Author Topic: Lunar Gateway Debate  (Read 29023 times)

Online A_M_Swallow

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Re: Lunar Gateway Debate
« Reply #100 on: 08/05/2018 08:18 PM »
Even if BO or SpaceX by then has a demonstrable, less expensive HLV, the refrain will be, "But SLS and ORION are built into the LG architecture.  It will be too expensive and time wasting to switch the entire LG access architecture now at this late date!  And we must continue LG because of all the science, etc."

I do not see substantive scientific or other compelling reasons for constructing a LG as proposed.
It depends on the costs.
If commercial alternatives pop up where the cost of replacing the whole station is substantially less than completing one more module, ...

The Orion, Dragon 2 and CST-100 all implement the NASA Docking Standard. That means they can all support a lunar spacestation (given a launch vehicle that can get them there).

Offline ThereIWas3

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Re: Lunar Gateway Debate
« Reply #101 on: 08/05/2018 09:12 PM »
Saturn V was designed to meet the goal of delivering X tons to the Moon.   LOP-G and other NASA plans are being designed to be something that SLS can accomplish, and ignoring other missions that might be possible using a different launcher - exactly backwards.

I have not seen any particular science goals that would be met by either temporary or permanent visits to the Lunar surface in the time frames being discussed for LOP-G.
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Online ncb1397

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Re: Lunar Gateway Debate
« Reply #102 on: 08/05/2018 10:41 PM »
Saturn V was designed to meet the goal of delivering X tons to the Moon.   LOP-G and other NASA plans are being designed to be something that SLS can accomplish, and ignoring other missions that might be possible using a different launcher - exactly backwards.

It was more fluid than that. The Moon mission was designed around the limitations of the Saturn V. The Apollo service module was sized to lift the crew module off the lunar surface, but NASA didn't have a reasonable launch vehicle that could put the fueled CSM on the surface. LOR is portrayed as some kind of stroke of genius, but NASA was basically a cornered rat and had to use it. It was probably for the best though. Just as there is a mass penalty in taking the re-entry vehicle to the lunar surface, there is a somewhat smaller mass penalty in taking your re-entry vehicle to low lunar orbit. The heat shield, parachutes, aeroshell, flotation devices and whatever else don't have any use in LLO. They have some use in burning off energy from a high energy return, but you don't get any more of that from LLO vs. other possible lunar orbits.
« Last Edit: 08/05/2018 10:47 PM by ncb1397 »

Offline TripleSeven

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Re: Lunar Gateway Debate
« Reply #103 on: 08/05/2018 11:01 PM »
Saturn V was designed to meet the goal of delivering X tons to the Moon.   LOP-G and other NASA plans are being designed to be something that SLS can accomplish, and ignoring other missions that might be possible using a different launcher - exactly backwards.

It was more fluid than that. The Moon mission was designed around the limitations of the Saturn V. The Apollo service module was sized to lift the crew module off the lunar surface, but NASA didn't have a reasonable launch vehicle that could put the fueled CSM on the surface. LOR is portrayed as some kind of stroke of genius, but NASA was basically a cornered rat and had to use it. It was probably for the best though. Just as there is a mass penalty in taking the re-entry vehicle to the lunar surface, there is a somewhat smaller mass penalty in taking your re-entry vehicle to low lunar orbit. The heat shield, parachutes, aeroshell, flotation devices and whatever else don't have any use in LLO. They have some use in burning off energy from a high energy return, but you don't get any more of that from LLO vs. other possible lunar orbits.

Hmm I dont agree with much of that.  LOR is all about making a Saturn V sized vehicle capable of doing the limited job that Apollo was tasked with.  the Service module was "oversized" but the "direct to the lunar surface" requires a far larger booster...they called it NOVA

Online Markstark

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Lunar Gateway Debate
« Reply #104 on: 08/08/2018 04:38 PM »
https://twitter.com/spacebrendan/status/1026990492800757765?s=21

Recent Bridenstine interview discussing the Gateway. He discusses desire to use reusable elements for all aspects of the lunar architecture. He also notes that the PPE will be able to change orbits from NRHO to Lagrange points as needed.
« Last Edit: 08/08/2018 04:38 PM by Markstark »

Offline theinternetftw

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Re: Lunar Gateway Debate
« Reply #105 on: 08/08/2018 08:45 PM »
Recent Bridenstine interview discussing the Gateway.

Quick transcript of this for those who'd like it: https://gist.github.com/theinternetftw/8cbb257253221f06a7bf593d2808f55f

Offline Archibald

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Re: Lunar Gateway Debate
« Reply #106 on: 08/09/2018 04:56 AM »
https://twitter.com/spacebrendan/status/1026990492800757765?s=21

Recent Bridenstine interview discussing the Gateway. He discusses desire to use reusable elements for all aspects of the lunar architecture. He also notes that the PPE will be able to change orbits from NRHO to Lagrange points as needed.

Quote
but with Solar Electric Propulsion, it's not just going to be in an orbit around the moon, it's going to actually go to L2 and L1 and give us more access to more parts of the moon than ever before.

I wish Robert Farquhar had lived long enough to read these lines. Also thinking about  Harley Thronson, who spent the last two decades hammering the idea of a Gateway  at a libration point (see his FISO group).



« Last Edit: 08/09/2018 05:01 AM by Archibald »
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Offline Proponent

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Re: Lunar Gateway Debate
« Reply #107 on: 08/09/2018 01:30 PM »
It was more fluid than that. The Moon mission was designed around the limitations of the Saturn V. The Apollo service module was sized to lift the crew module off the lunar surface, but NASA didn't have a reasonable launch vehicle that could put the fueled CSM on the surface. LOR is portrayed as some kind of stroke of genius, but NASA was basically a cornered rat and had to use it. It was probably for the best though.

It's true that the SM's propulsion system was sized to propel the CSM from the lunar surface back to Earth.  That's because the contract was let before the mode decision had been made*.  At the time, almost all architectures under consideration (Earth-orbit rendezvous, direct, lunar surface rendezvous, the Army's Project Horizon, the Air Force's Lunex) envisioned the return of the crew directly from the lunar surface.

There was an extensive debate among NASA's and its contractors' engineers as to the best architecture for reaching the moon -- you can read about it in great detail in documents on NTRS.  Firstly the politicians set the goal, and then the engineers chose the best way of doing it.  What's happening now is, as ThereWasI3 says, is "backward":  the politicians, not the engineers, have chosen the hardware.  Imagine that the politicians had usurped the engineers' role in 1961 as well, when JFK announced the moon goal.  They almost certainly would not have selected LOR, because few had even heard of it then:  it was an idea out of left field.  As a result, Apollo would have been much more expensive (relying on either two Saturn V's or a single Nova for each mission) and would likely have missed the end-of-decade deadline.



*An illustration, incidentally, of the hazards of building your hardware before you've decided what you're going to do with it.  That's happening on a much larger scale with Orion/SLS.
« Last Edit: 08/09/2018 01:43 PM by Proponent »

Offline Lunadyne

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Re: Lunar Gateway Debate
« Reply #108 on: 08/09/2018 08:09 PM »
Quote
He also notes that the PPE will be able to change orbits from NRHO to Lagrange points as needed.

Do we have a paper we can cite for that?  Or is it just the NASA Administrator trying to minimize the effects of the obnoxious EML-1 crowd?  What would be the purpose in moving it back and forth from NRHO to EML-1?  Why complicate the overall architecture that way?  What would it do at EML-1?  I'm just trying to picture SLS delivering to LOP-G in NRHO, and then the LOP-G changing its orbit with SEP to deliver a crew to EML-1 (or EML-2 for that matter for the dV purists) for...something.  What kinds of timeframes are we talking about here?

Sorry, but the comment strikes me more as political image management (don't worry EML-1 nerds; we're thinking of you) than actual strategic thinking about cislunar architectures.

And I am serious, I would like to see a paper on what the Administrator is describing.  I'm a bit of an orbital mechanics geek and so would be interested in what they're envisioning.

Online Markstark

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Re: Lunar Gateway Debate
« Reply #109 on: 08/09/2018 08:38 PM »
Recent Bridenstine interview discussing the Gateway.

Quick transcript of this for those who'd like it: https://gist.github.com/theinternetftw/8cbb257253221f06a7bf593d2808f55f

Awesome! Thanks!

Online Markstark

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Re: Lunar Gateway Debate
« Reply #110 on: 08/09/2018 08:40 PM »
Quote
He also notes that the PPE will be able to change orbits from NRHO to Lagrange points as needed.

Do we have a paper we can cite for that?  Or is it just the NASA Administrator trying to minimize the effects of the obnoxious EML-1 crowd?  What would be the purpose in moving it back and forth from NRHO to EML-1?  Why complicate the overall architecture that way?  What would it do at EML-1?  I'm just trying to picture SLS delivering to LOP-G in NRHO, and then the LOP-G changing its orbit with SEP to deliver a crew to EML-1 (or EML-2 for that matter for the dV purists) for...something.  What kinds of timeframes are we talking about here?

Sorry, but the comment strikes me more as political image management (don't worry EML-1 nerds; we're thinking of you) than actual strategic thinking about cislunar architectures.

And I am serious, I would like to see a paper on what the Administrator is describing.  I'm a bit of an orbital mechanics geek and so would be interested in what they're envisioning.

I believe I saw a reference to using the PPE to change orbits in a Gateway presentation on the  public NASA Tech Reports Server. Iíll look for it and get back to you. However, I donít think it elaborated on why.

Offline ThereIWas3

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Re: Lunar Gateway Debate
« Reply #111 on: 08/09/2018 08:55 PM »
It might just be the usual NASA tendency to try to keep all the different "center" factions happy.  Next thing you know, they'll throw a VASIMR on it.
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Online A_M_Swallow

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Re: Lunar Gateway Debate
« Reply #112 on: 08/10/2018 12:20 AM »
It might just be the usual NASA tendency to try to keep all the different "center" factions happy.  Next thing you know, they'll throw a VASIMR on it.

LOP-G does not need an engine as powerful as a VASIMR but Mars transfer vehicles could use VASIMR thrusters.

NRHO is a viable orbit for a lunar spacestation because only a little station keeping fuel is needed. The LOP-G could be used as a staging and refuelling depot for the lunar lander.

EML-1 (or EML-2) makes a good staging point for trips to Mars. A solar electric vehicle can take months spinning out from LEO to EML-1 where the crew join them using chemical rockets. Two spacestations can be used - one each at NRHO and EML-1 - but moving the station between the two locations may be cheaper (double check).

Offline TrevorMonty

Re: Lunar Gateway Debate
« Reply #113 on: 08/10/2018 01:16 AM »
Quote
He also notes that the PPE will be able to change orbits from NRHO to Lagrange points as needed.

Do we have a paper we can cite for that?  Or is it just the NASA Administrator trying to minimize the effects of the obnoxious EML-1 crowd?  What would be the purpose in moving it back and forth from NRHO to EML-1?  Why complicate the overall architecture that way?  What would it do at EML-1?  I'm just trying to picture SLS delivering to LOP-G in NRHO, and then the LOP-G changing its orbit with SEP to deliver a crew to EML-1 (or EML-2 for that matter for the dV purists) for...something.  What kinds of timeframes are we talking about here?

Sorry, but the comment strikes me more as political image management (don't worry EML-1 nerds; we're thinking of you) than actual strategic thinking about cislunar architectures.

And I am serious, I would like to see a paper on what the Administrator is describing.  I'm a bit of an orbital mechanics geek and so would be interested in what they're envisioning.

I believe I saw a reference to using the PPE to change orbits in a Gateway presentation on the  public NASA Tech Reports Server. Iíll look for it and get back to you. However, I donít think it elaborated on why.
Being able to move between cislunar locations is primary requirement of Gateway.

Online Markstark

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Re: Lunar Gateway Debate
« Reply #114 on: 08/10/2018 02:22 AM »
Quote
He also notes that the PPE will be able to change orbits from NRHO to Lagrange points as needed.

Do we have a paper we can cite for that?  Or is it just the NASA Administrator trying to minimize the effects of the obnoxious EML-1 crowd?  What would be the purpose in moving it back and forth from NRHO to EML-1?  Why complicate the overall architecture that way?  What would it do at EML-1?  I'm just trying to picture SLS delivering to LOP-G in NRHO, and then the LOP-G changing its orbit with SEP to deliver a crew to EML-1 (or EML-2 for that matter for the dV purists) for...something.  What kinds of timeframes are we talking about here?

Sorry, but the comment strikes me more as political image management (don't worry EML-1 nerds; we're thinking of you) than actual strategic thinking about cislunar architectures.

And I am serious, I would like to see a paper on what the Administrator is describing.  I'm a bit of an orbital mechanics geek and so would be interested in what they're envisioning.

Hey Lunadyne,

Check out this presentation from the PPE Industry Day that took place four weeks ago. Slide 23 addresses using SEP for changing orbits but isn't as explicit as Mr. Bridenstine.

Side note: I was surprise to see SpaceX send four people to this event considering this project is strictly electric propulsion.

https://govtribe.com/project/spaceflight-demonstration-of-a-power-and-propulsion-element-ppe/activity


Online Markstark

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Re: Lunar Gateway Debate
« Reply #115 on: 08/10/2018 02:31 AM »
Also this from the Q&A that's also publicly available. Again, not as explicitly stated as the Administrator.

Online Markstark

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Lunar Gateway Debate
« Reply #116 on: 08/10/2018 12:49 PM »
Quote
He also notes that the PPE will be able to change orbits from NRHO to Lagrange points as needed.

Do we have a paper we can cite for that?  Or is it just the NASA Administrator trying to minimize the effects of the obnoxious EML-1 crowd?  What would be the purpose in moving it back and forth from NRHO to EML-1?  Why complicate the overall architecture that way?  What would it do at EML-1?  I'm just trying to picture SLS delivering to LOP-G in NRHO, and then the LOP-G changing its orbit with SEP to deliver a crew to EML-1 (or EML-2 for that matter for the dV purists) for...something.  What kinds of timeframes are we talking about here?

Sorry, but the comment strikes me more as political image management (don't worry EML-1 nerds; we're thinking of you) than actual strategic thinking about cislunar architectures.

And I am serious, I would like to see a paper on what the Administrator is describing.  I'm a bit of an orbital mechanics geek and so would be interested in what they're envisioning.

Also found this in a recent Gateway commercialization RFI:
Quote
The Gateway will be located in a Near-Rectilinear Halo Orbit (NRHO) around the Moon and can be relocated in cislunar

Source: https://govtribe.com/project/gateway-commercial-opportunities-request-for-information/activity
« Last Edit: 08/10/2018 12:50 PM by Markstark »

Offline Archibald

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Re: Lunar Gateway Debate
« Reply #117 on: 08/11/2018 03:08 PM »
Delta-v between NRHO and EML-1 / EML-2 are barely 100 m/s. I'd be surprise if the PPE and its electric thrusters couldn't handle that.
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Offline Lunadyne

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Re: Lunar Gateway Debate
« Reply #118 on: 08/11/2018 06:14 PM »
Okay, so I looked through the PPE Industry Day slides, which I admit make many assertions that the LOP-G will be able to maneuver to various Lagrange points, especially EML-1 and EML-2, as part of its functionality.

So I looked through the Attachment D to the BAA, which covers the NASA Unique Requirements, and while I do see references to the PPE being able to put itself into an NRHO, station keep, and slew for various functions like docking and keeping Orion's butt towards the Sun while docked, what I don't see are references to PPE being able to propulse the LOP-G stack to other destinations in cislunar space.  Maybe I just missed it.

I'm pretty sure I saw a reference to an orbital summaries doc buried somewhere in the many slides of administrivia, so I'm going to see if I can refind that, although from what I remember you have to contact NASA to get a copy as it's considered export-sensitive, and since I'm not actually associated with the BAA process it's unlikely I'll be able to get one.

This isn't my first rodeo, so I know how these things work.  Any contractor looking to win a contract is going to look to the formal documents for the requirements to be met.  Any pretty powerpoint platitudes mean absolutely zero.  Zilch.  Nada.  All I'm seeing so far are promises, allegations and blarney. 

I'm also having a hard time buying into the 09/2022 launch window.  If Orion and SLS is any indication of the rate of progress in the industry, I would expect that four-year timeframe to double or more.  Ample time for things like cislunar maneuverability to be scrapped to get to the end product.

So I'm still sticking with my original position, which is that this whole emphasis of maneuverability to EML-1 is just a last-minute add-on to try to get the Lagrange nerds on board with the iffy LOP-G project.  Political consensus building, and not a real thing to which we can actually look forward.

Offline speedevil

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Re: Lunar Gateway Debate
« Reply #119 on: 08/11/2018 08:00 PM »
This isn't my first rodeo, so I know how these things work.  Any contractor looking to win a contract is going to look to the formal documents for the requirements to be met.  Any pretty powerpoint platitudes mean absolutely zero.  Zilch.  Nada.  All I'm seeing so far are promises, allegations and blarney. 
It might be plausible that it is impractical to meet for reasonable designs 'put itself into NHRO', station-keep for x years at y m/s*kgs - without also having the capacity to switch orbits of the whole stack - if supplied with enough Xenon.

If the ion engine has sufficient life, and is run directly off solar panels, and has enough fuel, it doesn't care if it's run for a couple of months at a time, or twenty minutes once every two weeks for stationkeeping.
« Last Edit: 08/11/2018 08:02 PM by speedevil »

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