Author Topic: MCT Speculation and Discussion Thread 4  (Read 621402 times)

Offline hkultala

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Re: MCT Speculation and Discussion Thread 4
« Reply #800 on: 10/16/2015 04:20 AM »
So, how often have liquid boosters went "boom" in the US?
How important is it to protect against that one failure mode?

Antares, October 28, 2014.

Falcon 9, June 28, 2015.

That's two in the past 12 months.

At least launching from Earth, it's pretty important. As you mentioned, for early MCT missions with a small crew, send the crew up on a Dragon 2.

Dragon survived the Falcon 9 second stage failure, that was not a "boom".

If there had been humans onboard the craft, and the software would have sent the command to open the parachutes, they would have survived even without LAS.

And now they've added the command to open the parachutes to their software ;)


Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #801 on: 10/16/2015 07:15 AM »
You say that a six month transfer to Mars is intolerable for passengers, so you guys are proposing that we go to these great lengths to avoid it.  And the identical six month transfer back from Mars is...  more tolerable?

100 people out, mostly colonists, 15-20 back, mostly crew. Different rules.

Dragon survived the Falcon 9 second stage failure, that was not a "boom".

All RUDs are "booms", eventually.

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #802 on: 10/16/2015 07:43 AM »
You say that a six month transfer to Mars is intolerable for passengers, so you guys are proposing that we go to these great lengths to avoid it.  And the identical six month transfer back from Mars is...  more tolerable?

100 people out, mostly colonists, 15-20 back, mostly crew. Different rules.

The 100 day transfer was not about making it acceptable for people. The sole reason is doing a return flight during one launch window so MCT would be able to launch again in the next window. Elon Musk was very clear on this. In that sense any flight duration would be acceptable as long as it allows the reuse goal. That is why it applies to cargo as well as crew - economy. That would mean though if fast transfer doubles the cost or halves the payload it is no longer economic and it would be better to use slow transfers. But assuming that it mostly needs fuel to LEO and launching is cheap he has come to the conclusion that fast transfer is the economic way. If it serves to make the flight more bearable to the colonists that's an added bonus.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #803 on: 10/16/2015 08:58 AM »
Great work, but could you please break out your math a bit more rather than listing totals?  For example, what dV do you assume for Mars Ascent leg?

I described the math in the first section, for each of these I took the apihelion, perihelion values you provide, then took the mars Vinf squared it added mars escape velocity at surface squared and then take the root.  That would give you the needed escape velocity on a direct escape burn without stopping in orbit.  I did not account for any drag or gravity loss in this calculation but both should be much less then on Earth.


Also: 300 tons of propellant in Mars orbit is not a very high amount, given that you can use SEP all the way and the gear ratio is excellent on that;  If you want a short transit you have to send more launches worth of propellant to deep elliptical earth orbit for the outbound leg than to LMO for the inbound leg (using your SEP propellant tug idea), which in turn is far fewer than if you avoided DEO rendezvous altogether and stuck to LEO rendezvous only.

Using SEP it is a possibility, I should have prefaced that statement that it was a lot if it had to be brought up from mars surface in multiple loads by a tanker vehicle such as a second MCT.  I will run some numbers on delivering propellant to LMO by SEP with rendezvous their.

Impaler: I don't think Musk mentioned 100 day trajectory on the return trip, just on the way there. Also, exactly 100 is a little bit of, um, spurious precision. 102 days is essentially the same thing. (I know you know this, just want to point it out.)

Not sure SpaceX would start at LEO. A high orbit seems more realistic, as it allows you to leverage SEP without actually including SEP on MCT directly. SEP would be just used to haul up propellant from LEO. This helps reduce IMLEO a LOT.

But yeah, I still think MCT will start on the surface of Mars and go straight to Earth, with a much-longer-than-100-day trajectory.

I don't think we will actually see 100 day transits mainly do to capture g-force limitations, Musk may have wanted that for archiving a 1 synod mission but I'm not really seeing a viable means to that particularly early in the exploration.  I'm focusing on what I think may be a sweet spot at 150 days, a month faster then the previous 'best' of 180 days in mainstream studies but not the blazing 100 day transit.

The use of SEP as a leveraging tool on a MCT vehicle which is itself fully chem powered is what I've tried to demonstrate and I think it's clear that a small MCT with modest DeltaV when combined with SEP can do just about any conceivable outbound trajectory and transit time that the really large IBMCT concepts could achieve from LEO if not faster ones.

The ability to do direct earth return from mars surface on a slow hohmann comes in at just over 6 km/s, as I've said this is just within possible propellant fractions.  But unless the advocate of such a trajectory also embraces some form of radical propellant less aerocapture for Earth then your not going to survive re-entry their.


You say that a six month transfer to Mars is intolerable for passengers, so you guys are proposing that we go to these great lengths to avoid it.  And the identical six month transfer back from Mars is...  more tolerable?

Agreed, and I do not think this issue can be brushed away by claiming that their are few (or no) return passengers.  All trips to mars will come with FREE return according to Musk, and I fully expect all personnel to rotate in and out at a rate that is so close to 1:1 that it might as well be that.

Remember out whole REASON for fast transit is health and cumulative radiation exposure so inbound/outbound time are completely equal in harm and concern.  And if we are worried about physiological issues due to confinement/stress etc etc, these are likely to actually be worse on the return because of accumulated stress of being on mission for some 3 years by this point.


Some further calculations

5022 m/s escape velocity on mars surface
4880 m/s escape velocity from 200 km mars
3451 m/s orbital velocity 200 km circular mars

Rough analysis looks like to do the ~150 day return will require a 2.5 to 1 wet/dry ratio from Mars orbit.  As my MCT concept is for a vehicle which would have dry mass of 100 mT at this point we need 150 mT of propellants which I think might be deliverable by SEP.  This would provide a mission with 3 SEP tugs, one to move the MCT to EML1, one to move the outbound propellants to EML1 and a third to move another propellant load to low mars orbit.  The mission would have two refueling rendezvouses, one at EML1 and one in low mars orbit with only the later one really being critical, aka failure would result in LOC.
« Last Edit: 10/16/2015 09:05 AM by Impaler »

Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #804 on: 10/16/2015 04:59 PM »
Why is it that for every other Mars mission architecture, people want to be risk-averse and say stuff such as "landing crew in heavy payloads (dozens of tons) is too hard and risky, a 'showstopper'; we must land the crew separately and with a small, fully propulsive, dedicated lander" or "the mission must be divided into 10 or 20-ton chunks on Mars as a not-too-ambitious extension of current EDL capabilities"

and yet people here easily accept that MCT will be capable of landing dozens of people in the same vehicle that was used for the interplanetary transfer, or up to 100 tons of cargo?
« Last Edit: 10/17/2015 12:30 AM by Pipcard »

Offline Jim Davis

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Re: MCT Speculation and Discussion Thread 4
« Reply #805 on: 10/16/2015 05:11 PM »
and yet people here easily accept that MCT is going to land dozens of people and/or dozens of tons of cargo?

Because of his successes, Musk's statements, even his off the cuff remarks, receive far more credibility than they might otherwise.

If Interorbital Systems were proposing the MCT it would be greeted with snorts of derision. But Musk has succeeded so often in the past, and is saying something we all fervently want to be so, that we sometimes forget that Musk is only human after all.

Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #806 on: 10/16/2015 05:18 PM »
and yet people here easily accept that MCT is going to land dozens of people and/or dozens of tons of cargo?
Because of his successes, Musk's statements, even his off the cuff remarks, receive far more credibility than they might otherwise.

If Interorbital Systems were proposing the MCT it would be greeted with snorts of derision. But Musk has succeeded so often in the past, and is saying something we all fervently want to be so, that we sometimes forget that Musk is only human after all.
SpaceX having succeeded in launching resupply missions to the ISS as well as satellites to LEO and GTO doesn't make statements about "Mars colonization plans" (which are vastly more ambitious and difficult) any more credible.

(That doesn't mean I don't want them to succeed, however)
« Last Edit: 10/16/2015 05:23 PM by Pipcard »

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #807 on: 10/16/2015 05:25 PM »
and yet people here easily accept that MCT is going to land dozens of people and/or dozens of tons of cargo?
Because of his successes, Musk's statements, even his off the cuff remarks, receive far more credibility than they might otherwise.

If Interorbital Systems were proposing the MCT it would be greeted with snorts of derision. But Musk has succeeded so often in the past, and is saying something we all fervently want to be so, that we sometimes forget that Musk is only human after all.
SpaceX having succeeded in launching resupply missions to the ISS as well as satellites to LEO and GTO doesn't make statements about "Mars colonization plans" (which are vastly more ambitious and difficult) any more credible.

SpaceX succeeded in going from the Earth's surface to launching resupply missions to the ISS at a development cost of about one tenth NASA estimates and a fraction of a single Shuttle launch, has become highly competitive with the world's commercial launch providers, is shortly going to totally outcompete all of their designs for medium-large launch vehicles, and is a privately held company whose explicit purpose is achieving the dream of multiplanetary civilization.

All these discussions are part of a design exercise: We don't know exactly what cards Musk is holding, but we're trying to figure out what could possibly work to achieve the admittedly extreme ends he aims for.
« Last Edit: 10/16/2015 05:30 PM by Burninate »

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Re: MCT Speculation and Discussion Thread 4
« Reply #808 on: 10/16/2015 05:33 PM »
and yet people here easily accept that MCT is going to land dozens of people and/or dozens of tons of cargo?
Because of his successes, Musk's statements, even his off the cuff remarks, receive far more credibility than they might otherwise.

If Interorbital Systems were proposing the MCT it would be greeted with snorts of derision. But Musk has succeeded so often in the past, and is saying something we all fervently want to be so, that we sometimes forget that Musk is only human after all.
SpaceX having succeeded in launching resupply missions to the ISS as well as satellites to LEO and GTO doesn't make statements about "Mars colonization plans" (which are vastly more ambitious and difficult) any more credible.

You must study Mr. Musk more. He is a genius. If he says 100 tons by 2020, maybe it will be 75 tons by 2025, but by 2030 it will be 125 tons. He does not throw unfounded speculations out there, maybe optimistic but always grounded in sound basic principles/calculations.

But this is still way so much further than anyone else is aiming at. And this is where his cred is coming in.

Everyone has always in the past told him that he is crazy, he is lying, it is impossible, etc. But he has so far always delivered, maybe late, maybe not 100% but he does, and then he evolves it to surpass what he previously said. That is Mr Musk.
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Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #809 on: 10/16/2015 05:39 PM »
NASA has already landed several rovers on Mars, so they have at least some experience with Mars missions. SpaceX still hasn't even landed their own demonstration payload there yet.
« Last Edit: 10/16/2015 06:03 PM by Pipcard »

Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #810 on: 10/16/2015 05:45 PM »

SpaceX having succeeded in launching resupply missions to the ISS as well as satellites to LEO and GTO doesn't make statements about "Mars colonization plans" (which are vastly more ambitious and difficult) any more credible.


Actually it does.

Both of those you have mentioned SpaceX was the first none-govermental agency to do so. It was also the first none-govermental spaceflight agency to get to orbit with a liquid fueled rocket. They are the first space agency in the world to try stage recovery from orbital launches, and have nearly made the tech work. They are going to be one of the two leaders in the commercial crew program. They are designing the first reentry capsules that have the capacity to land on a planetary body without the intervention of parachutes. They have proven that they are remarkably failure resilient and have an exceptionally rapid rate of Research and Development.

In short, they have a record of impressive firsts that they keep aspiring to top every time they succeed. Colonising Mars is just another impressive first, and just another item on the list. Viewed from that perspective, it's entirely rational to believe SpaceX has at least mildly good odds of getting to Mars, instead of overwhelmingly negative odds.

Edit: I strongly recommend you get L2 if you haven't already for reasons such as this one - it's one of the few paywalls on the internet that is entirely worth the money.  :-X
« Last Edit: 10/16/2015 05:49 PM by The Amazing Catstronaut »
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Re: MCT Speculation and Discussion Thread 4
« Reply #811 on: 10/16/2015 05:54 PM »
NASA has already landed several rovers on Mars. SpaceX still hasn't even landed their own demonstration payload there yet.

And this has what to do with anything? They have already done so many things that none other than goverment agencies has done them... so why is that going to stop them now? If anything is going to stop them, it will be economics not technical, but that is years away. If they have come far enough by then, maybe NASA will step in and "help" (order something  :P).
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Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #812 on: 10/16/2015 06:57 PM »
[Dragon's trunk] It is 2/3 of the way to a lifeboat on a biconic MCT.

It really, really isn't.

Yes, you are correct.  I see no similarities.

Offline oiorionsbelt

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Re: MCT Speculation and Discussion Thread 4
« Reply #813 on: 10/16/2015 07:37 PM »
NASA has already landed several rovers on Mars, so they have at least some experience with Mars missions. SpaceX still hasn't even landed their own demonstration payload there yet.
To add to what others have said, they are also the first and only entity so far to do supersonic retro propulsion. In fact NASA learning from SpaceX with respect to this aspect of a Mars landing.

Quote
An innovative partnership between NASA and SpaceX is giving the U.S. space agency an early look at what it would take to land multi-ton habitats and supply caches on Mars for human explorers, while providing sophisticated infrared (IR) imagery to help the spacecraft company develop a reusable launch vehicle

http://gcd.larc.nasa.gov/2014/10/nasa-spacex-share-data-on-supersonic-retropropulsion/#.ViFQlup-yrU

Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #814 on: 10/16/2015 09:08 PM »
Oh yeah, you're right about that.

Still, imagine if that risk-averse mentality (e.g. we must have smaller payloads because EDL for larger ones is a "showstopper"; we must have separate, all-propulsive, dedicated crew landers; etc.) was applied to MCT.
« Last Edit: 10/17/2015 01:04 AM by Pipcard »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #815 on: 10/16/2015 11:06 PM »
I find the whole 'NASA risk aversion' myth so annoying and dumb.  People seem to forget all the failed NASA missions and development efforts that were so crazy ambitious.  Dose anyone remember the X-33 which was in all likelihood a less ambitious vehicle/mission profile then MCT?  NASA isn't caviler with astronaut lives and neither is SpaceX nor will they ever be if they want to actually sell tickets to normal people.

I get this sense form folks who repeat this 'risk-averse' meme that this allows them to resolve the cognitive dissidence of why we don't live in the Buck-rogers Sci-fi future they feel was promised.  It's like something out of post WWI Germany that says they WERE wining until the 'stab in the back', with the culprit being some combination of government funding inadequacy or some kind of self-loathing on the part of NASA itself. 

I do not want to get into why we are not on mars, or how much actual money or time it will actually take to do by SpaceX or anyone else.  These things are nearly impossible to figure out for the top experts in aerospace, we are groping in the dark pointlessly.  We can at best examine our speculations and assign them rank order difficulty as we try to identify better solutions then the ones we have available now.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #816 on: 10/16/2015 11:17 PM »
...

Agreed, and I do not think this issue can be brushed away by claiming that their are few (or no) return passengers.  All trips to mars will come with FREE return according to Musk, and I fully expect all personnel to rotate in and out at a rate that is so close to 1:1 that it might as well be that....
...then you aren't describing a real colonization effort. A colony isn't just a "bigger base." Either there's a much larger net flux toward Mars than away /or/ MCT won't be needing to carry 100 passengers anyway because not enough people will be going. And then you shouldn't call it MCT.

In an emergency situation, people going back to Earth in a full MCT will just have to tolerate the longer trip. But other than that, and assuming MCT is actually used to transport colonists, there will be much more space per passenger.

This thread is about MCT, not about what Impaler thinks a Mars architecture should be. As such, we need to assume the same assumptions about MCT as have been mentioned by SpaceX in the past.

You have to link the assumptions together, or the architecture doesn't close. You can't drop the "much greater influx than outflux" assumption without then changing the "~100 day transfer to Mars" (but not necessarily the other way around) assumption. And if you drop both those assumptions, then you're no longer talking about MCT in a meaningful way. No problem with that, but you should use a different thread.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #817 on: 10/16/2015 11:27 PM »
...
I don't think we will actually see 100 day transits mainly do to capture g-force limitations...
What, exactly, are you talking about? Humans can withstand 6 gees for at least 10 minutes, which is 36km/s of delta-v, usually while still doing simple tasks (unnecessary in this case, since capture/entry/reentry would be automated). Such a long period of fairly constant deceleration is possible using a lifting (re)entry, actually including negative lift. Once captured, your next trip through the atmosphere can be for landing (possibly with a skip). So you just need to get rid of your hyperbolic velocity on the first pass because the next pass will take care of actual (re)entry.

I don't think this is any more radical than anything else SpaceX is doing. And isn't more radical than Shuttle's reentry. Sure, we need a good estimate of Mars' atmospheric state, but that is also a solvable problem.

36km/s of hyperbolic velocity is much more than enough for a 100 day transfer.


...lifting (re)entry is well within the state-of-the-art for both Mars and Earth. SpaceX already does this fairly regularly with Dragon. SpaceX also has a very good heatshield material (PICA-X) that they're very familiar with. I don't have any clue why they would shoot themselves in the foot by not leveraging these things to their full potential.
« Last Edit: 10/16/2015 11:33 PM by Robotbeat »
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Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #818 on: 10/17/2015 12:02 AM »
I find the whole 'NASA risk aversion' myth so annoying and dumb.  People seem to forget all the failed NASA missions and development efforts that were so crazy ambitious.  Dose anyone remember the X-33 which was in all likelihood a less ambitious vehicle/mission profile then MCT?  NASA isn't caviler with astronaut lives and neither is SpaceX nor will they ever be if they want to actually sell tickets to normal people.

NASA is not monolithic. Nor is NASA unchanging through time. Some elements of current NASA are not risk averse, but other elements are. But risk aversion is not bad by itself, unless it is taken to the extreme. (Human spaceflight being part of that - Witness Orion/SLS, the "Apollo revived with Shuttle parts" mixture, designed to be as conservative as possible)

A side note: Your X-33 example would carry more weight if it actually flew.  ;)

Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #819 on: 10/17/2015 12:39 AM »

NASA is not monolithic. Nor is NASA unchanging through time. Some elements of current NASA are not risk averse, but other elements are. But risk aversion is not bad by itself, unless it is taken to the extreme. (Human spaceflight being part of that - Witness Orion/SLS, the "Apollo revived with Shuttle parts" mixture, designed to be as conservative as possible)

A side note: Your X-33 example would carry more weight if it actually flew.  ;)

NASA's risk-aversion historically depends on what it's asked to do (and how firmly it is asked to do it) by the government. Mercury, Gemini, Apollo and the Space Transportation System are all reflective of their time of conception. Dreams that did not become realities usually happened due to the governmental sense of risk aversion, be it technical, fiscal or regarding the value of human life, didn't equate to the requirements of the program. This is not an objectively bad thing, and whilst it (may) have kept us off the moon and away from Mars, it's also saved billions of dollars, the lives of a good few people, and the careers of many, many more. This applies by extension to every government funded agency in every democratic nation. The NASA with the greatest funding and the most impressive mandate took the widest steps - Apollo - and Apollo was a gratuitously nutty program. It's a testament to the team geniuses they had there that the moon landings occurred without greater contingencies than did actually occur.

SpaceX doesn't have as many factors to add up (they still have a ridiculous number, but not an equivalent number), so they have greater freedom in how risk-averse they can choose to be, and the answer is: very. There's a different between making extremely well educated chances and taking leaps of faith with dubious expertise, capabilities and data to support those leaps. F1 and F9 were such leaps; much of what has come after, has come on the back of greater awareness, consciousness and conscientiousness.
« Last Edit: 10/17/2015 12:44 AM by The Amazing Catstronaut »
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