Author Topic: Lunar Gateway Debate  (Read 138618 times)

Offline DreamyPickle

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Re: Lunar Gateway Debate
« Reply #120 on: 08/11/2018 09:07 pm »
A more interesting application of PPE-derived craft would be to shuttle payloads from Earth to Lunar orbit. Is there any indication NASA is looking at this? The trip would take many months through the Van Allen belts but could deliver 10-20 ton modules from LEO launchers.

Offline Endeavour_01

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Re: Lunar Gateway Debate
« Reply #121 on: 08/13/2018 06:48 pm »
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.

I'm gonna stick with what is in the RFI and what has been reiterated multiple times by the NASA administrator and others. The current plan is for the LOP-G to be capable of changing orbits, including from NRHO to EML-1 and EML-2. Like Archibald said its not that difficult to do from a delta-V perspective.

You may think LOP-G is a terrible idea but argue against it on the merits of what is being proposed, not your belief that NASA is just pretending to want this orbit-changing capability.
I cheer for both NASA and commercial space. For SLS, Orion, Falcon 9, Falcon Heavy, Dragon, Starship/SH, Starliner, Cygnus and all the rest!
I was blessed to see the launch of Space Shuttle Endeavour on STS-99. The launch was beyond amazing. My 8-year old mind was blown. I remember the noise and seeing the exhaust pour out of the shuttle as it lifted off. I remember staring and watching it soar while it was visible in the clear blue sky. It was one of the greatest moments of my life and I will never forget it.

Offline Markstark

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Re: Lunar Gateway Debate
« Reply #122 on: 08/13/2018 09:28 pm »
He just emphasized it again twice today at an all hands in Michoud. I’m going to assume it’s more than a talking-point at this point.

Offline DreamyPickle

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Re: Lunar Gateway Debate
« Reply #123 on: 08/13/2018 11:08 pm »
This is a more basic question: How exactly is the PPE going to perform station keeping? The simplest way to do attitude control on a spacecraft is to have many small thrusters all around and use them to rotate, however the PPE seems to have a single large engine and multiple modules assembled on one side.

Will the PPE rotate the entire station before firing the main engine? In this case "orbital changes" and reboost would be it's main capability.

Offline Markstark

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Lunar Gateway Debate
« Reply #124 on: 08/13/2018 11:28 pm »
This is a more basic question: How exactly is the PPE going to perform station keeping? The simplest way to do attitude control on a spacecraft is to have many small thrusters all around and use them to rotate, however the PPE seems to have a single large engine and multiple modules assembled on one side.

Will the PPE rotate the entire station before firing the main engine? In this case "orbital changes" and reboost would be it's main capability.

Note sure if this answers the mail, but here’s what I found from public available documents found in the link I included above:

p.s. mods please let me know if all this orbit stuff is off-topic!
« Last Edit: 08/13/2018 11:29 pm by Markstark »

Offline Lunadyne

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Re: Lunar Gateway Debate
« Reply #125 on: 08/13/2018 11:55 pm »
Quote
argue against it on the merits of what is being proposed

That's exactly what I'm trying to do.  I looked at the BAA for the PPE, and as noted did not see any references to visiting other destinations in cislunar space like EML-1. 

Quote
I'm gonna stick with what is in the RFI

I looked at the RFI, and the only thing I could find was:

"3A PPE Propulsion Capability - The PPE will be capable of providing orbit transfers for a stack of TBD mass with a center of gravity of TBD."

Not a whole lot of guidance there.  Orbit transfer can mean a lot of things and is very ambiguous.  Now, if it said something along the lines of:

"The PPE will be capable of transferring the DSG/LOP-G stack from NRHO to other destinations of interest in cislunar space such as EML-1 or EML-2"

then I would be much more convinced.  So, looking at the Synopsis for NextSTEP BAA Appendix-C: Power and Propulsion Element Studies, we can see that the priorities are as follows:

"Studies intend to address key drivers for PPE development such as but not limited to potential approaches to:
-meeting the intent of human rating requirements;
-concept and layout development;
-attitude control;
-propulsive maneuverability;
-power generation;
-power interface standards;
-power transfer to other Gateway Elements;
-hosting multiple International Docking System Standard (IDSS) compatible docking systems;
-batteries/eclipse duration;
-15 year lifetime;
-communications;
-avionics, assembly integration and test approaches;
-extensibility;
-accommodations of potential (international or domestic partner provided) hardware such as robotic fixtures, science and technology utilization and other possible elements; and
-options for cost share/cost contributions.

Sure, one might get excited about "propulsive maneuverability", but it has to demonstrate that to get into the NRHO, so I'm having a hard time reading too much into that.

See, I was trained that documents are everything.  If it's not in the document, then you can't rely on it.  People can make all the shiny promises they like, and politicians really like to make promises, but again, if it's not in the documentation, then you cannot rely on it.  Documents are what you take into the courts, and are legally binding.  "But he said..." is not.

Please, show me where this information is documented.  Where does it say in the BAA, or the RFI for that matter, that the DSG/LOP-G stack has to be capable of getting to EML-1 or EML-2 or other destinations of interest in cislunar space, be it GEO, L-5, or wherever?  I'd like to take what the Administrator says on faith, but my science/engineering background is telling me to see the facts and the evidence.  I do not see it as being unreasonable to ask for such.  Maybe I'm not looking in the right place.  That's why I keep asking for cites.  I'm not trying to be obstreperous, just trying to get some real data.

Because if they do intend what they're saying, the next logical question is why?  Why is this capability being built into the system?  What are their intentions?  I mean, I do already know, they're going to utilize the capabilities of the LOP-G to stage the MARS mission from EML-2.  In theory.  But as someone who has an interest in cislunar development (q.v. Cislunar Econosphere at The Space Review) that doesn't really float my boat.  If it can get to EML-1, why not just park it there and start taking advantage of all that it has to offer (q.v. EML-1: The Next Logical Destination at The Space Review) instead of backing into it for some unknown reason(s).  Are they proposing these transfers while crewed?  What kind of timeframes are we talking about here, because I've seen the math in Vallado and electric propulsion is not fast. Something's just not adding up...

[Edit: And, yup, MarkStark found the smoking gun.  EML-2.  To MARS!  Ares! uber alles!  Because yeah, it makes sense to park hardware over the radio-quietest spot in the Solar system...] 

Offline Markstark

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Re: Lunar Gateway Debate
« Reply #126 on: 08/14/2018 12:25 am »
Happy to help Luna!

I wonder if this requirement/capability moves the needle for some of the Gateway critics. Not saying it should, just wondering if does. 
« Last Edit: 08/14/2018 12:26 am by Markstark »

Offline Archibald

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Re: Lunar Gateway Debate
« Reply #127 on: 08/14/2018 07:03 pm »
http://www.thespacereview.com/article/2027/1

http://www.thespacereview.com/article/1764/1

Are you Ken Murphy or just a fan of him ? (just asking !)

The second article I linked is pretty good. By the way, if you look at the comment section, you can see "Ann Onymous" - it's me !!!!

I've closely followed the development of the Gateway station since 2008 (when I joined this forum). Tracked down libration points history since Bob Farquhar. I crammed my HD with a boatload of related documents. If anybody interested, I can link some of them.
« Last Edit: 08/14/2018 07:15 pm by Archibald »
Han shot first and Gwynne Shotwell !

Offline A_M_Swallow

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Re: Lunar Gateway Debate
« Reply #128 on: 08/15/2018 12:40 am »
How viable is it to move a spacestation from a near-rectilinear halo orbit (NRHO) to Earth-Moon Lagrange Point 2 (EML-2) and back again every couple of years?

The spacestation is likely to mass 40-50tonne and have 40kW available for electric ion propulsion. I do not know what the delta-v from NRHO is but Low Lunar Orbit to EML-2 is about 0.65km/s. Ion thrusters are slow so travel time is important.

Offline Eric Hedman

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Re: Lunar Gateway Debate
« Reply #129 on: 08/15/2018 06:07 am »
How viable is it to move a spacestation from a near-rectilinear halo orbit (NRHO) to Earth-Moon Lagrange Point 2 (EML-2) and back again every couple of years?

The spacestation is likely to mass 40-50tonne and have 40kW available for electric ion propulsion. I do not know what the delta-v from NRHO is but Low Lunar Orbit to EML-2 is about 0.65km/s. Ion thrusters are slow so travel time is important.
According to Archibald's post earlier in the thread:

"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."

Offline Archibald

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Re: Lunar Gateway Debate
« Reply #130 on: 08/15/2018 10:14 am »
The way I see the entire thing... when I say "cislunar space" to me it is a very large, broad zone that starts from GEO and extends to SEL-1 / SEL-2, basically Earth sphere of influence.

As far as distances go: 36 500 km to 1.5 million km.
As far as delta-v goes, it starts at Earth escape, more or less 3.1 km/s (although GEO is a very peculiar, counter-intuitive case, related to satellites and their 24 hour orbit).

It is easier to over-simplify a little and just ask yourself "well, 3.1 km/s, Earth escape, now WHAT and WHERE ? Which destination ?"

From Earth escape into that broad "cislunar space" I mentionned, there are plenty of orbits or locations to go.

To be fully honest, DRO and NHRO were completely unknown to me before ARM and LOP-G. I thought it was either "GEO, LLO, libration points, or burst". Then again, I'm no astrodynamicist by any mean, and there are probably an infinity of different orbits high there - halo orbits and DRO aplenty.

The basic numbers are as follow (from LEO)
- Earth escape: 3.1 km/s
- Low Lunar Orbit (LLO) 4.1 km/s
- Lunar surface: +2.5 km/s, one way, from LLO.

What is kind of interesting is that...

- "exit-from-GEO-to-cislunar"
-  all ten Earth-Moon / Sun-Earth libration points (EML and SEL)
- LLO
- and those new DRO and NHRO orbits

...are all stuck between 3.1 km/s (Earth escape) and 4.1 km/s (LLO).

The entire thing, the entire "cislunar sphere" merely spans 1 km/s of delta-v, which is not a lot (when compared to those daunting SSTO numbers, Earth surface to LEO, a whopping 10 km/s).

What is really interesting is that 1 km/s of delta-v is small enough to be handled by either chemical or electric propulsion or both (think PPE vs Orion Service Module) at reasonable weight of propellants.

EDIT

According to this thread... https://forum.nasaspaceflight.com/index.php?topic=34858.0

Earth escape to DRO seems to be 300 m/s (so that would be 3400 m/s from LEO), close from EML-2 "best case" as found by Bob Farquhar and mentionned by Kirk Sorensen in the thread "An alternative lunar architecture" (the one that made a libration point groupie in the first place)
« Last Edit: 08/15/2018 05:00 pm by Archibald »
Han shot first and Gwynne Shotwell !

Offline Lunadyne

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Re: Lunar Gateway Debate
« Reply #131 on: 08/15/2018 05:36 pm »
Yes, I am that Ken Murphy.  Lunadyne, or a unit of Moon force, is one of my noms de plume, murphydyne is another.

I stumbled into what I call the cislunar econosphere concept when I read Human SMAD from cover to cover while pursuing a Masters degree at ISU.  I further explored the concept during my internship at Boeing's HSF&E.  Once I got a briefing on the same basic concepts from the NExT team during a NASA Academy field trip to KSC I realized that there was really something of value here.  Coupled with my background in international business and economics, and training as an economist, it became obvious that any kind of near-future human commercial expansion into space is bounded by the Moon as an 'anchor tenant' of the market space, and is already happening in cislunar space at GEO mainly but also LEO.

I am very careful about my use of the term cislunar.  While Archibald gives a rather broad definition, a prima facie reading (cis-: bounded by or on the near side of; lunar: of or relating to the Moon) would delimit the space to:
-Suborbital
-LEO
-MEO/HEO
-GEO
-EML1
-EML3, 4, 5
-Moon
-EML2 as a courtesy

Then rotate into a sphere because space is 3-D and voila, cislunar econosphere.  I do often see people exclude cis-GEO space which is odd given that LEO is obviously in the volume of space bounded by the Moon's orbit.  Moving out to the Sun-Earth lagrange points you're still in Earth's gravity well but beyond the Moon (translunar space).  So some combination of cis, terra, fons and gravitas?

Taking the stricter definition of cislunar space, IF you have gas stations in LEO, EML-1 and on the Moon, then you can get everywhere you want to go or at least to a place to gas and go for <4 km/s of delta-V.  The exception is LEO to GEO, which has always been a bear because deep gravity wells suck.  Once you're staging at EML-1, the bulk of GEO operations will likely shift there to become the logistics point for work at GEO (and most other places).  Plus you can get to EML-1 from any LEO orbital inclination which is a huge plus transportation logistics-wise.

As Archibald notes, DRO and NRHO are relatively recent inventions, and arose from the desire to bring back an asteroid to near-Earth space but not so near as to scare the crap out of everyone, so hey, let's park it around the Moon!  Well, them pesky mascons make stable orbits difficult, and so a search was undertaken to find something, anything that was a stable orbit around the Moon.  Much number-crunching later a number of orbits fell out of the mix, which generally followed the way I described it previously - stay far away (DRO) or use a Molniya-type orbit to not stay long (NR[H]O).  Given the risks, I would much rather have anyone trying to bring a big rock back to near-Earth space park it at SEL-4 or SEL-5 to demonstrate that they can control it, and then move it closer.  While orbital mechanics is a beautiful and well-night perfect math, engineering is not and there have been fiction stories about people trying to bring an asteroid to Earth and some engineering cock-up leaves it on an uncontrolled collision course.

What would be far more interesting to me would be if the PPE was proposed as part of a modular orbital transfer vehicle (OTV, to use the SEI parlance) for cargo in cislunar space.  As a station-keeping element it would seem to be most applicable in situations where you need constant orbit adjustments, like a space station in LEO to keep it aloft.  Would a facility at EML-1 need constant orbital station-keeping adjustments, or would periodic bursts suffice?  For the LOP-G, it would seem that it is currently envisioned as a way to move the stack to EML-2 to act as a staging point for a journey to MARS! 

Meh...

Offline Proponent

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Re: Lunar Gateway Debate
« Reply #132 on: 08/16/2018 01:49 am »
Would a facility at EML-1 need constant orbital station-keeping adjustments, or would periodic bursts suffice?

The attached JSC presentation (see p. 11), foresees station-keeping burns of about a meter per second once a week or so.  But the answer to your question must depend on the tolerable excursions.

Quote
For the LOP-G, it would seem that it is currently envisioned as a way to move the stack to EML-2 to act as a staging point for a journey to MARS!

But is it obvious that a permanent facility is needed at the staging point?  NASA's Evolvable Mars Campaign, for example, foresees staging in lunar DRO but places no permanent infrastructure there.  Given that just maintaining LOP-G is likely to cost over $3 billion per year (just to send one Orion/SLS there annually), it's really not clear to me that LOP-G wouldn't hinder a Mars effort more than it would help.

EDIT:  "place" -> "places"
« Last Edit: 08/25/2018 06:32 pm by Proponent »

Offline Archibald

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Re: Lunar Gateway Debate
« Reply #133 on: 08/16/2018 07:06 pm »
Quote
While orbital mechanics is a beautiful and well-night perfect math, engineering is not and there have been fiction stories about people trying to bring an asteroid to Earth and some engineering cock-up leaves it on an uncontrolled collision course.

Stephen Baxter Titan (which is as bad as Voyage was good) has the chinese making such a mistake... oops, kaboom, there goes Earth civilization !

Quote
What would be far more interesting to me would be if the PPE was proposed as part of a modular orbital transfer vehicle (OTV, to use the SEI parlance) for cargo in cislunar space.

A while back was the OASIS study, which had a pretty clever Earth-Moon OTV, called the hybrid propulsion module. It had both chemical and SEP, to try and get the best of both worlds, notaly high thrust to cut those looooooooong SEP transit times of months...
https://spacecraft.ssl.umd.edu/old_site/academics/484S03/oasis_docs/OASIS_FY01_FINAL.PDF

I'm not a great fan of xenon and LH2, and felt ammonia could do both jobs of chemical and SEP, with a single tank of propellant.
« Last Edit: 08/16/2018 07:11 pm by Archibald »
Han shot first and Gwynne Shotwell !

Offline speedevil

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Re: Lunar Gateway Debate
« Reply #134 on: 08/16/2018 07:20 pm »
But is it obvious that a permanent facility is needed at the staging point?  NASA's Evolvable Mars Campaign, for example, foresees staging in lunar DRO but place no permanent infrastructure there.  Given that just maintaining LOP-G is likely to cost over $3 billion per year (just to send one Orion/SLS there annually), it's really not clear to me that LOP-G wouldn't hinder a Mars effort more than it would help.
For it to be cheaper, ISRU really needs to have kicked off in a massive way, so that lunar fuel makes it worthwhile.

At three billion a year, commercial launch (todays prices) can get some 1000 tons of propellant to orbit, in off-the-shelf tanks that will last three years before boiloff without shading. They will need to be spun very lightly, as they are designed for earth.
(LOX/methane, hydrogen is more annoying)


Offline Markstark

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Lunar Gateway Debate
« Reply #135 on: 08/25/2018 03:29 pm »
Gateway Debate. Live and in color. Going to watch it now.



Edit: Okay I watched the video. First, I’ll make my bias clear and state that I’m for the Gateway. Anyhow, I didn’t think either made a great case but the case against from Dr. Zubrin was a bit more clear. I thought Mr. Mankins’ Eminem 8 mile approach where he says self deprecating things first kinda back fired. I appreciate Dr. Zubrin not making a Mars vs Moon debate and instead focusing on lunar surface vs orbit. I also appreciate Mr. Mankins willingness to go into the lions den.
« Last Edit: 08/25/2018 05:06 pm by Markstark »

Offline QuantumG

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Re: Lunar Gateway Debate
« Reply #136 on: 08/26/2018 02:22 am »
Neither speaker wants to accept the political reality. LOP-G is modelled on the ISS because the ISS has proven uncancellable. Mankins' concluding remarks are the closest either got to saying that. The goal of LOP-G is to ratchet up the sustainable funding of in-space architecture. If you're a fan of government expenditure on uncancellable space projects, you should be cheering LOP-G, or presenting an alternative that is equally as uncancellable. Zubrin's suggestion of a lunar village as an international project (with Mankins nodding on) doesn't cut the mustard.
Human spaceflight is basically just LARPing now.

Offline su27k

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Re: Lunar Gateway Debate
« Reply #137 on: 08/26/2018 03:51 am »
Neither speaker wants to accept the political reality. LOP-G is modelled on the ISS because the ISS has proven uncancellable. Mankins' concluding remarks are the closest either got to saying that. The goal of LOP-G is to ratchet up the sustainable funding of in-space architecture. If you're a fan of government expenditure on uncancellable space projects, you should be cheering LOP-G, or presenting an alternative that is equally as uncancellable. Zubrin's suggestion of a lunar village as an international project (with Mankins nodding on) doesn't cut the mustard.

Why is an international lunar village more cancellable than LOP-G?

Offline RonM

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Re: Lunar Gateway Debate
« Reply #138 on: 08/26/2018 04:39 am »
Neither speaker wants to accept the political reality. LOP-G is modelled on the ISS because the ISS has proven uncancellable. Mankins' concluding remarks are the closest either got to saying that. The goal of LOP-G is to ratchet up the sustainable funding of in-space architecture. If you're a fan of government expenditure on uncancellable space projects, you should be cheering LOP-G, or presenting an alternative that is equally as uncancellable. Zubrin's suggestion of a lunar village as an international project (with Mankins nodding on) doesn't cut the mustard.

Why is an international lunar village more cancellable than LOP-G?

Because LOP-G gives SLS/Orion something to do. Congress is willing to fund that and can get international partners to chip in with some of the modules. An international lunar village would require an expensive crewed lunar lander and not necessarily need SLS/Orion. LOP-G fits in with current NASA plans and will be cheaper than a lunar village.

Don't worry about lunar exploration. Ten years from now both BFR and NA should be flying. Reusable large payload rockets should make a lunar village more affordable.

Offline QuantumG

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Re: Lunar Gateway Debate
« Reply #139 on: 08/26/2018 06:23 am »
"lunar village" to me means robotic. Crew landers are the next administration's problem (and always will be?)


Human spaceflight is basically just LARPing now.

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