Dale Christopher

Looking for opinions about how optimal NASA’s Lunar Gateway plan...

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I’ve recently been designing my own Mun mission and in so doing I’ve looked into NASA’s lunar orbital gateway plan. 

I’ve seen it said that the HALO orbit planned to house the station provides a convenient staging point for lunar missions but I’ve also seen criticisms about sending missions to a intermediate point before continuing on to their objective and whether there’s any significant benefit to this rather than just parking mission relevant tech into mission optimised orbits IF required rather than constructing a space station staging point that may not be strictly necessary.

Is an orbital hub really beneficial?

What are some alternatives?

What are some justifications for NASA’s planed gateway station?

I suppose when humans are in the mix, purely optimising DV and logistics isn’t the only concern... 

I just was wondering what people’s thoughts were on this method of progressing the cause of lunar exploration... what would be people’s ideal solution? 

 

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There are many pros and cons about Gateway, but I myself think that it's a great platform for future orbital and lunar missions. Gateway can serve as a "pitstop" in space, whether it be for more fuel or to stay. With the addition of commercial companies assembling Gateway themselves, it also can prove for durability and performance of these commercial companies. Trusting Maxar to build the PPE or trusting companies to provide landers will all help commercial companies thrive and excel their knowledge of how to build a great spacecraft. 

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6 hours ago, Dale Christopher said:

whether there’s any significant benefit to this rather than just parking mission relevant tech into mission optimised orbits

There’s a general assumption that you can’t just let an uncrewed lander chill in orbit without an attendant facility.

Similar to how the ISS was supposed to build Mars ships.

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In RL, lunar orbits tend to decay because of mass concentrations that perturb orbits. There are some low, "frozen" orbits that avoid this, however.

Generally speaking Gateway involves an extra several hundred meter per second delta v to missions. The idea is that such a station is supposed to allow for reusable vehicles.

The reality of course is that unless the lander is a single stage to the surface and back, little is saved, and even in that case, the propellants delivered to the Gateway (assuming it can transfer those) come in a stage themselves, which is then thrown away (somehow). If you need, say 40 tons of propellant at Gateway for a given lander sortie, how do you get those there? Presumably you could use a slow, efficient tug (ion) if the props were storable. But then you need to get them to the tug in the first place. Pretty much closing that system requires something akin to Starship. A 100% reusable vehicle to deliver props to LEO, so that those props can be delivered to a depot to be used for missions.

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Posted (edited)

I think we need as many people as possible, doing as much as possible around the Moon. The more, the better. 

That said.

Gateway is intended to have a lander/ferry going to the surface and back many times, with crew staying there three months at a time and possibly making multiple trips to the surface. They would use ISRU at the south pole to refuel the lander. I think that's very handwavey, because we've never actually done ISRU on another planet. We don't know how difficult it will be to extract and purify the water in the Moon on a large enough scale to produce a full tank of propellant for a lander-shuttle. 

My main gripe, though, is probably with SLS. SLS is expensive just like the Saturn V was, and Saturn V lost support from short-sighted politicians after a few moon landings because of the cost. I don't know if SLS can keep support long enough to keep doing flight after flight the way a moon station requires. 

I also feel that SLS is a sunk cost when Starship and New Glenn are even in development. An expendable launch vehicle with the size and complexity of SLS is too expensive to make space travel accessible to everyone. Starship is designed to be built in a factory, not a lab, be as reusable as Falcon 9, and have the capability to build bases on the Moon. NASA should fund development of launch vehicles like these, and make payloads for them. Instead, they always try to do things with as many steps as possible, which causes things to happen slowly and expensively.

If SLS works out, and NASA manages the funds to pump out launches the way they need to build Gateway, I will still be very happy. I just think it's very dangerous to bank on an expendable rocket being able to do the things that NASA wants to do at the Moon.

Edited by cubinator

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Current ideas for a Gateway-->Moon lander have:

Ascent Module, AM (returns to Gateway for refilling with props, presumably).

Descent Module, DM (brings Ascent M to lunar surface from LLO)

Tug (brings AM/DM stack from Gateway to LLO, and possibly AM back to Gateway).

The problem of course is that any "tanker" to bring propellants from Earth to Gateway might as well be a throw away stage. Even refilling the small AM takes an autonomous vehicle that might as well be a new one, particularly given the at best 1/year flight rate. To make any sense at all, a lunar prop depot pretty much requires Starship, or something functionally identical: Relatively inexpensive to fly to LEO, that can be topped off in LEO, that can then deliver propellants to Gateway, and return to Earth for reuse. I can't see a prop depot case closing without a 100% reusable (and not reused via expensive refurb, either) vehicle.

If FH/NG/etc can get the 3 lander elements to Gateway, then any use of them to get just props to the same location actually wastes capacity. The only savings is the cost of the vehicles. The tug should be no more expensive than any tanker, since any tanker has to be able to operate and dock at Gateway, anyway. That only leaves the cost of the ascent stage. Making such a stage so that it can refill, AND such that it can live in space and be reused over years is likely more expensive than making a 1-off version that gets thrown away.

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Posted (edited)

I have a feeling that the Gateway is supposed to be more of a 'lifeboat' than anything else. When something goes wrong on the surface you go up and dock to the station. It probably takes less time and ∆V to rendezvous with a lunar station than going back to Earth/LEO/whatever or send a rescue mission from Earth. Also rotation, as some polar regions (AFAIK) are in the shade and can't use solar power for about six months. So the crews could rotate every 6 months or so. Pretty sure that's about the same time most astronauts spend on the ISS during each rotation/mission.

That being said, that's the only real uses I can see for it. Really not sure what kind of research can be done there that can't be done on the ISS, LEO or a lab.

Edited by Wjolcz

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12 minutes ago, Wjolcz said:

Really not sure what kind of research can be done there that can't be done on the ISS, LEO or a lab.

It being outside Earth's magnetosphere could make for some useful experiments. 

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Posted (edited)
28 minutes ago, cubinator said:

It being outside Earth's magnetosphere could make for some useful experiments. 

Like what? Solar wind?

Edit: If the answer is yes, then wouldn't it be easier to send a probe into a heliocentric orbit to stay outside of the magnetosphere for its whole mission? The Gateway would go through Earth's magnetic tail every month. Maybe they could do some radiation shielding research too, but as I said: pretty sure you can do that in a lab by bombarding tiny pieces of said materials with radiation. Seems waaaay cheaper than shielding a whole station just to test it. Or even better: Just wrap a probe with some shielding and send it way out into the heliocentric orbit.

Edit 2: I'm not trying to hate the Gateway btw. I love the ISS because it makes me think about how amazing the 21st century is. A lunar station doesn't seem much of an upgrade though. It won't do much more research than that the ISS has already done. It probably won't build a Mars ship either. It's a lifeboat and I feel like  BFR could work just as well while being much, much cheaper.

Edited by Wjolcz

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Posted (edited)

@cubinator

Yer I’m of the same mind regarding SLS. I think there’s a lot of political influence surrounding that project, but with New Glen and Starship probably directly competing with SLS for a fraction of the cost it will be interesting to see how they try and sell the idea of SLS launches...

It was certainly interesting to see Bridenstine saying how they were looking into all options for getting the next mission to the moon on time and that mightn’t necessarily be on the SLS, but it seems he’s now saying that SLS is the way they are going. I wonder how much of that was due to backlash from ULA and how much of all that was just Bridenstine trying to light a fire under ULA’s ass.

One of the things I’m struggling with regarding the idea of using the gateway as a refuelling point for landers is that most of the focus for missions will apparently be at the South Pole and that will probably be where most of the ISRU fuel production will be concentrated so there would seem to be little need to orbit at all... It would seem to be only necessary hop around the Southern Polar region, and if we are talking using the Gateway as a home for astronauts between missions, surely having some gravity would be better  than a zero G environment.

It seems as though sending an empty “hopper” craft to a polar ISRU staging point and fuelling there would be more efficient than shipping fuel up to orbit and then returning to orbit after every trip/mission

Edited by Dale Christopher

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It makes sense to use an upper stage to go from the upper atmosphere to a circular lunar orbit, then detatch the lander.  

It seems ridiculous to me to bring empty fuel tanks home, when they could be worth a lot in lunar orbit for structural material.  

 

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Posted (edited)

@tater

2 hours ago, tater said:

Current ideas for a Gateway-->Moon lander have:

Ascent Module, AM (returns to Gateway for refilling with props, presumably).

Descent Module, DM (brings Ascent M to lunar surface from LLO)

Tug (brings AM/DM stack from Gateway to LLO, and possibly AM back to Gateway).

I assume the descent stage is expendable/left on the surface. If so this doesn’t seem to work well with the long term goals of creating ground based capabilities, I imagine repeated travel to the same destinations (moon bases etc...) would leave a pile of descent stages building up at these places >_<...

@farmerben

56 minutes ago, farmerben said:

It makes sense to use an upper stage to go from the upper atmosphere to a circular lunar orbit, then detatch the lander.  

It seems ridiculous to me to bring empty fuel tanks home, when they could be worth a lot in lunar orbit for structural material.  

 

They may be useful but who is going to disassemble and or refit these things in Lunar space? Are we planning on a rostering a crew of astronauts on scrap metal duties when they aren’t doing science?

Edited by Dale Christopher

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Posted (edited)

Another thing I’m wondering about is that the propellant most likely to be derived from the moon for all this is Hydrogen+Oxygen and so now aren’t we also having to deal with boil-off @_@! (Not conducive to long term storage!)

Edited by Dale Christopher

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1 hour ago, Wjolcz said:

Like what? Solar wind?

Humans. Nobody's ever been outside the magnetic field for more than a couple of weeks, and NASA would like to use Gateway to study how the human body reacts to being in deep space for months at a time, before shooting a crew off to Mars and saying "'k see ya in two years".

1 hour ago, Wjolcz said:

It probably won't build a Mars ship either. It's a lifeboat and I feel like  BFR could work just as well while being much, much cheaper.

"Yes"

-Elon Musk

I agree. The delta-V gain from departing from the Moon to Mars is negligible at best, negative at worst, besides adding considerable time to the mission and making transfer windows even more difficult. And BFR will be way, way cheaper for larger payloads and more delta-V. But until that thing has already been flying operationally for years, its utility will be passed off as science fiction by most.

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Posted (edited)
1 hour ago, Dale Christopher said:

@tater

I assume the descent stage is expendable/left on the surface. If so this doesn’t seem to work well with the long term goals of creating ground based capabilities, I imagine repeated travel to the same destinations (moon bases etc...) would leave a pile of descent stages building up at these places >_<...

@farmerben

They may be useful but who is going to disassemble and or refit these things in Lunar space? Are we planning on a rostering a crew of astronauts on scrap metal duties when they aren’t doing science?

I'm suggesting leaving large empty fuel tanks in orbit around the moon, so that they can be attatched to things.  

An empty oxygen tank is a perfect hab, all it needs is a door.  Hydrogen gas is the best radiation shield for everything except gammas, per unit mass that exists.  The middle stage of a rocket has tremendous compression strength and hardpoints at both ends.

Edited by farmerben

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Just bear in mind with the comments towards the SLS that the SLS is the only SHLV that currently exists and isn't a paper rocket. BFR has only two test vehicles (not full scale) and New Glenn is still paper only. Once one or both of these vehicles are routinely flying and man rated- assuming Block 2 isn't accelerated and NASA can trim costs through economies of scale in production- the SLS will be phased out to superior commercial vehicles. As I've always said- SLS is merely a stop gap until the commercial market can catch. Right now we only have two companies with the financial support and in house production and assembly teams- Blue Origin, United Launch Alliance and SpaceX. Of which only one has the achievement of 'building flight articles' and that being SpaceX. Even then, it could be the better part of a decade before SpaceX has a proven and ready vehicle (after all we're talking Musk time) and even longer before NASA can reliably trust the vehicle to be man rated and ready for spaceflight to deep space (currently I am not aware of how Musk plans to have the BFR handle deep space radiation such as from the VA belts and general cosmic radiation which would be a big consideration for NASA recruiting the BFR into their missions). 

As to LOP-G and how all of this stands- LOP-G is a midpoint. It is not the most efficient middle ground, but it is a middle ground between deep space and the moon. I support the concept of LOP-G since it forces us to maintain, develop, grow and expand the station and it's utilities as we have had to with the ISS. As no politician wants to explain to Congress why a multibillion dollar space station in deep space should be abandoned as we did the Apollo program. Which the Artemis program is planned to be vastly more complex than- and to ensure that it is as feasible and as politically appealing as possible, NASA plans on handing off many objectives and tasks to it's commercial and international partners. With a commercial company making the PPE core, and another company launching it (likely ULA or SpaceX, but potentially Blue Origin if they can get the New Glenn ready). Another appeal to LOP-G is that we can assemble and prepare deeper space missions such as missions to Mars using the Deep Space Exploration spacecraft which would be launched to LOP-G and return back to it, where crews would board an earlier deployed transfer vehicle and return back to Earth instead of launching a return craft along with the transport vehicle to and from Mars. There's always been the notion to build things on the surface of the moon but that requires relaunching orbital assets back into orbit and there's always the point of 'once in orbit, you're halfway to everywhere' and that certainly helps when building larger interplanetary vehicles or simply acting as a waypoint between the moon and Mars. 

Just my thoughts! 

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Posted (edited)

I’m excited to see NASA develop experience with manned electric propulsion on the station. 

The Artemis plan will rely on commercial launch vehicles (and other components) and orbital assembly sans shuttle, which they have little experience with.

Edited by Nightside

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Posted (edited)
53 minutes ago, ZooNamedGames said:

the SLS is the only SHLV that currently exists and isn't a paper rocket.

None of them have flown. I'd even wager that SLS is exactly as existent as BFR right now - a test vehicle under construction.

I like your points on the political grounds for Gateway's viability to keep the Artemis program together, though.

Edited by cubinator

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1 hour ago, cubinator said:

None of them have flown. I'd even wager that SLS is exactly as existent as BFR right now - a test vehicle under construction.

 

That's a bold wager. SLS has total and actual flight hardware, you can count any rocket first flight as a "test" so you'd be better off labeling it as a prototype. Starhopper is merely a water tank with a nosecone being built not by SpaceX but by steel contractors. As we know of it right now, there's no indication that Starhopper is actual flight hardware except Raptor. 

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8 hours ago, ZooNamedGames said:

BFR has only two test vehicles (not full scale) 

Starship has two full scale orbital prototypes under construction and one (almost) functioning hopper vehicle. Sure, Starship has a long way to go and is obviously behind SLS, but its not nothing.

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3 hours ago, NSEP said:

Starship has two full scale orbital prototypes under construction and one (almost) functioning hopper vehicle. Sure, Starship has a long way to go and is obviously behind SLS, but its not nothing.

Even then- it’s useless to NASA without the Super Heavy Booster. If I recall someone calculated that Starship has just enough DV to get to orbit, but only when flying light (no payload). Even if it did have enough DV to SSTO to orbit- it still lacks DV to reach the moon which is where all of this is actually needed.

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The delta-V metro map.

LEO is well-known and boring.
It's clear that a human can survive a 2 year flight in zero-G, it's obvious that even a half-year in zero-G is too much.
So, not much sense in LEO crewed flights continuation until big nukes allow building really large stations with artificial gravity.

So, further spaceflight studies should study flights in interplanetary conditions. To design spaceships allowing the crew to survive in interplanetary flights.
Hulls, equipment, communication, logistics, everything should be tested in the interplanetary medium.
I.e. outside of the magnetosphere, under solar and galactic winds and rays, during solar flashes, etc.
Not just pieces of materials, but whole ship appartments.

It takes ~11.5 km/s to get into geosynch orbit, and ~13 km/s into LMO.

What can they do in the geonsynch orbit? Nothing special.
What can they do in LMO? They can at once study the Moon.

So, I believe, both LOP-G and Orion are not for the Moon (and not for the Mars). They are testpads for further technological investigations.
The Moon is just a test site for them, occasionally laying next to the road.

So, LOP-G and Orion should be evaluated in terms of pure R&D, not in terms of the optimal Moon exploration.
In this case, they are optimal. They won't just hang in orbit, they will also study something on the Moon.

Also LOP-G is a lunar vault in case if a lunar lander can reach the orbit. They can either dock to the lander with the ship and return to the Earth, or try to approach the station and wait several months for the rescue ship.

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58 minutes ago, ZooNamedGames said:

Even then- it’s useless to NASA without the Super Heavy Booster. If I recall someone calculated that Starship has just enough DV to get to orbit, but only when flying light (no payload). Even if it did have enough DV to SSTO to orbit- it still lacks DV to reach the moon which is where all of this is actually needed.

Im pretty sure they will begin construction on the Super Heavy booster this year. I think i read they were planning to construct it in August but i can't confirm. They could have a Starship/Superheavy stack ready by next year at the pace they currently build these things, but it all depends on how well the development goes.

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15 hours ago, cubinator said:

Humans. Nobody's ever been outside the magnetic field for more than a couple of weeks, and NASA would like to use Gateway to study how the human body reacts to being in deep space for months at a time, before shooting a crew off to Mars and saying "'k see ya in two years".

This is not an ethical experiment. Expose people to known, high radiation, just to see how they are harmed? The radiation environment is already well understood, as are health effects. Putting people at Gateway doesn't help at all.

2 hours ago, ZooNamedGames said:

Even then- it’s useless to NASA without the Super Heavy Booster. If I recall someone calculated that Starship has just enough DV to get to orbit, but only when flying light (no payload). Even if it did have enough DV to SSTO to orbit- it still lacks DV to reach the moon which is where all of this is actually needed.

Starship/Super Heavy is more real than Vulcan or NG right now. It has a tested, flight-ready engine, and they are actually bending metal.

All uncrewed Gateway plans right now are predicated on 1 extant SpaceX vehicle (FH), and one ULA vehicle, DIVH. All other launches require (not counting Starship) vehicles that don't actually exist, Vulcan/NG.

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Posted (edited)

They're bending metal for Vulcan, too (there was a post in the ULA thread about that a good while ago). And their engine is not any more flight-proven than BE-4, unless you count the flying test stand that is Starhopper. I'd say that Vulcan, with its more conservative design (Delta-IV derived tanks, a fat Centaur for the upper stage), is more real than Starship, if anything.

Edited by Dragon01

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