New Mars Forums

Thats a good one.  My only concern is keeping the more complex surface from the accumulation of dust.

To protect from dust, I suggest a greenhouse at near ambient pressures to encase the solar panels.  While I am aware that that would deminish the output from the cells, I will suggest a side process that might justify this loss, and turn it into a gain.

In the bottom of the greenhouse a tray which can contain a weak alcohol solution to be evaporated by the collected waste heat.

An electric pump would collect the concentrated alcohol vapors, and force a condensation into metal tubes immersed in water tanks.  The water tanks would be used to supply heat for living confort, particularly at night, and perhaps bathing water, or alternately aquariums to grow organisms.

I am going to post an article which suggests where this alcohol might come from.

There's a bunch of things that I'm intrigued about regarding Mars missions but this is the bit related to landings.

Let's suppose the following two scenarios are viable.

A: This is the "conventional" scenario. Some of your hardware is already in place on the surface of Mars, but when you land, you land seated inside some larger structure which also happens to be all or a large part of your habitat. The conventional wisdom here is some kind of biconic heat shield or perhaps a ballute or some form of large (earth orbit assembled) structure which also serves as a very large heat shield. Or some combination of the above.

B: In this scenario you land everything on Mars first except for the humans. The humans arrive in one or two dragon style capsules. You have the capability of precision landing, but just to be sure you also carry some form of lightweight transport.

To my mind, trying to land humans along with something that weighs upwards of 60 tonnes, along with all the EDL issues that comes with that is taking more risk with the crew than needed.

If you decouple the crew and the habitat then you end up with scenario B. Of course this has its own risks and complexities.

Just briefly, if you were flying to Mars, what would you bet your life on?

The reason I asked the questions I did is the history of government behavior re: space since the space race ended with Apollo 11.  You don't get to do what's smart because no one wants to spend the money.  You actually get to do very little in the way of missions. 

Private corporations are largely even worse:  they invest in nothing that's not near-term profitable.  Musk's Spacex launcher business is exactly that.  His Mars dreams are the exception to the rule.  I cannot name one other.

I rather suspect the US government (probably partnered with the others) will support 1,  or maybe 2,  trips to Mars with men,  and that will be it.  No more.  Period.  All else is fantasy. 

The prospecting and resource development you spoke of,  and the real exploration that makes it possible (that I keep yammering about),  will have to get done in those 2 missions,  or else no one will ever have the necessary info to successfully locate a  survivable settlement!  You can't turn over rocks peering down from an orbiting robot,  that's just not good enough. 

We do not have the resources or the opportunities to go there and do these things in too-small a way on each mission,  because there won't be enough missions to get it all done that way.  It's going to have to be just about all-or-nothing,  on each mission. 

A smart plan responding to a financial squeeze like that would be a multi-landing exploration on the first mission,  based from orbit.  The more sites (identified from all these probes) the better,  and concept prototypes for ISRU also get tried out as experiments.  That was the gist of my paper at the Mars Society convention in Dallas last August. 

The second mission visits the best one (or at most 2) sites,  as verified from the first mission,  but is based on the surface,  located at that one site or two.  That mission does the heavy-duty prospecting and tries out engineering-prototype ISRU equipment identified as promising from the first mission. 

Then,  later,  if "somebody" decides to fund a permanent base or settlement of some sort,  it'll be the best one of those sites verified by the second mission.  That's about where Musk might jump in,  in the lead role.  And if he is successful,  others might follow.  But the governments will not.  They never have.  Never will. 

"Cassandra has spoken" (and her news is never good)

GW

Since these pieces must be broken down to allow for the connection from one to the next then there will be another increase in each sections mass and while they may not push it to beyond one more that will make it a 4 unit heavy for a lunar mission.

Actually, Louis, I've been thinking about your question about small payloads, and maybe I have misunderstood you. What do you mean by "small"? And when do you favor small payloads?

For the first mission or two, I wouldn't favor dividing the mission into a bunch of small pieces, because the landing technology won't have been perfected yet and because you need to maximize your chance of success; otherwise, you could lose public opinion and the funding for future missions. You need to get the crew and the essentials of their mission to the surface in the fewest landings possible, so as to avoid the possible problem of losing essentials. Zubrin's Mars Direct does that pretty elegantly: three vehicles, two being identical Earth Return Vehicles to guarantee the crew can get home. If you lose one of the two ERVs, you still have the other. If you lose the hab, you lose the crew. If we can reduce that even further, to two ERVs (one with the arriving crew) maybe that's better. Or maybe not.

But if you plan to expand beyond arrival of 3 or 4 astronauts every 26 months (and leaving before the next crew arrives) then yes, cargo landers are essential. The first two or three manned vehicles won't be bringing a body imager and there's a good chance no one will get sick enough to need one, but eventually 10 tonnes of medical equipment, then 20, then 30 tonnes of medical equipment will be needed on Mars. Those don't need to come with a crew; better that they come slowly on a Hohmann trajectory. And if they are lost, they can be sent out again 26 months later.

The size of the cargo lander will have a lot to do with the size of the terrestrial boosters. The Falcon heavy, which can launch 53 tonnes to low Earth orbit, can land 11 tonnes on the Martian surface, according to Zubrin. That's possible if the 53 tonnes includes a properly sized LOX/liquid hydrogen TMI stage. Of the 11 tonnes, probably 1 tonne will have to be the fuel tanks for the landing fuel, a cargo platform, and landing legs. So a Falcon Heavy could land 10 tonnes of useful cargo on Mars. I could see Elon Musk adding TMI stages and landers to his rocket factory in southern California and mass producing them. If he can put 53 tonnes into low Earth orbit for $100 million, he can probably get 10 tonnes of medical equipment to Mars for $200 million, or $20,000 per kilogram (about the cost of the space shuttle to get cargo to the International Space Station!). Once that's done a dozen times, the technology will become more reliable and costs will go down further.

The next stage beyond that may be a reusable Mars shuttle. Cargo would be aerobraked into Martian orbit; the Falcon Heavy can put 14 tonnes into Martian orbit. I suspect a fairly small unmanned vehicle (total mass, 30 tonnes or so, fully fueled, if my fast back of the envelope calculation is right) would be able to take off from the Martian surface, go into orbit, rendezvous with the cargo pallet, and deorbit it. Such a vehicle could also launch Martian products into Martian orbit or boost them to trans-Earth injection (eventually colonies will have exports, after all; gold, rare metals like platinum, and heavy water are all possibilities).

Before the list of design comes the research phase to know what we question currently about mans ability to survive. A small peice of the radiation question may be in some of the collected data from the MSL as it travels.

http://www.jpl.nasa.gov/news/news.cfm?release=2012-088

One of Curiosity's 10 science instruments, the Radiation Assessment Detector (RAD) has been collecting data for three months, monitoring the natural radiation environment in interplanetary space. This information, particularly effects RAD has measured from recent solar flares, is crucial for design of human missions to Mars.

Then again the untried Sky hook will also lead to a future or.....lets hope for a positive to happen.

Actually, I wonder whether slowling down in orbit really helps that much. Let's say you are in a circular low Mars orbit at the altitude of 100 miles (160 km, 160,000 meters). You fire your engines and stop dead in space.

Now you fall like a rock towards Mars, gaining 3.8 meters per second per second.

s = 1/2a t2 (s = distance traveled, a = acceleration from Martian gravity, t2 = time squared) where 1/2a is 1.9 meters per second per second and s = 160,000 meters. So t-squared is 160,000/1.9 = 84,210; square root and you get a t (time) of 290 seconds. 290 x 3.8 = 1,102 meters per second = 3,967 kilometers per hour = 2,459 mph.

So you'd still approach the surface at almost mach 4; too fast to deploy a parachute, and you would gain almost all that speed before the atmosphere was thick enough for a parachute to be useful, anyway. Basically, it does no good to fire an engine in orbit and slow yourself down up there.

But I think canted thrusters make sense and most likely solve the problem. Of course, at a 45 degree angle, a delta-v of 1000 meters per second will only produce a vertical delta-v of 707 meters per second because it also produces a horizontal delta-v of 707 meters per second, if I recall my trigonometry right.

Oh, regarding Louis's point that a small lander might solve the problem: the article I provided the link for was an interview with the guy who designed the descent systems for Spirit, Opportunity, and the Mars Science Lab. He said the parachute/thruster combination couldn't even be scaled up for Mars Science Lab. Basically, the parachute/thruster combo doesn't work when the payload exceeds about a tonne.

GW Johnson, I wasn't asking whether canted thrusters would work. That's a simple matter of physics. I was wondering whether we are sure it would solve the problem that is caused when one fires engines into a hypersonic air stream. If you fire your engines straight in the direction of movement, the hypersonic airstream and exhaust gasses build up in front of the vehicle and buffet it violently; so I gather from the article listed above. Here's the exact quotation:

But using current thruster technology in Mars’ real, existing atmosphere poses aerodynamic problems. “Rocket plumes are notoriously unstable, dynamic, chaotic systems,” said Manning. “Basically flying into the plume at supersonics speeds, the rocket plume is acting like a nose cone; a nose cone that’s moving around in front of you against very high dynamic pressure. Even though the atmospheric density is very low, because the velocity is so high, the forces are really huge.”

Manning likened theses forces to a Category Five hurricane. This would cause extreme stress, with shaking and twisting that would likely destroy the vehicle. Therefore using propulsive technology alone is not an option.

End of quote.

Canted thrusters at least get the rocket plume mostly out of the way, but will that be enough? No one has tested such a system, though I suppose an expert would be able to make some calculations, and eventually someone will perform a wind tunnel test. A test could also be performed high in the earth's atmosphere.

Have you all seen this?

http://www.universetoday.com/7024/the-m … ed-planet/

It basically says that you can't land a large manned vehicle on Mars with the standard heat shield-parachute-thruster combination because the heat shield can't be large enough to slow the vehicle down to Mach 2 (when you can deploy parachutes) before you hit the ground. The atmosphere is too thin. But it's too thick to fire thrusters straight ahead of you at Mach 2+ because the exhaust plume is too dynamic and the resulting shaking could shake your vehicle apart. It advocates a "hypercone," a big inflatable structure, at Mach 5, to slow down the ship. I suppose a super-large heat shield, assembled in Earth orbit, would do it as well; that possibility is hinted at.

I think you have to consider what you can actually accomplish with 1-3 astronauts landed (hopefully not a one-way suicide mission) at one single site on Mars,  and maybe just barely enough gear to go home.  This matters little whether the return gear is prepositioned,  locally produced, or carried with them.

Your not going to accomplish very much beyond flag-and-footprints and a couple of tow sacks of surface rocks.  Even if you have a rover,  the surface sampling will only be a few dozens of km apart.  That's basically the same model as we used with Apollo going to the moon,  and,  in hindsight,  that never really "explored" the moon. 

It's been the probes since Apollo that did what "real exploration" we actually have accomplished (on the moon and on Mars).  Exploration fundamentally answers two deceptively-simple but difficult questions:  "what all is there?" and "where exactly is it?".  A lot of the stuff we'd like to find is buried deep,  sometimes very deep.  And it is never,  ever uniformly distributed. 

I haven't seen in any of the Mars mission proposals,  even Zubrin's,  anything that addresses doing real exploration.  Not in all these years since the "battlestar galactica" concepts first dreamed up in the 1950's. 

But "real exploration" is exactly the prerequisite for siting bases,  prospecting,  and eventually establishing permanent settlements.  You cannot utilize local resources effectively until you answer those two questions.  And it is not easy to answer them.  Some can be done by robots,  some of it must be done with men.  That's just life. 

Mars is a lot farther away than the moon.  For a robot,  that's no problem,  for humans it is.  I have not seen since Skylab in the 70's a habitat spacious enough to support a mentally-healthy crew for the 2+ year round trip to Mars,  with the kind of rockets we have. 

And nobody seems to want to face up to the need for artificial gravity,  either.  The only spinning designs have been "battelstar galactica" concepts from NASA mostly,  or else complicated nonrigid cable things that cannot be course corrected without disassembling everything. 

It doesn't need to be that way.  But,  you have to give up the Apollo flag-and-footprints model,  and you have to face up to the question of safely sending healthy people all that way,  and getting them back alive.  That is not done with a minimalist approach.  It is constraint driven. 

Those constraints are a time limit of 1 year to endure zero gee,  cosmic radiation near the tolerable limit but that we can't shield and that will be a career limit in one round trip,  solar flare dangers than can be shielded,  and the need for a Skylab volume for 3 (to no more than 6) men that is not jammed full of stuff either. 

Back to "real exploration":  it's a very long trip to Mars.  If we're going to all the trouble of sending men there,  then why not plan on more than one landing?  Really do a proper sampling all around the planet.  That's not a minimalist design,  but it need not be "battlestar galactica" either. 

And once you're past the 25 ton shuttle payload,  anything you send can be assembled in LEO from docked payloads.  It's the lowest cost per payload mass that counts.  Falcon heavy is 53 tons at $800-1000 per pound.  So who needs a gigantic launch rocket?

Just some things to think about. 

GW