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Dr. Robert Zubrin Further Clarifies His Concept For A Two-Person Mars Mission
Robert Zubrin's ultralight Mars Mission proposal has generated some controversy. Over atNASASpacefight website people have beendissecting the proposal. The main problems have to do with the Dragon's modest volume and issues regarding microgravity and radiation. Dr Zubrin has posted his answers to these concern. I'm pleased to see that he agrees with me that the Dragons trunk area can take a pressurised module that would alivate the living space issue. . Below Zubrin answers is critics.:
Friends;
I apologize for not being able to include all the details of the proposed mission plan in my WSJ op ed, which had a 1000 word limit.
In answer to some of the objections raised in this forum, you may note the following:
1. There is no need for zero gravity exposure. Artificial gravity can be provided to the crew by tethering the Dragon off the TMI stage, in the same way as is recommended in the baseline Mars Direct plan.
2. Cosmic ray radiation exposure for the crew is precisely THE SAME as that which would be received by those on any other credible Mars mission, all of which would use the 6 month Conjunction class trajectory to Mars, both because that is the point of diminishing returns (the "knee of the curve") where delta-V trades off against trip time, and because it is uniquely the trajectory that provides a 2-year free return orbit after launch from Earth. Assuming the baseline mission, the total cosmic ray dose would be no greater than that already received by a half dozen cosmonauts and astronauts who participated in long duration missions on Mir or ISS, with no radiation induced health effects having been reported. (Cosmic ray dose rates on ISS are 50% those of interplanetary space. The Earth's magnetic field does not shield effectively against cosmic rays. In fact, with a crew of 6, the current planned ISS program will inflict the equivalent of 30 man-years of interplanetary travel GCR doses on its crews over the next decade. This is an order of magnitude more than that which will be received by the crew of the mission proposed here. ) There are enough consumables on board to provide shielding against solar flares.
3. The preferred method of Mars capture is aerocapture, rather than direct entry. This means that the Dragon aeroshield, which has some lifting capability, may well be adequate. To see this with a back of the envelope calculation, consider a loaded Dragon system with an entry mass of 17000 kg, an effective shield diameter of 4 meters, a drag coeffecient of 1, coming in with an entry velocity of 6 km/s at an altitude of 33 km, where the Mars atmospheric density is 0.8 gm/m3. Setting drag equal to mass times deceleration, you can see that the system would decelerate at a speed of 42 m/s2, or a little over 4 gs. It could thus perform a 1 km/s deceleration in about 25 seconds, during which time it would travel about 140 km. This deceleration is sufficient to capture the spacecraft from an interplanetary trajectory into a loosely bound highly elliptical orbit around Mars. If the perigee is not raised, the craft will reenter again, and again, progressively lowering the apogee of its orbit, until either a desired apogee for orbital operations is achieved or the craft is committed to entry for purposes of landing. That said, if a larger aerobrake were desired, this could be created by adding either a flex-fabric or inflatable skirt to the Dragon core shield.
4. The habitable volume is admittedly lower than optimal. However it should be noted that with 5 cubic meters per crew member, it is 2.5 times higher than the 2 cubic meters per crew member possessed by Apollo crews. It could be expanded in space by the use of inflatable add-on modules. Extra space could be provided on the ground by using a 4th launch to preland another Dragon loaded with supplies, including one or more inflatable modules which could be set up by the crew after they land.
5. The mission architecture is much safer than any based on complex mega systems requiring orbital assembly, since the quality control of orbital assembly does not compare with that which can be accomplished on the ground. It would be better to have a crew of 4, but if we are to do it with Falcon 9 heavy's, a crew of 2 is all we can do, and while it lacks a degree of redundancy otherwise desirable, it offers the counter benefit of putting the fewest number of people at risk on the first mission. It's quite true that not flying anywhere at all would be safer, but if you want to get to Mars, you have to go to Mars.
Re: Zubrin's Falcon Heavy Mars Mission
« Reply #79 on: 05/15/2011 11:55 PM » Reply with quote
Friends;
Here are further answers relating to concerns that have been advanced.
1. Habitable volume.
As noted, if the Dragon capsule alone is used, this provides 5 m3 living volume per crew member, which compares to 2 m3 per crew on an Apollo capsule, 9 m3 per crew member on the Space Shuttle, or 8 m3 per crew member on a German U-Boat (Type VII, the fleet workhorse) during WWII. This would be uncomfortable, but ultimately, workable by a truly dedicated crew. However these limits can be transcended. The Dragon has a 14m3 cargo area hold below the aeroshield. Into this we could pack an inflatable hab module, in deflated form, but which if inflated, could be as much as 8 m in diameter and perhaps 10 m long, thereby providing 3 decks, with added volume of 502 m3 and a total floor space equal to 1.5 times as much as that in the Mars Society's MDRS or FMARS stations, which have proved adequate in size for crews of 6. After Trans Mars injection, the Dragon would pull away from the cargo section and turn around, then return to mate its docking hatch with one in the inflatable. It would then pull the inflatable out of the cargo hold, much as the Apollo command module pulled out the LEM. The inflatable could then be inflated. The other end of the inflatable would be attached to the tether, which is connected to the TMI stage, for use in creating artificial gravity.
Upon reaching Mars the inflatable could either be expended, along with the tether system and TMI stage, prior to aerocapture. Alternatively, and optimally, the tether and TMI stage alone would be expended, but the inflatable deflated and retained for redeployment as a ground hab after landing.
2. EDL
Using just its aeroshield for deceleration, the Dragon would have a terminal velocity of around 340 m/s on Mars at low altitude (air density 16 gm/m3). So we could either give it a rocket delta-V capability of 600 m/s (a 20% mass hit assuming storable or RP/O2 propulsion, Isp~330 s) to land all propulsive, or we could use a drogue to slow it down (a 20 m diameter chute would slow it to ~70 m/s) and then employ a much smaller rocket delta-V for landing.
Heres the original article as published in the WSJ
By Robert Zubrin, Wall Street Journal, 05.14.11
SpaceX, a private firm that develops rockets and spacecraft, recently announced it will field a heavy lift rocket within two years that can deliver more than twice the payload of any booster now flying. This poses a thrilling question: Can we reach Mars in this decade?
It may seem incredible—since conventional presentations of human Mars exploration missions are filled with depictions of gigantic, futuristic, nuclear-powered interplanetary spaceships whose operations are supported by a virtual parallel universe of orbital infrastructure. There’s nothing like that on the horizon. But I believe we could reach Mars with the tools we have today, or will have in short order. Here's how it could be done:
The SpaceX’s Falcon-9 Heavy rocket will have a launch capacity of 53 metric tons to low Earth orbit. This means that if a conventional hydrogen-oxygen chemical rocket upper stage were added, it would have the capability of sending 17.5 tons on a trajectory to Mars, placing 14 tons in Mars orbit, or landing 11 tons on the Martian surface.
The company has also developed and is in the process of demonstrating a crew capsule, known as the Dragon, which has a mass of about eight tons. While its current intended mission is to ferry up to seven astronauts to the International Space Station, the Dragon’s heat shield system is capable of withstanding re-entry from interplanetary trajectories, not just from Earth orbit. It’s rather small for an interplanetary spaceship, but it is designed for multiyear life, and it should be spacious enough for a crew of two astronauts who have the right stuff.
Thus a Mars mission could be accomplished utilizing three Falcon-9 Heavy launches. One would deliver to Mars orbit an unmanned Dragon capsule with a kerosene/oxygen chemical rocket stage of sufficient power to drive it back to Earth. This is the Earth Return Vehicle.
A second launch will deliver to the Martian surface an 11-ton payload consisting of a two-ton Mars Ascent Vehicle employing a single methane/oxygen rocket propulsion stage, a small automated chemical reactor system, three tons of surface exploration gear, and a 10-kilowatt power supply, which could be either nuclear or solar.
The Mars Ascent Vehicle would carry 2.6 tons of methane in its propellant tanks, but not the nine tons of liquid oxygen required to burn it. Instead, the oxygen could be made over a 500-day period by using the chemical reactor to break down the carbon dioxide that composes 95% of the Martian atmosphere.
Using technology to generate oxygen rather than transporting it saves a great deal of mass. It also provides copious power and unlimited oxygen to the crew once they arrive.
Once these elements are in place, the third launch would occur, which would send a Dragon capsule with a crew of two astronauts on a direct trajectory to Mars. The capsule would carry 2500 kilograms of consumables—sufficient, if water and oxygen recycling systems are employed, to support the two-person crew for up to three years. Given the available payload capacity, a light ground vehicle and several hundred kilograms of science instruments could be taken along as well.
The crew would reach Mars in six months and land their Dragon capsule near the Mars Ascent Vehicle. They would spend the next year and a half exploring.
Using their ground vehicle for mobility and the Dragon as their home and laboratory, they could search the Martian surface for fossil evidence of past life that may have existed in the past when the Red Planet featured standing bodies of liquid water. They also could set up drilling rigs to bring up samples of subsurface water, within which native microbial life may yet persist to this day. If they find either, it will prove that life is not unique to the Earth, answering a question that thinking men and women have wondered upon for millennia.
At the end of their 18-month surface stay, the crew would transfer to the Mars Ascent Vehicle, take off, and rendezvous with the Earth Return Vehicle in orbit. This craft would then take them on a six-month flight back to Earth, whereupon it would enter the atmosphere and splash down to an ocean landing.
There is nothing in this plan that is beyond our current level of technology. Nor would the costs be excessive. Falcon-9 Heavy launches are priced at about $100 million each, and Dragons are even cheaper. Adopting such an approach, we could send expeditions to Mars at half the mission cost currently required to launch a Space Shuttle flight.
What is required, however, is a different attitude towards risk than currently pervades the space policy bureaucracy. There is no question that the plan proposed here involves considerable risk. So does any plan that actually involves sending humans to Mars, rather than talking about it indefinitely. True, there are a variety of precursor missions, technology developments, and testing programs that might be recommended as ways of reducing risk. There are an infinite number of such potential missions and programs. If we try to do even a significant fraction of them before committing to the mission we will never get to Mars.
But is it responsible to forgo any expenditure that might reduce somewhat the risk to the crew? I believe so. The purpose of the space program is to explore space, and its expenditures come at the cost of other national priorities. If we want to reduce risk to human life, there are vastly more effective ways of doing so than by spending $10 billion per year for the next two or three decades on a human spaceflight program mired for study purposes in low Earth orbit. We could spend the money on childhood vaccinations, fire escape inspections, highway repairs, better body armor for the troops—take your pick. For NASA managers to demand that the mission be delayed for decades while several hundred billion dollars is spent to marginally reduce the risk to a handful of volunteers, when the same funds spent elsewhere could save the lives of tens of thousands, is narcissistic in the extreme.
The Falcon 9 Heavy is scheduled for its first flight in 2013. All of the other hardware elements described in this plan could be made ready for flight within the next few years as well. NASA’s astronauts have gone nowhere new since 1972, but these four decades of wasteful stagnation need not continue endlessly. If President Obama were to act decisively, and bravely embrace this plan, we could have our first team of human explorers on the Red Planet by 2016.
The American people want and deserve a space program that is really going somewhere. It’s time they got one. Fortune Favors the Bold. Mr. President, seize the day.
Dr. Zubrin is president of Pioneer Astronautics and of the Mars Society (www.marssociety.org). An updated edition of his book, “The Case for Mars: The Plan to Settle the Red Planet and Why We Must,” will be published by The Free Press this June.
>
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Tuesday, May 17, 2011
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Dr. Robert Zubrin's Brilliant Plan TO Put Two Humans On Mars In Ten Years
How We Can Fly to Mars in This Decade – And on the Cheap
The technology now exists and at half the cost of a Space Shuttle flight. All that is lacking is the political will to take more risks.
By Robert Zubrin, Wall Street Journal, May 14, 2011
SpaceX, a private firm that develops rockets and spacecraft, recently announced it will field a heavy lift rocket within two years that can deliver more than twice the payload of any booster now flying. This poses a thrilling question: Can we reach Mars in this decade?
It may seem incredible—since conventional presentations of human Mars exploration missions are filled with depictions of gigantic, futuristic, nuclear-powered interplanetary spaceships whose operations are supported by a virtual parallel universe of orbital infrastructure. There’s nothing like that on the horizon. But I believe we could reach Mars with the tools we have today, or will have in short order. Here’s how it could be done:
The SpaceX’s Falcon-9 Heavy rocket will have a launch capacity of 53 metric tons to low Earth orbit. This means that if a conventional hydrogen-oxygen chemical rocket upper stage were added, it would have the capability of sending 17.5 tons on a trajectory to Mars, placing 14 tons in Mars orbit, or landing 11 tons on the Martian surface.
The company has also developed and is in the process of demonstrating a crew capsule, known as the Dragon, which has a mass of about eight tons. While its current intended mission is to ferry up to seven astronauts to the International Space Station, the Dragon’s heat shield system is capable of withstanding re-entry from interplanetary trajectories, not just from Earth orbit. It’s rather small for an interplanetary spaceship, but it is designed for multiyear life, and it should be spacious enough for a crew of two astronauts who have the right stuff.
Thus a Mars mission could be accomplished utilizing three Falcon-9 Heavy launches. One would deliver to Mars orbit an unmanned Dragon capsule with a kerosene/oxygen chemical rocket stage of sufficient power to drive it back to Earth. This is the Earth Return Vehicle.
A second launch will deliver to the Martian surface an 11-ton payload consisting of a two-ton Mars Ascent Vehicle employing a single methane/oxygen rocket propulsion stage, a small automated chemical reactor system, three tons of surface exploration gear, and a 10-kilowatt power supply, which could be either nuclear or solar.
The Mars Ascent Vehicle would carry 2.6 tons of methane in its propellant tanks, but not the nine tons of liquid oxygen required to burn it. Instead, the oxygen could be made over a 500-day period by using the chemical reactor to break down the carbon dioxide that composes 95% of the Martian atmosphere.
Using technology to generate oxygen rather than transporting it saves a great deal of mass. It also provides copious power and unlimited oxygen to the crew once they arrive.
Once these elements are in place, the third launch would occur, which would send a Dragon capsule with a crew of two astronauts on a direct trajectory to Mars. The capsule would carry 2500 kilograms of consumables—sufficient, if water and oxygen recycling systems are employed, to support the two-person crew for up to three years. Given the available payload capacity, a light ground vehicle and several hundred kilograms of science instruments could be taken along as well.
The crew would reach Mars in six months and land their Dragon capsule near the Mars Ascent Vehicle. They would spend the next year and a half exploring.
Using their ground vehicle for mobility and the Dragon as their home and laboratory, they could search the Martian surface for fossil evidence of past life that may have existed in the past when the Red Planet featured standing bodies of liquid water. They also could set up drilling rigs to bring up samples of subsurface water, within which native microbial life may yet persist to this day. If they find either, it will prove that life is not unique to the Earth, answering a question that thinking men and women have wondered upon for millennia.
At the end of their 18-month surface stay, the crew would transfer to the Mars Ascent Vehicle, take off, and rendezvous with the Earth Return Vehicle in orbit. This craft would then take them on a six-month flight back to Earth, whereupon it would enter the atmosphere and splash down to an ocean landing.
There is nothing in this plan that is beyond our current level of technology. Nor would the costs be excessive. Falcon-9 Heavy launches are priced at about $100 million each, and Dragons are even cheaper. Adopting such an approach, we could send expeditions to Mars at half the mission cost currently required to launch a Space Shuttle flight.
What is required, however, is a different attitude towards risk than currently pervades the space policy bureaucracy. There is no question that the plan proposed here involves considerable risk. So does any plan that actually involves sending humans to Mars, rather than talking about it indefinitely. True, there are a variety of precursor missions, technology developments, and testing programs that might be recommended as ways of reducing risk. There are an infinite number of such potential missions and programs. If we try to do even a significant fraction of them before committing to the mission we will never get to Mars.
But is it responsible to forgo any expenditure that might reduce somewhat the risk to the crew? I believe so. The purpose of the space program is to explore space, and its expenditures come at the cost of other national priorities. If we want to reduce risk to human life, there are vastly more effective ways of doing so than by spending $10 billion per year for the next two or three decades on a human spaceflight program mired for study purposes in low Earth orbit. We could spend the money on childhood vaccinations, fire escape inspections, highway repairs, better body armor for the troops—take your pick. For NASA managers to demand that the mission be delayed for decades while several hundred billion dollars is spent to marginally reduce the risk to a handful of volunteers, when the same funds spent elsewhere could save the lives of tens of thousands, is narcissistic in the extreme.
The Falcon 9 Heavy is scheduled for its first flight in 2013. All of the other hardware elements described in this plan could be made ready for flight within the next few years as well. NASA’s astronauts have gone nowhere new since 1972, but these four decades of wasteful stagnation need not continue endlessly. If President Obama were to act decisively, and bravely embrace this plan, we could have our first team of human explorers on the Red Planet by 2016.
The American people want and deserve a space program that is really going somewhere. It’s time they got one. Fortune Favors the Bold. Mr. President, seize the day.
Dr. Zubrin is president of Pioneer Astronautics and of the Mars Society (www.marssociety.org). An updated edition of his book, “The Case for Mars: The Plan to Settle the Red Planet and Why We Must,” will be published by The Free Press this June.
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Tuesday, May 10, 2011
Mary Roach Talks About Her Book Packing For Mars
We simply weren't made to live without gravity. That fact has always been the biggest challenge about space travel. Think rocket science is hard? Try building a toilet that works in zero gravity.
In "Packing for Mars," Mary Roach explores all the crazy, gross, odd and fascinating physiological challenges that have confronted space engineers and scientists for the past 50 years of human space flight, and which make a trip to Mars a seeming impossibility. Roach — whose previous books include "Stiff," about cadavers, and "Bonk," about the science of sex — carefully researches the awkward details of life in space then describes what's she found with enthusiasm and great humor.
I interviewed Roach while she was in Austin late last month to promote the paperback release of "Packing for Mars." Here's an edited transcript:
American-Statesman: You were a kid in the 1960s, during NASA's heyday. Have you always been interested in space travel?
Mary Roach: No, surprisingly enough. I was born in 1959, so I was pretty young then, but I don't remember the moon landing. I was not at all a space-obsessed child. I'm a late bloomer to space flight.
What got you interested in the subject?
Years ago I had an assignment from Discover magazine about the neutral buoyancy tank, which is that huge tank where NASA trains astronauts for spacewalking. I got to the Johnson Space Center, and it was just like the magical kingdom. There was just so much bizarre, amazing, interesting stuff going on. The day I was there they were rehearsing what would be a six-hour spacewalk. The rehearsals were amounting to 250 hours of time in the tank. I had no idea the amount of training and work that goes into living in space.
One question you always hear astronauts asked is, how do you use the bathroom in space? That question ties in with your fascination with the human body in all its messy glory.
Well, yeah. I have a chapter in the book about going to the bathroom in space — it's only one chapter, but it picks up a disproportionate amount of the coverage of the book, which reflects, I think, a universal fascination. To me it was fascinating not just because of the tee-hee value but because it's a wonderful example of the unbelievable challenges of life without gravity. The things we take for granted — you don't really think of the toilet as something that requires gravity, but in zero gravity, the "material," to use a NASA euphemism, doesn't fall into the toilet. So you've got to completely rethink the toilet. That's a fascinating thing.
The book underscores two things: You really aren't aware how much you need gravity until you try to live without it. And so much for the glamorous life of an astronaut.
I know. It isn't glamorous, but I think most astronauts happily accept the inconveniences — the smells, the awkwardness, the lack of creature comforts — for the ability to be where they are, in this place with this amazing view that so few people have ever had. It's like backpacking times a hundred. You know, backpacking is difficult. It's a pain to sleep on the ground, you eat bad food, but it enables you to get to these amazing places that you don't ordinarily get to.
Do you use humor in your writing to make your subject more accessible? Or does your humor come from a natural, absurdist point of view?
The latter, I would say, more than the former. It's not a conscious tool that I use to draw the reader in. I'm not really using it in that much of an intentional way; it's how I enjoy writing and I guess it's how I see the world. It doesn't work everywhere, but I think it's more fun for the reader and it's certainly more fun for me as the writer.
You and I are roughly the same age. When we were kids, we were promised a future with jet backs, moon colonies and trips to Mars. But, really, there was no giant leap for mankind after Apollo 11. Our future was a fantasy, wasn't it?
It does seem to be dragging its feet. I remember "The Jetsons," "Lost in Space," "2001" a little bit later — yeah, "2001." Not quite! I do feel a little ripped off that I don't have a jet pack.
You know, Apollo happened so quickly. Obviously there were political pressures to get the moon landing done, make it happen and get there first. You look at some of the conferences that went down in the '60s, and everybody was saying, "OK, next up, Mars!" It did seem back then that that's where we were going to go. Then everything kind of slowed down.
As NASA grew, it became this sort of lumbering, decision-by-consensus bureaucracy. It's also the case that getting to Mars is just not as easy as people thought. And we don't have the pressure of, problems be damned, we are getting there first.
Do you think there's value in at least trying for Mars?
I do. You're thinking so far out of the box when you're dealing with zero gravity — everything has to be rethought and miniaturized and automated. There's just tremendous creativity that goes into it and I think that would be beneficial. Also, inspiring kids to go into engineering and science — you look at the number of kids doing math and science today and how far the U.S. is falling behind, I don't think that's insignificant.
And if you have a global mission with a lot of countries contributing money and expertise, it doesn't have to sap the budget the way it might if it were a one-nation effort.
I understand the other side of the argument: We have a lot of problems on Earth. But it's not like if you take money away from the space program it will automatically be applied to education or health care. It never works that way.
jseaborn@statesman.com; 445-1702
Packing for Mars
The Curious Science of Life in the Void
Mary Roach
Norton; $15.95 (paperback)
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