The TRL levels of the hardware mentioned in the paper are said to be at TRL 6 or better. Which specific parts are you concerned about?
Uhhhh.... These?
It will probably come as a surprise to some that the asteroid capture mechanism itself is "assumed" to be at TRL6. As is DSH, ECLSS, 40 kW class SEP, and more.
More? "reliable robotic anchoring capability"; "Structural characterization, especially of the surface layers"; "dust levitation and settling behavior [mitigation thereof]"; "gravity tractor (GT) concept"; "Proximity operations"; "extraction and purification of water"; "autoreduction of the major mineral magnetite"; "using the released CO as a reagent for the extraction, separation, purification, and fabrication of iron and nickel products". All of these assumed to be at TRL6. No exceptions given.
After re-reading the paper, I misunderstood what it was saying about TRL 6. As you said, it's not a claim, it's an assumption they used for the cost estimates. SEP and the capture mechanism are included in this assumption. I don't see the SEP being a problem, it seems a modest enhancement of current production hardware, clustered together. There's no doubt the actual capture operation is risky, but I don't see any problems building the hardware. You are talking about billions of dollars to design this? The design presented can be executed in a straightforward manner. If you want to test it, capturing can be tested in LEO or GEO using a dead satellite, for much less than a billion.
DSH, ECLSS, anchoring capability, gravity tractor, autoreduction, extraction/purification of water, are outside the scope of this project. Even at that, whatever project does include the ones besides DSH and ECLSS will not assume TRL-6: the point of such a project at this asteroid would be to DEVELOP those technologies, not to depend on their maturity.
The only mentions of manned missions in the Keck report are described as strictly notional possible applications once the asteroid is available: it's like a car salesman saying once you possess one, a minivan could be used to get groceries, go on vacations, take kids to school, etc. You don't then fault the salesman for not including the price of groceries, vacations, and schooling in the price of the vehicle. Criticizing a report detailing an unmanned asteroid capture program for not including the entire budget of the manned program is just not getting it.
The most critical piece of the timeline is starting to characterize and identify NEAs, and that's the piece in next year's budget. Virtually everybody agrees it needs to be done, although various groups strongly believe NASA should give them the money to get the job done.
Nice handwave about how a "capture" isn't a "capture".
I suppose I didn't word it clearly: the question is who is doing the capturing, the ~15 tonne object, or the ~500 tonne object? Where does the 500 tonne asteroid go? Wherever the hell it wants to, with very minor and persistent respectful suggestions from our little spacecraft and thrusters. The desired end result is a capture, but at the start the asteroid is dictating the speed, direction, and rotation. Point is, one of the connotations of "capture" is that the captor is dictating the terms, whereas in this case the captive has a lot of weight to throw around.
We are talking the 2021-2025 time frame...how many events in 2021 have you planned out in detail?
Nice ad hominem. Somehow my personal schedule pertains to the accomplishment of this mission?
It's not an
ad hominem. And it's not about the accomplishment of the mission, but about the impracticality of making precise plans about something so far in the future. Change is certain. There is nothing wrong with not having detailed plans for 2021...and that's the point.
This mission, properly costed, is probably closer to $46B than to $2.6B. Above, I've included some of the line items that have not yet been discussed, but which have been deliberately handwaved away, while deceiving policymakers about the accurate costing and feasibility of the asteroid retrieval mission.
Re: $46 billion...You're a loonie! Now THAT'S an
ad hominem.

I don't know if lawmakers have been deceived: right now they are funding some astronomy to characterize NEAs. And that's what they'll be getting. In the future, they may choose to fund an unmanned asteroid capture and retrieval mission. Separately, they have chosen to fund the development of the SLS launcher, and Orion capsule, and they are getting said development. That development is planned to include several test flights, demonstrating expanding capability, one of which has repeatedly been mentioned to include flying toward/around the moon. If the asteroid is at the moon then, that mission might well visit the asteroid. If NASA wants to use a DSH to visit the asteroid, then NASA may choose to ask for funding, but that hasn't happened and is just one of several possibilities. If NASA wants to develop ISRU gear to be tested by a manned or unmanned mission, and it is costly enough not to stick in their normal tech development programs, then they may ask for that too.
If the asteroid were in place by EM-2, that mission almost certainly would not include a DSH, in the same way Apollo 8 did not include a LEM. In that case, trips to the asteroid might be used to inform the design of the DSH, or material from the asteroid might be used to augment shielding of a later-produced DSH. Even without a DSH, or even without SLS, or even without a manned space program, the asteroid would provide valuable opportunities, though obviously its value and the ability to take advantage of it increase with each of those.
Did they mention that the asteroid is "unique"? Yeah. Here: "There are roughly a hundred million NEAs approximately 7-m diameter".
The paper characterized the situation with asteroids pretty well, I thought: lots of them, few well known, and the search is for one with extremely specific characteristics. The initial part of the project is to start identifying and characterizing NEAs, looking for the desired properties. (Recognizing that those without the desired properties for this mission are still interesting for other reasons.)
Because our ability to move heavy objects far from earth is limited, we are looking for one in a precise orbit. It needs to share a very similar orbit to earth's, periodically slowly approaching the earth, and whose synodic period needs to be such that we can observe it when it's close on one approach and have a second approach a few years later around the time the spacecraft reaches it. The spacecraft will nudge that close approach just enough closer for lunar capture.
In addition to its orbit, the authors specify a particular composition, a carbonaceous C-type asteroid. Finding such an asteroid (right orbit, right size, right composition) should not be hard given plenty of time, but as you try to compress the timeline, it becomes very hard to impossible. I say impossible now, because the example they chose, NEA 2008 HU4, cannot be brought to the moon much before 2026, as I understand it. (And we have no idea whether it is C-type.) To make 2021, the spacecraft would need more thrust/coast time, such that it should have already started by now. So we'd need another candidate that has a close approach in 2021, and AFAIK there isn't one known right now. We can find one, but that takes time, and as time goes on the available synodic periods is dropping (eight years or less now, seven years or less next year, for a 2021 capture), and the possible thrust/coast time is getting less.
That's the problem to tackle now, and it seems to me 2025 is ambitious.
They mention another approach, picking one of the larger 100m better characterized asteroids and grabbing a 7m rock from it, or scooping up ~500 tonnes of material from it. I'm not sure that approach has as much synergy with the manned program. The need to accomplish most of the science at the 100m asteroid grows, and the usefulness of the return product for ISRU/extraction/attachment/deflection is a bit diminished. That mission starts to look like an unmanned visit to an asteroid, with a very large sample return by virtue of the use of the high lunar orbit.