NASA adopts the best of Zubrin's ideas, eventually

[QuantumG]

Once upon a time, it seemed that Zubrin's name was unspeakable at NASA.. and you can understand why.

They used to dismiss the leverage of Mars ISRU, but now it's a standard part of any architecture. Same with promoting conjunction class missions over opposition class, to reduce total radiation exposure times.

I think Zubrin's next contribution will be dismissing the myth that crew safety can be improved with hyperbolic transfer trajectories (aka VASIMR pixie dust), as no-one has been doing cost-benefit analysis of the reduced radiation exposure to the elimination of abort modes.

Another good point he's made lately is to remind us that we simply don't know what prolonged exposure to galactic cosmic radiation does to the human body. We have hunches, and assumptions, but no hard data. Human factors experts and flight surgeons may be overly cautious. Wouldn't it be good to actually go test it? If NASA goes ahead with the L2 exploration gateway, they will be.

On the other hand, NASA seems dedicated to the medical mitigation of long term zero-g exposure, whereas Zubrin remains an advocate of artificial gravity - particularly using a rotating tether. This may end up being a point he backs down on, especially when NASA starts saying they have the drugs to do a Mars mission.

[Dalhousie]

Tissue cultures can be flown on the ISS for years and should provide much of the data needed on the effects of GCRs.  I am surprised this has not been done as yet.

I agree that the zero gravity issue is well on the way to being solved with a combnation of exrcise, diet, and medication.

[ciscosdad]

You are correct about Zubrin, but I think he may be a little over optimistic in some cases. NASA on the other hand is (perhaps understandably) over cautious.
Zero G seems less of a problem than advertised given that multiple cosmonauts have spent more than 9 months in it with no long term ill effects provided simple precautions are followed.
Given the time of one leg of the Mars expedition is about that and the middle interval is ~500 days on the surface in .38g, there may actually be no problem at all.
Of course if there was an abort midway that forced them to do the return leg immediately, that may be a problem, as I don't believe anyone has spent that amount of time (18 consecutive months) in zero G have they?
I'd like to see a low g (Lunar or Martian) gravity module on ISS. Pity its never been funded. Some tether work in orbit would be useful too.

[Sparky]

Tissue cultures can be flown on the ISS for years and should provide much of the data needed on the effects of GCRs.  I am surprised this has not been done as yet.

I agree that the zero gravity issue is well on the way to being solved with a combnation of exrcise, diet, and medication.

We send large amounts of tissue cultures to ISS all the time. We call them astronauts. But ISS is situated well within the Earth's Magnetic field, which protects from much of the radiation. The radiation environment in LEO is very different than what would be experienced on a deep space mission.

[MATTBLAK]

Artificial gravity with tethers is one of those great ideas in principle. But actually doing this sort of engineering without first practical testing to exhaustive levels will be difficult, not hand-wavingly simple. And VASIMR - a damn cool idea hampered by a couple of sobering facts: How will funding and approval get passed to build a 100 megawatt-plus space worthy nuclear reactor then go fly it?

Zubrin knows this, that's why he has advocated chemically propelled missions. And ISRU? Damned nice to have - maybe even a mission success deal-breaker. But NOT essential in terms of actually going there. Though without ISRU, shortcuts in crew size and mission duration/capability would have to be made, reducing the value of even doing it in the first place. And as for L-2 Gateway Station? I'd say it was almost essential.

[QuantumG]

And VASIMIR - a damn cool idea

What's cool about it? It's just a magnetic mirror with radio frequency heating, pre-tokamak fusion technology that never delivered. Just getting it working for full length burn times requires superconducting magnets which don't exist. Testing it requires vacuum chambers larger than any that exist, or in-space testing. And in the end, you get a thruster that's not much better than existing - flight proven - electric thrusters.

Zubrin knows this, that's why he has advocated chemically propelled missions.

He's advocating chemically propelled missions because he thinks they are the best way to do it. Even if all the ponies fell from the sky to make VASIMR work he'd be advocating chemical. Same with artificial gravity, ISRU and heavy lift.

[MikeAtkinson]

The cancer situation is much more complex than just increased rates due to radiation.

Cancers are caused by multiple factors including lifestyle, diet, exercise, viruses and pollutants and the chances of dying of those cancers depends on age, fitness, cancer type, immune system, early detection and medical care among others. The chances of dying from a cancer changes over time as new treatments are found and risk factors change.

Being accepted onto an astronaut program alters all those risk factors, going on a Mars mission alters them again.

It is by no means certain that radiation ill cause the greatest increase in cancer risk as compared to other factors. And other factors may actually cause a decrease in overall cancer risk. Going on a Mars mission and the greater health monitoring before during and after the mission means that it is highly likely that cancers are picked up earlier than otherwise. Astronauts are likely to receive healthcare second to none for the rest of their lives, meaning that treatments are more likely to be successful than for the general population.

Cancer is complex. Zubrin's naive approach to assessing its risk from Mars missions should not be followed.

[MikeAtkinson]

It is really difficult to predict technology over the long term, so I would not rule VASIMIR out completely.

However from what we know now, VASIMIR seems very unlikely to be useful for early Mars missions. It is certainly not necessary.

This makes it a sideshow. Lets continue to develop the technology together with that for other electric thruster types, but don't put it anywhere on plans and certainly not on the critical path.

One problem with all electric thrusters which hasn't been mentioned so far is the long operational life required, this requires long development, test and qualification runs which makes development slow.

[MATTBLAK]

And VASIMIR - a damn cool idea

What's cool about it? It's just a magnetic mirror with radio frequency heating, pre-tokamak fusion technology that never delivered. Just getting it working for full length burn times requires superconducting magnets which don't exist. Testing it requires vacuum chambers larger than any that exist, or in-space testing. And in the end, you get a thruster that's not much better than existing - flight proven - electric thrusters.

Zubrin knows this, that's why he has advocated chemically propelled missions.

He's advocating chemically propelled missions because he thinks they are the best way to do it. Even if all the ponies fell from the sky to make VASIMR work he'd be advocating chemical. Same with artificial gravity, ISRU and heavy lift.

What's cool about it? I'm surprised I have to point it out to you: the ability to - theoretically - take a crew to Mars in about 40 days. But like you, here's where I would disconnect from the fantasy and join reality. Such huge nuclear reactors for space wont get approved or funded, probably in our lifetimes. Anti-nuke sentiment is far too powerful, therefore, VASIMR and - sadly - nuclear thermal rocket motors wont get approved anytime soon either. Too many people (space cadets?) don't seem to get this fact. And one of the main reasons for Zubrin advocating chemical propulsion is cost - its cheaper and goes hand-in-glove with ISRU.

[Dalhousie]

I agree that the zero gravity issue is well on the way to being solved with a combnation of exrcise, diet, and medication.

We send large amounts of tissue cultures to ISS all the time. We call them astronauts. But ISS is situated well within the Earth's Magnetic field, which protects from much of the radiation. The radiation environment in LEO is very different than what would be experienced on a deep space mission.
[/quote]

The magnetic field protect the astronauts to some extent from the most intense SPEs, they have little or no impact on the GCRs which are far more energenic.  Even the protection from SPEs is only partial, as the particles are trapped to form the VABs.    Since the ISS traverses part of the VABs (the SAA) the average dose is still significant.  The nadir shielding from the Earth is probably more important for the GCR, but it just mans dose times have to be doubled.

Tissue cultures are a way of investigating long term low level dosed well beyond what is practical for crewed mission and complements work from short term high level does in the lab.

However quite a few people have accummulated career doses similar to what you would get on a Mars mission

[MATTBLAK]

Cosmonauts like Sergei Krikalev? I'd love to know what his career dosage has been!

[Dalhousie]

As far as I can determine, annual GCR dose in interplanetary space is ~250 mSv, therefore ~125 mSv in LEO or the surface of the Moon of Mars.

A conjunction-class mission to Mars would expose an astronaut to ~430 mSv.  Krikalev, with 803 days in LEO, has been exposed to 260 MsV.

Because of repeated passes through the SAA he would have accumulated a significant dose from high energy protons and electons - equivalent to higher on average than interplanteray space.  It is hard to get accurate figures, but annual total dose equivalents on the ISS are said to be as low as 180 mSv per year and as high as 400 mSv.

So Krivalev could have accumulated as low as 400 mSv or as high as 880 mSv.

Cumulative dose equivalent estimates on a conjunction mission range between 350 and 950 mSv.

[spectre9]

BAD MDOT IS BAD.

That's all you really need to know about electric propulsion in regards to manned missions.

It's good for super small space probes and super light satellites but not for massive human rated interplanetary spacecraft.

By the time you're jacking out enough thrust to get humans on a high energy 6 month trajectory to Mars the electric drive system be it solar or nuclear is completely unrealistic.

NASA has gone from nuclear thermal to solar electric and it's all just bogus. Nuclear thermal would've been ok if they matured the technology but at this point it's just best to go with storable fuels like those that were used to safely return man from the moon. Important demonstration of hypergols I reckon and should be built on.

[Robert Thompson]

Same with artificial gravity

Is Zubrin dismissing tether architectures?
Favoring accelerate till midpoint, reverse, decelerate till destination?

[MATTBLAK]

To get the best of 'what's around' for Mars:

Earth Departure: LOX/LH2 and/or LOX/Kerosene. Or LOX/CH4 if the buildup of mission hardware is going to take awhile but you still want next-best performance after LOX/LH2. LOX/CH4 is better Isp than LOX/Kerosene, but Hypergols are not much worse. LOX/Ethanol anyone? Technology Risk: Low-to-moderate.

Mars Arrival: Option 1 - Aerocapture then powered & parachute/powered descent. Propellant? Storables, because of the long voyage through interplanetary space: devoting mass and technology to zero-boiloff will reduce Hab/Lander down mass. Option 2 - Direct descent with no aerocapture; parachute & powered descent. Propellant; again storables. Technology Risk: Medium-High.

Mars Ascent to Orbit: Option 1 - Storables all the way, but mission down mass reduced. However, low technology risk. Option 2 - ISRU for LOX by 'cracking' the Martian CO2 atmosphere: solar & RTG-powered ISRU plant. Fuel? Kerosene or Ethanol. Technology Risk: Moderate.

Earth Return Vehicle from Martian orbit: Storables. Technology Risk: Low. This vehicle would be waiting in Martian orbit to do its job for at least two years, so proven hypergolic technology it should be.

*Bonus Category: Launchers - OPTION 1: Mixed fleet of Delta IV-Heavy (uprated to 40+plus tons = known, simple upgrade options), Atlas V, Falcon Heavy and Ariane V. OPTION 2: SLS & Falcon Heavy. Earth Re-entry spacecraft? Either Orion or Dragon, I have no preference.

[MikeAtkinson]

MATTBLAK, I'm not sure what you mean by Technology Risk here, within each of those paragraphs there are several technologies mentioned.

It is better to discuss this in terms of technology readiness level (NASA version)

Aerocapture is probably only TRL 6/7 because although it has been demonstrated in space, those missions were much smaller in terms of mass than a Mars mission would be.

Mars Entry Descent and Landing EDL is difficult to quantify in terms of TRL as demonstrated methods do not scale up the manned mission masses. Red Dragon type approaches could probably scale up to the required size and maybe, just maybe, we might have it demonstrated this decade, then it would be at TRL 7. The DRM 5 method would be sufficient as well, component technologies though are still quite immature.

Technology risk is not the only risk, there are program, financial, safety, cancellation, political (and probably several other risks as well) risks. These need to be balanced in the overall program to get the highest return for the least cost. President+Congress+NASA seem to have been pretty poor at creating manned spaceflight programs which balance all the risks to arrive at something that can be implemented successfully.

[MATTBLAK]

Thanks for your post! I'm aware that Manned Mars Missions themselves are chock-full of Technology Risks - nature of the beast. But my context was for the getting there-and-back propulsion. We can't do or are not ready for nuclear propulsion of any sort. Neither are we ready for Zero-boiloff LOX/LH2 propulsion on the grand scale readiness needed for Mars. And we're not quite there with LOX/CH4 yet.

But we can do storable propellant propulsion on a big scale already, and probably LOX/Kerosene, too.

[laszlo]

So who's Zubrin?

Serious question, not a troll.

Laszlo

[MATTBLAK]

So who's Zubrin?

Serious question, not a troll.

Laszlo

http://en.wikipedia.org/wiki/Robert_Zubrin

http://www.marssociety.org/

[Jim]

We have hunches, and assumptions, but no hard data. Human factors experts and flight surgeons may be overly cautious. Wouldn't it be good to actually go test it?

Mars Odyssey, MRO, and MSL have radiation sensors.