Author Topic: MCT Speculation and Discussion Thread 4  (Read 566618 times)

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1880 on: 04/03/2016 02:32 PM »
The Morpheus moon lander testbed uses methane/LOX RCS thrusters and does just fine. That problem is solvable and I am convinced they will not use another fuel for that purpose.

Will they use sparkplugs or laser igniters? The russians are working on or already have laser igniters. Spark plugs do an impressive number of ignitions in ICE motors.

Online AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #1881 on: 04/03/2016 03:37 PM »
An ICE is a really bad idea. Batteries work great. Solar panels also work great. 100 days is much too long to be using a ICE. An ICE throws away 70-80% of your energy. At least a fuel cell only throws away half. And you already have to throw away about half your energy to produce the methane and oxygen in the first place. So you're left with a round-trip efficiency of between 10 and 25%, ie you're left with only one tenth to one fourth of the energy you started with. Bad bad bad. Solar panels, on the other hand, are producing energy and are also improving all the time.

I take it this applies to ACES IVF system as well? AIUI, its powered by a Roush Racing built ICE.

It's hard to imagine Elon Musk taking SpaceX down the internal combustion engine road (i.e., Tesla, Giga-battery factories, Solar City, ZBO Methlox, minimal mass-to-orbit limitations, etc.), but the remaining ACES/IVF concepts are great and almost can be assumed to be part of BFS/MCT.
« Last Edit: 04/03/2016 03:56 PM by AncientU »
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Online kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1882 on: 04/04/2016 12:36 AM »
It's hard to imagine Elon Musk taking SpaceX down the internal combustion engine road (i.e., Tesla, Giga-battery factories, Solar City, ZBO Methlox, minimal mass-to-orbit limitations, etc.), but the remaining ACES/IVF concepts are great and almost can be assumed to be part of BFS/MCT.
Elon did say that you can make all modes of transportation electric on the exception of rockets.  A rocket engine by definition is a combustion engine, adding an internal combustion engine to MCT is no big deal.

Kaoru

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1883 on: 04/04/2016 12:53 AM »
It's hard to imagine Elon Musk taking SpaceX down the internal combustion engine road (i.e., Tesla, Giga-battery factories, Solar City, ZBO Methlox, minimal mass-to-orbit limitations, etc.), but the remaining ACES/IVF concepts are great and almost can be assumed to be part of BFS/MCT.
Elon did say that you can make all modes of transportation electric on the exception of rockets.  A rocket engine by definition is a combustion engine, adding an internal combustion engine to MCT is no big deal.

Kaoru

I imagine the advantage of using an ICE is much bigger with LH/LOX than methane/LOX. It is not that hard to get methane/LOX to zero boil off and purely for electric power I believe solar is the better solution, especially beyond LEO.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #1884 on: 04/04/2016 01:00 AM »
It's hard to imagine Elon Musk taking SpaceX down the internal combustion engine road (i.e., Tesla, Giga-battery factories, Solar City, ZBO Methlox, minimal mass-to-orbit limitations, etc.), but the remaining ACES/IVF concepts are great and almost can be assumed to be part of BFS/MCT.
Elon did say that you can make all modes of transportation electric on the exception of rockets.  A rocket engine by definition is a combustion engine, adding an internal combustion engine to MCT is no big deal.

Kaoru

I imagine the advantage of using an ICE is much bigger with LH/LOX than methane/LOX. It is not that hard to get methane/LOX to zero boil off and purely for electric power I believe solar is the better solution, especially beyond LEO.

Hmm I think LH/LOX makes for better efficiency in a fuel cell than ICE and methane/lox could be used that way too, however there are lots of methane powered diesels out there.
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!

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1885 on: 04/04/2016 02:12 AM »
ICE is super dumb for MCT.

The specific energy of methane with stoic oxygen (best case) is 11MJ/kg. At an optimistic 33% efficiency, it's 3.7MJ/kg of electricity (A lithium-ion battery is 1MJ/kg, by the way, though there are some better ones in the lab). You know how long it'd take a 120W/kg solar array to make that much electricity? Less than 9 hours. And that's assuming the actual ICE and dynamo and tanks are massless!

Using an ICE (or even a fuel cell) to provide power for 100 days when you have access to solar energy without any clouds is the height of stupidity. Just use a solar panel! It's literally over a hundred times better!
« Last Edit: 04/04/2016 02:16 AM by Robotbeat »
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Offline lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #1886 on: 04/04/2016 02:39 AM »
It's hard to imagine Elon Musk taking SpaceX down the internal combustion engine road (i.e., Tesla, Giga-battery factories, Solar City, ZBO Methlox, minimal mass-to-orbit limitations, etc.), but the remaining ACES/IVF concepts are great and almost can be assumed to be part of BFS/MCT.
Elon did say that you can make all modes of transportation electric on the exception of rockets.  A rocket engine by definition is a combustion engine, adding an internal combustion engine to MCT is no big deal.

Kaoru

Yes it is.  A typical orbital insertion burn for MCT uses 700 tonnes of propellant, producing 15 GW for 320 seconds.
A short transit of 150 days to Mars is 12 960 000 seconds.  divide 15 GW by the travel time and you will find that the same 700 tonnes will only produce a continuous output of 300 kW.  And that's 300 kW of heat.  The electrical power will be about 100 to 130 kW.  So you need to burn 700 tonnes of methane and oxygen to produce 100 kW continuously.
With solar cells, supposing 4 kg/m2 (conservative) 800 m2, or 3.2 tonnes of cells, will produce 260 kW continuously at Earth, and still produce 100 kW when you reach Mars.
ICE just don't make sense.  700+ tonnes compared to 3 or 4 tonnes.

It does make for large panels though, and likely a pain to deploy and furl in.  But certainly doable.



Online kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1887 on: 04/04/2016 05:58 PM »
Of course, I have no special insight or secret sauce for knowing the power requirements for MCT.  However, doing a scale model is providing insight on how large and number of solar panels are possible (assuming roll-up/flexible panels with good efficiency).  Look at the ISS, its panels are huge for just 6 people and modest demand.  MCT will have a huge demand for energy (IVF/ISRU/Sabatier reactor) both on orbit and on surface.  Given the requirements of having panels deployed on orbit AND ON Mars surface, there's not enough to generate the necessary energy and/or impractical due to the required size/surface area.  However, a combination of solar/battery power and an efficient ICE generator with offloading of pumps/compressors to ICE *may* be the secret sauce in meeting the power requirements "in the different modes".  Yes, you'll be burning CH4/O2 (fuel) for electricity and/or to run pumps/compressors but that would only be on peak/active demand.  The best analogy would be a hybrid car.

Also, fundamentally the MCT will require refuelling both from a depot and ISRU.  Obviously, the architecture is geared to provide the required energy accordingly.  Having lived up north where the only electricity is from an old diesel generator running 7/24 for months on end with fuel deliveries every 6 months, I know it can be done.  The trick is knowing how much energy is needed then planning ahead.  I speculate that using an ICE to supplement solar power/batteries and using it in on demand situations where you need mechanical energy (ie. pumps/compressors) is how the energy budget will be balanced.

Kaoru

Offline JasonAW3

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Re: MCT Speculation and Discussion Thread 4
« Reply #1888 on: 04/04/2016 07:12 PM »
Adding things like internally stored cargo

Where else would you put the cargo for a vehicle capable of EDL on a planet with an atmosphere?

As the cargo won't be returning to Earth, how about in a separate one shot landing module?
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Offline JasonAW3

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Re: MCT Speculation and Discussion Thread 4
« Reply #1889 on: 04/04/2016 07:17 PM »


Guys, what happened to "Keep It Simple Stupid"?

...

Not to disagree with the rest of your post, I'd like to suggest that by the time this thing gets built, Musk's and his engineers' concept of Simple will be interesting to behold.

Also, completely aside, I'd note that that phrase, addresses stupid, which people building MCT are not

     Never said that they were, but engineers just LOVE to add new and useful features!  As has been said. "the question isn't weather we can do a thing, the question is whether we SHOULD do a thing".

     Sometimes, people, (myself included) will look at a project and come up with some tremendously complex and unwieldy ways of doing something when a much simpler approach would be both cheaper and easier.
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Online kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1890 on: 04/05/2016 05:00 AM »
Here is the latest model of my design speculation.  For context, the attached image shows the engineering module focusing on the lower part.  Specifically I'm only showing the pressure vessel which would contain (not shown) IVF, Sabatier reactor, batteries, pumps/compressors, etc. which are serviceable.  The very lower part would be storage/cargo containing hoses/lines, etc. to hook up the systems externally/on surface or to another module via the CBM ring.  Outside the pressure vessel, would contain structure and tankage for various systems, mostly CH4, O2, CO2, etc..  The top deck (which is not done yet) will contain removable water tanks, ECLSS, and other life support systems.  Total height as shown is 26.5 meters (87 feet) which obviously does not include the payload (aka crew decks or cargo/consumables/propellants).

Kaoru

Offline lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #1891 on: 04/06/2016 02:31 AM »
Here is the latest model of my design speculation.  For context, the attached image shows the engineering module focusing on the lower part.  Specifically I'm only showing the pressure vessel which would contain (not shown) IVF, Sabatier reactor, batteries, pumps/compressors, etc. which are serviceable.  The very lower part would be storage/cargo containing hoses/lines, etc. to hook up the systems externally/on surface or to another module via the CBM ring.  Outside the pressure vessel, would contain structure and tankage for various systems, mostly CH4, O2, CO2, etc..  The top deck (which is not done yet) will contain removable water tanks, ECLSS, and other life support systems.  Total height as shown is 26.5 meters (87 feet) which obviously does not include the payload (aka crew decks or cargo/consumables/propellants).

Kaoru

A 10m core diameter?  Have you provided for extra insulation for the tanks?
Where does the cargo go?  And how does it all fit on the BFR?

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #1892 on: 04/06/2016 04:03 PM »
Elon has said the Raptor thrust would not be the previously cited 1.5 million lbf but would be "over 230 metric tons" or around 515 Klbf.  Optimal point for T/W ratio for an engine compared to the previous 3x greater design point.

SPECULATION:
Given that rival Bezos is in the news again with another successful re-use of his BE-3 engine rocket and that the Blue Origin BE-4 methalox engine is reported to have 550 Klbf thrust, I wonder if Elon's September reveal will have Raptor at higher than 515 Klbf, maybe ~600 Klbf?  Reduces the ~27 engine BFR to the low 20s at similar total thrust.
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1893 on: 04/07/2016 08:03 AM »
I see no reason for Raptor thrust or any other part of Musks design to change in response to Bezos's rocket design, if anything the comparable thrust levels mean both engines could be interchangeable on ULA's Vulcan which the Airforce would would look upon very favorably.

Offline Craig_VG

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Re: MCT Speculation and Discussion Thread 4
« Reply #1894 on: 04/09/2016 01:26 AM »
Hi! Elon just said this on Twitter, do we think he could be talking below the $500,000 point?

https://twitter.com/elonmusk/status/718598761832968192

"Tickets to orbital hotels, the moon and Mars will be a lot less than people think."

Offline Oli

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Re: MCT Speculation and Discussion Thread 4
« Reply #1895 on: 04/09/2016 12:59 PM »
Hi! Elon just said this on Twitter, do we think he could be talking below the $500,000 point?

https://twitter.com/elonmusk/status/718598761832968192

"Tickets to orbital hotels, the moon and Mars will be a lot less than people think."

First time Elon talking about orbital hotels and the moon, to my knowledge. Might indicate a shift towards more "attainable" goals. As for "what people think". NASA will pay $58m per seat on average to LEO. That's the reality.
« Last Edit: 04/09/2016 12:59 PM by Oli »

Offline su27k

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Re: MCT Speculation and Discussion Thread 4
« Reply #1896 on: 04/09/2016 01:56 PM »
Hi! Elon just said this on Twitter, do we think he could be talking below the $500,000 point?

https://twitter.com/elonmusk/status/718598761832968192

"Tickets to orbital hotels, the moon and Mars will be a lot less than people think."

First time Elon talking about orbital hotels and the moon, to my knowledge.

He mentioned the Moon several times before, you can find it on http://shitelonsays.com/, a very good example that explains Moon's place perfectly is

Quote
I don't think the Moon is a necessary step, but I think if you've got a rocket and spacecraft capable of going to Mars, you might as well go to the Moon as well - it's along the way. That's like crossing the English Channel, relative to Mars. So, it's like, if you have these ships that could cross the Atlantic, would you cross the English Channel? Probably. It's definitely not necessary, but you'd probably end up having a Moon base just because, like, why not, ya know.

As for space hotels, that's probably because BEAM is in this mission.

Online AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #1897 on: 04/09/2016 03:15 PM »
Hi! Elon just said this on Twitter, do we think he could be talking below the $500,000 point?

https://twitter.com/elonmusk/status/718598761832968192

"Tickets to orbital hotels, the moon and Mars will be a lot less than people think."

First time Elon talking about orbital hotels and the moon, to my knowledge. Might indicate a shift towards more "attainable" goals. As for "what people think". NASA will pay $58m per seat on average to LEO. That's the reality.

You mean revenue, right?
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Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #1898 on: 04/09/2016 03:43 PM »
https://twitter.com/NASASpaceflight/status/718570618917150725

Mr Bergin, I'd just like to take this moment to ask you to stop giving us heart attacks. We do need to sleep sometimes if we're going to make it through to 2025. Thank you.

~ Yours truly, everyone.
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Offline Ben Hawes

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Re: MCT Speculation and Discussion Thread 4
« Reply #1899 on: 04/09/2016 04:24 PM »
Chris, and I'll report my own post so Chris reads it. You seem to know things about SpaceX's Mars plans. Is it true you've kept some of it to yourself or is it all in L2?

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