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Weighted suits won't replicate in full 1G effects but on Mars they will I think improve greatly upon a 0.38G environment. Wearing a 1G suit will not make the wearer any more tired than operating in 1G on Earth. I think a properly designed day suit would probably resolve 95% of the muscle and bone loss issue.
For the flight, there are some potential amelioration strategies:
https://www.theguardian.com/science/201 … rs-mission
I don't think we are going to get a full range of solutions at this stage but we can do enough to ensure the crew return in reasonable good health. We know that after his marathon 437 days flight Valeri Polyakov was able to walk immediately with help and by himself later the same day after landing.
See this article:
https://www.upi.com/Feature-Excerpt-2-f … 100584800/
This has an interesting quotation:
"Moreover, his bone loss had been very low, only around 7 percent in some of his weight-bearing bones, a rate of 0.5 percent per month, confirming once again his belief, shared by other Russian doctors, that the exercise program had kept that loss low -- low enough for him to survive a two-year trip to and from Mars."
He was an incredibly determined individual. You need to inculcate that in the crew. Would be no good to fill them with foreboding and expectations of medical disaster when there is no reason to think along those lines.
I wish people would stop assuming that weighted suits on Mars will compensate for the gravitational differential, which is a scientific fallacy. The extreme exercise routines done on the ISS have done little to alleviate the effects of microgravity disease. All that wearing a weighted suit on Mars will do is make the wearer tired and reduce productive output. To make this assumption is simply dismissive of reality and morally irresponsible.
Robert Zubrin didn't dismiss this problem; for Musk to do so is overlooking one of the major stumbling blocks in his plan to colonize Mars.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Louis, we've discussed this before. Weighted suits address (inadequately as Oldfart1939 pointed out) bone loss and muscle weakening. It likely does not address heart atrophy (I don't believe anybody really knows yet).
It cannot address vision problems from fluid distribution imbalance, which do appear to have permanent effects. It cannot address immune system degradation, which is a recent discovery about which we know only that such damage exists. It cannot address genetic changes, the latest discovery, about which nothing is known; and which was a very unexpected surprise.
Doing spin gravity addresses every single one of those effects. The choice is utterly clear: just DO it! Why deliberately take risks you already know how to avoid? THAT is stupidly and vilely unethical.
And, yeah, you can do spin gravity in Musk's BFS. You need two flying together. Dock them tail-to-tail, just they they already plan to do for refilling in LEO. Then spin the pair end over end at about 4 rpm. You'll get around half a gee in all the pressurized spaces, as eyeball-scaled from their inboard profile illustrations.
Such is more important for the Earth return than for the outbound trip to Mars. The peak gees are lower at Mars for a wider range of entry angles. At Earth, it might be possible to ride home at 4 peak gees, but you will run considerable risk of bouncing off the atmosphere. Apollo came in at about 2 degrees below tangent, and peaked at 11 gees.
GW
Last edited by GW Johnson (2018-06-21 08:08:45)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Weighed suits are what we use for diving to keep the diver from rising as they are trying to descend to the bottom of the pool from the bouyancy. It does just as Oldfart1939 and other have said in that it will just make the wearer tire out more rapidly. It is well known that exercise will only do so much for the crew.
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GW,
Actually we do already know that weighted suits don't address cardiac muscle atrophy. Chris said that was a known quantity and nothing they tried was able to completely prevent it. The upper body muscles did not atrophy and he said he actually gained upper body muscle from his time on the space station. However, nothing tried to date has prevented bone loss in the femurs and pelvic girdle or muscle loss there. That's required to walk and support a heavy load on your back. They still don't even know what causes the bone decalcification and vision problems, so there's definitely no way to prevent this. All they know is that it happens immediately upon exposure to microgravity. Chris said you start pissing out calcium from day one. That's a pretty clear indicator that there's only one sure way to fix the problem, until we can suppress whatever unknown mechanism is causing the problem.
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No one has ever tested a 1G equivalent weighted suit on the Moon or Mars. I suspect it would definitely address pelvic leg bone muscle/bone loss when combined with the effects of the 0.38 natural gravity.
GW,
Actually we do already know that weighted suits don't address cardiac muscle atrophy. Chris said that was a known quantity and nothing they tried was able to completely prevent it. The upper body muscles did not atrophy and he said he actually gained upper body muscle from his time on the space station. However, nothing tried to date has prevented bone loss in the femurs and pelvic girdle or muscle loss there. That's required to walk and support a heavy load on your back. They still don't even know what causes the bone decalcification and vision problems, so there's definitely no way to prevent this. All they know is that it happens immediately upon exposure to microgravity. Chris said you start pissing out calcium from day one. That's a pretty clear indicator that there's only one sure way to fix the problem, until we can suppress whatever unknown mechanism is causing the problem.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Doing spin gravity addresses every single one of those effects. The choice is utterly clear: just DO it! Why deliberately take risks you already know how to avoid? THAT is stupidly and vilely unethical.
GW
Primum non nocere.
As a physician, I perfectly agree with you on the necessity to spin the ship to not damage the astronauts: whatever it costs, is far less than the cost of a dead or at least severely crippled crew.
Joining two ships tail-to-tail and spinning them needs to redesign the power system: either spinning the two ships on the ecliptic plane and mounting the solar panels on a counter-rotating platform, or using a nuclear reactor (the latter IMHO is wiser, given they need to produce a huge amount of propellant for coming back.)
Last edited by Quaoar (2018-06-22 14:59:43)
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I still don't understand this rear to rear refueling thing. What happens if you collide? Gonna trash the heat shields and engines on two ships at the same time? If the probes extend, then I take less of an issue with the tanking solution, but hazarding your one and only means home is a very bad idea, plain and simple. People make mistakes and computers make mistakes if they were programmed by humans.
The ship was clearly intended to take a compressive load directly through the structure during flight and through the landing legs. Now we're gonna put torque on it, too? Maybe there's some way to connect and lock the landing legs together after extension to provide some stand-off between the two vessels. The landing legs should be able to handle some torque in the case of an off-nominal landing. That would increase the radius of the crew compartment, too. More gravity is better until you hit 1g, right?
How hard is it to construct a spinning wheel and counter-rotate a water tank, or just the fluid inside the tank, inside the core module that the wheel is connected to in order to contend with gyroscopic precession? Compared to landing a rocket vertically in the sand, this should be child's play.
like this:
Spaceships in Mars orbit by James Vaughan
or this:
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Why on earth (or in space) would they collide? We have cars on Earth that can do pinpoint robotic parking time after time after time. We have railways that have robot trains that never collide. And - think about it - putting two rockets together in pretty much empty space is a lot simpler task than developing self-drive cars which have to cope with a highly complex environment comprising humans, vehicles, road markings, traffic lights, signs and natural objects like trees.
I still don't understand this rear to rear refueling thing. What happens if you collide? Gonna trash the heat shields and engines on two ships at the same time? If the probes extend, then I take less of an issue with the tanking solution, but hazarding your one and only means home is a very bad idea, plain and simple. People make mistakes and computers make mistakes if they were programmed by humans.
The ship was clearly intended to take a compressive load directly through the structure during flight and through the landing legs. Now we're gonna put torque on it, too? Maybe there's some way to connect and lock the landing legs together after extension to provide some stand-off between the two vessels. The landing legs should be able to handle some torque in the case of an off-nominal landing. That would increase the radius of the crew compartment, too. More gravity is better until you hit 1g, right?
How hard is it to construct a spinning wheel and counter-rotate a water tank, or just the fluid inside the tank, inside the core module that the wheel is connected to in order to contend with gyroscopic precession? Compared to landing a rocket vertically in the sand, this should be child's play.
like this:
Spaceships in Mars orbit by James Vaughan
or this:
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Why do you think people are going to die from being in zero G/ microgravity when no one has died from that to date, despite several hundred astronauts/cosmonauts having gone into space for extended periods? Polyakov was in zero G for well over 400 days and was able to function well within days on return to 1G.
You are risking people's lives much more by trying to develop a novel solution that has not yet been tried in a serious manner. One slight error and you could find your rocket being propelled in completely the wrong direction and a crew potentially being put into the equivalent of a rollercoaster ride while having to make life and death decisions.
The risk of zero and micro gravity has been hugely exaggerated. Stick with what we know. No one will die. No one will get ill by any meaningful definition of "ill". There will be some negative effects, that's all. The equivalent of being forced to lie in bed solidly for a few weeks. No more than that.
GW Johnson wrote:Doing spin gravity addresses every single one of those effects. The choice is utterly clear: just DO it! Why deliberately take risks you already know how to avoid? THAT is stupidly and vilely unethical.
GWPrimum non nocere.
As a physician, I perfectly agree with you on the necessity to spin the ship to not damage the astronauts: whatever it costs, is far less than the cost of a dead or at least severely crippled crew.Joining two ships tail-to-tail and spinning them needs to redesign the power system: either spinning the two ships on the ecliptic plane and mounting the solar panels on a counter-rotating platform, or using a nuclear reactor (the latter IMHO is wiser, given they need to produce a huge amount of propellant for coming back.)
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Louis-
You need to pay attention to the reasons outlined by GW, re: reentry at hi gees. Please don't play the innocent game of brushing aside reasons not in accordance with your desires.
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The risk of zero and micro gravity has been hugely exaggerated. Stick with what we know. No one will die. No one will get ill by any meaningful definition of "ill". There will be some negative effects, that's all. The equivalent of being forced to lie in bed solidly for a few weeks. No more than that.
The astronauts will make a fiery re-entry through the Earth's atmosphere at more than 500mph, Shedding hardware it no longer needs, it will re-enter the atmosphere with a parachute slowing it down to a more manageable 179mph or so, before rocket engines slow it further as it gets closer to the ground.
http://www.dailymail.co.uk/sciencetech/ … s-ISS.html
The astronauts are carried rom the capsule tired and exhausted.
'They arrived in space like baby birds barely able to fly and now they soar home as eagles. Great job Kjell and Kimiya!'
Health is just one thing as the article points out even with constant cargo going to the station.
The pantry got a little too empty for NASA's taste over the past year - besides the two lost commercial shipments to the ISS, Russia also endured a failed supply run.
The men completed hundreds of experiments during their time in space, including a study of the effect of microgravity on the bone marrow and research into plant growth in space. They also completed space walks. Shkaplerov completed a record-setting space walk timed at 8 hours and 13 minutes, the longest in Russian space program history, in February.
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GW has never been able to cite a Space X source to confirm that is their plan. I don't believe it is. It will not be an Apollo style high G re-entry.
Louis-
You need to pay attention to the reasons outlined by GW, re: reentry at hi gees. Please don't play the innocent game of brushing aside reasons not in accordance with your desires.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Pics of astronauts being carried are irrelevant. They are inside heavy and restrictive space suits. They have been in zero G for a long time. They aren't going to be able to perform somersaults for a while. But they haven't been made horribly ill. They are simply transitioning from one gravity state to another. If you've been in a swimming pool for 8 hours solid it's not that easy to start running at your top speed immediately on exiting the pool. There's just a lot of hysteria about this.
Loius wrote:The risk of zero and micro gravity has been hugely exaggerated. Stick with what we know. No one will die. No one will get ill by any meaningful definition of "ill". There will be some negative effects, that's all. The equivalent of being forced to lie in bed solidly for a few weeks. No more than that.
The astronauts will make a fiery re-entry through the Earth's atmosphere at more than 500mph, Shedding hardware it no longer needs, it will re-enter the atmosphere with a parachute slowing it down to a more manageable 179mph or so, before rocket engines slow it further as it gets closer to the ground.
http://www.dailymail.co.uk/sciencetech/ … s-ISS.html
The astronauts are carried rom the capsule tired and exhausted.
'They arrived in space like baby birds barely able to fly and now they soar home as eagles. Great job Kjell and Kimiya!'
Health is just one thing as the article points out even with constant cargo going to the station.
The pantry got a little too empty for NASA's taste over the past year - besides the two lost commercial shipments to the ISS, Russia also endured a failed supply run.
The men completed hundreds of experiments during their time in space, including a study of the effect of microgravity on the bone marrow and research into plant growth in space. They also completed space walks. Shkaplerov completed a record-setting space walk timed at 8 hours and 13 minutes, the longest in Russian space program history, in February.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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https://en.wikipedia.org/wiki/Free-return_trajectory
The speed at a perigee of 6555 km from the centre of the earth for trajectories passing between 2000 and 20 000 km from the moon is between 10.84 and 10.92 km/s regardless of whether the trajectory is cislunar or circumlunar or whether it is co-rotational or counter-rotational.
https://en.wikipedia.org/wiki/Atmospheric_entry
Earth atmospheric reentry speeds might substantially increase for return missions to Mars, with entry speeds in the 15-21 km/s range, depending on trajectory and time of launch.
simple atmosphere reentry guidance scheme for return from the manned Mars mission
A study was made to determine the capability of a fixed attitude, r o l l controlled type of lifting body to accomplish the atmosphere reentry at speeds up to 21 km/sec (maximum estimated speed for return from Mars missions) and to develop a guidance scheme requiring only a limited amount of logic and simple calculations for mechanization.
LUNAR ENTRY DOWNMODE OPTIONS FOR ORION
AN EARTH ENTRY VEHICLE FOR RETURNING SAMPLES FROM MARS
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Why on earth (or in space) would they collide? We have cars on Earth that can do pinpoint robotic parking time after time after time. We have railways that have robot trains that never collide. And - think about it - putting two rockets together in pretty much empty space is a lot simpler task than developing self-drive cars which have to cope with a highly complex environment comprising humans, vehicles, road markings, traffic lights, signs and natural objects like trees.
Accidents happen, Louis. A car doesn't weigh as much as a frigate. This is like two of the heaviest mining trucks in the world, carrying full payloads, hitting each other intentionally just to transfer fuel. In this case, the mining trucks are as light as we can possibly make them. A vehicle as large as a jumbo jet, with a fraction of the jet's structural mass, is not going to fare well if anything more significant than the slightest of impacts occurs. Heat shields are not indestructible and neither are rocket engine nozzles. A piece of insulating foam hit the strongest part of Columbia's wing and she's gone, along with all of her crew.
A 50mm/s closure rate would produce a force equivalent to a .44 Magnum round. You can't shoot at the heat shield or rocket engines without damaging something. So closure rates will have to be extremely precise. The orbiters dock at ISS with a terminal closure rate of 33mm/s and the maximum vehicle mass with payload is about 1/9th that of BFS. Doable? Yes. Dangerous? Needlessly so. It's simple kinetic energy. A stuck thruster valve at the wrong moment can prevent two vehicles from simply landing. How hard could a refueling probe be to design?
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Why do you think people are going to die from being in zero G/ microgravity when no one has died from that to date, despite several hundred astronauts/cosmonauts having gone into space for extended periods? Polyakov was in zero G for well over 400 days and was able to function well within days on return to 1G.
Sure, but then they made a safe reentry from orbit at 4-5 gee, not a direct entry from a Mars-Earth transfer orbit at 14-20 gee.
After spending more than 6 months in microgravity for the outward journey, 18 months at 3.9 gee on Mars surface - we still don't know if 3.9 gee are enough healthy - and other 6 month in microgravity for the inward journey, the astronauts would very likely have an hearth failure due hearth hypotrophy.
Ignoring this issue is not taking a risk, is committing a homicide.
And there is also another consideration: when the astronauts arrive on Mars, after 6-8 months in microgravity, they won't find a rehabilitation center, but an almost unknown alien planet, and they must be in perfect physical shape to cope with the hostile environment.
Last edited by Quaoar (2018-06-23 04:47:13)
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It sounded like you were referencing more the negative health effects of zero/micro-gravity, rather than the challenge of re-entry at Mars transfer velocities, since you were talking of the necessity of spinning the ship during transit to avoid a dead crew...
You want a spinning ship that then hits the Earth's atmosphere at such a hyperspeed, returning from Mars? Doesn't sound like a good idea to me.
I am not suggesting we ignore the issue of high G re-entry. Musk is clearly aware of the problem...
https://www.youtube.com/watch?v=2AaTfQcte8U
He doesn't spell out in detail what the solution is but it appears to be a combination of high performance heat shield and propulsive landing. Space X appears to think they can keep G forces down to 2-3 on return to Earth, which the crew should be able to cope with.
louis wrote:Why do you think people are going to die from being in zero G/ microgravity when no one has died from that to date, despite several hundred astronauts/cosmonauts having gone into space for extended periods? Polyakov was in zero G for well over 400 days and was able to function well within days on return to 1G.
Sure, but then they made a safe reentry from orbit at 4-5 gee, not a direct entry from a Mars-Earth transfer orbit at 14-20 gee.
After spending more than 6 months in microgravity for the outward journey, 18 months at 3.9 gee on Mars surface - we still don't know if 3.9 gee are enough healthy - and other 6 month in microgravity for the inward journey, the astronauts would very likely have an hearth failure due hearth hypotrophy.Ignoring this issue is not taking a risk, is committing a homicide.
And there is also another consideration: when the astronauts arrive on Mars, after 6-8 months in microgravity, they won't find a rehabilitation center, but an almost unknown alien planet, and they must be in perfect physical shape to cope with the hostile environment.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Artifical gravity spin or tumble is stopped a few days before it is time to arrive at the edge of the atmospher as a few days will have no effect on the crew, just look at the crews that came back on the shuttles from each 10 to14 day stay on orbit as they all walk off under no assistance unlike the crews that come down after months to a year barely able to move.
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But no one has ever performed this manouevre at hyper-speed have they? To my mind it's an untried and untested proposal that could potentially kill the crew.
Artifical gravity spin or tumble is stopped a few days before it is time to arrive at the edge of the atmospher as a few days will have no effect on the crew, just look at the crews that came back on the shuttles from each 10 to14 day stay on orbit as they all walk off under no assistance unlike the crews that come down after months to a year barely able to move.
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Uh--Louis. You need a serious review of your analytical mechanics. The spacecraft on a Hohmann trajectory may be treated in space as a body at rest. the superposition of various rotational modes can be accomplished at any speed the system travels. The problems are separable. The rotational movements can be cancelled before any atmospheric entry.
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Louis, if you had even a minimal understanding of high school physics, you would not bring up your latest strawman ("has anyone ever tried such a maneuver at such speed") to avoid addressing microgravity diseases.
The speed along the interplanetary trajectory has ABSOLUTELY NOTHING TO DO with the forces or dynamics experienced spinning-up or de-spinning an object moving along that trajectory. If you can do it sitting still on the ground, you can do it flying at 25 miles per second in interplanetary flight. It is the same.
I cannot cite something from Spacex about Earth entry gees in BFS returning from Mars because Spacex has published NOTHING about this.
That does not negate the fact that all spacecraft experience peak gees on entry that get nonlinearly larger with higher entry speed, nonlinearly larger with shallower grazing angle relative to the surface, and nonlinearly larger with lower (not higher) ballistic coefficient.
There is a database of entry experience stretching back to the first ICBM warheads 6 decades ago demonstrating the validity of this, and it applies to all spacecraft of any kind. And that includes the BFS.
I hate to rub your nose in it, but you cannot dispute well-established facts. The physics of entry is way beyond high school physics, but it is something professionals in the field have done. My first graduate school engineering experience was in a hypersonic wind tunnel, exploring the entry of the space shuttle. Among other things, we found the narrow window of angle-of-attack that was survivable.
Spacex did not even publish the gees for Mars entry trajectory simulation they published on their site, nor have I bothered to back-calculate gees from their velocity-time points in the simulation. But everything I have done toward Mars entry suggests 2-3 gees is quite feasible for 6-7 km/s entry speeds and angles around 2 degrees below horizontal, at their effective ballistic coefficient.
I think I posted those results already on these forums, and in my reverse engineering of BFS capabilities posted over at "exrocketman". Among other things, it should be clear enough that I have real engineering experience and capabilities towards entry design analysis calculations.
I did some Earth stuff at the low end of entry speeds (near 11-12 km/s, and got 3-4 gees possible at near-1 degree entry angles. That's a lot shallower angle than Apollo, running a higher risk of bouncing off. If you hit faster, or steeper, gees goes 11+ VERY quickly. Spacex has posted ZERO about this issue with their design.
Heading off other suggestions, my reverse-engineering of the performance capabilities shows there is NO propellant available to do a deceleration burn prior to entry. Nor is there propellant available to enter orbit instead of direct entry. There is almost no potential for a faster-than-Hohmann 8.5 month trip home, either. The numbers don't lie, the mass ratio and Isp just isn't there to do those things.
Now, Kbd512 raised an objection to tail-to-tail docking. Spacex does say publicly they intend to do that for refilling in LEO. It isn't the docking force that transfers the propellant. According to the illustrations posted, it is direct tail-to-tail docking without any landing legs extended. They say they fire thrusters on the nose of the refilled vehicle to push it into the tanker at micro-acceleration levels, for an extended period of time. The micro-acceleration is an effective "gravity" that induces propellant flow from tanker to refilled vehicle.
I did notice that the posted information on the Spacex website says not one word about the change in the orbit that this low but sustained thrust would induce. I would hope they are smart enough to do this as a plane-change vector, so as not to change the apogee and perigee of the docked pair. I suspect they say nothing because they haven't given this issue much thought yet. It's a nuisance, not a show-stopper.
For the artificial gravity spin-up that I suggested, it is the same docking, followed by nose-mounted attitude thrusters 90 degrees off axis, that spin up the docked pair. There are torques and shear/bending loads to worry about, yes, but I saw nothing catastrophic about this, since the thruster forces are not large. They don't have to be.
GW
Last edited by GW Johnson (2018-06-24 09:45:54)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Louis,
Some of us want a true ITV built piece by piece, just like ISS was. After the ITV is assembled in space, it stays in space and never reenters. The ITV will be propelled by high-power solar electric propulsion because that drastically lowers the tonnage of propellant required to go anywhere else. It will spiral out from Earth / moon / L2 and spiral in to LMO once it arrives at Mars. The crew doesn't have to be aboard for the spiral out to the moon or L2. I never proposed aerobraking because it isn't necessary. All high-acceleration maneuvers like aerobraking from interplanetary velocity are acts of desperation from lack of Isp required to establish a stable orbit.
If we can afford to launch BFS-T five times to send each BFS-P or BFS-C to Mars, then we can certainly afford five flights to assemble a real ITV that makes a half dozen tanker flights for every trip to Mars unnecessary. The reduction in tanker flights enables an increase in cargo and passenger flights. Launches always cost money, so the more launches that deliver useful tonnage, otherwise known as things that will actually be used on Mars, the better.
BFS is the wrong technology for use on Mars and will remain so until a multi-megawatt solar farm, propellant plant, and proper landing pads are built there. There is no infrastructure on Mars to serve as a miniature version of Kennedy Space Center. My suggestion is a series of landers that deliver the individual components on mobile platforms, like super-sized version of Curiosity. Since the platforms can move, albeit at low speeds, the infrastructure can be sited at locations more appropriate for the intended use. I'm not aware of any instance where someone lived in a rocket / power station / cryogen plant for a couple years while propellant was being loaded. There's too many problems with doing that here on Earth. On Elon Musk's say-so, we're going to start doing that on another planet without ever testing any of those technologies there first. And pigs will fly...
Mobile Platform Payloads:
* solar panels, power conversion equipment, power cables
* propellant plant
* propellant storage tanks
* surface habitation module
Every single problem with this "BFR is the answer to everything" idea has been hand-waived with this absurd "Musk knows everything" attitude. ITS wasn't built because it was a bridge too far. Similarly, "BFR for everything" is a bridge too far. I can promise you that BFR can't and won't overcome basic physics. Elon Musk didn't invent electric cars or reusable rockets. His engineers took bits and pieces of existing ideas and technologies that worked well for specific purposes and integrated them to create novel solutions to known problems. Grid fins came from Russian missiles. Reusable rocket engines were first built by NASA with the technology that existed at the time. Propulsive landings have been around since the LM landed on the moon.
Examples of real problems:
* crew spends months in microgravity
* hitting a reentry angle perfectly every single time
* industrial scale LOX/LCH4 plant that nobody has ever built using resources nobody has ever characterized - nobody has ever collected a single drop of water or a single cubic foot of CO2 on Mars, but we're going to go from never having attempted this to operating an industrial scale facility with little to no maintenance, no unexpected failures, and little to no support from Earth
* landing a 50m tall rocket on uneven ground with a narrow landing gear base
* repeatedly docking two ships weighing hundreds of tons without damaging ship
* requirement to use storable chemical propellants without IVF
* requirement for radiation protection in a paper thin rocket stage
All of that adds to the complexity of a single machine that has to fulfill so many roles exceptionally well. None of that was actually addressed, except with the insistence that there is no problem. The rest of us would have to suspend belief in current technology reality for all of that to be true. Time will tell as to whether or not the rest of the world is too conservative or the people doing all the hand waving are simply flailing about because they don't have any answers to those problems.
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So you're having them go from 1 G to 0 G to 20 G in the space of what? A few days? Doesn't sound that great to me.
Uh--Louis. You need a serious review of your analytical mechanics. The spacecraft on a Hohmann trajectory may be treated in space as a body at rest. the superposition of various rotational modes can be accomplished at any speed the system travels. The problems are separable. The rotational movements can be cancelled before any atmospheric entry.
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So you're having them go from 1 G to 0 G to 20 G in the space of what? A few days? Doesn't sound that great to me.
What are you saying here? This statement has no relevance to the quote.
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It sounded like you were referencing more the negative health effects of zero/micro-gravity, rather than the challenge of re-entry at Mars transfer velocities, since you were talking of the necessity of spinning the ship during transit to avoid a dead crew...
I referred both the issues: the reentry is the more lethal, but even with an orbit-orbit ship I prefer artificial gravity because I would like to have an healthy crew to explore an unknown planet, rather than a crew of almost seek zombie-walking people with osteoporosis, anemia, impaired vision and muscular hypotrophy.
You want a spinning ship that then hits the Earth's atmosphere at such a hyperspeed, returning from Mars? Doesn't sound like a good idea to me.
You can find a way to pair two ships and spinning them, then separate and de-spin them before entry. But my preference lies with a NTR orbit-to-orbit spaceship, able to spin during coasting, that do all propulsive maneuvers. If we find a way to develop some kind of mini-magnetosphere that may shield even from GCR - there are many interesting researches on the issue - we will have a ship that can bring us almost every were in the solar system, from Mercury to the moons of Jupiter.
I am not suggesting we ignore the issue of high G re-entry. Musk is clearly aware of the problem...
https://www.youtube.com/watch?v=2AaTfQcte8U
He doesn't spell out in detail what the solution is but it appears to be a combination of high performance heat shield and propulsive landing. Space X appears to think they can keep G forces down to 2-3 on return to Earth, which the crew should be able to cope with.
In a previous post GW has answered this topic far better than I could do.
Anyway, Musk is far from going to Mars, because it will pass many years before he will have a reliable ISRU-device, able to produce 1100 metric tons of LOX-LCH4 (I still don't know if the SpaceX guys have just started the R & D for the ISRU).
Probably, in waiting for the ISRU-device, the BFR will be used to go to the Moon - it has enough delta-V to do it, after refueling in elliptical orbit - where the transfer time is too short to have microgravity health problems. It can deliver 20-30 tons of stuff on the Moon surface every mission, that can be used to build a Moon-base.
So, to recap, IMHO, SpaceX Mars Mission has three main weak-points:
1) the lack of artificial gravity
2) the tail-landing which needs a perfect knowledge of the stability of the terrain
3) the ISRU which needs a prefect knowledge of the alleged buried glaciers in equatorial latitudes
Last edited by Quaoar (2018-06-24 14:42:54)
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