Author Topic: Differences between Direct and SLS  (Read 6644 times)

Offline woods170

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Re: Differences between Direct and SLS
« Reply #20 on: 02/06/2012 07:28 PM »
IIRC - the Authorisation Act specifically required an integrated US/EDS; I've got the feeling that Congress were specifically thinking of the J-2X version of the Jupiter Upper stage or something similar to this.

Yup, you got it. NASA is ignoring that requirement, supposedly in order to meet the 130 ton requirement. Although I would be willing to bet that Congress was more likely to be referencing the existing Ares-V design than anything from DIRECT.

From Section 302(c)(1):

Quote
(A) The initial capability of the core elements, without
an upper stage, of lifting payloads weighing between 70
tons and 100 tons into low-Earth orbit in preparation for
transit for missions beyond low-Earth orbit.
(B) The capability to carry an integrated upper Earth
departure stage bringing the total lift capability of the
Space Launch System to 130 tons or more.

Mark S.
To me item B of that section does not translate into "an integrated upper stage/Earth Departure Stage". It does not say that. It says "integrated upper Earth departure stage". That sort of language can be interpreted as something completely different.

Offline Mark S

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Re: Differences between Direct and SLS
« Reply #21 on: 02/06/2012 07:54 PM »
To me item B of that section does not translate into "an integrated upper stage/Earth Departure Stage". It does not say that. It says "integrated upper Earth departure stage". That sort of language can be interpreted as something completely different.

Yes, I've heard that before. So, please explain how those requirements can be interpreted in such a way that simply by adding an in-space-only stage would increase the total lift capability of SLS to 130 tons.

Answer: You can't. You can only interpret it that way by assuming the addition of some other unmentioned dedicated upper non-EDS stage to the SLS stack, which is what NASA has done.

Congress explicitly mentions every other major component of the Space Launch System. Why would they leave out a dedicated upper stage, if it was going to be impossible to meet their requirements without it? Especially when they already specified an "integrated upper Earth departure stage"?

Offline Pheogh

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Re: Differences between Direct and SLS
« Reply #22 on: 02/06/2012 08:19 PM »
I'm pretty sure I've seen options of Direct with the 5 segment boosters?

Why the stretched core? ( besides the politics.)

What are the advantages of a third stage?

Overall, in terms of mass to orbit, which is the better rocket?

Are the added expenses of SLS worth it?

There were (5 segs) but they were stretching the DIRECT philosophy past it's founding principles. However we did look at them as a growth option for BEO. I'm not sure who mentioned this but the primary difference between DIRECT and SLS is that the Jupiter Core was designed to evolve from LEO and Cis-Lunar to BEO operations and then perhaps Mars DRMs.

SLS is designing right out of the gate for BEO under what I imagine is a philosophy that believes commercial will handle the space in between? Only trouble is the country is very nearly bankrupt.

Not to be a broken record but if NASA botches $L$ for whatever reason I believe their HSF days should be over. This taxpayer will no longer go to bat for an organization that seems run by Trustafarian's of the Federal government (tax payers)

Offline mrbliss

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Re: Differences between Direct and SLS
« Reply #23 on: 02/06/2012 08:48 PM »
Another, softer difference between DIRECT and SLS:

DIRECT was meant to be implemented in a timely manner, to ease the transition between STS and its follow-on program.  The DIRECT team worked a lot of sandcharts and timelines to determine how to keep the shuttle army gainfully & productively employed and to reduce the 'gap' where the US had no HSF capability.

Offline alexterrell

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Re: Differences between Direct and SLS
« Reply #24 on: 02/07/2012 01:39 PM »
Another, softer difference between DIRECT and SLS:

DIRECT was meant to be implemented in a timely manner, to ease the transition between STS and its follow-on program.  The DIRECT team worked a lot of sandcharts and timelines to determine how to keep the shuttle army gainfully & productively employed and to reduce the 'gap' where the US had no HSF capability.
and DIRECT was designed to be affordable.

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