Author Topic: MCT Speculation and Discussion Thread 4  (Read 610338 times)

Online RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #1000 on: 10/31/2015 02:03 PM »
Quick thought that I haven't seen anyone mention.

When ISS visiting vehicles are opened up, the crew wear masks to avoid floating debris - and this is after the loading crews make efforts to avoid contamination.

For a crew that are living out of MCT on the surface, or even just making occasional visits, ISTM they will trek in a lot more debris than the CRS vehicles suffer.

How would this be mitigated? Crew wear masks and the ventilation turned to max to filter the air as quickly as possible?

Cheers, Martin

Checkout the thread where NASA is looking into this:

Mars Surface Tunnel Element Concept

http://forum.nasaspaceflight.com/index.php?topic=38733.0

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150019637.pdf

One possibility for MCT would be to use suit port spacesuits in a suit lock airlock. Instead of the suit ports being directly exposed to the outside, they are located in an airlock. This also protects the suits from reentry and takeoff. Nothing from the surface is ever brought into the crew areas. The only exception would be a little dust getting in if an incapacitated astronaut had to be carried in from the suit lock. As long as astronauts can pull themselves out of their suits no one ever has to enter the contaminated suit lock.

Offline MP99

Re: MCT Speculation and Discussion Thread 4
« Reply #1001 on: 10/31/2015 04:27 PM »
Thanks - I had seen that, and it helps.

But I am assuming that so much habitable volume may be used throughout its stay on the surface, and humans generate a lot of debris just in day to day living and eating.

Of course, they will do the same during transit in zero g, but the transition from surface to orbit could release debris created throughout the surface stay.

I guess this is an issue that Apollo had to deal with.

Cheers, Martin

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1002 on: 10/31/2015 04:59 PM »
The reason they wear facemasks when opening CRS vehicles is because in zero-gee, stuff floats around and you could inhale it (also, there's a worry of stale air or some sort of outgasing). Even very slight gravity would mitigate those effects (there'd be natural convection and debris would pretty much just fall to the ground) such that facemasks would not be required.


...of course, if you have a lot of dust tracked in to your airlock, that would probably make some sort of simple mask a good idea even with Earth gravity.
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Offline MP99

Re: MCT Speculation and Discussion Thread 4
« Reply #1003 on: 10/31/2015 05:04 PM »


The reason they wear facemasks when opening CRS vehicles is because in zero-gee, stuff floats around and you could inhale it...

Yup, that was exactly what I was discussing. Human occupation of the MCT on Mars' surface will create a debris problem once it's launched back to LMO.

Cheers, Martin

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1004 on: 10/31/2015 05:08 PM »


The reason they wear facemasks when opening CRS vehicles is because in zero-gee, stuff floats around and you could inhale it...

Yup, that was exactly what I was discussing. Human occupation of the MCT on Mars' surface will create a debris problem once it's launched back to LMO.

Cheers, Martin
Oh, right. Once a base is set up with separate habs, you'd probably have a time when you'd clean out the MCT before launch. Swab the deck, etc. Before that, with small crews and such, you'd probably wear dust masks when you got in orbit.

Anyway, we have a VERY good historical analogue: what did Apollo do? They tracked a bunch of dust inside, since they had a one-room lander.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1005 on: 10/31/2015 05:25 PM »
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.

But anyway, it doesn't have to take a large rover. Something the size of a Bobcat can do a LOT of work, and that could be landed on Mars using Red Dragon. From Ames' Red Dragon research, Dragon would be capable of landing at least 2 tons. Bobcats weigh about 1-2 tons, and the vast majority of their mass is steel. Aerospace alloys and composites can have a strength-to-weight ratio about 20 times as great as steel, thus allowing your 2 ton mass budget to land a MUCH more capable vehicle than a typical bobcat. And like a bobcat, you'd use ballast boxes filled with Mars regolith to increase your traction. This could give you the equivalent of, say, a 10-20 ton bulldozer. Of course, you'd also need to land a solar array set to recharge from and you'd want to use lithium-sulfur batteries (500Wh/kg) or something like that.

I don't think you've actually thought through exactly how big of something you could land on Mars using Red Dragon. Given Dragon's fairly large internal volume and 1-2 ton payload capability, it could be quite significant indeed, enough to do some serious civil engineering.


And I know as a matter of fact that research is being done to see how to build a prepared landing pad using a rover and in-situ rocks. Even if we're limited to something like a Bobcat, there's a LOT that can be done, especially with the right landing site.

EDIT: See this tweet:
https://twitter.com/DrPhiltill/status/659882680943775744
« Last Edit: 10/31/2015 05:37 PM by Robotbeat »
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Offline Hauerg

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Re: MCT Speculation and Discussion Thread 4
« Reply #1006 on: 10/31/2015 05:28 PM »
15 years ago I had a bobcat working around my house. I fail to see how you get that into the and out of the Dragon 2.

Online RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #1007 on: 10/31/2015 07:03 PM »
15 years ago I had a bobcat working around my house. I fail to see how you get that into the and out of the Dragon 2.

Yeah, Red Dragon is a good idea for getting some experiments to Mars without having to design a custom lander, but something like a small robotic bulldozer will need a custom lander.

Offline cro-magnon gramps

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Re: MCT Speculation and Discussion Thread 4
« Reply #1008 on: 10/31/2015 07:42 PM »
15 years ago I had a bobcat working around my house. I fail to see how you get that into the and out of the Dragon 2.

Yeah, Red Dragon is a good idea for getting some experiments to Mars without having to design a custom lander, but something like a small robotic bulldozer will need a custom lander.

Give it to a guy from CREME; the Creme' de la Creme' and he'll find a way... anyway, whatever is happening with Red Dragon is happening behind "THE CURTAINS" at SpaceX and as we have been told, we'd think them crazy for what they are working on.. a Bobcat in a Dragon may be one of the lessor crazy stunts they want to work on... my Samhain Celebration opinion  :o in other words, you give Engineers too little credit for their ingenuity / ability to improvise a successful outcome...

Cheers and a Merry Samhain to all and sundry...

Gramps
"Hate, it has caused a lot of problems in the world, but it has not solved one yet." Maya Angelou
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Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1009 on: 10/31/2015 09:26 PM »
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across", but not in good enough detail to build a DEM with them;  That can only work with much larger surfaces, or with a big program of shadow inference at dawn/dusk.  Nevertheless, MRO is not the last imaging satellite we will send to Mars.  Let's dismiss that point.
2) MRO cannot resolve objects that are belowground before MCT's landing engines expose them.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1010 on: 10/31/2015 09:37 PM »
It seems like SpaceX went to some pain to eliminate hydrazine RCS from Falcon 9, replacing it with compressed nitrogen at a much poorer performance level.

What exactly would be used for high-frequency, low-latency thrust in an MCT?  One of the ideas I'm tossing around is supplementing the massive methalox tanks & Raptor engines with a moderate amount of hydrazine + NTO, and using SuperDracos.  This fulfills the need for RCS (which I don't think raptors are suited for), does not introduce any new engines (which SpaceX have specified: they're only working on one) and gives some thermal benefits relative to methalox alternatives.

An alternative might be one of the upcoming green propellant blends.
« Last Edit: 10/31/2015 09:40 PM by Burninate »

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1011 on: 10/31/2015 09:47 PM »
I am quite sure they will use pressure fed methalox thrusters for RCS. The pressurized tanks can be small and get refilled from the main tanks when needed. The morpheus moon lander testbed has not only the main engine but methalox thrusters too. I would not see this as a contradiction to working on one engine only. Thrusters are not engines in that sense.


Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #1012 on: 10/31/2015 09:50 PM »
It seems like SpaceX went to some pain to eliminate hydrazine RCS from Falcon 9, replacing it with compressed nitrogen at a much poorer performance level.

What exactly would be used for high-frequency, low-latency thrust in an MCT?  One of the ideas I'm tossing around is supplementing the massive methalox tanks & Raptor engines with a moderate amount of hydrazine + NTO, and using SuperDracos.  This fulfills the need for RCS (which I don't think raptors are suited for), does not introduce any new engines (which SpaceX have specified: they're only working on one) and gives some thermal benefits relative to methalox alternatives.

An alternative might be one of the upcoming green propellant blends.

The obvious answer seems to be pressurized MethaLOX, if is it practical. A smaller set of tanks pressurized at a igh pressure. But whatever is chosen, it would have to be something that could be made from ISRU at Mars.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1013 on: 10/31/2015 10:57 PM »
15 years ago I had a bobcat working around my house. I fail to see how you get that into the and out of the Dragon 2.
Red Dragon would necessarily have modifications to allow egress of equipment.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1014 on: 10/31/2015 10:59 PM »
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across"...
MRO has a resolution of ~30cm per pixel. Multiple exposures of the same site from different angles and ESPECIALLY with the Sun at high angles (thus casting long shadows) can identify hazards.
« Last Edit: 10/31/2015 11:07 PM by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1015 on: 11/01/2015 12:01 AM »
I am quite sure they will use pressure fed methalox thrusters for RCS. The pressurized tanks can be small and get refilled from the main tanks when needed. The morpheus moon lander testbed has not only the main engine but methalox thrusters too. I would not see this as a contradiction to working on one engine only. Thrusters are not engines in that sense.

Agreed, drawing off the common propellant supply and using a small pressurization vessel sounds good, but do the pumps have to do the pressurizing or would you rely on a pressurant gas obtainable on mars such as CO2, or perhaps generate gaseous O2 and Methane to pressurize each tank respectively?  The piston-pump system XCOR developed looks like it might be an interesting way to go.

I'd place these thrusters around the vehicles nose/flanks so they can perform the final touch-down without cratering the ground.
« Last Edit: 11/01/2015 01:53 AM by Impaler »

Offline Vultur

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Re: MCT Speculation and Discussion Thread 4
« Reply #1016 on: 11/01/2015 01:35 AM »
If your backing off to a hohmann transfer speed direct from mars that would indeed be ~6 km/s and comes in at a dry mass fraction of 20%, considerably more reasonable and well below the mass fraction of SSTO vehicles of any propellant, if you were to include an efficient aerocapture system like magneto-plasma I could even see this vehicle being possible all be it optimistic.  But the transit time is now no good for passengers, only cargo.

I dunno, 8-9 months in zero-g isn't THAT bad, the Russians have done 14 months and that guy (Valeri Polyakov)  was able to walk out of the capsule afterwards.

Radiation would be an issue of what regulations they have to deal with, probably not a "real" concern - those cancers develop so slow that you're talking 2050-60 medical tech ... so modern estimates of death risk from them are meaningless.

Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #1017 on: 11/01/2015 03:47 AM »
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across"...
MRO has a resolution of ~30cm per pixel. Multiple exposures of the same site from different angles and ESPECIALLY with the Sun at high angles (thus casting long shadows) can identify hazards.

Perhaps, but that kind of coverage does not exist. Yes. And even when it does, it tells you nothing about the relative strength of the surface. It could be the Martian equivalent of quicksand for all we know.

But it is still irrelevant. MCT will need to be able to land on unprepared terrain, it will be necessary to allow of off-nominal EDL and abort scenarios. So it will need a sturdy gear, and you seem reluctant for some reason to admit that.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1018 on: 11/01/2015 04:16 AM »
Probably because it's another nail in the idea that MCT will have single digit dry mass percentage.

Lets look at what landing gear will likely mass.  The primary driver is touchdown mass which would be 100 mT + vehicle dry mass + reserves from the landing propellants.  I'd call that all 200 mT, and no we do not get to deduct because of mars gravity, the vehicle has kinetic energy at touchdown which is independent of gravity.  If you expect a hover-slam landing like F9 the vehicle would experience comparable stress.

The landing legs on F9R are said to be 10% of the empty stage mass (and that's with use of carbon-fiber) so I take this as my basis for MCT legs structure.  Around 20 mT, though I expect them to telescope inside the vehicle rather then be on the surface.

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1019 on: 11/01/2015 07:57 AM »
Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across"...
MRO has a resolution of ~30cm per pixel. Multiple exposures of the same site from different angles and ESPECIALLY with the Sun at high angles (thus casting long shadows) can identify hazards.

Perhaps, but that kind of coverage does not exist. Yes. And even when it does, it tells you nothing about the relative strength of the surface. It could be the Martian equivalent of quicksand for all we know.

But it is still irrelevant. MCT will need to be able to land on unprepared terrain, it will be necessary to allow of off-nominal EDL and abort scenarios. So it will need a sturdy gear, and you seem reluctant for some reason to admit that.

You should have watched the NASA workshop for selecting Mars landing sites. They do know a lot. They have identified landing spots with a hard surface that allow for safe landing. They do have a lot of coverage for different kinds of observation already and the teams can request more observations for each of the proposed 40 landing sites. They can do very thorough orbital survey for multiple data once they have narrowed down to few potential sites.

MCT will certainly not need to be designed for landing on any not suitable off target landing sites so don't try to include such requirements into your mass budget.

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