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3 minutes ago, tater said:

Yeah, it really is tricky as what you are refilling looks exactly like what you need to bring the props (because the tanker must function as a complete spacecraft).

The only reason for refilling operations WRT Artemis is because there are not LVs capable of lifting what is needed by themselves, but as you say, the LVs that can throw refilling props to the Moon are the same LVs that threw the lander parts in the first place, and can just send a new set of parts (Ascent, Descent, transfer stage).

The one place it might make vague sense is refilling the ascent vehicle. The tanker does not need a proper engine, after all (it can rendezvous with LOP-G on RCS alone), so you sorta save the weight of a single engine, as opposed to replacing the tanks and engine each flight (that's if you plan on reusing the ascent vehicle anyway). However, that's also the MOST critical engine of the whole affair, so you don't really want to reuse it too many times.

3 minutes ago, tater said:

Stage disposal is also an issue.

It's not too bad. There are zero-cost trajectories away from NRHO that impact the moon or enter heliocentric orbit; they just take a long time.

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4 minutes ago, sevenperforce said:

However, that's also the MOST critical engine of the whole affair, so you don't really want to reuse it too many times.

Yeah, particularly with the abysmal flight cadence of the only crew vehicle to there (SLS/Orion), since it means the stage sits at Gateway for a year between uses.

6 minutes ago, sevenperforce said:

It's not too bad. There are zero-cost trajectories away from NRHO that impact the moon or enter heliocentric orbit; they just take a long time.

I guess if they can be ejected from orbit at low cost*, I was thinking more with refilling since it would take multiple extra flights to refill a stage, and each needs to be disposed of.

*Impacting too many stages... dunno, it bugs me :)

 

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15 minutes ago, tater said:

Yeah, particularly with the abysmal flight cadence of the only crew vehicle to there (SLS/Orion), since it means the stage sits at Gateway for a year between uses.

Exactly. If there is any mission-critical component you want to replace each time, it's the ascent engine.

The more I think about it, the more convinced I am that replaceable, expendable, pressurized hypergolic drop tanks present the lowest barrier to realizing near-term component reuse. Someone, probably LockMart or ADS, would need to develop a reusable structural coupling that would be able to transfer propellant at high flow rates and handle significant force loading. Then they just need a lightweight pressurized hypergolic+helium tank and a grapple fixture on the back end. 

A prototype (subscale tank, full-scale coupling) could easily be sent up to the ISS for Canadarm testing. Such a tank could be used to extend Orion's capabilities (e.g., letting it act as a lifeboat to rescue a stranded ascent module in LLO), re-equip a "space taxi" ascent module, and so forth. Tankage weight is the least reusable part of the Artemis architecture, because a refill supply ship HAS to carry the props somewhere. The only disadvantages -- you can't regeneratively heat the helium pressurant, and you don't have quite as much of a square-cube advantage as other systems. Otherwise it is the most sustainable, mass-efficient way to progress cislunar reuse until we have cryogenic ISRU.

With such capabilities, you could theoretically use distributed launch here in LEO to do each lunar lander mission with just a single commercial TLI launch. Send up a "pallet" of the expendable tanks on an Atlas V or a Vulcan, then send up a new lander/ascent module on Falcon Heavy to rendezvous while still connected to the Falcon upper stage. Autonomously mate, push as far toward TLI as possible, and then let the lander/ascent module do the rest of the TLI (plus LOP-G rendezvous) using props from the expendable tanks.

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What about sending the hypergolic drop tanks ahead to Gateway with ion engines? It's not like speed matters. Or indeed the entire lander. Assemble it at ISS, then dock it to an ion engine tug, and let it crawl to Gateway over as long as it takes.

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6 minutes ago, tater said:

What about sending the hypergolic drop tanks ahead to Gateway with ion engines? It's not like speed matters. Or indeed the entire lander. Assemble it at ISS, then dock it to an ion engine tug, and let it crawl to Gateway over as long as it takes.

ISS has been extended to 2030 so it's possible, though I think they want to get away from ISS dependency. I was re-reading the HLS Concept of Operations publication and noted that they allow for up to 120-day transits to NRHO for uncrewed modules to save dV.

An ion crawl from the ISS to LOP-G would cost about 7.2 km/s, which is not unprecedented -- Deep Space 1 achieved over 7 km/s and Dawn achieved over 11 km/s. However, that velocity change by Dawn took nearly six years of thrusting. A fully-stacked lunar sortie vehicle would be more than fifty times the mass of Dawn. If we want the lander stack to make the journey from LEO to LOP-G in under a year, we would need 630+ ion thrusters and a 2.1 MW solar array. For reference, that's more than twenty times the power generation capability of the main ISS solar array.

The HLS ConOp did mention that there would not be a Canadarm at LOP-G during the initial phase, which complicates the use of expendable drop tanks.

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7 minutes ago, sevenperforce said:

ISS has been extended to 2030 so it's possible, though I think they want to get away from ISS dependency. I was re-reading the HLS Concept of Operations publication and noted that they allow for up to 120-day transits to NRHO for uncrewed modules to save dV.

An ion crawl from the ISS to LOP-G would cost about 7.2 km/s, which is not unprecedented -- Deep Space 1 achieved over 7 km/s and Dawn achieved over 11 km/s. However, that velocity change by Dawn took nearly six years of thrusting. A fully-stacked lunar sortie vehicle would be more than fifty times the mass of Dawn. If we want the lander stack to make the journey from LEO to LOP-G in under a year, we would need 630+ ion thrusters and a 2.1 MW solar array. For reference, that's more than twenty times the power generation capability of the main ISS solar array.

The HLS ConOp did mention that there would not be a Canadarm at LOP-G during the initial phase, which complicates the use of expendable drop tanks.

Yeah, it might take a few decades. Not sure that makes much of a difference, frankly ;)

Also, spacesuits:

 

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44 minutes ago, tater said:

Also, spacesuits:

 

Oh I love how dorky that suit mock-up looks in red, white, and blue. :P

The flexibility looks very good though. I'm wondering whether that's how flexible the suits will actually be. I guess that mainly depends on how much commonality that mock-up has with the real deal.

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5 minutes ago, jadebenn said:

The flexibility looks very good though. I'm wondering whether that's how flexible the suits will actually be. I guess that mainly depends on how much commonality that mock-up has with the real deal.

It has more to do with the fact that in the video the inside and outside of the suit are at the same pressure.

Ninjaed by @.50calBMG lol

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8 minutes ago, jadebenn said:

Oh I love how dorky that suit mock-up looks in red, white, and blue. :P

The flexibility looks very good though. I'm wondering whether that's how flexible the suits will actually be. I guess that mainly depends on how much commonality that mock-up has with the real deal.

It seems they've done a combo hard-suit/soft-suit with that stiff coupled joint at the waist. Smart. But man, I still feel like there's got to be a way for form and function to interlock a little better.

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12 minutes ago, tater said:

It has more to do with the fact that in the video the inside and outside of the suit are at the same pressure.

Yeah, I get that. The suit in the video's got to be little more than a hollowed out casing - would be way too heavy to wear in Earth gravity otherwise - but the way the joints on the arms and lower torso move as she walks looks like it'll be very good news for flexibility in actual lunar conditions.

9 minutes ago, sevenperforce said:

It seems they've done a combo hard-suit/soft-suit with that stiff coupled joint at the waist. Smart. But man, I still feel like there's got to be a way for form and function to interlock a little better.

The design looks a lot cleaner when it's less... uh, loud.

And, yeah, the xEMU is a hybrid suit design. More mass than the Apollo designs, but that was deemed to be an acceptable trade-off for the increased flexibility.

 

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5 minutes ago, sevenperforce said:

Some other clips show the ability to bend and pick up a rock from the ground with both hands.

Yeah, that was impressive---assuming it is possible with the suit pressurized.

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8 minutes ago, tater said:

Yeah, that was impressive---assuming it is possible with the suit pressurized.

Should be. The dynamics that make a soft suit stiff when pressurized don't apply to areas with discrete joints. 

On a side note, one of the interesting features of the xEMU suits is the capability for variable pressurization. Instead of an astronaut slowly decompressing in the airlock before entering the suit, the xEMU is capable of being pressurized to the spacecraft's ambient pressure, allowing astronauts to jump in and work as the suit slowly lowers the pressure to a more flexible level over time. This should allow astronauts to be much more productive prior to EVAs.

Edited by jadebenn
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8 minutes ago, tater said:

2 atm? (so the relative pressure is the same)?

He didn't say the pressure, only that it was pressurized.

I will say that I don't think it's a coincidence that the engineer demonstrating the spacesuit had to take interview questions from inside it. The pressure must've been high enough that she couldn't just step out afterwards.

Edited by jadebenn
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It deeply annoys me that in 2019, women are still expected to maintain a frozen smile in public like that. Kristine's face looked like it hurt. Compare to Jim -- he's not forcing a smile the entire time they are evaluating the suit.

They said she will be at 8 psi 100% oxygen, but the suit drops pressure to 4 psi gradually to add mobility. Presumably the suit was pressed to around 22 at 60% oxygen in the demonstration, based on what Jim said. Though Jim's technical knowledge is not necessarily trustworthy.

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7 minutes ago, sevenperforce said:

It deeply annoys me that in 2019, women are still expected to maintain a frozen smile in public like that. Kristine's face looked like it hurt. Compare to Jim -- he's not forcing a smile the entire time they are evaluating the suit.

How many times do engineers get to be on TV, potentially which might end up on the evening news with like a gazillion people watching? The ISS astronauts (women) seem perfectly natural to me when I see their vids, I think it has more to do with familiarity (astronauts know what they are getting into, and might have different personality types). Bridenstine was a pol, remember, same thing, has to be outgoing or he'd not have gotten elected. More eng/sci people I know are not terribly public people.

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Just now, tater said:

How many times do engineers get to be on TV, potentially which might end up on the evening news with like a gazillion people watching? The ISS astronauts (women) seem perfectly natural to me when I see their vids, I think it has more to do with familiarity (astronauts know what they are getting into, and might have different personality types). Bridenstine was a pol, remember, same thing, has to be outgoing or he'd not have gotten elected. More eng/sci people I know are not terribly public people.

This veers OT but I think there is still a societal expectation for a female displaying a suit to "model" it in a way that wouldn't be expected of a man. Not a NASA-specific thing or even something specific to Kristine; just how society functions.

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