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Old 29th September 2017, 03:00 PM   #41
dudalb
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Originally Posted by William Parcher View Post
Musk is saying that he will bring people to Mars five years from now? If so, I think that that is unrealistic optimism. Maybe he has a crazy eccentric cell in his brain that sometimes causes him to say crazy things like that.

Now I get dogpiled, right?
Not from me. I have the suspicion there is a scam going on here somewhere. I am all in favor of Space Travel,but not to the point of ignoring that Musk's plans have almost zero chance of succeeding, for economic reasons if no other.
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Old 29th September 2017, 03:16 PM   #42
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Originally Posted by dudalb View Post
Not from me. I have the suspicion there is a scam going on here somewhere. I am all in favor of Space Travel,but not to the point of ignoring that Musk's plans have almost zero chance of succeeding, for economic reasons if no other.

Funny how many times that's been said, and yet...
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Old 29th September 2017, 03:17 PM   #43
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Originally Posted by GlennB View Post
From the article:

"For a trip to Mars, he said the craft would be able to hold about 100 people in 40 cabins."

He's planning to land these people, not just have them in orbit while a few recon the surface.

So... some sort of small shuttle craft would be out of the question? I can see how no one would want to even consider such a thing, given how practical it would be.
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Old 29th September 2017, 03:18 PM   #44
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Originally Posted by luchog View Post
Funny how many times that's been said, and yet...
And yet what?

For every one of Tesla's invention, there was some silly nonsense that went nowhere. Musk seems cut from the same cloth, and as an added bonus his car company is called Tesla.
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Old 29th September 2017, 03:19 PM   #45
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Originally Posted by Argumemnon View Post
And yet what?

For every one of Tesla's invention, there was some silly nonsense that went nowhere. Musk seems cut from the same cloth, and as an added bonus his car company is called Tesla.

Can you point me to where I said anything about Tesla?
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Old 29th September 2017, 07:33 PM   #46
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Originally Posted by Ziggurat View Post
Having to adapt to an uneven surface is going to be critical. It doesn't even have to be an outcropping, even just a gentle slope requires the legs to be uneven in balance, or the rocket can tip over. And they don't just have to be able to change lengths, they'll have to be able to pick the right length for each leg. So that needs to be engineered, and it's not trivial. But it's also just engineering, we're not bumping up against any limits of physics or even our understanding of it.
Originally Posted by GlennB View Post
Tiny mass and tiny rockets in comparison. Also squat in design making them more stable, and much lower gravity to contend with.
A couple of things I picked up in the live broadcast.

► Musk said that the upper stage of the BFR was about the "height of an eight-storey building". That would make it about 30m long, much shorter than Stage 1 of a Block 3 Falcon 9 (48m) which they have landed successfully back on Earth over dozen times now. Also, the Falcon 9 Stage 1 is only 3.7m in diameter (spans between 9 and 12m with the legs extended) while BFR is over three times wider at 12m (17m across the fins). This makes it shorter, wider and heavier so in theory, it should be more stable.

► He wants to make launching BFR's a very high reliability system. Reliability has to be right up there with commercial aviation, or he would not consider using it to make regular/scheduled Earth-to-Earth flights with fare-paying passengers until that reliability has a proven track record.

In all, he makes a lot of sense. If we are going to take people to Mars to make humans a multi-planetary species then, aside from all the huge engineering challenges, we have to consider two concepts.

► We will need a repeatable, reusable & reliable way of getting hundreds of people there at a time. Going there four, five, six or even seven at a time is a waste of time, effort, money and resources.

► You need to design a spacecraft that can get you to Mars and back, be refuel able in orbit, and capable of taking you to other places in the solar system.

If you have a ship that can launch from the Earth, go to Mars, enter the Martian atmosphere and land on its rockets. then lift off from Mars and come back to Earth, re-enter the Earth's atmosphere and land on its rockets... then leaving out the Mars trip is a logical step that makes perfect sense.
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Old 29th September 2017, 11:27 PM   #47
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Originally Posted by luchog View Post
So... some sort of small shuttle craft would be out of the question? I can see how no one would want to even consider such a thing, given how practical it would be.
Nobody's saying it's out of the question, just that it isn't the plan. The plan is to land the main ship on Mars with 100 passengers.
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Old 30th September 2017, 06:31 AM   #48
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The Martian atmosphere is so thin that a BFR will have great difficulty in burning off much of its orbital speed by aero braking. Of course, it can decelerate using rocket power instead, but that uses up extra fuel. I suppose if the plan is to refuel the rocket on Mars ready for its take off and return journey, then it makes sense to land it. A shuttlecraft making multiple journeys to and from the surface to ferry the passengers might be more fuel efficient - but you have to somehow get the shuttlecraft to Mars in the first place and if it rides on the BFR that might be more mass than the extra fuel - and it would probably be more difficult to refuel the BFR for its return journey if it's in orbit around Mars rather than on the surface.
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Old 30th September 2017, 06:43 AM   #49
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Elon Musk wants to fly you anywhere in the world in less than an hour

Originally Posted by CNN
Elon Musk predicts rockets will one day be able to fly people from New York to Shanghai in just 39 minutes.

Most journeys between points on this planet will take less than 30 minutes, he predicted, and none should take longer than an hour.

In an Instagram post after the presentation, Musk said the cost per seat "should be about the same as full fare economy in an aircraft."

That's the same rocket (BFR) that Musk says could be used to zoom people from city to city on Earth, traveling as fast as 27,000 kilometers per hour (17,000 mph)...
Anywhere in the world in less than an hour. Flying at 17,000mph. A ticket for a seat will cost the same as economy jet airliner.

I'm skeptical.


http://money.cnn.com/2017/09/29/tech...vel/index.html
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Old 30th September 2017, 06:56 AM   #50
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Originally Posted by William Parcher View Post
Elon Musk wants to fly you anywhere in the world in less than an hour

Anywhere in the world in less than an hour. Flying at 17,000mph. A ticket for a seat will cost the same as economy jet airliner.

I'm skeptical.

http://money.cnn.com/2017/09/29/tech...vel/index.html
Indeedy, but it's a long way off.

In other news, the Raptor BFR is being designed to use methane fuel throughout, so no worries about switching fuel for the return trip. It's just a question of manufacturing the stuff and refuelling.
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Old 30th September 2017, 07:24 AM   #51
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Originally Posted by GlennB View Post
Indeedy, but it's a long way off.
When is Musk planning to have this done?
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Old 30th September 2017, 07:40 AM   #52
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Originally Posted by GlennB View Post
Tiny mass and tiny rockets in comparison. Also squat in design making them more stable, and much lower gravity to contend with.
Squat makes them less stable, not more. It's easier to balance long and thin objects, due to the higher moment of inertia resisting toppling. Try balancing a ruler on one edge, versus one end.

Honestly, first stage reuse is something we could have been doing for decades, but the established players have had little motivation to reduce costs. For those sporadic attempts to come up with something better (notably not initiated by those established players), we've been too enamored with revolutionary supertech spaceplanes and SSTOs instead of following a reasonable development path that takes advantage of the benefits of staging and allows incremental improvement.


Originally Posted by luchog View Post
Why is it necessary to land the entire rocket? Why can't they leave the BFR in orbit as a station, and use a smaller Apollo-style lander to get on and off the planet? Obviously it'll need to be bigger than Apollo due to the higher gravity and larger fuel requirement, but nowhere near as big as a full interplanetary rocket.
It takes a lot more propellant to brake into orbit than it does to land after reentry (roughly 6 km/s of delta-v that has to be done with engines instead of heat shielding), and the Apollo lander left most of itself on the surface, which is a bit of an obstacle for reuse. And if your main craft can't land, then after you return to Earth, you've got to brake into orbit there and use something else to get back to the ground, while your big craft is in orbit where maintenance and repair are far more difficult.

SpaceX isn't interested in a quick visit with throw-away hardware, their system is intended to refuel and return to Earth to be used again.
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Old 30th September 2017, 08:01 AM   #53
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Originally Posted by luchog View Post
Can you point me to where I said anything about Tesla?
Why would I do that, since I'm the one who brought him up as a parallel?
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Old 30th September 2017, 08:04 AM   #54
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Originally Posted by William Parcher View Post
Elon Musk wants to fly you anywhere in the world in less than an hour



Anywhere in the world in less than an hour. Flying at 17,000mph. A ticket for a seat will cost the same as economy jet airliner.

I'm skeptical.


http://money.cnn.com/2017/09/29/tech...vel/index.html
Probably a large motivation for mentioning this possibility is just to get attention of the press, something the system would technically be capable of doing, not something they have serious plans for. However, it's something they might consider doing at cost or even at a loss to keep the system active and flying...it's bad for safety and reliability to have a system that is only operated rarely (one of the major problems with the planned every-other-year cadence of the SLS). If/when would depend on what other business they can find for it.

Multiple geographically separated launch sites would also make it easier to manage the tanker flights for refueling (multiple launch windows per day to a given plane), and flying might be the easiest way to get the upper stages where they need to be in a timely manner. They might take these as opportunities to send a couple years worth of space tourists on a nearly-orbital flight that makes New Shepard and SS2 look like bouncing on a trampoline.
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Old 30th September 2017, 08:15 AM   #55
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We know that jets crash from time to time. Usually everyone on board dies and in some cases people on the ground die too. If a BFR crashes we would also expect passengers to die. But what about people on the ground? Is a crashing BFR a bigger ground disaster than a jet?
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Old 30th September 2017, 09:36 AM   #56
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Originally Posted by cjameshuff View Post
Squat makes them less stable, not more. It's easier to balance long and thin objects, due to the higher moment of inertia resisting toppling. Try balancing a ruler on one edge, versus one end.
Sorry, but this is nonsense. The most stable arrangement for a ruler is the squattest - i.e. flat.

I've been dealing with wooden battens much of the day, 100cm x 6cm x 4cm, making planting boxes. If I balanced one on its 6x4 end a slight breeze would knock it over. On its 100 x 4 edge it's pretty damn stable, on its 100 x 6 edge the most stable. Things tend to fall when their c-of-g leaves their footprint, which is easier to achieve for tall, slender things.
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Old 30th September 2017, 09:45 AM   #57
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Falcon 9 lands, tips over and explodes - on video.

https://www.youtube.com/watch?v=I8tO-vUrEsI
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Old 30th September 2017, 10:45 AM   #58
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Originally Posted by Beelzebuddy View Post
After all, I don't see anyone else landing their rockets on anything.
I assume you mean except NASA. This technology came straight from DC-X dating back to 1996. I assume if reusable becomes practical then NASA will return to it.
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Old 30th September 2017, 11:12 AM   #59
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Originally Posted by GlennB View Post
Sorry, but this is nonsense. The most stable arrangement for a ruler is the squattest - i.e. flat.

I've been dealing with wooden battens much of the day, 100cm x 6cm x 4cm, making planting boxes. If I balanced one on its 6x4 end a slight breeze would knock it over. On its 100 x 4 edge it's pretty damn stable, on its 100 x 6 edge the most stable. Things tend to fall when their c-of-g leaves their footprint, which is easier to achieve for tall, slender things.
Your reasoning is limited to objects resting on solid surfaces with disturbing forces trying to tip them over. Try balancing that ruler flat...actually balancing it on a point, not resting it on a surface. You'll have a hard time just finding the right point with the ruler flat, while you can easily adjust for poor placement when balancing it on one end. You could even balance it on one corner. For another example, take a typical hexagonal pencil. Balance it on one edge...virtually impossible, it tips before you can react. Balance it on the sharpened tip...not all that difficult.

Rockets in flight aren't at static rest with breezes pushing them over, and the concept of keeping CoG within a footprint doesn't even apply to them. Actually, even the balancing object analogy is incorrect because the force vector is fixed, but it suffices to demonstrate the difference the moment of inertia makes. What matters is that the vector of thrust from the engines go through the CoG. With a squat and wide rocket, CoG errors due to payload distribution, propellant slosh, etc can drive the CoG far from the line of thrust, and due to their placement right up close to the CoG, the engine will have to gimbal more widely to correct, which will slow its ability to correct the error while the vehicle is responding more quickly to the thrust error due to the lower moment of inertia around the relevant axes.
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Old 30th September 2017, 11:39 AM   #60
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Originally Posted by barehl View Post
I assume you mean except NASA. This technology came straight from DC-X dating back to 1996. I assume if reusable becomes practical then NASA will return to it.
The technology goes a lot further back, nobody's claiming it's SpaceX's invention, they're just the first to actually move forward with using it for first stage reuse. Also, DC-X was not a NASA project, had little internal support from NASA after being transferred to them, and was promptly killed off when the vehicle was destroyed due to a leg failure. NASA favored their X-33 super-duper-SSTO-spaceplane, which they poured over a billion dollars into before finally canceling.

In the meantime, they kept flying the first generation Shuttle despite it proving to be one of the most expensive ways to deliver mass to orbit (and having numerous fundamental issues), and now they're building the SLS based on the same hardware, primarily as a result of Congress mandating that they do so, despite the fact that each launch will cost more than the X-33 boondoggle.

On the other hand, we have SpaceX which has successfully driven launch costs down by a large factor and is actually reusing first stages of a full scale launch vehicle on operational flights while taking the majority of the world's commercial space launch market. So I'm not sure why you'd prefer NASA support as an indicator of something being economical or practical.
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Old 30th September 2017, 11:46 AM   #61
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Originally Posted by cjameshuff View Post
Your reasoning is limited to objects resting on solid surfaces with disturbing forces trying to tip them over. ....
Scroll back and read what we were talking about. It's precisely 'resting on a solid surface' that we were discussing, in relation to a SpaceX rocket landing on an irregular rocky surface and whether a flat landing pad might be necessary . A squat design like the Lunar Lander has an advantage on the irregular surface.
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Old 30th September 2017, 01:47 PM   #62
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Originally Posted by GlennB View Post
Scroll back and read what we were talking about. It's precisely 'resting on a solid surface' that we were discussing, in relation to a SpaceX rocket landing on an irregular rocky surface and whether a flat landing pad might be necessary . A squat design like the Lunar Lander has an advantage on the irregular surface.
Sorry, yes, that's correct. Typically when the subject comes up, it's someone talking about the landing burn itself, not sitting on the ground afterward, and you're lucky if they don't suggest a tractor configuration to "solve" the problem.

Fortunately neither destination has much to worry about in terms of wind, but they'll have to carefully select their landing surface based on orbital imagery (or resurrect Red Dragon as a precursor probe). It doesn't sound like they envision robotically deploying an ice drill and solar panels, but it would be a good idea to have the first landers send out some rovers to scout good sites for the followup landers, and maybe do something to clear debris, spray some radar-reflective paint, etc. Even with level ground, I wouldn't be surprised if some of the first vehicles to land ended up stuck there due to damage from flying rocks, and some simple work with rovers could reduce that risk.
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Old 30th September 2017, 02:14 PM   #63
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Originally Posted by cjameshuff View Post
Sorry, yes, that's correct. Typically when the subject comes up, it's someone talking about the landing burn itself, not sitting on the ground afterward, and you're lucky if they don't suggest a tractor configuration to "solve" the problem.

Fortunately neither destination has much to worry about in terms of wind, but they'll have to carefully select their landing surface based on orbital imagery (or resurrect Red Dragon as a precursor probe). It doesn't sound like they envision robotically deploying an ice drill and solar panels, but it would be a good idea to have the first landers send out some rovers to scout good sites for the followup landers, and maybe do something to clear debris, spray some radar-reflective paint, etc. Even with level ground, I wouldn't be surprised if some of the first vehicles to land ended up stuck there due to damage from flying rocks, and some simple work with rovers could reduce that risk.
Yes, that was my thought too hence the idea of a landing pad, though that poses some serious technical questions. But (also) given that the current rovers can manage to haul themselves around and not a huge amount more, how could they clear those 500kg boulders that might pose a real risk to the stability of the rocket? Ziggurat suggested self-leveling legs, and that could work, but with such a leg perched on the edge of a boulder and then the rocket unloads, shifting the weight maybe ... ? It all sounds rather flakey.
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Old 30th September 2017, 03:35 PM   #64
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Originally Posted by GlennB View Post
Yes, that was my thought too hence the idea of a landing pad, though that poses some serious technical questions. But (also) given that the current rovers can manage to haul themselves around and not a huge amount more, how could they clear those 500kg boulders that might pose a real risk to the stability of the rocket? Ziggurat suggested self-leveling legs, and that could work, but with such a leg perched on the edge of a boulder and then the rocket unloads, shifting the weight maybe ... ? It all sounds rather flakey.
They're not limited to equipment launched with an Atlas V and dropped onto the surface with a skycrane. There's 150+ metric tons of payload to work with in this system. The first to land is still going to have to rely on luck, good orbital imagery, and whatever robustness they can design into the legs, but if the first succeeds, the second will have much better chances.

Even if every transport finds a nice flat spot to land, there's going to be crap in the way of other stuff, so, a remote operated bulldozer with mechanisms to place and detonate blasting charges would likely see plenty of use. Maybe it could also unpack some solar panels to recharge itself and keep the transport operating until the manned craft arrive. Or they could do something quite different...these are details that could be approached in a number of different ways. One thing I've considered for early operations after they've drilled into a glacier is to use water ice as a paving material for temporary pads...fill up what's essentially a large plastic bag to keep it liquid and in place as it freezes.
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Old 30th September 2017, 04:51 PM   #65
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Originally Posted by William Parcher View Post
Falcon 9 lands, tips over and explodes - on video.

https://www.youtube.com/watch?v=I8tO-vUrEsI
Yeah, this was their FIRST attempt, and they have ironed out a lot of the bugs. Quoting that video, is rather like showing some video of the early pre-Mercury launch failures giving it an an example of modern rocketry

Since that landing failure, they have successfully landed 16 in a row, and each one went perfectly. They have made taking a 40m long, 4m diameter cylinder doing 4000 km/h at an altitude of over 100 km and soft-landing it upright on the earth look routine and easy, which it is anything but.

The haters and doubters all said it was impossible... well SpaceX are making the impossible look easy.

ETA: Perhaps this would be a good chance to review NASA's early record. Prior to the first manned launch when Alan Shepard flew sub-orbital on a Redstone rocket , NASA launched 17 unmanned missions... only eight total successes (less than 50%), five total failures and four partial successes (i.e. some but not all mission objectives were a success)
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Old 30th September 2017, 11:11 PM   #66
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Originally Posted by smartcooky View Post
Yeah, this was their FIRST attempt, and they have ironed out a lot of the bugs. Quoting that video, is rather like showing some video of the early pre-Mercury launch failures giving it an an example of modern rocketry

Since that landing failure, they have successfully landed 16 in a row, and each one went perfectly. They have made taking a 40m long, 4m diameter cylinder doing 4000 km/h at an altitude of over 100 km and soft-landing it upright on the earth look routine and easy, which it is anything but.

The haters and doubters all said it was impossible... well SpaceX are making the impossible look easy.

ETA: Perhaps this would be a good chance to review NASA's early record. Prior to the first manned launch when Alan Shepard flew sub-orbital on a Redstone rocket , NASA launched 17 unmanned missions... only eight total successes (less than 50%), five total failures and four partial successes (i.e. some but not all mission objectives were a success)
I think William Parcher was illustrating the point about how a slightly misaligned tall, slender thing tends to fall over - which was the subject being discussed at the time - rather than knocking SpaceX's ability to land things. Their terrestrial landings are on purpose-built pads, not rough rocky surfaces.
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Old 1st October 2017, 03:08 AM   #67
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Originally Posted by GlennB View Post
I think William Parcher was illustrating the point about how a slightly misaligned tall, slender thing tends to fall over - which was the subject being discussed at the time - rather than knocking SpaceX's ability to land things. Their terrestrial landings are on purpose-built pads, not rough rocky surfaces.

Yeah, but that failure wasn't a good landing followed by some inherent instability due to the tallness of the rocket causing it to fall over. This happened because of mechanical failure. The locking mechanism on one the legs failed to latch into place. It doesn't matter how squat the spacecraft is, if it loses a leg, it will fall over. One of the LM legs breaking like this in the Apollo landings would likely have been a death sentence for the two astronauts.
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Old 1st October 2017, 03:14 AM   #68
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Originally Posted by smartcooky View Post
Yeah, but that failure wasn't a good landing followed by some inherent instability due to the tallness of the rocket causing it to fall over. This happened because of mechanical failure. The locking mechanism on one the legs failed to latch into place. It doesn't matter how squat the spacecraft is, if it loses a leg, it will fall over. One of the LM legs breaking like this in the Apollo landings would have been a death sentence for the two astronauts.
I agree, but a 'leg landing on a hefty rock or in a hole' could have the same effect.

I like cjameshuff's idea of first sending up small bulldozers to clear the area, though I'd also like to see such concepts tested in advance.
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Old 1st October 2017, 03:40 AM   #69
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Originally Posted by GlennB View Post
I agree, but a 'leg landing on a hefty rock or in a hole' could have the same effect.
I can't imagine that with the technical people at SpaceX being as brilliant as they are, that they would not have thought of this.

The solution could be quite tricky. For example, legs that can electro-mechanically change their angle, using a combination of pressure sensors on the legs and a tilt sensor to keep the ship upright. Hell they could even take a leaf out of Andy Weir's book (The Martian) and use the RCS thrusters to stabilise the ship while the legs get into position.
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Old 1st October 2017, 10:32 AM   #70
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Originally Posted by smartcooky View Post
I can't imagine that with the technical people at SpaceX being as brilliant as they are, that they would not have thought of this.

The solution could be quite tricky. For example, legs that can electro-mechanically change their angle, using a combination of pressure sensors on the legs and a tilt sensor to keep the ship upright. Hell they could even take a leaf out of Andy Weir's book (The Martian) and use the RCS thrusters to stabilise the ship while the legs get into position.
Yes, but we have an example above of a technical failure that led to a rocket toppling and exploding on landing. However 'brilliant' they were it was still a failure.

This brings me back to a point I've made a few times now - those early SpaceX failures were relatively cheap, and the time to next trial was short. A failure of a significant BFR on Mars (the one carrying the aforementioned bulldozer, say) is a different matter. It's ****** expensive and windows for Mars missions are not so easy to find. What's more, if future missions depend on 'the bulldozer working' then it sets back a whole series of missions, stretching some years into the future, and it's a commercial enterprise after all.

They need to test this stuff on Earth. The ships , the fuel-generation setup, the unloading and loading of payloads and fuel, the robotics that will perform all the grunt work ... it's going to be not only ferociously expensive but it's also going to involve developing a lot of advanced technology that doesn't yet exist. SpaceX is strangely silent on the matter.

Way back I calculated here the absolute minimum (insanely so, deliberately) energy cost of synthesising methane from materials on Mars, assuming 100% process efficiency and ignoring the cost of actually getting the raw materials (H2 and CO2) into place. It turned out to be the equivalent of about 1000 typical domestic solar arrays running for a full year, or something equally improbable. I'll search back and get the figures, but the energy of enthalpy for methane synthesis is well known.

Like the man said in the original article - "Eventually vision has to give way to engineering" (paraphrasing there). It also sometimes has to give way to economics.
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Old 1st October 2017, 11:58 AM   #71
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Originally Posted by GlennB View Post
Yes, but we have an example above of a technical failure that led to a rocket toppling and exploding on landing. However 'brilliant' they were it was still a failure.
Its a technical failure, not a failure to anticipate an obvious potential pitfall.

So far from 2010 to 2017 there have been 107 air accidents resulting in 2926 fatalities, and yet over 1 million people willingly get on aeroplanes to fly to their destinations every day.


Originally Posted by GlennB View Post
This brings me back to a point I've made a few times now - those early SpaceX failures were relatively cheap, and the time to next trial was short. A failure of a significant BFR on Mars (the one carrying the aforementioned bulldozer, say) is a different matter. It's ****** expensive and windows for Mars missions are not so easy to find. What's more, if future missions depend on 'the bulldozer working' then it sets back a whole series of missions, stretching some years into the future, and it's a commercial enterprise after all.

They need to test this stuff on Earth. The ships , the fuel-generation setup, the unloading and loading of payloads and fuel, the robotics that will perform all the grunt work ... it's going to be not only ferociously expensive but it's also going to involve developing a lot of advanced technology that doesn't yet exist. SpaceX is strangely silent on the matter.

Way back I calculated here the absolute minimum (insanely so, deliberately) energy cost of synthesising methane from materials on Mars, assuming 100% process efficiency and ignoring the cost of actually getting the raw materials (H2 and CO2) into place. It turned out to be the equivalent of about 1000 typical domestic solar arrays running for a full year, or something equally improbable. I'll search back and get the figures, but the energy of enthalpy for methane synthesis is well known.

Like the man said in the original article - "Eventually vision has to give way to engineering" (paraphrasing there). It also sometimes has to give way to economics.
An optimized Sabatier reaction system massing 50 kg is projected to produce 1 kg/day of O2:CH4 propellant ... with a methane purity of 98+% while consuming 700 Watts of electrical power. Its not enough, they will need to be thinking in the 10's of kilowatts, and IMO, they will either have to go the nuclear reactor or nuclear battery way.

http://www.world-nuclear.org/informa...for-space.aspx

Getting one to Mars is likely to be problematic.
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Old 2nd October 2017, 03:00 PM   #72
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Another way to look at it: they are relying on the ability to reuse spacecraft to reduce costs, with the eventual goal of returning spacecraft within the same synod. It's likely going to take more than one BFR loaded with solar panels to deploy enough solar production to support one BFR return per synod, so you're going to end up with a bunch of BFRs stuck on the ground waiting for subsequent synods for a chance to go home. Even for those that can do so, this means there's a good chance that they won't be able to make it back to Mars with another payload that synod, or will have a reduced payload if they can.

Even if they ultimately want solar to be the primary power source, a nuclear power system in one of the first flights could drastically speed deployment, maybe allowing them to transport a bunch of manufacturing equipment instead of stacks of panels and set up local solar panel production. And it'll have to be a reactor...a multi-megawatt nuclear battery would be rather tricky to transport, not to mention the quantity of radioactive material required.

There's been some work on microreactors that might be relatively easily adaptable to Mars. The Toshiba 4S, for example, a fast neutron sodium-cooled reactor.
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Old 2nd October 2017, 05:31 PM   #73
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Originally Posted by cjameshuff View Post
Another way to look at it: they are relying on the ability to reuse spacecraft to reduce costs, with the eventual goal of returning spacecraft within the same synod. It's likely going to take more than one BFR loaded with solar panels to deploy enough solar production to support one BFR return per synod, so you're going to end up with a bunch of BFRs stuck on the ground waiting for subsequent synods for a chance to go home. Even for those that can do so, this means there's a good chance that they won't be able to make it back to Mars with another payload that synod, or will have a reduced payload if they can.

Even if they ultimately want solar to be the primary power source, a nuclear power system in one of the first flights could drastically speed deployment, maybe allowing them to transport a bunch of manufacturing equipment instead of stacks of panels and set up local solar panel production. And it'll have to be a reactor...a multi-megawatt nuclear battery would be rather tricky to transport, not to mention the quantity of radioactive material required.

There's been some work on micro reactors that might be relatively easily adaptable to Mars. The Toshiba 4S, for example, a fast neutron sodium-cooled reactor.
I wonder whether, long term, the best solution would be to use some of the several different "Mars Cyclers" (a la Andy Weir's Hermes spacecraft). Initial cost is enormous, but its almost the ultimate in reusability so cost per mission comes down dramatically. There are about 19 different valid Mars Cyclers that have Earth-Mars flight times of between 75 and 280 days. There are five with flight times less than 100 days. Pick the right orbits and you could have a spacecraft on a Mars Cycler passing the Earth(or Mars) every few months with no more than a 14 week trip either way.

Take as an example, the Aldrin Cycler; a single eccentric loop around the sun from Earth to the Martian orbit. It takes 146 days to fly outbound from Earth to Mars, spends the next 16 months beyond the orbit of Mars and then flies past Mars inbound taking another 146 days from Mars back to Earth, spending another 14 months or days inside the Earth's orbit.
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Old 2nd October 2017, 08:50 PM   #74
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Originally Posted by smartcooky View Post
I wonder whether, long term, the best solution would be to use some of the several different "Mars Cyclers" (a la Andy Weir's Hermes spacecraft). Initial cost is enormous, but its almost the ultimate in reusability so cost per mission comes down dramatically. There are about 19 different valid Mars Cyclers that have Earth-Mars flight times of between 75 and 280 days. There are five with flight times less than 100 days. Pick the right orbits and you could have a spacecraft on a Mars Cycler passing the Earth(or Mars) every few months with no more than a 14 week trip either way.

Take as an example, the Aldrin Cycler; a single eccentric loop around the sun from Earth to the Martian orbit. It takes 146 days to fly outbound from Earth to Mars, spends the next 16 months beyond the orbit of Mars and then flies past Mars inbound taking another 146 days from Mars back to Earth, spending another 14 months or days inside the Earth's orbit.
Cyclers are useful for transporting things like passengers who like large spaces, low radiation, and other perks of low mass constraints, but they aren't any help for moving cargo. You've got a lot of cargo to move before you can support enough people for the cyclers to be useful. You also still need a spacecraft along the lines of the BFR transport to get passengers between Earth, the cycler, and Mars, and the delta-v budget for that spacecraft will actually need to be larger to accommodate rendezvous with the cycler, so it won't get around the need to produce propellant at Mars.
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Old 3rd October 2017, 12:35 AM   #75
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Originally Posted by cjameshuff View Post
Another way to look at it: they are relying on the ability to reuse spacecraft to reduce costs, with the eventual goal of returning spacecraft within the same synod. It's likely going to take more than one BFR loaded with solar panels to deploy enough solar production to support one BFR return per synod, so you're going to end up with a bunch of BFRs stuck on the ground waiting for subsequent synods for a chance to go home. Even for those that can do so, this means there's a good chance that they won't be able to make it back to Mars with another payload that synod, or will have a reduced payload if they can.

Even if they ultimately want solar to be the primary power source, a nuclear power system in one of the first flights could drastically speed deployment, maybe allowing them to transport a bunch of manufacturing equipment instead of stacks of panels and set up local solar panel production. And it'll have to be a reactor...a multi-megawatt nuclear battery would be rather tricky to transport, not to mention the quantity of radioactive material required.

There's been some work on microreactors that might be relatively easily adaptable to Mars. The Toshiba 4S, for example, a fast neutron sodium-cooled reactor.
Something along those lines, though that "microreactor" is still damn big and heavy - 3.5m diameter reactor vessel and a length I'd estimate at 10x that, plus steam generator and turbine. Plus the reactor needs to be underground in a purpose-built bunker with the rest of the gear in a substantial building above ground.
Toshiba 4S presentation
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Old 3rd October 2017, 04:45 AM   #76
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Originally Posted by GlennB View Post
Something along those lines, though that "microreactor" is still damn big and heavy - 3.5m diameter reactor vessel and a length I'd estimate at 10x that, plus steam generator and turbine. Plus the reactor needs to be underground in a purpose-built bunker with the rest of the gear in a substantial building above ground.
Toshiba 4S presentation
It's split up into road-transportable parts, and being a sodium-cooled fast reactor, it doesn't have the immensely heavy pressure vessel PWRs would require. And the standard version is meant to be buried in a silo when permanently deployed on Earth, it may be adaptable to other approaches when used as bootstrap power on Mars...say a pyramid of sandbags in a crater. The design will likely require modification anyway (natural convection will not transfer as much heat in Mars gravity).

If all goes well, there will be 4 transports with 600 metric tons of supplies and equipment waiting before the first human landing, and they'll bring more with them. It should be possible to squeeze in enough gear to handle the construction work for something like this, though the specific materials and structures may be a bit different.
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Old 3rd October 2017, 05:12 AM   #77
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Originally Posted by cjameshuff View Post
It's split up into road-transportable parts, and being a sodium-cooled fast reactor, it doesn't have the immensely heavy pressure vessel PWRs would require. And the standard version is meant to be buried in a silo when permanently deployed on Earth, it may be adaptable to other approaches when used as bootstrap power on Mars...say a pyramid of sandbags in a crater. The design will likely require modification anyway (natural convection will not transfer as much heat in Mars gravity).

If all goes well, there will be 4 transports with 600 metric tons of supplies and equipment waiting before the first human landing, and they'll bring more with them. It should be possible to squeeze in enough gear to handle the construction work for something like this, though the specific materials and structures may be a bit different.
It's a sideline discussion really, interesting but not too relevant. SpaceX say they're planning to use solar panels.
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Old 3rd October 2017, 12:16 PM   #78
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Originally Posted by Argumemnon View Post
Why would I do that, since I'm the one who brought him up as a parallel?

Irrelevant nonsense, got it.
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Old 3rd October 2017, 05:38 PM   #79
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Originally Posted by GlennB View Post
It's a sideline discussion really, interesting but not too relevant. SpaceX say they're planning to use solar panels.
They show fields of solar panels in the promotional video, but as I recall, Musk has talked about the possibility of using nuclear power. My feeling is that they'll go solar to get established enough to set up a nuclear plant, and largely nuclear to get built up enough to start producing solar panels from local resources. Beyond that...solar's not as effective on Mars and is subject to dust, but it's a hell of a lot easier to plop down some solar panels to power a remote research outpost.

If they do go nuclear, it's not going to be right away...not unless BFR is badly delayed by even the standards of SpaceX's development timelines. Nothing involving nuclear power happens quickly, and any commercial reactors would require heavy customization. Non-commercial reactors...I'm not sure I'd rely on NASA to produce a nuclear reactor any time this century and for less than the cost of the entire colony effort.
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Old 4th October 2017, 02:20 AM   #80
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Why would Musk want to rely on NASA at all, for any of this project?

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