Author Topic: MCT Speculation and Discussion Thread 4  (Read 610465 times)

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1260 on: 01/01/2016 12:06 AM »
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.
...
Not accurate.
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Offline Stardhingy

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Re: MCT Speculation and Discussion Thread 4
« Reply #1261 on: 01/01/2016 01:11 AM »
If its a 15m section, a spherical tank works out to ~1000mt of propellent. You aren't going to save much drymass by going to smaller tanks, you either use tanks that don't take up the whole diameter and provide support, or you have mass inefficient pancake shaped tanks. What does a couple meters of mostly empty rocket weigh?

It seems to me if you can have a 75mt ship with 300mt of propellent, 1000mtof propellent is only going to bump the dry mass up to say, 80mt. That trade would be well worth it since it would bump your mass fraction up to .93. Now you may not even be able to launch it with full tanks, but fully fueled In GTO you could put 300 mt on trans-Jupiter insertion and boostback to orbit.
« Last Edit: 01/01/2016 01:26 AM by Stardhingy »

Offline QuantumG

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Re: MCT Speculation and Discussion Thread 4
« Reply #1262 on: 01/01/2016 02:27 AM »
Even at 15m, it's still a baby compared to the Sea Dragon ;)
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1263 on: 01/01/2016 02:28 AM »
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.
...
Not accurate.

Can you be more specific?

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Does that include your self-deployable, disposable, wire landing/launch pad?

It is just for launch and would be directly under the engines with a total area of ~100 m^2, even thick 6 gauge steel wire at a 1 inch spacing would be only 1,220 kg, add in stakes and simple rams that push the wire onto the ground and pin it and your still looking at a tiny fraction of the cargo capacity which is where it is accounted for.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1264 on: 01/01/2016 05:39 AM »
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

I was extremely critical of this aspect in the past on the basis that a habitat which needs to hold 100 passengers for 1000 days with 1000 days of food, survive reentry, and produce its own propellant on the other end is probably going to be several times that dry mass;  But I'm increasingly moving towards backing off this conjunction of requirements, and assuming they will not occur simultaneously.

Even so;  Something like the Bigelow BA-2100 is supposed to be heavier than this.  On what basis do you propose 75 tons instead of 9 tons or 400 tons?

Offline Vultur

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Re: MCT Speculation and Discussion Thread 4
« Reply #1265 on: 01/01/2016 05:47 AM »
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

I really expect it to be less - F9 has very good mass ratios IIRC, and MCT will be more like a stage (with cargo bay) than a capsule. (I would expect the passenger accommodations to count against the cargo-version 100mt payload.)

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1266 on: 01/01/2016 06:07 AM »
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

I was extremely critical of this aspect in the past on the basis that a habitat which needs to hold 100 passengers for 1000 days with 1000 days of food, survive reentry, and produce its own propellant on the other end is probably going to be several times that dry mass;  But I'm increasingly moving towards backing off this conjunction of requirements, and assuming they will not occur simultaneously.

Even so;  Something like the Bigelow BA-2100 is supposed to be heavier than this.  On what basis do you propose 75 tons instead of 9 tons or 400 tons?

Yes the dry mass to cargo mass is optimistic as nothing so far has had a greater then 1:1 ratio.  The cargo mass though is just a little under half ~46% the mars atmospheric entry mass though as propellants would be ~18% and the lander dry mass would be 36% of the total.

Of the requirements you site I see almost none of these requirements being simultaneous.

I see a transit habitat being used for the 100 count passengers and their life-support needs with the landing vehicle holding them for only a few days at a time in something like air-plane densities.  I see re-entry being from much lower orbital speeds at Earth and Mars rather then direct entry.  The propellant production will be done with systems that take up most or all of a single landers cargo capacity, the system will be deployed to the surface and remain their, none of it will be integrated to the vehicle but the vehicle that landed it will remain connected and drink-up the first batch of propellant and use that to slowly return to Earth completely empty of cargo.  Crew return will be in two legs with the lander just returning to mars orbit and then using SEP to return to Earth orbit.

Offline stoker5432

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Re: MCT Speculation and Discussion Thread 4
« Reply #1267 on: 01/01/2016 06:11 AM »
It is just for launch and would be directly under the engines with a total area of ~100 m^2, even thick 6 gauge steel wire at a 1 inch spacing would be only 1,220 kg, add in stakes and simple rams that push the wire onto the ground and pin it and your still looking at a tiny fraction of the cargo capacity which is where it is accounted for.

So not only do you have to worry about rocks, you would also have the possibility of long stakes flying up at your spacecraft. Way to many variables in ground composition and installation among other issues to be a viable option. Permanent launch pads will have to be built and by default will become landing pads.
« Last Edit: 01/01/2016 06:14 AM by stoker5432 »

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1268 on: 01/01/2016 06:36 AM »
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

I was extremely critical of this aspect in the past on the basis that a habitat which needs to hold 100 passengers for 1000 days with 1000 days of food, survive reentry, and produce its own propellant on the other end is probably going to be several times that dry mass;  But I'm increasingly moving towards backing off this conjunction of requirements, and assuming they will not occur simultaneously.

Even so;  Something like the Bigelow BA-2100 is supposed to be heavier than this.  On what basis do you propose 75 tons instead of 9 tons or 400 tons?

Yes the dry mass to cargo mass is optimistic as nothing so far has had a greater then 1:1 ratio.  The cargo mass though is just a little under half ~46% the mars atmospheric entry mass though as propellants would be ~18% and the lander dry mass would be 36% of the total.

Of the requirements you site I see almost none of these requirements being simultaneous.

I see a transit habitat being used for the 100 count passengers and their life-support needs with the landing vehicle holding them for only a few days at a time in something like air-plane densities.  I see re-entry being from much lower orbital speeds at Earth and Mars rather then direct entry.  The propellant production will be done with systems that take up most or all of a single landers cargo capacity, the system will be deployed to the surface and remain their, none of it will be integrated to the vehicle but the vehicle that landed it will remain connected and drink-up the first batch of propellant and use that to slowly return to Earth completely empty of cargo.  Crew return will be in two legs with the lander just returning to mars orbit and then using SEP to return to Earth orbit.

Sounds intriguing.  Some of these ideas I have explored myself.  Got anything written up on this?

Note that a transit habitat tends to be mutually exclusive with a fast transit, which is required for 1-synod reuse.  SEP from LMO to Earth is also going to be fairly slow.

Offline Oli

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Re: MCT Speculation and Discussion Thread 4
« Reply #1269 on: 01/01/2016 07:33 AM »
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

There are many previous estimates. Only with HIAD you get to 0.75 or better, from what I've seen. For a non-reusable lander.

I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

I really expect it to be less - F9 has very good mass ratios IIRC, and MCT will be more like a stage (with cargo bay) than a capsule. (I would expect the passenger accommodations to count against the cargo-version 100mt payload.)

The mass ratio you're talking about refers to the total mass divided by the dry mass. What I refer to is the dry mass divided by the payload mass. Apart from that F9 stats are not really applicable to a Mars lander.
« Last Edit: 01/01/2016 07:43 AM by Oli »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1270 on: 01/01/2016 07:48 AM »
It is just for launch and would be directly under the engines with a total area of ~100 m^2, even thick 6 gauge steel wire at a 1 inch spacing would be only 1,220 kg, add in stakes and simple rams that push the wire onto the ground and pin it and your still looking at a tiny fraction of the cargo capacity which is where it is accounted for.

So not only do you have to worry about rocks, you would also have the possibility of long stakes flying up at your spacecraft. Way to many variables in ground composition and installation among other issues to be a viable option. Permanent launch pads will have to be built and by default will become landing pads.

You just seem to be fishing for negatives at this point, stakes driven into the ground are not going to come out in the time scale of a 2g launch.  Ground composition could be an issue and this may mean that their will be a lower maximum boulder size at an acceptable landing site then otherwise.

Note that this wire-mesh is intended just for the initial automated landings in place of the pre-cursor vehicles favored by others.  Once settlements are established I would expect a more permanent pads to be built but they will most likely consist of a larger area of mesh put down over cleared and compacted regolith, not concrete or anything resembling a pad on Earth and the lander will simply omit the drop mesh I described.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1271 on: 01/01/2016 07:53 AM »
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

There are many previous estimates. Only with HIAD you get to 0.75 or better, from what I've seen. For a non-reusable lander.


I'm looking at a kind of mechanical flap at the base of the vehicle and telescoping or umbrella-like system that performs as a HIAD while being fully retractable and reusable to achieve most deceleration down to sub-sonic followed by brief landing burn.

Online docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #1272 on: 01/01/2016 08:01 AM »
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

There are many previous estimates. Only with HIAD you get to 0.75 or better, from what I've seen. For a non-reusable lander.


I'm looking at a kind of mechanical flap at the base of the vehicle and telescoping or umbrella-like system that performs as a HIAD while being fully retractable and reusable to achieve most deceleration down to sub-sonic followed by brief landing burn.

Like TVG's Michelle-B?

http://www.thespacereview.com/article/409/1
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Offline jabe

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Re: MCT Speculation and Discussion Thread 4
« Reply #1273 on: 01/01/2016 01:57 PM »
Not sure if this video has been posted yet..but a schematic of a 100MT lander is illustrated at 46 min mark.
Interesting vid but warning lots of physics!! :)
Cheers
Jb
« Last Edit: 01/01/2016 01:58 PM by jabe »

Offline stoker5432

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Re: MCT Speculation and Discussion Thread 4
« Reply #1274 on: 01/01/2016 04:06 PM »
You just seem to be fishing for negatives at this point, stakes driven into the ground are not going to come out in the time scale of a 2g launch.  Ground composition could be an issue and this may mean that their will be a lower maximum boulder size at an acceptable landing site then otherwise.

A less than optimal launch, loose soil, or a manufacturing defect in your unproven wire mesh could lead to a very bad day. You still haven't explained exactly how this pad gets installed. Are you going to depend on a machine that can break down or crew members that might make a mistake? How to you handle quality control when your trying build a new pad for every MCT launch?

As long as your permanent mesh landing/launching pads can hold up to the weight of the MCT and can work for multiple landing and launches, I'm perfectly fine with that.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1275 on: 01/01/2016 07:36 PM »
Not sure if this video has been posted yet..but a schematic of a 100MT lander is illustrated at 46 min mark.
Interesting vid but warning lots of physics!! :)
Cheers
Jb


Very passionate student, and a huge nerd. Watch his "resume" video for applying to the SpaceX internship position:

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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1276 on: 01/02/2016 01:32 AM »

Like TVG's Michelle-B?

http://www.thespacereview.com/article/409/1

Somewhat, I see a nose first entry with the decelerator hinged from a high position on the vehicle perhaps just behind the nose cone, the entire outer skin below that point lifts up and forms part of the decelerator.  This removes the need for a door as the interior of the vehicle is naturally opened by this action.  After deceleration to terminal velocity of around 500 m/s the vehicle then needs to turn to land on it's base, the decelerator might serve as a quasi parachute during the later stages of landing if it can spread far enough to be clear of the ground, ideally it would invert slightly to to put the vehicle mass at the bottom and allow unrestricted access to the vehicle interior after landing.

For a bit of a visual on what it might look like see this video on the large parasols in Meca, as far as I know these are the largest mechanical umbrella like devices in the world.  A vehicle of 200 mt would need an area of about 4 of these to reach a low ballistic coefficient comparable to prior mars landers like MER.  Naturally the ribs would need to be made of light materials like carbon-fiber and the fabric must be something like Nomex or some other high strength incombustible material.


Offline matthewkantar

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Re: MCT Speculation and Discussion Thread 4
« Reply #1277 on: 01/02/2016 02:07 AM »
What would be wicked pissah would be a well conceived poll where we could select our BFR/MCT parameters before Elon makes his BFR/MCT announcement* and see who is at least in the ballpark.


* OK, I'm optimistically assuming we'll still be alive at that time.

I have been thinking about a poll just for number of engines on the first stage. I would choose 36.

Enjoy, Matthew

Offline KelvinZero

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Re: MCT Speculation and Discussion Thread 4
« Reply #1278 on: 01/02/2016 02:53 AM »
What would be wicked pissah would be a well conceived poll where we could select our BFR/MCT parameters before Elon makes his BFR/MCT announcement* and see who is at least in the ballpark.


* OK, I'm optimistically assuming we'll still be alive at that time.

I have been thinking about a poll just for number of engines on the first stage. I would choose 36.

Enjoy, Matthew
More difficult: but I would like to see an enumeration of all the basic configurations that are popular.. though I accept the most straightforward design is probably correct. All those wacky ideas just give me a "magnificent men in their flying machines" moment.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1279 on: 01/02/2016 04:02 AM »
You just seem to be fishing for negatives at this point, stakes driven into the ground are not going to come out in the time scale of a 2g launch.  Ground composition could be an issue and this may mean that their will be a lower maximum boulder size at an acceptable landing site then otherwise.

A less than optimal launch, loose soil, or a manufacturing defect in your unproven wire mesh could lead to a very bad day. You still haven't explained exactly how this pad gets installed. Are you going to depend on a machine that can break down or crew members that might make a mistake? How to you handle quality control when your trying build a new pad for every MCT launch?

As long as your permanent mesh landing/launching pads can hold up to the weight of the MCT and can work for multiple landing and launches, I'm perfectly fine with that.

Manufacturing defects in 6 gauge wire is your concern now?  Even the Russians have better quality control then that.  Seriously your practically trolling at this point.

I already described the deployment process it's in a roll under the vehicle and simply drops to the ground or is on a swing arm that releases to bring it to the ground.  It can be unrolled by having the the wire under tension so it wants to expand as soon as released, if that's not enough you inflating a tube that was wrapped inside the roll this will pneumatically extend it even rolling up and over small obstacles.  This is how you autonomously deploy a single use mesh for one vehicle.

To build permanent pads you have human crews operate heavy machinery like bull-dossers, rollers and compactors, then lay down the best covering material they can afford to bring or make and try to attach it as securely as possible to the surface.  Some kind of prefabricated interlinking metal object is the likeliest solution.  If mass budgets are low it's probably a welded wire mesh or chain-mail like material linked together into a single huge piece.  If mass budgets are more generous it might resemble a Marston Mat made from aluminum.  https://en.wikipedia.org/wiki/Marston_Mat

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