Over at Wired, Adam Mann has a piece on the technical requirements. I’d take issue with this:
NASA estimates it would need to fire at least seven of its new SLS rockets to deliver to orbit the people, supplies, and ships necessary for a Mars mission. While no cakewalk, that’s a great deal easier, faster, and cheaper than what we could do today.
There is no evidence to substantiate this statement, and a great deal of counterevidence, from NASA’s own internal studies.
Some facts:
Radiation exposure was recently measured at 1.84 milliSieverts (mSv) per day for the cruise phase to Mars. Exposures on the ISS average 150 mSv per year, or 0.41 mSv per day. So the radiation exposure on a trip to Mars is about 4.5 times as great as the exposure on the ISS.
Also it’s different radiation.
As I understand it, there’s currently no easy solution to shielding against high energy cosmic radiation. That may be a major limitation to long term habitation in interplanetary space
If transit times are 6 months each way, yes. If you can get there in a few weeks, not so much.
With a cycler ship you could do it even if transit times were long.
First off, nobody has tested what radiation exposure levels would be like for a realistic manned Mars mission with a proper “storm shelter” where the crew would retreat during reports of flares headed their way.
More importantly, radiation shielding is very nearly a solved problem, technologically. Using a pulsed m2p2 type system it would be possible to dramatically reduce radiation exposure levels, by orders of magnitude. And the most significant engineering hurdles for such a system are precisely the same that would need to be solved in general for manned Mars exploration (such as high output power sources).
Here’s a paper on the subject: http://www.ess.washington.edu/Space/M2P2/rad.shielding.pdf
“…that’s a great deal easier, faster, and cheaper than what we could do today.”
Cheaper I think is overstatement without any facts.
Given that we have NO system for a space launch and no system for inter-planetary carrying of personnel or eqpt, the easier and faster with a ‘planned’ and possible future system, than with the NO system at all that we have now, easier and faster seems reasonable.
What do you mean, “given that we have NO system for a space launch”? We have several launch systems. Or did you mean a spacecraft?
I’m not a ‘wonk’ on space like may others here. That’s why I read this blog, for my personal education.
But I wasn’t aware that WE [the U.S.] currently had a launch system big enough to put people into LEO any longer. I know we can put satellites up, but even at that, I’m not personally knowledgeable [beyond what I learn here] of how much weight we can currently lift.
If we can put people up to the level of ISS, then WHY are we hitchhiking with the Russians? Or have I completely missed something?! And if I have missed something, please tell me. You can’t hurt my feelings by teaching me something.
SpaceX’s Falcon 9 + Dragon are “big enough” to send people to ISS (they’ve sent up tons of cargo), but NASA requires some additional features (e.g. a launch escape system) before it will put people aboard.
Congress could accelerate the availability of a US ISS crew transportation option, but instead it’s starved the commercial crew program of funds, extending our dependence on Russia.
Jim,
I was talking abut NASA when I said “…WE [the U.S.]…”.
The quoted paragraph Rand started with says, “NASA estimates…”.
I know the privateers are capable. And I knew about NASA and the escape system plan. So I guess I should said NASA in my blurb. And things are as I said then,
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“… WE [the U.S.] currently had a launch system big enough to put people into LEO any longer.”
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I guess I went off the rails when I didn’t add what I did know to my comment. You confirmed what I thought I’d learned from reading here and reading where Rand and others point me to also. Thanks for that.
I looked around but I never found how much tonnage the private guys can lift right now.
In addition to Space-X’s Falcon 9 and Dragon, the Atlas and Delta Heavy versions could put Orion in LEO. All need additional work before their first flight. And all are commercially made. No need for NASA to develop one, any more than they need to develop trucks to carry cargo.
Recognizing that it will play havoc on the weight, just how much shielding are we talking about if we resort to various brute force approaches? How much sand? How much ice? Inches? Feet? Meters?
A few feet of dirt will do the job but, with current in-space industrial capability, it doesn’t make much sense to attempt to do anything about it for the cruise phase.
Actually, Trent, …your definition of “few” may be larger than mine. There are several problems with radiation shielding. The radiation that is particulate is particularly problematical. Not only must we deal with the Radiation Equivalents in Man(REMs) of the particles that get through (mostly protons), but we must deal with their secondary particles, because the protons smash atoms in the shield, and the pieces of those are also deadly.
This means that just “a few feet” of dirt will usually give us a higher REM dose than open space would do. We’d be substituting shot-gun blasts for random rifle bullets. Even 30 years ago, it was accepted that at least 6 *meters* of dirt would be needed to stop the secondaries, and health physics has pushed allowable doses well below what they were then.
In addition, in the last 15 years we are seeing concern about a small percentage of cosmic rays that are nuclei of heavier elements, up to Iron, which apparently give a more numerous set of secondary particles, because both they and the nucleus they run into would shatter. The theoretical best shielding mass would be meter after meter of Liquid Hydrogen, which would, when hit, simply mean you have 2 protons at lower velocity, where you had one before. This is hardly a practical continuous shielding solution, however.
Our research team in Portland still favors the innate shielding of lavatube caves on both the Moon and Mars. Possibly in carbonaceous chondrite asteroids there will also be out-gassed voids under the surface as well to be used. These would have more than enough rock in their ceilings to shield humans on a permanent basis.
For mobile solutions, I still favor the work of Dr. Winglee at UW, for creating very large plasma tori to use as magnets that can express magnetic fields 10s of kilometers in diameter. The size of these fields means they can be lower intensity, consume less current, and still turn a cosmic ray proton before it intersects the side of a spaceship.
These are not infallible solutions for every radiation situation (for instance the rad levels on most inner moons of Jupiter), but they give options otherwise unavailable.
Nice essay. The great thing about being wrong about exactly how much dirt you need to pile on top of a Mars habitat is that you have more dirt available. All these “creative” solutions to the radiation-in-transit problem beg the question that it’s actually something worth solving. If the people willing to travel to Mars are aware of their 5% greater risk of getting cancer sometime in their remaining lifetime, and choose to go anyway, why bother?
Not to mention that treatment may be cheaper than prevention, if the greater risk of cancer becomes realized.
Given our baseline risk of cancer on Earth’s surface, having treatment options on Mars would be pertinent for any colonization effort.
If the people willing to travel to Mars are aware of their 5% greater risk of getting cancer sometime in their remaining lifetime, and choose to go anyway, why bother?
Um, because astronauts are not the people who will be voting for the program on the floor of the United States Congress?
Was that a trick question?
In general, I agree with you on that, Trent. I am concerned that people need the freedom to act to get settlement done privately. I see the hurrrrrrible bugaboo of radiation as one of the primary excuses to deny that freedom in the US Congress. So, having the solutions at hand to a problem pols may blat about, in order to restrict our action, …seems, …prudent.
Here’s an article on how Inspiration Mars is thinking of doing it,
http://medcitynews.com/2013/03/mars-spaceships-sewer-system-will-shield-astronauts-from-cosmic-radiation/
There are also some interesting ideas involving magnetic shields, though my guess is those are a few years off. Right now, you’d need a rather large magnet, which would add a couple of tons of weight. If they ever come up with a room temperature superconductor, it suddenly becomes very easy.
Hrmmm. I thought the whole excuse for SLS was that in-orbit assembly is too hard and costly? Yet, that’s what they’d need to do with SLS.
So, what’s the real difference between doing in-orbit assembly with 50 ton components vs. 70 ton components (for the early versions of SLS… the proposed later upgrades would enable more, theoretically, if they ever happen).
I can only think of one major difference; if existing (or in development) non SLS launch vehicles are used, then there might be enough money for the mission hardware. But, if it’s all squandered on SLS, there won’t be.
I want to see how they plan to land an SLS sized payload on Mars. MSL is the biggest thing we have landed and it is hard to imagine landing things that people are talking about.
Of course SLS could have many smaller sized payloads but then that brings us back to the debate about SHLV or many smaller launches.
“I want to see how they plan to land an SLS sized payload on Mars. MSL is the biggest thing we have landed and it is hard to imagine landing things that people are talking about.”
We could simply stop believing the fantasy that Mars is easier to get to then the Moon and treat Mars as having some atmosphere, but basically it’s like the Moon but requires more delta-v to land on it.
Generally, Mars require less delta-v to land on then a vehicle from LEO needs to directly land on the Moon. It may bad idea to have something directly go from LEO to the lunar surface, but not it’s insurmountable problem.
So separate crew from cargo. Land crew one way, and land cargo with aeroshells and parachutes.
Though another problem is they are going to Mars wrong, so for shorter crew travel time one need kill a lot of the Earth to Mars trajectory- and that requires an aeroshell.
So, I guess, an additional reason Curiosity took 8 1/2 month to reach Mars- rather than a shorter patched conic trajectory.
If John Slough’s tests this summer work out, we can solve the radiation problems by having a Mars transit time of 30 days.
http://nextbigfuture.com/2013/04/components-being-developed-for-nuclear.html
I know that the propellant depot studies inside NASA had support at JSC. But MSFC hated it. They wanted to build a bigger Saturn V, not a depot and deep space boosters.
Sigh.
You don’t even need a depot, just a refuelable spacecraft and that’s much easier. But NASA always wants to develop newer and bigger systems, because that’s where the money is. So now we have thirty year old technology still not being used because there is always one more feature we can try to convince people is necessary.
“You don’t even need a depot, just a refuelable spacecraft and that’s much easier. But NASA always wants to develop newer and bigger systems, because that’s where the money is. So now we have thirty year old technology still not being used because there is always one more feature we can try to convince people is necessary.”
Yes one could just have refuelable spacecraft. But a depot allows a launch of the craft which bringing the fuel to be more flexible. Or one can know the rocket is there, before you launch the vehicle that needs to be refueled.
Plus you can specialize the fuel depot. So fuel depot can have added mass which store rocket fuel [LOX is crogenic fuel] and the depot can have most of the capability to dock with another spacecraft. It doesn’t have to, but it could have robotic arm for example. So extra mass requirement involved with docking a refueling can be mostly part of the fuel depot. So vehicle that bring fuel or a vehicle getting the fuel does need this as much added complexity- instead one make an effort to put most of it on the fuel depot.
Now if you don’t have fuel depot which full of rocket fuel or it’s less massive, you also have fuel depot going to spacecraft. And if you ion thruster, it’s low thrust might make docking easier. Or instead entire depot moving- depot could have tug, which docks with spacecraft and ferries to depot.
So your normal gas station on Earth could have hand pump in which customers are suppose fill the gasoline tank, but gas station give you fast deliver of gasoline and generally cause less hassle for motorists.
Same thing will depots- they can do stuff that makes easier to refill rocket fuel.
And ultimately you want them privately operated, else, you will forever be doing stuff like using hand pumps.
Sure, depots are great, I was just pointing out they aren’t necessary. That’s a good thing to know.
The fastest trajectory which has ever went from Earth to Mars is 7 months.
We need a faster trajectory to Mars.
To make it faster than 7 and not 6 1/2 months, one shouldn’t use a Hohmann transfer.
People may talk about getting to Mars in month or whatever, but they seem to skimp over that fact this can’t be a Hohmann transfer.
And I kind of think that an important bit in point out about getting to Mars quickly.
A elliptical orbit from Mercury distance [or nearer the Sun] to Mars distance, has faster orbital speed than an Earth distance to Mars distance.
This orbital path has a shorter year.
So a rock traveling for perihelion of Mercury distance to Mars distance has shorter year than a rock with Earth distance perihelion to Mars aphelion.
A Earth to Mars rock is 8 1/2 months times 2. Or hohmann transfer leg to Mars is 8 1/2 months.
Mercury to Mars is about 1 year [12 months]. Or about 6 month for hohmann transfer leg.
Now, the 6 month Mercury to Mars leg will cross Earth’s orbital distance and from point it crosses Earth’s orbital distance to Mars will take about
3 months.
So you match this trajectory from Earth and get to Mars faster [and arrive at low velocity relative to Mars].
And if want get there even faster then you have the perihelion is closer to the Sun.
And taking it to an extreme, would be a perihelion which intersect the sun.
So IF there were there people living on Mercury and if one limited it to only Hohmann transfer, then they get to Mercury quicker than from Earth. Same with people on Venus, quicker than Earth.
But if Earthlings use a non Hohmann transfer they get to Mars quicker than Mercurians or the Venus chaps.
The inner solar system people pay more delta-v for their faster Hohmann transfers, and Earthling using non- Hohmann transfers pay more paid more than their delta-v costs to get to Mars faster.
It’s somewhat French in the equality department and the guy in the middle {Venus} might be said to get the better of both worlds- but you know, Venus is quite hellish.
Quicker trips include their own risks. People like the idea of a free return.
But taking some risks could mean meeting up with landers in space rather than orbit. The crewed ship might be three months into its journey and meet up with a lander that’s taken over a year to be in the same spot (matching velocities may burn up too much fuel from the landers. A real rocket scientist would have to answer that question.) Once the crew has transferred to the lander it would also be less expensive to redirect the empty crew ship for a return.
“Quicker trips include their own risks. People like the idea of a free return.”
I think it’s possible to go quickly [meaning anything under 3 months] and have a free return. Though getting “free returns” and fast [or not fast] limits
the launch windows.
“But taking some risks could mean meeting up with landers in space rather than orbit. The crewed ship might be three months into its journey and meet up with a lander that’s taken over a year to be in the same spot (matching velocities may burn up too much fuel from the landers. A real rocket scientist would have to answer that question.) Once the crew has transferred to the lander it would also be less expensive to redirect the empty crew ship for a return.”
That is one way to get a free return of vehicle, but it seems what mostly is desired is abort option for crew. Though if empty crew ship could occupied, that would be a crew abort.
I think having return vehicles already at Mars, is generally the best abort option. And generally for exploration not too much emphasis on reusing spacecrafts, unless cost of doing this is low.
So for exploration tend to do expendable, as the exploration matures works upon lower costs. Though I favor starting the whole exploration process by using fuel depots, which is a reusable path from the beginning. Though part of doing fuel depot could involve fuel delivery vehicles being expendable [single use- though perhaps saved for later scrap value].
I don’t know if you left out a negative in your second paragraph; a fast trip out and a free return is not particularly easy (it could be done, but the return trip would last years).
Cyclers have a pretty high up-front cost (there’s a lot of mass to be launched; how much depends on the various risk and comfort trade-offs); they can be set up to have a quick trip one way and a slow return trip, but the higher delta-V requirements eat up the cost savings of the cycler fairly quickly. Anyway, pretty much by definition cyclers have a free return.
Probably better to launch the return ship first (assuming there’s going to be a return, I suppose). Even better if it can use in situ resources for the fuel. I ran through the numbers a while back, I don’t remember which side of feasible SSTO from Mars using CO/O2 was.
“I don’t know if you left out a negative in your second paragraph; a fast trip out and a free return is not particularly easy (it could be done, but the return trip would last years).”
So, as said, what I mean is not hohmann trajectory.
And there no doubt a hohmann trajectory requires least delta-v.
But also no doubt that one can’t use a Earth to Mars
hohmann trajectory if you want to get to Mars 6 months or less and have use least amount of delta-v.
So I would agree that getting to Mars in less time than 7 months is not easy. And I think NASA should go to Mars in 3 months of less. And using a considerable amount of delta-v- but if starting from High Earth rather than LEO or Earth surface, not too excessive amount of Delta-v [around 7 km/sec of delta-v from High earth [such as Earth/Moon L-1].
A way to do this is to match a orbit which like a Mercury or Venus hohmann trajectory to Mars and you matching this orbit from Earth.
Now you actually send a spacecraft to say Venus, and have go to Mars via hohmann trajectory, and from Earth send crew to match this trajectory. So similar to Mars Cycler or version of a Cycler.
Or just send spacecraft from Earth which on this trajectory
{which is not a Earth to Mars hohmann trajectory}.
So second option is sending crew and focused on just sending crew- so you end up with crew only at Mars near a base [so in spacesuit travel to their base] bringing only themselves and the spacesuits.
So all the non crew is delivered using at the slower, and more efficient Earth to Mars hohmann trajectory.
So since it’s some orbit like a Venus to Mars hohmann, the free return could do some gravity assist off Venus and thereby get back to Earth.
But using Venus [or Mercury] for free return would limit the number launch windows.
But in terms of time, I don’t have the trajectory or a date it would need to be, but it seemed *could* be faster than the typical free returns that have been mentioned in various place.
So for example, conjunction trajectories as discussed here:
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/22610/1/97-1121.pdf
And I think I have also seen paper involving free returns involving using Venus. But I don’t have any references describing the trajectories I am talking about. But stuff regarding Cyclers is similar to what I am talking about.
If the outbound leg to Mars is fast then you arrive at Mars at considerably over Mars orbital velocity; normally that orbit would take you way past Mars before heading back. It would be possible to do a close fly-by of Mars in order to bend the orbit back towards the inner solar system, but Mars is small and the amount it can modify the orbit is limited. I suspect but haven’t confirmed that reasonably fast return options are pretty limited if you’re doing a fast trip out.
Daver
June 4, 2013, 8:24 am
If the outbound leg to Mars is fast then you arrive at Mars at considerably over Mars orbital velocity; …
A Earth to Mars Hohmann transfer arrives at Mars at slower orbital speed than a Mars orbit. If at aphelion of a Earth to Mars hohmann you add delta-v it becomes a Mars orbit.
Or if one doesn’t add velocity at the aphelion, the orbital velocity is such that it falls to Earth orbital distance at the trajectory’s perihelion.
So a hohmann transfer from Earth to Mars has a faster than velocity at Earth distance than Earth and a slower velocity at Mars distance than Mars.
The same applies to a Venus to Mars hohmann transfer trajectory and a Mercury to Mars trajectory.
Plus the orbital time [or year of the orbit] of the Venus or Mercury hohmann transfer trajectory is shorter than a Earth to Mars hohmann transfer trajectory.
A Venus to Mars Hohmann trajectory crosses Earth’s orbit and it cross at angle to Earth orbit.
So I am talking about changing the Earth’s orbit’s vector with rocket delta-v to match the same angle the Venus to Mars Hohmann transfer crosses Earth’s orbital path.
Changing a trajectory vector is only commonly done with gravity assists. Most gravity assists are *mostly* about changing the vector.
“Gravity assistance can be used to accelerate (both positively and negatively) and/or re-direct the path of a spacecraft.”
http://en.wikipedia.org/wiki/Gravity_assist
Changing the vector other than by using a gravity assist is typically regard as wasteful in terms of rocket delta-v, but when one talking a gravity assist adding delta-v to a spacecraft trajectory most of the delta-v added is typically changing it’s vector and the spacecraft trajectory travels a shorter orbital path to say, Jupiter than without a the gravity assists [so even if bounce around Venus, Mercury and Earth- the total miles traveled in shorter].
So a 7 month Earth to Mars hohmann trajectory that got Spirit rover to Mars, traveled 500 million km from Earth to Mars.
By changing Earth orbital vector you travel a shorter distance [less than 200 million km] and thereby get to Mars quicker.
So want saying is use rocket power to change a orbital vector and it wouldn’t be a gravity assist, though one might call it a powered gravity assist.
So since one matching the trajectory of something like a Venus to Mars Hohmann trajectory, you could arrive at Mars at lower orbital speed than Mars, and you would travel a shorter distance to Mars. And it’s the shorter distance traveled which makes it faster.
“So want saying is use rocket power to change a orbital vector and it wouldn’t be a gravity assist, though one might call it a powered gravity assist.”
Fix this to:
So what I am saying is, use rocket power to change earth’s orbital vector. [Whereas Hohmann transfer adds to earth’s orbital velocity]
This wouldn’t be a gravity assist [or called one] though it might be called a powered gravity assist.
One thing not mentioned by Wired (unless I missed it): development of small nuclear power generators, to provide power for ISRU on the surface.
It was good that they at least mentioned the Falcon Heavy in passing.
Please fix the first paragraph.
What We Need To Get To Mars: is $2 billion and guts in exchange for an entire world.