Reasons against Mars Direct

clark · 2003-12-22 13:07:02

All this talk about what amount of gravity, whether or not there should be gravity, or on what leg of the journey they should have gravity is a bit, well, head-spinning.

Nice to see so many informed responses!

So, let me coin a phrase I haven't seen yet (problem of not getting out enough I suppose): Gravity-lag, or grav-lag for short... sort of.

grav-lag: A temporary disruption of bodily rhythms caused by immediate changes to the normalized gravity, typically experienced on space ships.... or something to this effect.

So all of this meandering has led me to suggest this:

If we decide that artifical gravity is indeed a neccessary thing fro space travel to Mars, might I suggest that we increase the gravity on any outbound trip from Earth to Mars by .1g to .3g's over standard? The reason being that any long term micro-g on mars might have physical consquences on humans- better to beef up prior to landing and living in those conditions.

What's the point of getting 'acclaimated' to a weaker gravity any sooner than neccessary? Wouldn't it be better to have them feel like 'supermen' once they land, so they can do a lot of that heavy lifting (that everyone says they will have to do) once they land?

On the inbound from Mars to Earth, start at Mars gravity, then slowly ramp it up to whatever level is good for recovery (more research).

The reasoning of acclaimating astronauts to their new gravity before they arrive has never made much sense to me. Perhaps someone can explain that.

RobertDyck · 2003-12-22 14:19:41

According to my first year physics text book, acceleration is a = r * w^2 where w is actually the lower case Greek letter omega. Omega represents angular velocity, which is calculated as w = delta-theta / delta-t where delta is "change of" and theta (an O with a horizontal line through it) represents angle in radians, and "t" represents time in seconds. There are pi radians in 180? so 2*pi is a circle. Let's pick a letter for rotation rate, if r is radius then let R be rotation rate in revolutions per second. Therefore R=0.016667 would represent 1 rpm. Substituting we get a = r * (2*pi*R/s)^2 so that means a tether with radius of 86 metres spun at a rate of 1 rpm will have acceleration of a = 86 * (2*pi*0.016667)^2 = 0.943 m/s^2. Earth has an equatorial surface gravity of 9.78 m/s^2 so that is 0.0964 of Earth's gravity. What am I missing? To get 1 Earth gravity of acceleration with a rotation rate of 1 rpm you would need 9.78 / (2*pi*0.016667)^2 = 891.829 metre radius, or 1783.658 metre tether. That?s very close to what Shaun Barrett calculated. At 3 rpm for 1G that works out to 99.09 metres radius.

If that's measured at the floor of the upper story then you can subtract the height from the floor to the apex of the dome. The measurement point should be the centre of gravity, so for the habitat it is very close to the floor of the upper story. The counterweight will be the spent upper stage, and you would also measure from the centre of gravity of it, so subtract half of its length. If the mass of the habitat is not the same as the upper stage, then you must worry about forces. To get the same force you must ensure the mass of the habitat multiplied by the acceleration from rotation as measured at the centre of gravity is equal to the mass of the spent stage times its acceleration. After calculating the acceleration required for the spent stage, calculate the radius of rotation then subtract the distance from the tether attachment point to the centre of gravity.

As for rotation rates, this was a major point of discussion at the Humans in Space conference last May. The traditional limit was challenged. A couple references I found on the web are Angular Speed of a Training Centrifuge which describes 20-66 rpm, but that's for high-G training, not long-term exposure. NASA's Space Settlement web page describes 3 rpm as the limit for individuals who are adapted to it.

You could design the mission to use 2 tethers: one for 0.38G with the spent TMI stage for the trip to Mars. The one for the return trip could use the spent TEI stage with acceleration gradually increasing from 0.38G to 1.0G during the trip. Let's assume the spent stage has the same mass and approximate size as the habitat and uses 3 rpm. Robert Zubrin's original habitat with just 1 story and lower storage for a pressurized rover, surface science equipment, life support equipment, fuel tanks and landing rocket, and landing legs, had a mass of 27.82 tonnes plus the tether. To create 0.38G (3.72m/s^2) at the floor of that would require 37.69 metre radius, subtract 2 metres (6' 6.740") for the ceiling at the outer perimeter, and 1 metre (3' 3.370") for the apex of the dome. I know, the old image doesn't show a dome roof but all new designs do. A dome holds pressure better. That leaves 34.69 metre tether at one end; again assume the same mass and approximate dimensions for the spent stage, so 68.38 metre tether length. To hold 27.82 * 2 = 55.64 tonnes at that length with a 4x safety factor, a Krypton-K tether would have to be 5.65 times as strong as a single 3/4" rope; or 1.78273" diameter. That would mass 219.9 pounds or 0.09975 tonnes. That is a lot less than the 0.60 tonnes that Robert Zubrin estimated. We would have to add attachment rings, bolts, some sort of reel, and a cutting device, but it's still quite light.

Bill White · 2003-12-22 15:57:17

That would mass 219.9 pounds or 0.09975 tonnes. That is a lot less than the 0.60 tonnes that Robert Zubrin estimated. We would have to add attachment rings, bolts, some sort of reel, and a cutting device, but it's still quite light.

My reading of this is that the weight of the tether is NOT a significant obstacle to MarsDirect. Any disagreement? If 3/8th gee were the Mars-bound target pseudo-gravity then a rotational rate of 2 rpm would seem to result in a rather short tether. 3 rpm means a very short tether to generate 3/8th gee.

The NASA site RobertDyck linked pointed out that psuedo-gravity has other side effects related to the motion of fluid in the inner ear and that fact that dropped objects will not fall straight. Thus rpm and tether length seem to require balancing. Shorter tether generally good (less mass) lower rpm generally good (less Coriolis, right?) therefore there is a trade-off needed to find appropriate compromise between conflicting factors.

Higher gee generally good as well which calls for either/or longer tether & higher rpm.

(A 3/8ths pseudo-gravity sports arena in LEO would be waaay cool as basketballs (for example) would not follow "true" trajectories from Earth-based expectations. All eye-hand coordination instincts in a spinning environment will therefore be suspect. Becoming a skilled pseudo-gravity juggler will be quite an accomplishment!)

Use a Soyuz-Progress experimental tandem spun to simulate 3/8ths gee - - moving between the Orbital Module and the Descent Module would directly involve psuedo-gravity gradient effects and Coriolis effects on human perception, nausea, and eye-hand coordination. Perhaps potential MarsDirect astronauts could be screened and evaluated based on their ability to function effectively in 3/8th psuedo-gravity spun up at MarsDirect tether lengths and rotational rates.

Soyuz/Progress could also be used to help fine tune optimal tether lengths and rotational rates with respect to these human factors.

Shaun Barrett · 2003-12-23 07:45:26

Robert Dyck:-

... so that means a tether with a radius of 86 metres spun at a rate of 1 rpm will have acceleration ... that is 0.0964 of Earth's gravity. What am I missing?

You're not missing anything as far as I can see; you're figures are all correct.
Perhaps what is causing the feeling that something is wrong is the fact that increasing the rotation rate for a given tether radius causes a larger change in acceleration (artificial gravity) than might be expected.

For a tether radius of 86 metres, we get the following figures for artificial gravity at various rotation rates:-
1 rpm .... 0.096g
2 rpm .... 0.384g
3 rpm .... 0.865g
6 rpm .... 3.462g
(Taking 1g to be 9.81 m/s/s )

The relationship clearly isn't linear.

Shaun Barrett · 2003-12-23 19:05:54

To an extent, I agree with Clark's reasoning in that it seems sensible to keep the astronauts in a high gravity situation for as much of the mission as possible.
In view of the probability (in my opinion) that the astronauts' bodies will quickly lose high-g conditioning as soon as they take up residence on Mars, I wonder whether artificial gravity set at a level higher than 1g is really necessary. Whether you've been in 1g or 1.2g for the six month outward voyage, you'll feel like a 'superman' or 'superwoman' for only a limited time when you arrive - perhaps only a week or two.
And besides, I'm having enough trouble talking people into 1.8 km of cable, 1 rpm, and ONE g !! Never mind upping the ante to 1.2 or 1.3g !

I think the reasoning behind creating only 0.38g on the way to Mars is two-fold: Firstly, it looks technically easier to do than creating a full 1g and saves the weight of a longer cable and, secondly, there may be a valid argument that the astronauts will be better 'primed' to gauge and control their physical actions and reactions more accurately if they're acclimatised to martian gravity before they get there.
But this scenario is usually presented as part of a bigger picture which includes a return flight to Earth with no rotation at all. In other words, it's a bare-bones compromise to ensure the explorers can function adequately when they reach Mars but which pays little attention to their long-term well-being when they get home.

If I read Clark's attitude correctly then I agree with what he's saying, that a full 1g (at least! ) should be provided almost all the way to Mars. Rotation should be halted at least 48 hours before arrival to allow for the period of space sickness which afflicts more than 50% of astronauts when they hit zero-g.
Rotation should be arranged for the return trip also - gradually increasing from 0.38g to 1g during the course of the journey.
If the above plan can be implemented with a rotation rate of only 1 rpm (i.e. with long cables), then I believe we'll have done everything feasible for the physical well-being of the crew.

Aside from the weight of the cable, spool, and small ion thrusters for spinning-up and spinning-down, I don't see any significant problem with this scheme and I believe it is in the best interests of the people we send on these missions.
An added advantage, if sufficient warning can be supplied, is that the counterweight could be used as an additional shield against solar flares if it could be manoeuvred into the right position in time.

RobS · 2003-12-24 02:27:54

It seems to me the best argument in favor of .38 gee on the flight out is for the astronauts to adjust to the feel of it. A cup of coffee has to be picked up with the right amount of acceleration or you spill it. Until one adjusts to a lower gee, one will be clumsy in it. On the other hand, the Apollo astronauts seem to have adjusted to 1/6 gee pretty well.

-- RobS

Palomar · 2003-12-24 12:51:12

Aurora

*What do the brainiacs here think of this idea?

A thread about Aurora was created last year by someone (2002) regarding this plan (I checked for "Aurora" with our Search feature, to see if it had been brought up recently -- it hasn't). However, the link provided in that previous thread now leads to something else entirely (web master changed pages, I guess). So I'm bringing it up again, here.

I scanned that thread yesterday, and most of the input came from folks who no longer -- or rarely -- post at New Mars.

Just curious what you guys think of the Aurora plan, how similar or dissimilar it is to Mars Direct, more feasible (regardless of ESA), etc.

--Cindy

Palomar · 2003-12-26 13:58:05

Aurora
*What do the brainiacs here think of this idea?
A thread about Aurora was created last year by someone (2002) regarding this plan (I checked for "Aurora" with our Search feature, to see if it had been brought up recently -- it hasn't). However, the link provided in that previous thread now leads to something else entirely (web master changed pages, I guess). So I'm bringing it up again, here.
I scanned that thread yesterday, and most of the input came from folks who no longer -- or rarely -- post at New Mars.
Just curious what you guys think of the Aurora plan, how similar or dissimilar it is to Mars Direct, more feasible (regardless of ESA), etc.
--Cindy

*Well, it -is- the holiday season and there are no obligations to "have to" respond to posts of course.

However, I can't helping being curious as to why the party *seems* to have suddenly ground to a halt when I mentioned "Aurora."

(interloper? albatross? party crasher?)

--Cindy

Rxke · 2003-12-26 14:42:52

Cundy, i guess it"s just a case of holiday-off-line-ness...

ALL the boards sem to be lower traffic, these days...

What does that tell us? People visit boards mainly during their working hours? (evil grin)

RobertDyck · 2003-12-27 00:35:07

*Well, it -is- the holiday season and there are no obligations to "have to" respond to posts of course.
However, I can't helping being curious as to why the party *seems* to have suddenly ground to a halt when I mentioned "Aurora."
(interloper? albatross? party crasher?)
--Cindy

I haven't read the entire Aurora plan. What I'm most concerned about is the schedule that doesn't have the first manned mission to Mars until 2033. I'll be a senior citizen by then.

They have a very slow plan with many developmental steps for things that NASA already completed. True, ESA hasn't successfully demonstrated a man-rated entry vehicle before, but NASA certainly has. The Exo-Mars probe doesn't appear to be much more than NASA's Mars Exploration Rovers that will land next month. Mars Sample Return is a good idea, but their plan requires 2 launches with the second not schedules until 2014. I'm not sure what their Technology Precursor mission of 2018 will accomplish that couldn't be accomplished by the MSR. The Human Mission Technologies Demonstrator could be conducted on ISS now, there's no reason to wait until 2014. The Human Moon Mission of 2024 is a re-do of Apollo and is just a distraction if it's just intended as preparation for Mars. The Automatic Mars Mission of 2026 using the same equipment as will be used for the manned mission is a good idea, I just see no reason to wait until 2026. The Cargo Element of first Human Mission; why wait 3 years between it and the first humans? If the goal is to prove the equipment before sending humans, then the Automatic Mars Mission should do that. If the goal is ISPP, then humans should follow 26 months later at the next launch window. Following Mars Direct's overlap schedule, the return vehicle for the crewed mission could be sent with the primary vehicle for the automated mission.

The entire schedule could be compressed and cost reduced by reducing the number of precursor missions. I don't know what politics is like in Europe, but keeping politicians focused for 3 decades seams difficult.

Wim · 2003-12-27 03:54:45

Maybe they think about it this way:

If we bring up a timelined plan about missions to the red planet we better anticipate delays (mostly dollar/euro delays) so instead of planning each 2 earth-years a mission to Mars we will come up with more missions and separate the 'important' ones a bit further. Then if there are the delays, we can stay on track and don't loose public interest ?

Does this make sense or is there still X-mas turkey in my face ?

Beagle 2 is alive and kicking but he waits to send some tune untill it has enough media attention. :;):

Shaun Barrett · 2003-12-27 07:02:02

That was a good question, Cindy, and I have to admit we don't seem to talk as much about Aurora as we do about Mars Direct for some reason. It's probably for the reasons Robert outlined above; Aurora is too 'deliberate' in its planning. Everything they say sounds O.K. (except the MSR, which I think we can do without ... just send people to do the analysing! ) but it trails off into the far distant future and sees the first human reaching Mars in 2033 !!!!

I find that timetable more than a little disappointing after cutting my teeth on Dr. Zubrin's go-get-'em plan. I'm sure Robert Dyck is quite right when he points out all the ways in which the whole thing could be fast-tracked and maybe 10 years shaved off the agenda.
I can't see any technological reason why we shouldn't have bootprints in the martian sand by 2020 at the latest. It's just a case of setting the goal and pushing the right buttons.

Gennaro · 2003-12-27 07:58:14

Everything they say sounds O.K. (except the MSR, which I think we can do without ... just send people to do the analysing! ) but it trails off into the far distant future and sees the first human reaching Mars in 2033 !!!!

- On the contrary, the way things are going in space, 2033 sounds pretty optimistic in my opinion. I'll be 63 by then.
I rather have a hunch that the first manned mission to Mars will be launched *precisely* somewhere between 2046 and 2057 at the earliest and don't ask me why, it's just my intuition. Maybe it's because I wasn't alive in the 60's.
It's not that we can't do it now. We've been able to do it "in the next ten years" for a looong time. It's only that I sense our political culture, and the way our civilization is presently working, has to change in profound ways.
Yet again, maybe the Chinese will do it. They still have the guts to do things...

My impression of Aurora, when it comes to Mars, is that the good parts of it seem largelly derived from Dr Zubrin, one way or the other. For much of the rest I find myself agreeing with RobertDyck.
All the same, I'll admit that as an EU-citizen, I still take some pride in it. Perhaps mostly because we at least have a plan.

Palomar · 2003-12-27 10:28:00

*Robert, Shaun and Gennaro: Thanks for reminding me that I am in SERIOUS denial regarding the passage of time and the aging process. 2033, bah! I'll still be young. Senior citizen? That will never apply to me (no, it won't -- I'm defiant! haha).

Yes, I agree with Gennaro about the similarities/derivation issue of Aurora to Mars Direct. And Shaun:

"I find that timetable more than a little disappointing after cutting my teeth on Dr. Zubrin's go-get-'em plan. I'm sure Robert Dyck is quite right when he points out all the ways in which the whole thing could be fast-tracked and maybe 10 years shaved off the agenda.
I can't see any technological reason why we shouldn't have bootprints in the martian sand by 2020 at the latest. It's just a case of setting the goal and pushing the right buttons."

Yeah, the sooner the better. Although I am (extremely reluctantly) beginning to acknowledge that my pushing for going on to Mars might just be for the next generation entirely...or the generation after that. Not too long ago, the Apollo astronauts were suiting up and taking off...now they're old men. We all know this of course.

In the face of all other ills, set-backs, and apathy, though...2033 isn't so bad. But hopefully no later than that.

Okay, so it's the timing factor.

--Cindy

Shaun Barrett · 2003-12-27 19:48:38

Cindy:-

Thanks for reminding me that I am in SERIOUS denial regarding the passage of time .. ..

Ha - ha !! :laugh:

Aren't we all?!!! :;):

RobertDyck · 2003-12-29 13:51:10

Everything they say sounds O.K. (except the MSR, which I think we can do without ... just send people to do the analysing! )

The reason I think a MSR mission is a good idea is primarilly as a technology demonstrator. NASA administrators are afraid of In-Situ Propellant Production, so prove it works with a Sample Return mission. However, the primary mission objective must be a technology demonstrator for ISPP, with the Mars sample as secondary only. You could send a hollow gold ball, or some other useless cargo to Mars and back, just to prove you can. But there will be the temptation to avoid actually landing on the surface of Mars and taking off again. There would also be the temptation to just lift to Mars orbit and claim that is a success. A sample return mission must get all the way to Mars, stop long enough to collect a sample, take off and return to Earth surface safely. If you can't do that then you can't safely send humans to Mars. A sample return is a goal to require all the technologies necessary to safely return humans to Earth. In fact, you could question whether an automated mission with a full-up spacecraft is necessary after MSR. Apollo 8 was supposed to be automated; it only had astronauts onboard after an automated Soyuz did that mission. Considering all the failures on Mars, an automated mission sounds like a good idea. But those two precursor missions, MSR and an automated mission with the full-size spacecraft, should be enough. And MSR could be done now, launched in 2005. In parallel the human technology demonstrators could be sent to ISS starting 2004; it's just a question of how quickly they can be built. The ground prototype of the Sabatier reactor and reverse proton exchange membrane electrolysis devices have already been demonstrated at the Johnson Space Center's Advanced Life Support facility. If NASA got off its butt, a recycling life support system could be incorporated in the U.S. habitation module for ISS as the next module. There may be power issues determining the assembly sequence; I think the HAB was scheduled for September 2005 before the Columbia accident.

Shaun Barrett · 2003-12-29 19:35:23

O.K. Robert!
The way you say it, the MSR sounds like a perfectly reasonable technology test-bed.
Hell ... with you running NASA, I could even learn to love a sample return mission!!

[Especially the "If NASA got off its butt" part of the deal. ]

Bill White · 2003-12-30 09:38:01

Membrane technology will simplify in situ fuel production.

IMHO - Zubrin's MarsDirect architecture has inspired large numbers of scientists to find seemingly minor tweaks to the orignal plan. While each "tweak" may be small the combiend effect will be a significant reduction in the cost of doing MarsDirect and a significant increase in the robustness of the mission architecture.

The genius of this story from Jefferson County Colorado is that the local residents can take pride that some of their own helped put men on Mars. Maybe we can't all go to Mars, but perhaps folks shopping at the local Safeway can rub shoulders with some professor who heped make it possible.

Why would we want to stop this creative thinking and replace it with a top down "wait a few decades" mentality?

Shaun Barrett · 2003-12-30 18:34:13

Beautiful .. I love it!

Yang Liwei Rocket · 2004-09-20 12:53:09

... worries about how quickly they might de-adapt. After all, a manoeuvre such as aerobraking into martian orbit may require an A-1-normal vestibular reflex condition and hand-eye coordination.
De- adapting could be a problem... But not for aerobreaking, etc. As much as we like the mental picture of a 'hot' space-pilot, doing incredible manoevring, it all should be totally automatic. Of course if things go totally SNAFU, there would be some manuall-override capabilities, but i don't think humans are capable to do all that high-precision stuff. The real steerin must be done with computers, some button-pushing by astronauts should be good to give them at least the morale-boosting impression they make a difference, but that'd be merely symbolical.
De-adapting on the surface, OTOH... imagine that all of a sudden you have to de-adapt AND put on your heavy suit, climb off a rickety ladder, and negociate a rock strewn plain... That could be one small stumble for a man, a giant circus for mankind... :laugh:

I feel there is still much work to be done, the direct route could be a way which causes many risks

SpaceNut · 2004-09-20 13:04:22

Yup so true but most of the work can not proceed if the funding is not there. Even if spare parts were over purchased and volunteer time was used to assemble the first ship we would still be in the same problem until the shuttle and the Iss are off Nasa's plate.

SpaceNut · 2018-11-25 17:22:04

The gateway for the moon does go against going to Mars

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