Author Topic: MCT Speculation and Discussion Thread 4  (Read 504140 times)

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1820 on: 03/03/2016 04:19 PM »
Back to BFR/MCT. I believe I have heard about MCT using densified subcooled propellant but may remember wrong. The discussion about the SES flight showed that subcooling is not compatible with self pressurizing. So what do you think? Falcon 9 needs densification to have more propellant in the available volume. MCT would not be volume restricted in the same way so it seems to me they will not use subcooling to enable self pressurizing.

Offline R7

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Re: MCT Speculation and Discussion Thread 4
« Reply #1821 on: 03/03/2016 04:40 PM »
The discussion about the SES flight showed that subcooling is not compatible with self pressurizing.

Subcooled prop won't work with VaPak style self pressurization but it does not prevent autogenous pressurization where the propellant is pumped by the engine and then some of it gets boiled and ducted back to the prop tank to keep it pressurized.
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Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1822 on: 03/03/2016 05:55 PM »
 My understanding from what I researched (for my model), for long term storage in zero g requires autogenous pressurization with either ullage motors and special channels (to utilize surface tension to keep the propellant together), or an inflating bladder.  The point of the pressurization is to get the propellant to the pump intake.

In my model, the main tanks will be the first method and the RCS would be the second method.  To maintain the pressures, a ICE (part of IVF) running compressors, etc. to cool and pressurize the system.  The CO2 produced could be used in the RCS tanks bladders and slush tanks with excess vented.

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1823 on: 03/03/2016 07:07 PM »
Subcooled prop won't work with VaPak style self pressurization but it does not prevent autogenous pressurization where the propellant is pumped by the engine and then some of it gets boiled and ducted back to the prop tank to keep it pressurized.

Thanks for the explanation. Do I understand this correctly? The tanks would be brought to flight pressure with inert gas, probably from ground support equipment. Then in flight the pressure would be maintained using hot propellant from the engines?

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1824 on: 03/03/2016 08:08 PM »
Subcooled prop won't work with VaPak style self pressurization but it does not prevent autogenous pressurization where the propellant is pumped by the engine and then some of it gets boiled and ducted back to the prop tank to keep it pressurized.

Thanks for the explanation. Do I understand this correctly? The tanks would be brought to flight pressure with inert gas, probably from ground support equipment. Then in flight the pressure would be maintained using hot propellant from the engines?
Correct, and that's basically how it's ALREADY done, except you'd use hot/warm methane/oxygen instead of hot/warm helium for the system we're talking about.
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Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1825 on: 03/04/2016 07:16 PM »
A speculation piece re the MCT on SpaceFlightInsider.com

http://www.spaceflightinsider.com/organizations/space-exploration-technologies/spacexs-mars-colonial-transporter-rumors-realities/
Note the kicker at the end

"his facility will be powered by a compact nuclear reactor (6 meters tall and 5 meters in diameter) "

If people the BFR & MCT are going to cost a lot, wait till they see the fill for that
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1826 on: 03/05/2016 03:24 AM »
Right. Doesn't have to be a lot, should be less than BFR/MCT. Small modular reactors are supposed to be around $5000/kW (much of that site fees, etc), and I expect SpaceX would be working with some other company, so there'd be development cost sharing for the reactor portion. There are some as small as 11MWe, so about the right size.

...got to solve that heat transfer problem, though, with Mars' thin atmosphere.
This article

http://www.theguardian.com/environment/2015/nov/24/mini-nuclear-reactors-answer-to-climate-change-crisis

from the UK quotes a Rolly Royce engineer (who develop British navy reactors) that SMR's will need about £500m to do the DDT&E with a market of 40-70 units. That's $710m.

While these designs are relatively small they are not mass constrained and may be surprisingly heavy.

The real question would be can an Earth based SMR design be adapted for Mars, because the market for Mars specific inits will be very small.  :(

OTOH like IVF "waste" heat is (potentially) a valuable resource for site heating, ice melting and some lower temp chemical reactions, softening plastics etc.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Offline Vultur

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Re: MCT Speculation and Discussion Thread 4
« Reply #1827 on: 03/05/2016 04:49 AM »
What about getting the permits to launch a nuclear reactor, though?

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #1828 on: 03/05/2016 07:16 AM »
What about getting the permits to launch a nuclear reactor, though?

Why would that be difficult? Provided you haven't run it before launch, it's a big lump of metal and ceramic, with some low-level radioactive fuel which is routinely transported around the world. (And the fuel rods/pellets can be launch separately from the reactor itself.) Should be easier than getting permission to launch an RTG.

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1829 on: 03/05/2016 07:57 AM »
Only the fuel would need permission for launch. And you'd likely want a high burn-up ratio. That means either highly enriched uranium or a partially breeding/high-burn-up design.

To ensure safety, fuel would likely be encased in steel and perhaps even launched in a Dragon with abort capability.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline sghill

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Re: MCT Speculation and Discussion Thread 4
« Reply #1830 on: 03/05/2016 12:32 PM »
I was in institution-scale solar for years. There's a bunch of over thinking the MCT ground use-panels on this thread (plus it's OT, we have a thread for solar panels on Mars in that area).

Instead of complicated schemes to deploy PV panels or schemes like reflectors to get more power out them, it is far easier and cheaper to just have a longer spool of thin film panels to make up for inefficiencies.

Additionally,  no automated unfurling system is needed. Just set the spool on the ground and roll it out- over the rocks and everything, then plug it in to the junction box (on board power will be DC). Hammer in some ground stakes every 2m.

A UV coating will be needed. They make that stuff in "space application" strength, so there's no new technology there.

Quote
...However, while fine in space, I do have to ask how you intend to structurally support all those PV panels while the MCT is on the martian surface?  They'd have to have support arms underneath, or else lay flat on the dirt and roll out like a tongue ...

I absolutely NAILED this one last year!

http://www.nasa.gov/mission_pages/station/research/experiments/2139.html

« Last Edit: 03/05/2016 12:37 PM by sghill »
Bring the thunder Elon!

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1831 on: 03/05/2016 11:02 PM »
Although I like and agree with your idea (Cooper at MIT published a paper on the topic), I'm not sure ROSA shows you're such a prophet. Roll-out arrays were used originally for Hubble.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1832 on: 03/06/2016 03:20 AM »
I was in institution-scale solar for years. There's a bunch of over thinking the MCT ground use-panels on this thread (plus it's OT, we have a thread for solar panels on Mars in that area).

Instead of complicated schemes to deploy PV panels or schemes like reflectors to get more power out them, it is far easier and cheaper to just have a longer spool of thin film panels to make up for inefficiencies.

Additionally,  no automated unfurling system is needed. Just set the spool on the ground and roll it out- over the rocks and everything, then plug it in to the junction box (on board power will be DC). Hammer in some ground stakes every 2m.

A UV coating will be needed. They make that stuff in "space application" strength, so there's no new technology there.

Quote
...However, while fine in space, I do have to ask how you intend to structurally support all those PV panels while the MCT is on the martian surface?  They'd have to have support arms underneath, or else lay flat on the dirt and roll out like a tongue ...

I absolutely NAILED this one last year!

http://www.nasa.gov/mission_pages/station/research/experiments/2139.html

erm...

Offline TomH

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Re: MCT Speculation and Discussion Thread 4
« Reply #1833 on: 03/07/2016 06:30 PM »
Back to BFR/MCT. I believe I have heard about MCT using densified subcooled propellant but may remember wrong. ...MCT would not be volume restricted in the same way (as F9) so it seems to me they will not use subcooling to enable self pressurizing.

This brings up a related point in my mind.

Obviously, ISRU will be used to manufacture prop on Mars. Given the constraints of being on Mars (low density atmosphere, limited power supply) vs. being on Earth, how much more difficult would it be to super-cool/densify the prop as opposed to only chilling it to standard cryo temperatures. IOW, you can densify by supercooling on Earth, but is doing the extra cooling going to be more difficult on Mars due to the low density atmosphere as a heat dump and by not being on a massive power grid?

If it is a problem, could BFS use super cryo temp on Earth launch, but only normal cryo temp. on Mars launch?
« Last Edit: 03/07/2016 06:42 PM by TomH »

Offline R7

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Re: MCT Speculation and Discussion Thread 4
« Reply #1834 on: 03/07/2016 07:26 PM »
'Subcooling' is actually easier on Mars because the sub part refers to temperatures below the nominal boiling point at 1atm. Or boiling points at subatmospheric pressures. On Mars the low pressure of ambient atmosphere means you can drop pressures inside your LV (during prop load) and storage tanks below 1atm without fear of imploding things. Wiki says average surface pressure on Mars is 600Pa. LOX boils at 59K in this pressure, only five Kelvins above freezing point.
« Last Edit: 03/07/2016 07:28 PM by R7 »
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Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1835 on: 03/07/2016 07:30 PM »
However that still leaves the problems of dust storms for solar arrays

http://www.nasa.gov/feature/goddard/the-fact-and-fiction-of-martian-dust-storms

It looks like you'd have to wait it out, but it could be weeks or months worst case.

However this really comes under payloads for an MCT.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Offline TomH

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Re: MCT Speculation and Discussion Thread 4
« Reply #1836 on: 03/07/2016 08:02 PM »
'Subcooling' is actually easier on Mars because the sub part refers to temperatures below the nominal boiling point at 1atm. Or boiling points at subatmospheric pressures. On Mars the low pressure of ambient atmosphere means you can drop pressures inside your LV (during prop load) and storage tanks below 1atm without fear of imploding things. Wiki says average surface pressure on Mars is 600Pa. LOX boils at 59K in this pressure, only five Kelvins above freezing point.

I am aware of the Ideal Gas Law and how that works. I didn't know there's only 5 degree K difference between the two state changes. How much difference is there for methane? Also, once you hit the state change temperature between liquid and freezing, how much enthalpy of state change is there?  i.e. how much do you have to worry about a shock that solidifies the liquid? As either of these enters the enthalpy of state change to solid, do they expand, contract, remain same volume? You surely wouldn't want to tip over into solid, especially if it expands. A cracked tank would be catastrophic.

In any case, it sounds like the lower atmospheric pressure of Mars will not allow the liquids to be densified as much there, thus the energy density will be less? It also sounds like you need to be really careful about keeping the O2 between those state change temps on Mars due to the narrow temperature difference and not having the degree of mechanical control you have over the process on Earth.

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Re: MCT Speculation and Discussion Thread 4
« Reply #1837 on: 03/07/2016 08:16 PM »
They will have plenty of nitrogen from processing the atmosphere for CO2. Venting liquid nitrogen to near vacuum Mars atmosphere can provide subcooling. If they want to go through a complex process like this on Mars is another matter.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1838 on: 03/07/2016 09:50 PM »
'Subcooling' is actually easier on Mars because the sub part refers to temperatures below the nominal boiling point at 1atm. Or boiling points at subatmospheric pressures. On Mars the low pressure of ambient atmosphere means you can drop pressures inside your LV (during prop load) and storage tanks below 1atm without fear of imploding things. Wiki says average surface pressure on Mars is 600Pa. LOX boils at 59K in this pressure, only five Kelvins above freezing point.

Can I get a factcheck / primer on this?

Is 'slush propellant' the same concept as 'subcooled propellant', or is it a subset?  Does propellant ever actually see 1atm?

Offline john smith 19

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Re: MCT Speculation and Discussion Thread 4
« Reply #1839 on: 03/08/2016 09:24 AM »
What about getting the permits to launch a nuclear reactor, though?

Why would that be difficult? Provided you haven't run it before launch, it's a big lump of metal and ceramic, with some low-level radioactive fuel which is routinely transported around the world. (And the fuel rods/pellets can be launch separately from the reactor itself.) Should be easier than getting permission to launch an RTG.
That's pretty wishful thinking.

Historically space reactors have used HEU IE bomb grade enriched Uranium which makes the fuel very expensive and governments very twitchy about who uses and who has it. The reactors themselves will probably need to meet standards for on orbit radiation affecting other payloads as they pass by them so they don't fry other peoples electronics as they get where they're going. If launched loaded with fuel extensive modelling will be needed to show it won't go critical if it crashes in the sea, given seawater makes a good moderator. This includes if the coolant (even a molten metal that will be frozen at launch) is fully replaced by seawater.

Ground reactor certification has also been geared toward big static power generators which have issues which (in principal) small ones can avoid.

And of course there is the market for the design.

When you've done all that work how many? 2? 4? 10?

The nearest "off the shelf" you could get to this would be the units in nuclear submarines.  These units are roughly in the 10s of MW range (so plenty of power) and historically have been sealed-for-life (I think modern ones are refuelable about every decade)  but expect a very plentiful supply of seawater and because of their use are highly classified. I've no idea what one weighs but being for use in submarines mass was not a key driver.

Has any small reactor reached prototype stage yet? I mean actually built. Toshiba have been talking about their 4S design but AFAIK the only small reactor design that's gone critical was a pebble bed design in South Africa.


I mean what are current figures of merit for PV arrays and radiators? In 2008 80-100W/Kg for a rigid array was SoA.  The same report gave thin film systems around 2000W/Kg It lists ISS as roughly 1W/Kg, a staggeringly low number IMHO.

http://www.spacefuture.com/archiveearly_commercial_demonstration_of_space_solar_power_using_ultra_lightweight_arrays.shtml
The MIT report on a potential 6Kw/Kg is interesting. That would make the ISS array weigh about 36Kg. However t there is much more to a full array than just the blanket.

A key question would be should such an array be able to survive launches & landings?

In principal given the MIT technique uses high vacuum (readily available on orbit) you could make them single use and discard after every trip. Attaching them to the MCT on orbit for the trip and setting up a PV array mfg unit in Mars orbit for the return journey.

I'm not advocating it. I merely point it out as an option. Seems wasteful but if you can recycle the materials after use you get a fresh array for each journey. A copy of the array mfg unit would probably be needed to mfg cells for Mars, which could be more robust or also single use (during the visit).

Assuming a reusable blanket (the conservative option) you're going to need a)Storage containers b)Unroll mechanism c)Roll up mechanism and (probably) d) Power transfer coupling so the array can track the sun independently of MCT orientation. All of which will knock down specific power.

Some of these can be varied, for example the aspect ratio of the array will affect the shape (but not the overall volume) of the storage box, which has implications on materials selection for the box, array stiffness and surface area of the MCT taken up by the array storage versus other uses for the same surface, like radiators, antenna etc.

Note that a transformer based coupling design from NASA and the University of Bangor in Wales has shown data transfer rates in the mbs and power transfer in the 100s of Kw with no rubbing contacts.

Note that even if this reduced array specific power 6x (using the MIT technology) it would still be 1000x better than ISS specific power (if the figures in the original article are correct), provided the array itself can survive launch and landing.  :(

Which sounds like a good candidate for a small test payload for a recoverable F9 first stage to carry.

« Last Edit: 03/08/2016 09:30 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

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