Author Topic: MCT Speculation and Discussion Thread 4  (Read 613804 times)

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #920 on: 10/26/2015 05:27 AM »

If NASA is to be the first customer the concept is dead in the waterspace. It would introduce decades of delay as you yourself state. It is not going to happen.

First customer for mars bound flights, private colonists are not going to be the first humans on mars.  Astronauts from NASA along with possible international partners are the only foreseeable first mission personnel which means selling them transport services similar to how NASA buys commercial crew trips to ISS.  Their would be a decade of earlier commercial customers using BFR in cis-lunar space so SpaceX has an initial customer base without relying on NASA as the sole purchaser.

It is also unfeasible on technical grounds but no one seems willing to admit this.

How do you come to that conclusion?

Propellant mass fractions that are on par with SSTO vehicles combined with re-entry conditions that make lunar return look mild.  It's really not that hard to figure out, the proposed super-direct mission requires performance from the vehicle which is beyond that required of several different vehicles.  Higher entry speed then Apollo capsules, 4x the payload of Shuttle at the same mass or less, carrying more propellant mass then the Shuttle external tank, all able to land and take off from rough terrain without servicing.

It's the engineering equivalent of asking for a flying submarine monster-truck.
« Last Edit: 10/26/2015 05:28 AM by Impaler »

Offline sublimemarsupial

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Re: MCT Speculation and Discussion Thread 4
« Reply #921 on: 10/26/2015 05:29 AM »
The system must be viable at a lower initial volume so it can survive to ramp up over decades.

This is where your core assumption is incorrect. The system does not have to be viable on its own at all - only SpaceX as a company does. Listen to what Elon has been saying, and look at how they have operated - they will operate on a overall cash flow basis for the foreseeable future, with the revenues from their commercial Falcon launches and their internet satellite constellation funding the development and operation of the MCT fleet until it can get the marginal cost down to where the ticket price for a trip to Mars covers the operational costs of the vehicle.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #922 on: 10/26/2015 05:48 AM »
No that is not at all reasonable, they will put money generated in other areas into development but they would not RUN the whole system at a loss for decades waiting for volume to grow.  That would  suck up all their surplus from other activities leaving nothing for continued development and upgrading the system, you make a profitable system and then make it more profitable with your profits. This is completely counter to the entire history of careful and financially cautious development done by SpaceX up till now.

Like the old adage "Every complex program that has ever worked has evolved from a simple program that worked, not a complex program that didn't work".


Offline sublimemarsupial

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Re: MCT Speculation and Discussion Thread 4
« Reply #923 on: 10/26/2015 06:08 AM »
No that is not at all reasonable, they will put money generated in other areas into development but they would not RUN the whole system at a loss for decades waiting for volume to grow.  That would  suck up all their surplus from other activities leaving nothing for continued development and upgrading the system, you make a profitable system and then make it more profitable with your profits. This is completely counter to the entire history of careful and financially cautious development done by SpaceX up till now.

Like the old adage "Every complex program that has ever worked has evolved from a simple program that worked, not a complex program that didn't work".

You have a seriously flawed view of how SpaceX has operated. They have pretty much been exactly the opposite of  careful and financially cautious - a careful company wouldn't completely abandon it its only money making product (Falcon 1) in favor of an unproven and much more difficult development project (F9 v1.0), and then do that again (F9v1.0 to F9v1.1) and again (F9v1.1 to F9 Full Thrust), each time betting the farm that the new rocket will work. Nor would they have come within several days of bankruptcy in 2008. Furthermore, THE MARS COLONY IS THE ENTIRE REASON THE COMPANY EXISTS, Elon has said it over and over. Its the mission statement of the company - make life multiplanetary. Everything they have done up until now has been almost singularly focused on that objective, to the point where they have abandoned projects they have felt don't help them learn anything that would help them with Mars (Stratolaunch) and dropped projects cold as soon as they no longer have benefit for Mars (Falcon 1).

They will budget sufficiently to operate and improve Falcon and do their satellites, but all revenue on top of that will go to the Mars program and BFR+MCT, and those programs will run at a loss, 100% guaranteed.
« Last Edit: 10/26/2015 06:13 AM by sublimemarsupial »

Offline GregA

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Re: MCT Speculation and Discussion Thread 4
« Reply #924 on: 10/26/2015 07:50 AM »
Can we move the financing talk to the financing thread (or elsewhere?)

Offline oiorionsbelt

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Re: MCT Speculation and Discussion Thread 4
« Reply #925 on: 10/26/2015 02:47 PM »
Will BFR/MCT do a full mission - to Mars - refuel - back to Earth unmanned before the first crew? Elon has mentioned Droids and automation as being essential elements.

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #926 on: 10/26/2015 04:13 PM »
Will BFR/MCT do a full mission - to Mars - refuel - back to Earth unmanned before the first crew? Elon has mentioned Droids and automation as being essential elements.

It is not part of NASA's plans. Let's see what is the plan for SpaceX. They could do a test flight of MCT to the moon. Land it there and get it back to earth. If they feel they need to test two entries of the heatshield they can land the same MCT twice. Going to Mars and back would delay a manned landing at least by two years.

BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #927 on: 10/26/2015 04:26 PM »
BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #928 on: 10/26/2015 04:58 PM »
BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Not doom. They would not be colonists but they will IMO likely stay for a full synod until a replacement crew arrives. Probably a few stay on to extend their experience to the next crew. Worst case something goes wrong and they stay two synods. On the next synod they would receive spare parts to get fuel ISRU going.


Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #929 on: 10/26/2015 10:42 PM »
BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Not doom. They would not be colonists but they will IMO likely stay for a full synod until a replacement crew arrives. Probably a few stay on to extend their experience to the next crew. Worst case something goes wrong and they stay two synods. On the next synod they would receive spare parts to get fuel ISRU going.
Musk is borrowing somewhat from Mars Direct (or is it Semi-Direct?) where an already-fueled ascent vehicle is fueled up on the surface. I don't see a good reason not to have a fueled up vehicle ready when they arrive.
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Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #930 on: 10/27/2015 01:32 AM »

BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Not doom. They would not be colonists but they will IMO likely stay for a full synod until a replacement crew arrives. Probably a few stay on to extend their experience to the next crew. Worst case something goes wrong and they stay two synods. On the next synod they would receive spare parts to get fuel ISRU going.

Mostly Irrelevant, because they are not going to risk crews on the first mission and landing anyway. And the first unmanned missions need to provide a proof of concept that the ISRU equipment functions. So since they will already have hardware on the ground, making it an all-up test that produces propellant makes the most sense.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #931 on: 10/27/2015 02:24 AM »

BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Not doom. They would not be colonists but they will IMO likely stay for a full synod until a replacement crew arrives. Probably a few stay on to extend their experience to the next crew. Worst case something goes wrong and they stay two synods. On the next synod they would receive spare parts to get fuel ISRU going.

Mostly Irrelevant, because they are not going to risk crews on the first mission and landing anyway. And the first unmanned missions need to provide a proof of concept that the ISRU equipment functions. So since they will already have hardware on the ground, making it an all-up test that produces propellant makes the most sense.

Agreed, the two things that will retire the most risk are.  1) Testing the landing system and ISRU process at full scale and 2) Doing a mission to mars orbit/moons and back of the full duration of the intended surface mission.  Once these are completed (which could be simultaneously) the next logical step is the crewed surface landing.
« Last Edit: 10/27/2015 02:25 AM by Impaler »

Offline Vultur

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Re: MCT Speculation and Discussion Thread 4
« Reply #932 on: 10/27/2015 03:43 AM »
Propellant mass fractions that are on par with SSTO vehicles

Not really, there's a huge difference between what's needed for 6.5-8 km/s vs. 9.5 km/s. (I get a mass ratio of about 5.75 for 6.5 km/s, 8.6 for 8 km/s, 12.8 for 9.5 km/s).

Quote
combined with re-entry conditions that make lunar return look mild.

Yeah but they also have a better heat shield material than Apollo. 

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #933 on: 10/27/2015 04:35 AM »
Propellant mass fractions that are on par with SSTO vehicles

Not really, there's a huge difference between what's needed for 6.5-8 km/s vs. 9.5 km/s. (I get a mass ratio of about 5.75 for 6.5 km/s, 8.6 for 8 km/s, 12.8 for 9.5 km/s).

Did you remember to factor in the ISP differences, all thouse SSTO vehicles were going to use Hydro-Lox at 450 ISP.  When you use use that kind of ISP the 9.5 km/s DeltaV requires an 8.62 ratio.  So yes they are quite equivalent.

Quote
combined with re-entry conditions that make lunar return look mild.

Yeah but they also have a better heat shield material than Apollo.

Their are g-forces, entry corridor width and landing accuracy to consider as well as heating, all of which come from the underlying driver, entry velocity.  And I've never gotten any firm numbers on how massive the Dragon heat-shield is to give a quantification of how much shielding mass has dropped by or if it has dropped enough to not completely consume the entire vehicle mass on it's own.  Also my understanding is that our better ability to model super-sonic heating and greatly reduce unnecessary margins are the main drivers of today's thinner shields, not the materials.

And remember it is not any ONE performance metric that's unfeasible it is having them all together in one package.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #934 on: 10/27/2015 05:45 PM »
The only thing that might make sense for an HLV is if you had some good rationale for flying enough payloads per year that you could take FULL advantage of a full manufacturing line (multiple shifts) /and/ full advantage of full reuse (both first and second stages). To keep a production line busy, you probably need at least 10 flights per year. To do that with multiple shifts, probably about 40 first stage cores per year (and more upper stages). To make first stage reuse make sense, you need to reuse the stage at least ten times. To make full reuse make sense, you need to reuse the first stage at least 100 times and the upper stage 10-30 times. That's roughly a thousand launches per year at a minimum. Partial reuse can get by with maybe 100 launches per year, 40 per year if some are expendable. Otherwise, it's not really the economic optimum. Unless you get to 1000 launches per year, though, you probably aren't launching enough to gain anything by using an HLV. (In fact, you'd reduce your economic efficiency since you wouldn't be reusing as much.)

We do keep hearing high numbers from SpaceX. Fleets, scouting the globe for launch locations to move a lot of people. But I don't think we think in the right scale yet.


"Fleet" is a relative term.  The Space shuttle orbiters built were regularly referred to as the "fleet", but there were never more than 4 operational at any one time. 

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #935 on: 10/27/2015 06:49 PM »

Also, you're missing a really important point: There isn't actually a market for HLV launch. Nobody* wants more than about EELV Heavy capability (except for exploration, but even then it's not required). There aren't even commercial or military processing facilities for payloads over 5 meters in diameter. There isn't a commercial launch need for BFR, and NASA doesn't even have any payloads that need an HLV. F9 and Falcon Heavy are MORE than enough for all the commercial, civil, and military payloads. I've held this viewpoint for years, I've been vocal about it, and I haven't actually changed my mind on it. The only thing that might make sense for an HLV is if you had some good rationale for flying enough payloads per year that you could take FULL advantage of a full manufacturing line (multiple shifts) /and/ full advantage of full reuse (both first and second stages). To keep a production line busy, you probably need at least 10 flights per year. To do that with multiple shifts, probably about 40 first stage cores per year (and more upper stages). To make first stage reuse make sense, you need to reuse the stage at least ten times. To make full reuse make sense, you need to reuse the first stage at least 100 times and the upper stage 10-30 times. That's roughly a thousand launches per year at a minimum. Partial reuse can get by with maybe 100 launches per year, 40 per year if some are expendable. Otherwise, it's not really the economic optimum. Unless you get to 1000 launches per year, though, you probably aren't launching enough to gain anything by using an HLV. (In fact, you'd reduce your economic efficiency since you wouldn't be reusing as much.)


Customers don't care how big the rocket is they care how much it costs.  In order to get anywhere near the cost structure Musk desires the cost to launch the BFR would need to be well in the range where it would be a cost effective commercial launcher.  While it may cost more then one sat customer would be willing to pay for we already have a NORMAL practice in the industry of launching multiple satellites simultaneously so it is not at all hard to see a viable commercial sat launch market for BFR if it achieved the full reusability which is it's main goal.


Keep in mind that most likely Falcon won't be going anywhere even once BFR flies.  SpaceX is investing if 4 pads for it.  Even if they were to turn 39A into a BFR pad at some point, that's still 3 pads.  It's sized good for comsats, and you aren't putting a 4mt comsat going to GTO on something the size of Saturn V or bigger.  Multiple payloads are a possibility, but ArianeSpace is moving away from that, not doubling down on it with Ariane 6.  Otherwise, why not make an Ariane 6 that's larger than Ariane 5 and can launch 5 or 6 sats at once?  Becuase it's a bit of a challenge to get just two sats going to close enough of the same orbits that can launch together...much less more.
So I don't see comsats being launched in big clusters by BFR.  That's what F9 is for and it'll do a nice job of that.
Bigger than F9 would be an FH with 3 reusable boosters.

So what -could- BFR/MCT launch besides crewed, propellant, cargo, or depot versions of MCT?  Even a fully reusable BFR/MCT which requires only nominal processing between flights (unlike STS) will have a fair cost...but could be less than say a D4H, or an FH-E or A5-551 or whatever the heavy Vulcan variant is.   So it could be the most affordable launcher for those big government birds.
It could also do planetary probes with an expendable kick stage.
It could do a Bigelow module or large space telescope or something too, but those would be pretty rare, more one time events.  Big telescopes are expensive and you only need so many big Bigelow modules in orbit.  Cargo service to a big Bigelow station is a possible routine job for BFR though. 

So those are some potential markets for BFR, I'm pretty sure it's not going to take over F9R/FHR's markets.

Quote
... So, the Block One MCT will likely again be different from the MCT that lands the first crew on Mars June 2033 following the un-crewed MCT bringing the ISRU equipment May 2031.
I have no doubt MCT will evolve, but your timeline is not the same as SpaceX's timeline. They expect crewed missions much earlier. Which makes sense, as it doesn't make sense to develop a capability and then essentially just let it languish, sucking up money while nothing is accomplished (another mistake NASA is making, though this is mostly Congress's fault).

Which is exactly why an integrated 2nd stage is a bad idea, it makes the launcher too narrow and unable to serve any other role efficiently.  It is also unfeasible on technical grounds but no one seems willing to admit this.

Unfeasible?  I don't know about that.  How so?  Because keep in mind, even if you have a dedicated reusable 2nd stage, and MCT sits on top, that 2nd stage will still almost certainly be some sort of biconic.  It might get away with a more blunted nose and ballistic reentry like the reusable Falcon 9 upper stage, but it will still have to come in nose first...just like MCT.   And since it's likely to come back from GTO trajectories if it's to deploy sats where most customers want them deployed, it'll be coming in faster than from just LEO. 
Which an integrated MCT platform would already be designed to do.  But would a dedicated S2 be designed for that?  It'd only ever need to go to LEO for purposes of launching MCT, and taking propellant to a LEO depot.  It'd need to have HEO return capability built into it's TPS...again, like the integrated stage already will have.

Which is what RobotBeat has hit on in a few posts.  These are complementary tasks, not competing tasks.  Where there is overlap anyway, why not go with it?  Why have a separate 2nd stage that will have to be designed to do basically the same thing as the MCT basic platform?

And how will it be easier to launch unmanned payloads from a biconic 2nd stage that cannot carry people (in any version) than it is from a biconic 2nd stage that can carry people when configured in a certain way?
I'm not seeing the advantage...or how the later is technically unfeasible.  If you can do one, you should be able to do the other.  Either way, you need some sort of payload carrier that can be built in behind the nosecone cap (which would be used for docking and propellant transfer in either the integrated or non integrated concepts), or have some sort of expendable payload fairly that would mount on the nose.

The only real advantage of a dedicated 2nd stage, as best I can see, is to allow an MCT to launch unfueled with fast reaction whole-vehicle abort capability.  Something that cannot be done with the integrated design.  But that's immaterial for the purpose of launching unmanned payloads to space.




 

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #936 on: 10/27/2015 07:12 PM »
BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Not doom. They would not be colonists but they will IMO likely stay for a full synod until a replacement crew arrives. Probably a few stay on to extend their experience to the next crew. Worst case something goes wrong and they stay two synods. On the next synod they would receive spare parts to get fuel ISRU going.
Musk is borrowing somewhat from Mars Direct (or is it Semi-Direct?) where an already-fueled ascent vehicle is fueled up on the surface. I don't see a good reason not to have a fueled up vehicle ready when they arrive.

This would be safest.  However, I've always been skeptical about the ability for the MCT to produce enough propellant to refuel itself unmanned before the first crew arrives.  It'd need a lot of power, which means a lot of solar panels runrolled on the surface.  And that assumes mining moisture out of the air or bringing LH2 feedstock with it. 

Once there's a crew on the surface, they can set up large arrays of solar film all over the ground until they have enough, just unsure how that gets done prior to the first crew.

An alternative would be to send an unmanned MCT first with all of that propellant hardware, and lots of spare parts and extra provisions.  It'll sit and wait for the first crew.  Then when the first crew arrives, they can use that propellant hardware to set up shop and start production.  Their own MCT will have rovers and other manned surface equipment for exploration.   If there's a problem with their own MCT, then could fuel up the unmanned MCT and return on that.  So they'd always have a backup. 
Additionally, if another ship and crew are coming in the next launch window anyway, they will have help coming if something's going really wrong.  They'll need to get by until it arrives...but that's not quite being Marooned.  Wouldn't they be marooned until the next return window comes once they land anyway?  I don't think they can just go home whenever they want to (I'm not expert on Mars trajectories though)

If everything goes well, they'll return the next return window, while the next ship is inbound, and they'll leave a spare ship and propellant production equipment for the next crew to use.

This may be the more practical alternative, as I'm not sure how difficult it will be to fuel up a whole MCT unammned on Mars and just having it sitting there waiting for the crew when they get there.



 

Offline mvpel

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Re: MCT Speculation and Discussion Thread 4
« Reply #937 on: 10/27/2015 09:44 PM »
It could do a Bigelow module or large space telescope or something too, but those would be pretty rare, more one time events.  Big telescopes are expensive and you only need so many big Bigelow modules in orbit.

Personally, I suspect they'll be launching as many Bigelow modules as they can as fast as they can much sooner than anyone expects. A dozen nations will have their own space stations with daisy chains of Bigelow modules, International Hotels Group will become Interplanetary Hotels Group, and if the price of oil goes back up Saudi princes will vacation in private gold-plated BA-2100's. The BFR will probably be chucking BA-330's and supporting hardware to the libration points and the moon too. We used to have Raytheon Polar Services, so I reckon we'll eventually have to design a Raytheon Lunar Services logo too.

There's a reason they're working diligently towards RTLS and "gas-and-go" operations for the Falcon - if Skylon can't keep up, they'll be launching crewed and cargo Dragons one after the other all week long. You won't have to plan months in advance to see a Falcon launch, you'll just stop by Playalinda some afternoon when it's convenient for you and watch the 2:30.

This whole thread is about speculation about the technology required for building a new branch of human civilization on Mars, and absolutely nothing above is any more implausible than that. Indeed, I see it as a natural outgrowth of such a venture. The kind of technology needed to travel to and settle on Mars will enable and empower the blossoming of a spacefaring society with thousands of people in various orbits and on the lunar surface pursuing their own goals, be it profit or something else. I think that the launch of the first 100-person MCT trip to Mars will be watched by people on at least two celestial bodies.
« Last Edit: 10/27/2015 09:45 PM by mvpel »
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #938 on: 10/28/2015 01:04 AM »
An interesting all be it old study on fast transit trajectories to and FROM mars.

http://www.dtic.mil/dtic/tr/fulltext/u2/a272591.pdf

Many folks have speculated about a trajectory that would allow a one synod mission cadence rather then the traditional every other synod cadence.  Most folks are familiar with 'Opposition' type trajectories which can get you back in one synod but at the cost of spending nearly the entire synod in deep space. 

The return leg is what makes this trajectory so long and the reason is the phase angle between Earth and Mars, essentially which planet would be ahead of the other when viewed from the perspective of the sun.  Normally we depart Earth when Mars is ahead of the Earth, the vehicle leaves Earth and falls behind the Earth and meets Mars well after the Earth is past mars. 

The optimum return from mars starts with the same configuration, Earth is behind and catching up with mars, the vehicle leaves mars and move ahead of mars meeting Earth well after Earth has past Mars.  This means we can't do BOTH of these things back to back and have to wait on Mars for years in the conventional 'Conjunction' trajectory.

But if you go SO FAST that your vehicle is from a phase perspective racing ahead of Earth on the outbound flight, has a week long stop over on mars right when Earth is passing mars and then can catch-up with with Earth on the return flight it becomes possible to do.  The velocities are very near solar-escape though and the transit time is a mind blowing 76 days each way.

The DeltaV from LEO for the outbound leg is around 8 km/s but the mars return is 16 km/s and that's from mars orbit not the surface.  Entry velocities are also off the charts, 18.8 km/s at mars, 15.4 km/s at Earth.  These are far beyond what even the most optimistic people could believe in.

It is interesting to note that at Hohmann transfer speeds the departure DeltaV and Entry velocity are higher at Earth then corresponding departure DeltaV and entry velocities at Mars.  As speed increases the DeltaV and entry velocities go up at both Earth and Mars, but they go up FASTER at Mars and entry velocities reach parity at 12.9 km/s for 106 day transfer, note that this requires much more velocity to be shed at mars so dose not represent equal difficulty in Aerocapture.  The DeltaV crossover point between LEO and mars orbit looks to be around 125 days at 5 km/s, and may not cross-over at all if your coming from mars surface at Hohmann bottoms out at around 4 km/s which is what you need just reach mars orbit. 

Finally for Earth return of >100 days the lower deltaV is obtained with Aphelion at Mars, where as <100 days it is with Perihelion at Earth.  For Earth departure Perihelion should always be at Earth.  So for a most discussions a simple symmetrical in/out trajectory is not the optimum.
« Last Edit: 10/28/2015 01:17 AM by Impaler »

Offline ThereIWas3

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Re: MCT Speculation and Discussion Thread 4
« Reply #939 on: 10/28/2015 01:52 AM »
The big safety reason to send the unmanned ISRU equipment first is so that if it breaks down, all the humans are still back on Earth.  You don't even launch the crew until you know that the ISRU worked and the fuel (and other stuff, like water and oxygen) is in storage.
"If you want to build a ship, don’t drum up people to collect wood and don’t assign them tasks and work, but rather teach them to long for the endless immensity of the sea" - Antoine de Saint-Exupéry

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