Shelby has anything to say about it that schedule date will shift left(not that moving the schedule around will change when SLS finally launches).

It may not be SLS readiness related. If EM-1 goes on a different launcher and they need a payload to test the vehicle on before EM-2, payload readiness might be the driving factor.

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Re: SLS General Discussion Thread 3
« Reply #533 on: 03/15/2019 01:24 am »
It may not be SLS readiness related. If EM-1 goes on a different launcher and they need a payload to test the vehicle on before EM-2, payload readiness might be the driving factor.

Eric Berger has said that this date does not consider the latest fracas.  It's what would have happened anyway.

Edit: Dug up the tweet and added it below.

https://twitter.com/SciGuySpace/status/1106338091806179329

Also another related comment: what's pushing SLS this far back isn't the hardware, it's "the stuff you can't see."

https://twitter.com/SciGuySpace/status/1106348088711622656
« Last Edit: 03/15/2019 01:31 am by theinternetftw »

Online envy887

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Re: SLS General Discussion Thread 3
« Reply #534 on: 03/15/2019 02:12 am »
What is currently envisioned in this dual launch is a bare bones uncrewed four person spacecraft and then what amounts to a propulsion module to get it around the moon (not even lunar orbit).

I don't think that is accurate.

EM-1 is baselined with lunar orbit insertion. FH+DIVH, FH+AV551, and possibly DIVH+AV551 all offer the performance to keep the lunar orbit part of the mission.

If a free-return is planned, FH can do that without a second launch, since it only has to get Orion high enough for the SM to finish TLI. SpaceX advertises 26,700 kg to GTO-1800, which is more than the mass of Orion and more than high enough for the SM to get it to a free-return.
Can the Delta Heavy achieve the same thing? Could a stretched FH complete the whole mission with Lunar orbit? (yeah I know that won't happen).

Definitely not, and probably not.

Offline leovinus

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Re: SLS General Discussion Thread 3
« Reply #535 on: 03/15/2019 12:06 pm »
Though the question remains could all this be ready sooner then finding funding for the EM-1 SLS?

Do we know that even more money would solve the problem?  SLS has been well funded for many years now, yet it has slipped and slipped.

According to Eric Berger, Pence asked if more money would let them make the schedule.  The answer was no, and might be what precipitated this whole business.

Firstly, one way to answer the "funding question" can be taken from the book "The Mythical Man-Month: Essays on Software Engineering",  Frederick P. Brooks Jr. Required reading on software engineering and project management. It basically say "Adding more manpower to a late project makes it later". After 30 years of software engineering, I do not disagree.

Secondly, when you read the last 3 or 4 NAC HEOC quarterly reports here and look for reports on how the software is going, there are a few projects of which the completion dates keep moving to the right every quarter. Specifically the Flight Control Application Software (FCAS) from the Software Test Lab (MSFC), and ATLO from the Integrated Test Lab (ITL). While I am not privy to the scope of these items, the fact that the deadlines keep moving points to underlying issues which probably cannot be solved by funding.

Just my 2pc.
« Last Edit: 03/15/2019 12:07 pm by leovinus »

Offline ZachF

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Re: SLS General Discussion Thread 3
« Reply #536 on: 03/15/2019 01:32 pm »
https://twitter.com/SciGuySpace/status/1106337152177180675

Quote from: Eric Berger
Am hearing varying ranges as NASA assesses new dates for first SLS flight. Median is around November, 2021. Supposed to be announced later this spring.

So basically 2022...

This is just absurd at this point. I'm sure Boeing somehow will get the maximum performance bonuses too.

The schedule at this point is moving farther to the right faster than the passage of time.
« Last Edit: 03/15/2019 01:39 pm by ZachF »
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Offline oldAtlas_Eguy

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Re: SLS General Discussion Thread 3
« Reply #537 on: 03/15/2019 01:53 pm »
Except for little things like tornadoes and multiple week government shutdowns the hardware issues and slips have been normal and pretty much as expected.

As a software engineer I am familiar with what happens to software development schedules when there is requirements creep. In many cases depending on the requirement, it may be easier to start over.

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Re: SLS General Discussion Thread 3
« Reply #538 on: 03/15/2019 02:58 pm »
Analysis and diagrams of a single launch private EM-1 architecture which only requires the development of one new piece of hardware and mitigates the need for distributed launch and docking. It also removes the need for creating larger fairing for the Falcon Heavy.

Link to PDF: https://documentcloud.adobe.com/link/track?uri=urn%3Aaaid%3Ascds%3AUS%3A0651efde-15dd-4d5e-885a-87bd...

It seems like people in this thread are much more capable than me with Delta-V calculations and such. If you would take some time to read the proposal and let me know what you think. I would love to see what the numbers come out to.

Fully expended Falcon Heavy delivering the ICPS and Orion + ESM. The two payloads together are about 56t. Mass wise the FH is capable of getting it to LEO but I'm not sure how close it could bring it to the desired 1800km elliptical orbit.

Offline Rocket Science

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Re: SLS General Discussion Thread 3
« Reply #539 on: 03/15/2019 03:00 pm »
https://twitter.com/SciGuySpace/status/1106337152177180675

Quote from: Eric Berger
Am hearing varying ranges as NASA assesses new dates for first SLS flight. Median is around November, 2021. Supposed to be announced later this spring.

So basically 2022...

This is just absurd at this point. I'm sure Boeing somehow will get the maximum performance bonuses too.

The schedule at this point is moving farther to the right faster than the passage of time.
And continue to get paid for it... ;)
« Last Edit: 03/15/2019 03:17 pm by Rocket Science »
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