Phobos First

Quaoar · 2015-01-11 05:12:25

Antius wrote:

I have raised this post to explore the advantages and disadvantages of a Phobos-First approach for Mars exploration and colonisation.
I believe a Phobos First approach offers numerous advantages. Most significantly, it allows manned exploration of the Mars system to begin at lower state of technological readiness and with smaller initial investment than would be required for manned Mars surface missions and with more rapid returns of investment. As the Phobos regolith likely contains a high percentage of ejected Martian material, a Phobos scientific base would also allow the existence of Martian microbial life to be determined.

Sorry but I found 3 problems in your planned mission:

1) Phobos has no atmosphere, so astronaut will be exposed at an higher dose of cosmic ray during stay.

2) Phobos has no gravity, so astronauts have to spend more than 2 years in micro-gravity, risking blinding for optical nerve damage, hearth failure at reentry for hearth hypotrophy, and multiple bone fracture due to severe osteoporosis (entry velocity for a Mars-Earth transfer orbit is almost 14 km/s). Probably astronauts will not survive a high gee atmospheric entry after 2 years in micro-gravity.

3)Phobos is very little and will be very difficult to spend there 600 days waiting the launch window in good metal health.

Antius wrote:

Using the rocket equation for an ISP of 4190s and delta-V of 6200m/s, reveals that a 10 tonne vehicle travelling from LEO to Phobos Lagrange 1 (2.5km above Stickney) would consume just 1.6tonnes of propellant. If ten ion thrusters are used and supplied with 100kWe of power from solar panels with a specific power of 0.2kW/kg, then the total propulsion system mass is 830kg with 1600kg of propellant. Throwing in another 500kg for reaction control, computer, Earth communication, payload faring and Phobos landing thrusters, still allows a total payload of 7 tonnes, for each 10 tonnes delivered to LEO.

You cannot apply the deltaV tables for Hohmann transfer to non impulsive transfer: a Hohmann transfer orbit require a short and strong burn, with a very powerful rocket (chemical or nuclear thermal). With a low thrust slow spirally electric thruster gravity losses are high, so the Earth-Mars deltaV will be more than double.

Impaler · 2015-01-11 12:01:29

The numbers I have seen show that from LEO to Mars (for a reasonable 6 month trip with continual thrust) about half of your DeltaV is in the Spiral up to high Earth orbit, and the other half is in the Helocentric transfer.

The first half is basically a fixed amount of DeltaV for a continual low-thrust vehicle, the lower the thrust the longer it takes but DeltaV total remains the same.
The Heliocentric trip portion is much more 'normal' in the sense that you can get to the destination faster by raising the total mission DeltaV requirement AND the thrust requirement.

Last edited by Impaler (2015-01-11 13:03:07)

JCO · 2015-01-23 12:38:28

Some issues that I have not seen here. For manned exploration I believe making the first mission to be one to Phobos would "appear" to many to be not worth the effort. As much as I would like it to be otherwise appearances make a big difference on if a mission ever gets funded. If any manned mission was proposed to go to Mars that did not include landing it would never get approved. Also though much of the science that could be carried out on the martian surface could be done on Phobos much of the science could not be done on Phobos. In addition the result done on Phobos could not be as conclusive as results from research done on the surface of Mars.

The issue for a colony deal first with resources. All of of Phobos would only provide the same resources available 500 m down with 60 km of the colony. The resources available are likely to contain more water and other resources that will be essential to a colonies survival. This can be ensured by carefully choosing the colony site, something that will not be much of an option on Phobos. Making a colony economically viable on Mars is likely to be much easier than on Phobos. Finally the building of a colony on Phobos would likely deal with much bigger engineering challenges.

I think Phobos is a logical location to build facilities to support activities already ongoing on the martian surface but I do not see it as being the first stop.

SpaceNut · 2015-10-12 20:40:40

The Phobo's first plan is what Nasa JPL has put forth as the leverage point to getting man to Mars.

Here is another topic where we talked about both moons in comparison http://www.newmars.com/forums/viewtopic.php?id=6239

The initial link has changed "Comparing Deimos and Phobos for Human Exploration"

archive
http://spirit.as.utexas.edu/~fiso/archivelist10-12.htm
http://spirit.as.utexas.edu/~fiso/archivelist07-09.htm

Antius · 2016-05-10 05:41:00

Establishing a base on Phobos would require many of the technologies needed for missions to the larger asteroids. Key problems would be: (1) Maintaining a stable base on a world with 1/1000th Earth gravity; (2) Avoiding space radiation; (3) Providing artificial gravity; (4) Employing technologies for insitu resource utilisation. These issues can be solved by providing a means of mining the body and burrowing beneath its surface.

I recently gave attention to a forum discussing the use of pulsed lasers as weapon systems and I believe the same technology could be used for drilling into asteroids and other small airless bodies. Attempting to drill using a standard tunnelling machine is a bad option, due to the enormous mass of the machine and the lack of gravity, which would be needed to keep the cutting head against the surface. Cutting using lasers is another option that could reduce these issues.

A continuous beam laser is an inefficient means of cutting because the blast ejecta and plasma tend to obscure the beam. Hence, most of the energy is lost heating the ejecta rather than ablating the surface. The way around this is to operate the laser in pulsed mode. A millisecond pulse hits the surface, vaporises a small quantity of material that then expands, creating a pressure wave that mechanically ablates the surface. The second pulse does not arrive until the blast debris have cleared, which is on the order of milliseconds. The energy needed to create a roughly hemispherical crater can be calculated using the following equation:

E (joules) = 4x10^15 x D^3
Where D is measured in kM.

To blast a crater 2m wide and 1m deep would require 32MJ. To drill a 2m wide hole into Phobos and reach a depth of 5000m, would require approximately 5000 laser pulses with total energy 160GJ. Using a 10MW solar power source from a solar arcjet propulsion system, and assuming 30% efficiency for an infra-red pulsed laser, would allow the job to be completed in about 15 hours. Accounting for day-night interruption, and energy storage losses for the pulsed laser, this would increase to perhaps a couple of days. According to Louis’ estimates of a solar cell mass of 5g/m2 for solar panels and assuming an efficiency of 10% and solar constant 600W/m2, the power supply would weigh less than 1 tonne.

I solved my shell world spreadsheet for a body 20km in diameter with a density of 1800kg/m3. An internal cavity could be up to 11km in diameter if pressurised to 1 bar. These are the limits at which self-gravity of the overlying material would balance the internal pressure. By mining out Phobos at the bottom of the shaft, a huge internal cavity could be created. The interior of this cavity would provide a shirt-sleeve environment within which to construct a base, eventually expanding into a city. Artificial gravity would be provided in rotating habitats hanging from the inside of the cavity. Power would be provided by solar arrays on the surface of Phobos. The excavated material could initially be dumped on the surface or used as arcjet propellant. Ultimately, it would be employed in space manufacturing in Mars orbit.

Inline with principles discussed elsewhere, we would start small - excavating a cavity large enough for a small base - perhaps 10m in diameter. Mining would gradually expand the space allowing the base to add additional modules and capabilities. Initially, the base would be used to operate robotic probes on the Martian surface. From Phobos, these could be controlled in real time and the amount of science achievable using VR should begin to rival what could be achieved using human explorers. Ultimately, Phobos would become the gateway to human exploration of the planet, using SSTO's between Phobos and the any point on the Martian surface.

The Phobos first plan therefore allows us to begin exploring the Martian system using human eyes, without the initial need for Mars entry systems and high-thrust landers. The entire mission can be completed using low-thrust propulsion and mission mass is correspondingly reduced.

Last edited by Antius (2016-05-10 05:53:42)

Tom Kalbfus · 2016-05-10 08:40:14

We could have another asteroid mission instead. How about a manned mission to 1620 Geographos instead?

https://en.wikipedia.org/wiki/1620_Geographos

Aphelion 1.6630 AU (248.78 Gm)
Perihelion 0.82764 AU (123.813 Gm)
Semi-major axis 1.2453 AU (186.29 Gm)
Eccentricity 0.33541
Orbital period 1.39 yr (507.61 d)
Dimensions 5.0×2.0×2.1 ± 0.15 km[1] [1]
Mean radius 1.28 ± 0.075 km

Phobos
Dimensions 27 × 22 × 18 km
Mean radius 11.2667 km
Mars
Aphelion 1.6660 AU 249.2 Gm
Perihelion 1.3814 AU 206.7 Gm
Semi-major axis 1.523679 AU 227.9392 Gm
Eccentricity 0.0934
Orbital period 1.8808 Julian years

Now which do you think would make a better precursor mission before going to Mars?

Last edited by Tom Kalbfus (2016-05-10 08:41:25)

Antius · 2016-05-10 10:57:14

Geographos would work. It’s orbital characteristics suggest it might be possible to reach with lower dV than Mars. However, the eccentricity of its orbit might be problematic, both in terms of reaching it with regular low dV launch windows and in terms of using solar energy when there, the intensity of which would vary be a factor of 4 between aphelion and perihelion.

In terms of drilling to produce a habitable cavity (shell world approach), the asteroid is both smaller and more irregular than Phobos or Deimos. With a minimum dimension of 2km and assuming density of 2000kg/m3, the cavity can be no greater than 160m in diameter in order to sustain a 1bar pressure, though it could perhaps be elongated – my spreadsheet only works for spheres.

One huge advantage that Phobos and Deimos have is their strategic location. They provide a staging post for exploration and colonisation of Mars. From these bases we can teleoperate surface robots in real time, refuel SSTOs and even manufacture stuff to assist access to the planet. Geographos isn’t really useful from that point of view, though it may be a valuable source of rare metals.

Tom Kalbfus · 2016-05-10 14:11:05

I notice the asteroid shuttles between Earth and Mars orbit. Maybe it could be converted into a Cycling Spaceship.

Antius · 2016-05-10 14:49:52

Tom Kalbfus wrote:

I notice the asteroid shuttles between Earth and Mars orbit. Maybe it could be converted into a Cycling Spaceship.

Could work. I think the problem with the idea of cyclers is that there is no control of the cyclers orbit. You may have to wait decades for the orbits of Earth, Mars and the asteroid to line up well enough to make the cycler remotely useful as a vehicle. If it costs several billions of dollars to set up, it doesn't look like a good investment. OK though if you only need to use it once and can do so at little extra cost.

If we could locate several dozen small asteroids on Earth-Mars transit orbits, a spacecraft could shadow an asteroid for a large part of the journey and use it as a radiation shield. The asteroid might only need to be a few metres in diameter to be useful in this way. Heading further out, a nuclear powered reaction driven spacecraft could rendezvous with a small asteroid and cannibalize it for propellant. Using an asteroid in this way might put Jupiter in range of manned spacecraft that would otherwise be too small, unprotected and lacking in consumables to make the journey. Maybe this way an Orion capsule, bigallow module and small nuclear power source could make it to Callisto.

Last edited by Antius (2016-05-10 15:19:24)

Tom Kalbfus · 2016-05-10 21:23:58

Geographos is large enough to make an O'Neill colony out of.

I like this picture, haven't seen it before, must be new. Yes I believe Geographos is big enough to make this. What you looking at is the inside of an Island Three Space colony, from somebody's patio overlooking a pool. With adjustable mirrors it can compensate for the varying distance from the Sun. Travelers heading to Mars can spend the trip sunning themselves by this pools side, maybe enjoying a pinna colada. So much better than traveling in a small tin can, isn't it?

Antius · 2016-05-11 05:41:15

Tom Kalbfus wrote:

Geographos is large enough to make an O'Neill colony out of.
http://s3files.core77.com/blog/images/3 … ankphX.jpg
I like this picture, haven't seen it before, must be new. Yes I believe Geographos is big enough to make this. What you looking at is the inside of an Island Three Space colony, from somebody's patio overlooking a pool. With adjustable mirrors it can compensate for the varying distance from the Sun. Travelers heading to Mars can spend the trip sunning themselves by this pools side, maybe enjoying a pinna colada. So much better than traveling in a small tin can, isn't it?

The O'Neill cylinder idea is definitely a better long-term use of resources. The hollow asteroid idea is really a cheap-skate way of creating habitable space if you turn up with limited equipment. You drill in and use the weight of the overlying material in its own gravity field to balance internal pressure. But it isn't really an efficient use of resources as the required overlay is at least a kilometre thick in the asteroid's weak gravity. For asteroids less than 2km in diameter it doesn't work well at all. With an O'Neill cylinder you rely on the tensile strength of materials and the shell can therefore be much thinner. Its just a question of whether you can afford the manufacturing effort needed to build it.

Terraformer · 2016-05-11 05:53:49

On the other hand, how do they both handle meteorite impacts?

Most of what's available is silicate, right? Is there much you can actually do with that?

Tom Kalbfus · 2016-05-11 06:36:58

Terraformer wrote:

On the other hand, how do they both handle meteorite impacts?
Most of what's available is silicate, right? Is there much you can actually do with that?

I am sure it is not a block of glass. Silicates still contain plenty of iron, the silicon parts can be used to make the large windows which take up half of the floor space of this particular O'Neill colony.

Antius · 2016-05-11 08:06:45

Island 3 designs are quite vulnerable to small meteor impacts due to the large longitudinal windows. Some of O’Neill’s spherical designs had mirror arrangements that avoided the need for direct exposure of windows to space.

To shield out cosmic rays at least 2m of silicate shielding is typically assumed. This would protect the pressure vessel from impactors up to about 20cm in diameter (~10kg). Anything bigger than that would show up on radar whilst hundreds of km from the cylinder. Maybe we could deflect them with pulsed lasers?

Anyway, back to the topic of Mars’ moons. Could we feasibly mount a manned mission to Phobos or Deimos within the launch capacity of a single Falcon Heavy (54 tonnes to LEO) launch? Assuming some mixture of low-thrust electric propulsion and rocket propulsion, how much mass could be delivered to Phobos L1?

Tom Kalbfus · 2016-05-11 13:03:21

Antius wrote:

Island 3 designs are quite vulnerable to small meteor impacts due to the large longitudinal windows. Some of O’Neill’s spherical designs had mirror arrangements that avoided the need for direct exposure of windows to space.

On the other hand, the location of these windows, right on the floor, makes them quite easy to repair, as you can walk right on top of them. the windows are also quite thick, meters thick in fact, you can pull out a gun and shoot the windows, and the bullets will ricochet right off of them. Most of the likely meteor impacts will be quite small, and the windows won't be solid sheets of glass, but divided into a number of panes. Also the Island Three design contains quite a but of air, so a hole blown in one of the windows will take quite some time to empty out the O'Neill, people can live in this environment as the windows leak air into space, there is plenty of time to repair them.

Antius wrote:

To shield out cosmic rays at least 2m of silicate shielding is typically assumed. This would protect the pressure vessel from impactors up to about 20cm in diameter (~10kg). Anything bigger than that would show up on radar whilst hundreds of km from the cylinder. Maybe we could deflect them with pulsed lasers?
Anyway, back to the topic of Mars’ moons. Could we feasibly mount a manned mission to Phobos or Deimos within the launch capacity of a single Falcon Heavy (54 tonnes to LEO) launch? Assuming some mixture of low-thrust electric propulsion and rocket propulsion, how much mass could be delivered to Phobos L1?

Last edited by Tom Kalbfus (2016-05-11 13:04:03)

SpaceNut · 2016-05-11 19:49:19

A cycler is barely on topic for going to the mars moons with a human mission and unless we have lots of them going to mars the timeframe as they are just to long....

Tom Kalbfus · 2016-05-12 08:40:29

Well the one I mentioned is rather big, but a Cycler is more of a space station than a space ship, it expends minimum propellents to stay in its orbit and its orbit does all the work of carrying it between Earth and Mars and from Mars to Earth. To make full use of cyclers, you need two. One where the short arc is going from Earth to Mars and the other where the short arc goes from Mars to Earth. Probably completing the Mars to Earth cycler should take priority, followed by the Earth to Mars cycler.

I'm trying to imagine the World in which "The Martian" occurs. The year is 2029, this is 13 years in our future. What else do you suppose they would have going on besides a manned mission to Mars? I think there will be cars that drive themselves on our highways, I think there will by flying cars. A computer keyboard will be an add-on, most people will talk to their computers and their computers will understand them. There will be more robust automatic translation devices, for instance the people of NASA will be able to communicate with their Chinese counterparts without knowing each other's language, or having a human translator in between, a computer translator will do an adequate job with few mistakes. Computer screens will render images in three dimensions, some of the screens will be flexible, you will be able to roll them up or fold them up and fit them in your pocket.

Massive layoffs of the workforce will be occurring due to technological obsolescence, and just ten years after that, we will be building our first space colonies, constructed mostly through robotic labor, with very few human hands involved in the process, except in deciding what's to be built. After that, we'd better watch out, because machines will increasingly be making their own decisions, some of them might escape our control entirely. The people taking that Island Three to Mars probably won't have much to do, they will probably be on social security, and robotic labor would make most things affordable enough, that you could pay for a trip to Mars with nothing more than the income you receive from social security. Machines would do all the labor on the space colony, unless humans volunteer to do some of their own, such as planting a garden, while they wait to arrive at Mars. And when they get to Mars, there will be huge domes awaiting them, machines will be running everything, the humans there will either be tourists or residents all living off of social security, regardless of their age.

There will be children in schools learning interesting stuff, and attendance will be voluntary, the children don't need to prepare for anything, as when they graduate, they will be ready to retire and do whatever they want off their Social Security check. This is a vision much different from the one Gerard O'Neill offered, and I'm not sure it would be good for humanity to live like this, but with automated labor, you can build enormous things in space, as you can build the labor you need to get the job done, then you dispose of the labor or shut them down when no longer needed until they are repurposed for doing other things. The limitations on the economy will basically be that of energy and matter.

Last edited by Tom Kalbfus (2016-05-12 08:40:56)

Antius · 2016-05-12 10:10:44

Tom Kalbfus wrote:

Well the one I mentioned is rather big, but a Cycler is more of a space station than a space ship, it expends minimum propellents to stay in its orbit and its orbit does all the work of carrying it between Earth and Mars and from Mars to Earth. To make full use of cyclers, you need two. One where the short arc is going from Earth to Mars and the other where the short arc goes from Mars to Earth. Probably completing the Mars to Earth cycler should take priority, followed by the Earth to Mars cycler.
I'm trying to imagine the World in which "The Martian" occurs. The year is 2029, this is 13 years in our future. What else do you suppose they would have going on besides a manned mission to Mars? I think there will be cars that drive themselves on our highways, I think there will by flying cars. A computer keyboard will be an add-on, most people will talk to their computers and their computers will understand them. There will be more robust automatic translation devices, for instance the people of NASA will be able to communicate with their Chinese counterparts without knowing each other's language, or having a human translator in between, a computer translator will do an adequate job with few mistakes. Computer screens will render images in three dimensions, some of the screens will be flexible, you will be able to roll them up or fold them up and fit them in your pocket.
Massive layoffs of the workforce will be occurring due to technological obsolescence, and just ten years after that, we will be building our first space colonies, constructed mostly through robotic labor, with very few human hands involved in the process, except in deciding what's to be built. After that, we'd better watch out, because machines will increasingly be making their own decisions, some of them might escape our control entirely. The people taking that Island Three to Mars probably won't have much to do, they will probably be on social security, and robotic labor would make most things affordable enough, that you could pay for a trip to Mars with nothing more than the income you receive from social security. Machines would do all the labor on the space colony, unless humans volunteer to do some of their own, such as planting a garden, while they wait to arrive at Mars. And when they get to Mars, there will be huge domes awaiting them, machines will be running everything, the humans there will either be tourists or residents all living off of social security, regardless of their age.
There will be children in schools learning interesting stuff, and attendance will be voluntary, the children don't need to prepare for anything, as when they graduate, they will be ready to retire and do whatever they want off their Social Security check. This is a vision much different from the one Gerard O'Neill offered, and I'm not sure it would be good for humanity to live like this, but with automated labor, you can build enormous things in space, as you can build the labor you need to get the job done, then you dispose of the labor or shut them down when no longer needed until they are repurposed for doing other things. The limitations on the economy will basically be that of energy and matter.

Fascinating I’m sure. But the purpose of this thread is to establish how useful Mars moons could be in establishing a near term ‘foot-in-the-door’ for Mars exploration and/or colonisation. A separate thread should be established for cyclers.

Tom Kalbfus · 2016-05-12 12:50:12

Antius wrote:

Tom Kalbfus wrote:
Well the one I mentioned is rather big, but a Cycler is more of a space station than a space ship, it expends minimum propellents to stay in its orbit and its orbit does all the work of carrying it between Earth and Mars and from Mars to Earth. To make full use of cyclers, you need two. One where the short arc is going from Earth to Mars and the other where the short arc goes from Mars to Earth. Probably completing the Mars to Earth cycler should take priority, followed by the Earth to Mars cycler.
I'm trying to imagine the World in which "The Martian" occurs. The year is 2029, this is 13 years in our future. What else do you suppose they would have going on besides a manned mission to Mars? I think there will be cars that drive themselves on our highways, I think there will by flying cars. A computer keyboard will be an add-on, most people will talk to their computers and their computers will understand them. There will be more robust automatic translation devices, for instance the people of NASA will be able to communicate with their Chinese counterparts without knowing each other's language, or having a human translator in between, a computer translator will do an adequate job with few mistakes. Computer screens will render images in three dimensions, some of the screens will be flexible, you will be able to roll them up or fold them up and fit them in your pocket.
Massive layoffs of the workforce will be occurring due to technological obsolescence, and just ten years after that, we will be building our first space colonies, constructed mostly through robotic labor, with very few human hands involved in the process, except in deciding what's to be built. After that, we'd better watch out, because machines will increasingly be making their own decisions, some of them might escape our control entirely. The people taking that Island Three to Mars probably won't have much to do, they will probably be on social security, and robotic labor would make most things affordable enough, that you could pay for a trip to Mars with nothing more than the income you receive from social security. Machines would do all the labor on the space colony, unless humans volunteer to do some of their own, such as planting a garden, while they wait to arrive at Mars. And when they get to Mars, there will be huge domes awaiting them, machines will be running everything, the humans there will either be tourists or residents all living off of social security, regardless of their age.
There will be children in schools learning interesting stuff, and attendance will be voluntary, the children don't need to prepare for anything, as when they graduate, they will be ready to retire and do whatever they want off their Social Security check. This is a vision much different from the one Gerard O'Neill offered, and I'm not sure it would be good for humanity to live like this, but with automated labor, you can build enormous things in space, as you can build the labor you need to get the job done, then you dispose of the labor or shut them down when no longer needed until they are repurposed for doing other things. The limitations on the economy will basically be that of energy and matter.
Fascinating I’m sure. But the purpose of this thread is to establish how useful Mars moons could be in establishing a near term ‘foot-in-the-door’ for Mars exploration and/or colonisation. A separate thread should be established for cyclers.

I think the moons of Mars are as useful as any asteroid. One thing you can do with the moons of Mars is build O'Neill colonies out of them, you can regulate the gravity by adjusting the spin, You can have whole communities in orbit around Mars. The atmosphere of Mars makes a great decelerator, so you save fuel on the inbound leg, however if you don't travel so far, you can colonize an near earth asteroid. I think we can give Venus a moon, there are some Venus crossing asteroids, if we can alter their course a little, and with a little atmosphere grazing, Venus can have some moons as well. The deceleration needs to be slight, too much and the asteroid will break up in the atmosphere, and some of it might even impact on the planet below!

SpaceNut · 2016-05-12 18:44:13

The main reason to use an asteriod or other large rock that cycles where we would want is to use it as a launch plus landing pad and as a shielded habitat is that its a natural resource for insitu use....

GW Johnson · 2016-05-17 16:55:08

My problems with cyclers are two-fold: (1) these things only have favorable orbit geometries every several years, not every 2 years, and (2), by the time you do all the delta-vees to get from the cycler to Mars, or from the cycler to Earth at end-of-mission, you have spent just about the same propellant as for flying straight to Mars without the cycler at all.

That being the case, what is the point? Radiation protection? No, I don't think so.

Radiation protection is something we can supply on any Mars ship using water, wastewater, and frozen food. So, why do we need an asteroid for such radiation protection?

That being the case, my question is: what is the point of a cycler? Can someone give me a compelling argument why such a thing is really attractive?

GW

Last edited by GW Johnson (2016-05-17 16:58:54)

Antius · 2016-05-18 05:30:02

Good luck trying to shield a volume more than a few cubic metres using consumables. The shielding needed to screen out secondary cosmic ray particles is something like 200grams/cm2. To shield a 1m3 volume would require something like 60m3 of consumables and wastes in the right geometry. You could shield asteronaut bunks in that way, if the geometry of the craft is creative. Static magnetic fields might work better.

None the less, your point stands, there are other ways to solve the radiation problem. I can't see many advantages to a cycler if it adds to the delta-v required to complete the mission. Landing on the thing adds to mission risk and means that you have to build a propulsion system for that purpose.

There might be some advantage if you could use the object for materials or consumables in some way. If you could extract reaction mass for the propulsion system, or process the surface materials to provide water and oxygen. That way, the take-off mass for the mission is reduced. Heading to the outer planets this might be a strategy that offers value. But its a mission specific, one-time use of a body of the right composition on the right orbit. Without doing arithmetic, it is difficult to guage the real practicality of these things. Straight off I can see that any large scale processing of surface materials for consumables means taking a nuclear reactor to the asteroid and leaving it there afterwards. Ca-ching! Ca-ching!

GW Johnson · 2016-05-18 09:33:55

Cosmic rays are a very thin drizzle of really-high energy particulate radiation that peaks in years when the sun is less active, at about 60 REM annual dose. The astronaut max allowable dose is 50 REM annual, based on what they think is a 3% increase in cancer late in life (although I do not trust the statistical models they use with low dose radiation). In active-sun years, the cosmic ray dose is closer to only 24 or 25 REM annual. It would take very little shielding effect to cut 60 to 50 REM annual in a peak year; in an off year it's just not much of a credible threat.

GCR is simply not the threat that some make it out to be.

The real danger is short but intense low-energy particulate radiation from the sun: the solar flare event. The last really big one was in 1972, between two of the Apollo landings on the moon. It would have been fatal within hours to any crew in a plain capsule anywhere outside the Van Allen belts. These events are bursts only hours in duration, but are similar in effects to standing in the fallout from an atomic bomb blast: 100's, 1000's, even 10,000's of REM within hours not years.

That kind of radiation is essentially well-shielded by only 15-20 cm thickness of water (liquid or solid, doesn't matter). If you have life support for people, then you have water and wastewater tanks. If you are doing spin gravity (which enables free-surface water cooking, and allows the use of frozen food), then you will likely have frozen food, which is rich in ice content. You only need a small space surrounded by these things for the crew to shelter for a few hours.

I suggest that the vehicle's flight control station be the shelter, so that any critical maneuvers could still be flown, regardless of the solar weather. It really isn't hard to design this way at all. But current capsule designs do not allow for such arrangements. However, if you are building a real orbit-to-orbit vehicle "from scratch", it is easy to include arrangements like this in the basic design.

Having an asteroid or other body to hide behind just makes the shielding effects on GCR that much more effective. You get that effect while in low Mars orbit, even though Mars has no shielding magnetic field. The planet blocks out (crudely) half the sky.

GW

Last edited by GW Johnson (2016-05-18 09:38:58)

Antius · 2016-05-19 05:14:34

GW Johnson wrote:

Cosmic rays are a very thin drizzle of really-high energy particulate radiation that peaks in years when the sun is less active, at about 60 REM annual dose. The astronaut max allowable dose is 50 REM annual, based on what they think is a 3% increase in cancer late in life (although I do not trust the statistical models they use with low dose radiation). In active-sun years, the cosmic ray dose is closer to only 24 or 25 REM annual. It would take very little shielding effect to cut 60 to 50 REM annual in a peak year; in an off year it's just not much of a credible threat.
GCR is simply not the threat that some make it out to be.
The real danger is short but intense low-energy particulate radiation from the sun: the solar flare event. The last really big one was in 1972, between two of the Apollo landings on the moon. It would have been fatal within hours to any crew in a plain capsule anywhere outside the Van Allen belts. These events are bursts only hours in duration, but are similar in effects to standing in the fallout from an atomic bomb blast: 100's, 1000's, even 10,000's of REM within hours not years.
That kind of radiation is essentially well-shielded by only 15-20 cm thickness of water (liquid or solid, doesn't matter). If you have life support for people, then you have water and wastewater tanks. If you are doing spin gravity (which enables free-surface water cooking, and allows the use of frozen food), then you will likely have frozen food, which is rich in ice content. You only need a small space surrounded by these things for the crew to shelter for a few hours.
I suggest that the vehicle's flight control station be the shelter, so that any critical maneuvers could still be flown, regardless of the solar weather. It really isn't hard to design this way at all. But current capsule designs do not allow for such arrangements. However, if you are building a real orbit-to-orbit vehicle "from scratch", it is easy to include arrangements like this in the basic design.
Having an asteroid or other body to hide behind just makes the shielding effects on GCR that much more effective. You get that effect while in low Mars orbit, even though Mars has no shielding magnetic field. The planet blocks out (crudely) half the sky.
GW

That is good news. A while back I read an article concerning the use of magnetic fields for radiation shielding of interplantary space craft. It had previously been assumed that huge fields with strengths of 100s of Tesla would be required. These were clearly impractical for small spacecraft and required super-conductors. Recalculation revealed that fields of around 1Tesla were adequate to protect a radius of 100-200m from cosmic radiation. This is within the limits of non-superconducting iron core solenoids. Whilst still relatively heavy, it would be easy to incorporate such items within a static base on Mars, the Moon or Phobos, effectively eliminating one of the big problems of thin or non-existant atmospheres. Something like this would not be difficult to fabricate from local materials.

SpaceNut · 2018-01-14 10:49:50

Wrapping up past discusion with the current is always a challenge when we keep creating new topics that drift rather than staying focussed on the topics with them. The BFR alternative has done just that again and here is another of why we should go to the moons of mars.

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