Artificial 1g Gravity on Mars vs in Space

louis · 2017-04-05 05:01:44

Valeri Polyakov was in zero G space for over 14 months in one session - the equivalent of a Earth-Mars double transit.

https://en.wikipedia.org/wiki/Valeri_Polyakov

He showed no impairment of functioning or mood beyond a couple of minor dips.

He was a highly motivated individual who wanted to prove people can be in space for a long duration.

So, the lesson I take away is that we shouldn't panic. It is very likely that highly motivated individuals will be able to cope with the zero G transits given the "rest and recovery" on Mars in natural 0.38 gravity supplemented by weighted suits that enable replication of a 1 G environment. The motivation is highly important I think. It's not enough to say send a geologist to Mars and expect them to cope well with zero G - you need someone who is extremely fit and who has a fierce determination to do well in zero G.

Remember also that Polyakov's duration record dates back to the mid 90s. Exercise regimes/technology and space medicine will have moved on in the intervening 20 plus years. The likelihood is that the chances of a good result have improved hugely during this time. Space medicine tends to be a rather closely guarded secret in my view.

GW Johnson · 2017-04-05 09:18:42

There seems to be a difference between partial gee and zero gee, in that fluid currents and pressure gradients exist in partial gee but not zero gee. This has some mostly-unknown effect on biology, because we foolishly never built the facilities in orbit to experiment with it. But there does have to be some effect, because of those differences.

What we have found experimenting only with full gee vs zero gee is two-fold: (1) you can stave off some (but not all) of the deleterious effects of zero gee for times between 6 months to a bit over a year (as far as we know right now) with exercise, to support a 4-gee ride home from orbit, and (2) there likely won't be any benefit to sleeping in a centrifuge, because prone sleep seems to be an experimental surrogate for zero-gee exposure in many ways.

The exercise thing on Mars at 0.38 gee will likely provide adequate fitness for a max 4-5+ gee ride back to orbit and from there starting the voyage home, no matter how long the stay on Mars. Maybe even much more gee exposure, who knows? At least it seems likely. Experience will tell the real tale.

But a ride home in zero gee for 6-8 months will decrease fitness to the 4 gee level, even with exercise. That is inadequate for anything involving 4+ gee arrivals at Earth, including emergency free-return bailouts, which will be in the 12-15 gee class.

The way around that dilemma is quite simple: provide 1 gee artificial spin gravity during the voyage home, and they will be fully fit for a 12-15 gee arrival, if need be. It is years past time for everyone, NASA included, to face up to that simple requirement.

The moon is a problem: the ride home is only 3 days, to an 11 gee arrival. No time to recover high-gee fitness in spin gravity. I suspect lots of exercise at 0.16 gee would be good for better-than-4-gee fitness, but it's hard to imagine being able to exercise enough for 11 gee fitness while on the moon for a long stay.

Until we gain the experience to tell what is really going to happen, it is hard to choose between shorter stays and building centrifuges for longer stays. We cannot yet know, and the situation is different than for Mars. A lot more than just surface gravity figures into this. Not the least of which being the length of the trip home.

I would suggest that we start with shorter stays on the moon, and work up to longer stays, while checking out the exercise thing in low gravity. It may or may not be enough for the 11 gee arrival. We cannot know until we try it.

I surely would like to see spin gravity added to Musk's Mars ship for at least the return home. Right now he's betting (1) that Mars gravity is "good enough", and (2) that there is no possibility of encountering the 12-15 gee arrival home with his ship. Those are bets, not certainties.

Rules of thumb for running calculations: (1) 1 gee occurs at 56 m radius and 4 rpm spin rate, (2) gee produced is proportional to radius, and to spin rate squared, (3) untrained, unacclimatized personnel can adapt almost immediately to long-term exposure to spin rates up to roughly 3-4 rpm, and (4) it takes serious training and acclimatization to make long-term exposure to 6-8 rpm tolerable. In this context, "long term" experimentally means more than just several minutes; hours-to-days is implied.

One final comment: spinning of rigid structures is a well-understood set of dynamics, including the transients of start/stop and response to perturbing forces. None of this is a ready-to-apply technology with cable-connected structures. If your vehicle design depends upon unproven technology actually working, you will never fly. You will spend your budget developing the unproven technology instead.

GW

Last edited by GW Johnson (2017-04-05 17:43:56)

louis · 2017-04-06 07:39:50

Where are you getting this 12-15 G force from? What is an "emergency free-return bailout"? As far as I know, the lunar astronauts only had the one chance to get back. What is wrong with that approach for a Mars mission? Can you elaborate a bit on this as it is important...

GW Johnson wrote:

There seems to be a difference between partial gee and zero gee, in that fluid currents and pressure gradients exist in partial gee but not zero gee. This has some mostly-unknown effect on biology, because we foolishly never built the facilities in orbit to experiment with it. But there does have to be some effect, because of those differences.
What we have found experimenting only with full gee vs zero gee is two-fold: (1) you can stave off some (but not all) of the deleterious effects of zero gee for times between 6 months to a bit over a year (as far as we know right now) with exercise, to support a 4-gee ride home from orbit, and (2) there likely won't be any benefit to sleeping in a centrifuge, because prone sleep seems to be an experimental surrogate for zero-gee exposure in many ways.
The exercise thing on Mars at 0.38 gee will likely provide adequate fitness for a max 4-5+ gee ride back to orbit and from there starting the voyage home, no matter how long the stay on Mars. Maybe even much more gee exposure, who knows? At least it seems likely. Experience will tell the real tale.
But a ride home in zero gee for 6-8 months will decrease fitness to the 4 gee level, even with exercise. That is inadequate for anything involving 4+ gee arrivals at Earth, including emergency free-return bailouts, which will be in the 12-15 gee class.
The way around that dilemma is quite simple: provide 1 gee artificial spin gravity during the voyage home, and they will be fully fit for a 12-15 gee arrival, if need be. It is years past time for everyone, NASA included, to face up to that simple requirement.
The moon is a problem: the ride home is only 3 days, to an 11 gee arrival. No time to recover high-gee fitness in spin gravity. I suspect lots of exercise at 0.16 gee would be good for better-than-4-gee fitness, but it's hard to imagine being able to exercise enough for 11 gee fitness while on the moon for a long stay.
Until we gain the experience to tell what is really going to happen, it is hard to choose between shorter stays and building centrifuges for longer stays. We cannot yet know, and the situation is different than for Mars. A lot more than just surface gravity figures into this. Not the least of which being the length of the trip home.
I would suggest that we start with shorter stays on the moon, and work up to longer stays, while checking out the exercise thing in low gravity. It may or may not be enough for the 11 gee arrival. We cannot know until we try it.
I surely would like to see spin gravity added to Musk's Mars ship for at least the return home. Right now he's betting (1) that Mars gravity is "good enough", and (2) that there is no possibility of encountering the 12-15 gee arrival home with his ship. Those are bets, not certainties.
Rules of thumb for running calculations: (1) 1 gee occurs at 56 m radius and 4 rpm spin rate, (2) gee produced is proportional to radius, and to spin rate squared, (3) untrained, unacclimatized personnel can adapt almost immediately to long-term exposure to spin rates up to roughly 3-4 rpm, and (4) it takes serious training and acclimatization to make long-term exposure to 6-8 rpm tolerable. In this context, "long term" experimentally means more than just several minutes; hours-to-days is implied.
One final comment: spinning of rigid structures is a well-understood set of dynamics, including the transients of start/stop and response to perturbing forces. None of this is a ready-to-apply technology with cable-connected structures. If your vehicle design depends upon unproven technology actually working, you will never fly. You will spend your budget developing the unproven technology instead.
GW

GW Johnson · 2017-04-06 09:59:37

Most of the Mars missions assume non-recovery of the transport vehicle that brings the crew home. The crew hits the atmosphere in a capsule for an aero-braked one-pass direct entry landing. This takes place from the interplanetary trajectory at speeds well above Earth escape speed.

Like returning from the moon, there is a narrow window of trajectory angles that are survivable: too steep is crushed to death by the peak deceleration gees, too shallow is bounced off into space forever. Entry speed coming home from Mars is in the 16-17 km/s class, instead of "only" 11 km/s returning from the moon. Assuming somewhat similar timelines, ratio up Apollo's 11 gee ride by the entry speeds.

That's where 12-15 peak gees comes from. It's crude, but it is definitely in the ballpark.

The only way to avoid that is to brake into Earth orbit from that interplanetary trajectory. You can reduce the braking gees if you do it with rocket power, at the cost of having to ship that rocket stage all the way there and back again.

Or you can attempt a grazing-shot aero-braking from interplanetary speed into some sort of elliptical capture orbit that slowly circularizes by repeated passes into the atmosphere at perigee. That first capture pass will be high peak gee very much like the direct entry. And it repeats at lower and lower peak gee until done. The first few passes are still pretty high gee, perhaps like Apollo at ~10 gee on the second one.

For the low-gee rocket braking option, there is still the chance that the rocket may fail to operate after years in space. The "way out" is to abandon the vehicle and hit the atmosphere in a "bail-out" capsule: the free-return direct entry, just done as a bail-out option if something fails. That's still very high at 12-15 gee.

So, no matter what you plan to do, you have to be prepared for direct entry at 12-15 gees, even if it is only your emergency backup. Astronauts with hearts weakened by months in zero gee simply will not survive 12-15 gees for ~2 minutes at peak deceleration. There's a reason people with circulatory disease do not ride astronaut training centrifuges or in 6+gee military airplanes. Same reason that roller coaster operators exclude them from 4-5 gee loop-the-loops: they would die of heart failure.

Not to plan for this outcome is unethical in the extreme.

GW

Last edited by GW Johnson (2017-04-06 10:07:30)

louis · 2017-04-06 17:14:35

From the Wikipedia link above:

"It was also revealed that Polyakov did not suffer from any prolonged performance impairments after returning to Earth. In light of these findings, researchers concluded that a stable mood and overall function could be maintained during extended duration spaceflights, such as manned missions to Mars".

Are you sure that astronauts in the current era suffer the equivalent of major heart disease?

I think it is rather odd to assume rocket failure in transit. On that basis you wouldn't leave Earth, full stop. We have to assume the rocketry will work - we can't entirely eliminate risk.

I would favour some combination of retro rocket firing and aerocapture...an extra month in orbit around Earth wouldn't be a major problem if that's what it takes to ensure a safe return.

GW Johnson wrote:

Most of the Mars missions assume non-recovery of the transport vehicle that brings the crew home. The crew hits the atmosphere in a capsule for an aero-braked one-pass direct entry landing. This takes place from the interplanetary trajectory at speeds well above Earth escape speed.
Like returning from the moon, there is a narrow window of trajectory angles that are survivable: too steep is crushed to death by the peak deceleration gees, too shallow is bounced off into space forever. Entry speed coming home from Mars is in the 16-17 km/s class, instead of "only" 11 km/s returning from the moon. Assuming somewhat similar timelines, ratio up Apollo's 11 gee ride by the entry speeds.
That's where 12-15 peak gees comes from. It's crude, but it is definitely in the ballpark.
The only way to avoid that is to brake into Earth orbit from that interplanetary trajectory. You can reduce the braking gees if you do it with rocket power, at the cost of having to ship that rocket stage all the way there and back again.
Or you can attempt a grazing-shot aero-braking from interplanetary speed into some sort of elliptical capture orbit that slowly circularizes by repeated passes into the atmosphere at perigee. That first capture pass will be high peak gee very much like the direct entry. And it repeats at lower and lower peak gee until done. The first few passes are still pretty high gee, perhaps like Apollo at ~10 gee on the second one.
For the low-gee rocket braking option, there is still the chance that the rocket may fail to operate after years in space. The "way out" is to abandon the vehicle and hit the atmosphere in a "bail-out" capsule: the free-return direct entry, just done as a bail-out option if something fails. That's still very high at 12-15 gee.
So, no matter what you plan to do, you have to be prepared for direct entry at 12-15 gees, even if it is only your emergency backup. Astronauts with hearts weakened by months in zero gee simply will not survive 12-15 gees for ~2 minutes at peak deceleration. There's a reason people with circulatory disease do not ride astronaut training centrifuges or in 6+gee military airplanes. Same reason that roller coaster operators exclude them from 4-5 gee loop-the-loops: they would die of heart failure.
Not to plan for this outcome is unethical in the extreme.
GW

GW Johnson · 2017-04-07 11:51:07

Louis:

I don't know if the terminology "equivalent of major heart disease" is the right way to say it, but yes, weakened heart muscle is exactly what they have observed. That's what all the aerobic exercise stuff in zero gee is supposed to fight. It does, but only to a certain extent; it's just not effective enough to permit "indefinite" stays in zero gee. Put a weakened heart under enough stress, and it quits beating. That's the risk involved with 12-15 gee reentry coming home from Mars, or even 11 gees returning from the moon.

As best we understand it, you recover within days to months upon returning to a 1 gee environment when you come home. That's why I view the 6-8 month ride home from Mars as an opportunity to get fully Earth-fit. But it only works if you give the crew 1 gee of spin gravity. We know ZERO about the efficacy of partial gee for this. So, go with what you know: 1 full gee.

The bone density decreases and muscle weakening can be fought while in zero gee with simple weight training, as well as aerobics at high force levels. Again, this works, but not effectively enough to permit indefinite stays in zero gee. Weight training (or other resistance exercise) does little to nothing for the heart, though. You MUST get heart rates up to double normal with aerobics to do any good for the heart muscle. That's as true "out there" as it is "down here".

The scientists simply do not understand what is going wrong with immune system degradation in zero gee. And the fluid imbalances that damage vision cannot be fought with exercise, as best we understand it. That simply requires adequate gravity to get the pressure distributions right, and no one yet knows what defines "adequate". All we know is that we evolved these features at 1 full gee.

The more the scientists look at the zero gee problem, the more deleterious effects they find from prolonged exposure. It takes a lot of time and effort and resources to research all of this, only to maybe find some effects that you simply cannot mitigate (like that immune thing and the vision thing). These outcomes add ammunition to the arguments of those who do not want us to go.

On the other hand, the notions of spin gravity have been around since the dawn of the 20th century. Seems wiser to just get on with doing something we already know and understand, and spend the resources and efforts on those other things we also know we need to address: radiation exposures and adequate living space, as well as advanced recycling life support.

GW

Last edited by GW Johnson (2017-04-07 12:02:54)

SpaceNut · 2017-04-07 18:17:31

So going forward we will want a ship that can spin and or tumble end over end. The attributes of both require different assembly techinques and sizing to make either possible.

Both methods of rotation and a method to spin and despin its rotation of which hopefully we can use no fuel to control the function.

The end over end tumble requires a center of balance control to be able to shift the length effect out of the rotation of it.

The spin rotation take nothing other than a controlled distance for the fixed rotation.

GW Johnson · 2017-04-08 08:17:25

Hi Spacenut:

Initially choices are: (1) cable-connected, and (2) rigid. Rigid spinning dynamics is something long fully understood. Cable-connected spin dynamics requires much development effort. If you base your vehicle on an undeveloped technology, you will never fly. Programs to develop technology are quite necessary, don't get me wrong. But do not mix that activity into a program where you build and fly.

Assuming rigid, the choices are: (1) connecting modules with truss structures to get the radius you need, or (2) using ship components you already need anyway to be that radius. Truss structures add only to vehicle inert weight. Ship components that you already need will add to inert weight, but if tankage, will also add to propellant weight. A vehicle is not a space station. The "tyranny" of the rocket equation says do not use use trusses if you possibly can avoid it.

Assuming built of components you already need, the choices are: (1) spin about the longitudinal axis, presumed to be the long dimension, like a rifle bullet, or (2) spin about some other axis, like a baton. Dynamics says you either spin with the greatest or the least moment of inertia, not the intermediate one. Spinning like a rifle bullet means your radius is associated with the smallest vehicle dimension, while spinning like a baton means your radius is associated with the largest vehicle dimension. Not building budget-busting "battlestar galacticas" means you spin like a baton.

Final choice: how big/what shape? That is driven by design gee level, available radius, and tolerable spin rates for long-term exposure. Design gee level is 1, for reasons already discussed. Tolerable spin rate is no more than 4 rpm, for reasons already discussed. So, you need 56 m radius.

That means your vehicle is a baton shape on the order of 112 m long as a minimum. It does not need to be very wide. Two to four sticks of tanks docked end-to-end and fastened together in parallel allow you to stage-off empty tanks after each burn, without requiring reassembling the baton after each burn.

The habitat itself can be part of the radius, as not everywhere in it must have one full gee. If need be, sleeping quarters can be near the center at near zero gee, as there is no benefit to gee exposure while sleeping prone at 1 full gee down here on Earth. That last must be true, or else bed rest studies would have no usefulness at all in low-gravity research.

Put the daily work shift stations out near the tip at as near to one full gee as possible. Recreation and dining can be at some intermediate location with partial gee. Put your gymnasium facilities at the very tip, at a little over 1 gee, for increased effectiveness.

Make your flight control station the radiation shelter for solar flares, so that maneuvers may be flown regardless of the solar weather. Put some shielding around the sleeping quarters to reduce cosmic ray exposure a tad. Use the water, wastewater, and frozen food as shielding, along with propellant tanks.

Use electric motor-driven flywheels in a module at the center to spin the stack up and de-spin it, so that the rocket equation does not apply to that function. Heavy habitat stack at one end, engines at the other. Mount solar panels and return capsule at the center to reduce centrifugal loads on them.

There I went and wrote you a little handbook for deep space vehicle design.

GW

Oldfart1939 · 2017-04-08 09:18:03

I haven't written much on this topic as yet, so here goes. I like the concept of a rigid structure connecting the spinning modules, but how to accomplish such without incurring an unacceptable amount of mass which has consequences through the tyrannical rocket equation. First question to pose is what's at either end of the spinning mass structure, and how far apart must we make them in order to avoid Coriolis effects of induced nausea, etc. One way of getting sufficient parts into a trajectory towards Mars is by employing a "convoy" philosophy in the initial stages of exploration. The first vessels will be small, so we'll need something to carry necessary cargo and equipment. I'm going to suggest we send a group of 3 vessels, maybe even 5, in a "Convoy." One vessel, possibly larger that the others (also unmanned) becomes the central "hub" of this rotating structure. It has 20 meter tubular "passageway" elements able to fold out sideways from it's center. These should be lightweight but strong reinforced carbon fiber structures. These should be connected as hinged elements capable of deploying from the hub some 60 meters in either direction from a 10 meter diameter central structure. Employ 2 smaller modules each with similar fold out tunnel structures, each one adding another 130 meters of "passageway." The 2 crewed ship elements in the "convoy" could be carrying a similar single 40 meter element in their cargo trunks. These would be attached at the docking hatches atop the capsules. All added together, we would result in a semi-rigid structural element allowing passage of crew members to the central supply hub and transfer between the 2 primary spacecraft, and allowing controlled rotation at a low rpm to develop some centripetally induced artificial gravity. At the end of Hohman transfer trajectory, the tunnel, or passageway structures are discarded and the 3 or 5 vessels make atmospheric entry. This obviously doesn't solve the problem for the Earth return, but keeps the Mars crew in excellent and functional condition. As a backup feature, all these units could have embedded in the carbon fiber structure a strong aircraft grade cable, should any one module be damaged.

Last edited by Oldfart1939 (2017-04-08 09:25:35)

GW Johnson · 2017-04-08 21:07:37

Hi Oldfart1939:

I had a somewhat similar concept for a manned transport posted 5-28-16 over at “exrocketman”. The name of the article is “Mars Mission Outline 2016” or something quite like that. It’s near the top, you need not scroll down very far to find it. It was the old 1950’s Von Braun concepts that Disney made into a film that inspired my design rough-out (and that’s all it is: rough-out for feasibility).

Mine’s based on a “slender” spinning baton as the manned orbit-to-orbit transport. It is recovered in LEO at mission’s end, for resupply, re-fueling, and re-use. Outfitted for different durations and delta-vees, it can take crews to Mars, Venus, even Mercury, and out to the asteroids. This particular version requires a crew acclimatized to 6-7 rpm for long term exposure, to get 1 full gee at the outer floors. (A 5 module form is heavier, but much roomier, and need only spin at 4-5 rpm to get 1 gee.)

The core that is recovered and reused is two modified B330 inflatables and a center hard shell module that contains the flywheels for spin-up/spin-down, an airlock, and the solar panels, as well as the crew return capsule. There’s 700 cu. m for a crew of 6 max. That’s over 100 cu. m per person! That core is about 65 tons unladen. Engines on one end, water and wastewater “slim-line” tanks wrap the inflatable at the other end, for radiation shielding. That one has the flight control station as the designated solar flare radiation shelter.

In LEO, you dock sticks of MMH-NTO propellant tanks about it for LMO arrival, which add shielding during the transit. It uses an expendable LOX-LH2 departure stage to leave LEO for Mars, that stages off before you spin up.

At Mars, you de-spin, and use your propellant to enter orbit. Towards end of stay, you dock in LMO with the return propellant sent ahead by SEP. Otherwise, the core spins for gravity in LMO. I do NOT send everybody to the surface simultaneously (you cannot effect a rescue if you do).

The Earth arrival propellant you cluster about the inflatables for extra shielding, and you dock the cluster of Mars departure tanks to the end opposite the engines. These you stage off after departure from LMO, then you spin up for the transit home. The crew return capsule needs to be rated for free-return entry, just in case capture into LEO isn’t going to work, for whatever reason.

The only expendables are life support supplies, the LEO departure stage, and empty propellant tanks. All else is recovered for reuse. I didn’t really explore it, but the SEP tugs could be brought home for re-use. Even the departure stage could possibly be recovered, if it had an SEP rig as part of it.

What I had in mind also ties in with your odd-number in the crew, for command. I split my crew of 6 into 2 crews of 3 at Mars. They alternate missions to the surface, with one crew in orbit staying healthy, watching over the surface crew, and doing science from orbit. The other crew takes a one-stage reusable lander to the surface, and camps out in it for up to about a month, because it’s actually pretty spacious inside.

I send 3 landers so that I always have one ready to use for surface rescue, even if one of the three craps out. These get sent ahead unmanned to LMO with extra propellant for multiple trips each. No one goes down unless a rescue lander is available! (I do everything I can to design-out the loss of a crew.)

The version of the article posted at “exrocketman” posits propellant for 3 trips per lander. I have to keep one in reserve for rescue, so that’s 8 trips to the surface and back in the one mission. That’s up to 8 different sites that can be explored in the one mission! I have seen NO other architectures since 1956 that could do that kind of multi-site exploration in the one trip. For a little more money, you can send more lander propellant, and do even more in the one trip. You have 13 months while at Mars.

I need to land NO surface habitat modules that I have to leave behind! I have NO separate ascent vehicles to pre-position on the surface! I send one reusable lander vehicle down to each site, and can visit as many different sites as I send lander propellant supply. The surface crew is self-sufficient as-is, without having to chase any other landed equipment down. (They do have a little 1-ton rover car.)

Everything is NTO-MMH, so I can rob one propellant supply to use it for other purposes, if need be. I leave the landers parked in LMO at mission’s end. They can be reused if refueled. Just send ahead some more propellant for them, and some for Earth return, and send the transport again. The round trip propellant quantity to the surface and back is about the same as for visiting Phobos from LMO.

Multiple sites, a “way out” at every step, mostly recovered and reused hardware! This is way more than “Apollo flag-and-footprints”, which landing at only one site inherently approaches. And I was estimating well under $100 B to do it, if “old space” is not involved.

While Musk’s giant ship is far more impressive (and expensive), he is planning to visit only one site. I like my design better, because it does far more for very much less. But he’s right about reusability being the key; I just arranged mine differently.

GW

elderflower · 2017-04-09 04:22:43

You might use less fuel for multisite surface exploration if you use your lander as a hopper for some of the movements, rather than returning to orbit for each movement. Then the crews could rotate using a much smaller capsule with room for 3 guys and some stores and fuel to return it to orbit.
Did you allow for manufacture of any fuel on the surface?

SpaceNut · 2017-05-09 13:08:24

Another timely bump by a spammer but we should start looking at the tumble, and spinning means within the lengths of actual pieces that we can use.

GW Johnson · 2017-05-10 10:31:05

To answer Elderflower's question in post #36, no I did not allow for manufacture of propellants on site, because the propellants I assumed were NTO-MMH, neither of which can currently be made in-situ on Mars. I chose those specifically because they are far more easily long-term storable in space, based on decades of similar use.

The propellants that could be made on Mars with known processes and equipment are oxygen, and either hydrogen or methane or both. All three are cryogens, which means you must resort to not-so-lightweight Dewar vessels as your tanks, with sun shields, external insulation, and some sort of cryo-cooler equipment. And you will still experience significant boiloff over long times, even doing all of that.

With the storables, an insulated single wall tank with a sun shield and a modest heater will store propellants for years at modest pressure, demonstrated by past experience. Unfortunately, we have no way to make these on Mars yet.

IRFNA is even more storable than NTO as an oxidizer, but costs significant performance. That's why most modern spacecraft thrusters use NTO-MMH as the bi-propellant of choice. That seems to be the best trade-off between performance and required efforts to protect the storability, given current technologies.

But, for applications in which you can accept the lower Isp for the thrust, IRFNA-MMH is a really good choice. IRFNA is also not something we currently know how to make on Mars.

GW

Last edited by GW Johnson (2017-05-10 10:31:42)

elderflower · 2017-05-10 14:45:18

Thanks, GW.
Well we know there is ice, but we haven't assessed it's quality and we haven't got a plan to extract and purify it. We can also get water by compressing the atmosphere then chilling it, or by using adsorption beds, but that gives limited quantities and only some of the time. So anything involving Hydrogen must come from earth- at least for the first few missions. That Hydrogen or methane or Aerozine etc would be reserved for mars escape, I expect. The only propellants we could make on Mars for the first missions are CO and O2. Not the best combination but not totally hopeless and might make a hopper practicable from the beginning. I read that some group is designing an engine for this combination but it's probably just another paper job.

louis · 2017-05-10 16:02:13

For an 885 Kg machine you can get 45 kgs per sol through the summer (for 15 KwE input). That could be say something like 6.5 tonnes per (earth) annum. We can pre land the machine. It could be operating for 6 Earth years and produce 39 tonnes of water. These are significant amounts aren't they?

That said, I feel we have other priorities apart from generating large amounts of propellant for rockets on Mission One. Perhaps a small robot hopper to aid exploration would be a good compromise for Mission One.

elderflower wrote:

Thanks, GW.
Well we know there is ice, but we haven't assessed it's quality and we haven't got a plan to extract and purify it. We can also get water by compressing the atmosphere then chilling it, or by using adsorption beds, but that gives limited quantities and only some of the time. So anything involving Hydrogen must come from earth- at least for the first few missions. That Hydrogen or methane or Aerozine etc would be reserved for mars escape, I expect. The only propellants we could make on Mars for the first missions are CO and O2. Not the best combination but not totally hopeless and might make a hopper practicable from the beginning. I read that some group is designing an engine for this combination but it's probably just another paper job.

GW Johnson · 2017-05-11 13:18:20

What I was wishing "they" would do is pick a site with a buried glacier. The first mission could then experiment with what I list here. Followup missions could put it into full swing.

If the ice is massive enough, you don't need to mine it, you can drill it with a process not unlike steam extraction secondary recovery in the oil business. Given a steam source, this is a whole lot less effort than cooking tons of regolith for ounces of water, and a whole lot faster than processing atmosphere with some gimcrack for ounces of water per day. I'm talking tons per day.

The water may be salty and dirty. That's OK, a settling tank and some filters takes care of the solids. Use the salt as the electrolyte for electrolysis to make hydrogen and oxygen from some of it. Vacuum flash some of the rest for freshwater, that's just a form of distillation. Let the brine waste freeze, and use it for subsurface building materials.

Don't put your assets right on top of where you steam extract the water. There is a cave-in risk once the void space gets large enough.

The rest of the salty water can be used to make "icecrete" and other similar stuff, probably just as it is.

You'll need lots of freshwater to wash the salts and perchlorates out of any soil you want to use for growing food.

None of this is possible if you fail to land near a massive buried glacier, though. Sure would be nice to confirm one is there before we send the first crews and bet their lives on it, don't you think?

Now, just how can we do that from a Red Dragon unmanned probe? Ideas?

GW

Last edited by GW Johnson (2017-05-11 13:22:49)

SpaceNut · 2017-05-11 19:25:47

Since the Red Dragon is going unmanned lets strip the hell out of that design to get more down mass....Have 2 units sent together with one staying in orbit to practice precise landing via a beacon turned on after the first lands for it to home in on.

What is the mission design will dictate what we are able to put into each unit.

louis · 2017-05-11 19:36:44

If we are talking about Mission One, I don't think we have to obsess about water ice glaciers, given we can extract plenty of water from the atmosphere. The mission location should be good from a number of points of view: water, certainly, but also interesting geology, iron ores, other metal ores, basalt and sand.

GW Johnson wrote:

What I was wishing "they" would do is pick a site with a buried glacier. The first mission could then experiment with what I list here. Followup missions could put it into full swing.
If the ice is massive enough, you don't need to mine it, you can drill it with a process not unlike steam extraction secondary recovery in the oil business. Given a steam source, this is a whole lot less effort than cooking tons of regolith for ounces of water, and a whole lot faster than processing atmosphere with some gimcrack for ounces of water per day. I'm talking tons per day.
The water may be salty and dirty. That's OK, a settling tank and some filters takes care of the solids. Use the salt as the electrolyte for electrolysis to make hydrogen and oxygen from some of it. Vacuum flash some of the rest for freshwater, that's just a form of distillation. Let the brine waste freeze, and use it for subsurface building materials.
Don't put your assets right on top of where you steam extract the water. There is a cave-in risk once the void space gets large enough.
The rest of the salty water can be used to make "icecrete" and other similar stuff, probably just as it is.
You'll need lots of freshwater to wash the salts and perchlorates out of any soil you want to use for growing food.
None of this is possible if you fail to land near a massive buried glacier, though. Sure would be nice to confirm one is there before we send the first crews and bet their lives on it, don't you think?
Now, just how can we do that from a Red Dragon unmanned probe? Ideas?
GW

SpaceNut · 2017-05-11 19:51:05

The "talking about Mission One, and water ice glaciers," has to do with insitu methane refueling.... to which appears to be the only way to get back to orbit as a Red Dragon can not even if we had all the fuel we needed to relaunch it with what we have today for capsule capable of landing on Mars. So we need something bigger for a mars lander for one and for the second so that man can go.

Red Dragon is at 2 mT of payload with a capsule mass all fueled up at orbit near 10mT bringing the on orbit to near 12 mT...Working the way back to earth orbit takes alot of mass to push the Red Dragon to mars.

Dave_Duca · 2017-05-12 07:47:01

Besides the need for HYDROGEN at Mars, the most important "mindset" required is
..."the Von Neumann Universal Constructor" approach.

Just like Robert Zubrin said: "Use the local resources - live off the land"
A sort of: "work smarter not harder scenario, yeah?

Seriously....
....why are people forgetting to REVIEW: The Mars Underground documentary?

Honestly - where are the Mensa people stepping forward and proving their intellect?

Last edited by Dave_Duca (2017-05-12 07:48:03)

GW Johnson · 2017-05-13 09:09:45

Any crew in any scenario trying to survive an extended stay (about 13 months between 6-to-8.5 month transits) on Mars is going to need water, and is going to need oxygen. Not to mention food. And in multi-ton quantities.

Everyone on this forum and elsewhere bitches and moans about the cost of shipping those tons to Mars, always forgetting that the cost of a dead crew is far, far, far higher. Be that as it may, creating water, oxygen, and maybe food, locally on site is the only way not to have to ship those tons to Mars.

Now, it takes some sort of machinery to do those things, and those machines are tons that must be shipped. How big and heavy they are depends upon how much they must produce. Their success at producing may be dependent upon site conditions. So, it's a tradeoff, not an either-or situation.

If I need to produce 5 tons (an arbitrary number) of drinking water for a 13 month stay, that's a production rate of 5000 kg/(13*30 days) = ~13 kg/day. I may need much more that if I want to wash clothes or do any greenhouse irrigation. Yet most of these laboratory gimcracks I hear about are down in the grams to a kg per day.

These gimcracks are going to need a huge scale-up in size to support a crew on Mars. The gap between what is needed and what has been done is more than an order of magnitude. Scaling up the gimcrack means you ship tons of gimcrack instead of just tons of water.

Sooner or later, you shoot yourself in the foot, trying to concentrate and isolate a very diffuse resource. Go for the concentrated resource, and avoid all that. That's the smart thing to do.

Why process hundreds of tons of regolith (or hundreds of tons of 0.7% density atmosphere meaning hundreds of thousands of cubic meters) to get only a handful of tons of water? It's just too much effort for too little return. Doesn't matter that it's possible, it just ain't smart.

You want the buried glacier. The bigger, the better. Think tons of water per day, not kg. That is what sets up your base, and eventually your colony. And it would be trivially easy to connect a steam generator to one of the turbo-generator heat transfer points of a Safe-400 reactor rig. Let the solar PV do electricity; if you need heat, use a heat source. Direct. Simple. Efficient.

Now if you bet the lives of the crew on resource extraction like that, you'd better be damned sure the resource is really there. So, send a Red Dragon to the site with a robot drill rig and find out. Drill 100 m or more down to see. Do it for every potential site.

Which means guilt-edged priority number one for a manned mission to Mars is that pathfinding robot drill rig capable of 100+m even in hard rock. No one has such a device. It can be done, but has not been done. It must be done, and quickly!

You can make all the oxygen and hydrogen you want from that much water (tons/day). You can irrigate all the greenhouses you can build with that much water. You can make all the concrete or mud bricks you could ever use with that much water. Vast quantities of water is THE key! And pathetic little gimcracks producing water (or oxygen) at a few kg/day is NOT the way to get it.

To get what you need, you'd ship tons of these gimcracks, more tons of gimcrack for the more water and oxygen you think you need. There comes a point where you might as well just ship the tons of water and oxygen instead.

The way out of that impasse is to go for the concentrated resource, not the dilute one. Millennia of mining history are screaming that result at you, if you but have ears to hear.

GW

Last edited by GW Johnson (2017-05-13 09:15:55)

RobertDyck · 2017-05-13 09:36:52

Dave_Duca wrote:

Besides the need for HYDROGEN at Mars, the most important "mindset" required is
..."the Von Neumann Universal Constructor" approach.
Just like Robert Zubrin said: "Use the local resources - live off the land"
A sort of: "work smarter not harder scenario, yeah?
Seriously....
....why are people forgetting to REVIEW: The Mars Underground documentary?

Honestly - where are the Mensa people stepping forward and proving their intellect?

"The Mars Underground" was produced in 2007. What aspect of this film do you refer?

Full movie:

SpaceNut · 2019-10-17 19:23:47

Here it is for the AG which was talked of for the International Space Station (ISS / Alpha) which was cancelled and still sits on the ground for people to view.

So how do we get the spin, rotation of tumble to be what we desire as the rough effect is not going to be equal as we feel it here on earth.

https://www.artificial-gravity.com/sw/SpinCalc/

http://www.artificial-gravity.com/Space … v3p192.pdf
HABITABILITY FACTORS IN A ROTATING SPACE STATION

It means designing for the period of time that we are working in the gravity that is used for the longest part of the journey to mars and not the shortest of time span which is launch.

SpaceNut · 2019-10-17 19:49:37

Gravity deprivation (weightlessness) leads to a multitude of problems for people during spaceflight. For reasons of health, comfort, and practicality, scientists have often proposed to provide artificial gravity by spinning the spacecraft. The spin-induced centripetal acceleration would act as an imperfect surrogate for natural gravity.

http://ssi.org/2010/SM14-proceedings/De … arroll.pdf
Design Concepts for a Manned Artificial Gravity Research Facility

http://www.spacearchitect.org/pubs/ICES-2016-194.pdf
Artificial Gravity in Theory and Practice

https://www.reddit.com/r/Colonizemars/c … l_gravity/

https://forum.nasaspaceflight.com/index … c=48541.60

https://forum.nasaspaceflight.com/index … c=22210.40

http://www.artificial-gravity.com/NASA- … 030807.pdf

The passengers on the bfr are going to have a real problem with the shape of the nose where we are spending the journey in cabins since it tapers from the large diameter to the pointed nose.

elderflower · 2019-10-18 04:27:43

If I understood correctly, there is a tank in the nose for C of G adjustment. I don't know how big it is.

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