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Scientists Petition U.S. Congress for Return to the Moon.
www.space.com

   Bob Clark

Robert Zubrin wrote a critique of VASIMR propulsion here:

The VASIMR Hoax
By Robert Zubrin | Jul. 13, 2011
http://www.spacenews.com/article/vasimr-hoax

The primary criticism is that it would require unrealistically lightweight nuclear propulsion. However, Zubrin doesn't even like the idea of fast propulsion to allow short travel times to Mars. He argues in favor of using 6 month or more one-way travel times to allow free return trajectories at Mars. But the health disadvantages of long travel times such as radiation exposure, bone and muscle loss, and the recently found eye damage and vision loss suggest we should investigate such short travel times.

Now we find there is also another reason: mechanical breakdowns on such missions of 2 or more years round trip length, such as found with the coolant system on the ISS.

Note that the argument about free return trajectories does not hold with respect to planets with atmospheres. The Apollo missions did do a free return around the Moon, but there was no non-propulsive method to slow down at the Moon. On return to the Earth though, even Apollo had a trajectory that would send it off into space if the angle was too shallow or plunging too steeply into the Earth's atmosphere to burn up if the angle was too steep. The same could be used in addition to the propulsive method whose high efficiency would also allow it to be used for slow down at Mars.

So it is important to note we may have a short term power source instead of nuclear power, for plasma propulsion such as Vasimr at the needed lightweight.

The key point is that the power source does not need to be nuclear. According to Zubrin's article on the Vasimr it requires a power source of 1,000 watts per kg power density. This is 100 times better than what has been done with nuclear space power at 10 watts per kg. However, it is only 10 times better than standard solar space cells at 100 watts per kg. Actually more recent space solar cells get 200 watts per kg, so it is only needs to be 5 times better than those.

Now the key fact is that solar cells can put out more power if they have more concentrated light shone on them. Estimates of how much power solar cellls put out are based on the solar insolation at the Earth's distance from the Sun. But if that light is concentrated they can put out more power. In fact some Earth solar power systems get more power by using inexpensive mirrors or lenses to concentrate light over a larger area rather than using expensive solar cells over that larger area.

A disadvantage is this increases the loss due to heat and also if the light is too intense it can overload the solar cells so they don't work at all. However a recent report claims they can use concentrated light at thousands of times higher than solar insolation:

SEPTEMBER 07, 2013
Stacked Solar Cells Can Handle Energy of 70,000 Suns.
This work is important because photovoltaic energy companies are interested in using lenses to concentrate solar energy, from one sun (no lens) to 4,000 suns or more. But if the solar energy is significantly intensified – to 700 suns or more – the connecting junctions used in existing stacked cells begin losing voltage. And the more intense the solar energy, the more voltage those junctions lose – thereby reducing the conversion efficiency.
http://nextbigfuture.com/2013/09/stacke … nergy.html

Several reports in fact claim solar concentration at hundreds to thousands of Suns:

FEBRUARY 20, 2009
Breakthrough Solar Concentrator:low cost with high efficiency.
http://nextbigfuture.com/2009/02/breakt … -cost.html

FEBRUARY 17, 2011
Concentrated solar power at half the cost of thin film solar.
http://nextbigfuture.com/2011/02/concen … -cost.html

DECEMBER 16, 2011
Tiny Solar Cell Could Make a Big Difference
http://nextbigfuture.com/2011/12/tiny-s … e-big.html

This will be dependent on having lightweight mirrors or lenses. However another key fact is that the parabolic mirrors do not have to be telescope grade accuracy. Indeed you can find on the net videos of amateurs making their own homemade solar furnaces that also require light to be concentrated to high intensity. These homemade mirrors can be as simple as aluminum foil spread onto a cardboard frame and still concentrate light to generate thousands of degrees. Not requiring high accuracy for the mirrors suggest they can be made lightweight.

DARPA is also funding lightweight space lenses:

DECEMBER 08, 2013
DARPA shoots for 20 meter folding space telescope.
http://nextbigfuture.com/2013/12/darpa- … space.html

These methods would concentrate sunlight onto solar cells. However, solar cells are typically low efficiency, in the range of 30%. Another method would eliminate the need for solar cells. That is to use a solar furnace. These can get temperatures as hot as the surface of the Sun by concentrating sunlight. By thermodynamics very high temperatures correspond to high efficiency conversion of heat to other forms of energy, 90% and above.

  Bob Clark

Renewed Congressional Push for a NASA Return to the Moon.
Sparked by Chinese Chang'e 3/Jade Rabbit.
Mark Whittington, Yahoo Contributor Network
Dec 21, 2013

  Bob Clark

DARPA Robotics Challenge Trials Live Broadcast.
http://www.youtube.com/watch?v=mwWm3HaDbnQ

  Bob Clark

I like the idea of not relying on ISRU for first manned mission, which means carrying all the propellant from Earth. But about the propellant modules it looks like in your drawings such as Figs. 15,18, and 19 that you are keeping the expended modules. Wouldn't you get a better mass fraction by dispensing with them? This would be analogous to Phil Bono's proposed orbital launchers from the 60's:

Encyclopedia Astronautica.
Rombus.

Rombus SSTO
Rombus SSTO Launch Vehicle
Credit: © Mark Wade
http://www.astronautix.com/lvs/rombus.htm

ICARUS/Ithacus.
Posted on December 2, 2013 by admin   

http://www.aerospaceprojectsreview.com/blog/?p=1435

In fact, Bono wanted to use these with orbital refueling for lunar and Mars missions:

Encyclopedia Astronautica.
Project Selena
http://www.astronautix.com/craft/proelena.htm

Encyclopedia Astronautica
Project Deimos
http://www.astronautix.com/craft/proeimos.htm

Also, what are the mass fractions of the propellant modules in your design?

    Bob Clark

Another recent article on the Dava Newman suit:

BioSuit: The Future of Space Gear Is Being Built Out of MIT.
New materials and designs could allow outer-space travelers to move more freely.
By Steve Annear | Boston Daily     | December 10, 2013 12:08 pm
http://www.bostonmagazine.com/news/blog … va-newman/

She says using "active materials" they are able to get to the 30% of an ATM they need for the suit.

   Bob Clark

Are these the mountains Curiosity is headed to? I would like to see some measurements made when Curiosity is in the midst of this fog or haze.

  Bob Clark

GW, the ceramic aerogel tiles on the shuttle have a specific gravity of  .144. Are you sure of that .03 number for your tiles, equivalent to a density of only 30 kg/m^3?

  Bob Clark

GW, I agree with you multiple robotic ISRU missions need to be sent to Mars first before we do a manned mission using ISRU. But you don't seem too optimistic about either surface or atmospheric ISRU being doable in the near term. Do you think a mission that does not use ISRU will be doable?

  Bob Clark

Lunar ISRU is not a prerequisite for Martian ISRU if you use atmospheric ISRU on Mars for propellant production. But when you consider the recent evidence of large amounts of near surface ice even at mid-latitudes on Mars, the same type of ISRU you would use on the Moon also becomes possible on Mars.
Doing the ISRU to turn ice into hydrolox is fairly easy. It's a debatable point which of the surface or atmospheric ISRU methods would be easier.

Here's an article by return-to-the-Moon propellant Dr. Paul Spudis that argues testing ISRU on the Moon should be done as a precursor to a Mars flight:

The Road to Mars Is Paved in Lunar Rock (Op-Ed).
By Paul D. Spudis   |   June 25, 2013 02:39pm ET

http://www.space.com/21713-mining-moon-resources.html

  Bob Clark

Apparently doing artificial gravity is not as trivial a technical problem as portrayed, at least NASA doesn't think so. I looked at several of the NASA Mars Design Reference Missions and none of them contain artificial gravity despite the fact NASA has known about the problem of long zero-g exposure for decades:

Human Exploration of Mars: The Reference Mission of the NASA Mars Exploration Study Team.(NASA Mars DRM 3.0)
July, 1997
Shorter transit times reduce the time spent by
the crew in zero g to the length of typical
tours of duty for the International Space
Station. (Thus, the Mars Study Team chose
not to use artificial gravity spacecraft designs
for the Reference Mission.)
http://www.nss.org/settlement/mars/1997 … ission.pdf

Human Exploration of Mars Design Reference Architecture 5.0.
July, 2009
The current Mars DRA 5.0 study efforts considered “thrust-only” NTR engines, zero-gravity
crewed MTV designs, and photovoltaic arrays (PVAs) to supply spacecraft electrical power.
http://www.nasa.gov/pdf/373665main_NASA-SP-2009-566.pdf

It is notable these both use nuclear propulsion and the transit time is still several months. Also the effects of long stays at zero-g at the ISS actually shows some of the astronauts will likely be incapacitated for days to weeks on arrival.

A discussion on this other forum showed for departing from HEO, or from the Moon or L2, a delta-V in the range of 10 to 11 km/s would allow a travel time of about 35 days:

Math needed for 5-week flight from Earth to Mars.
http://orbiter-forum.com/showthread.php … stcount=17

This would result in a high arrival speed at Mars and it also assumes aerobraking/aerocapture is used so no or minimal propellant is required to slow down on arrival.

But 11 km/s is about the delta-v the Saturn V launcher needed to send 45 metric tons (mT) to translunar injection. Then if we had a Saturn V size rocket departing from the Moon or L2 we could send about 45 mT to Mars for a one-way trip time of about 35 days.
But remember almost all the mass of the rocket is just propellant, which we can get from the Moon. You would not need to send the entire 3,000 mT mass of a Saturn V size vehicle to the Moon or L2, only the dry mass components. And probably with 3d-printing even the dry mass components that needed to be sent from Earth could also be reduced.

This is for a one-way flight. For the return flight, you would have the dry mass components for the return vehicle already sent to Mars beforehand on a slow flight so not needing as large a departure rocket. The propellant for the return flight would be obtained at Mars by ISRU.

  Bob Clark

In addition to the radiation dangers, longer stays in space are now known to damage eyesight:

Does space travel damage eyesight?
An increasing number of astronauts who've spent a month or more aboard the International Space Station are visiting the optometrist.
By The Week Staff  | March 14, 2012.
http://theweek.com/article/index/225533 … e-eyesight

Astronauts And Mice Return From Space With Altered Eyes.
By Francie Diep Posted 10.25.2013 at 4:00 pm

The debilitating effects of zero-g for bone and muscle loss are also well known now. The bone loss in zero-g proceeds at a rate 10 times that of rate of the elderly suffering from osteoporosis.

Expedition 37 returned to Earth from the ISS Monday evening:

A Warm Welcome for the Crew - YouTube

Karen Nyberg looked pretty wiped out after the landing. Luca Parmitano looked pretty energetic. Fyodor Yurchikhin was somewhere in between.
Karen also didn't appear at the news conference with the other two astronauts, on doctors orders:

Expedition 37 Discusses Mission - YouTube

I'm not making a comment about the effects of long space exposure on women,  by the way. Sunita Williams seemed pretty energetic on her return from the ISS, while Chris Hadfield looked wiped out after his.
What I am arguing is that NASA should be focusing on short travel times for Mars missions. You can't afford to have 1/3rd of the crew members incapacitated for days or even weeks when the crew lands. Not even a 6 month travel time using nuclear propulsion that NASA scientists have proposed would be sufficient.
However, by first setting up propellant stations on the Moon, the travel time could be cut to weeks instead of months.

   Bob Clark