Author Topic: Exploring a lightweight Mobile Hab based HTM architecture  (Read 118268 times)

Offline Michael Bloxham

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Re: Mobile Hab based architecture
« Reply #80 on: 07/23/2010 12:09 PM »
Why not simply include a hydrogen liquefaction unit, so you can keep boil-off losses minimal on the surface? You're going to bring along a large solar array anyway, so it should be possible to actively cool the tank. It's not that large, remember.

AFAIK, takes too much power to run. It's a lot more efficient if you can processs the H2 into something more storable at a rate that keeps up with the natural boil-off rate. But again, I am no expert with these things so don't hold me to that!

Even with optimized ISRU process scheduling, we're generating cryogenic byproducts (methane and later, LOX) pretty quick; which have to be stored over the long period of time required to generate all the oxygen (long because of the low-power output of even a large solar array; compared to the more power-dense nuclear option). Keeping those products liquid already requires quite a lot of power. I wonder whether we can afford to run both a cryogenic cooler for the seed H2 and process it at the same time.

Our latest ISRU study for the MAV (again by David Gooding) can be found here: http://xa.yimg.com/kq/groups/20840137/1799667952/name/ISRU

Note that in this study we attempted to compare the various ISRU options, and see if it was feasible to cram all the systems needed (including the required solar array) into a single lander.

I know David is always looking for feedback for his studies, so be sure to let us know if you see anything needing improvement / clarification etc. There's quite a bit of detail in there!

- Mike
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Offline MickQ

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Re: Mobile Hab based architecture
« Reply #81 on: 07/28/2010 07:42 AM »
It seems that bringing along a little hydrogen is the smaller problem. With good insulation and some additional hydrogen to cover boil-off losses, it should not really be a problem.

I'd probably agree with that. From the research that our own David Gooding has done, we can probably conclude that H2 storage is only problematic once on the surface (because multi-layer insulation (MLI) only works well in a vacuum; it is quickly permeated by an atmosphere).

Edit: That is not to say that H2 storage is not a problem during the long 6+ month journey in deep space! But with the aid of a single large well-designed tank, with adequate MLI insulation and sun-shielding, this problem can probably be overcome by simply adding excess H2 than is needed and accepting some boil-off losses.

This is even more of a problem when you are using photovoltaics rather than a nuclear power source. The solution that I suggest (and this is included in the architecture diagram) is to have a very large unfurlable solar array which is sent separately from the MAV on a "cargo rover". This rendezvous within days or, at most, weeks after the MAV has landed. This may allow us to have a much larger solar array and thus we can run the ISRU process more quickly; thereby consuming the hydrogen before it gets a chance to boil off.

Although in saying that, can't the RWGS reaction also be used to generate CO and O2 (rather than the more problematic direct electrolysis of CO2)?

- Mike

If you are going to cary H2 to Mars, what about taking it as H2O2 ?  I know that you are trading hydrogen for oxygen but peroxide is easily stored and it breaks down into water steam (at about 600 deg C) and oxygen when catalyzed.  The steam could drive turbines for either power gen or gas compression and on Mars you could never have too much Oxygen, could you ?

Mick.

Offline Michael Bloxham

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Re: Mobile Hab based architecture
« Reply #82 on: 07/28/2010 10:17 AM »
Mick, I'm no chemistry-expert, but the thing to remember is that the oxygen atom is 16 times heavier than that of hydrogen. H2O2, therefore, has a mass 17 times greater than H2 (but yet contains the same amount of the needed hydrogen atoms)! Clearly any benefit in terms of storability, etc. will have to be weighed against that huge mass penalty. CH4 is better at a ratio of 4:1 to H2. But with the large quantity of ISRU propellant needed to fuel the ascender, and the small surface payload of "realistic" landers, even this is probably not viable.

I don't think the concept of using seed-H2 is all that tricky. With efficient insulation, perhaps some active cooling, and initial loading to compensate for boiloff, I believe the problem of storage during the 6+ month transit can be solved. On the surface (where the insulation will be much less effective than in the vacuum of deep-space), the challenge is to process the H2 quickly enough that boiloff isn't a significant problem. Again, I think that this can be done. With the split-MAV approach we are using we can afford to fit a much larger solar array than otherwise; thereby allowing the seed-H2 to be processed much more quickly. And with two landers instead of one, there is more margin available for us to do this.
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Offline MickQ

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Re: Mobile Hab based architecture
« Reply #83 on: 07/29/2010 04:15 AM »
Mick, I'm no chemistry-expert, but the thing to remember is that the oxygen atom is 16 times heavier than that of hydrogen. H2O2, therefore, has a mass 17 times greater than H2 (but yet contains the same amount of the needed hydrogen atoms)! Clearly any benefit in terms of storability, etc. will have to be weighed against that huge mass penalty. CH4 is better at a ratio of 4:1 to H2. But with the large quantity of ISRU propellant needed to fuel the ascender, and the small surface payload of "realistic" landers, even this is probably not viable.

I don't think the concept of using seed-H2 is all that tricky. With efficient insulation, perhaps some active cooling, and initial loading to compensate for boiloff, I believe the problem of storage during the 6+ month transit can be solved. On the surface (where the insulation will be much less effective than in the vacuum of deep-space), the challenge is to process the H2 quickly enough that boiloff isn't a significant problem. Again, I think that this can be done. With the split-MAV approach we are using we can afford to fit a much larger solar array than otherwise; thereby allowing the seed-H2 to be processed much more quickly. And with two landers instead of one, there is more margin available for us to do this.

Yes.  I hear you.  I was just putting up ideas.

Another one.  Someone recently proposed using inflatable Bigelow style habs on your rovers.  Could you inflatable containers for gas/liquid storage both in transit to and after landing ?

Mick.

Offline Michael Bloxham

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Re: Mobile Hab based architecture
« Reply #84 on: 07/29/2010 08:49 AM »
Another one.  Someone recently proposed using inflatable Bigelow style habs on your rovers.  Could you inflatable containers for gas/liquid storage both in transit to and after landing ?

Mick.

That is an interesting idea! However, from my small amount of knowledge in this area I would say that it is not really viable: For living volumes, you are only looking at containing pressures of up to about 1 Bar. But for the storage of cryogenics you want the pressure vessels to withstand up to ~300 Bar! Although the thought occurs to me that, with substantial cryo-cooling, you don't actually need the pressures to go up that far. But even if you could store the fluid at 1 Bar you'd still have trouble dealing with the fact that the fluid is really really cold and would likely make the containment material very brittle. You'd also need a impermeable flexible liner to contain the H2 (which has a tendency to leak through absolutely anything, given that it is such a small molecule). But again, these are just musings as I am no expert on the matter.

- Mike
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Offline MickQ

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Re: Mobile Hab based architecture
« Reply #85 on: 08/05/2010 05:55 AM »
Another one.  Someone recently proposed using inflatable Bigelow style habs on your rovers.  Could you inflatable containers for gas/liquid storage both in transit to and after landing ?

Mick.

That is an interesting idea! However, from my small amount of knowledge in this area I would say that it is not really viable: For living volumes, you are only looking at containing pressures of up to about 1 Bar. But for the storage of cryogenics you want the pressure vessels to withstand up to ~300 Bar! Although the thought occurs to me that, with substantial cryo-cooling, you don't actually need the pressures to go up that far. But even if you could store the fluid at 1 Bar you'd still have trouble dealing with the fact that the fluid is really really cold and would likely make the containment material very brittle. You'd also need a impermeable flexible liner to contain the H2 (which has a tendency to leak through absolutely anything, given that it is such a small molecule). But again, these are just musings as I am no expert on the matter.

- Mike

OK.  I'll try another idea.  In Advanced Concepts there is ' A Breakthrough in Radiation Shielding ' to do with magnetic fields.  Would this be worth looking at for your mobile habs ?

The report also speaks of areas of localized magnetic fields on Mars which, IMHO, may be worth looking at as landing or base sites if the shielding effect works.

Mick.

Offline Michael Bloxham

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Re: Mobile Hab based architecture
« Reply #86 on: 08/05/2010 08:14 AM »
Mick,

AFAIK, these draw too much power to be viable. And it's arguable that such exotic radiation-mitigation systems are not really required; especially once on the surface. I believe that we can provide "adequate" shielding via traditional methods. That probably means having an internal water bladder around the inside of the hab, and perhaps also a smaller shelter around the sleeping quarters with a thicker bladder to which the water can be pumped during solar storms or just for sleeping (if that helps?). The shielding water might be a combination of fresh water and waste water (stored separately of course!). Methane or methanol fuel (used to fuel the mobile habs) would also make for good radiation shielding. There is also the fact that, with the mobile hab architecture, the crew may spend much less time outside their highly-shielded hab (as they no longer need to commute to remote sites via the traditional small rover). So this might also help somewhat.

You mention areas on the surface where localized magnetic fields could offer some protection... I would also offer the possibility that, with the mobile hab architecture, you could drive right up to these areas, or just a physically sheltered locale, so that radiation exposure was further minimized. But I wouldn't have the mission rely on these things...

- Mike
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Offline alexterrell

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Re: Mobile Hab based architecture
« Reply #87 on: 08/05/2010 09:57 AM »
Mick,

AFAIK, these draw too much power to be viable. And it's arguable that such exotic radiation-mitigation systems are not really required; especially once on the surface. I believe that we can provide "adequate" shielding via traditional methods. That probably means having an internal water bladder around the inside of the hab, and perhaps also a smaller shelter around the sleeping quarters with a thicker bladder to which the water can be pumped during solar storms or just for sleeping (if that helps?). The shielding water might be a combination of fresh water and waste water (stored separately of course!). Methane or methanol fuel (used to fuel the mobile habs) would also make for good radiation shielding. There is also the fact that, with the mobile hab architecture, the crew may spend much less time outside their highly-shielded hab (as they no longer need to commute to remote sites via the traditional small rover). So this might also help somewhat.

You mention areas on the surface where localized magnetic fields could offer some protection... I would also offer the possibility that, with the mobile hab architecture, you could drive right up to these areas, or just a physically sheltered locale, so that radiation exposure was further minimized. But I wouldn't have the mission rely on these things...

- Mike
According to the New Scientist article, power requirements should not be too great, especially if you use a superconducting coil.(A use for liquid H2).

Regarding the natural areas of magnetic protection, one would expect these to be surrounded by an area of higher radiation, where diverted particles are driven and perhaps trapped - a bit like the Van Allen belts around Earth. So drive quickly through the interim region.

Offline Michael Bloxham

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Re: Mobile Hab based architecture
« Reply #88 on: 09/12/2010 10:03 AM »
Regarding the natural areas of magnetic protection, one would expect these to be surrounded by an area of higher radiation, where diverted particles are driven and perhaps trapped - a bit like the Van Allen belts around Earth. So drive quickly through the interim region.

Good point. Perhaps this is another potential advantage of using small mobile-habs? With a fixed-hab architecture, what happens if you land right on top of one of these radiation-trapping regions? :D. But I guess that would be incredibly unlikely...
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Offline Michael Bloxham

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Re: Mobile Hab based architecture
« Reply #89 on: 09/12/2010 11:04 AM »
According to the New Scientist article, power requirements should not be too great, especially if you use a superconducting coil.(A use for liquid H2).

I'm not an expert on these things so I really can't ascertain their viability. But anything which needs a cryogenically-cooled "superconducting coil" sounds a bit tricky to me. I think you have to ask, is such technology really necessary?

Also, I don't see a reason to have anything more than a thimble-full of liquid H2 onboard the crewed mobile habs during their mars-bound journey. Dealing with the storage of a few tonnes of seed H2 during the >6-month transit aboard the MAV and few months on the surface is problematic enough (although we think we may be able to get away with purely conventional low-boiloff tech atm; so long as the ISRU process begins rapidly enough when on the surface)!
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Offline Michael Bloxham

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Re: Mobile Hab based architecture
« Reply #90 on: 09/12/2010 11:35 AM »
Okay guys, I just want to make a call-out: We need more people involved with the refinement of these ideas! Clearly I think there is some concensus emerging about the potential merits of small-crew mobile hab architectures over more traditional big fixed-hab architectures (I have noticed that a few people here, including Kaputnik, Ross Tierney, and others, have explored their potential somewhat). And I think there is a great deal to be said about the potential to realistically approach the idea of a humans-to-mars mission without resorting to speculative technology as has been done in the past (i.e. assumptive EDL, zero boiloff, etc.). And this is greatly facilitated by the potential capability of a Jupiter-esque HLV - specifically its large payload volume capacity with the larger 12m diameter PLFs - which would in turn allow the use of large but heritage-derived mars entry vehicles with adequate surface payload for these smaller mobile habs.

So again: Please help us to refine these ideas! Any comment or question or whatever would help a lot! And if you really want to get involved please do not hesitate to offer: Tell us what your skills / interests are and we might be able to fit you in to a role later on. We need more engineer-types specifically so we can reduce the workload on our poor David Gooding :).

Here are a few links to mull over if you want to know what we've been up to:

http://groups.yahoo.com/group/marsdrivemission/attachments/folder/0/list

http://tech.groups.yahoo.com/group/marsdrivemission/

My "baseline" architecture (not representative of the concensus at MarsDrive but rather an excercise in integration of some ideas that would benefit from analysis and feedback in any case):

http://forum.nasaspaceflight.com/index.php?topic=22056.msg620189#msg620189

Please get involved if you can!

Thanks,
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Offline JohnFornaro

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Re: MarsDrive MobileHab-based architecture
« Reply #91 on: 09/12/2010 03:20 PM »
I'm not an engineer, yet I've noticed a few technical mistakes in this Mars Drive proposal.  Do you have any engineers on the team?

Which mistakes might those be?
Sometimes I just flat out don't get it.

Online Robotbeat

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Re: Mobile Hab based architecture
« Reply #92 on: 09/14/2010 07:46 PM »
Regarding superconducting magnets: They really only need liquid nitrogen temps, not liquid helium (although you get better performance if you get colder). You could do it with only cryocoolers, too. The highest critical temperature superconductors under certain conditions can reach about -110 degrees Celsius, which isn't too far at all from night temperatures on Mars (~-90 deg C).

Anyways, superconductors don't always need liquid helium or hydrogen, anymore.

EDIT:I am still of the opinion that space radiation, especially on the surface of Mars, is quite tolerable, even for long periods of time: http://www.angelfire.com/mo/radioadaptive/ramsar.html
« Last Edit: 09/14/2010 07:48 PM by Robotbeat »
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Offline Patchouli

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Re: Mobile Hab based architecture
« Reply #93 on: 09/15/2010 10:35 PM »
Regarding superconducting magnets: They really only need liquid nitrogen temps, not liquid helium (although you get better performance if you get colder). You could do it with only cryocoolers, too. The highest critical temperature superconductors under certain conditions can reach about -110 degrees Celsius, which isn't too far at all from night temperatures on Mars (~-90 deg C).

Anyways, superconductors don't always need liquid helium or hydrogen, anymore.

EDIT:I am still of the opinion that space radiation, especially on the surface of Mars, is quite tolerable, even for long periods of time: http://www.angelfire.com/mo/radioadaptive/ramsar.html

You probably could keep the superconductors cool with nothing more then a couple of sterling cycle coolers.
The power requirements over all may be just a few KWh a day which would be trivial to supply.
If you're going to do anything serious on Mars you'll probably have a large solar array or a small nuclear reactor supplying 30 to 100KW.
The mag shield's power requirements would be fairly small compared to the fuel plant,rover, and closed loop life support.
« Last Edit: 09/15/2010 10:36 PM by Patchouli »

Offline Michael Bloxham

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Re: Mobile Hab based architecture
« Reply #94 on: 09/23/2010 01:50 PM »
A post made at MarsDrive that I thought I'd share here:

***

I put a little thought into MP4 today: I was thinking about how such a heritage-derived architecture would best be "sold"; and thinking about the heritage part I played around with a couple of data points in excel (attached) to show how a mars lander big enough to be suitable for a humans-to-mars mission needn't be so far removed from the evolutionary trend. Here I have assumed the same critical ratios (mass/area, parachute mach number, etc.) as MER, MSL, etc. Of course we'd have to crunch the numbers to get the real EDL performance but from the same mass/area assumptions as MSL an 11.5m diameter aeroshell would seem capable of delivering a 14 tonne rover; which would seem adequate for a medium-sized 2-person mobile hab. Note that this is using *exactly* the same critical ratios as the MSL lander which flies next year. (Whereas Rons' EDL assumptions were around 1.5 times more dense than this, I think.) - The 'chutes (probably three of them - each about 30m in diameter; MSL is 20m dia.) open at the same mach number as MSL (2.05), etc.
 
I think it would make a real statement to the space community if we were to use such ultra-conservative numbers yet still come up with a workable architecture!
 
Now you might notice I've added a placeholder titled "MSR". I put this in to show where the most logical interem step between MSL and this DRM might be. This will be something to think about once we pick our DRM. This particular vehicle is 6.5m in diameter and capable of delivering 4 tonnes of payload with an IMLEO that should come in under 23 tonnes - making it suitable for delivery via a variety of existing international and in-the-works commercial LVs. I would suggest that something around this size would be suitable for a 2-part sample return precursor, and would also work well as a supplementary vehicle - capable of delivering extra science equipment, spares, fuel, etc. in support of crews on the surface - as per the original orbital caching idea (which is something I would like to re-assess in the future if possible).
 
I would also think that the mobile habs themselves could easily be portrayed as a logical extension of the trend from Sojourner -> MER -> MSL. (MSL is already as big as a small car.) If we choose to pursue anything like MP4, then this is a point that I would really like to drive home: We don't need super-revolutionary tech to go to Mars. We just need to continue to evolve the existing state-of-the-art. IMHO, this could make a very effective statement.
 
- Mike

***
« Last Edit: 09/23/2010 02:00 PM by Michael Bloxham »
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Offline Michael Bloxham

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Re: Mobile Hab based architecture
« Reply #95 on: 09/25/2010 06:28 AM »
Attachment shows a nice evolution from MPF / MER -> MSL -> MP4. This nicely illustrates how a viable humans-to-mars architecture need not be so far removed from the current trend of progression.

14 tonnes surface payload may not seem like a lot (other architectures usually require surface elements above 25 tonnes each); but again, if the traditional big hab is split up into two smaller 2-crew mobile habs, and the ISRU/MAV lander is similarly split, then 14 tonnes at a time becomes a great deal more attractive.

The utilization of such heritage-derived entry vehicles for a humans-to-mars architecture would be a lot more attractive then spending literally tens of billions of dollars in the design and qualification of more exotic EDL systems.
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Offline Michael Bloxham

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Re: Mobile Hab based architecture
« Reply #96 on: 09/25/2010 02:22 PM »
2 more ;)
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Offline Michael Bloxham

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Re: Lightweight Mobile Hab based architecture
« Reply #97 on: 09/25/2010 03:51 PM »
A small update to the mission profile overview image:

Notice the previous image of the MPV or "power rover" in the bottom left hand corner has been replaced with an image that better shows the unfurlable flexible solar array coiled up on the back of the remotely-driven hab-less chassis. This is over 5 tonnes of PV array which is plugged into the ISRU/MAV vehicle and then slowly rolled out. Once the array is deployed the MPV rover may be used as a teleoperable logistics / support vehicle for when the crews arrive in their small mobile habs.

The figures have also been revised among other small changes.

Edit: I doodled with the tiny images a bit more for better clarity ;)

- Mike
« Last Edit: 09/25/2010 04:59 PM by Michael Bloxham »
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Offline Michael Bloxham

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Re: Lightweight Mobile Hab based architecture
« Reply #98 on: 09/29/2010 11:08 AM »
Hi guys. While contemplating how a subset of this hardware could be utilized for a humans-to-phobos mission, I was wondering: For an opposition-class mission, would it be possible to delay aerocapture and / or also the TEI burn so as to decrease the time spent in Mars' orbit (at the expense of slightly longer transit times if need-be). This may seem a little backwards (the name of the game is usually to decrease transit times and increase time spent at Mars), but I think that for a humans-to-phobos mission this is different.

The idea is to use artificial gravity (by either tethering off the TMI and [later] the TEI stage, or having two independent vehicles tethered nose-to-nose) on both the inbound and outbound legs as much as possible; while minimizing time spent in zero-g near Phobos. I'm assuming here that it is not worth the difficulty of employing artificial gravity while the crew is in the vicinity of Phobos. (This assumption is made for a variety of reasons.)

Currently, I can envision the ERV vehicle meeting the role of the primary crew vehicle during all three major stages of the mission. It will already be designed to allow AG on the return leg for the surface missions. Perhaps there would be two of them, with 2 or 3-crew each, for dual-redundancy and to allow extra margin, etc. This would require a total of 4 SDLV launches if the current ERV design closes.

Any takers?

Thanks,

- Mike
« Last Edit: 09/29/2010 11:14 AM by Michael Bloxham »
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Offline Michael Bloxham

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Re: Lightweight Mobile Hab based architecture
« Reply #99 on: 09/29/2010 12:20 PM »
ERV general concept. Crossed-box indicates location of tether to TEI stage (hence why the men are upside-down).

This is the biggest hab area I could accomodate while keeping enough room for the return capsule at one end and TEI stage at the other end of the aeroshell. I'm thinking the TEI stage shouldn't need too much space: It is heavy but the methane/LOX fuel is quite dense. But this might not do if we are to minimize boil-off losses (which require fewer more rounded tanks that take up more space but minimize surace area). This hab area is quite big (~200m^3!). For a maximum crew of 4 for 6+ months (for the surface mission return leg) the lower limit may be aroun 80m^3. So there should be plenty of space to work with. I'm not sure about having the crew return capsule hung off the bottom of the hab while using AG though... But I can't seem to think of a better alternative...
« Last Edit: 09/29/2010 12:20 PM by Michael Bloxham »
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