Author Topic: MCT Speculation and Discussion Thread 4  (Read 621865 times)

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #240 on: 06/24/2015 04:08 AM »
PICA-X is a very good insulator.
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #241 on: 06/24/2015 04:36 AM »

If there is an issue with thermal flux to the structure / pressure vessel, a layer of insulation could be added between them over most of the area.  If it gets as hot as you say, your design will probably need this insulation layer too because your load bearing layer will lose strength at elevated temperatures.

In your design isn't the "little sheet metal wall for the payload bay" a critical and heavy load bearing member?  It has to support the load of the propellant tanks, propellant, TPS, and aerodynamic drag during launches.  If it is a combined S2 on earth launch (full prop tanks at max Q and MECO) I would say the added mass requirement is a non-starter.  If your MCT launches as an empty S3 then the load is much less but still significant.  Hard to say if Earth or Mars launch would be a higher peak load without doing the math.

For nose first reentry that wall has to support the load of the engines and cargo during max G.  You said you were using a low speed entry, so probably not a major constraint.  Are you accomplishing this propulsively with an oberth burn at Mars?  SEP deceleration?  Slower transits?  Aerobraking?  EM drive?

I think your design would be much better and lighter if you made your crew pressure vessel (and cargo containers) load bearing. They could still be modular and removable.

Structural framework would be be in the gap between the TPS and the bay wall, the TPS system would be connected to the frame at only a few points that are designed to minimized heat-transfer.

The rest of your questions indicate that your confusing my proposal with that of Lobo and the differences would easily be answered by going back a few pages and reading my posts just a few pages prior in which I provide a full description.

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1390895#msg1390895
« Last Edit: 06/24/2015 07:32 AM by Impaler »

Offline AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #242 on: 06/24/2015 04:38 PM »
So it would take one MCT depot to refuel one MCT going to Mars.  The Depot if emptied each time it goes up could come back to be refueled and checked out then.  No need to worry about boil off.  Launch the Fuel depot, launch the MCT to dock, refuel and head to Mars.  Fuel depot returns, refuels, and relaunches with the next MCT. 

I too like the idea of a cylinder MCT. It could be stretched for a fuel depot without much expense.
Not clear from your post that you need multiple refuel flights.  A single launch does not have enough propellant for a MCT TMI.  Even the most optimistic mission designs require at least 3 refuel flights.  I have seen some estimates as high as 8.

Having the depot semi-permanently in orbit with good insulation / shading and active cooling allows the operational freedom to launch propellant all throughout the synod.  As opposed to a high flight rate sprint followed by 20 months of inactivity.

A permanent depot infrastructure is the optimum as discussed frequently on this and other strings.  LEO ZBO depots are much tougher technically than HEO/EML-1/2 depots, and you are still stuck with the delta-v problem of getting out of Earth's gravity well. 

Not sure if this has been posted elsewhere or of the veracity of the quote (bold mine):
Quote
Musk and his team have already designed a methane-based rocket for the job, and the idea would be it for it to refuel once outside of the Earth’s orbit at a type of fueling station and then make a high-speed journey to Mars in three months.

http://www.bloomberg.com/news/articles/2015-06-24/elon-musk-first-martian-a-serious-conversation-about-the-future-in-space

If the quote is true, which I cannot determine independently, then it shows that there will be a DEPOT SYSTEM... deliver fuel to LEO, say with FH-R in 50mT increments, and then transfer it to outside of the Earth's orbit as staging for the MCT.  This is exactly the concept published by ULA for their ACES depot system.  (Ref below)

http://www.ulalaunch.com/uploads/docs/Published_Papers/Exploration/DepotBasedTransportationArchitecture2010.pdf

EML-2 is the optimum location delta-v-wise for depots, exploration outpost(s), and Mars departures.  EML-1 is almost as good.  I have proposed EML-1 as the refit location and EML-2 as fuel topping and departure staging point for the fleet.  Some of the fuel could be loaded in LEO, and then the vehicle immediately departs for EML-1/2 for fit-out as a hybrid approach.

« Last Edit: 06/24/2015 04:40 PM by AncientU »
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Offline AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #243 on: 06/24/2015 05:04 PM »
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)
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Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #244 on: 06/24/2015 05:07 PM »
Question:
Why do we cite EM-L1/L2 which require active stationkeeping propulsion instead of the more stable EM-L4/5 points for orbital depots?
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Offline RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #245 on: 06/24/2015 05:15 PM »
Question:
Why do we cite EM-L1/L2 which require active stationkeeping propulsion instead of the more stable EM-L4/5 points for orbital depots?

Because the goal is to get MCT to Mars. Less delta-v from L1 and especially L2.

Offline AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #246 on: 06/24/2015 05:50 PM »
Question:
Why do we cite EM-L1/L2 which require active stationkeeping propulsion instead of the more stable EM-L4/5 points for orbital depots?

Because the goal is to get MCT to Mars. Less delta-v from L1 and especially L2.

Here is an easy table:
https://en.wikipedia.org/wiki/Delta-v_budget

LEO to EML-1  3.77 (km/s)
LEO to EML-2  3.43
LEO to EML-4/5  3.97

Escape from EML-1  0.14
Escape from EML-2  0.14
Escape from EML-4/5  0.43
« Last Edit: 06/24/2015 06:03 PM by AncientU »
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #247 on: 06/24/2015 06:15 PM »
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)

Don't be pedantic.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #248 on: 06/24/2015 06:29 PM »
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)

Don't be pedantic.
It is not pedantic, as was pointed out earlier in the thread by the quote from Max Faget TPS is unnecessary because there in fact is no such flow of matter dense enough to provide any convective heating.
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 #249 on: 06/24/2015 06:56 PM »
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.
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Offline UberNobody

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Re: MCT Speculation and Discussion Thread 4
« Reply #250 on: 06/24/2015 07:48 PM »
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

The modifications to do that would be significant.  Rockets aren't legos, after all.  Not saying it isn't possible, but I think it's unlikely.

Elon was at one point considering refueling in a high elliptical orbit, which has delta-v advantages, but launch opportunity is more limited.  Who knows if he has switched to LEO or L2.  It's anybody's guess.

Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #251 on: 06/24/2015 08:15 PM »
A modified first stage seems like it would only require 3-4 vacuum Raptors instead of about 30, and no landing legs.  Once in orbit, it can be filled by any number of ways and rockets, with universal docking adapters and connections.  A full first stage size tank could probably refuel 2-3 MCT's and can be filled during the off synod.  L2 would lesson boiloff, LEO might need some shading, insulation, and/or solar powered refrigerating equipment. 

ESA, Russia, China, NASA, or any private company who wants a share of colonizing Mars might pay by helping fuel the depot(s). 

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #252 on: 06/24/2015 09:09 PM »
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)

Don't be pedantic.
It is not pedantic, as was pointed out earlier in the thread by the quote from Max Faget TPS is unnecessary because there in fact is no such flow of matter dense enough to provide any convective heating.

Yes it is pedantic, he is not disputing the content, he is nitpicking my use of terms, hot air vs plasma.  He fails to considered that I might have been using simplified terms because I'm responding to someone who doesn't have all the basics on re-entry and I might not be try to intimidate people with technical terms like describing detached shock-layers and radiative heating which DOSE heat the back side of the vehicle.

Some decade old sour-grapes quotes from Max Faget dose not constitute a counter argument to the fact that EVERY entry vehicle has had a back-shell with thermal protection.

http://www.parabolicarc.com/2014/09/01/heat-shield-installed-orion-spacecraft/

Quote
But the space shuttles traveled at 17,000 miles per hour, while Orion will be coming in at 20,000 miles per hour on this first flight test. The faster a spacecraft travels through Earth’s atmosphere, the more heat it generates. So even though the hottest the space shuttle tiles got was about 2,300 degrees Fahrenheit, the Orion back shell could get up to 3,150 degrees, despite being in a cooler area of the vehicle. - See more at: http://www.parabolicarc.com/2014/09/01/heat-shield-installed-orion-spacecraft/#sthash.eNwEh6dP.dpuf

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #253 on: 06/24/2015 09:18 PM »
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

The modifications to do that would be significant.  Rockets aren't legos, after all.  Not saying it isn't possible, but I think it's unlikely.

Elon was at one point considering refueling in a high elliptical orbit, which has delta-v advantages, but launch opportunity is more limited.  Who knows if he has switched to LEO or L2.  It's anybody's guess.
When did he mention an elliptical orbit? I had considered that as well, but have never seen Musk mention a kind of orbit. Please put it in the MCT source quotes thread.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #254 on: 06/24/2015 09:39 PM »
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)

Don't be pedantic.
It is not pedantic, as was pointed out earlier in the thread by the quote from Max Faget TPS is unnecessary because there in fact is no such flow of matter dense enough to provide any convective heating.

Well, I kinda was being pedantic.  Sorry Impaler.

Sometimes a simplified explanation becomes technically incorrect, but still can be useful.  (Full disclosure: I do this all the time with non-technical listeners to get the big picture point across.)
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Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #255 on: 06/24/2015 09:50 PM »
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)

Don't be pedantic.
It is not pedantic, as was pointed out earlier in the thread by the quote from Max Faget TPS is unnecessary because there in fact is no such flow of matter dense enough to provide any convective heating.

Yes it is pedantic, he is not disputing the content, he is nitpicking my use of terms, hot air vs plasma.  He fails to considered that I might have been using simplified terms because I'm responding to someone who doesn't have all the basics on re-entry and I might not be try to intimidate people with technical terms like describing detached shock-layers and radiative heating which DOSE heat the back side of the vehicle.

Sorry but simplifying (which might mean explaining the process) and simply misinforming (inventing an analogy to something that is in fact completely dissimilar and creates a false idea of the physics and then not even identifying the inaccuracy) is not the same.  Radiative heating is real but is protected against quite differently than convective.  If someone explained a Tesla or Prius braking as winding up a spring to slow the car down then reversing that spring to start it up again I would not feel it was pedantic to correct that.


Some decade old sour-grapes quotes from Max Faget dose not constitute a counter argument to the fact that EVERY entry vehicle has had a back-shell with thermal protection.

http://www.parabolicarc.com/2014/09/01/heat-shield-installed-orion-spacecraft/

Quote
But the space shuttles traveled at 17,000 miles per hour, while Orion will be coming in at 20,000 miles per hour on this first flight test. The faster a spacecraft travels through Earth’s atmosphere, the more heat it generates. So even though the hottest the space shuttle tiles got was about 2,300 degrees Fahrenheit, the Orion back shell could get up to 3,150 degrees, despite being in a cooler area of the vehicle. - See more at: http://www.parabolicarc.com/2014/09/01/heat-shield-installed-orion-spacecraft/#sthash.eNwEh6dP.dpuf

And if you read that article it is saying "could" and "will be tested" to actually determine how much heating those areas get and whether micro meteoroid impacts will affect it.

Note that the Max Faget comments are relevant as they were about the Apollo capsule which also re-entered at the speeds in question from your quote.

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!

Offline R7

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Re: MCT Speculation and Discussion Thread 4
« Reply #256 on: 06/24/2015 10:36 PM »
Some decade old sour-grapes quotes from Max Faget dose not constitute a counter argument to the fact that EVERY entry vehicle has had a back-shell with thermal protection.

Apollo imagery of people fishing out the capsules with leeward side in near pristine condition proves that Faget was right.

India's SRE-1 proves that you are wrong.

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Offline GORDAP

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Re: MCT Speculation and Discussion Thread 4
« Reply #257 on: 06/24/2015 10:57 PM »
Impaler, let me push back a bit against the premise of what you are pushing.  If I understand you correctly, you advocate lower speed reentry, such as from an orbit (both on Mars and Earth) than direct reentry for the MCT, primarily because then one could use metallic TPS rather than ablative TPS (i.e. PICA-X).  And that this is practically necessary to ensure high reusability and high flight rates.  Do I have that right?

But is avoiding ablative TPS really that important in the grand scheme?  Doesn't SpaceX intend to rapidly and frequently reuse the Dragon 2, which will surely have PICA-X.  What do we suppose is the answer here?  Is PICA-X something that can be de-ablated (reblated?) back on to the bottom of a capsule without too much hassle.  I'm imagining that there is an inch or so of the material, and half an inch ablates off during reentry (a little more some places, a little less others) and then then additional PICA-X is applied and added to what remains before the next flight - sort of like retreading a tire.  Or conversely, the entire backshell of PICA-X is designed and installed as a bolt on module, and a new one will be bolted onto the capsule for each flight (i.e. changing the tires).  I ask because I don't know.

But in any case, this seems to solve the problem fully, without a great deal of bother.  Surely a simpler solution than radically modifying the flight profiles to include orbital insertion on each end, which requires a great deal of additional fuel, don't you think?

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #258 on: 06/24/2015 10:57 PM »


Not sure if this has been posted elsewhere or of the veracity of the quote (bold mine):
Quote
Musk and his team have already designed a methane-based rocket for the job, and the idea would be it for it to refuel once outside of the Earth’s orbit at a type of fueling station and then make a high-speed journey to Mars in three months.

http://www.bloomberg.com/news/articles/2015-06-24/elon-musk-first-martian-a-serious-conversation-about-the-future-in-space

If the quote is true, which I cannot determine independently, then it shows that there will be a DEPOT SYSTEM... deliver fuel to LEO, say with FH-R in 50mT increments, and then transfer it to outside of the Earth's orbit as staging for the MCT.  This is exactly the concept published by ULA for their ACES depot system.  (Ref below)

http://www.ulalaunch.com/uploads/docs/Published_Papers/Exploration/DepotBasedTransportationArchitecture2010.pdf

EML-2 is the optimum location delta-v-wise for depots, exploration outpost(s), and Mars departures.  EML-1 is almost as good.  I have proposed EML-1 as the refit location and EML-2 as fuel topping and departure staging point for the fleet.  Some of the fuel could be loaded in LEO, and then the vehicle immediately departs for EML-1/2 for fit-out as a hybrid approach.

Outside of Earth's orbit?  As in outside of the Earth's orbit around the sun?  That'd have to be Earth-Sun L-2.  The Earth-Moon L-points are inside Earth's orbit half the time.  ESL1 is inside Earth orbit as well.  I Guess EML1 or EML2 work when the moon is in the correct spot.  Or outside of the orbit around the Earth?

Or was it just a misstatement, and they meant something like "out in Earth's orbit"?  A depot outside of LEO would change the look of the mission profiles as most of us have been assuming a LEO depot. 
Also means MCT would need to be able to put 100mt plus the dry mass of MCT-spacecraft into whatever L-point they are looking at.  Or would they be now looking at staging a SEP MTV like in Boeing's proposal, with the spacecraft really only then needing to get itself form Mars orbit down to the Mars surface, refuel, and back up to MArs orbit fro MOR with the MTV for the trip back to the Earth L-point, and then get itself back down on the Earth's surface? 
I guess that would mean MCT-spacecraft wouldn't need much fuel when at EArth's L-point, just enough for Mars EDL outbound, and Earth EDL inbound.  Then it fills up for Mars Ascent on the surface. 
It'd be more efficient, but also require more new hardware development. 
Although I suppose the Mars-MCT, if full at the L-point, could be the kick stage that Boeing proposed using a DCSS or something for to get the big MTV/Lander stack moving.

Also means a pretty big booster to get an MCT spacecraft plus 100mt payload all the way out to an L-point in one shot.  Or would there be LEO refueling, before heading out to the L-point?

Hmmmm...sure like to get some more on this to support or refute this.


Offline UberNobody

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Re: MCT Speculation and Discussion Thread 4
« Reply #259 on: 06/25/2015 12:53 AM »
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

The modifications to do that would be significant.  Rockets aren't legos, after all.  Not saying it isn't possible, but I think it's unlikely.

Elon was at one point considering refueling in a high elliptical orbit, which has delta-v advantages, but launch opportunity is more limited.  Who knows if he has switched to LEO or L2.  It's anybody's guess.
When did he mention an elliptical orbit? I had considered that as well, but have never seen Musk mention a kind of orbit. Please put it in the MCT source quotes thread.

I can't figure out how to quote myself, so here is a link
http://forum.nasaspaceflight.com/index.php?topic=36805.msg1352680#msg1352680

I'll put the info into the quotes thread.

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