Author Topic: MOXIE payload  (Read 10826 times)

Offline savuporo

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Re: MOXIE payload
« Reply #20 on: 10/17/2016 06:19 PM »
High combustion temperature?  Not according to these calculations (refer to the column labeled "Ctemp").

Attached is what i got. Methane burns hotter at stoichiometric mixture, but thats not the only difficulty. Can we maybe move this off to another CO rocketry thread ?
« Last Edit: 10/17/2016 06:19 PM by savuporo »
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Offline IainMcClatchie

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Re: MOXIE payload
« Reply #21 on: 10/17/2016 08:01 PM »
Can i refer you to a very recent dissertation called Risk-value optimization of performance and cost for propellant production on Mars that factors in all the previous work, including NASA DRM 3 and DRA 5 studies, everything that Dr. Rapp has written and then some, and does actual modelling and design trades ? The conclusions are well worth a read.

This paper was a good read.  Thank you.

The small bit of modelling I've done on a Mars return mission settled on essentially a three-stage return, using only a single vehicle type.  Two sit in orbit as propellant depots and one cycles from surface to orbit to fill them.  The return trip drains nearly all the propellant from one and then uses the other as a boost stage from orbit.

On-orbit propellant transfer makes it possible for a pair of vehicles to act almost like a staged vehicle... but you don't have to design, build or move the lower stage.  There is a huge amount of leverage in this scheme.

One consequence is that a three-stage return is a lot less sensitive to the Isp of the propellants than a one stage (ITS) or two stage (DRA and your referenced dissertation) return.  Maybe that's why CO-O2 propellant looks pretty decent.  With my propellant plant efficiency assumptions, methalox still beats it, but not by huge margins.  Maybe next weekend I'll incorporate the better plant efficiency assumptions from this thesis to see if there is any change.

Offline savuporo

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Re: MOXIE payload
« Reply #22 on: 04/01/2017 08:05 PM »
http://www.hou.usra.edu/meetings/lpsc2017/eposter/2410.pdf

Quote
One of the risks to MOXIE is the dust in the Martian atmosphere. To protect MOXIE
from dust, a High Efficiency Particulate Arrestance (HEPA) filter is fitted at the inlet
(Fig. 2). However, as the filter accumulates dust, the pressure drop across the filter
will increase. If the pressure drop becomes large enough, there is a risk that the CO2
compressor (a scroll pump) will not be able to deliver the required 1 atm outlet
pressure for electrolysis [2]

Although HEPA filters have been widely studied on Earth (e.g. [3]), their performance
under Martian conditions is less well known. We investigated the effect of dust
loading, filtration velocity, and ambient pressure on the filterís pressure drop.

Quote
CONCLUSION

Suspended dust at typical background levels is unlikely to produce a problematic
filter pressure drop during the operational lifetime of MOXIE (30 hours), with margin
to 300 hours. However, 30 hours is a small fraction of the total mission, during which
the filter will be continuously exposed to the environment. Therefore, long-duration
testing is needed to study dust ingestion from landing, winds, dust devils and storms.
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Offline Rei

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Re: MOXIE payload
« Reply #23 on: 04/03/2017 07:55 AM »
High combustion temperature?  Not according to these calculations (refer to the column labeled "Ctemp").

Attached are two older papers on oxygen-CO, the second of which maps out the conditions under which the combination ignites.  There are some tricks to ignition, but it does not seem an insurmountable problem.

Indeed. Not high temperature, just lousy performance and even more cryogenic than methalox. I think they were confusing CO with (CN)2. Which is pretty good performance (and non-cryogenic), but blazing hot (unless you burn it with MON rather than LOX, and/or burn it with some hydrogen-bearing material (e.g. ~5% H2, 15% CH4, etc)).

Re, LOX/CO - also, in addition to ignition challenges, it has issues with incomplete combustion because its burn is so slow.  But that can be overcome with high pressure engines. Overall, it would probably be superb for "hopper" rockets on Mars if storage doesn't prove too challenging. Possibly an ascent stage to LMO, but it'd have a poor payload fraction. I don't think it'd be particularly good for anything more than that, due to the low ISP.

I'm not always onboard with Zubrin, but I have to agree that it makes more sense if you're doing round trips to Mars just to bring hydrogen for propellant production to get a higher propellant ISP until you're able to produce it in-situ.
« Last Edit: 04/03/2017 08:00 AM by Rei »

Offline guckyfan

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Re: MOXIE payload
« Reply #24 on: 04/03/2017 07:59 AM »
I think even Zubrin has abandoned the idea of bringing H2. It was used because at the time they did not know there is so much water on Mars.

Offline Rei

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Re: MOXIE payload
« Reply #25 on: 04/03/2017 08:01 AM »
I think even Zubrin has abandoned the idea of bringing H2. It was used because at the time they did not know there is so much water on Mars.

Really? Has he written something about giving up the idea? Yes, there's a lot of water on Mars, but the TRL is 2-3. MOXIE will push the TRL on SOFCs for CO/O2 production to 8.
« Last Edit: 04/03/2017 08:02 AM by Rei »

Offline guckyfan

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Re: MOXIE payload
« Reply #26 on: 04/03/2017 01:42 PM »
TRL is really not applicable here. When we send pepople water from Mars will be used. So the required technology will have to be developed. It is not rocket science.

Offline Rei

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Re: MOXIE payload
« Reply #27 on: 04/03/2017 04:21 PM »
TRL is really not applicable here. When we send pepople water from Mars will be used. So the required technology will have to be developed. It is not rocket science.

Actually, ISRU production of propellant is very much is rocket science.

And TRL is everything when it comes to real-world space missions. I know it's fun to pretend that everything is just about launch costs and willpower, but in practice engineering, validation, and operations/analysis are the big ones.  Random example - Cassini. $3,27B. Launch vehicle: $422M. 13% of the cost of the mission. Of NASA's $2,6B, $1,442B (55%) was spent on pre-launch development (a majority of the rest on operations). And nowadays the fraction spent on launch could be far less (e.g. FH rather than Titan IVB)

Aerospace systems development is expensive.
« Last Edit: 04/03/2017 04:22 PM by Rei »

Offline guckyfan

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Re: MOXIE payload
« Reply #28 on: 04/03/2017 05:57 PM »
Are you trying to draw parallels between Cassini and a mining robot that digs through regolith?

Edit: A mining robot designed and built by SpaceX.
« Last Edit: 04/03/2017 06:06 PM by guckyfan »

Offline Rei

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Re: MOXIE payload
« Reply #29 on: 04/03/2017 09:33 PM »
Are you trying to draw parallels between Cassini and a mining robot that digs through regolith?

On a percentage basis, yes (not an absolute dollar basis). Launch costs are rarely the majority of a robotic mission, and generally a rather small fraction of it. An ever-decreasing fraction.

Quote
Edit: A mining robot designed and built by SpaceX.

Yes, because if there's anything SpaceX has experience with, it's mining and robots?


« Last Edit: 04/03/2017 09:33 PM by Rei »

Offline Dalhousie

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Re: MOXIE payload
« Reply #30 on: 04/03/2017 10:14 PM »

Edit: A mining robot designed and built by SpaceX.

Link please!  A quick Google reveals only the usual arm waving and hot air.
« Last Edit: 04/03/2017 10:33 PM by Dalhousie »
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Offline guckyfan

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Re: MOXIE payload
« Reply #31 on: 04/04/2017 06:43 AM »

Edit: A mining robot designed and built by SpaceX.

Link please!  A quick Google reveals only the usual arm waving and hot air.

Try formulating it less rude and I will consider an answer.

Offline Rei

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Re: MOXIE payload
« Reply #32 on: 04/04/2017 08:13 AM »

Edit: A mining robot designed and built by SpaceX.

Link please!  A quick Google reveals only the usual arm waving and hot air.

Try formulating it less rude and I will consider an answer.

Or you could try just answering their very simple request; either way.

Offline guckyfan

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Re: MOXIE payload
« Reply #33 on: 04/04/2017 09:57 AM »
Or you could try just answering their very simple request; either way.

Since it is you asking, I will.

Mission statements  on Red Mars in the IAC presentation.

Mission Objectives
........
Identify and characterize potential resources such as water.
........
Demonstrate key surface capabilities on Mars.

That quite clearly indicates capability to get to water and find out what is mixed into it. Not a stretch from there to a small digging robot. Certainly much less of a stretch than the comparison of Cassini to a basic mining robot.

As to the experience of SpaceX. They did the Roomba, they can do a lot of things if they set their mind to it.





Offline Dalhousie

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Re: MOXIE payload
« Reply #34 on: 04/04/2017 11:01 AM »
Or you could try just answering their very simple request; either way.

Since it is you asking, I will.

Mission statements  on Red Mars in the IAC presentation.

Mission Objectives
........
Identify and characterize potential resources such as water.
........
Demonstrate key surface capabilities on Mars.

That quite clearly indicates capability to get to water and find out what is mixed into it. Not a stretch from there to a small digging robot. Certainly much less of a stretch than the comparison of Cassini to a basic mining robot.

As to the experience of SpaceX. They did the Roomba, they can do a lot of things if they set their mind to it.

In other words. no evidence, just speculation and extrapolation.  This is what I thought.
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Offline Rei

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Re: MOXIE payload
« Reply #35 on: 04/04/2017 11:40 AM »
Mining is a very difficult activity on Earth (particularly hard rock mining, aka if you're dealing with permafrost (ice + regolith). Even on Earth, mining and ore processing equipment are very prone to wear and breakdowns.  This in environments we have well quantified. What we don't have quantified well is Martian permafrost. What dissolved compounds are in it and in what ratios? How much particulate / debris, and in what size ratios, and how does that vary as you progress through a play with respect to depth and location? How does the play thickness vary? How does sublimation affect things as you work through a play? We know very, very little about what we'd be mining through.  Just making a little rock abrasion tool or sampler arm for loose material is challenging enough. And when you're talking about enough ice to make propellant for whole fleets of ITS-sized vehicles, you're talking about large scale mining. Meaning equipment with heavy parts that are hard to replace, and where if you mess up you can knock down a wall or bend important pieces of equipment. Equipment that can kill people.

Right now, the TRL for ice mining on Mars is 2-3, according to NASA analyses of the different approaches.  There's lots of different approaches proposed. None are remotely mature.

And if the best thing you have to show that SpaceX has this under wraps is some document saying that they plan to do it, and the fact that they built a "roomba" that will probably move a couple hundred meters in its lifetime across a uniform flat steel deck with guidance sensors all around it in temperate conditions and humans present to maintain it at will in a shirtsleeves environment with every resource known to man available to them... well, that's enough said about the topic.
« Last Edit: 04/04/2017 03:50 PM by Rei »

Offline guckyfan

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Re: MOXIE payload
« Reply #36 on: 04/04/2017 12:28 PM »
So I show a document by SpaceX that says they are planning to do it and you just brush it aside as speculation?


Offline Rei

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Re: MOXIE payload
« Reply #37 on: 04/04/2017 03:49 PM »
So I show a document by SpaceX that says they are planning to do it and you just brush it aside as speculation?

You're confusing "planning to do it" with "the technology is mature and / or trivial to mature"

Offline guckyfan

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Re: MOXIE payload
« Reply #38 on: 04/04/2017 04:08 PM »
So I show a document by SpaceX that says they are planning to do it and you just brush it aside as speculation?

You're confusing "planning to do it" with "the technology is mature and / or trivial to mature"

This is moving beyond ridiculous now. Nobody has landed a mining robot on Mars yet. We all know this. I was talking about plans, I provided the proof for those plans existing. Get over it.

Offline Rei

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Re: MOXIE payload
« Reply #39 on: 04/04/2017 07:16 PM »
So I show a document by SpaceX that says they are planning to do it and you just brush it aside as speculation?

You're confusing "planning to do it" with "the technology is mature and / or trivial to mature"

This is moving beyond ridiculous now. Nobody has landed a mining robot on Mars yet. We all know this. I was talking about plans, I provided the proof for those plans existing. Get over it.

First off, please, no belligerence. There's no need for statements like "get over it" or refusing to answer questions from other people. We're all friends here, even if we have disagreements. Right?

Secondly, the statement that both Dalhousie and myself are contesting from you is " So the required technology will have to be developed. It is not rocket science."

It is rocket science. It is not trivial like you make it out to be. Nobody is contesting what SpaceX's plans are. You brought that up on your own and nobody but you has talked about it.
« Last Edit: 04/04/2017 07:18 PM by Rei »

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