Author Topic: MCT Speculation and Discussion Thread 4  (Read 618191 times)

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #60 on: 06/16/2015 03:32 PM »
If the MCT is completely refueled on Mars for launch back to earth, all of the fuel will not be needed to get the TEI burn.  There will be quite a bit of fuel left.  So the MCT could fire and slow down before earth reentry, or it could slow down using aerocapture for a few orbits to slow down.  Also, there will probably be only a crew return, not 100 people.

Crew?
Why?
MCT should be able to return to Earth empty.  (And as needed provide occasional return transport for humans needing to return)

On the way out assuming several 10s of passengers it would be astounding if there were not several engineers capable of specialized training as "flight engineers" to repair anything repairable by humans.  No astronaut corps test pilots needed, just FEs similar to on the shuttle.

Crew mass & life support is wasted mass and money. 
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Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #61 on: 06/16/2015 03:39 PM »
Yeah but,..
Any chance they would use both.  We have seen the results of firing an engine in a braking burn. (F-9 booster recovery attempts)  Also they showed computer modeling of hypersonic reentry with engine firing.  ISTM the results show the engine pushes the superheated plasma from reentry, away from the spacecraft.

So say they use an appropriately sized engine to push the plasma away from the spacecraft, but the majority of the braking is done by the atmosphere.  Would lead to less wear on the pica-X heat shield and is reusable by refueling the engine.
The wear on the PICA-X is infinitesimal compared to the propellant needed to prevent it. If you already have a heatshield, you should be maximizing it's use when possible. For Mars entry, you'll still need retropropulsion while supersonic, but for Earth you should be subsonic before you start the landing burn.
« Last Edit: 06/16/2015 03:40 PM by Robotbeat »
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Online spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #62 on: 06/16/2015 04:16 PM »
I think one of the previous concerns was the high speed reentry from Mars vs orbital reentry.  They were thinking of the MCT crushing itself with the high g slowdown.  That was the reason for some retro burn before entering the atmosphere, not really about the heat shield.  From the moon the reentry was 25,000 mph while orbital it is 17,000 mph.  The MCT could be built with titanium supports to be held together, or it might require slowing down to 17,000 mph before atmospheric entry so it wouldn't be a slam into the atmosphere.  For a large spacecraft reentry from Mars, this is a concern. 

Offline JasonAW3

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Re: MCT Speculation and Discussion Thread 4
« Reply #63 on: 06/16/2015 04:28 PM »
Try crushing a beer can containing several bars of pressure against your forehead.

Or better - don't.  :)

But if you do, make sure it's empty first!
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Offline JasonAW3

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Re: MCT Speculation and Discussion Thread 4
« Reply #64 on: 06/16/2015 04:40 PM »
The hardest reentry is back to earth. If it can do that, Mars speed is no problem.

But it CAN'T that's the rub, the vehicle can't be the large low density tank people are imagining, it would be crushed.  The Apollo heat shield alone was 15% of the mass, the structure was 27% and this was to for a compact and easy to protect shape.  So we can't just wave our arms and say MCT will be able to do this.

How much retro-propulsion do you think we can do upon return to Earth?  Any propellent to do this with is added to our DeltaV from Mars surface which is already 6-7 kms for a direct Earth return.  The propellent fraction is already near the limits of credibility.

     If you're applying the Cube Square law directly and we hadn't had over fifty years of materials technology advancement behind us, you'd possibly be correct, but as the newer designs can take advantage of engineering advances, plus, structures can be made VASTLY stronger for less than half the mass that was required in the past, plus the reusable TPS system is lower mass than the TPS system that Apollo required, I think that it's likely that the craft, while heavier than Gucky seems to think it'll be, will still be far lighter than you suspect it'll be.

     As is, I suspect that SpaceX will most likely use a multiple pass aerobraking maneuver to achieve orbit and reentry.  This would reduce the requirements for a retropropulsive burn for Earth entry, and as the craft will be FAR lower mass than when it originally launched, (Having shed the 100 colonists and all of their associated cargo) actual fuel requirements for both the return trip and actual landing will like wise be far lower.
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Online spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #65 on: 06/16/2015 04:40 PM »
I think that is what he was referring to, and empty MCT.  Empty of fuel and cargo, thus being much lighter and easier to crush when slamming into the earths atmosphere, even with a good heat shield.  Thus the idea of a retro burn to slow down before entering earths atmosphere.  Also, coming from Mars one MCT at a time, an orbit or two would help in enabling a more precise landing at the launch site, instead of the middle of the ocean or the jungle somewhere. 

Offline RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #66 on: 06/16/2015 04:45 PM »
I think that is what he was referring to, and empty MCT.  Empty of fuel and cargo, thus being much lighter and easier to crush when slamming into the earths atmosphere, even with a good heat shield.  Thus the idea of a retro burn to slow down before entering earths atmosphere.  Also, coming from Mars one MCT at a time, an orbit or two would help in enabling a more precise landing at the launch site, instead of the middle of the ocean or the jungle somewhere.

Being empty will not make the structure weaker. MCT isn't an Atlas fuel tank.

Offline JasonAW3

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Re: MCT Speculation and Discussion Thread 4
« Reply #67 on: 06/16/2015 04:47 PM »
If the MCT is completely refueled on Mars for launch back to earth, all of the fuel will not be needed to get the TEI burn.  There will be quite a bit of fuel left.  So the MCT could fire and slow down before earth reentry, or it could slow down using aerocapture for a few orbits to slow down.  Also, there will probably be only a crew return, not 100 people.

Crew?
Why?
MCT should be able to return to Earth empty.  (And as needed provide occasional return transport for humans needing to return)

On the way out assuming several 10s of passengers it would be astounding if there were not several engineers capable of specialized training as "flight engineers" to repair anything repairable by humans.  No astronaut corps test pilots needed, just FEs similar to on the shuttle.

Crew mass & life support is wasted mass and money.

     You may be correct aboutthe need for a crew, but people are still a bit primitive.  They'd be more than a bit nervous to trust their lives to nothing more than machines.  I'm pretty sure that they'd want at least a minimal crew orf pilot, navigator/copilot and at least one engineer.  (A dedicated doctor/medic would also likely be a good idea).  If nothing else, to keep the passengers calm during the flight.

     While machines are pretty good at doing their jobs, nobody will want to risk a several billion dollar investment on the possibility that a IC chip will fry because of a stray cosmic ray and send the craft wandering off into space or worse, come c rashing down on Earth at 6 to 7 KMS.
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Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #68 on: 06/16/2015 04:59 PM »
I think that is what he was referring to, and empty MCT.  Empty of fuel and cargo, thus being much lighter and easier to crush when slamming into the earths atmosphere, even with a good heat shield.  Thus the idea of a retro burn to slow down before entering earths atmosphere.  Also, coming from Mars one MCT at a time, an orbit or two would help in enabling a more precise landing at the launch site, instead of the middle of the ocean or the jungle somewhere.

Being empty will not make the structure weaker. MCT isn't an Atlas fuel tank.
Atlas stages aren't weak when empty, they're weak when not pressurized. If MCT isn't pressurized, there would be other, bigger problems to worry about.
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Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #69 on: 06/16/2015 05:03 PM »
While machines are pretty good at doing their jobs, nobody will want to risk a several billion dollar investment on the possibility that a IC chip will fry because of a stray cosmic ray and send the craft wandering off into space or worse, come c rashing down on Earth at 6 to 7 KMS.

90% may be cargo flights and those will not carry any crew. So that is no reason for crew to return on a crew vehicle. True, maybe a technician and a medic might be on board in the unlikely case no one of the settlers would be capable of filling that function. This is assuming they are flights with settlers. An exploration crew will be even more likely to have those skills.

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #70 on: 06/16/2015 05:10 PM »
If MCT isn't pressurized, there would be other, bigger problems to worry about.

This discussion gets me to another thought. I had anticipated cargo flights might not be pressurized. But they will likely need to be pressurized, not only for the benefit of the cargo but to give them stability.

Getting slightly OT, I wonder if equipment will have to be pressurized all the way, which would make unloading quite difficult. Or if it could be exposed to the near vacuum of Mars for a short time during unloading. Some equipment would be designed to work on the surface, no problem there. But a lot of stuff would go into habitats.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #71 on: 06/16/2015 05:19 PM »
The hardest reentry is back to earth. If it can do that, Mars speed is no problem.

But it CAN'T that's the rub, the vehicle can't be the large low density tank people are imagining, it would be crushed.  The Apollo heat shield alone was 15% of the mass, the structure was 27% and this was to for a compact and easy to protect shape.  So we can't just wave our arms and say MCT will be able to do this.

How much retro-propulsion do you think we can do upon return to Earth?  Any propellent to do this with is added to our DeltaV from Mars surface which is already 6-7 kms for a direct Earth return.  The propellent fraction is already near the limits of credibility.

Quote
It would literally be crushed like an empty beer can against ones forehead when it hits the Earth's atmosphere.

Is there any reason the tanks couldn't be pressurized for EDL?  As was done with Atlas SM-65 to keep it from collapsing under it's own weight, or Centaur to keep the payload from crushing it like a beer can, prior to fueling?
Probably use GOX and GCH4 rather than GN2 as was done with Atlas and Centaur though.  Just allow some boiloff of each to adequate pressure.

Beer cans don't crush against one's forehead if they are pressurized.  (Even if they are gas only with no liquid)






Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #72 on: 06/16/2015 05:31 PM »

At these kinds of packaging densities you would need 1200-5000 m^3 to use that mass effectively for launching satellites.  But their is no way the vehicle can have such a huge cargo hold, it would make the overall vehicle too large and require too much structural mass to make it survive re-entry.
This is an entirely wrong assumption. An Ariane V, per your words, has ~390 cubic meters of volume and can manage to bring two satellites into GTO and costs about $200 million per launch, at a price of $100 million per satellite. A falcon 9 has ~275 cubic meters and can get a single satellite into GTO in fully expendable mode at a price of $90 million per launch/satellite.

Therefore, the only thing a MCT needs to do in order to be competitive as a satellite delivery platform is lower the cost of getting satellites into GTO, not increase the amount of satellites into GTO and since the goal of the MCT is to be rapidly reusable, a "gas & go" type of system, the only costs involved with the launch would be processing, operation and the cost of the methalox rather than building an entire vehicle, the MCT is cheaper and if the internal volume of its cargo bay is only equal to that of an Ariane V fairing, it can still get two satellites into GTO so the only way a MCT is not competitive is if the cost of its launch approaches the $200 million mark.

And given the MCT's much touted price tag of $50 million per 100 people ($500 000 per passenger) I just don't see that as a likely event.
Commercial communication satellites are LOW DENSITY, just look at the size of current payload fairing and you can see that their is no way you could put 100 mT of satellites into the kind of volumes were looking at for a MCT cargo-hold.

Falcon 9 payload fairing has a volume of ~275 m^3 and it launches only 5 mT to GTO, Ariane 5 has ~390 m^3 and launches a maximum of 12 mT to GTO.  Shuttle had ~300 m^3 payload bay and could carry 24 mT to LEO. 

At these kinds of packaging densities you would need 1200-5000 m^3 to use that mass effectively for launching satellites.  But their is no way the vehicle can have such a huge cargo hold, it would make the overall vehicle too large and require too much structural mass to make it survive re-entry.

Volume is VERY important, MANY space launch systems face volume limitations, Dragon capsule for example is volume rather then mass limited for most cargoes that need to be launched to ISS.
You would never pack 100 metric tonnes' worth of satellites in a MCT.

Mostly because an MCT without refuelling can do much less than that in tonnes to GTO. (I remember that a number of 10-15 tonnes was mentioned somewhere in the previous topic, which amounts to 2 conventional satellites or 3-4 SEP ones, so about an Ariane 5 worth of payload to GTO). The reason why you'd want to do this without refuelling is to lower operating costs and complexity of the mission.

So you pack it with as many satellites as you can given the volume and mass constraints and that still makes the volume of the MCT a non-issue because it's still cheaper than the alternatives and has enough of a capability for at least 2 satellites.

The only time when the volume of a MCT becomes an issue is if you consider a commercial depot stationed in LEO, to which the MCT could deliver its full payload in mass and from which tugs would take over. But even then it'd still be cheaper

If SpaceX were to plan to put an expendable (or parachute recoverable) PLF on the front of MCT, like they would have with F9US-R, then volume will be immense, depending on PLF length.

Additionally, if MCT is just dropping the payload and a kick stage off in LEO, and then returning to the launch site, the kick stage would be very low volume compared to it's mass.  Whether that's a liquid kick stage like the F9US, or a solid one like the Intertial Upper stage the Shuttle dropped off in LEO with sats like Magellan and Galileo.

If talking about some sort of multi-purpose internal payload area inside of MCT which could carry a sat, or cargo to Mars, or a hab with crew to Mars, etc, then it would most likely be much more volume constrained.  As well as tricky to deploy remotely.  Which is why a traditional PLF on the nose as they envisioned doing with F9US-R seems like it would me more reliable, simple, and versatile (larger volume). 
MCT could still have an internal area which could be configured for cargo for the Mars surface, or crew.  But it doesn't necessary have to try to make that work for deploying unmanned sats.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #73 on: 06/16/2015 05:41 PM »
Using a BFR and MCT to launch satellites is comparable to using the Queen Mary as an ore barge.
We should also acknowledge that and move on.

It will also refuel at least twice, so Apollo-like 'missions' to Mars are off the table... for SpaceX anyway.

It all depends on cost.  It will be reusable.  Which means, the more it flies, the cheaper per launch overall it will be. 

I couldn't see SpaceX really delaying their plans just so sats could fly on MCT.  But SpaceX is a private company, and a paying customer is a paying customer, whether it's putting NASA astronauts on the Moon or putting a load of bricks into LEO.  As long as SpaceX is making a profit on each launch and it's not interferring with their own Mars plans...why wouldn't they use it to launch sats that would otherwise need possibly a more expensive expendable FH?

At the end of they day, F9R and FHR will be doing the vast bulk of the sat launches.  But I'd expect if there's a rare paylaod that would need a fully expendable FH, then they could launch it with MCT...assuming MCT is designed with the capability to do so...which it may or may not be.

But anything that can fly on F9R and FHR will do so, I'm sure.  SpaceX isn't investing in all of those F9/FH pads for nothing.


Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #74 on: 06/16/2015 06:08 PM »


That brutal 12-14 kms entry to Earth is something everyone who is talking about this direct Earth return is glossing over, that is beyond Apollo speeds, the only thing that can survive that kind of heat, dynamic pressure and g-force is a dense capsule with thick heavy ablatives.

This is why it is not valid to design spacecraft by only looking at Delta-V and tank sizes and imagining that a giant 2nd stage can do the job of direct Earth return from Mars surface just because it can hold the propellents to launch to Earth.  It would literally be crushed like an empty beer can against ones forehead when it hits the Earth's atmosphere.

A 2nd stage that can return from Earth orbit is a vastly simpler thing to do because the speed is half (and the energy is a quarter), and it is fairly easy to slow down the 2nd stage by several kms with residual propellents, and to employ disposable things like parachutes because it only needs to perform ONE landing before servicing rather then two, and lastly it can be made much less reliable in landing because it's unmanned, no one dies horribly if it crashes or burns up on reentry unlike MCT.

The thing is....this is all a moot point to your argument.  Whether MCT is it's own 2nd stage to LEO or it sits atop a dedicated unique 2nd stage won't change the fact that MCT will need to have -large- tanks.  It will be mostly propellant tank by volume just to do the TMI burn and Mars EDL retropropulsion....and to get itself off the surface of Mars, even if it were only going to LMO before getting refueled there rather than all the way back in one shot.
It will be mostly a large propellant tank, with some legs, engines, and some cargo or hab internal volume.

Having MCT be it's own 2nd stage rather than having a separate dedicated 2nd stage won't change that.  MCT can't then become just a simple larger Dragon capsule. 
With a dedicated reusable 2nd stage, then it's just a giant 3rd stage, rather than a giant 2nd stage.  Maybe a little smaller.  Not much else changes.  So it's a bit of a moot argument.

Yes, designing a vehicle that is returning just form LEO is vastly more simple than designing one that's coming back from interplanetary speeds.  You are correct.  But, there's not an either/or option.  SpaceX must figure out how to get a large rocket stage back from Mars and land it on Earth.  They already need to solve that long pole issue.  A vehicle they design to handle that, can already return to Earth from LEO easily enough, without the [easy] development of a separate LEO only vehicle even necessary. 


« Last Edit: 06/16/2015 06:12 PM by Lobo »

Online oldAtlas_Eguy

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Re: MCT Speculation and Discussion Thread 4
« Reply #75 on: 06/16/2015 06:29 PM »
What difference is there between MCT and a reusable upper stage? Just the habitable portion on top. They will need similar performance (~6.5-7km/s). Both need reentry and landing capability (legs, etc).

The problem with Shuttle is there were only a few of them made, no custom ones. With MCT, thousands will be made, so no problem making some that lack the habitable portion or that act as tankers or that are only used for cargo. The requirements for these things are similar but the MCTs can be modified to fit the purpose instead of having one vehicle type do everything at once.

I don't know about THOUSANDS of MCT's being built, dozens and maybe hundreds, but by that time, I expect newer designs will superceed the current design scheme.

Sharing the development costs between a large number of ships is a key requirement.  A 10 billion dollar development cost over 100 ships is 'only' 100 million dollars per ship, and if each ship can do 50 trips, then it's 2 million $ per trip, and a small portion of the 50 million dollar fare per ship.  So perhaps 100 ships per design generation?
50 reuses is far too many. My guess is the MCTs may last about 3 decades, one reuse every ~2 years (every synod), so only 12-15 reuses is practical.

Musk has said 80,000 people per year (and ten times as many cargo shipments), which is 1000 Passenger MCTs at once, plus 10,000 cargo MCTs (or actually, there ways around this, but it remains to be seen if they're worth it). So yeah, at any one time, there would need to be thousands of MCTs.

Once you get to this level you are talking about huge cycler vehicles ->40,000 persons in a 15m diameter tube at 1000m diameter wheel with .5g at a rotation rate of 1RPM. This configuration has over 2 million m^3 of volume. 4 of these would be launched every 2 years during the 2 month Mars departure window. In order to stop the spin or start it takes 100m/sec delta V. Spin must be stopped when the vehicle is realigned for a major burn. There would be 560 100mt propellant tanks (arranged in groups of 8 every 15m along a support structure 1050m long that stick 500 m out to each side of the wheel and 50 Raptor engines at each end for doing the orbit change burns

For cargo, there would be a vehicle tug 1800m long that can carry 4000 100mt cargo containers on a similar propulsion arrangement as the habitat cycler. 5 of these would be launched during the 2 month Mars departure window oin order to deliver the 10,000 100mt cargo deliveries.

The MCT's and BFR's except for just a handful of emergency vehicles HSF MCT's to transfer personnel between habitats and 8 on each cargo cycler for the operations and maintenance crew. The rest of 100's of MCT's at Earth and Mars are used only locally for ferry to and from orbit the personnel and cargo. In order to get all this into orbit would take about 3000 flights of BFR and MCT's out to L2 every year or about 8 every day. With a 50 flight usage for the propulsion busses and BFR stages and 100 flight usage for the personnel container and a 500 usage for the cargo and tanker containers: 60 MCT busses and BFR's manufacture each year; 30 personnel carriers manufacture each year , 6 cargo and 6 tankers carriers manufacture each year. the cycler vehicles have a 30-50 year life with good maintenance. representing 5-8 round trips. The vehicle has to stay at each destination 2 years for unloading and loading.

Edit fixed a value from 4 years to 2 years.
« Last Edit: 06/16/2015 08:04 PM by oldAtlas_Eguy »

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #76 on: 06/16/2015 07:17 PM »
Just to shake things up a bit and challenge some of the preconceptions here:

Assuming that for each MCT departure to Mars there are several BFR launches for the MCT itself, Fuel, and maybe more cargo, and some FH launches for personnel for those MCT's that carry passengers (at least initially as it maybe a while before the BFR is human rated).

Do we have a propellant depot in LEO?  If yes I suspect that it will have an attached/nearby habitat.  If not the logistics of launching to Mars will be constrained around the refueling procedures I imagine and will only take place serially with a 'launch season' seeing launches one after another, each on a somewhat different course. Yes a rendezvous between MCT's on the way might be possible, but mainly with ones relatively close in the launching order without using up the ΔV needed for Mars landing. This may constrain manned MCTs to launching in the middle of the 'launch season' for safety protocols.  There may be other constraints. Certainly it means that each MCT must be rendezvoused with several times, with a depot, the depot is the rendezvous point, could even be for people transiting. The Mars bound MCTs could launch, fill completely with fuel, board passengers if manned, take on any last minute cargo if there was any then head out.  I favour the depot, but for another reason too.

On returning from Mars the MCT, at a LEO periapsis is moving about 2kms faster than escape velocity, to shed just a little more than that in an aerocapture maneuver requires far more TPS than all of Mars entry from the interplanetary speeds there, but still significantly less than going in for landing. Subsequent aerobraking maneuvers could shed velocity in smaller increments and each would start at a much less energetic state (relative the atmosphere it would be braking in). So going back to the idea that MCTs might not return to earth to be recycled, what if, as well as being a propellant depot, we also had MCTs parked where they could have their TPS refreshed, and engines inspected, and if any were not good for at least 2 more flights, have it replaced (there would be a steady stream of vehicles coming up with new or recently Earth refurbished engines they could swap with) designing the engine and pump system to be space or Mars swapable only makes sense.  I also take it as a given that at least initially many MCTs would be staying on (or at) Mars at least for a few years. They might be a source of spare engines too if some didn't pass inspection on Mars.

This would suggest that although we intend to ramp up cargo and personnel flights to Mars with each successive launch season, we could do it with a steady state of MCT production, say one a month or less. That makes planning production simple.

Now as soon as we have a few spare MCT's hanging around in LEO waiting for launch season, someone else might want to lease a few to start up lunar ISRU for fuel and maybe something else.
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 guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #77 on: 06/16/2015 07:41 PM »
Do we have a propellant depot in LEO?

It is part of the plan laid out by Elon Musk. However for the first few conjunctions when only 2-4 flights go to Mars, it may be easier to just refuel directly in LEO. When the number of flights increases, depots will soon become necessary.

Edit: I could imagine that a manned MCT would be refuelled draining a full cargo MCT that would then be fuelled up for a second time. That may count as a kind of depot and avoid a delay for the crew.

I also take it as a given that at least initially many MCTs would be staying on (or at) Mars at least for a few years. They might be a source of spare engines too if some didn't pass inspection on Mars.

Nothing to have a disagreement on but I believe only the first 2 or 3 would stay, probably forever. I believe it is safer to send them back after unloading and only a few weeks stay on Mars rather than having them there for a full synod and then relying on their continued function and safety without means for a thorough inspection.

This would suggest that although we intend to ramp up cargo and personnel flights to Mars with each successive launch season, we could do it with a steady state of MCT production, say one a month or less. That makes planning production simple.

Now as soon as we have a few spare MCT's hanging around in LEO waiting for launch season, someone else might want to lease a few to start up lunar ISRU for fuel and maybe something else.

Sounds good. I would guess though that it will be some time until production rate is ramped up to one a month. Depending on funds.
« Last Edit: 06/16/2015 07:43 PM by guckyfan »

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #78 on: 06/16/2015 08:31 PM »
Do we have a propellant depot in LEO?

It is part of the plan laid out by Elon Musk. However for the first few conjunctions when only 2-4 flights go to Mars, it may be easier to just refuel directly in LEO. When the number of flights increases, depots will soon become necessary.

Edit: I could imagine that a manned MCT would be refuelled draining a full cargo MCT that would then be fuelled up for a second time. That may count as a kind of depot and avoid a delay for the crew.


I can imagine that the first 'launch season' where an MCT is launched sees only 2-4 go. But by even the next one I expect that they have at least a dozen if not twice that, more built. Depending when the first MCTs go, and how much preparation might have been done in the launch season before the previous conjunction, there might or might not be people going in that first wave. However, baring serious complications, I am certain that the second wave will have people, and with those people both those who intend to stay and build up the outpost, as well as those there for one or two synods worth of scientific study.

I also don't believe that an MCT acting as fuel freighter, or for that matter any upper stage for a BFR, can carry enough propellant to fully fuel an MCT bound for Mars, which if it massed 160mt dry weight would have to mass a minimum 600mt fully fueled with the most optimistic landing maneuver planned. 440mt seems to be at the absolute minimum 4 BFR and MCT used as tanker launches or 2 dedicated expendible tanker BFR US or 3 reusable ones.

While a depot isn't absolutely needed, I think at the scale even of sending 10 MCTs over a 3 month period (the 2nd launch season) it would save on total launch mass.  A LEO depot, or MCT waiting for days partly fueled needs to be able to actively cool propellant far more than the MCT does once it leaves LEO. Rather than equipping each MCT with the ability to do that level of active cooling lets go with the depot and only design into the MCT the cooling required once heat radiated from Earth is no longer a factor.

I also take it as a given that at least initially many MCTs would be staying on (or at) Mars at least for a few years. They might be a source of spare engines too if some didn't pass inspection on Mars.

Nothing to have a disagreement on but I believe only the first 2 or 3 would stay, probably forever. I believe it is safer to send them back after unloading and only a few weeks stay on Mars rather than having them there for a full synod and then relying on their continued function and safety without means for a thorough inspection.

I am thinking that some would be used point to point and surface to orbit as well. Potentially these could be used dozens of times from a TPS point of view, but might no longer, after a few uses have the TPS level required for return to Earth.



This would suggest that although we intend to ramp up cargo and personnel flights to Mars with each successive launch season, we could do it with a steady state of MCT production, say one a month or less. That makes planning production simple.

Now as soon as we have a few spare MCT's hanging around in LEO waiting for launch season, someone else might want to lease a few to start up lunar ISRU for fuel and maybe something else.

Sounds good. I would guess though that it will be some time until production rate is ramped up to one a month. Depending on funds.

Well how about this timeline for you (totally ex cathedra from my belly button and as chock full of assumptions and extrapolations as popular breakfast cereals have calories and artificial flavours):

2019: Raptor ready for flight test, first 4 flight ready are put on a mock up MCT for initial hover and landing tests
2020: MCT with TPS tested in suborbital flight to an ASDS, First suborbital tests of BFR.
2021: Raptor production now at 10 per month; first orbital tests.
2022: October launch of first MCT To Mars 4 more in the next three months.

by the 2025 launch season a full expedition of 12 MCT's ready to go.

Optimistic yes. Impossible no. Including raptor development I think it could be accomplished with $3 - $4B by the end of the 2025 launch season not including payloads.
« Last Edit: 06/16/2015 08:33 PM by nadreck »
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 RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #79 on: 06/16/2015 08:36 PM »
This discussion gets me to another thought. I had anticipated cargo flights might not be pressurized. But they will likely need to be pressurized, not only for the benefit of the cargo but to give them stability.

Getting slightly OT, I wonder if equipment will have to be pressurized all the way, which would make unloading quite difficult. Or if it could be exposed to the near vacuum of Mars for a short time during unloading. Some equipment would be designed to work on the surface, no problem there. But a lot of stuff would go into habitats.

Cargo handling will be complicated and require tradeoffs.

If the cargo hold on the MCT needs to stay pressurized, then some sort of pressurized truck will be needed to move the cargo from the MCT to the habitats. The truck would dock with the MCT and the habitats. This requires a special vehicle for cargo handling.

If cargo is packed in pressurized containers, say pallet sized, then the containers could be exposed to Martian atmosphere or even vacuum during flight. These containers could be transported to the habitats by various means. This requires special pressurized containers and would not be mass efficient. The containers would pickup dust from the outside and may need cleaning before being unloaded.

Equipment could be made to survive low pressure or vacuum. Even packaging for items such as food or clothing. That would increase mass due to packaging and get back to the dust and cleaning issue. On the plus side, if a module depressurized, items packed like this would still be usable once the module was repaired and re-pressurized.

The entire pressurized MCT cargo hold could be a removable module. The module could be added to the current base and converted to whatever living or workspace the base needs. Remove the cargo to other sections of the base and refit the module. But how do you move something that large?

I'm sure there are many other possible scenarios. Each potentially has an impact on MCT design.

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