Author Topic: MCT Speculation and Discussion Thread 4  (Read 569637 times)

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2020 on: 05/13/2016 02:17 AM »
May I ask if anyone has a conception how MCT is supposed to RETURN from Mars?

It was mentioned a few times that the return leg, surface to LMO and LMO to TEI, constitutes the most challenging aspect ('long pole') for the entire architecture.  Yet I have read almost no discussion of how this could be achieved.  Basically, there seem to be two extreme possibilities, plus a range of intermediates.

1) Mars surface is reached by a larger version of the Dragon, with engines suitable for precision landing.  But can the same engines take the craft back to orbit?

2) Mars surface is reached by a larger version of the F9R, with engines suitable for both orbital launch and precision landing.  But can such a craft launch without a launch complex and its infrastructure?  And can such a craft return to earth without replenishing propellants from a tanker in LMO?

Apologies if I have overlooked any information pertaining to these points!
Neither. Or rather, something in between.

You need maybe 6-7km/s to return to Earth from the surface of Mars. You can do that in a single stage with TPS, though it is hard.
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Re: MCT Speculation and Discussion Thread 4
« Reply #2021 on: 05/13/2016 08:08 AM »
For example, one of the chips I like to use the most in residential downlighting applications, masses 3kg per 100 units. including shipping packaging. Something even lighter, like a Bridgelux COB array comes in at 130-150 lumens per watt, ~1300-2500 lumens delivered, ....

Most while light LED units have an annoying peak around 450nm or so which is not good for the circadian rhythm (I work in this area). iirc the ISS replaced all their lighting with a custom system to attempt to simulate the changes in chromaticity that you would normally experience through the day. This is probably going to be something needed both in transit and on mars (since the changes in colour throughout the day there will be very different to earth).
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Re: MCT Speculation and Discussion Thread 4
« Reply #2022 on: 05/13/2016 01:18 PM »
Or for 400kg extra, have a backup solar array that can provide 20-40kW indefinitely. A solar array and a generator have about the same mass, but the solar array isn't going to explode, won't wear out or require maintenance or fluid, and needs no fuel and can operate indefinitely, and doesn't have exhaust.

Just. Stop. Stop trying to make "internal combustion engine in space" happen. It's not happening.


What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.
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Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #2023 on: 05/13/2016 01:34 PM »

What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.

Batteries whilst the storm lasts, shrouds to close over the panels before the storm happens/orient the panels away from the wind/roll the panels back in/put something over them. Any of these objects are less resource intensive than an ICE.
« Last Edit: 05/13/2016 01:35 PM by The Amazing Catstronaut »
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Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #2024 on: 05/13/2016 01:56 PM »
May I ask if anyone has a conception how MCT is supposed to RETURN from Mars?

It was mentioned a few times that the return leg, surface to LMO and LMO to TEI, constitutes the most challenging aspect ('long pole') for the entire architecture.  Yet I have read almost no discussion of how this could be achieved.  Basically, there seem to be two extreme possibilities, plus a range of intermediates.

1) Mars surface is reached by a larger version of the Dragon, with engines suitable for precision landing.  But can the same engines take the craft back to orbit?

2) Mars surface is reached by a larger version of the F9R, with engines suitable for both orbital launch and precision landing.  But can such a craft launch without a launch complex and its infrastructure?  And can such a craft return to earth without replenishing propellants from a tanker in LMO?

Apologies if I have overlooked any information pertaining to these points!

Well Martian ISRU helps out a great deal, and gravity and atmospheric losses on mars are considerably lower - the lowered gravity losses are especially helpful when it comes to exiting the gravity well.

As for launching without a launch complex, the craft is going to require fueling whilst on mars, and perhaps a rudimentary pad of some kind - quite likely the area will need to be cleared of potentially harmful debris that could be kicked up when the engines fire.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2025 on: 05/13/2016 02:05 PM »
Or for 400kg extra, have a backup solar array that can provide 20-40kW indefinitely. A solar array and a generator have about the same mass, but the solar array isn't going to explode, won't wear out or require maintenance or fluid, and needs no fuel and can operate indefinitely, and doesn't have exhaust.

Just. Stop. Stop trying to make "internal combustion engine in space" happen. It's not happening.


What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.
If you're landing away from the pad, you're in a survival situation. You're going to be dead very soon, power or no, without a rescue party. You may have even needed to bail out of the vehicle.

Wasting tons on the corner-case of a corner-case (in a way that still is inferior to other solutions) is not a good idea.

An internal combustion engine on MCT is a bad idea that simply won't die. People keep bringing it back up. It's a zombie idea.
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Re: MCT Speculation and Discussion Thread 4
« Reply #2026 on: 05/13/2016 02:30 PM »

What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.

Batteries whilst the storm lasts, shrouds to close over the panels before the storm happens/orient the panels away from the wind/roll the panels back in/put something over them. Any of these objects are less resource intensive than an ICE.

The limitation of a battery is that it can hold as much power as the capacity of the battery. For something that is fuelled, the limitation is the amount of fuel that you have (that can be built up in situ for a methane burner on mars). Wind's not an issue, just the dust, though there is probably an element of abrasion in the long term. (iirc the most violent storms on mars would feel light a light breeze, because the air is so thin)
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Re: MCT Speculation and Discussion Thread 4
« Reply #2027 on: 05/13/2016 02:32 PM »
Or for 400kg extra, have a backup solar array that can provide 20-40kW indefinitely. A solar array and a generator have about the same mass, but the solar array isn't going to explode, won't wear out or require maintenance or fluid, and needs no fuel and can operate indefinitely, and doesn't have exhaust.

Just. Stop. Stop trying to make "internal combustion engine in space" happen. It's not happening.


What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.
If you're landing away from the pad, you're in a survival situation. You're going to be dead very soon, power or no, without a rescue party. You may have even needed to bail out of the vehicle.

Wasting tons on the corner-case of a corner-case (in a way that still is inferior to other solutions) is not a good idea.

An internal combustion engine on MCT is a bad idea that simply won't die. People keep bringing it back up. It's a zombie idea.

even on-pad. Though that depends on what the constituents of the base are early on. You're right about it generally being useless in space, but if it's worth having one on mars, then it may as well be compatible with the rest of the infrastructure.
For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled. -- Richard Feynman

Offline baldusi

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Re: MCT Speculation and Discussion Thread 4
« Reply #2028 on: 05/13/2016 02:58 PM »
If you're landing away from the pad, you're in a survival situation. You're going to be dead very soon, power or no, without a rescue party. You may have even needed to bail out of the vehicle.

Wasting tons on the corner-case of a corner-case (in a way that still is inferior to other solutions) is not a good idea.

An internal combustion engine on MCT is a bad idea that simply won't die. People keep bringing it back up. It's a zombie idea.
You keep saying that. But there are engineering methods to define when something makes sense and when it doesn't. It's called a trade. So help him make the technical trade on mass and simply let the numbers speak for themselves.

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Re: MCT Speculation and Discussion Thread 4
« Reply #2029 on: 05/13/2016 03:03 PM »
Interesting, so what's being said is that it is impossible for a scenario, say an explosion, which both sets up an uncontrolled rotation and takes out the roll control system. This prevents the solar panels from operating with any efficiency, if at all. So you're willing to bet the life and safety of the crew of the MCT on one single mode of power generation.

I deal with critical life support where failure isn't an option, and would result in certain death. A proposal that's analogous to a single mode of power generation would simply not be  entertained.
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Re: MCT Speculation and Discussion Thread 4
« Reply #2030 on: 05/13/2016 03:05 PM »
Interesting, so what's being said is that it is impossible for a scenario, say an explosion, which both sets up an uncontrolled rotation and takes out the roll control system. This prevents the solar panels from operating with any efficiency, if at all. So you're willing to bet the life and safety of the crew of the MCT on one single mode of power generation.

I deal with critical life support where failure isn't an option, and would result in certain death. A proposal that's analogous to a single mode of power generation would simply not be  entertained.

Surely that scenario would also create problems for a liquid fuel system too, since the forces in the lines would keep changing directions. Additionally how long would you expect such a scenario to last? would it be longer than the on-board battery supply?
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2031 on: 05/13/2016 03:19 PM »
If you're landing away from the pad, you're in a survival situation. You're going to be dead very soon, power or no, without a rescue party. You may have even needed to bail out of the vehicle.

Wasting tons on the corner-case of a corner-case (in a way that still is inferior to other solutions) is not a good idea.

An internal combustion engine on MCT is a bad idea that simply won't die. People keep bringing it back up. It's a zombie idea.
You keep saying that. But there are engineering methods to define when something makes sense and when it doesn't. It's called a trade. So help him make the technical trade on mass and simply let the numbers speak for themselves.
I already have done that. Doesn't seem to matter, the zombie idea keeps coming up.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2032 on: 05/13/2016 03:26 PM »
Interesting, so what's being said is that it is impossible for a scenario, say an explosion, which both sets up an uncontrolled rotation and takes out the roll control system. This prevents the solar panels from operating with any efficiency, if at all. So you're willing to bet the life and safety of the crew of the MCT on one single mode of power generation.

I deal with critical life support where failure isn't an option, and would result in certain death. A proposal that's analogous to a single mode of power generation would simply not be  entertained.
What. I can tell you didn't actually read what I wrote, just what people snipped. I don't care that you work with critical life support systems, because your analysis is ridiculous.

When you include the overhead and the inefficiency of small IC, lithium batteries are actually superior from a mass and energy standpoint besides being far more reliable. I SHOWED THIS ABOVE (15% typical efficiency for small IC, plus methane--or diesel--operating at stoichiometric mix gets you about 400Wh/kg plus the mass of the tanks and the actual ICE itself, primary lithium can do up to 700Wh, state-of-the-art rechargable can do 300-400Wh/kg). And if you want long-term use, solar array beats everything.

The problem here is that everyone is using their intuition from Earth, where you get free oxygen (which is a kind of ISRU). Oxygen is the vast majority of the mass.

It's a freaking zombie idea. LET IT DIE.
« Last Edit: 05/13/2016 03:28 PM by Robotbeat »
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Online Johnnyhinbos

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Re: MCT Speculation and Discussion Thread 4
« Reply #2033 on: 05/13/2016 03:28 PM »

Interesting, so what's being said is that it is impossible for a scenario, say an explosion, which both sets up an uncontrolled rotation and takes out the roll control system. This prevents the solar panels from operating with any efficiency, if at all. So you're willing to bet the life and safety of the crew of the MCT on one single mode of power generation.

I deal with critical life support where failure isn't an option, and would result in certain death. A proposal that's analogous to a single mode of power generation would simply not be  entertained.

Surely that scenario would also create problems for a liquid fuel system too, since the forces in the lines would keep changing directions. Additionally how long would you expect such a scenario to last? would it be longer than the on-board battery supply?
I would expect the lines to be pressurized. And I'd expect the time to resolution to be sometime just past the capacity of the battery backup, because that's exactly how Murphy works. And yes, there's a careful balance in trade offs between redundancy and practicality. I'm not saying that an IC engine is the solution (though I could be), rather I'm saying its foolhardy to have only one method to generate power.

I dive in circumstances where if your LSS has an issue, heading to the surface is certain death. So you build in redundancy that is variable. Example: my rebreather has not one but three separate and different methods for checking on CO2 buildup. It has a chemical sensor (so think of that as the solar panels, as it would get the job done). But it also knows my metabolic rate because it counts the number of times the O2 solenoid fires. From this the amount of CO2 generated can be calculated. Completely independent of the first method. Finally, there is a series of temperature probes mounted inside the CO2 scrubber canister that are used to quantify the chemical reaction between absorbent and CO2, thereby determining efficiency of system and potential for CO2 breakthrough. Again, fully independent and functionally different.

Don't even get me started on the O2 system.

Point being, when you are in a hostile environment that a human body can not possibly survive on its own, and where's there's zero chance of someone coming to your aid, you don't put all your critical eggs in one basket...
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2034 on: 05/13/2016 03:29 PM »
Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.

NO ONE is saying not to have redundancies and margin. What we're saying is ICE is the wrong solution.
« Last Edit: 05/13/2016 03:33 PM by Robotbeat »
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Re: MCT Speculation and Discussion Thread 4
« Reply #2035 on: 05/13/2016 03:42 PM »

Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.
Sigh. I'm not sure why you are being so aggressive here. It's a conversation. I did mention that the focus is not on using an IC, rather that there should be a completely independent power generator that shares no commonality with solar.

But to answer your question, my rebreather uses three battery systems, all independent and in physically different enclosures. Each is rated to power the system longer than the consumables could last (O2, diluent, and scrubber). With the loss of one the system can feed off the others. The system uses a digital bus called DiveCAN derived from the ubiquitous auto CAN bus and even with a physical cut between main computer and O2 delivery system, O2 will continue to inject at the current set point. I also have a 100% independent system (literally everything is independent) which allows me to fly the unit manually in the advent of complete system failure. Finally there's an orifice in the O2 side that delivers, depth independent, metabolic rate O2 into the loop (0.6 l/m).

Anyway, I've no desire to argue with you. I respect your posts. I just humbly suggest, IMO, that the real MCT will no doubt have an independent power generator to solar.
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Re: MCT Speculation and Discussion Thread 4
« Reply #2036 on: 05/13/2016 03:43 PM »
Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.

NO ONE is saying not to have redundancies and margin. What we're saying is ICE is the wrong solution.

Yeah I'm struggling to think what other options there are beyond solar/battery power combo and an ICE, unless there is some useful power that can be dragged out of the cooling system (I'm assuming that there won't be nuclear power or RTG on the crew transports)
« Last Edit: 05/13/2016 03:46 PM by Jet Black »
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2037 on: 05/13/2016 03:53 PM »

Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.
Sigh. I'm not sure why you are being so aggressive here. It's a conversation. I did mention that the focus is not on using an IC, rather that there should be a completely independent power generator that shares no commonality with solar.

But to answer your question, my rebreather uses three battery systems, all independent and in physically different enclosures. Each is rated to power the system longer than the consumables could last (O2, diluent, and scrubber). With the loss of one the system can feed off the others. The system uses a digital bus called DiveCAN derived from the ubiquitous auto CAN bus and even with a physical cut between main computer and O2 delivery system, O2 will continue to inject at the current set point. I also have a 100% independent system (literally everything is independent) which allows me to fly the unit manually in the advent of complete system failure. Finally there's an orifice in the O2 side that delivers, depth independent, metabolic rate O2 into the loop (0.6 l/m).

Anyway, I've no desire to argue with you. I respect your posts. I just humbly suggest, IMO, that the real MCT will no doubt have an independent power generator to solar.
As I said, the backup would be batteries. But you'd also build-in redundancy in the solar array. For life support, no doubt you'd actually have a few oxygen candles and chemical scrubbers, or rely on the large volume of the MCT as a buffer.

EDIT: And you could have a completely passive and manually operated system for life support if you wanted. A certain type of regenerative scrubber, if you have access to vacuum, just needs some valves opened and closed. That could be done manually. You could also dispense oxygen manually as well, though that would be tougher. In any case, such things only need a tiny amount of power.
« Last Edit: 05/13/2016 03:57 PM by Robotbeat »
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Offline belegor

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Re: MCT Speculation and Discussion Thread 4
« Reply #2038 on: 05/13/2016 03:56 PM »
Is there a guess on the minimum power required to maintain basic functionality of the craft? (I.e. basic life support, basic thermal control, minimal comms, emergency lighting only, basic GNC, etc.)

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #2039 on: 05/13/2016 03:57 PM »
Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.

NO ONE is saying not to have redundancies and margin. What we're saying is ICE is the wrong solution.

Yeah I'm struggling to think what other options there are beyond solar/battery power combo and an ICE, unless there is some useful power that can be dragged out of the cooling system (I'm assuming that there won't be nuclear power or RTG on the crew transports)
Methane/oxygen fuel cells
Hydrogen/oxygen fuel cells
Stirling engine based on catalytic Methane/Oxygen reaction
Turbine based on Methane/Oxygen combustion
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

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