Author Topic: Mars Direct - Problems and Solutions  (Read 87870 times)

Offline QuantumG

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Mars Direct - Problems and Solutions
« on: 11/14/2013 07:49 pm »
A quick review of the Mars Direct mission mode:

1)
 a) A heavy lift launch vehicle in the 100 ton to LEO class launches an Earth Return Vehicle (ERV).
 b) After remote checkout in LEO, the LH2/LOX Earth departure stage throws the ERV to an 8 month transit to Mars.
 c) The ERV aerobrakes into Mars orbit, and remote checkout is made again.
 d) Entry into the Mars atmosphere is made, the heat shield is discarded and parachutes are deployed.
 e) The parachutes are detached and the ERV lands under rocket power.

2)
 a) A hatch opens on the ERV, an a rover carrying nuclear reactor and trailing an electrical cable is deployed.
 b) It drives the nuclear reactor some distance away and preferably over a hill or two.
 c) The nuclear reactor is offloaded and started.
 d) The ERV begins processing the Mars atmosphere to produce methane and LOX, using a supply of LH2 brought from Earth.
 e) The rover searches for an appropriate landing site and marks it with a radar beacon.

3)
 a) A heavy lift launch vehicle in the 100 ton to LEO class launches another Earth Return Vehicle (ERV).
 b) See steps 1 and 2, a different landing site is chosen within travel range of the first landing site.

4)
 a) A heavy lift launch vehicle in the 100 ton to LEO class launches a "tuna can" habitat with 4 astronauts.
 b) After checkout in LEO the LH2/LOX Earth departure stage throws the hab on a 6 month transit to Mars.
 c) The now spent upper stage is used as counterweight to spin up the hab on a ~150m tether, at 2 rpm, to produce artificial Mars gravity for the crew.
 d) After aerobraking into Mars orbit, the crew inspects the landing site for weather, marker signal strength, etc.
 e) Entry into the Mars atmosphere is made, the heat shield is discarded and parachutes are deployed.
 f) The parachutes are detached and the crew lands under rocket power at the transponder.

5)
 a) 500 day ground operations begins
 b) The crew drive a pressurized rover to the ERV to obtain methane and LOX for powering the rover and breathing, etc.

6)
 a) When it's time to leave, the crew get into the ERV and liftoff.
 b) The ERV returns directly to Earth.
 c) Reentry is direct (the ERV doesn't go into orbit first).
 d) Landing is preferably on land for quick recovery.

Fundamental Problems

1)
 a) There is no HLV in the 100 ton to LEO class available, and there is no LH2/LOX Earth departure stage of the required size available.
 b) As there is no current commercial use for a 100 ton to LEO class vehicle, the total cost of development and operations would have to be borne by NASA.
 c) The average flight rate of one launch per year (two every two years) is too low to anticipate reliable operations, increasing both loss of mission and loss of crew risk.
 d) The low flight rate also increases operations cost.

2)
 a) The artificial gravity system is immature, with no tethers of the required length ever flown successfully in space.
 b) Without artificial gravity, the tuna-can hab is possibly too small to maintain crew health in zero-g.

3)
 a) Radiation exposure is possibly too harsh, depending on the solar cycle.

4)
 a) No nuclear reactors are available and this is seen by some as a political roadblock.

Remedies

1)
 a) Use commercially available rockets to maximize cost sharing and higher launch rate benefits.
 b) As these are at least half the payload-to-LEO class (53t for Falcon Heavy), and of smaller core size (~5m diameter payload), at least the habitat (~9m diameter) will have to be redesigned.
 c) The various parts of the ERV and hab will need to be staged and assembled on-orbit during the two year build-up between each Mars transit window.
 d) Docking of fuel tanks can be done last to minimize boil-off of cryogenic propellants.

2)
 a) Although artificial gravity experiments could be done, the now modular habitat design allows larger, while lighter, structure, suggesting a zero-g transit may be preferred.
 b) Astronauts will utilize exercise equipment and zero-g mitigation drugs to maintain bone and muscle mass.

3)
 a) A long column of water can be used as a solar radiation shield.

4)
 a) Use flexible photovoltaic power. The rover will need to be able to unpack and lay out the power system under remote control.

Human spaceflight is basically just LARPing now.

Offline M129K

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Re: Mars Direct - Problems and Solutions
« Reply #1 on: 11/14/2013 08:06 pm »
Problem: the ERV cabin is way too small for so long. I recall it being only 7 ton, about as much as a Dragon. A slightly modified architecture a la Mars Semi Direct would remedy this, but I can't see it being solved within the original two launch architecture.

Quote
a) There is no HLV in the 100 ton to LEO class available, and there is no LH2/LOX Earth departure stage of the required size available.

I see no reason either of those couldn't be developed. You're going to Mars, an HLV is only a drop in a full bucket of expenses.

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #2 on: 11/14/2013 08:18 pm »
I see no reason either of those couldn't be developed. You're going to Mars, an HLV is only a drop in a full bucket of expenses.

NASA can't afford to develop and operate their own launch vehicles anymore.

The reason why the robotic exploration program continues to actually achieve anything is that they launch on commercially available vehicles.

You either get a rocket program or space program, choose.
Human spaceflight is basically just LARPing now.

Offline sdsds

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Re: Mars Direct - Problems and Solutions
« Reply #3 on: 11/14/2013 09:25 pm »
Nice summary!

Fundamental Problems
3)
 a) Radiation exposure is possibly too harsh, depending on the solar cycle.

Remedies
3)
 a) A long column of water can be used as a solar radiation shield.

Are you intentionally disregarding concerns about GCR?
— 𝐬𝐝𝐒𝐝𝐬 —

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #4 on: 11/14/2013 09:37 pm »
Nice summary!

Thanks!

Quote
Are you intentionally disregarding concerns about GCR?

1. There's not a lot you can do about them.
2. No-one has ever shown how they're a mission risk.

Sure, your astronauts might have an increased lifetime cancer risk of 1 or 2%, but so what?
Human spaceflight is basically just LARPing now.

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #5 on: 11/14/2013 10:15 pm »
Instead of staging from LEO, stage at L-1.
Testing tethers for artificial gravity would more like environment of Earth to Mars transit.

How about two spacecraft with 2 crew instead one with 4 crew. And with tether one could pilot from both ends. 

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #6 on: 11/14/2013 10:21 pm »
Instead of staging from LEO, stage at L-1.

I didn't suggest staging from LEO, did I? :)

Quote
Testing tethers for artificial gravity would more like environment of Earth to Mars transit.

Sorry, what?

Quote
How about two spacecraft with 2 crew instead one with 4 crew. And with tether one could pilot from both ends.

Double the mission risk, double the mass, double the isolation.. why?

Human spaceflight is basically just LARPing now.

Offline Vultur

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Re: Mars Direct - Problems and Solutions
« Reply #7 on: 11/15/2013 12:16 am »
Problem: the ERV cabin is way too small for so long. I recall it being only 7 ton, about as much as a Dragon. A slightly modified architecture a la Mars Semi Direct would remedy this, but I can't see it being solved within the original two launch architecture.

Can this be mitigated by proper crew selection? (Sounds crazy but a serious question, if you have millions of people to pick from. Tolerance to long time in small spaces sounds like something that could be tested for on Earth.)

EDIT: To expand that a little more: was this simply not considered in the original proposal? Or was it considered and thought to be workable (but others disagree)?
« Last Edit: 11/15/2013 12:20 am by Vultur »

Offline cleonard

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Re: Mars Direct - Problems and Solutions
« Reply #8 on: 11/15/2013 01:18 am »
I didn't suggest staging from LEO, did I? :)

The Oberth effect says that using your EDS down in LEO will be more efficient than at L1. 

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #9 on: 11/15/2013 01:34 am »
I didn't suggest staging from LEO, did I? :)

The Oberth effect says that using your EDS down in LEO will be more efficient than at L1.

Oh that old myth! You can stage in L1 and still use your EDS in LEO, and if you do you need less delta-v to get to escape.
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Offline gospacex

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Re: Mars Direct - Problems and Solutions
« Reply #10 on: 11/15/2013 02:03 am »
Problem: the ERV cabin is way too small for so long. I recall it being only 7 ton, about as much as a Dragon. A slightly modified architecture a la Mars Semi Direct would remedy this, but I can't see it being solved within the original two launch architecture.

Can this be mitigated by proper crew selection? (Sounds crazy but a serious question, if you have millions of people to pick from. Tolerance to long time in small spaces sounds like something that could be tested for on Earth.)

It is being tested in prisons every day.
Tell Nelson Mandela how awful it is to be in solitary confinement for 6 months ;)

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #11 on: 11/15/2013 03:14 am »
Instead of staging from LEO, stage at L-1.

I didn't suggest staging from LEO, did I? :)

Quote
Testing tethers for artificial gravity would more like environment of Earth to Mars transit.

Sorry, what?

Quote
How about two spacecraft with 2 crew instead one with 4 crew. And with tether one could pilot from both ends.

Double the mission risk, double the mass, double the isolation.. why?

Assuming that one is creating artificial gravity- in terms isolation it's one ship with two living quarters far apart [separated by tether] so I would think of it as more privacy than isolation.
Assuming ships are the same, it's redundancy. If in abort/emergency option one ship can have 4 crew survive.
Yes, double mass. Or more crew per vehicle is more efficient.
So, say have 2 dragon capsules. So Dragon designed for 7 crew for couple days. Modified one could put 4 in it, or just 2 crew. So having for 2 crew but could hold 4 in emergency abort options.
Far as risk, it's higher chance of 2 crew surviving. Or lower chance that mission control gets results of crew lost for unknown reasons. Plus if one ship can have 4 crew in abort situation, more chance that 4 will survive.

I am not really in favor of 6 month travel times {or 8 months}- prefer 3 month. And with 3 month I would skip any attempt of using artificial gravity. And only use one ship.
But if going to do 6 month and if going to have artificial gravity- then maybe two ships??

With the 3 month or 6 month, I think one would not do much in terms of recycling water- would use lots of water [and later sewage] for shielding. Emergency solar flare shelter would be sleeping quarters. So with emergency abort option [doubling up on one ship] Emergency shelter would need to hold 4 crew [not comfortably]. But normally one crew sleeping and enough room for 2 comfortably.

Re: Sorry, what?
I just thought if in L-1, then before going anywhere, one test the artificial gravity and that L-1 would more like deep space than LEO. But since not going to stage in LEO, it's moot.

As said I think 3 month or less is best to start sending crew, though perhaps later crew trips might be 6 months, 8 months, 4 , 6 or 8 crew, and doing the artificial gravity thing and improving water use, various improvements and etc.

Offline MATTBLAK

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Re: Mars Direct - Problems and Solutions
« Reply #12 on: 11/15/2013 03:39 am »
If you are going fast enough to reach Mars in 3 months; either you use a HELL of a lot of propellant to propulsively capture into Martian orbit - or you are going way too fast for aerocapture!!  :o
« Last Edit: 11/15/2013 10:57 pm by MATTBLAK »
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Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #13 on: 11/15/2013 05:35 am »
...
3)
 a) Radiation exposure is possibly too harsh, depending on the solar cycle.
...
3)
 a) A long column of water can be used as a solar radiation shield.
...
Someone, I think it might have been Robot Beat, produced some evidence here that radiation from solar flares does not travel just in a straight line from the sun, so you might need shielding in all directions.
This link mentions 20gm/cm^2, equivalent to a wall of water 20cm thick (disregarding that you would already get about 1/3 - 1/2 that shielding from the vehicle structure itself). Whats wrong with the 'panic room' surrounded with ships stores like I think was in the original idea? (I may have that wrong, i think I got that from the Mars Underground doco)

(edit.. oops forgot the link:)
http://science1.nasa.gov/science-news/science-at-nasa/2005/27jan_solarflares/
« Last Edit: 11/15/2013 05:39 am by KelvinZero »

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #14 on: 11/15/2013 06:53 am »
Someone, I think it might have been Robot Beat, produced some evidence here that radiation from solar flares does not travel just in a straight line from the sun, so you might need shielding in all directions.

For the purposes of shielding solar radiation I can't imagine why you'd need more than a column. While the flux might not come from the direction of the Sun, it will come from just the one direction at a time. So you "just" need to be able to point it.
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Offline spectre9

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Re: Mars Direct - Problems and Solutions
« Reply #15 on: 11/15/2013 06:57 am »
It's really starting to become obvious to me that large chunk solutions to human Mars landings aren't very efficient.

You're just driving up the size of the rocket which drives down the launch rate.

Zubrin disses "Battlestar Galactica" style plans yet his ERV and tuna can HAB qualify as such when you add on all the hardware you need to send them through TLI and put them on the surface of Mars. 100mt to TMI or 50mt on the surface of Mars is simply massive and beyond what even a 130mt to LEO SLS can do. If you think that these payloads can be done lighter than that you're drinking the *censored* beverage.

The solution of having a 3rd vehicle being a dedicated "MAV" that just does the Mars ascent seems like a good idea to me.

The tuna can habs need to be smaller so you can encapsulate them in realistic EDL technology. I think non circular heat shields are very difficult. Even in the thick Earth atmosphere circular shapes have been embraced (Dragon, CST-100, Soyuz, Shenzhou). Then just use many of them. This way there is a bit of redundancy and the astronauts will have some privacy being able to have a hab each. The same landing system could also be used for all sorts of stuff like extra cargo and rovers. Putting them all in one package just seems extremely difficult to me.

I believe the idea with Mars direct is to fold out the heat shield. I think it could be an inflatable around the edges but the nose might need to be rigid.

I'm starting to think it all comes back to launch rates. You can't split up the payloads if you can't launch your rocket more than once in a blue moon. This is where SLS fails the test. NASA not only needs both shuttle pads but they need multiple launches per year per pad... I'm not trying to bash SLS I'm just trying to be realistic. It's either the problems are tackled or the mission just won't ever be done. Medium rockets don't have the throw mass which requires depots. Mars Direct as in the word "DIRECT" wants to avoid this.

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #16 on: 11/15/2013 08:06 am »
Someone, I think it might have been Robot Beat, produced some evidence here that radiation from solar flares does not travel just in a straight line from the sun, so you might need shielding in all directions.

For the purposes of shielding solar radiation I can't imagine why you'd need more than a column. While the flux might not come from the direction of the Sun, it will come from just the one direction at a time. So you "just" need to be able to point it.
That's a misconception. It comes from very widely varying angles. The average velocity of a particle over one gyration is in the same direction, but because the radius of gyration is large, they end up coming at you from all sorts of different angles (possibly even from behind you, though not as common).

Elon himself doesn't realize this.
« Last Edit: 11/15/2013 08:07 am by Robotbeat »
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Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #17 on: 11/15/2013 08:25 am »
Someone, I think it might have been Robot Beat, produced some evidence here that radiation from solar flares does not travel just in a straight line from the sun, so you might need shielding in all directions.

For the purposes of shielding solar radiation I can't imagine why you'd need more than a column. While the flux might not come from the direction of the Sun, it will come from just the one direction at a time. So you "just" need to be able to point it.
Adding to what RB said, if a lunar base only needs 20gm/cm it seems quite manageable for a small area you only need to huddle in for a few hours. It wouldn't be a long column as such.

I reckon if you had a Bigelow-style layout with a lightweight inflated area around a rigid core and all the structural and life support elements huddled around there you could have good shielding for an area in the center.

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #18 on: 11/15/2013 08:31 am »
FWIW, lithium hydroxide is the best shielding material I've found (if you take into consideration liquid hydrogen's impracticality). It's fairly dense, and is about twice as effective by weight than water (or plastic) is and is effective longer than water is (shielding materials tend to nearly plateau in effectiveness as you make them thicker... some even have a region of /negative/ marginal effectiveness for GCRs until you make them very, very thick). It's also a solid at room temp, though it does react with air.
« Last Edit: 11/15/2013 08:32 am by Robotbeat »
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Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #19 on: 11/15/2013 09:21 am »
Would you use Lithium hydroxide on a mars mission though? I looked it up and found mention that it wasnt regenerative (that google search being the sum of my knowledge on the subject :) )
http://en.wikipedia.org/wiki/Carbon_dioxide_scrubber#Regenerative_carbon_dioxide_removal_system
(the link was a bit confusing though, it implies lithium is not a metal)

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #20 on: 11/15/2013 09:50 am »
What do you mean? You'd just use it as shielding material. Doesn't need to do dual purpose as a carbon dioxide scrubber.
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Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #21 on: 11/15/2013 10:12 am »
That's a misconception. It comes from very widely varying angles. The average velocity of a particle over one gyration is in the same direction, but because the radius of gyration is large, they end up coming at you from all sorts of different angles (possibly even from behind you, though not as common).

Not at the same time.

Quote
Elon himself doesn't realize this.

You could fill a book with stuff like that..
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Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #22 on: 11/15/2013 11:12 am »
That's a misconception. It comes from very widely varying angles. The average velocity of a particle over one gyration is in the same direction, but because the radius of gyration is large, they end up coming at you from all sorts of different angles (possibly even from behind you, though not as common).

Not at the same time....
Yes, at the same time. The solar particles are gyrating all over the place at large angles.
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Offline guckyfan

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Re: Mars Direct - Problems and Solutions
« Reply #23 on: 11/15/2013 11:23 am »

Not at the same time....
Yes, at the same time. The solar particles are gyrating all over the place at large angles.

From all directions with similar intensity or would there be a direction where the bulk of the particles come from?


Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #24 on: 11/15/2013 11:35 am »

Not at the same time....
Yes, at the same time. The solar particles are gyrating all over the place at large angles.

From all directions with similar intensity or would there be a direction where the bulk of the particles come from?
Not /exactly/ similar intensity, but generally pretty isotropic, other than I believe downwind which is reduced (but not eliminated).
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Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #25 on: 11/15/2013 03:05 pm »
If you are going fast enough to reach Mars in 3 months; either you use a Hell of a lot of propellant to propulsively capture into Martian orbit - or you are going way too fast for aerocapture!!  :o

It's quicker to do hohmann transfer from Venus distance to Mars, than Earth distance to Mars. It is shorter time of travel, because Venus distance has faster orbital velocity and the distance traveled using  hohmann transfer is shorter from Venus as compared to Earth.

Of course we starting from Earth. It isn't a shorter distance to start from Earth, go to Venus, then go to Mars.
But it is a shorter distance if starting from Venus. It is a even a shorter distance if starting from Mercury distance. Or if you starting from distance halfway between Earth and Mars, and doing hohmann transfer, you travel a longer distance than if did hohmann transfer from Earth distance.

This because a hohmann transfer is 1/2 a year plus some- from Earth 6 months + 2 months.
Rather than 365 days, Venus year is 224.7. Or with 30 day months, Venus year is 7 1/2 months.
So it's 3 3/4 months + 2 months [roughly].
Venus orbital speed is faster, than Earth, but with hohmann transfer, as you near Mars distance you are *roughly* going the same velocity as Mars.

If divide the Venus to Mars hohmann transfer into two parts: The Venus to Mars trajectory that goes from Venus and crosses Earth distance and second part being Earth distance to Mars, the first section is mostly about the faster velocity, and the second part is mostly about a shorter distance.

Or if you were to match the Venus to Mars hohmann trajectory from Earth, you are using  "a Hell of a lot of propellant" to change the vector of Earth orbital velocity of [29.8 km/sec], you get to Mars quicker, because you are traveling a lot less distance as compared to a Hohmann transfer trajectory of Earth to Mars and NOT because you are traveling at a high velocity. So if you do this, it's not a hohmann transfer, but you get to Mars quicker and not have large difference of velocity relative to Mars.

And if you do this from Earth, you get to Mars quicker, than hohmann transfer starting from Venus.

If this is not fast enough, then Mercury to Mars hohmann transfer is even a shorter distance. But I am talking about Mercury distance [or Venus distance], so one can use distance between Venus and Mercury, also.
To reduce the Hell of a lot of propellant, one should start from a high point in Earth gravity well- have the most potential energy as a starting point. Then fall towards earth, and add delta-v at Earth's perigee. Gaining the Oberth effect of high velocity. This also allowing more of the thrust to be occurring at this high velocity, as compared starting from LEO. Or 1 lb rocket fuel at high earth gets more thrust than 1 lb rocket fuel at LEO. So if starting from high in Earth gravity one is going to use less Hell of a lot of propellant, as compared to starting at LEO.

Of course you have to get the rocket fuel up to the the high point in Earth's gravity well- so you paying for this additional energy [if you shipping rocket fuel from Earth's surface].
Of course it would nice to get rocket fuel from the Moon. And it's easier to ship rocket fuel from the Moon to high earth, than to ship it to LEO.

The seemingly logically way to go to Mars, is NASA goes to Moon, mines lunar water, and makes rocket fuel and ships rocket fuel to high Earth orbit. Then it get lots of rocket fuel for Hell of a lot of propellant needed.
But though apparently logical, I would say it doesn't work.
Instead I would suggest, than NASA develop fuel depots, explore the Moon, to determine where there is best locations to mine lunar water. THEN Stop. And go to Mars. To start exploring Mars without first having mined lunar water, and instead ship the rocket fuel needed from Earth to high Earth.
If NASA had unlimited budget and dictatorial power, and was capable mining stuff on Earth in fashion which was profitable, than NASA mining lunar water could make sense.  But this is not reality.

Instead what you want is independent body, making the decision of whether lunar water is actually minable- that all the investment needed to do this can be cheaper than shipping the rocket fuel from Earth.
So lunar water should mined if this would be profitable to do. And throwing public money at it, doesn't make this occur, even if one could get the money from Congress.
So people might think it's worth it, if NASA were to "try" to mine lunar water. I don't.
« Last Edit: 11/15/2013 03:24 pm by gbaikie »

Offline MikeAtkinson

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Re: Mars Direct - Problems and Solutions
« Reply #26 on: 11/15/2013 03:58 pm »

Not at the same time....
Yes, at the same time. The solar particles are gyrating all over the place at large angles.

From all directions with similar intensity or would there be a direction where the bulk of the particles come from?
Not /exactly/ similar intensity, but generally pretty isotropic, other than I believe downwind which is reduced (but not eliminated).

I've tried to do a google search for this, but have come up blank. H+ solar wind has a radius of gyration of between 10km and 100km according to one source, but their velocity of gyration will be small (I think) in comparison to their forward velocity, so should seem to come from one direction.

I've found nothing about Coronal Mass Ejections, if I understand correctly they carry a magnetic field with them so the solar wind results don't hold.

As this is so important for spacecraft shield design do you have a reference or can you provide a calculation

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #27 on: 11/15/2013 06:11 pm »
....but their velocity of gyration will be small (I think) in comparison to their forward velocity, so should seem to come from one direction. ...
incorrect. the angle can be quite large. Anywhere from 0 to almost 180 degrees.
« Last Edit: 11/15/2013 06:11 pm by Robotbeat »
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Offline RanulfC

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Re: Mars Direct - Problems and Solutions
« Reply #28 on: 11/15/2013 07:10 pm »
I loved "Mars Direct" when it first came out because it seemed to answer the "problems" with the whole "90-day-study" massive program. But I had doubts even from the initial article. "The Case for Mars" only solidifed and hardened those doubts. Zubrin's "solution" seemed simply to be a road-map for an "Apollo-to-Mars" type program with the same built in dead ends and "expectations" that once accomplished the government would for some unspecified reason NOT cancel it at some point.

Apollo wasn't they "way" to do the Moon if you intended to go back and really stay and "Mars Direct" falls right into the same rut. It "gets" you there faster at the expense of NOT building any "staying" power over time along with high cost and vulnerabilit to changing priorities of government.

The main problem with the 90-day study was that it took GB1 at his word and "planned" to not only go to Mars but to extend man's reach to the whole solar system :) Not something that anyone really expected to be the "goal" of the program :)

Mars Direct is the "solution" if your "problem" is how to launch a "Mars" mission with only a couple of BFR launches per year. But if that is NOT your only "problem" then Mars Direct isn't really going to "solve" your other problems for you.

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Re: Mars Direct - Problems and Solutions
« Reply #29 on: 11/15/2013 07:14 pm »
Mars Semi-Direct has always been my preference for the concept - with a dedicated MAV, so you don't have to manufacture heaps of ISRU propellant to fly all the way to Earth, just to Martian orbit. Similar to NASA's DRM-3 but with less 'bloat'. Would still like a HLV capable of throwing 40 tons to TMI, but perhaps a commercially-derived launcher by Space X or similar. If the Commercial HLV was partially or fully re-usable, all the better.

Though with a Propellant Depot(s) in Earth Orbit or one of the Lagrange points, you only need a booster with a big enough payload shroud to launch an empty, or propellant-offloaded Earth Departure Stage to the Depot. Delta IV-H or Falcon Heavy are powerful enough to get a horizontal configured Mars Lander or Transit Hab up to the Depot, then another launcher sends an EDS to the Depot, fills it, then the Lander/Hab mates with the fueled EDS and gets on its way...

Anyone good at doing Powerpoint illustrations for this DRM?! ;)
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Re: Mars Direct - Problems and Solutions
« Reply #30 on: 11/15/2013 10:56 pm »
Hey, gbaikie - something about my Hell of a lot of propellant bothering you? ;)

I was merely pointing out that if you are traveling to Mars from Earth orbit at a velocity that would get you there in 3 months (what shape "Hohmann trajectory" would that be?! And how fast - 11kms?) then you are going to need a lot of delta vee to scrub that velocity for a propulsive Mars orbit insertion; even a very 'lopsided' orbit. And as for doing the 'seven minutes of terror' direct descent to Mars at that kind of velocity...
« Last Edit: 11/16/2013 03:56 am by MATTBLAK »
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Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #31 on: 11/15/2013 11:14 pm »
It wouldn't be a Hohmann transfer.

http://en.wikipedia.org/wiki/Hohmann_transfer_orbit
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Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #32 on: 11/15/2013 11:50 pm »
What do you mean? You'd just use it as shielding material. Doesn't need to do dual purpose as a carbon dioxide scrubber.
Oh ok. My argument is that you probably do not need to include any mass just for shielding a 'panic room' (for solar flares) based on the numbers in that earlier link. A bigelow type design seems ideal if you want to cluster all your structural mass and life support, supplies etc around one small column in the center.

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Re: Mars Direct - Problems and Solutions
« Reply #33 on: 11/16/2013 01:22 am »
It wouldn't be a Hohmann transfer.

http://en.wikipedia.org/wiki/Hohmann_transfer_orbit

 
At those sorts of velocities, you are quite correct.
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Offline M129K

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Re: Mars Direct - Problems and Solutions
« Reply #34 on: 11/17/2013 10:51 am »
NASA can't afford to develop and operate their own launch vehicles anymore.

So they can't afford the 5-10 billion for an HLV, but they can afford the over 100 billion dollars to go to Mars? Right.

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #35 on: 11/17/2013 10:55 am »
NASA can't afford to develop and operate their own launch vehicles anymore.

So they can't afford the 5-10 billion for an HLV, but they can afford the over 100 billion dollars to go to Mars? Right.

If it costs that much, they're not going. Perhaps you missed the thread title. Mars Direct is all about avoiding the Battlestar Galactica sticker shock. I think it does a pretty good job of that, but falls down with the comparisons to the 1960s - particularly the assumption that recreating a Saturn V class vehicle is a viable option for future exploration.
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Offline M129K

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Re: Mars Direct - Problems and Solutions
« Reply #36 on: 11/17/2013 11:04 am »
If it costs that much, they're not going. Perhaps you missed the thread title. Mars Direct is all about avoiding the Battlestar Galactica sticker shock. I think it does a pretty good job of that, but falls down with the comparisons to the 1960s - particularly the assumption that recreating a Saturn V class vehicle is a viable option for future exploration.

I recall Mars Semi Direct being estimated at 55 billion dollars back in 1993. In modern day dollars, that's almost $90 billion. Mars Direct, even when avoiding an HLV, would still be well over 50 billion dollars and probably closer to $80 billion.

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #37 on: 11/17/2013 11:28 am »
Most of the cost is the NASA-use-only HLV. Both development and operations.

Using commercial launchers could eliminate a lot of that cost.

Of course, there's plenty of other ways you could make it more affordable, but I think that's the big one.
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Offline M129K

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Re: Mars Direct - Problems and Solutions
« Reply #38 on: 11/17/2013 11:40 am »
Here is a study from 2007 about a mission to Mars, and includes a detailed cost breakdown. Launch vehicles are $14 billion from the $96 billion, and those LVs are Ares 1 and Ares V, two launchers which were anything but low cost, even for HLVs. The general mission architecture isn't too different from Mars Direct, and while LVs are a significant part, they are not a majority.

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #39 on: 11/17/2013 11:51 am »
Are you kidding me?

Quote
No In-situ Propellant Production: No ISRU (In-Situ Resource Utilization) or local production of liquid propellands (typically Methane) or buffer gasses (N2, O2) is assumed for this study. By eliminating ISRU, we eliminate a development and operational risk assiciated with this technique, as well as the costs to demonstrate the technology as a precursor mission. We recognize that the availability of in-situ propellants would have a significant and positive impact on the required transportation system, but the current funding climate at NASA does not place a high priority on developing a mature propellant production capability on Mars by 2030.

That's the entire lynchpin of the architecture, and the reason why the costs are supposedly so much lower for Mars Direct.

Oh, and none of the development costs for the HLV are included in the costing in that paper. So it's not just 14% of the total cost, plus the facilities costs, etc, it's some unspecified amount. As we saw, that amount kept growing and growing for Ares I and Ares V..
« Last Edit: 11/17/2013 12:05 pm by QuantumG »
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Offline M129K

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Re: Mars Direct - Problems and Solutions
« Reply #40 on: 11/17/2013 01:30 pm »
Are you kidding me?

Quote
No In-situ Propellant Production: No ISRU (In-Situ Resource Utilization) or local production of liquid propellands (typically Methane) or buffer gasses (N2, O2) is assumed for this study. By eliminating ISRU, we eliminate a development and operational risk assiciated with this technique, as well as the costs to demonstrate the technology as a precursor mission. We recognize that the availability of in-situ propellants would have a significant and positive impact on the required transportation system, but the current funding climate at NASA does not place a high priority on developing a mature propellant production capability on Mars by 2030.

That's the entire lynchpin of the architecture, and the reason why the costs are supposedly so much lower for Mars Direct.

Oh, and none of the development costs for the HLV are included in the costing in that paper. So it's not just 14% of the total cost, plus the facilities costs, etc, it's some unspecified amount. As we saw, that amount kept growing and growing for Ares I and Ares V..
No, I'm not kidding you. The development costs for an HLV could be about 5 billion dollars according to Zubrin, and the cost estimates for Mars Direct assumed a single, 120 ton HLV based off of existing systems, rather than a completely new 130 ton system and a new 25 ton system sharing almost nothing with the shuttle like the study I linked to assumed. Both development and operational costs were far lower for the original Mars Direct plan. Mars Direct would be very similar in cost if a cost estimate was done today with the same LV assumptions, and launcher cost would still be a relatively small chunk of the architecture. Mars doesn't become magically attainable when you don't develop any new LVs. In my opinion, it puts it even further away.

Also, ISRU didn't make Mars Direct so much cheaper, it reduced the mass of the systems to allow fewer launches and no on-orbit assembly, the study I linked to did this by reducing crew size. It did not have huge influences on the cost of the architecture, aside from one or two fewer launches and a simpler (and uncomfortably small) return craft.

Edited for grammar and clarity.
« Last Edit: 11/17/2013 01:59 pm by M129K »

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #41 on: 11/17/2013 02:51 pm »
Hey, gbaikie - something about my Hell of a lot of propellant bothering you? ;)
I am merely agreeing with you. Or I am not bothered by the Hell of a lot of propellant.

Or Robert Zubrin offered idea of government buying a lot space launch. Hmm where
is that ref. Here:
http://www.thespacereview.com/article/1850/1
Similarly I think US government should not be shy about buying lots rocket propellent.
I don't think the engineer obsession over using least amount rocket fuel [propellent/delta-v] and damn the time it takes [time developing project on ground and time traveling in space] is good path.

Quote
I was merely pointing out that if you are traveling to Mars from Earth orbit at a velocity that would get you there in 3 months (what shape "Hohmann trajectory" would that be?! And how fast - 11kms?) then you are going to need a lot of delta vee to scrub that velocity for a propulsive Mars orbit insertion; even a very 'lopsided' orbit. And as for doing the 'seven minutes of terror' direct descent to Mars at that kind of velocity...


And telling you, not using a Earth to Mars Hohmann trajectory, rather using, say, a Venus Hohmann trajectory starting from Earth orbital distance.

If we were are at Venus and did Hohmann trajectory to Mars, one arrives at Mars about about same velocity difference as if we started at Earth and did Earth to Mars Hohmann trajectory.

So the Hell of a lot of propellant is used to match a trajectory of a Venus to Mars Hohmann trajectory as it would cross Earth orbital distance- you starting the Venus to Mars Hohmann trajectory at Earth distance.  This is not a "normal" Hohmann trajectory. If you calling a  New Horizon, Earth to Jupiter hohmann transfer which crosses Mars orbit, a "normal" fast Hohmann trajectory to Mars

But to be precise if at anything going to Mars in less than 8 month can not use a Earth to Mars Hohmann trajectory.
Or for example, one can never use ion thrust [or any low thrust] and do anything resembling a Hohmann trajectory.

Or going to Mars in 7 months was not a Earth to Mars Hohmann transfer. It was a Hohmann transfer beyond Mars orbital distance, with patched conic to adjust the trajectory to meet Mars orbital distance.

In kind of weird way what I am talking about is a truer hohmann transfer to Mars than these Hohmann transfers with patched conic [7 months to Mars done by Opportunity Rover mission].
And in terms any ion thrust trajectory, this is straight up [not weird] more resembling a hohmann transfer.

Because an essential aspect of hohmann transfer is "instantaneous" thrust. And what I am talking about would also be an "instantaneous" thrust.

So everything you ever heard regarding fast trips to Mars are not hohmann transfers- what I am talking is can be said to be the closest thing to hohmann transfer or it is mimicking a hohmann transfers from different orbital distance other than Earth [Venus and Mercury type orbital distances].

Edit: Story. Inhabitants of Venus send spacecrafts to Mars. They say how lucky they are because they can get to Mars quicker than any inhabitant on Earth. One day the Venus inhabitants discover gravity assists, wow, now we get to Mars even faster, with gravity assist off Earth and changing our trajectory so we can get to Mars even faster.
[Edit, edit: The Venus space engineers are happiest, because now they can get to Mars with less delta-v, by using gravity assist off Earth {and it's faster}.]
But they have to wait for times in which Earth gets in the right spot. So the inhabitants of Venus, mostly continue their normal hohmann transfers to Mars, except when planets align so they use Earth to add some velocity. Plus gravity assist using Earth gives them more launch opportunities.

Now the trajectory of that the inhabitants of Venus were using planet Earth as gravity assist to get to Mars can be used from Earth.
You make a spacecraft match the same velocity [speed/vector] as spacecraft from Venus would have had, and it will do the same trajectory.
In addition Earthling can use this trajectory more often than inhabitants of Venus [Earthlings don't need planet Venus to be in right orbital position]. Nor do Earthlings need to use Venus exact orbital distance, therefore with varying amounts of delta-v used, one has bigger *launch* window to get to Mars.
« Last Edit: 11/17/2013 04:26 pm by gbaikie »

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #42 on: 11/18/2013 06:04 pm »
Problem: the ERV cabin is way too small for so long. I recall it being only 7 ton, about as much as a Dragon. A slightly modified architecture a la Mars Semi Direct would remedy this, but I can't see it being solved within the original two launch architecture.

Quote
a) There is no HLV in the 100 ton to LEO class available, and there is no LH2/LOX Earth departure stage of the required size available.

I see no reason either of those couldn't be developed. You're going to Mars, an HLV is only a drop in a full bucket of expenses.

Depending on the design of the ERV, perhaps it could have an inflatable Bigelow module to act as the habitat for the ride home?  Perhaps if there was a 3-component ERV.  An ascent/TEI propulsion module, a Hab module, and the small ERV module.  They are together in a stack for EDL on Mars, with the propulsion module doing a propulsive laning on Mars, using up it's methalox propellant. Then the on-board LH2 is used to refill those tanks.  Those same tanks and engines are then used to lift off of Mars and directly through TEI. 
I picture an Apollo like S-IVB/LEM/CSM stack, but shorter and wider and biconic for Mars EDL, with TPS on one side of the stack.   Like much of the Mars Direct ERV graphics floating around on the web.
After ascent and TEI, the propulsion module is jettisoned.  When it is, it takes an interstage adaptor shell with it, revealing an uninflated BA-330-like hab module.  (like the S-IVB petals, or something)  The crew in the ERV itself for ascent and TEI, detatches, and turns around, like Apollo, and then docks wtih the hab module the way Apollo did with the LEM.  The crew can then enter the Hab module and stay in it for the trip home.  On final approach to Earth, the crew re-enters the ERV, and jettisones the Hab module to burn up.  They go directly to Earth EDL.

That's just one idea, there'd probably be other and better ways to do it.

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #43 on: 11/18/2013 06:34 pm »
A quick review of the Mars Direct mission mode:


Quantum.  Good thread!   I've advocated myself, when speculating on a future NASA DRM, or some potentical SpaceX mission, to start as simple as possible in your concept.  The lowest common denominator that might land people on Mars and get them home with as little development and complexity as possible.  Once you have that, start adding in new development and complexity as needed to get the functionality that is required.  The most simple way is probably the least capable way, although perhaps the cheapest.

Mars Direct is pretty simple.  About the only think more simple would be to have a superheavy lift vehicle of some kind (SpaceX FXH or FXX for example if they have over 200mt of LEO capacity) and do it all with a single craft.  You send the crew on the way out on that single launch of that single vehicle, send them directly to the Mars surface, and then directly back through TEI from the surface and directly to the Earth's surface.  That's about as -basic- of a Mars mission as there could be.  If you could get it to work, you'd probably have very little capability for surface equipment.  (And you need a super heavy lift vehicle).

So...you start with an all-in-one launch, and work your way out from there until you get the desired balance of simplicity and cabability.

A quick review of the Mars Direct mission mode:

Fundamental Problems

1)
 a) There is no HLV in the 100 ton to LEO class available, and there is no LH2/LOX Earth departure stage of the required size available.
 b) As there is no current commercial use for a 100 ton to LEO class vehicle, the total cost of development and operations would have to be borne by NASA.
 c) The average flight rate of one launch per year (two every two years) is too low to anticipate reliable operations, increasing both loss of mission and loss of crew risk.
 d) The low flight rate also increases operations cost.

2)
 a) The artificial gravity system is immature, with no tethers of the required length ever flown successfully in space.
 b) Without artificial gravity, the tuna-can hab is possibly too small to maintain crew health in zero-g.

3)
 a) Radiation exposure is possibly too harsh, depending on the solar cycle.

4)
 a) No nuclear reactors are available and this is seen by some as a political roadblock.


But SLS Block 1B is most likely in the works, so we may have one available and it'll be right at about that 100mt class, with the ability to send well over 30mt through TMI.

We may or may not need artificial gravity for a 6-month trip each way, with exercise and other methods to combat micro gravity.  Plus after the first 6-month drip, the astronauts will only be experiencing 1/3 earth gravity rather than the full pull of Earth gravity, so they should be quicker to adapt and get up and running once on the surface.  Once on the Mars surface, running around regularly in their pressure suits and working should help get them to get back into shape.  especially after a long duration surface stay.  Potentially they could get back to about where they were prior to launch from Earth.  Even in the hab, they could have weight suits on to give them weight similar to that on Earth.  That's the nice thing about having -some- gravity.  With -some- gravity, you can add mass to approximate weight resistance on your muscles.  In zero-G, no amount of mass you add will do anything.  (As a side note, I think that's one major study that some sort of long term lunar outpost would be good for.  With a long stay on the Lunar surface, with the aid of weight suits, and regular EVA work with heavy EVA suits, can muscle and bone loss be effectively combated?)

After the 6-month trip home, the astronauts shouldn't be any different than if they'd just gotten off the ISS.  and there will be crews and medics to help them as with returning ISS crews.

Radiation exposure is a concern.

Tuna Can Hab could be augmented with an expendable Bigelow mission module if necessary.

A nuclear reactor would probably be a problem politically.  I think Steve Pietrobon estimated an isotope power generator could be made of sufficient size to convert the LH2 to methalox for such a lander though (although that might have been a Mars Semi-Direct lander which has lower fuel needs.  I can't quite remember)
Also to look at, is there any way to robotically deploy a solar array large enough to do the job?  It'd have a couple of years to do it so it doesn't need to be particularly fast.  Although you want to get it done before you boiloff too much LH2 in a slow process.


Remedies

1)
 a) Use commercially available rockets to maximize cost sharing and higher launch rate benefits.
 b) As these are at least half the payload-to-LEO class (53t for Falcon Heavy), and of smaller core size (~5m diameter payload), at least the habitat (~9m diameter) will have to be redesigned.
 c) The various parts of the ERV and hab will need to be staged and assembled on-orbit during the two year build-up between each Mars transit window.
 d) Docking of fuel tanks can be done last to minimize boil-off of cryogenic propellants.

2)
 a) Although artificial gravity experiments could be done, the now modular habitat design allows larger, while lighter, structure, suggesting a zero-g transit may be preferred.
 b) Astronauts will utilize exercise equipment and zero-g mitigation drugs to maintain bone and muscle mass.

3)
 a) A long column of water can be used as a solar radiation shield.

4)
 a) Use flexible photovoltaic power. The rover will need to be able to unpack and lay out the power system under remote control.

Possible, but probably unlikely that SLS will go away.  And if it does it might damage NASA enough that no Mars program succeeds it.  Depending on how it's death is handled, and the ramifications thereof.

Certainly something like FH could be used in such an event...if there was still a NASA HSF program after an SLS cancellation anyway.  But perhaps I'd be better to just aid SpaceX in developing their Next Gen methalox HLV?  And have NASA partner directly with SpaceX on a Mars plan where SpaceX develops the LV for their own purposes (assuming Elon plans to develop it anyway...and it looks like that's the case) and a the vehicles that get cargo to the surface, and NASA can focus specifically on development of that cargo.  Rovers, inflatable surface habs, etc.  SpaceX is the transportation service for the packages that NASA makes to send. 

A hypothetical future where SLS is cancelled, and NASA is reorganized and reprioritized to facilitate such radically new PoR would not take place for some time anyway.   Perhaps time enough where SpaceX's plans for that bigger LV of their which would mean less in-orbit assembly would be close enough to go with?
And crews could still be launched on Dragon on F9 for EOR with the Mars stack prior to TMI, so you don't have to put crews on some new big HLV.  It can be a cargo launcher only.




Offline catiare

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Re: Mars Direct - Problems and Solutions
« Reply #44 on: 11/18/2013 06:42 pm »
The link below points to a paper from 2006, called Mars for Less, where a variant of the Case for Mars solution was made using 25-tonne rockets to LEO. This was pre-SpaceX-FH9. I'm sure a "middle of the road" variant can be accomplished with less amount of launches using FH9.

http://www.marsdrive.com/Libraries/Downloads/Reaching_Mars_for_Les_-_The_Reference_Mission_Design_of_the_MarsDrive_Consortium.sflb.ashx

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #45 on: 11/18/2013 06:43 pm »

I am not really in favor of 6 month travel times {or 8 months}- prefer 3 month. And with 3 month I would skip any attempt of using artificial gravity. And only use one ship.
But if going to do 6 month and if going to have artificial gravity- then maybe two ships??

I'm no expert, but based on my limited understanding, there are problems with 3 month travel times.

The 6 month travel time to Mars is like the Apollo 3 day travel time to the Moon.  We could get there faster, but then we'd be going so fast that it would take an unreasonable amount of propellant for LOI.
As I understand Mars is the same way.  To get there faster, you need to go faster.  To go faster you need more dV requirements to brake into Mars orbit.  I think much faster than the 6- month time, your velocities are so fast that aerobraking/aerocapture become difficult or impossible.  (if I'm incorrect, someone with more knowledge please correct me.  :-)  )  and then you need a lot of fuel to brake.

So that's part of the reason why that 6 month transit time is so often uses as the minimum time. 
I think one of the only concepts I've seen that speeds that up is VASIMR.  And that's because it is so ISP efficient, it accelerate to VERY fast speeds for the first half of the trip, and then decelerates itself for the 2nd half, so when it arrives at Mars it can perform it's own MOI.  Otherwise it'd get to Mars going so fast it'd fly right on by out for deep space.

VASIMR is pretty cool but i'd not want to hitch my wago to it at first, and stick with more traditional chemcial tech to get things going, while keeping VASIMR cooking in the background with the hope someday technology catches up with it and it becomes feasible.  Now you have a really great "Mars Colonial Transporter".
;-)


Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #46 on: 11/18/2013 06:43 pm »
If you are going fast enough to reach Mars in 3 months; either you use a HELL of a lot of propellant to propulsively capture into Martian orbit - or you are going way too fast for aerocapture!!  :o

Whoops.   Posted my last before I read down to Matt's comments here.

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #47 on: 11/18/2013 06:56 pm »
Mars Semi-Direct has always been my preference for the concept - with a dedicated MAV, so you don't have to manufacture heaps of ISRU propellant to fly all the way to Earth, just to Martian orbit. Similar to NASA's DRM-3 but with less 'bloat'.


Agreed.  Although with MArs Semi-Direct you need to bring your TMI propellant with you and put it in Mars orbit for years.  The appealing thing about something like Mars Direct is you bring LH2 with you, but you make both Ascent and TMI prop on the surface.  Although, I think Mars Semi-Direct actually pencils out to less mass thrown through TMI from Earth despite that.  Bacause you have to get so much more dry mass off the surface.


Would still like a HLV capable of throwing 40 tons to TMI, but perhaps a commercially-derived launcher by Space X or similar. If the Commercial HLV was partially or fully re-usable, all the better.


SLS Block 1B looks like it will get in excess of 30mt to LEO.  Almost 33mt with MB-60's.  My guess is with advanced boosters added to Block 1B...making a Block 2B...you'd get enough of a boost to get 40mt or so through TMI.  So there you go. 
SpaceX may do that or more, depending on how their MCT development unfolds.


Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #48 on: 11/18/2013 07:30 pm »
If it costs that much, they're not going. Perhaps you missed the thread title. Mars Direct is all about avoiding the Battlestar Galactica sticker shock. I think it does a pretty good job of that, but falls down with the comparisons to the 1960s - particularly the assumption that recreating a Saturn V class vehicle is a viable option for future exploration.

I recall Mars Semi Direct being estimated at 55 billion dollars back in 1993. In modern day dollars, that's almost $90 billion. Mars Direct, even when avoiding an HLV, would still be well over 50 billion dollars and probably closer to $80 billion.

While I'd never pretend Mars is cheap, there's a few factors to consider when looking at Zubrin's estimes.

1)  No HLV in development, unlike today. Money's already been spent on it, where Zubrin was probably factoring a full HLV development into his estimates.

2)  No BLEO spacecraft in development of any kind.  Today we have Orion well along in development, with Dragon being a potential base for other cargo and crew vehicles capable of going to Mars and landing back on Earth.  In a new Mars plan, we could either use Orion or a crewed Dragon/RedDragon as a building block.

3)  No inflatable hab tech in 1993.  Today we have various Bigelow options which at least have had prototypes flown, and another due to go to the ISS for testing in a few years.  An inflatable module has the potential to be used as a lower cost/larger volume Habitat for tranfer to Mars, from Mars, and on the surface of Mars.  Some NASA DRM's have shown landers with inflatable upper decks.  And I think that tech could be easily translated into a separate deployable surface habitat.

4)  No methalox engines in 1993, which Zubrin wanted to use for in-situ propellant.  Today we have SpaceX with a methalox engine in some phase of development, and some work done by the Russians on one too.
As well as various degreees of methalox RCS thruster research. 

5)  We've landed a few rovers on Mars since 1993, and probably have better understanding if what we need to design for and what we don't.  That could make things cheaper...or more expensive...depending on that knowledge.  But usually more knowledge translates into cheaper price, as you don't need to design in for things if you know they won't be a consideration.

6)  Various long term systems have been developed for the ISS which would be translated into a Mars mission like liquid recycling.  In 1993 all we pretty much had was the shuttle and I think we used water from the fuel cells and just dumped it when used up.  I'd imagine Zubrin assumed water recycling as a tech to develop for MArs so we don't have to take 2 years worth of water for a crew with us.  That's a tech that isn't a brand new development any more. 

7)  Zubrin assumed development of a nuclear rover.  That might be too politically problematic.  But...we have much more efficient solar cell tech which could be used instead with much less development costs.  Perhaps isotope power as well.

8)  We didn't have any development of a new rover as NASA has today.  So that would be a brand new development, where now NASA has been working on some various concepts which would be utilized for a Mars rover.

9)  COmputers.  In 1993 I think a 486 PC was the state of the air in commercial user computing.   Now we have many times that power in our phones.  So I think certain electronic things that would have been an expensive development in 1993, are no as much today.

So...Mars will be expensive...no doubt.  But, in 1993 there wasn't much available that was applicable to Mars in either NASA or teh private sector.  Today we have new capsules, new LV's, new long term crew tech, new habitat tech, new engine tech, and much, MUCH faster/better/more reliable computers. 

If NASA could be hauled in to live in the realm of practicality instead of the most bleeding edge possible, then some of these things could reduce development time and costs.
But if NASA instead tries to develop everything brand new and cutting edge...then they'll bypass all the developments of the past 20 years and make everything as expensive as possible.  And we won't go anywhere.


Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #49 on: 11/18/2013 08:14 pm »
In a later chapter of The Case For Mars, an on-orbit refueling variety of Mars Direct is outlined.

The discussion is in the context of SSTOs, but a TSTO with an upper stage that can do the required ~5km/s delta-v from the surface of Mars is actually more appropriate.

Falcon 9-R would be much too small, but if it's just a pathfinder for a larger vehicle then it's apparent how it could be used for a Mars Direct-style minimal mission.
Human spaceflight is basically just LARPing now.

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #50 on: 11/19/2013 01:45 pm »

I am not really in favor of 6 month travel times {or 8 months}- prefer 3 month. And with 3 month I would skip any attempt of using artificial gravity. And only use one ship.
But if going to do 6 month and if going to have artificial gravity- then maybe two ships??

I'm no expert, but based on my limited understanding, there are problems with 3 month travel times.

The 6 month travel time to Mars is like the Apollo 3 day travel time to the Moon.  We could get there faster, but then we'd be going so fast that it would take an unreasonable amount of propellant for LOI.
Nothing has ever gotten to Mars in 6 months, unless one includes fly-by or crossing Mars orbit- such as New Horizon: "Launch date: January 19, 2006, 19:00:00 UTC ...
On 7 Apr 2006 at 10:00 UTC, the spacecraft passed the orbit of Mars"
http://en.wikipedia.org/wiki/New_Horizons
[**Edit: I am not aware of a spacecraft which has entered Mars orbit or landing on Mars surface which arrive at Mars from Earth in less than 6 1/2 months (195 days)].
It launched on January 19 and it got to Mars orbital distance on 7 Apr 2006, so it reached Mars orbital distance in less than 3 month, but there no means that a spacecraft could stop at Mars from such a trajectory.

As far getting to Moon, 3 days is the time it took to get from LEO to lunar orbit with Apollo :

[Launch date: December 7, 1972, 05:33:00 UTC]
"At 3:46 AM EST, the S-IVB third stage was re-ignited to propel the spacecraft towards the Moon.

At approximately 2:47 PM EST on December 10, the Service Propulsion System engine on the Command/Service Module ignited to slow down the CSM/Lunar Module stack into lunar orbit"
http://en.wikipedia.org/wiki/Apollo_17

Edit: Getting to the Moon in 3 days was not like getting to Mars in 6 months, rather it's like getting to Mars in 8 months

Quote
As I understand Mars is the same way.  To get there faster, you need to go faster.  To go faster you need more dV requirements to brake into Mars orbit. 
This true, if you don't change the vector of Earth's orbital velocity.

Up to this point in time, changing a vector of a trajectory has only done with gravity assists rather
then using the thrust of a rocket.
[Though in terms minor or multiple/constant impulses these are always changing the vector. So one can say changing the vector is done when using high efficient low thrust rocket engines- such as ion engines [and yet to be flown VASIMR or other concepts] and all mid-trajectory course corrections or patched conic are also changing the vector with thrust of a rocket].
 
Quote
I think much faster than the 6- month time, your velocities are so fast that aerobraking/aerocapture become difficult or impossible.  (if I'm incorrect, someone with more knowledge please correct me.  :-)  )  and then you need a lot of fuel to brake.

Right. And I am talking about changing earth's orbital velocity's [29.8 km/sec] vector.

So hohmann transfer to go out towards Mars by adding to Earth's orbital velocity, or to go inwards to
Venus, one reduces earth's orbital velocity.
With a hohmann trajectory it appears to slowly bend away from Earth's orbital path.
Or one could say Earth path is curved due to it's velocity around the sun, if you increase this velocity
it's less curved by the gravity of the sun.

Hohmann transfer is throwing a baseball either in direction train is going or behind the train.
I am talking about throwing the ball sideways from the train.
This requires a lot of delta-v to get to Mars.

Quote
So that's part of the reason why that 6 month transit time is so often uses as the minimum time. 
I think one of the only concepts I've seen that speeds that up is VASIMR.  And that's because it is so ISP efficient, it accelerate to VERY fast speeds for the first half of the trip, and then decelerates itself for the 2nd half, so when it arrives at Mars it can perform it's own MOI.  Otherwise it'd get to Mars going so fast it'd fly right on by out for deep space.

With VASIMR, or high high thrust, high efficient propulsion you not using a Hohmann transfer.

Or to use a Hohmann transfer if you have to have an instantaneous thrust at apogee or apoapsis- otherwise you are changing the vector of orbit/trajectory.

What I am talking about is efficient means to change vector.
Which can only done with high thrust- or chemical rockets.  I am talking about traveling a shorter distance- not higher velocity.

So major part of the reason, New Horizon reached Mars orbital distance in less than 3 month is it
traveled a shorter distance to Mars orbit.
Because the sun escape trajectory has "higher angle" relative to earth's orbital path than a normal Earth to Mars Hohmann transfer.
And what I am talking about would have a "higher angle" than New Horizon but traveling slower velocity throughout the trajectory and it will not be like New Horizon which crosses Mars orbit at high angle, instead it will travel parallel to Mars orbit and slower than Mars orbital velocity.
And if it doesn't enter the gravity of Mars, then it falls back toward the sun.
Or it's orbital trajectory which is has it's Aphelion at Mars distance and Perihelion at around Venus orbital distance.
So if one does a hohmann transfer from Venus to Mars, the angle that this trajectory crosses Earth orbital path is at higher angle than New Horizon angle to Earth's orbital path.
And it will travel shorter distance. And the shorter distance of New Horizon is main reason New Horizon got to Mars orbital distance in less the 3 months- rather than the total velocity it achieved by adding to Earth's orbital velocity.

 
Graphics:
http://forum.nasaspaceflight.com/index.php?topic=25742.0 
The top post has two pictures of different trajectories, one New Horizon and the other Cassini.
Cassini going to Jupiter, New Horizon going to fly by Pluto.
New Horizon on graph says it's going 154,000 kph
Cassini has 137,000 kph
New Horizon appear nearly parallel to Earth orbit, Cassini at crossing at high angle.
Both are 5 days out from Earth [Cassini did gravity assist off Earth, having got gravity assists from inner our planets, and it does these gravity assist *mainly* to change it vector- not *mainly* to increase it's speed/velocity].

So obviously don't want as much velocity as Cassini [it went to Jupiter for gravity assist to Saturn] but want this similar angle relative to earth but not have such angle on arrival to Mars orbital distance [because you going slower].


« Last Edit: 11/20/2013 12:15 am by gbaikie »

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #51 on: 11/19/2013 05:39 pm »
Direct-entry, my friend! ;)

10 gees, bah! Give me 20! They can take it!
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline M129K

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Re: Mars Direct - Problems and Solutions
« Reply #52 on: 11/19/2013 05:43 pm »
Direct-entry, my friend! ;)

10 gees, bah! Give me 20! They can take it!
Give em a nice suit made out of 2 meters of gel and I'm sure they won't mind  ;D

Offline Zed_Noir

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Re: Mars Direct - Problems and Solutions
« Reply #53 on: 11/19/2013 07:59 pm »
Direct-entry, my friend! ;)

10 gees, bah! Give me 20! They can take it!
Give em a nice suit made out of 2 meters of gel and I'm sure they won't mind  ;D

Take a page from some recent SciFi writers. Use an oxygenated water filled capsule for taking high accelerations in a spacecraft.  ;D

Heck you would be carrying the water for radiation shielding & consumption anyway.


Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #54 on: 11/19/2013 09:27 pm »
Nothing has ever gotten to Mars in 6 months, unless one includes fly-by or crossing Mars orbit-

Wow, that took three minutes of googling:

Mars Odyssey launched 7 April 2001, Mars orbital insertion on 24 October 2001.

Unless you intend to make some argument about rounding, that's 6 months isn't it?
Human spaceflight is basically just LARPing now.

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #55 on: 11/19/2013 10:34 pm »
The link below points to a paper from 2006, called Mars for Less, where a variant of the Case for Mars solution was made using 25-tonne rockets to LEO. This was pre-SpaceX-FH9. I'm sure a "middle of the road" variant can be accomplished with less amount of launches using FH9.

http://www.marsdrive.com/Libraries/Downloads/Reaching_Mars_for_Les_-_The_Reference_Mission_Design_of_the_MarsDrive_Consortium.sflb.ashx

Very interesting.  Looks kinda like Mars Direct, but with something like an Atlas V-heavy.  Looks like it utilizes the economics of scale.  Keep things standardized and simple, and make a lot of them.  namely the cyro stages.  Launch the ERV, and then launch a bunch of Centaurs or DCSS's to LEO and stack them up behind it and do a multiple stage boost.  (Actually it'd be a CPS with a fairly long duration loiter capability)
Wonder if there'd be problems with so many stages linking in orbit and operating properly?

On the subject of their ERV and Hab lander, I'd been pondering this myself.  What is does look like?  Kinda like a big dragon capsule to me.  It's been shown that a Dragon capsule could land on Mars with it's LAS system and heat shield.  So...could that just be scaled up?  A much larger Dragon Capsule, with methalox engines on it's sides rather than hypergolic superdracos?  It would trade a smaller heat shield with less dV for more propulsion to make up for it.  I think such a craft to get on the surface pretty readily, but getting it back off the surface could be an issue with it's engines angled off in the sidewall.  That makes for a big performance hit I think for ascent and TEI.  So, is there any mechanical way to reposition those sidewall engines so that they do point directly down?  Could they pivot, or actuate, out and down so the downward plume would not impinge on the craft too much?
They wouldn't need to do that during EDL, just while on the surface prior to lift off. 

No need for that on the Hab lander.  It's not getting back off the surface.

Side mounted engines also means the lander itslef can be closer to the surface, with out landing on it's engines.

This would assume a larger LV like FX/FXX/MCT rather than the smaller EELV class in this paper.

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #56 on: 11/19/2013 11:53 pm »
Nothing has ever gotten to Mars in 6 months, unless one includes fly-by or crossing Mars orbit-

Wow, that took three minutes of googling:

Mars Odyssey launched 7 April 2001, Mars orbital insertion on 24 October 2001.

Unless you intend to make some argument about rounding, that's 6 months isn't it?

That is close to 6 months.

6+ months
Or about 6 1/2 months.
I had thought that Opportunity and Spirit had been the fastest [and they did it about 7 months] but it appears Mars Odyssey is faster trip time.

But I did mean in 6 months in the sense of within 6 months.
As likewise as I think NASA should try to get crew to Mars in less than 3 months. Or 2 to 3 months. Or in time period of 3 months.
Though I suppose if had to be 3 1/2 or up to 4 months it might be good enough.

Oh, wait. Opportunity is almost the same time period:
"Launched on July 7, 2003, Opportunity landed on Mars' Meridiani Planum on January 25, 2004 "
And Spirit took a few days longer:
Launch date: June 10, 2003. Landing date  January 4, 2004.

I suppose I tend to round up, and others round down.



Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #57 on: 11/19/2013 11:58 pm »
When anyone says "six months" they mean you count the months. The number of days is just nitpicking.

May, June, July, August, September, October = 6 months.

I really thought you weren't going to make a rounding argument, but you did. Do you know what this does to my faith in this forum? Please, try not to do that.
Human spaceflight is basically just LARPing now.

Offline catiare

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Re: Mars Direct - Problems and Solutions
« Reply #58 on: 11/20/2013 12:16 am »
The link below points to a paper from 2006, called Mars for Less, where a variant of the Case for Mars solution was made using 25-tonne rockets to LEO. This was pre-SpaceX-FH9. I'm sure a "middle of the road" variant can be accomplished with less amount of launches using FH9.

http://www.marsdrive.com/Libraries/Downloads/Reaching_Mars_for_Les_-_The_Reference_Mission_Design_of_the_MarsDrive_Consortium.sflb.ashx

Very interesting.  Looks kinda like Mars Direct, but with something like an Atlas V-heavy.  Looks like it utilizes the economics of scale.  Keep things standardized and simple, and make a lot of them.  namely the cyro stages.  Launch the ERV, and then launch a bunch of Centaurs or DCSS's to LEO and stack them up behind it and do a multiple stage boost.  (Actually it'd be a CPS with a fairly long duration loiter capability)
Wonder if there'd be problems with so many stages linking in orbit and operating properly?

On the subject of their ERV and Hab lander, I'd been pondering this myself.  What is does look like?  Kinda like a big dragon capsule to me.  It's been shown that a Dragon capsule could land on Mars with it's LAS system and heat shield.  So...could that just be scaled up?  A much larger Dragon Capsule, with methalox engines on it's sides rather than hypergolic superdracos?  It would trade a smaller heat shield with less dV for more propulsion to make up for it.  I think such a craft to get on the surface pretty readily, but getting it back off the surface could be an issue with it's engines angled off in the sidewall.  That makes for a big performance hit I think for ascent and TEI.  So, is there any mechanical way to reposition those sidewall engines so that they do point directly down?  Could they pivot, or actuate, out and down so the downward plume would not impinge on the craft too much?
They wouldn't need to do that during EDL, just while on the surface prior to lift off. 

No need for that on the Hab lander.  It's not getting back off the surface.

Side mounted engines also means the lander itslef can be closer to the surface, with out landing on it's engines.

This would assume a larger LV like FX/FXX/MCT rather than the smaller EELV class in this paper.

I just found the original paper in an old hard drive. Its from circa 2003 and the author presented an alternative to centaur by using a CH4/O2 Propulsion System and used a 20-Tonne budget instead.  Attached is the PDF.

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #59 on: 11/20/2013 01:17 am »
When anyone says "six months" they mean you count the months. The number of days is just nitpicking.

May, June, July, August, September, October = 6 months.

I really thought you weren't going to make a rounding argument, but you did. Do you know what this does to my faith in this forum? Please, try not to do that.

My understanding is that trajectory to Mars of 6 months takes extra delta-v as compared to 8 month. Or, it seems the 8 month Mars trip is similar to 3 day to Moon.
My point was to say that no spacecraft to Mars except [perhaps] flyby has reached Mars within a time frame- and that time frame was within 6 months. Which was mainly, a segue way to mention couple spacecraft which have reached Mars distance in less than 6 months. In order to then discuss, how one can  get to Mars in 3 months.

On topic of human spaceflight.
For human mission a common general the range is 120 days to 270 days to get to Mars, such as here:
http://www.marsjournal.org/contents/2007/0002/files/wooster_mars_2007_0002.pdf
"The conjunction trajectories explored in this paper include
both Earth-Mars and Mars-Earth legs in which the trip time
is constrained to specific durations between 120 and 270
days"
Or here:
"The crew will be on higher energy, faster trajectories lasting no longer than 180 days each way in order
to limit the crew’s exposure to radiation and other hazards."
http://www.ltas-vis.ulg.ac.be/cmsms/uploads/File/InterplanetaryMissionDesignHandbook.pdf

But no spacecraft has gone to Mars in 180 days or less. 6 months or less.
6 months would require more delta-v.
But of course I think a lot more than this amount of delta-v should be used to get crew to mars faster
than 6 or 4 months- that it should be done 3 months. 
And doing this doesn't require some non-chemical rocket.

Edit: So I did quick goggle I found I was wrong: "The total journey time from Earth to Mars takes between 150-300 days depending on the speed of the launch, the alignment of Earth and Mars, and the length of the journey the spacecraft takes to reach its target."
http://www.universetoday.com/14841/how-long-does-it-take-to-get-to-mars/#ixzz2lCXhfBPK
Continuing to quote above article:
"The next successful mission to Mars was Mariner 6, which blasted off on February 25, 1969 and reached the planet on July 31, 1969; a flight time of only 156 days. The successful Mariner 7 only required 131 days to make the journey."
So Mariner 6 & 7 were flyby missions:
"Closest approach for Mariner 6 occurred July 31, 1969, at 05:19:07 UT[3] at a distance of 3,431 kilometres" and "Closest approach for Mariner 7 occurred August 5, 1969 at 05:00:49 UT[2] at a distance of 3,430 kilometres"
http://en.wikipedia.org/wiki/Mariner_6_and_7
So don't count these in regards to within 6 months.
But going back to first article:
"Mariner 9, the first spacecraft to successfully go into orbit around Mars launched on May 30, 1971, and arrived November 13, 1971 for a duration of 167 days.

This is the same pattern that has held up for more almost 50 years of Mars exploration: approximately 150-300 days."
So June, July, August, Sept, Oct, and half of Nov- So 5 1/2 months to go from Earth to Mars.
Also as mentioned above was the Russian Mars 2:
Launch date    1971-05-19
Orbital insertion date: November 27, 1971
http://en.wikipedia.org/wiki/Mars_2
So Russian Mars 2 launched May 19 and arrived Nov 27 of 1971. So launched before US launch by 11 days and arrived 6 days after Mariner 9. So Russian Mars 2 required 6 months and one week.

But fastest travel time to Mars has been about 180 days. And in terms of flybys it could be as little as about 80 days. If using hohmann transfer and launching from Earth surface with the available chemical rockets. So for instance like New Horizon doing a Solar escape hohmann transfer and crossing Mars orbital path in 78 days.
Or from the earth surface one probably can't do better than 75 days reaching Mars orbital distance from Earth. Or around 2 1/2 months is near max from Earth surface.

Edit continue: But if were swap earth with Venus, so we and launching from Venus distance, we could get to Mars quicker using hohmann transfer and launching from earth surface- both orbiting/landing and flyby of Mars.
Because with hohmann transfer it's a shorter distance from Venus distance as compared to Earth distance.
Or roughly the hohmann transfer to Mars from Earth is about 8 months and from Venus it's about 6 months.
And one use same trajectory modification to reduce Venus to less than 6 month as is use to reduce Mars to
6 months. And using swapped Venus for gravity assist one could get even faster Mars and with less delta-v.
Too bad Venus surface is so hot- though is upper atmosphere is tolerable.

Anyways, my point is one can get to Mars in 2 to 3 month starting from Earth high orbit using chemical rockets. You simply make a spacecraft have same velocity as *if* it were coming from Venus and doing a gravity assist off Earth. Or it's not a hohmann transfer from Earth distance, it's a hohmann transfer from Venus distance [or range orbital distances near Venus or near Mercury distances].

Add another thing. If doing a hohmann transfer from Venus to Earth, your velocity when reach Earth distance is slower than Earth's orbital velocity. And then Earth gravity captures you and adds the velocity so one stay at Earth's orbit. That would the minimum delta-v needed to transfer from Venus to Earth distance.
Or you say that something from Venus hohmann transfer would impact earth at lower velocity than Earth escape velocity- earth's  gravity used keep it in Earth orbit. Same thing with Moon you could land on Moon at lower than it's escape velocity- not to confused velocity started from a lunar orbit. So some number less than 2.38  km/sec.
But if you coming from Venus with your plan of going to Mars, one could approaching Earth rather quickly.
But something you could do, is save some delta-v on spacecraft [have rocket fuel] to do powered gravity assist with Earth. So pass near to Earth and do rocket burn.
And doing such thing would most resemble what I mean by getting from High earth orbit  to Mars in 2-3 months.   

« Last Edit: 11/20/2013 04:56 pm by gbaikie »

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #60 on: 11/20/2013 05:17 pm »

I just found the original paper in an old hard drive. Its from circa 2003 and the author presented an alternative to centaur by using a CH4/O2 Propulsion System and used a 20-Tonne budget instead.  Attached is the PDF.

Interesting.  Thanks for sharing. 

I like how they talk about a SDHLV, and then says NASA has been resistant to change so such an LV cannot be assumed.  What a difference 10 years has made.  And maybe it's a matter of being careful what you wish for.

Since it would appear barring some big political shift, that SLS will be completed, and I'd have to assume the Block 1B path will be chosen, how would a Mars Direct or Mars semi-direct look with Block 1B SLS?  As we have some TMI numbers for that.
I'll assume a Block 2B would be about 40mt though TMI as a guess (as Block 1B does about 32mt) .  If so, what would it look like for that?
We'll probably run out of 5-seg SRB's before we would possibly mount a Mars mission (if we ever do) so Block 2B, whatever that looks like, will probably be the LV used for that.

Interestingly, I believe an SLS Block 2B...basically just replacing 5-seg boosters with Pyrios or Aerojet liquid boosters, will basically get the DUUS to LEO full.  Think if it as Block 1A, with the DUUS as a payload on top, although it will still have to do a kick burn.

So, could maybe a 60mt payload be launched to LEO with a DUUS mostly full.  Then another SLS Block 2B launches a DUUS that's completely full, and the two rendezvous in LEO and then burn for TMI.  That could probably put a pretty sizable ERV through to Mars and down on the surface for Mars Direct.  Where it would refuel itself.
Do it again 2 years later for the crew in a Hab/lander.  That's the equivalent of one launch per year, but you actually do two launches, then wait 2 years, and do two more.  (two ML's would be needed for this obviously, to launch them fast enough.)

The ERV would maybe be a two stage biconic vehicle like I mentioned above, which lands on it's tail.  After the mission, the crew enters an encapsulated Orion (or DRagon) capsule on the very top (long ladder climb, but the crew only needs to do it once.) Once the ERV lifts off and goes directly through TEI, the propulsion stage and upper stage biconic aeroshell is jettisoned, leaving just Orion CSM and a Bigelow Sundancer sized transhab.  Orion transaltes and docks with the BA-330 for the transit home.  It can do necessary trajectory corrections for the stack on the way home.  On Earth approach the Sundancer is jettisoned and the crew does EDL in Orion.
As the Orion CSM wouldn't actually need to perform any TEI burn, it's SM could be modified to have less SMME fuel and be lighter.  Assuming maybe a 15mt Orion CSM, and an 8mt Sundancer, that's 23mt that the ERV would need to get off the surface and through TEI.  Maybe that's too much?

Depends on what's a realistic mass we can lift off the Mars surface and put directly through TEI.  Not sure what that is.   

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #61 on: 11/20/2013 05:36 pm »
But fastest travel time to Mars has been about 180 days. And in terms of flybys it could be as little as about 80 days. If using hohmann transfer and launching from Earth surface with the available chemical rockets.


180 days ~ 6 months is what I've seen before, I believe in NASA DRM's and such.  (I think Zubrin too, but it's been awhile since I've read "The Case for Mars" so I can't remember for sure what he recommneded after evaluating several possibilities).
Maybe that's just a good confluence of speed to get there without exposing the crew to too much radiation and time in zero-g like some of the lower energy 270 day trajectories, not needing an unreasonable amount of propellant, and still not going so fast that aerobraking/aerocapture cannot be used?
Maybe that's why that transit time gets referenced as a baseline?
We have a lot of experience with crews in zero-g for 6 month stays on the ISS, but I don't know we've let anyone stay much longer than that.  That seems to be where our knowledge base is.  Although obviously the Russians have done longer.  We still need our crews to get to Mars and be able to function without a lengthy rehabilitation time.  So maybe that's a component of it, as well as leaving aerobraking/aerocapture options when we get there and not needing -too- much fuel to do it in that time like some of the shorter trajectories.


Anyways, my point is one can get to Mars in 2 to 3 month starting from Earth high orbit using chemical rockets. You simply make a spacecraft have same velocity as *if* it were coming from Venus and doing a gravity assist off Earth. Or it's not a hohmann transfer from Earth distance, it's a hohmann transfer from Venus distance [or range orbital distances near Venus or near Mercury distances].
 

My knowledge of orbital mechanics is limited enough that I cannot comment on the merrits of your concept.  I'd only ask why I can't recall seeing any concepts (other than VASIMR) that gets to Mars and can make Mars Oribt still that are faster than 6 months?
And VASIMR can do it because of game-changing propulsion that accelerates part of the trip and decelerates the other part.   And thus doesn't need any aerobraking/aerocapture when it gets to Mars.
Can your 2-3 month trajectory still do free returns back to Earth?  I think the 6 month ones can, but perhaps I'm mistaken on that.  That may be a consideration in case there's a problem en route.  They can always swing by and can still get home.  (which is a potential issue with Mars Direct or Semi-Direct.  On a free return trajectory back to Earth, I don't think a Hab Lander could get safely through EDL on Earth?)

But if it works, sure.  :-)  The faster the better, obviously. 

I also think using slower, less energetic trajectories for uncrewed missions can maximize payload when transit time isn't an issue, would be a good idea.

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #62 on: 11/20/2013 06:22 pm »
Perhaps a SpaceX variation of Mars Direct, with an Aldrin Cycler.

Send a MAV/ERV to Mars unmanned, and have it make it's return propellant per Mars Direct and Semi Direct.

Send a Large uncrewed Hab/cargo lander to Mars and landed next to the MAV/ERV.

Have a fully provisionsed Bigelow BA-300 (or even a BA-2100 assuming a new SpaceX HLV avaiable) Transit Hab inflatable module placed in an Aldrin Cycler orbit.

Launch your crew on a Dragon launch on a man-rated FH for rendezvous with the Cycler.  I think it should have enough capacity to get Dragon there. 
On arrival at Mars, the Dragon detatches and landers, per RedDragon at the mission location. 
The crew stays in the Hab module already there.

After the Mission, the crew boards the MAV/ERV, which is just a Dragon capsule with a methalox propulsion module on it.  The crew ascends and continues directly to rendezvous with the Bigelow module (or a different one if there are two cyclers operating at intervals), jettisons the propulsion module, and docks for the trip home.  Once back at Earth they detatch and go directly through EDL at Earth.

In this way, you could keep the crew ascending and descending in a Dragon capsule, which by that time in the future should be well tested in launches and propulsive landings with crews.  The Capsule is already designed to have crews in it for launch and EDL, so that the Hab/Equipment lander wouldn't have to be.  And if there's a problem with one of the uncrewed landers, you screw the mission before the crew ever takes off.
If there's a problem on the way out where the mission is scrubbed, the crew just stays on the Transit Hab module for the return.
Just make sure you make that Rendezvous for the trip out and the trip back...otherwise it'll be a LONG cramped ride to Mars or back from Mars!

That's be my concern especially on the trip back.  I think you'd have one narrow launch window to catch your ride home.  Or you are screwed. 
Can the crew launch to a slower trajectory in line with the cycler transit hab, and then let it catch up to it?  So that they could launch with a larger window?  Or launch a little after it and be designed with enough methalox that it has some ability to catch up to it?  To allow more margin in that critical rendezvous?


Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #63 on: 11/20/2013 09:04 pm »
One thing I happened to notice last night.. there's quite a number of people who have said the crew would return to Earth in zero-g in the Mars Direct scenario. I don't know where this came from, but it isn't Zubrin. He suggests the ERV should have a propulsion half and a cabin half, and the two could separate on a tether to produce artificial gravity, just like the tuna-can hab and the earth departure stage.
Human spaceflight is basically just LARPing now.

Offline JasonAW3

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Re: Mars Direct - Problems and Solutions
« Reply #64 on: 11/20/2013 09:16 pm »
This is going to kind of stretch things a bit but, I think a build up of more supplies and larger ground side habitable modules would be a much better idea, as the whole objective is to eventually establish a base camp / colony on Mars.
     This could, in theory be combined with other, complementary missions such as a pair of communications / mars observation satillites with a supply module, a pair of remote operable rovers with a habitat module, Arial Recon drones along with the ERV, etc.
     Yes, it would take longer before people could go, but enough redundancy will be built into the mission and the base, that mission success would be that much easier to achieve. (Plus, by prepositioning and deployment of critical systems, any unforseen situations can be observed before crew launch and replacement or augmentation equipment can be sent along with the crew.
My God!  It's full of universes!

Offline LegendCJS

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Re: Mars Direct - Problems and Solutions
« Reply #65 on: 11/20/2013 09:25 pm »
This is going to kind of stretch things a bit but, I think a build up of more supplies and larger ground side habitable modules would be a much better idea, as the whole objective is to eventually establish a base camp / colony on Mars.
     This could, in theory be combined with other, complementary missions such as a pair of communications / mars observation satillites with a supply module, a pair of remote operable rovers with a habitat module, Arial Recon drones along with the ERV, etc.
     Yes, it would take longer before people could go, but enough redundancy will be built into the mission and the base, that mission success would be that much easier to achieve. (Plus, by prepositioning and deployment of critical systems, any unforseen situations can be observed before crew launch and replacement or augmentation equipment can be sent along with the crew.

I agree any increase in pre positioned Mars infrastructure would have a positive effect on mission success, but its going to be really easy for detractors to attack if it starts to look like NASA spent close to a decade to build a Mars ghost town with no human flight to show for it.
Remember: if we want this whole space thing to work out we have to optimize for cost!

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #66 on: 11/20/2013 09:30 pm »
Plus there's the simple fact that we don't know where is best to build a Mars base yet. The argument can be made that significant exploration is required to choose the best first site for a base and that exploration is so significant that it's best to do it with humans.
Human spaceflight is basically just LARPing now.

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #67 on: 11/20/2013 10:19 pm »
One thing I happened to notice last night.. there's quite a number of people who have said the crew would return to Earth in zero-g in the Mars Direct scenario. I don't know where this came from, but it isn't Zubrin. He suggests the ERV should have a propulsion half and a cabin half, and the two could separate on a tether to produce artificial gravity, just like the tuna-can hab and the earth departure stage.

Yes, quite corret.  If I've mentioned it is in relation to a different version of Mars Direct that would address some of the problems with it you mention in your opening post.  Zubrin uses a teather between the discarded stage and vehicle, but it would have to be a long teather as the depleated stage would be so much lighter than the vehicle.  You need it long enouhg so that the vehicle is var enough out from the center of mass that they aren't rotating too fast.
But myself, if you are having 6 month transit times, I don't know that it's all that important to have.  The returning astronauts don't need to get to Earth ready to work.  They would be returning similar to a return from the ISS mission (assuming the gravity on Mars along with extra weight and work would get them back in decent shape after the zero-g trip out.)
If anything, it'd be more important for the trip out than the trip home.  And introduce unnecessary complexity.  But I don't even know that it's necessary on the way out.  We have lots of experience with 6 month stays in zero G.  Excercise and diet help combat bone and muscle loss.  At Mars, they are at only 1/3 gravity.  With a long stay they work themselves back into "game shape".  I picture form fitted weight suits that they wear around the habitat to approximate their weight on Earth...with weight distributed around it so that their center of gravity stays the same (vs. a heavy EVA suit where the CoG is all off...resulting in falls like the Apollo Astornauts had.)  On the surface they have their heavy pressurized EVA suits to resist them to work the muscles and bones. 
I think long term stays on the Moon would be very beneficial for studying the effects of such simulated weight in low gravity environments.  The idea being that it would give the astronauts the ability to resist the effects of low gravity mildly, but constantly.  Rather than trying to fit it all into an hour or two of vigorous (and sweating) exercise is they have to do in zero G.
Other than physically being on a less-than-one-G surface, we have no way to simulate the effects of long term low gravity on the human body, and what methods which would be employed to cope with it.
But as long as there's -some- gravity...you should be able to simulate higher gravity resistance on the body by adding additional mass to the human.




Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #68 on: 11/21/2013 12:16 am »
But fastest travel time to Mars has been about 180 days. And in terms of flybys it could be as little as about 80 days. If using hohmann transfer and launching from Earth surface with the available chemical rockets.


180 days ~ 6 months is what I've seen before, I believe in NASA DRM's and such.  (I think Zubrin too, but it's been awhile since I've read "The Case for Mars" so I can't remember for sure what he recommneded after evaluating several possibilities).
Maybe that's just a good confluence of speed to get there without exposing the crew to too much radiation and time in zero-g like some of the lower energy 270 day trajectories, not needing an unreasonable amount of propellant, and still not going so fast that aerobraking/aerocapture cannot be used?
Maybe that's why that transit time gets referenced as a baseline?
We have a lot of experience with crews in zero-g for 6 month stays on the ISS, but I don't know we've let anyone stay much longer than that.  That seems to be where our knowledge base is.  Although obviously the Russians have done longer.  We still need our crews to get to Mars and be able to function without a lengthy rehabilitation time.  So maybe that's a component of it, as well as leaving aerobraking/aerocapture options when we get there and not needing -too- much fuel to do it in that time like some of the shorter trajectories.

I believe that 6 or 8 months is doable.
I just there is a lot advantages of getting the crew there faster.
You need less food, water, and air to breath. And avoid problems of trying to
do things to lessen these requirements, such as processing urine.
There is argument that larger crews are better for psychology/sociological reasons.
So I believe smaller crews could be used if gotten there faster as this would
lessen the psychology/sociological problems. I believe there is difference
between being on the surface of Mars and traveling to Mars- maybe I am wrong-
it's my guess.
I also believe you want the crew in the best physical and mental conditions at the point
of landing on Mars and in beginning of establishment of Mars base.
So I would want crew to get to Mars the fastest in the first couple trips to Mars,
then after this *maybe* take slower trips.
I think getting the first crews to Mars is very valuable and worth spending a lot
of money on. So low cost program but a lot funding on aspect of getting first crew
to Mars safely. And major part of Mars program cost will not be the cost of sending
crew to Mars [even if you spend a lot of money on it]. Or people think
they send crew to mars for say 5 billion. Perhaps they could, but Mars Manned
program will cost 100 billion or more. Or NASA will spend 5 billion per year for
20 years. If it was a cheap NASA manned Mars program- which odds favor it
will not be as cheap as 100 billion. The only way to make a NASA manned Mars program
cheaper than 100 billion, is one, ignore real costs. Two screw up the Manned Mars program
so it doesn't actually do much exploration of Mars {flag and footprints].

And finally, I believe NASA as organization and US government will have a road block
due to radiation levels they must plan the crew will receive if it takes 6 months to sent
crew to Mars. Now such *problems* may or may not be issue for the Chinese or Russian
government.


Anyways, my point is one can get to Mars in 2 to 3 month starting from Earth high orbit using chemical rockets. You simply make a spacecraft have same velocity as *if* it were coming from Venus and doing a gravity assist off Earth. Or it's not a hohmann transfer from Earth distance, it's a hohmann transfer from Venus distance [or range orbital distances near Venus or near Mercury distances].
 
Quote
My knowledge of orbital mechanics is limited enough that I cannot comment on the merits of your concept.  I'd only ask why I can't recall seeing any concepts (other than VASIMR) that gets to Mars and can make Mars Oribt still that are faster than 6 months?
You can not do what I am talking about if launching from Earth surface. I not even sure you can do it from
LEO.
This because chemical rockets have a delta-v limit- which is about 18 km/sec. And what talking about requires about 20 km/sec from the earth surface.
And if you start from High Earth, you about 10 km/sec up the gravity well.
Few people realize one could or should leave from say Earth/Moon L-1. Lot's people accept it, NOW, but
it hasn't always been the case.
Nor is there much acceptance of the need for fuel depots. Which would also almost be requirement for what I am talking about. If not rocket depot, than at least docking with fully fueled stage. Or that docking a fulled fueled stage, would be something like, bring a fulled fuel stage to LEO, docking with another fully fuel stage to lift the fully fueled stage to high earth, then docking the fully fueled stage to Mars ship and then leaving for Mars.
Couple all this will idea that Mars doesn't require very much delta-v to get there. Mars fans constantly say it take less delta-v to get to Mars as compared to the moon. Which is only true in regard to cargo [or non-crew] to Mars. Though as I said it's not the crew which will be most of the costs, because of the need a lot of cargo sent to Mars.
So, short answer is they have not figured it out yet.

« Last Edit: 11/21/2013 12:42 am by gbaikie »

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #69 on: 11/21/2013 01:24 am »
Quote
And VASIMR can do it because of game-changing propulsion that accelerates part of the trip and decelerates the other part.   And thus doesn't need any aerobraking/aerocapture when it gets to Mars.
Well, since this thread is about Mars Direct and it's Zubrin's baby. Let's look at what Bob says about
VASIMR:

The VASIMR Hoax
By Robert Zubrin | Jul. 13, 2011
"VASIMR, or the Variable Specific Impulse Magnetoplasma Rocket, is not new. Rather, it has been researched at considerable government expense by its inventor, Franklin Chang Diaz, for three decades. More importantly, it is neither revolutionary nor particularly promising. Rather, it is just another addition to the family of electric thrusters, which convert electric power to jet thrust, but are markedly inferior to the ones we already have."
And:
"But wait, there’s more. To achieve his much-repeated claim that VASIMR could enable a 39-day one-way transit to Mars, Chang Diaz posits a nuclear reactor system with a power of 200,000 kilowatts and a power-to-mass ratio of 1,000 watts per kilogram. In fact, the largest space nuclear reactor ever built, the Soviet Topaz, had a power of 10 kilowatts and a power-to-mass ratio of 10 watts per kilogram. There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system."
http://www.spacenews.com/article/vasimr-hoax

I would have different arguments about it. But I will leave it there.

Quote
Can your 2-3 month trajectory still do free returns back to Earth? 
Probably, but I would not recommend it.
I would recommend a fully ready return ship at Mars, before crew leave Earth.
As emergency abort option.
And due to economic reasons, it would be not be a fast trip
home- 6 or 8 month return. So dependable, easily store able propellent.
Or a fuel depot at Mars which can store rocket fuel for extended periods.
So, some kind a capability to return crew to Earth would be already in Mars
orbit before crew leave for Mars.

Quote
I think the 6 month ones can, but perhaps I'm mistaken on that.
Yes. Generally called conjunction trajectories.
"A Mars mission planner has three choices:

A. Hohmann Transfer Orbit
B. Opposition Mission
C. Fact Conjunction Mission "
And
"I personally favor mission (C), for the following reasons: a Conjunction Mission leads to a longer time spent on the surface of Mars and less time wasted in transit. How would you like to spend 180 days getting to Mars, have only 30 days on the surface, and then spend 430 days going back? A Conjunction Mission spacecraft can also be made heavier with more backup systems and supports. And because the crew will spend less time in transit, they will have less exposure to zero gravity and radiation. Additionally, a conjunction mission offers what is called a "free-return" trajectory, where if the ships propulsion system fails or the mission needs to be aborted, the crew can get home safely, as was done with Apollo 13, which employed a free-return trajectory to the Moon. "
http://www.redcolony.com/art.php?id=0208170

[And what talking is not considered as one of options.]

 
Quote
That may be a consideration in case there's a problem en route.  They can always swing by and can still get home.  (which is a potential issue with Mars Direct or Semi-Direct.  On a free return trajectory back to Earth, I don't think a Hab Lander could get safely through EDL on Earth?)
I wouldn't sent hab in less than 3 month trajectory. It would be a 8 month trajectory, and would be at
Mars before crew left Earth. Though it could be in Mars orbit rather than on surface when crew arrive.
One major purpose of the mars crew would controlling things for building up infrastructure, so there isn't a time delay- mostly from Mars surface [want crew on surface fairly quickly]. But crew from orbit could be involved in landing lots of stuff, if already in Mars orbit- within hours or day or two. 

« Last Edit: 11/21/2013 01:27 am by gbaikie »

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #70 on: 11/21/2013 04:21 pm »
Quote
And VASIMR can do it because of game-changing propulsion that accelerates part of the trip and decelerates the other part.   And thus doesn't need any aerobraking/aerocapture when it gets to Mars.
Well, since this thread is about Mars Direct and it's Zubrin's baby. Let's look at what Bob says about
VASIMR:

The VASIMR Hoax
By Robert Zubrin | Jul. 13, 2011
"VASIMR, or the Variable Specific Impulse Magnetoplasma Rocket, is not new. Rather, it has been researched at considerable government expense by its inventor, Franklin Chang Diaz, for three decades. More importantly, it is neither revolutionary nor particularly promising. Rather, it is just another addition to the family of electric thrusters, which convert electric power to jet thrust, but are markedly inferior to the ones we already have."
And:
"But wait, there’s more. To achieve his much-repeated claim that VASIMR could enable a 39-day one-way transit to Mars, Chang Diaz posits a nuclear reactor system with a power of 200,000 kilowatts and a power-to-mass ratio of 1,000 watts per kilogram. In fact, the largest space nuclear reactor ever built, the Soviet Topaz, had a power of 10 kilowatts and a power-to-mass ratio of 10 watts per kilogram. There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system."
http://www.spacenews.com/article/vasimr-hoax

I would have different arguments about it. But I will leave it there.


I think you misunderstand what I meant.  I wasn't clear.  I think VASIMR -is- game changing technology....if it could be ever be feasibly built some day.  That includes the required nuclear power and mass requirements.  I don't think it's feasible at all today.  As much for the power requirements as the actual propulsion concept itself. 
What I mean by game changing, is a self contained vehicle that has enough on board propellant to get itself all the way to Mars, and all the way back with the fuel it leaves Earth with.  It uses both powered accelleration and powered descelleration.  And, hypothetically, it would generate at least some artificial gravity.  Maybe not enough to really combate the effect of low-g/zero-g on the crew, but even a little gravity will cause things floating in the air to settle on the deck.  Which I think makes living a bit easier.  A stray water globual will settl to the deck where it can be whiped up.  Same with stray hairs and fibers and particles from food and other things.  You could set something down and as long as you didn't bump it or blow on it, it should remain where you left it.
Ideally, you'd have enough accelleration and descelleration to generate some sort of useful gravity for the entire trip.  But I think that's far beyond even VASIMR to generate that much ascelleration and then that much descelleration, for that long.  Although I guess it wouldn't have to be for that long because pulling say 0.5g or something for several days would probably get you going very fast, and then decelerate at the same rate to generate 0.5g for the 2nd half of the trip....would make for a pretty fast trip.
Still...I think we're a long way from that.

But that is "game changing" to have a vessel capable of that....even capable of the VASIMR concept.  But the US would have to have a radically different idea about how much is worth investing in that research before such a thing would be practical any time to be useful.

In the mean time, I think if our crew transits were kept to 6-7 months each way, the effects of zero-g on the crew could be mitigated enough via conventional means that they'd arrive at Mars able to function fine, and then on the return trip, it's not necessary because it wouldn't be any different than a crew returning from a 6 month stay on the ISS.  Let's focus on what's -necessary- to develop, rather than adding the complexity of spinning tethers and artificial gravity.
Again, start with the lowest common denominator.  The most simple thing that would work, and then work out from there adding cost and complexity in exchange for capability until we find a happy medium. 

EDIT:  Everything that was left on after my comment here was an edit mistake.  Cleaned up.
« Last Edit: 11/22/2013 03:46 pm by Lobo »

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #71 on: 11/21/2013 07:09 pm »
Quote
And VASIMR can do it because of game-changing propulsion that accelerates part of the trip and decelerates the other part.   And thus doesn't need any aerobraking/aerocapture when it gets to Mars.
Well, since this thread is about Mars Direct and it's Zubrin's baby. Let's look at what Bob says about
VASIMR:

The VASIMR Hoax
By Robert Zubrin | Jul. 13, 2011
"VASIMR, or the Variable Specific Impulse Magnetoplasma Rocket, is not new. Rather, it has been researched at considerable government expense by its inventor, Franklin Chang Diaz, for three decades. More importantly, it is neither revolutionary nor particularly promising. Rather, it is just another addition to the family of electric thrusters, which convert electric power to jet thrust, but are markedly inferior to the ones we already have."
And:
"But wait, there’s more. To achieve his much-repeated claim that VASIMR could enable a 39-day one-way transit to Mars, Chang Diaz posits a nuclear reactor system with a power of 200,000 kilowatts and a power-to-mass ratio of 1,000 watts per kilogram. In fact, the largest space nuclear reactor ever built, the Soviet Topaz, had a power of 10 kilowatts and a power-to-mass ratio of 10 watts per kilogram. There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system."
http://www.spacenews.com/article/vasimr-hoax

I would have different arguments about it. But I will leave it there.


I think you misunderstand what I meant.  I wasn't clear.  I think VASIMR -is- game changing technology....if it could be ever be feasibly built some day. 
I feel the same way towards nuclear fusion electrical power plant for use on Earth. So it's unlimited cheap electrical energy, and it would be wonderful.
But they aren't developed.

And there are other ways to get unlimited cheap electrical power.
I think more money spend on NASA would be  better path to unlimited cheap electrical power, than money spent on fusion research.
But then again, rather than cut fusion research, I would have many other higher priority of government programs I would want cut, as compared to the apparent uselessness of fusion research.

Likewise VASIMR or something like VASIMR may be developed in the future. I would bet on cheap fusion power plant as more likely than VASIMR.
And likewise there ways to get to Mars which can as fast, but due to costs, I would limit it to 60 to 90 day Mars transit time for crew.  39 days to Mars would be quite challenging [expensive] with chemical rockets.
But if make rocket fuel in space, which means we develop electrical market in space, which means one could buy a lot electrical power- like a 100 million dollars worth at $10 per kW hour and get this much power within hour of time.
So one can get 10,000 MW hour of electricity and beam this energy at spacecraft which use the energy, one could manage to get some high velocities. Of course this quantity of energy would cheap compared to the laser that used it. Or energy storage you might need. But there was enough need for it- you had human settlement on Mars, it might worth the high costs. But point is if you have already the energy producing infrastructure being used for something else, then you don't have to start with building power plants, so can then make some laser.
Rather you can simply buy the electrical power you need for the project. So VASIMR might look quite different if it didn't have make a power plant and accelerate it's power plant.
 
Quote
What I mean by game changing, is a self contained vehicle that has enough on board propellant to get itself all the way to Mars, and all the way back with the fuel it leaves Earth with.  It uses both powered acceleration and powered deceleration.  And, hypothetically, it would generate at least some artificial gravity.
Well I am all for a race car having a coffee holder- as it doesn't affect the mass of the car.
But the only reason it not impossible to get into space is because of rocket stages.
Because we have used rocket stages perhaps someday we will have SSTO.
Likewise I would use stages to send crew to Mars as fast as we can.
LEO is a place to stage. And L-points is place to stage. And Mars orbit is a place to stage.

One of many reasons to get to Mars fast is not to need one more complication [though fairly minor] of
artificial gravity. We will need artificial gravity in the future in regards to stuff done in space
but we don't need it to explore the Moon or to explore Mars.
We will probably need it for settlements in space. Or people may be willing to pay for artificial gravity environments- perhaps nurseries in space will have artificial gravity or hotels will offer a variety of different
gee environments.
 

"Ideally, you'd have enough acceleration and deceleration to generate some sort of useful gravity for the entire trip. "
Well it could be useful to find things- they will tend to be at back of ship.
But a 1/10th of gee for one hour is .98 * 3600 or 3.5 km/sec. So 2 hr: 7 km/sec. 4 hr 14 km/sec and
8 hr 28 km/sec.
1/100th of gee is 8 hr: 2.8 km/sec, 16 hours: 5.6 km/sec, 32 hours is 11.2 km [and look out widow and Earth is still there:) ], 64 hours is 22.4 km/sec [Earth will be at fair distance away but Mars does not look closer].
1/1000th of gee:  64 hours is 2.24 km/sec [Earth hasn't moved much], 128 hours is 4.48 km [You certain Earth has moved away],  256 hours [10.6 days] is 8.96 km/sec [You feel like you making progress but Mars
does not look any closer.].
Now perhaps you start with 1/10th and do 1000th for rest of trip. But at 1/1000th of gee, 200 lbs is .2 lbs and many things will essentially float or bowling ball takes few minutes to hit the floor and bounce-surprising well.

Quote
In the mean time, I think if our crew transits were kept to 6-7 months each way, the effects of zero-g on the crew could be mitigated enough via conventional means that they'd arrive at Mars able to function fine, and then on the return trip, it's not necessary because it wouldn't be any different than a crew returning from a 6 month stay on the ISS.  Let's focus on what's -necessary- to develop, rather than adding the complexity of spinning tethers and artificial gravity.
Again, start with the lowest common denominator.  The most simple thing that would work, and then work out from there adding cost and complexity in exchange for capability until we find a happy medium. 
I think we could go to Mars in 6-7 months.
The problem is starting the program.
I think we start with fuel depots sooner. I think fuel depot would not cost a lot of money.
I think if NASA has fuel depots, they tend to use fuel depots. And the cost of using fuel depots
is not significant. The use of fuel depots [not talking about development] will be similar to NASA
COTS program. It's something people will argue about- arguing about whether 100 million is spent
in one year or not spending 100 million that year, etc.
And I think fuel depots will lower costs and enable more missions of varying types to be flown- the major
costs is it allows more possible missions. It's not the rocket fuel which is expensive it's the spacecraft that
uses them. But is a desirable situation.
And then with fuel depot things like Lunar and Mars program become more flexible. There are more options-
which is not always blessing, the general direction is good.
If you get commercial depots, what you will get is more of the hated lobbists, which are "selling" things to congress creatures. This is a good thing in in terms of getting NASA headed for Mars.
Rand Simberg, said there 3 rules regarding space policy:
Space is not important.
Space is not important.
Space is not important.
Fuel depots could make space more important.
« Last Edit: 11/21/2013 07:18 pm by gbaikie »

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #72 on: 11/22/2013 08:17 pm »
This is going to kind of stretch things a bit but, I think a build up of more supplies and larger ground side habitable modules would be a much better idea, as the whole objective is to eventually establish a base camp / colony on Mars.
     This could, in theory be combined with other, complementary missions such as a pair of communications / mars observation satillites with a supply module, a pair of remote operable rovers with a habitat module, Arial Recon drones along with the ERV, etc.
     Yes, it would take longer before people could go, but enough redundancy will be built into the mission and the base, that mission success would be that much easier to achieve. (Plus, by prepositioning and deployment of critical systems, any unforseen situations can be observed before crew launch and replacement or augmentation equipment can be sent along with the crew.

I agree any increase in pre positioned Mars infrastructure would have a positive effect on mission success, but its going to be really easy for detractors to attack if it starts to look like NASA spent close to a decade to build a Mars ghost town with no human flight to show for it.

Good point.  And you don't want to leave things there for -too- long, subjected to the surface conditions for years before humans are there if you can help it.

I think you make sure you have an adequate system of satillites for constant communications with Earth 24/7 for the duration of the mission.  (or in the case of Mars, 24.6/7.  Heh.)

Once you have that, I think you launch two HLV's in quick succession, to launch the MAV and ERV (if Mars Semi-Direct), or MAV and Hab lander (if using a Cycler), or just one launch for the ERV if goind Mars Direct.
Then two years later launch the crew.  So you don't have a "ghost town", just a couple of major elements ahead of the crew.



Offline JasonAW3

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Re: Mars Direct - Problems and Solutions
« Reply #73 on: 11/22/2013 08:27 pm »
This is going to kind of stretch things a bit but, I think a build up of more supplies and larger ground side habitable modules would be a much better idea, as the whole objective is to eventually establish a base camp / colony on Mars.
     This could, in theory be combined with other, complementary missions such as a pair of communications / mars observation satillites with a supply module, a pair of remote operable rovers with a habitat module, Arial Recon drones along with the ERV, etc.
     Yes, it would take longer before people could go, but enough redundancy will be built into the mission and the base, that mission success would be that much easier to achieve. (Plus, by prepositioning and deployment of critical systems, any unforseen situations can be observed before crew launch and replacement or augmentation equipment can be sent along with the crew.

I agree any increase in pre positioned Mars infrastructure would have a positive effect on mission success, but its going to be really easy for detractors to attack if it starts to look like NASA spent close to a decade to build a Mars ghost town with no human flight to show for it.

That's why you also include a couple of landers, rovers, satillites, etc with every preposition load.  If you're sending a load there anyway, why not add some SCIENCE! to it as well?
     Besides, the rovers landers and satillites would also provide additional usable communications relays and small equipment transportation.

Jason
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Offline JasonAW3

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Re: Mars Direct - Problems and Solutions
« Reply #74 on: 11/22/2013 08:48 pm »
This is going to kind of stretch things a bit but, I think a build up of more supplies and larger ground side habitable modules would be a much better idea, as the whole objective is to eventually establish a base camp / colony on Mars.
     This could, in theory be combined with other, complementary missions such as a pair of communications / mars observation satillites with a supply module, a pair of remote operable rovers with a habitat module, Arial Recon drones along with the ERV, etc.
     Yes, it would take longer before people could go, but enough redundancy will be built into the mission and the base, that mission success would be that much easier to achieve. (Plus, by prepositioning and deployment of critical systems, any unforseen situations can be observed before crew launch and replacement or augmentation equipment can be sent along with the crew.

I agree any increase in pre positioned Mars infrastructure would have a positive effect on mission success, but its going to be really easy for detractors to attack if it starts to look like NASA spent close to a decade to build a Mars ghost town with no human flight to show for it.

Good point.  And you don't want to leave things there for -too- long, subjected to the surface conditions for years before humans are there if you can help it.

I think you make sure you have an adequate system of satillites for constant communications with Earth 24/7 for the duration of the mission.  (or in the case of Mars, 24.6/7.  Heh.)

Once you have that, I think you launch two HLV's in quick succession, to launch the MAV and ERV (if Mars Semi-Direct), or MAV and Hab lander (if using a Cycler), or just one launch for the ERV if goind Mars Direct.
Then two years later launch the crew.  So you don't have a "ghost town", just a couple of major elements ahead of the crew.

The thing is, if you aero brake into orbit, you don't have to send everything down at once.

     Keep the habs and supply modules in orbit until you decide on a final landing zone.

     Use a flying probe to low level map possible landing sites.  (Radar could also be used to determine ground stability and if there are any potentile voids under the intended landing site).

     Use a lander to confirm the flyers observations (And to act as a beacon for the other equipment and hab landings.)

     Use a couple of rovers to scout out the potentile landing ellipse, and have them stand by the lander for additional assistance with the supply, Habitat and ERV module landings.  With beacons and proximity radar, you should be able to land fairly close together all the supplies and habitats.

     This would all be done by Earth about a week or two before the arrival of the crew.  Supplying mutiple habitats and supply modules reduces the potentile mission failure and increases available space and supplies allowing the crew to have less to concern themselves with.

     A Ground Tractor could either be sent ahead as one of the rovers, or brought with the crew.  Either way, it could be used to move habitats together and dock them as well as the supply modules. (Which, as they are unloaded, could also act as additional living space or supplie rooms).

     Either way, while not directly involved with colony preperation, the landers, flyers, rovers and satillites would be doing SCIENCE! until the arrival of the Humans.

     This could be expaned upon by also including supplies and habitats for the Martian moons as well as landers and rovers for both moons.

jason
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Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #75 on: 11/22/2013 08:53 pm »
I feel the same way towards nuclear fusion electrical power plant for use on Earth. So it's unlimited cheap electrical energy, and it would be wonderful.
But they aren't developed.


And really won't be any time soon, if ever.  And if it is, it'll be a long time before it could be made small enough to be useful for space flgiht.


And there are other ways to get unlimited cheap electrical power.
I think more money spend on NASA would be  better path to unlimited cheap electrical power, than money spent on fusion research.
But then again, rather than cut fusion research, I would have many other higher priority of government programs I would want cut, as compared to the apparent uselessness of fusion research.


I think the latest generation of Fission-breeder reactors would get us there.  Ones that can take in depleated uranion (which is 99.3% of the uranium ore.  0.7% is U235 fisile uranium for reactors.  But breeder reactors can turn that other 99.3% of the uranium (U238)  into PL-239 which is fisile like U235 and use it) and Thorium which are available in the Earth crust in vast supplies.  I've heard estimates of there being reserves of depleated Uranium and Thorium to supply the world' power anywhere from a few hundred thousand years on the conservative end, to over 1 billion years on the optimistic end.  By then we'll be dead or have figured out fusion.  ;-)
And the new gen reactors would consume most of the fission by products in the reaction and those that can't be consumed can be irradiated to have half lifes in the decades, not hundreds of thousands of years.
  And most of the expended fuel that's highly radio active and just sitting around Reactors waiting for the Federal Government to figure out if they can some day put it in Yucca Mountain or somewhere else, can be reprocessed and used in these reactors.  In using it...you start to solve the problem of what to do with it.  It's like having a much of cars sitting around that all just need a little work to make them run again, and scratching our heads saying, "we have a problem with cars.  They are just stacking up everywhere and we don't know what to do with them. They are a hazzard!"
Ummm...well...if you just fixed them and used them...you'd solve the problem of what to do with them.

All of the ignorant hype about nuclear power prevents this from happening.  With stupid politicians that know all they know about nuclear power from "The China Syndrome".  Instead they pursue other non-feasible energy sources while the closest thing we know to "unlimited energy" sits there untapped.


Likewise VASIMR or something like VASIMR may be developed in the future. I would bet on cheap fusion power plant as more likely than VASIMR.
And likewise there ways to get to Mars which can as fast, but due to costs, I would limit it to 60 to 90 day Mars transit time for crew.  39 days to Mars would be quite challenging [expensive] with chemical rockets.
But if make rocket fuel in space, which means we develop electrical market in space, which means one could buy a lot electrical power- like a 100 million dollars worth at $10 per kW hour and get this much power within hour of time.
So one can get 10,000 MW hour of electricity and beam this energy at spacecraft which use the energy, one could manage to get some high velocities. Of course this quantity of energy would cheap compared to the laser that used it. Or energy storage you might need. But there was enough need for it- you had human settlement on Mars, it might worth the high costs. But point is if you have already the energy producing infrastructure being used for something else, then you don't have to start with building power plants, so can then make some laser.
Rather you can simply buy the electrical power you need for the project. So VASIMR might look quite different if it didn't have make a power plant and accelerate it's power plant.
 

Well, that might be feasible.  But first, we only need to get the crew to Mars fast.  We can take the slow boat to China for cargo.  Low energy/high mass trajectories ahead of crewed missions.
But we need comfortable accomodations for the trip there and back, which takes mass.  Which then means a lot of dV to launch, and a lot of dV to pull up in Mars orbit.  Gotta say I'm starting to like the Cycler concept for that reason.  I'll have to read up on the Cycler trajetories, but if you can get one down to maybe 120 days (I though I read about an Aldrin Cycler orbit that was that short, but I might be misremembering)  then that's not a bad stay in zero-g really.  And you shouldn't have to worry much about trying to generate artificial gravity, or go to greath lengths to combate bone and muscle loss.  Just some moderate traditional methods of diet and exercise should be adequate.
So accelerate that Cycler hab into an orbit that gets from Earth to Mars fast, and then maybe a 2nd one that gets from Mars to Earth fast.  So a crew can ride one to Mars fast, but not back as I think the fast ones then pull way out wide and take a long time before they get back to Earth.   Then you have another that does the opposite.  Swings wide after Earth but goes very directly from Mars to Earth.  For the return trip.  All of your cargo landers go direct via low energy trajectories to maximize mass.
I like the idea of using Dragon rather than Orion for this reason.  Orion can't land on Mars, but Dragon can.  The crew can launch in Dragon, catch up and dock with the Cycler for a fast trip to Mars.  Disembark and go directly to Mars EDL.  (Dragon could have a full service module so that it has the dV and ability to changle planes as necessary to hit the correct EDL window).  Another Dragon on the MAV launches the crew back and directly to rendezvous with the cycler heading home for a fast trip home (if such trajectories exist.  I might be incorrect.  I need to do some more reading on them).  And then the crew comes directly to Earth EDL and propulsively lands on Earth.

Orion Can't do that, and so some other means of getting the crew to the surface is needed once at Mars.


Well it could be useful to find things- they will tend to be at back of ship.
But a 1/10th of gee for one hour is .98 * 3600 or 3.5 km/sec. So 2 hr: 7 km/sec. 4 hr 14 km/sec and
8 hr 28 km/sec.
1/100th of gee is 8 hr: 2.8 km/sec, 16 hours: 5.6 km/sec, 32 hours is 11.2 km [and look out widow and Earth is still there:) ], 64 hours is 22.4 km/sec [Earth will be at fair distance away but Mars does not look closer].
1/1000th of gee:  64 hours is 2.24 km/sec [Earth hasn't moved much], 128 hours is 4.48 km [You certain Earth has moved away],  256 hours [10.6 days] is 8.96 km/sec [You feel like you making progress but Mars
does not look any closer.].
Now perhaps you start with 1/10th and do 1000th for rest of trip. But at 1/1000th of gee, 200 lbs is .2 lbs and many things will essentially float or bowling ball takes few minutes to hit the floor and bounce-surprising well.


You could also do something like 1/10th g acceleration for part of the trip.  They have a zero-g cruise for part of the trip, and then do a 1/10th g decceleration for the last part and arrive at Mars at a speed that will go right into MOI.

So, the whole trip isn't under artificial gravity, but -some- is.  If that did say a 60 day trip to Mars, and you were under acceleration/decceleration for half of that time, that would be better than nothing. 

But again, that sort of ability is a long way out.  Maybe a SEP MTV with really really massive solar arrays and huge banks of ion drives could do something like that?
Something like Boeing's gateway concept.

Still, I think I'm liking the Cycler concept better.


Offline Solman

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Re: Mars Direct - Problems and Solutions
« Reply #76 on: 11/22/2013 10:11 pm »
 In reading this thread it occurs to me that it is not a big leap to say that chemical rocket propulsion is inadequate for cheap sustainable manned Mars travel. Its use requires too much propellant and longer than desirable transit times because of the limited energy from chemical reactions. VASIMR, breeder type fission, and fusion have been posited as answers but each are at present undeveloped to the necessary TRL and likely require considerable time and money to change that.
if this is accepted as true then shouldn't one look at the elephant in the room - the other obvious possibility?
I'm referring of course to solar. Now typically this means solar PV panels of large size and relatively poor specific power because only readily available high TRL technologies are considered.
Now I'm going to veer into crazy town and suggest that the centuries old tech of parabolic mirrors be considered. I say crazy town because space solar concentrators are seldom considered despite having been tested in Spartan 77 and L'Garde having made a prototype concentrator 50 ft. in dia. massing in at 15 kg for roughly 17 KW thermal/kg at 1 AU. This IS after all a fusion power system ;) . Can you imagine the excitement if a fusion propulsion/power system of this specific power was in the works?
Coupling this with concentrator PV which has the highest efficiency and far higher specific power, presents the possibility of fast transits using electric propulsion and also thermal using the concentrator(s). This EP need not be Hall thrusters but can be lower Isp types like resistojets and arcjets.
Now this may not all be off the shelf at the moment but how difficult/expensive would it be to develop to the requisite level of development should be the question IMO, not just where it is at today.
A Mars mission would begin with thermal and/or electric thrusts in LEO to raise to a HEO from which the final thrust at perigee would send the spacecraft to escape. Following that the EP takes over accelerating part way and then decelerating for MOI with thermal or electric with perhaps aerocapture after detachment of the solar propulsion/power part which would use EP to enter Mars orbit for rendevous with the rest of the spacecraft in orbit either before or after(if direct entry) it descends to the surface. Return to Earth would be similar and the solar propulsion/power module would be available for refueling and use on the next trip.
There are other ways to do it but the bottom line is that the high power available from the use of solar concentrators and solar concentrator PV might be war winning.   

 
 

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #77 on: 11/22/2013 10:21 pm »

The thing is, if you aero brake into orbit, you don't have to send everything down at once.

     Keep the habs and supply modules in orbit until you decide on a final landing zone.


I would think you'd have your landing zones chose well ahead of time and thus cargo landers would be sent from Earth in a trajectory so they could enter the Martian atmosphere in the correct plane to hit the desired landing zone.


     Use a flying probe to low level map possible landing sites.  (Radar could also be used to determine ground stability and if there are any potentile voids under the intended landing site).

     Use a lander to confirm the flyers observations (And to act as a beacon for the other equipment and hab landings.)


Again, once an actual manned landing was in the works, I would think there'd be a series of unmanned precursor missions.  That would include a rover going to a couple of potential landing sites to scout and then compare pros/cons of each site to pick a final one with the easiest landing and (if practical) best access to potential resources, as well as most potential scientific value.  Once a site is chosen for the first mission, I'd expect some unmanned demo landers to go to that site to demonstrat the sort of large scale EDL systems that woudl be necessary to bring crews and big cargo and MAV landers to the surface.  And if in-situe methalox manufacturing was part of the crewed plan, that would need to be demonstrated.  So I could see some sort of MAV lander going down, generating it's own return propellant, and then ascending from the surface and coming all the way back to Earth (with no crew...there's no need to have a return transit hab, so it could come all the way back to test all of the return phase systems).
Once a MAV has been demonstrated, and a large full scale lander with precisions EDL, then a crewed mission would probably proceed.






   

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #78 on: 11/22/2013 10:31 pm »
In reading this thread it occurs to me that it is not a big leap to say that chemical rocket propulsion is inadequate for cheap sustainable manned Mars travel. Its use requires too much propellant and longer than desirable transit times because of the limited energy from chemical reactions. VASIMR, breeder type fission, and fusion have been posited as answers but each are at present undeveloped to the necessary TRL and likely require considerable time and money to change that.
if this is accepted as true then shouldn't one look at the elephant in the room - the other obvious possibility?

No, I don't think your premise is true.  Current propulsion technology is adequate for sustainable Mars travel.  Chemical propellant is cheap and well tested.  The main choice, is do you use a HLV that can launch all that prop in a single launch?  Or do you use smaller LV's that could need in orbit assembly?  Both have pro's and con's. 

I think maybe SEP could be used, as Boeing proposed.  But I also think a Cycler could do the same thing, but not have to have this big ungangly MTV that needs to be braked into Mars orbit, and then get back out from Mars orbit. 

The less development we need for the propulsion, the more development budget can be spent for landers and surface equipment.  What -will- be necessary are EDL methods capable of landing several tonnes on the surface reliably and very accurately.  We will [likely] need methods of generating some propellant on the suface.  We will need development of inflatable habitat tech for having living and working space on the surface.  We will need new high efficiency solar arrays or isotope generators to power an expendition.

These are things that -must- be developed...not just things that would be -nice- to have developed.  Again, start with the lowest common denominator, and work your way out adding complexity (and cost) until you reach a balance of functionality and affordability.


Offline Solman

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Re: Mars Direct - Problems and Solutions
« Reply #79 on: 11/23/2013 09:03 pm »
@ Lobo I think you missed my point. Solar concentrator tech offers more than an order of magnitude improvement over existing solar PV. Currently solar panels of 200W(elec.)/kg are considered advanced. Concentrator PV using the L'garde concentrator would likely exceed 5000W(elec.)/kg. for perhaps 3+ KW/kg (at 70% efficiency and allowing for the mass of power supply equip. and the elec. engine itself) and any craft using it would also be able to use the concentrated sunlight directly in a solar thermal engine at over 8 KW/kg. ( 50% overall efficiency and the engne is very low mass). STR engines have been successfully tested at Marshall and other designs have exceeded 1000 sec. Isp. This allows use of the Oberth effect unlike SEP using regular solar panels for the LEO to HEEO part and perigee escape thrust and perhaps for MOI at high Isp.
 A fast trip using chemical requires much more propellant making it impractical without ISRU and with ISRU solar thermal with its ability to use a wide variety of propellants, offers potential advantage beyond its more than double Isp. The basic components are there the development would involve optimizing them to work together. IMO this would likely take less time and cost far less than what is being spent on the SLS upper stage alone.
 Faster transit has many advantages beyond convenience such as lower radiation exposure, more launch windows and lower food requirement.
Perhaps the biggest advantage is that concentrators also work with beamed power. Ultimately that is how we will travel between the two planets I believe because its efficiency beats even antimatter and we have the tech to do it today. !8 billion spent building a ground based laser array in the gigawatt range would make space travel routine cheap and fast. Too bad we aren't being that bold today IMO.


Offline kkattula

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Re: Mars Direct - Problems and Solutions
« Reply #80 on: 11/25/2013 03:43 am »
@ Lobo I think you missed my point. Solar concentrator tech offers more than an order of magnitude improvement over existing solar PV.
If you wanted hot water this might be right. If compared to using PV to make hot water in a home- sunlight to electric power and electrical power to make hot water- in terms of costs.
...
So on Earth concentrated solar power is not 10 times better unless you confining what you are comparing.
...

What has cost of generating electricity on Earth got to do with it? That's totally irrelevant. You're just pointlessly clogging up the thread.

Solman was clearly comparing Specific Power as a metric.  Current PV panels for use in space have a fairly low SP. I expect there are advanced designs that do a lot better, and still have higher TRL than concentrated solar PV and Thermal in space, but it's an interesting trade.

« Last Edit: 11/25/2013 03:52 am by kkattula »

Offline kkattula

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Re: Mars Direct - Problems and Solutions
« Reply #81 on: 11/25/2013 03:50 am »
My opinion on the Mars Direct plan is that landing an ERV is a poor idea.  Taking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture. I prefer to break down the mission into its discrete parts and design for each of those. Also to look beyond the first mission to consider what choices will facilitate follow on trips.

The journey phases are:

  1) Earth to Earth Orbit
  2) Earth Orbit to Mars Orbit
  3) Mars EDL
  4) Mars Surface Stay
  5) Mars to Mars Orbit
  6) Mars Orbit to Earth Orbit
  7) Earth EDL

The most expensive mass in terms of delta v and propellant multipliesrs in previous stages, is mass landed on Mars then returned to Earth or its vicinity.  Mars Direct accepts that penalty in return for fewer propulsive events, and being able to use ISRU for all the return propellant. But it leaves little or nothing for reuse by the next mission, and compromises the two, long, in space transits.

My preference is to assemble an SEP (or STP) MTV at EML2 (or in LEO and port to EML2). A realitively simple one, composed of three or four modules launched by commercial Heavy launchers. Also position an MTV minus the main propulsion as a gateway station.

  1) Propellant, supplies and disposable landers are sent to EML2 by commercial launchers. Crew travel in commercial 'cab'.
  2) MTV departs for Mars with optional STP or chemical boost to gain some Oberth advantage. Propulsive capture into HMO. 180 days?
  3) A final landing site is selected, then surface prep rover, habitat, supplies, ascent propellant or optional ISRU plant, are landed by 'standard' cargo landers. Crew follow in light weight vehicle that is also the empty ascent vehicle, mounted on a standard lander
  4) Crew explore using habitab and rover(s). Transfer or make ascent propellant. 500 days?
  5) Crew and samples ascend to HMO and rendezvous with MTV
  6) MTV departs for Earth and propulsively captures into EML2
  7) Crew transfer to commercial cab at the gateway station and return to Earth

Notes: 

i. MTV can be re supplied and make additional trips. Perhaps 5 or more over its working life. And to other destinations.

ii. A second MTV can depart EML2 at about the same time the first is leaving Mars, with the next crew. 

iii. Some of the crew could remain on Mars until the next crew arrives and leave in the next window.

iv. Additional supplies could be sent directly to the base, using the same 'standard' lander.

v. First mission could skip the crew anding and just visit Phobos & Deimos. Plus land one or more surface prep rovers in candidate locations, for tele-operation. Pilot ISRU plants too, so the first landing mission has one or more prepared sites with landing beacons, water, oxygen and rocket propellant available. If none of the pilot sites work out, they can send a second prep mission before having to commit to a crew landing.

Offline a_langwich

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Re: Mars Direct - Problems and Solutions
« Reply #82 on: 11/25/2013 03:53 am »
Concentrator PV using the L'garde concentrator would likely exceed 5000W(elec.)/kg. for perhaps 3+ KW/kg (at 70% efficiency and allowing for the mass of power supply equip. and the elec. engine itself)

References? 
Hardware built?

Offline sdsds

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Re: Mars Direct - Problems and Solutions
« Reply #83 on: 11/25/2013 05:22 am »
Taking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture. [...]

  5) Mars to Mars Orbit
  6) Mars Orbit to Earth Orbit

Are you certain the delta-v spent reaching a rendezvous orbit around Mars prior to TEI is worth the savings? Wouldn't a direct ascent from the surface to an Earth-bound escape trajectory have a lower delta-v than the sum of the two maneuvers you list?

Also, what is the "cost" (in terms of LOC risk if nothing else) of requiring the Mars-orbit rendezvous? Doesn't requiring a rendezvous constrain the Mars-surface launch window? And what about a rendezvous or docking or hatch-opening failure?
« Last Edit: 11/25/2013 06:51 am by sdsds »
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Offline guckyfan

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Re: Mars Direct - Problems and Solutions
« Reply #84 on: 11/25/2013 06:43 am »
Taking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture. [...]

  5) Mars to Mars Orbit
  6) Mars Orbit to Earth Orbit

Are you certain the delta-v spent reaching a rendezvous orbit around Mars prior to TEI is worth the savings? Wouldn't a direct ascent from the surface to an Earth-bound escape trajectory will have a lower delta-v than the sum of the two maneuvers you list?

Also, what is the "cost" (in terms of LOC risk if nothing else) of requiring the Mars-orbit rendezvous? Doesn't requiring a rendezvous constrain the Mars-surface launch window? And what about a rendezvous or docking or hatch-opening failure?

That's the big question. It's trading mission complexity with rendezvous and docking against the need to produce a lot more propellant using ISRU for the Mars ascent.

For a single mission the rendezvous and docking may be better.

For a  (semi)permanent base building ISRU on Mars is a one off and then enables simpler missions with a lot less mass lifted on earth. Fuel for the full return flight would be sourced on Mars instead of only the fuel for Mars ascent.

ISRU on Phobos would change the equation again.

« Last Edit: 11/25/2013 06:44 am by guckyfan »

Offline colbourne

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Re: Mars Direct - Problems and Solutions
« Reply #85 on: 11/25/2013 10:24 am »
I would assume the early missions to Mars would be one-way due to the low-cost, simplicity and desire to create a colony. Those who want to return to Earth probably dont have the right stuff.
We might still possess the infra-structure of reusable cyclers for crew comfort on the trip to Mars .
I think after a few years on Mars we should be able to   have enough ground equipment to allow for the safe launch to orbit and rendezvous with the cycler.

Offline guckyfan

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Re: Mars Direct - Problems and Solutions
« Reply #86 on: 11/25/2013 11:49 am »
I would assume the early missions to Mars would be one-way due to the low-cost, simplicity and desire to create a colony. Those who want to return to Earth probably dont have the right stuff.
We might still possess the infra-structure of reusable cyclers for crew comfort on the trip to Mars .
I think after a few years on Mars we should be able to   have enough ground equipment to allow for the safe launch to orbit and rendezvous with the cycler.

 ;D

They may go to stay. However their transfer vehicles will return to earth for reuse. And as they go back, those who don't want to stay can go back too. That's what Elon Musk said and so it must be true.

But I agree they may go for a minimum stay that is much longer than a year. People and cargo go first and then the infrastructure for refuelling and return will be built. That should bring cost and complexity of the mission way down.


Edit: Unmanned precursor missions will have to make sure that water can be produced, before people go, though.
« Last Edit: 11/25/2013 11:50 am by guckyfan »

Offline kkattula

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Re: Mars Direct - Problems and Solutions
« Reply #87 on: 11/26/2013 07:51 am »
Are you certain the delta-v spent reaching a rendezvous orbit around Mars prior to TEI is worth the savings? Wouldn't a direct ascent from the surface to an Earth-bound escape trajectory have a lower delta-v than the sum of the two maneuvers you list?

Yes, absolutely direct ascent has a lower delta v. However, that lower delta v has to be applied to the entire Earth Return Vehicle, rather than just a small capsule only intended to support the crew for a day or two. It's the difference between landing then launching a school bus or a Smart car.  The only way it wins is if the ERV is tiny, with more limited supplies and redundancy. And that increases the risk to the crew.

Quote
Also, what is the "cost" (in terms of LOC risk if nothing else) of requiring the Mars-orbit rendezvous? Doesn't requiring a rendezvous constrain the Mars-surface launch window? And what about a rendezvous or docking or hatch-opening failure?

INARS but I believe a direct Earth injection places a a constraint on the launch window too. I specified a High Mars Orbit for the MTV as that eases rendezvous constraints at the expense of higher delta v for the ascent vehicle. 

Again, delta v expended on the component with least mass is well spent.

So effectively the risk of rendezvous failure is the same as direct ascent trajectory failure.

TEI for the MTV from HMO is a more relaxed manoeuvre, in a proven vehicle, with plenty of time & options if the first attempt is aborted. So it doesn't add a lot of extra risk.

Backup for docking & hatch opening is the same as during Apollo: EVA from the ascent to the return vehicle.

IMO, if you can't plan on routinely docking and opening a hatch, you've probably got no business going to Mars.

Offline kkattula

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Re: Mars Direct - Problems and Solutions
« Reply #88 on: 11/26/2013 08:09 am »
That's the big question. It's trading mission complexity with rendezvous and docking against the need to produce a lot more propellant using ISRU for the Mars ascent.

For a single mission the rendezvous and docking may be better.

For a  (semi)permanent base building ISRU on Mars is a one off and then enables simpler missions with a lot less mass lifted on earth. Fuel for the full return flight would be sourced on Mars instead of only the fuel for Mars ascent.
...

I think you've got that around the wrong way. For a one-off mission, there's no need to re-use any component, so you can throw away your outbound habitat, propulsion systems, ERV, etc, and subject the crew to extreme conditions.

In an extended settlement scenario, you can't afford to send a new disposable ERV every time. Let alone all the rest.  I will grant you ISRU is more affordable across multiple missions, but it should lead to the path of re-usable descender/ascender.

Offline guckyfan

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Re: Mars Direct - Problems and Solutions
« Reply #89 on: 11/26/2013 11:19 am »
That's the big question. It's trading mission complexity with rendezvous and docking against the need to produce a lot more propellant using ISRU for the Mars ascent.

For a single mission the rendezvous and docking may be better.

For a  (semi)permanent base building ISRU on Mars is a one off and then enables simpler missions with a lot less mass lifted on earth. Fuel for the full return flight would be sourced on Mars instead of only the fuel for Mars ascent.
...

I think you've got that around the wrong way. For a one-off mission, there's no need to re-use any component, so you can throw away your outbound habitat, propulsion systems, ERV, etc, and subject the crew to extreme conditions.

In an extended settlement scenario, you can't afford to send a new disposable ERV every time. Let alone all the rest.  I will grant you ISRU is more affordable across multiple missions, but it should lead to the path of re-usable descender/ascender.

So where do you see a difference? It's exactly what I said too.


Offline Solman

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Re: Mars Direct - Problems and Solutions
« Reply #90 on: 11/27/2013 08:52 pm »
Concentrator PV using the L'garde concentrator would likely exceed 5000W(elec.)/kg. for perhaps 3+ KW/kg (at 70% efficiency and allowing for the mass of power supply equip. and the elec. engine itself)

References? 
Hardware built?

 have lost reference to the specific concentrator by L'Garde but it is somewhere in Nextbigfuture. Their website has it as well I believe
 For the concentratrator PV: http://www.spectrolab.com/DataSheets/PV/pv_tech/msce.pdf  p.69                 
re solar concentrator:  http://www.lgarde.com/papers/207.pdf  and an example with large concentrator currently in use in Australia:  http://www.psicorp.com/pdf/library/sr-1228.pdf 
 The PV has been tested at 900 suns so the mass of these cells id hundreds of times less per unit watt than one sun PV. Concentrators, even the L'garde ones are nowhere near the limit in terms of specific power since they can be made with holes smaller than the wavelengths of visible light. The PV requires a heat exchanger and radiator but operates at over 40% efficiency so I guess over 5KW/kg for system.
I'll try to find the L'Garde concentrator reference.


Offline baddux

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Re: Mars Direct - Problems and Solutions
« Reply #91 on: 11/28/2013 01:58 pm »
If Mars Direct as such was conducted would it be possible to utilize Orion in the ERV? Ideally one could combine Bigelow Sundancer-like hab and Orion (+ tanks, engines, ISRU power plant etc.) and send it to Mars with SLS as the ERV.

Anyway I think that the only way to fit Mars mission to NASA's budget is to build a reusable space station / cycler which could be sent to Mars orbit, MSL1 point or Phobos/Deimos. Then you could build the station and the HLV booster first, maybe test it in lunar orbit, keep it manned in LEO or EML1 like ISS now and then start developing MAV and Mars hab unit.
« Last Edit: 11/28/2013 02:00 pm by baddux »

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #92 on: 12/02/2013 10:59 pm »
My opinion on the Mars Direct plan is that landing an ERV is a poor idea.  Taking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture.


Actually I think the opposite.  I think it's probably the lowest common denominator of a Mars mission.  The most basic and simple (not complex) way to do a mission.
It's also the most mass inefficient way to do it. 
I agree with the rest of your post though.  Although it does leave a crew hab and equipment on the surface that future crews could access.  Zubrin's planned called for each subsequent mission to land within rover range of the previous mission hab lander, so if there was a problem with their hab lander, they could travel to the other one and use it as a life boat until the orbital mechanics were such they could enter their ERV and head home.  And each mission after would do the same, leap frogging accross Mars to establish a pattern of exploration. 

That was the idea anyway.

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #93 on: 12/02/2013 11:07 pm »
Taking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture. [...]

  5) Mars to Mars Orbit
  6) Mars Orbit to Earth Orbit

Are you certain the delta-v spent reaching a rendezvous orbit around Mars prior to TEI is worth the savings? Wouldn't a direct ascent from the surface to an Earth-bound escape trajectory will have a lower delta-v than the sum of the two maneuvers you list?

Also, what is the "cost" (in terms of LOC risk if nothing else) of requiring the Mars-orbit rendezvous? Doesn't requiring a rendezvous constrain the Mars-surface launch window? And what about a rendezvous or docking or hatch-opening failure?

That's the big question. It's trading mission complexity with rendezvous and docking against the need to produce a lot more propellant using ISRU for the Mars ascent.

For a single mission the rendezvous and docking may be better.

For a  (semi)permanent base building ISRU on Mars is a one off and then enables simpler missions with a lot less mass lifted on earth. Fuel for the full return flight would be sourced on Mars instead of only the fuel for Mars ascent.

ISRU on Phobos would change the equation again.

That's why I think a cycler could be interesting here.  There is still an orbital rendezvous event, just like if a MAV was rendezvouing with an ERV left in Mars orbit.  However, you don't have to brake that ERV into Mars orbit.  So that saves that mass penalty of a TPS system or extra fuel, depending on how you want to do MOI.  I don't think rendezvous with a cycler passing through vs. an ERV in Mars orbit is any more or less dangerous than the other.  You only have one shot at it either way.  (although if there was a problem with the ascent ignition, you could fix it and launch on the next ERV orbit.  But if there was a problem with anything after liftoff, you are screwed either way.  So MOR is a bit safer in case of an ignition problem only)

Direct Return is the most safe, obviously, because you'd have a pretty large window for ascent and direct TEI, with no rendezvous event necessary.

A cycler also leaves transit hab hardware available for future missions, where a tradition MOR like Mars Semi Direct does not.


Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #94 on: 12/02/2013 11:14 pm »
I would assume the early missions to Mars would be one-way due to the low-cost, simplicity and desire to create a colony. Those who want to return to Earth probably dont have the right stuff.
We might still possess the infra-structure of reusable cyclers for crew comfort on the trip to Mars .
I think after a few years on Mars we should be able to   have enough ground equipment to allow for the safe launch to orbit and rendezvous with the cycler.

Maybe later missions could be one way.  Early missions would almost surely have to be two way.  Even if everyone going had the full intention to stay, things change.  If someone gets very ill, or suffers from some sort of emotional problems and becomes dangerous to themselves and others because they want to leave, what do you do if you can't sent them back?  Do you kill them?  Do you try to incarserate them in a situation where every cubic foot of space is at a premium?
What happens if there's some equipment failures or premature wearing out on the surface making the hardware there incapable of sustaining the number of people there?

So you will need a way to send people back always.  Even if it's just a small number and not everyone.  However, early missions will be exposed to such new situations, I would fully expect a system that would return everyone for awhile while we are learning about the conditions and effects on humans during long duration stays on Mars.  Only later after those things are better understood and equipment and people have proven they can stay on Mars for long durations, would I ever expect to see a system that can't return everyone on a mission, with "permanent" people staying there.


Offline colbourne

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Re: Mars Direct - Problems and Solutions
« Reply #95 on: 12/04/2013 03:53 am »
It all depends on how much money you have available. The cheapest and simplest mission is going to be one-way and it also saves the danger of taking off from Mars, possibly having to rendevous with the return craft or alternatively ensuring the whole craft for the return trip arrives safely on the surface (with fuel on board or the extra complexity of manufacturing fuel from the Martian resources).

A well financed return mission, with the return equipment pre-delivered to Mars and tested,  could be the safest for the astronauts but I expect the probability of construction staff (Earth, LEO) being accidentally killed would be much higher on such a massive project. The project would also be so expensive, it will probably never happen.













Offline high road

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Re: Mars Direct - Problems and Solutions
« Reply #96 on: 12/04/2013 09:54 am »
It all depends on how much money you have available. The cheapest and simplest mission is going to be one-way and it also saves the danger of taking off from Mars, possibly having to rendevous with the return craft or alternatively ensuring the whole craft for the return trip arrives safely on the surface (with fuel on board or the extra complexity of manufacturing fuel from the Martian resources).

A well financed return mission, with the return equipment pre-delivered to Mars and tested,  could be the safest for the astronauts but I expect the probability of construction staff (Earth, LEO) being accidentally killed would be much higher on such a massive project. The project would also be so expensive, it will probably never happen.

How can a one way mission be cheaper than a return mission? I thought I had read somewhere on this forum that it takes about 7 times the fuel/kg of payload to return from Mars to Earth, than it takes to get from here to there. How can the supplies needed by the colonists for the rest of their lives, be less than 7 times the weight of the ERV? Especially if that ERV (and the separate launch vehicle) is designed to be as light as possible. I'm ignoring ISRU at the moment, because any technology suggested so far is actually going to be subjected to incredible heavy usage and wear, and is going to INCREASE the mass of the needed supplies.

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #97 on: 12/04/2013 10:38 am »
It all depends on how much money you have available. The cheapest and simplest mission is going to be one-way and it also saves the danger of taking off from Mars, possibly having to rendevous with the return craft or alternatively ensuring the whole craft for the return trip arrives safely on the surface (with fuel on board or the extra complexity of manufacturing fuel from the Martian resources).

A well financed return mission, with the return equipment pre-delivered to Mars and tested,  could be the safest for the astronauts but I expect the probability of construction staff (Earth, LEO) being accidentally killed would be much higher on such a massive project. The project would also be so expensive, it will probably never happen.

How can a one way mission be cheaper than a return mission? I thought I had read somewhere on this forum that it takes about 7 times the fuel/kg of payload to return from Mars to Earth, than it takes to get from here to there. How can the supplies needed by the colonists for the rest of their lives, be less than 7 times the weight of the ERV? Especially if that ERV (and the separate launch vehicle) is designed to be as light as possible. I'm ignoring ISRU at the moment, because any technology suggested so far is actually going to be subjected to incredible heavy usage and wear, and is going to INCREASE the mass of the needed supplies.
I agree.
I as guess I would say 5 years on Mars equals trip to Mars. So if stay longer than 5 years it costs more than
round trip.
But if send crew to Mars fast, and send supplies slow, then it's more like it's equal to 10 years stay on Mars.

So I would suggest small crews send to Mars fast, and have crew planned stay being 2 years with option to extend to say 4 years. So crew must be willing to stay 4 years, but could get back in 2 years, or back sooner with emergency abort.
So this mean bases with good radiation shielding, as one of first things accomplished with first crew.

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #98 on: 12/04/2013 11:13 am »
How can a one way mission be cheaper than a return mission? I thought I had read somewhere on this forum that it takes about 7 times the fuel/kg of payload to return from Mars to Earth, than it takes to get from here to there. How can the supplies needed by the colonists for the rest of their lives, be less than 7 times the weight of the ERV? Especially if that ERV (and the separate launch vehicle) is designed to be as light as possible. I'm ignoring ISRU at the moment

There's ya problem. Zubrin's claim for Mars Direct is that oxygen, buffer gases can be produced on the surface. Water will be mostly recycled, with only replacement water needed to be produced from the atmosphere. That leaves food, for which he estimates 1,200 kg of dry food and 2,400 kg of whole food will be needed for a 600 day stay for four people.

That's just 548.1 kg per person per (Earth) year.

Personally, I think one way trips really only make sense if you're convinced that you can grow crops on Mars.. but it appears sending a 10 ton resupply mission from Earth every launch window would be sufficient to keep a small crew alive on Mars indefinitely, if that's what you wanted to do.
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Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #99 on: 12/04/2013 07:30 pm »
Personally, I think one way trips really only make sense if you're convinced that you can grow crops on Mars.. but it appears sending a 10 ton resupply mission from Earth every launch window would be sufficient to keep a small crew alive on Mars indefinitely, if that's what you wanted to do.

@this.

I would pretty surely think that in any Mars architecture, SpaceX or NASA, that all of the first several crews would come back.  It wouldn't be until a much later time after a lot of technology on the surface of Mars has been demonstrated and proven, and a lot of study of the effects of stays on the Mars surface, before the first crew "stays" on the surface indefinately....for for a very long duration.

And even then as you say, they might want to be showing they can grow food and produce water in-situ reliably before that happens, otherwise any "colony" would be fully dependant on regular supply drops from Earth....which is entirely possibly if that's what they wanted to do.
« Last Edit: 12/04/2013 07:32 pm by Lobo »

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #100 on: 12/04/2013 09:16 pm »
I would pretty surely think that in any Mars architecture, SpaceX or NASA, that all of the first several crews would come back.  It wouldn't be until a much later time after a lot of technology on the surface of Mars has been demonstrated and proven, and a lot of study of the effects of stays on the Mars surface

..

they might want to be showing they can grow food and produce water in-situ reliably

I agree, but it should be mentioned that if you can prove in-situ production of consumables and food growing before sending any humans then the very first crew to go could be one way, without relying on (regular) resupply.

Thing is, if you can get resupply down to a reliable art and cut the costs significantly, one way to stay with just in-situ production of consumables - food resupplied until local food growing is online - becomes feasible too.

On the other hand, it's hard to see how the cost of sending an ERV to Mars can get much cheaper than that described in Mars Direct.
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Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #101 on: 12/04/2013 09:34 pm »
Pure fat (no water) has about 4000 kCal/pound. Or about 8800kCal/kg. That means one kg of pure fat contains over 4 days of calories for a person. 90kg of fat is sufficient for all the calories a person needs for a year. Double that to include carbs and protein and add in another 20kg for micronutrients, fiber, etc and you have a round 200kg of concentrated food per astronaut per year. 1mT of concentrated food is enough for 5 astronauts (at Earth-level metabolic rate) for a year. 10mT is enough for the rest of the life of a typical astronaut. 10mT per person of food. If you want variation, grow your own food.

I'm sure that number can be reduced by an order of magnitude if you could figure out how to synthesize lipids and carbohydrates (and feed it to mycoprotein along with ammonia to produce any protein you might need... also produces some fats and carbs using glucose, oxygen, ammonia, and some micronutrients as feedstocks). That is an unknown amount of mass, but I'd be supremely interested in what sort of machine is needed to synthesize glucose, ammonia, and perhaps some lipids. With those things synthesized on-site (along with the mycoprotein... though make sure you break down the nucleic acid first), you need an order of magnitude less per year of imported nutrients, possibly a single metric ton would be good for half a century.

http://www.biotopics.co.uk/edexcel/biotechnol/myco.html
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Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #102 on: 12/04/2013 09:54 pm »
Okay, I figured out a pathway for synthesizing sugars from martian air and water:
Methanol can be synthesized from carbon monoxide and hydrogen (which can be produced from CO2 and water respectively through electrolysis).
Formaldehyde can be synthesized from methanol.
Simple sugars can be synthesized from formaldehyde.

Fungi (like mycoprotein Quorn uses) consume simple sugars, oxygen (also produced from electrolysis), and ammonia (produced using the Haber process from electrolyzed hydrogen and Martian nitrogen gas) plus a small amount of micronutrients to produce lots of protein plus some dietary fiber, carbohydrates, and fats plus some vitamins.

I imagine all of the above could, at some scale, fit entirely inside a shipping container, taking only electricity, martian air, and water (plus a few micronutrients and top-up of catalysts every once in a while) as inputs. (Getting it to work /reliably/ with minimal human interaction and with food-safe output would be an enormous challenge!)

There is probably a much more straightforward metabolic pathway that can be used to produce edible proteins (and dietary fiber, lipids, and carbs) using H2, CO, NH3, and H20 as inputs (in addition to micronutrients). But as an upper bound to complexity, this would work.
« Last Edit: 12/04/2013 10:02 pm by Robotbeat »
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Offline high road

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Re: Mars Direct - Problems and Solutions
« Reply #103 on: 12/05/2013 08:15 am »
How much energy would that require? That's quite of an issue considering the limited powersource you can bring with you.

If you'd use a large tank, fill it with a mix of nutritious single celled organisms, that could produce about as much food per kg of payload. Add some other plants or a large supply of nutrition supplements for anything the algae can't produce, The only power required would be a few lights to increase growth speed. Select species with an affinity for human waste and water purification potential, and you're really making a dent in power needs. (not to mention: free oxygen while you're at it).

Pushing out the water could get you a few different textures: crackers, mash, goo and shake. A few tanks with different kinds of organisms and a range of herbs grown on Mars could get you more diverse tastes and colors. The astronauts would be thankful for that. Not to mention for a portion of soylent green at the occasional funeral to spice things up.

edit: if you're still short on power and you're planning on using algae anyway, maybe it's an idea to have a few tanks for of algae specialized in extracting nutrients from Martian soil or making fuel. No high octane level required for a Mars rover, so the energy needs for algae fuel production are greatly reduced.
« Last Edit: 12/05/2013 08:27 am by high road »

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #104 on: 12/17/2013 12:32 am »
Energy required totally depends... But you can get a lower bound by just counting the calories!!! 1000 kcal (half a day) is about 1kWh, very roughly. So each day's worth of food (per astronaut) takes at very minimum 2-3 kWh. Plus inefficiencies. :) So, if I'm just going to make up a number, I'd say the process would probably be at best 10% efficient (probably less than 1% before optimization), so ~24 kilowatthours per astronaut per day... Each person requiring 1kW average power. 10,000 people (a good start on a colony) would require 10MW of power for food production.

That's compared to about 50MWe for a nuclear sub reactor. 10MW of average power on Mars... 8 hours a day, at the equator, assuming 50% insolation... 500/3, about 150W/m^2 average power... at 33% efficiency... 50We/m^2, so about 450 m square of solar arrays as a starting guess (maybe round up to 25% more so a 500m square). Have to keep them free of dust. That works out to around 40,000 people who can be supported (in food) by the power output of a 1km square solar farm on Mars... That's more than the population density of Mumbai. So just the roof of the colony would probably have enough area to provide solar power to produce enough food for the colony.

Each person would need 20 square meters (or a square 4.5m or 15 feet on a side) of solar array to provide enough power (on average) for synthetic food. 1 kilowatt average per person.

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Offline Vultur

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Re: Mars Direct - Problems and Solutions
« Reply #105 on: 12/18/2013 05:04 am »
Would synthesis come out ahead of algae-farms? Sure, photosynthesis has low efficiency, but you don't necessarily have to provide the energy yourself (except possibly in the case of prolonged dust storms).

I think intensive algae-farming needs more work done.

EDIT: An algae farm would probably be more robust to breakdowns/problems than a complex technological synthesis, too. Or at least easier to fix. Especially if you are careful not to bring any pests/diseases/unwanted species from Earth.

And I'm not suggesting  pure algae as a diet. I'm just skeptical of reasonably-sized (taking mass limitations into account) greenhouses with conventional plant crops producing enough food for astronauts reliably. So you might need a more intensive, low-volume, low-mass source like algae farms to make up the calories.
« Last Edit: 12/18/2013 05:07 am by Vultur »

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #106 on: 12/18/2013 05:37 am »
Sure, algae would probably work, too, but you'd probably need a lot of that equipment anyway. For instance, you probably need to feed fixed nitrogen to the algae, so you'd need some kind of ammonia processing anyway.

The nice thing is that the photobioreactor-based algae is well-suited to growing on Mars, since it isn't exposed to the environment and is already stored in vessels that could be made able to withstand the low pressures of Mars.
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Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #107 on: 12/18/2013 06:08 am »
Ethylene can be produced pretty directly from methane (which we'll be making anyway). Ethylene is useful for all sorts of substances, but most relevant is that it can be made into Dyneema/Spectra pretty easily and can also be made into typical greenhouse plastic pretty easily. These two together can allow you to expand your living space or the space you grow stuff in relatively easily.

Imagine well-insulated (enough to prevent over-night freezing) giant bubbles of polyethylene with water, seed algae, and CO2 inside... distributed across the landscape (perhaps with simple aluminum reflectors to maximize output)... after the CO2 in the bubbles is consumed and converted into algae biomass, you collect the bubbles, suck out the O2 for use on the colony, suck out the water for recycling, then reprocess the rest into new plastic and food or something. You could design a machine would could produce these bubbles in an automated process, allowing a dramatic increase in growing area without a lot of infrastructure or work.
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Offline guckyfan

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Re: Mars Direct - Problems and Solutions
« Reply #108 on: 12/18/2013 07:39 am »
Ethylene can be produced pretty directly from methane (which we'll be making anyway). Ethylene is useful for all sorts of substances, but most relevant is that it can be made into Dyneema/Spectra pretty easily and can also be made into typical greenhouse plastic pretty easily. These two together can allow you to expand your living space or the space you grow stuff in relatively easily.

Actually, not it can't just yet. It would be a very useful process to have here on earth with increasing methane production but so far it is only a lab capability but cannot be done on a technical scale. Intense research is ongoing though to achieve it. Yes it will be very useful on Mars.

Imagine well-insulated (enough to prevent over-night freezing) giant bubbles of polyethylene with water, seed algae, and CO2 inside... distributed across the landscape (perhaps with simple aluminum reflectors to maximize output)... after the CO2 in the bubbles is consumed and converted into algae biomass, you collect the bubbles, suck out the O2 for use on the colony, suck out the water for recycling, then reprocess the rest into new plastic and food or something. You could design a machine would could produce these bubbles in an automated process, allowing a dramatic increase in growing area without a lot of infrastructure or work.

I think they would use pipes or hoses to circulate water for algae growth instead. Also very easy to manufacture once you have ethylene and does not need significant strength for the needed pressure. Also sunlight can get to the algae very easily. Efficiency would drop during duststorms but production would not stop if you can keep the temperature in the needed range.




Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #109 on: 12/18/2013 06:37 pm »
Ethylene can be produced pretty directly from methane (which we'll be making anyway). Ethylene is useful for all sorts of substances, but most relevant is that it can be made into Dyneema/Spectra pretty easily and can also be made into typical greenhouse plastic pretty easily. These two together can allow you to expand your living space or the space you grow stuff in relatively easily.

Actually, not it can't just yet. It would be a very useful process to have here on earth with increasing methane production but so far it is only a lab capability but cannot be done on a technical scale. Intense research is ongoing though to achieve it. Yes it will be very useful on Mars.
Lab-scale counts as "can." :)

Quote
Imagine well-insulated (enough to prevent over-night freezing) giant bubbles of polyethylene with water, seed algae, and CO2 inside... distributed across the landscape (perhaps with simple aluminum reflectors to maximize output)... after the CO2 in the bubbles is consumed and converted into algae biomass, you collect the bubbles, suck out the O2 for use on the colony, suck out the water for recycling, then reprocess the rest into new plastic and food or something. You could design a machine would could produce these bubbles in an automated process, allowing a dramatic increase in growing area without a lot of infrastructure or work.

I think they would use pipes or hoses to circulate water for algae growth instead. Also very easy to manufacture once you have ethylene and does not need significant strength for the needed pressure. Also sunlight can get to the algae very easily. Efficiency would drop during duststorms but production would not stop if you can keep the temperature in the needed range.
I agree. Tubes are a better plan.
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Offline guckyfan

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Re: Mars Direct - Problems and Solutions
« Reply #110 on: 12/18/2013 07:00 pm »
I agree. Tubes are a better plan.

Actually I saw a research facility at the Uni where my daugter was studying. They used plastic pipes of app. 10cm diameter for circulating algae. :)


Offline Vultur

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Re: Mars Direct - Problems and Solutions
« Reply #111 on: 12/19/2013 03:19 am »
Sure, algae would probably work, too, but you'd probably need a lot of that equipment anyway. For instance, you probably need to feed fixed nitrogen to the algae, so you'd need some kind of ammonia processing anyway.

Maybe. I dunno if any of the nitrogen-fixing cyanobacteria are edible to humans, but if they are, you might well be able to get along without it. This would certainly be ideal.

(Yes, cyanobacteria are not technically algae, but...)

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #112 on: 12/19/2013 05:48 am »
Sure, algae would probably work, too, but you'd probably need a lot of that equipment anyway. For instance, you probably need to feed fixed nitrogen to the algae, so you'd need some kind of ammonia processing anyway.

Maybe. I dunno if any of the nitrogen-fixing cyanobacteria are edible to humans, but if they are, you might well be able to get along without it. This would certainly be ideal.

(Yes, cyanobacteria are not technically algae, but...)
Ammonia is useful for other things, and it's one of the easier things to synthesize, given a stream of hydrogen and nitrogen.
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Offline Vultur

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Re: Mars Direct - Problems and Solutions
« Reply #113 on: 12/20/2013 12:11 am »
Sure, algae would probably work, too, but you'd probably need a lot of that equipment anyway. For instance, you probably need to feed fixed nitrogen to the algae, so you'd need some kind of ammonia processing anyway.

Maybe. I dunno if any of the nitrogen-fixing cyanobacteria are edible to humans, but if they are, you might well be able to get along without it. This would certainly be ideal.

(Yes, cyanobacteria are not technically algae, but...)
Ammonia is useful for other things, and it's one of the easier things to synthesize, given a stream of hydrogen and nitrogen.

How low mass can you get the synthesis equipment though? IIRC it involves pretty high pressures...

I don't think farms in a Mars colony would need very much fertilizer at all - on Earth massive fertilizer is needed because crops are removed from the system. But if human wastes are recycled into the agriculture, relatively little nitrogen will be lost.

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #114 on: 12/20/2013 05:19 am »
Sure, algae would probably work, too, but you'd probably need a lot of that equipment anyway. For instance, you probably need to feed fixed nitrogen to the algae, so you'd need some kind of ammonia processing anyway.

Maybe. I dunno if any of the nitrogen-fixing cyanobacteria are edible to humans, but if they are, you might well be able to get along without it. This would certainly be ideal.

(Yes, cyanobacteria are not technically algae, but...)
Ammonia is useful for other things, and it's one of the easier things to synthesize, given a stream of hydrogen and nitrogen.

How low mass can you get the synthesis equipment though? IIRC it involves pretty high pressures...

I don't think farms in a Mars colony would need very much fertilizer at all - on Earth massive fertilizer is needed because crops are removed from the system. But if human wastes are recycled into the agriculture, relatively little nitrogen will be lost.
I still think it'd be useful. You need it for synthesizing some plastics, etc.
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Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #115 on: 12/27/2013 07:15 pm »
My opinion on the Mars Direct plan is that landing an ERV is a poor idea.  Taking everything the returning crew needs down to the surface, only to have to launch it again? Unnecessarily complicates and constrains the architecture.


Actually I think the opposite.  I think it's probably the lowest common denominator of a Mars mission.  The most basic and simple (not complex) way to do a mission.
It's also the most mass inefficient way to do it. 
I agree with the rest of your post though.  Although it does leave a crew hab and equipment on the surface that future crews could access.  Zubrin's planned called for each subsequent mission to land within rover range of the previous mission hab lander, so if there was a problem with their hab lander, they could travel to the other one and use it as a life boat until the orbital mechanics were such they could enter their ERV and head home.  And each mission after would do the same, leap frogging accross Mars to establish a pattern of exploration. 

That was the idea anyway.

Actually, if SpaceX's MCT -is- really going to be an integrated upper stage/MTV/Mars Lander/MAV/ERV, all in one spacecraft...then that would be truely the lowest common denominator. 

Maybe call it "Mars Very Direct" or something....  ;-)

But, it could work similarly.  Start with an uncrewed MCT sent first which would refuel itself on the surface.  Then send the crew.  When they land, they actually transfer to the first MCT while the one they came on refuels itself for the next crew.  If there were some emergency, they might be able to abort and take right back off, depending on the oribtal mechanics and trajectories used.  Or wait for a return window that's shorter than it would otherwise by, and one they couldn't hit if waiting for their MCT to slowly refuel itself.

MCT is still refurbished and reused, just crews swap the one they use when they get to Mars.

Like Mars Direct, but just one craft instead of two.

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #116 on: 12/27/2013 07:42 pm »
Yeah, that's what it seems like it will be. Though I think it can fly with or without the hab module portion. Perhaps even be detachable (that way they can use MCT for launching commsats, too). Speculation, of course. But that's essentially what the Twitter exchange that Musk had with someone implied.
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Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #117 on: 12/27/2013 09:40 pm »
Yeah, that's what it seems like it will be. Though I think it can fly with or without the hab module portion. Perhaps even be detachable (that way they can use MCT for launching commsats, too). Speculation, of course. But that's essentially what the Twitter exchange that Musk had with someone implied.

Yea, I think that was from Tinker on the forum.

Yea, I would think there'd be either an expendable upper stage option (using the same tooling as the MCT hull and the cores, but just a dumb upper stage), or basically MCT, less the cargo/hab/ECLSS or other crew accomodations...depending on it's trajectory.  If it's going to escape, I don't think you can get the stage back.  A large planetary probe for example.
If going to a HEO, then it should be able to retain enough residual to put it on an orbit that will intersect back with Earth once the payload has been deployed?

A different stage, but with the same TPS system, same RCS sytem, same main engine, same landing legs, etc as MCT.  Since rockets aren't legos, it's probably not as simple as taking an MCT and removing a hab module from it.  It would probably be a different stage than MCT from many respects, but sharing tooling and systems with MCT.

I sort of picture a long cylinder (like the SpaceX reusable upper stage from the SpeaceX video) with heavy TPS on the nose, with lighter, secondary TPS along one side.   For atmospheric entry the nose takes the brunt of the heat energy at a slight angle letting the lighter TPS on the side take some.  After a certain amount of deceleration has been achieved, it pitches up and lays sideways presenting the large surface area for further deceleration from it's full side cross section.  Finally, shortly before landing, it pitches fully over so the main engine and landing gear point down, and lights the main engine for terminal decelleration, hover, and landing. 

If SpaceX is able to recover F9R boosters, they'll actually be doing the groundwork for doing just such maneuvers with a cylindrical shape.  If they can bring the 2nd stage back in this manner, they'll have already proven the concept on a smaller scale.  At least for Earth EDL.
After that, use FH to send the reusable 2nd stage to Mars with a loiter package (for the journey there) and test Mars EDL using that method.   If they can land a Falcon 2nd stage on Mars that way, the MCT concept would basically be proven then.  They'll just then need to test and demonstrate the ability to produce LCH4 adn LOX on the Mars surface to facilitate a return trip.

Kinda cool if that's the case, as the groundwork they to just make a reusable Falcon booster and upper stage would then already have them most of the way to proving MCT's systems and techniques.
If they had a small methalox engine available, they could make a modified Falcon upper stage that would use it, and -maybe- able to carry enough LH2 and an isotope generator and sabatier reactor enough that they could actually be testing the ability for such a system to refuel itself on Mars and come back with just FH hardware, because MCT's booster is flying.


Offline Russel

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Re: Mars Direct - Problems and Solutions
« Reply #118 on: 12/29/2013 09:41 am »
A quick review of the Mars Direct mission mode:

1)
 a) A heavy lift launch vehicle in the 100 ton to LEO class launches an Earth Return Vehicle (ERV).
 b) After remote checkout in LEO, the LH2/LOX Earth departure stage throws the ERV to an 8 month transit to Mars.
 c) The ERV aerobrakes into Mars orbit, and remote checkout is made again.
 d) Entry into the Mars atmosphere is made, the heat shield is discarded and parachutes are deployed.
 e) The parachutes are detached and the ERV lands under rocket power.

2)
 a) A hatch opens on the ERV, an a rover carrying nuclear reactor and trailing an electrical cable is deployed.
 b) It drives the nuclear reactor some distance away and preferably over a hill or two.
 c) The nuclear reactor is offloaded and started.
 d) The ERV begins processing the Mars atmosphere to produce methane and LOX, using a supply of LH2 brought from Earth.
 e) The rover searches for an appropriate landing site and marks it with a radar beacon.

3)
 a) A heavy lift launch vehicle in the 100 ton to LEO class launches another Earth Return Vehicle (ERV).
 b) See steps 1 and 2, a different landing site is chosen within travel range of the first landing site.

4)
 a) A heavy lift launch vehicle in the 100 ton to LEO class launches a "tuna can" habitat with 4 astronauts.
 b) After checkout in LEO the LH2/LOX Earth departure stage throws the hab on a 6 month transit to Mars.
 c) The now spent upper stage is used as counterweight to spin up the hab on a ~150m tether, at 2 rpm, to produce artificial Mars gravity for the crew.
 d) After aerobraking into Mars orbit, the crew inspects the landing site for weather, marker signal strength, etc.
 e) Entry into the Mars atmosphere is made, the heat shield is discarded and parachutes are deployed.
 f) The parachutes are detached and the crew lands under rocket power at the transponder.

5)
 a) 500 day ground operations begins
 b) The crew drive a pressurized rover to the ERV to obtain methane and LOX for powering the rover and breathing, etc.

6)
 a) When it's time to leave, the crew get into the ERV and liftoff.
 b) The ERV returns directly to Earth.
 c) Reentry is direct (the ERV doesn't go into orbit first).
 d) Landing is preferably on land for quick recovery.

Fundamental Problems

1)
 a) There is no HLV in the 100 ton to LEO class available, and there is no LH2/LOX Earth departure stage of the required size available.
 b) As there is no current commercial use for a 100 ton to LEO class vehicle, the total cost of development and operations would have to be borne by NASA.
 c) The average flight rate of one launch per year (two every two years) is too low to anticipate reliable operations, increasing both loss of mission and loss of crew risk.
 d) The low flight rate also increases operations cost.

2)
 a) The artificial gravity system is immature, with no tethers of the required length ever flown successfully in space.
 b) Without artificial gravity, the tuna-can hab is possibly too small to maintain crew health in zero-g.

3)
 a) Radiation exposure is possibly too harsh, depending on the solar cycle.

4)
 a) No nuclear reactors are available and this is seen by some as a political roadblock.

Remedies

1)
 a) Use commercially available rockets to maximize cost sharing and higher launch rate benefits.
 b) As these are at least half the payload-to-LEO class (53t for Falcon Heavy), and of smaller core size (~5m diameter payload), at least the habitat (~9m diameter) will have to be redesigned.
 c) The various parts of the ERV and hab will need to be staged and assembled on-orbit during the two year build-up between each Mars transit window.
 d) Docking of fuel tanks can be done last to minimize boil-off of cryogenic propellants.

2)
 a) Although artificial gravity experiments could be done, the now modular habitat design allows larger, while lighter, structure, suggesting a zero-g transit may be preferred.
 b) Astronauts will utilize exercise equipment and zero-g mitigation drugs to maintain bone and muscle mass.

3)
 a) A long column of water can be used as a solar radiation shield.

4)
 a) Use flexible photovoltaic power. The rover will need to be able to unpack and lay out the power system under remote control.

I usually go into a great deal of detail but for now I'll just note that one of my motivations in looking for alternative missions to Mars (at least the getting there and back part of the problem) is my misgivings about Mars direct.

Essentially how I feel about Mars direct is its a case of a simple and thus seductive idea, pushed too far.

And where it comes unstuck is the mass multiplier involved in getting an Earth return vehicle deep out of the Mars gravity well. It makes more sense in terms of mass and energy to have a return vehicle in orbit.

I also think people get carried away with the idea of manufacturing fuel (as opposed to oxidiser) on Mars.

Firstly, the mass multiplier for hydrogen is 4, not 18. The oxygen is improperly carried into the sum, but the fact is you can produce Oxygen easily from the Martian atmosphere, without any imported hydrogen. Once you add to that the fact that importing hydrogen means a bulky storage vessel, is difficult to store efficiently, and then you consider that landing said hydgrogen on Mars means yet more mass in terms of the added mass of the vehicle that contains the hydrogen (a factor of 2 to 3) and the supposed benefits of importing hydrogen diminish.

And of course fuel production means more landed mass for the machinery to do so, the power source and so on.

And when you take all of that and add to it the mass multiplier of getting your earth return vehicle at least as far as orbital velocity and you end up with a fuel plant that's unreasonably heavy and power hungry.

Ok, that's what I don't like about Mars direct. And why every time I've come at this I've ended up with the earth return vehicle pre-postioned in orbit, or some scheme to that effect.

For me all of this is a show stopper. Despite Mars direct appearing simple, its one of that cases where a simple idea just doesn't work in reality.

-Russel

Offline baddux

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Re: Mars Direct - Problems and Solutions
« Reply #119 on: 01/09/2014 12:10 pm »
I'm in favour of landing the whole ERV.

Today we are watching nervously unmanned rockets' stage separations and opening a hatch in the ISS and so on, so imagine what it would be with Mars orbit rendezvous with people on board with the spacecrafts that have been launched from Earth years ago. So having absolutely minimum amount of critical steps after launching the ERV is important.

About the ERV, did Zubrin plan it to be only a single module which would land on Earth? Or could it have separate hab module and landing capsule? With single module you would not have to turn the capsule and move the crew to the hab module after launch (which worked fine in Apollo though). And with hab + lander configuration you could probably have some abort possibility back to Mars if the launch fails (with vehicle like propulsive Dragon) and the heat shield mass would be smaller when landing only a small capsule to Earth.
« Last Edit: 01/09/2014 12:13 pm by baddux »

Offline Lobo

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Re: Mars Direct - Problems and Solutions
« Reply #120 on: 01/09/2014 05:30 pm »
I'm in favour of landing the whole ERV.

Today we are watching nervously unmanned rockets' stage separations and opening a hatch in the ISS and so on, so imagine what it would be with Mars orbit rendezvous with people on board with the spacecrafts that have been launched from Earth years ago. So having absolutely minimum amount of critical steps after launching the ERV is important.

About the ERV, did Zubrin plan it to be only a single module which would land on Earth? Or could it have separate hab module and landing capsule? With single module you would not have to turn the capsule and move the crew to the hab module after launch (which worked fine in Apollo though). And with hab + lander configuration you could probably have some abort possibility back to Mars if the launch fails (with vehicle like propulsive Dragon) and the heat shield mass would be smaller when landing only a small capsule to Earth.

I believe in Mars Direct, ZUbrin's ERV was a two stage vehicle.  It lands ahead of the crew, and refuels itself.  Then at the end of the mission, the crew boards it, and takes off directly for Earth.  The whole vehicle didn't land on Earth, only the top part.  It has a hab module too, although it's smaller than the one in the Hab lander, so the return trip would be fairly cramped, but not extremely so.
I think the whole hab came back to EArth as part of the crew module, but I'm not 100% sure about that.  Not sure if there was any Mars ascent abort options for it.
« Last Edit: 01/09/2014 06:21 pm by Lobo »

Offline baddux

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Re: Mars Direct - Problems and Solutions
« Reply #121 on: 01/09/2014 08:37 pm »
Thanks Lobo.

I believe it would make sense to do a precursor mission with only the ERV, so launch the ERV from Earth with people on board, keep it in LEO (or maybe lunar orbit or EML1) for 6-8 months and come back. That of course only if Mars Direct is generally feasible way to do Mars mission. NASA does not have money to do the whole Mars mission but they want to do something that some day enables Mars mission. That way you could develop half of the needed stuff and also proof that the ERV is not too small for 6-8 month journey back (or if it is you can land earlier).

Offline go4mars

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Re: Mars Direct - Problems and Solutions
« Reply #122 on: 02/09/2014 02:56 am »


Zubrin briefly outlines Mars Direct, and talks a little about what can be done with the Falcon Heavy. 

During the question period, he mentions that the one thing he would change about Mars Direct, is that he wouldn't send any cryogenic hydrogen.  Just make it there from Mars water. 
His company, Pioneer something, did a study -baking water out of soil that is 5% water (Mars obviously has a lot higher concentrations in some areas). 

It's fun to listen to these.  While I missed this one, I hope to make it to the Mars Society convention in Texas this August 7-10.  There's no better venue for Elon to unveil elements of his Mars architecture IMO.     
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Offline MikeAtkinson

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Re: Mars Direct - Problems and Solutions
« Reply #123 on: 02/09/2014 09:33 am »
Zubrin briefly outlines Mars Direct

Which still has the same problem: incredibly optimistic mass budget.


talks a little about what can be done with the Falcon Heavy. 

At 24:00

During the question period, he mentions that the one thing he would change about Mars Direct, is that he wouldn't send any cryogenic hydrogen.  Just make it there from Mars water. 
His company, Pioneer something, did a study -baking water out of soil that is 5% water (Mars obviously has a lot higher concentrations in some areas).

This improves the ERV by not needing 6.3 tonnes of hydrogen carried to Mars. If you have "The Case for Mars" note that there is no mass budget for the hydrogen tank or cryocooler.

But the ERV will have to mine over 1000 tonnes of martian soil and bake the water out. This is not a trivial operation to be done automatically on a mass and power budget.

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #124 on: 02/09/2014 01:13 pm »
Quote
But the ERV will have to mine over 1000 tonnes of martian soil and bake the water out. This is not a trivial operation to be done automatically on a mass and power budget.

Could use something like bunker buster which impacts areas of deeper permafrost.
So hit area where permafrost is 50 meters deep.
Which if can't anywhere else could be at Mars poles.
Design to penetrate 40 meters and have "warhead" kept intact and be made
radioactive material.
So have encased to survive something like 5 km/sec impact, and would also be safe to launch it
from earth.
You don't have slow it down, much, though want to be able aim it. And it could have a large
target area- assuming the area of 50 meter deep permafrost is large.

The impactor itself will make heat, but reactor would heating somewhat large volume which
is 40 meter underground.
So say want it to melt volume of equal to a 10 diameter sphere [500 cubic meters of ice].

So, to melt 500,000 kg ice. And ignore temperature and just look phase change:
334 kJ/kg times 500,000 is 167 million KJ.
And there is about 2.6 million seconds in month, that's 64,200 watts.
So say 50 KW of thermal heat.
Hmm. "Americium-241: Decay heat: 114 watts/kg"
http://en.wikipedia.org/wiki/Americium-241
About 440 kg of Americium-241 is about 50 KW
And Kinetic energy of 4000 kg at 5 km/sec. 50 million KJ

And energy to vaporize say 100,000 kg of water is 2,270 kJ/kg:
227 million KJ- so there is not enough energy involved to vaporize
as much as 100 tons of water.
Would guess within 1 month total amount of loss could around
a range of 10 tons or less. And have hundred tons or more of liquid
water available in about a month.


So have bunker buster impact a month before the ERV arrives at Mars.

 

Offline MikeAtkinson

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Re: Mars Direct - Problems and Solutions
« Reply #125 on: 02/09/2014 01:21 pm »
Quote
But the ERV will have to mine over 1000 tonnes of martian soil and bake the water out. This is not a trivial operation to be done automatically on a mass and power budget.

Could use something like bunker buster which impacts areas of deeper permafrost. ...


Doesn't sound much like something Zubrin would suggest for Mars Direct. Difficult to design, difficult to test, difficult to verify it has worked (water melted but drained away). I'm not sure that landing at the poles would be a good idea (at least initially).

Offline Ben the Space Brit

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Re: Mars Direct - Problems and Solutions
« Reply #126 on: 02/09/2014 01:37 pm »
Regarding Mars Semi-Direct (where the ERV remains in LMO rather than stages from Mars's surface) one thought that always occurred to me is that it makes the Mars Ascent Vehicle potentially overpowered. I suppose it means that you could carry 200% of the required propellent from the Martian surface to LMO and pump the remainder into the ERV, increasing its delta-V budget.

To me, Mars Direct always had one enormous problem and that was it was a hyper-optimistic plan assuming best cases in space environment, crew psychology, ISRU efficiency, politics and budget. Any real mission plan would probably have to be a lot more conservative.

[edit]
The Mars Drive paper looks interesting. Basically (and there is no getting around this), not having a SHLV means that you have to get creative and a bit less elegant in your mission design. However, there is a big argument in favour of 'do what works'; form over function and all that.
« Last Edit: 02/09/2014 02:06 pm by Ben the Space Brit »
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Offline Vultur

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Re: Mars Direct - Problems and Solutions
« Reply #127 on: 02/09/2014 03:47 pm »
But the ERV will have to mine over 1000 tonnes of martian soil and bake the water out. This is not a trivial operation to be done automatically on a mass and power budget.

I don't get the soil thing. Why not land near the ice cap and use ice that you can just cut out of the ice cap right on the surface? It will be incredibly cold anyway...

Offline guckyfan

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Re: Mars Direct - Problems and Solutions
« Reply #128 on: 02/09/2014 04:33 pm »
But the ERV will have to mine over 1000 tonnes of martian soil and bake the water out. This is not a trivial operation to be done automatically on a mass and power budget.

I don't get the soil thing. Why not land near the ice cap and use ice that you can just cut out of the ice cap right on the surface? It will be incredibly cold anyway...

Desirable landing spots will be much nearer the equator. However radar data and even a rover have found ice so if an appropriate landing spot is selected mining water should not be too difficult.


Offline M129K

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Re: Mars Direct - Problems and Solutions
« Reply #129 on: 02/09/2014 05:53 pm »
Regarding Mars Semi-Direct (where the ERV remains in LMO rather than stages from Mars's surface) one thought that always occurred to me is that it makes the Mars Ascent Vehicle potentially overpowered. I suppose it means that you could carry 200% of the required propellent from the Martian surface to LMO and pump the remainder into the ERV, increasing its delta-V budget.

To me, Mars Direct always had one enormous problem and that was it was a hyper-optimistic plan assuming best cases in space environment, crew psychology, ISRU efficiency, politics and budget. Any real mission plan would probably have to be a lot more conservative.
I'll attach Zubrin and Weaver's original Mars Semi Direct plan, in which he also described a "Mars Hybrid Direct" architecture. In that architecture, the MAV stage would be significantly bigger and the ERV in orbit would be just a hab parked there. The MAV stage would push the ERV back to Earth. This option gives the lowest mass budget out of all the options, but that's pretty much its only advantage.


Offline R7

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Re: Mars Direct - Problems and Solutions
« Reply #130 on: 02/09/2014 07:58 pm »
Zubrin briefly outlines Mars Direct, and talks a little about what can be done with the Falcon Heavy. 

12:30

Quote from: Zubrin
Because you can make so much propellant you make extra propellant that allows you to propel ground vehicles using chemical engines which is really what you want because ground vehicles using chemical engines, combustion engines, have much higher power to mass ratio than you can get with fuel cells or batteries or radio isotopes. And that's why they're so much more popular here on Earth. In a frontier environment like Mars where you really do need the long range, the speed, the torgue, the hauling capability of having real car instead of a golf cart you really want to have one. It's essential you are going to Mars to explore the key requirement is mobility.

Ha, Martian combustion engines vindicated! ;)
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Offline go4mars

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Re: Mars Direct - Problems and Solutions
« Reply #131 on: 02/09/2014 08:58 pm »
Ha, Martian combustion engines vindicated! ;)
Zubrin suggests ISRU demo on the sample cache rover mission, but I'd rather see a Red Dragon ISRU that's quick, cheap, and independent of a rover mission.  Then the next rover can land, unroll large solar arrays, fill its tanks, and drive hard to the next location -where it refills while examining rocks.  Big heavy thing, lots of instruments.  There'd be trades between internal combustion and big batteries like Tesla packs that I don't yet know enough to comment on.
« Last Edit: 02/10/2014 02:23 am by go4mars »
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Offline MikeAtkinson

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Re: Mars Direct - Problems and Solutions
« Reply #132 on: 02/09/2014 09:20 pm »
Quote from: Zubrin
Because you can make so much propellant you make extra propellant that allows you to propel ground vehicles using chemical engines which is really what you want because ground vehicles using chemical engines, combustion engines, have much higher power to mass ratio than you can get with fuel cells or batteries or radio isotopes. And that's why they're so much more popular here on Earth. In a frontier environment like Mars where you really do need the long range, the speed, the torgue, the hauling capability of having real car instead of a golf cart you really want to have one. It's essential you are going to Mars to explore the key requirement is mobility.

Ha, Martian combustion engines vindicated! ;)

I looked at this in some detail about 15 years ago. It is not so clear cut, the rover is likely to have electric motors in the wheel hubs and the rest of the power needs are electric as well. An IC engine has great power density, but when you consider the entire fuel/oxidiser + engine system it is not that much better than the alternatives and can be worse depending on the traverse. Despite the low temperatures on Mars it will be difficult to keep the cold end of a heat engine cold given how poor forced air cooling will be on Mars.
Batteries and fuel cells produce relatively little heat and could probably be contained within the pressure vessel making maintenance easy, because IC engines produce so much heat they cannot be kept within the pressure vessel without adding to the cooling burden, so maintenance would lead to an EVA.

The system that offered the best balance of efficiency and flexibility was a series hybrid system. In this the IC can be run at its peak efficiency and only needs to be sized for average power use. Peak power needs come from drawing down the battery. Over the last 15 years batteries have become much better. I still think the best system is series hybrid, but the solution would probably include more battery. Short excursions and use around the base would only need battery power which is much more efficient.

Given the options:
   1.  Base power -> charge battery -> discharge battery -> rover power
   2.  Base power -> fuel production -> IC engine -> generator -> rover power
the first is about 3x more efficient.

This makes a lot of difference if base power is provided by Solar cells.

The other thing that has changed over the last 15 years is that it seems water (and hence hydrogen) will be much easier to obtain on Mars. Because water was a scarce resource my rover design of 15 years ago had capture and storage of the IC engine exhaust. Now it i possible to dump the exhaust, which means less tanks and longer range (as the weight of the rover decreases over the traverse).

At the current pace of battery vehicle development it seems likely that they will be equal with IC engine vehicles within 20 years. So it could well be that a battery only solution is best on the timescales of the first Mars landing.


Offline MikeAtkinson

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Re: Mars Direct - Problems and Solutions
« Reply #133 on: 02/09/2014 09:28 pm »
Ha, Martian combustion engines vindicated! ;)
Zubrin suggests ISRU demo on the sample cache rover mission, but I'd rather see a Red Dragon ISRU that's quick, cheap, and independent of a rover mission.

I also would want to see an independent mission, MSL 2 (or whatever it is called) will have very limited mass, power, volume and time budgets for ISRU. Much better a dedicated mission with two or three orders of magnitude more in each of these dimensions. The difficulty in ISRU is making it reliable at full scale, but in proving that 19th century chemistry works, and ISRU demo on MSL2 does not seem to be able to retire much of the risk of full scale ISRU.

Offline guckyfan

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Re: Mars Direct - Problems and Solutions
« Reply #134 on: 02/09/2014 10:30 pm »
I also would want to see an independent mission, MSL 2 (or whatever it is called) will have very limited mass, power, volume and time budgets for ISRU. Much better a dedicated mission with two or three orders of magnitude more in each of these dimensions. The difficulty in ISRU is making it reliable at full scale, but in proving that 19th century chemistry works, and ISRU demo on MSL2 does not seem to be able to retire much of the risk of full scale ISRU.

I agree. A demo of ISRU may not be necesssary. I would love to see a rover though with radar that can detect water in the ground and verify by drilling or digging. Having such a vehicle on the ground can give the data required for selecting a suitable location.


Offline Vultur

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Re: Mars Direct - Problems and Solutions
« Reply #135 on: 02/12/2014 05:01 am »
Desirable landing spots will be much nearer the equator.

Why? Less delta-v?

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #136 on: 02/12/2014 07:27 am »
Desirable landing spots will be much nearer the equator.

Why? Less delta-v?

Probably meant not within arctic circle.
With Earth one gets 6 months of night, on Mars 11 months of night.
Of course also gets 11 months of daylight

But near equator due to Mars rotation would easier to land or leave.
Due to Mars smaller size it's less than Earth.
So Earth rotation speed at equator is about 1000 mph. And Mars is about 550 mph.

But comparatively Earth orbital velocity of 7.8 km sec much higher than Mars 3.5 km/sec,
so it's not as much, but as fraction of needed delta-v it's more.
« Last Edit: 02/12/2014 07:28 am by gbaikie »

Offline guckyfan

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Re: Mars Direct - Problems and Solutions
« Reply #137 on: 02/12/2014 07:43 am »
Desirable landing spots will be much nearer the equator.

Why? Less delta-v?

As gbaikie posted this is a point but not a major one. I think that a settlement is better placed in a region where summer/winter is not that much different as I assume much if not all energy will initially come from solar. That would place a settlement as near to the equator as they can find a suitable landing point, that is a very low basin with proven water ressources.

Edit: Growing plants with natural light will also be easier near the equator.
« Last Edit: 02/12/2014 07:44 am by guckyfan »

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #138 on: 02/12/2014 08:28 am »
I still think Hellas Basin is a good choice. I know it's dusty, but it's got the highest pressure and I believe contains buried glaciers. Pressure is high enough to be above the triple point of water. If you're using fission, it's a great spot.
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Offline guckyfan

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Re: Mars Direct - Problems and Solutions
« Reply #139 on: 02/12/2014 09:05 am »
I still think Hellas Basin is a good choice. I know it's dusty, but it's got the highest pressure and I believe contains buried glaciers. Pressure is high enough to be above the triple point of water. If you're using fission, it's a great spot.

At 30° on its northernmost part I think it fits also my wish to be near the equator well enough. Yes it looks like a good location with water and high pressure, good for landing.

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #140 on: 02/13/2014 04:03 am »
I still think Hellas Basin is a good choice. I know it's dusty, but it's got the highest pressure and I believe contains buried glaciers. Pressure is high enough to be above the triple point of water. If you're using fission, it's a great spot.

At 30° on its northernmost part I think it fits also my wish to be near the equator well enough. Yes it looks like a good location with water and high pressure, good for landing.

There is what I would guess is crater about 50 km in diameter at about 73 E and the 30 latitude South line cuts crater in half. And crater has central peak which is near to 30 latitude line.
http://upload.wikimedia.org/wikipedia/commons/7/74/Hellas_MOLA_zoom_64_medium.jpg

It seems like deep crater and there looks old crater which sort of "bridges" to another crater also about 50 km diameter.  And old crater "bridges" to much bigger crater [about 200 km diameter].  It seems like an interesting area.

Offline colbourne

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Re: Mars Direct - Problems and Solutions
« Reply #141 on: 02/13/2014 10:43 am »
There are some advantages of being near the polar ice caps ie.
1) There should be easily available water, which is an essential resource.
2) Solar power is not much different at the poles than at the equator due to the near vacuum of the atmosphere. In the summer this means solar power all the time. Nuclear power probably would be used in the winter.
3) I could see ice caves being used for living space.
4) This is an interesting area to explore due to the slight possibility of life and the effects of the ice.

Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #142 on: 02/14/2014 02:42 am »
There are some advantages of being near the polar ice caps ie.
1) There should be easily available water, which is an essential resource.
2) Solar power is not much different at the poles than at the equator due to the near vacuum of the atmosphere. In the summer this means solar power all the time. Nuclear power probably would be used in the winter.
3) I could see ice caves being used for living space.
4) This is an interesting area to explore due to the slight possibility of life and the effects of the ice.

It seems one should a NASA base at the Mars poles at some point, but question is should it be the first location of Mars base.

If had two bases choose which one live at- so go there in the summer.
This conflicts with my idea of first mars base, in which I would first crew stay longer than 2 years, but could work if one wanted the first crew staying for shorter time period.
Though one could have first crew establish two bases and travel across the globe to the other base.

Suppose bases were about 1000 km from the pole, which is about 70 latitude and well within the Mars arctic circle. If both are same longitude the distance between them is about 8500 km [+5000 miles].
So options could be supersonic flight, or suborbital/orbital travel.
It seems if doing suborbital/orbital one use non-reusable rocket stages. The burnt stage will hit mars surface at high velocity and could regarded as "exploration"- it's impactor. And could designed to hit in location one could further explore in future.

The size of Mars polar caps vary:
Northern Cap    
Winter diameter    2,500 miles
Summer diameter    600 miles
And:
Southern Cap    
Winter diameter    1,000 miles
Summer diameter    200 miles
http://www.ozgate.com/infobytes/mars_polar.htm

So at 1000 km [620 miles] from pole, at northern cap you outside of permanent polar cap but within
cap at winter- or be in ice when/if arrive at spring, and retreats away from you as approach late summer.

Since not going to very near the southern cap, you alter what said above, and have it about 1000 km from North pole [so you will be in winter ice cap] and be about 1500 km from south pole. So with south location one is at the arctic circle. And could just south of Hellas basin or roughly in rim area of Hellas basin.

So first landing would be spring in north arctic polar region- and land in region of ice [which melts as you go towards summer. And spend next 10 months establishing base, and mining ice. Then leave to land on southern base. Establish this base and focus on exploration of region. Then return to northern base, and prepare to have a crew return to Earth.

Offline CuddlyRocket

Re: Mars Direct - Problems and Solutions
« Reply #143 on: 02/14/2014 10:38 am »
2) Solar power is not much different at the poles than at the equator due to the near vacuum of the atmosphere.

Solar power is a lot less at the poles than at the equator - it's why the ice caps are at the poles!

Quote
In the summer this means solar power all the time. Nuclear power probably would be used in the winter.

Another reason why the first bases will be at the equator - no need to bother with nuclear power!

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #144 on: 02/14/2014 02:40 pm »
The difference between 33 degrees latitude (where the deepest point on Mars is, roughly, in Hellas Basin) and 0 degrees isn't enormous. It's like Albaquerque, New Mexico (35 degrees) which gets /plenty/ of sunshine.
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Offline gbaikie

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Re: Mars Direct - Problems and Solutions
« Reply #145 on: 02/14/2014 07:23 pm »
2) Solar power is not much different at the poles than at the equator due to the near vacuum of the atmosphere.

Solar power is a lot less at the poles than at the equator - it's why the ice caps are at the poles!

The sun will be low on horizon in Mars polar region and level surface will get less solar energy.
With Mars or the Moon when sun only gets as high as 30 degrees above horizon a level surface only gets
1/2 the solar energy- Mars distance: 600 watts is 300 watts per square meter. This also the same at morning and late afternoon in region in which sun reaches near 90 degrees at noon.

Another factor is amount of atmosphere the sun must pass thru before hitting the surface. On Mars one can have global or regional dust storms, and low angle with a lot dust in atmosphere will block a significant  amount solar energy from reaching surface.
But if normal levels of dust and sun is low on horizon if pointing solar panels at the sun [rather than having them lying on level surface] one can get almost as much watts per square as get with sun directly over head [and solar panel pointed at sun].

So with Earth, the earth distance from Sun has about 1360 watts per square, and when have clear skies
and sun directly over head you only get about 1000 watts per square meter- or over 300 watts is lost going thru Earth's 1 atm of atmosphere.  And this lost increases starting when sun at 45 degree or lower.
So our sun travels about 15 degrees across sky per hour, and times between 9 am to 3 pm is the 1/2 of the day where one gets a large majority of the solar energy.
Due to this factor, pointing solar arrays at sun does not add a lot of solar energy- instead have solar panel fixed at angle [which varies depending upon your latitude] and if in northern hemisphere in direction  of south. though if you are always pointing directly at sun you do get about 10% improvement [it varies latitude and season].

Offline go4mars

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Re: Mars Direct - Problems and Solutions
« Reply #146 on: 02/14/2014 07:36 pm »
Solar power is not much different at the poles than at the equator due to the near vacuum of the atmosphere.

Solar power is a lot less at the poles than at the equator - it's why the ice caps are at the poles!


But if normal levels of dust and sun is low on horizon if pointing solar panels at the sun [rather than having them lying on level surface] one can get almost as much watts per square as get with sun directly over head [and solar panel pointed at sun].
Although this is correct, I'm not sure if we know enough to quantify the impact of dust. 

There's tremendous heat transfer through atmospheric and oceanic circulation on Earth. Does anyone have any papers or speculation (or quantification guesstimates) of heat transfer driven by Corilolis on Mars? I suspect martian cyclones, and polar ice shapes imply it could be more significant than people assume. 

Google, as usual lends a hand to get started. 
http://www.lukew.com/marsgeo/introduction2.html

I wonder how this all factors in to site selection. 
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Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #147 on: 02/14/2014 07:40 pm »
On an airless body, the angle of the sun doesn't matter, as long as you have your arrays pointed at the right angle and don't self-shadow. For flat planels not tilted, then yeah, poles will have basically no sun at any time. But if you tilt the panels toward the sun, then as long as the sun is up, you'll get the same amount of sun as at the equator.
For an airless body.
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Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #148 on: 02/14/2014 10:44 pm »
Zubrin briefly outlines Mars Direct, and talks a little about what can be done with the Falcon Heavy. 

During the question period, he mentions that the one thing he would change about Mars Direct, is that he wouldn't send any cryogenic hydrogen.  Just make it there from Mars water. 
His company, Pioneer something, did a study -baking water out of soil that is 5% water (Mars obviously has a lot higher concentrations in some areas). 
One of my pet ideas is creating a water reservoir (for various possible motivations) by melting a shaft into an icecap. This exploits the fact that ice is a good heat insulator so you can build up heat underground quite effectively. For example at equilibrium a megawatt of waste heat would be enough to keep a kilometer wide sphere of water liquid. (it would take a very long time for a megawatt to even melt that much ice, it would probably take thousands of years to approach that equilibrium, but anyway..)

Maybe this same approach would also be an effective way of extracting water from ground which is only a few percent ice also. Drill a shaft, dump heat, some ice will melt and there would only be one exit for the water/gas: up the shaft. Even if there were cracks or porous ground, any water flowing that way would refreeze and seal those paths.

I know that even drilling a shaft is not trivial with teleoperation, but it could be much simpler than diggers and dumptrucks all running around by teleoperation before crew arrive. It could also be a good science goal.

edit: Oops: just noticed gbakie also mentioned heat underground too, here:
...
« Last Edit: 02/14/2014 10:56 pm by KelvinZero »

Offline Hop_David

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Re: Mars Direct - Problems and Solutions
« Reply #149 on: 02/16/2014 05:33 am »
On an airless body, the angle of the sun doesn't matter, as long as you have your arrays pointed at the right angle and don't self-shadow. For flat planels not tilted, then yeah, poles will have basically no sun at any time. But if you tilt the panels toward the sun, then as long as the sun is up, you'll get the same amount of sun as at the equator.
For an airless body.

Insolation is cosine(grazing angle) for a horizontal surface. At 84 degrees, insolation would be about 1/10.

You could tilt the arrays as you say. Then the shadows would be 10 times longer than the array height.

And recall the array will follow the sun as it moves along the horizon, 360ş over a day's time. To avoid self shadowing, not only must the north and south neighbor arrays be 10 times the distance, but same holds true for neighboring arrays to the east and west.

To avoid neighbor's shadows, arrays at 84ş latitude would have to be scattered over a land area 100 times greater than at the equator. At 87ş latitude, it'd be about 400 times greater. At 88ş about 800. At 89ş, about 3000.
« Last Edit: 02/16/2014 05:44 am by Hop_David »

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Re: Mars Direct - Problems and Solutions
« Reply #150 on: 09/06/2014 03:36 pm »
Did the original Mars Direct Proposal include the weight of the cryogenic equipment they'd need to keep the hydrogen from boiling off, or at least carry more hydrogen to offset the losses? From what I've heard of boiloff rates for hydrogen, at least a quarter of it would have boiled off by the time the Earth Return Vehicle had reached the Martian surface....
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Offline M129K

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Re: Mars Direct - Problems and Solutions
« Reply #151 on: 09/06/2014 03:55 pm »
I believe it didn't. His mass breakdown for the ERV doesn't note anything about hydrogen-specific tanks. Just 5.81 tons of hydrogen. That's enough to produce about 104 tons of methalox which is what would be required for Mars Direct. No additional hydrogen or additional cryogenic equipment seems to be included.

Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #152 on: 09/06/2014 04:25 pm »
I think I remember something about Robert Zubrin more recently going to the option of exploiting local water..

It just occurred to me I have never seen the option of using hydrogen fuel discussed for mars, just as lunar ISRU discussions only seem to consider hydrogen, even though the LCROSS evidence suggests there is more carbon monoxide than ice.

Offline Darkseraph

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Re: Mars Direct - Problems and Solutions
« Reply #153 on: 09/07/2014 12:09 am »
If the extra hydrogen to account for boil-off wasn't included, its a stunning omission...because it would make the entire launch vehicle require an extra 150 tons of gross mass, roughly speaking. I'm not sure what the cryogenic equipment would weigh, but I'd imagine it would be lighter than 2 tons.
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Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #154 on: 09/07/2014 12:23 am »
If the extra hydrogen to account for boil-off wasn't included, its a stunning omission...

LH2 boiloff was accounted for in the 1991 paper.

Quote from: Bob Zubrin
Since the hydrogen component of the bipropellant mixture represents only about 5% of the total propellant weight it can be imported from Earth. Heavy insulation of tanks with multi-layer insulation (MLI) can reduce in-space boiloff of liquid hydrogen to less than 1% per month during the 6 to 8 month interplanetary transit without any requirement for active refrigeration. Since the hydrogen raw material is not going to be directly fed into an engine, it can be gelled with a small amount of methane to prevent leaks. Gelling of the hydrogen cargo will also reduce boiloff further (as much as 40%) due to suppression of convection within the tank.

Referencing:

8. Aerojet Techsystems, "Gelled Cryogenic Fuels: Past Experience and Future Needs," presentation to McDonnell Douglas Corp. , St. Louis, MO, March 10, 1987.

It's actually more than I've seen any other architecture say about boiloff.
Human spaceflight is basically just LARPing now.

Offline Darkseraph

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Re: Mars Direct - Problems and Solutions
« Reply #155 on: 09/07/2014 12:29 am »
If the extra hydrogen to account for boil-off wasn't included, its a stunning omission...

LH2 boiloff was accounted for in the 1991 paper.

Quote from: Bob Zubrin
Since the hydrogen component of the bipropellant mixture represents only about 5% of the total propellant weight it can be imported from Earth. Heavy insulation of tanks with multi-layer insulation (MLI) can reduce in-space boiloff of liquid hydrogen to less than 1% per month during the 6 to 8 month interplanetary transit without any requirement for active refrigeration. Since the hydrogen raw material is not going to be directly fed into an engine, it can be gelled with a small amount of methane to prevent leaks. Gelling of the hydrogen cargo will also reduce boiloff further (as much as 40%) due to suppression of convection within the tank.

Referencing:

8. Aerojet Techsystems, "Gelled Cryogenic Fuels: Past Experience and Future Needs," presentation to McDonnell Douglas Corp. , St. Louis, MO, March 10, 1987.

It's actually more than I've seen any other architecture say about boiloff.

Oh fair enough, that avoids that problem. I've never seen it mention in any of the talks, slides, op-eds and other avenues of ranting that Zubrin takes to. Has this approach actually been tried or intended for use on say, propellant depots?
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." R.P.Feynman

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #156 on: 09/07/2014 12:33 am »
Oh fair enough, that avoids that problem. I've never seen it mention in any of the talks, slides, op-eds and other avenues of ranting that Zubrin takes to. Has this approach actually been tried or intended for use on say, propellant depots?

The gelling? Well, no, because LH2 in propellant depots is "going to be directly fed into an engine".

Human spaceflight is basically just LARPing now.

Offline Darkseraph

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Re: Mars Direct - Problems and Solutions
« Reply #157 on: 09/07/2014 12:46 am »
Oh fair enough, that avoids that problem. I've never seen it mention in any of the talks, slides, op-eds and other avenues of ranting that Zubrin takes to. Has this approach actually been tried or intended for use on say, propellant depots?

The gelling? Well, no, because LH2 in propellant depots is "going to be directly fed into an engine".


Not the gelling, just using multiple layers of insulation. I've heard of proposals to use a solar powered cry cooler or a sun shield but if layers of insulation give the biggest gains in reducing boil off (less than 1%) and its higher cost with diminishing returns for the remainder, would they not just go with that for a preliminary depot? The hydrogen has the highest boil-off with the lowest mass after all, so it doesn't cost as much to lift some more hydrogen as it would for liquid oxygen!
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." R.P.Feynman

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #158 on: 09/07/2014 12:51 am »
Solar powered cryocoolers are the low-tech solution - the general term is refrigeration.

Insulation and sun shades with careful thermal management are still the rage, I think.
Human spaceflight is basically just LARPing now.

Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #159 on: 09/07/2014 02:33 am »
Solar powered cryocoolers are the low-tech solution - the general term is refrigeration.

Insulation and sun shades with careful thermal management are still the rage, I think.

I had always assumed that was just for demonstrators. Active cooling can be investigated separately, and sure, it might not even prove necessary, depending on the application. Probably not a good idea for propellant depot proponents to bulk up the price with nice-to-haves in the current environment.

But the result is that people always quote values predicted for these passive demonstrators as if this is evidence that zero boil-off is impossible with our current knowledge. I have yet to see an argument that it is even hard.

On earth, zero boil-off that require power probably sounds a bit pointless. If the only point is power storage then losing fuel or requiring power are not that different. This might give the impression that zero boil-off is still a matter of research on earth, but the assumption is magically low power zero boil-off. (.. I am guessing)

Offline QuantumG

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Re: Mars Direct - Problems and Solutions
« Reply #160 on: 09/07/2014 02:36 am »
When the only funding available is from a "technology research" budget, you have to turn it into a science project.
Human spaceflight is basically just LARPing now.

Offline A_M_Swallow

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Re: Mars Direct - Problems and Solutions
« Reply #161 on: 09/07/2014 07:28 pm »
Test tiny zero boil-off technology in a cubesat.  See if you can do the whole lot, including launch, for half a million dollars.

Offline CuddlyRocket

Re: Mars Direct - Problems and Solutions
« Reply #162 on: 09/08/2014 08:49 am »
It just occurred to me I have never seen the option of using hydrogen fuel discussed for mars...

Hydrogen as fuel is unpopular with rocket designers unless the greater performance is a necessity because of the much greater difficulties in handling and storage etc. And that's on Earth with all its manpower and other resources.

Also, the Carbon in methane shouldn't be discounted. It may have a lower Isp than the Hydrogen (what would the Isp of Carbon be?) but it's readily available.

Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #163 on: 09/08/2014 09:56 am »
It just occurred to me I have never seen the option of using hydrogen fuel discussed for mars...

Hydrogen as fuel is unpopular with rocket designers unless the greater performance is a necessity because of the much greater difficulties in handling and storage etc. And that's on Earth with all its manpower and other resources.

Also, the Carbon in methane shouldn't be discounted. It may have a lower Isp than the Hydrogen (what would the Isp of Carbon be?) but it's readily available.
Fair enough, but the second part of my post was how it was strange that the moon ISRU always focuses on the water when the evidence suggests that there is even more carbon monoxide in the LCROSS result.

As for hydrogen fuel being unpopular with rocket designers, hasn't methane been much less popular? Who currently uses it?

I also don't really like the idea of hydrogen for manned missions far from home. A tiny crack and you lose all your fuel. I might be ok with it if there was a lot of unmanned missions with the same hardware, and enough redundancy that loss of fuel was survivable, (for example the ability to survive until another vehicle was sent)

Offline CuddlyRocket

Re: Mars Direct - Problems and Solutions
« Reply #164 on: 09/09/2014 08:56 am »
It just occurred to me I have never seen the option of using hydrogen fuel discussed for mars...

Hydrogen as fuel is unpopular with rocket designers unless the greater performance is a necessity because of the much greater difficulties in handling and storage etc. And that's on Earth with all its manpower and other resources.

Also, the Carbon in methane shouldn't be discounted. It may have a lower Isp than the Hydrogen (what would the Isp of Carbon be?) but it's readily available.
Fair enough, but the second part of my post was how it was strange that the moon ISRU always focuses on the water when the evidence suggests that there is even more carbon monoxide in the LCROSS result.

A fair point, but not one to be discussed in the Missions to Mars (HSF) section! :)

Quote
As for hydrogen fuel being unpopular with rocket designers, hasn't methane been much less popular? Who currently uses it?

Nobody. This is mainly historical. In the early days performance was an issue leading to the use of kerosene or alcohol on early stages and hydrogen for upper stages. Then you had all this acquired knowledge that produces rockets that are good enough leaving little incentive to develop engines working on a new fuel. In fact there have been few new rocket engines (of any fuel) developed recently by anybody; most rocket engines used today were designed decades ago. SpaceX have been driven to methane for Mars missions by a combination of a need for performance and availability.

Quote
I also don't really like the idea of hydrogen for manned missions far from home. A tiny crack and you lose all your fuel. I might be ok with it if there was a lot of unmanned missions with the same hardware, and enough redundancy that loss of fuel was survivable, (for example the ability to survive until another vehicle was sent)

Agreed.

Offline Jim

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Re: Mars Direct - Problems and Solutions
« Reply #165 on: 09/09/2014 09:08 am »

I also don't really like the idea of hydrogen for manned missions far from home. A tiny crack and you lose all your fuel. I might be ok with it if there was a lot of unmanned missions with the same hardware, and enough redundancy that loss of fuel was survivable, (for example the ability to survive until another vehicle was sent)

That would apply to all propellants and hence not a valid reason not to use H2.

Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #166 on: 09/09/2014 10:36 am »

I also don't really like the idea of hydrogen for manned missions far from home. A tiny crack and you lose all your fuel. I might be ok with it if there was a lot of unmanned missions with the same hardware, and enough redundancy that loss of fuel was survivable, (for example the ability to survive until another vehicle was sent)
That would apply to all propellants and hence not a valid reason not to use H2.
I admit this was totally a laymans guess but I thought I had good reasons. So you would argue H2 storage does not have increased risk of developing leaks?

The reason I assumed it would were:
(*) materials having to deal with greater cold.
(*) A greater motivation to optimize tank mass, since the tank is larger.
(*) The ability of the hydrogen molecule to slip through smaller cracks.

Does the history of hydrogen fueled rockets suggest they do not have increased risk of leaks?

Offline Jim

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Re: Mars Direct - Problems and Solutions
« Reply #167 on: 09/09/2014 11:34 am »
I admit this was totally a laymans guess but I thought I had good reasons. So you would argue H2 storage does not have increased risk of developing leaks?

The reason I assumed it would were:
(*) materials having to deal with greater cold.
(*) A greater motivation to optimize tank mass, since the tank is larger.
(*) The ability of the hydrogen molecule to slip through smaller cracks.

Does the history of hydrogen fueled rockets suggest they do not have increased risk of leaks?

Not enough to disqualify it from manned missions far away from home.

Offline muomega0

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Re: Mars Direct - Problems and Solutions
« Reply #168 on: 09/09/2014 01:37 pm »
Solar powered cryocoolers are the low-tech solution - the general term is refrigeration.

Insulation and sun shades with careful thermal management are still the rage, I think.

I had always assumed that was just for demonstrators. Active cooling can be investigated separately, and sure, it might not even prove necessary, depending on the application. Probably not a good idea for propellant depot proponents to bulk up the price with nice-to-haves in the current environment.

But the result is that people always quote values predicted for these passive demonstrators as if this is evidence that zero boil-off is impossible with our current knowledge. I have yet to see an argument that it is even hard.
 (.. I am guessing)
The passive boiloff rate of 1%/month (0.03%/day) per Zubrin provided by Mars One has not been demonstated nor is likely achieved.

The best anyone has projected is 0.5% per day with a few MLI wraps.   With some very careful design, a few have *conjectured* 0.1% per day, but be ready to deploy a JWST-like sunshield.  Make it cylindrical if the ship is spinning for artificial gravity.

This is a rather simple calculation, BTW, so can you provide references that it is "not hard".

For example, the solar constant is 1370 W/m2 for Earth, 588 W/m2 at Mars.  Perfect MLI reduces the heat load by 1/n+1.   the projected area of the tank is Do * L.  As an example, choose 5m by 6m Long and 99 layers of MLI.  So the heat load is now 13.70 W/m2 * 30 m2 or 411 Watts(Earth) or 176 Watts (Mars)--this is the amount of constant thermal load into the LH2.   Uh-Oh, what is the boiloff rate at this heat load?

In addition, please provide the reference on how to to wrap 100 "effective" layers of MLI around the tanks, or if only say 30 layers is achievable, the increased boiloff rate.

Offline truth is life

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Re: Mars Direct - Problems and Solutions
« Reply #169 on: 09/09/2014 07:55 pm »
For example, the solar constant is 1370 W/m2 for Earth, 588 W/m2 at Mars.  Perfect MLI reduces the heat load by 1/n+1.   the projected area of the tank is Do * L.  As an example, choose 5m by 6m Long and 99 layers of MLI.  So the heat load is now 13.70 W/m2 * 30 m2 or 411 Watts(Earth) or 176 Watts (Mars)--this is the amount of constant thermal load into the LH2.   Uh-Oh, what is the boiloff rate at this heat load?

I'm not sure where you're getting the numbers you're using from (since Kelvin didn't provide any), or why you're so focused on passive methods when both QuantumG and KelvinZero are clearly talking about using cryocoolers and actively cooling LH2?

Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #170 on: 09/10/2014 04:24 am »
Not enough to disqualify it from manned missions far away from home.
Fair enough. Assuming you have access to water (dubious initially, but a necessity if we stay long term), which do you think would be more practical: methane or hydrogen fuel ISRU, including storage and suitability for launching from Mars. Why?

Offline Silversheep2011

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Re: Mars Direct - Problems and Solutions
« Reply #171 on: 09/10/2014 06:00 am »
On subject of H˛ boil off: Is it possible reuse the hydrogen off that's being gassing off as part of a fuel cell ?
1. Generates drinkable water.
2. Generates electricity.
3. Excess H˛O then becomes a supplementary electrical power 'source' when reversed by  electrolysis.
this helps at nighttime hours if solar and nuclear power 'offline' for any reason including  if fuel cell landed on Martian surface.( see pages 4-5 of report)  Additionally its adding extra redundancy to whole system.

Offline muomega0

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Re: Mars Direct - Problems and Solutions
« Reply #172 on: 09/10/2014 03:17 pm »
For example, the solar constant is 1370 W/m2 for Earth, 588 W/m2 at Mars.  Perfect MLI reduces the heat load by 1/n+1.   the projected area of the tank is Do * L.  As an example, choose 5m by 6m Long and 99 layers of MLI.  So the heat load is now 13.70 W/m2 * 30 m2 or 411 Watts(Earth) or 176 Watts (Mars)--this is the amount of constant thermal load into the LH2.   Uh-Oh, what is the boiloff rate at this heat load?
I'm not sure where you're getting the numbers you're using from (since Kelvin didn't provide any), or why you're so focused on passive methods when both QuantumG and KelvinZero are clearly talking about using cryocoolers and actively cooling LH2?
100s of watts of cooling at 20K is a great engineering challenge when faced with mass and cost budgets.  Hence 'not hard' just does not seem to fit.  Conservative paper studies backed with low TRL data indicated the active concept can be achieved however, but over 100W of cooling!   Contrast this with other space cryocooler programs

On the passive side, the issue is that folks cite performance numbers, reduces losses, for example, without the associated weight penalty or impact to the architecture.  After decades of experience, i suppose it may look easy to achieve 0.1%/day, but that was the result of a significant amount of work.  Then enter the political side, where decades have passed with inadequate funding to raise TRL (and inadequate cooling).

As a starting point, consider:
Flight Data from Centaur, with estimates using more MLI
 3 layer MLI     LOX    2  %/day    LH2: 4-5 %/day    based on 1 hour hold  Table 2 and Table 4 :
20 layer MLI    LOX   0.8%/day     LH2  2.5%/day      + 100lbs

ULA then proposes a different passive approach to shift from a few hours before burn to a longer few month duration transfer stage to reduce the boiloff to perhaps 0.1%/day:  LOX or LH2? 

Mars direct sites 0.1%/month or 0.03%/day. What did they add to the concept to achieve such a low rate and did they also consider LH2 boiloff? Part of the reduction occurs from the solar flux changing from 1373 to 588 W/m2, Earth to Mars, of course. 

The SLS like Ares V boiled away 70 tons of propellant staging six flights for a Mars DRM 5 assuming 0.1% per day, and did not include any design hardware nor mass in the architecture to achieve this rate.
 
The other issue with Mars Direct is the 6 month trajectory and given Apollo 13 and the lack of equipment in this particular mission, likely a sound choice, since at least it provides the ~ 2 year free return.   Mars direct then continues to recommend that *if* supplies are pre-deployed (4 launches?), that this 2 year free return be retained.  Further, other aspects of risk should be addressed with the offset mass, but to *not* shorten the 6 month trip trajectory.   IOW, always take the train to Nova Scotia, but not the lear jet, and if the train has an issue, just spend 2.5yrs in GCR rather than 1 year.  Perhaps there is less risk for younger folks with later concept?

So what does this have to do with active systems and LH2?   When you are stating that its 'not hard',  where are you placing the active system(s) in the architecture?  It makes quite a difference.

Groups keep glossing over many details so its no wonder Mars mission has ranged in mass from 100 to 300 to 400 to 1200mT. 

Offline JasonAW3

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Re: Mars Direct - Problems and Solutions
« Reply #173 on: 09/10/2014 04:05 pm »
How hard would it be to crack methane so that you could combine the O2 and hydrogen for potable water?

Could a Fuel Cell be configured to use Methane to generate power and potable water?
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Offline bubbagret

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Re: Mars Direct - Problems and Solutions
« Reply #174 on: 09/10/2014 04:09 pm »
How hard would it be to crack methane so that you could combine the O2 and hydrogen for potable water?

Could a Fuel Cell be configured to use Methane to generate power and potable water?

Pure water is the primary byproduct produced by a methane fuel cell.

Offline truth is life

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Re: Mars Direct - Problems and Solutions
« Reply #175 on: 09/10/2014 07:15 pm »
100s of watts of cooling at 20K is a great engineering challenge when faced with mass and cost budgets.  Hence 'not hard' just does not seem to fit.  Conservative paper studies backed with low TRL data indicated the active concept can be achieved however, but over 100W of cooling!   Contrast this with other space cryocooler programs

I see a number of apparently successful programs that have had to meet performance constraints very different from those experienced by a propellant depot, which in no way convinces me that providing depot-level cooling would be an issue provided there was actual work being done on it (in fact, it rather tends towards convincing me that if they were to work on it, then they would be perfectly able to design and subsequently build a depot-scale cooling system). The fact that cryocoolers of similar capability (for liquefying deeply cryogenic liquids like hydrogen and helium, for example) are used on Earth every day, especially given the fact that they actually have a more challenging thermal environment than in-space ones due to the addition of convection and conduction heat transfer modes tells me that any lack of depot-scale cryocoolers is driven mostly by the lack of a depot program or any other program to build large-scale cryocoolers, not that in-space cryocooling is any special technical challenge (compared, eg., to Mars EDL). In other words, it's not hard. Just not funded.

Offline Vultur

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Re: Mars Direct - Problems and Solutions
« Reply #176 on: 09/11/2014 02:15 am »
I think I remember something about Robert Zubrin more recently going to the option of exploiting local water..

If you send the return vehicle + ISRU equipment before you send people, that seems like the better approach.

Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #177 on: 09/11/2014 02:39 am »
I think I remember something about Robert Zubrin more recently going to the option of exploiting local water..

If you send the return vehicle + ISRU equipment before you send people, that seems like the better approach.
Sounds fiddly though, with teleoperation. I think Im quoting someone here quoting Zubrin so I would look for a better reference.. Just thinking about it, it doesn't sound reasonable unless (a) it referred to later trips or (b) there is a really indepth concept of how it would be done.

Come to think of it there was a massive ongoing discussion about power on Mars but water is probably a more difficult one and equally important. My favorite is landing on thick ice and melting your powerplant into it but there are only a few places away from the poles that I am aware of with surface ice, such as some craters. You might also be able to bore into permafrost and do the same thing, but boring is meant to be very difficult unmanned.

Someone here reckoned you might be able to get the necessary water out of the air as well but I dont know the numbers on that. There does not seem to be much water in the air at all.

Offline ThereIWas3

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Re: Mars Direct - Problems and Solutions
« Reply #178 on: 09/14/2014 07:23 pm »
Hartmann's book on Mars (very highly recommended) says that water ice is at depths as follows:

Quote
Estimates are 200-450 meters at the equator, 50-200 meters at 30-55 degrees latitude, and less than 100 meters poleward of 55 degrees.

The book describes how they arrive at these figures.    The Phoenix mission landed at 68 degrees north and it found some ice just under the surface, but did not carry equipment to judge how substantial it was.

If the Hydrogen/Sabatier approach is not used, I would say locations near the poles would be seriously considered for a first landing, just to guarantee access to the ice.  Later missions migh want to bring deep drilling equipment.


Offline Vultur

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Re: Mars Direct - Problems and Solutions
« Reply #179 on: 09/14/2014 10:42 pm »
Sounds fiddly though, with teleoperation.

If you land on top of exposed ice it might not be that bad (melt and pump up). Poles are difficult for solar power though, but doesn't Mars Direct assume a reactor anyway?

If you are constrained to solar power, though, then yeah - bring the hydrogen.

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #180 on: 09/14/2014 10:45 pm »
Hartmann's book on Mars (very highly recommended) says that water ice is at depths as follows:

Quote
Estimates are 200-450 meters at the equator, 50-200 meters at 30-55 degrees latitude, and less than 100 meters poleward of 55 degrees.

The book describes how they arrive at these figures.    The Phoenix mission landed at 68 degrees north and it found some ice just under the surface, but did not carry equipment to judge how substantial it was.

If the Hydrogen/Sabatier approach is not used, I would say locations near the poles would be seriously considered for a first landing, just to guarantee access to the ice.  Later missions migh want to bring deep drilling equipment.
It's better than that. There are buried glaciers with ice just a few meters down at mid-latitudes. Not everywhere, but definitely present. Can see them clear due to impacts uncovering the ice temporarily.
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Offline KelvinZero

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Re: Mars Direct - Problems and Solutions
« Reply #181 on: 09/14/2014 11:08 pm »
http://en.wikipedia.org/wiki/Glaciers_on_Mars#Water_source_for_future_colonists

(but doesn't seem to have much information about depth)

I think you should definitely be sending some precursors to verify the ice and probably help with landing navigation. Possibly worth checking the ground is stable also. Couldn't a bit of the ice have since evaporated leaving just a crusty bit on top? that would be embarrassing  :P

Offline Robotbeat

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Re: Mars Direct - Problems and Solutions
« Reply #182 on: 09/15/2014 03:04 am »
http://en.wikipedia.org/wiki/Glaciers_on_Mars#Water_source_for_future_colonists

(but doesn't seem to have much information about depth)

I think you should definitely be sending some precursors to verify the ice and probably help with landing navigation. Possibly worth checking the ground is stable also. Couldn't a bit of the ice have since evaporated leaving just a crusty bit on top? that would be embarrassing  :P
We know the ice is there:
http://news.nationalgeographic.com/news/2009/09/090924-mars-ice-picture.html
We even have radar data telling us how thick it is.

No doubt you'd still want a small precursor mission, though.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline ThereIWas3

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Re: Mars Direct - Problems and Solutions
« Reply #183 on: 09/15/2014 01:07 pm »
That is great.  Hartmann's book ("A Traveller's Guide to Mars") was published in 2003 so this information was not available.  I wish he (or somebody) would write a sequel.

Offline Pipcard

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Re: Mars Direct - Problems and Solutions
« Reply #184 on: 04/02/2015 01:34 am »
What would you consider a more realistic mass breakdown for the components of Mars Direct or Semi-Direct?

I agree that it shouldn't be done with two direct launches of a SHLV (>100 mT). The mission should involve a smaller launcher (but large enough to launch the components) with little-to-no orbital assembly that takes place in LEO, with some trips to refuel a departure stage and take advantage of a slightly higher flight rate.
« Last Edit: 04/02/2015 02:28 am by Pipcard »

Offline Dalhousie

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Re: Mars Direct - Problems and Solutions
« Reply #185 on: 04/02/2015 02:43 am »
What would you consider a more realistic mass breakdown for the components of Mars Direct or Semi-Direct?

I agree that it shouldn't be done with two direct launches of a SHLV (>100 mT). The mission should involve a smaller launcher (but large enough to launch the components) with little-to-no orbital assembly that takes place in LEO, with some trips to refuel a departure stage and take advantage of a slightly higher flight rate.

Why do it smaller?  MD and MSM are close to the minimum as it is.  Smaller launchers  mean orbital assembly.  Orboyal feulewing adds extra development that is not neccessary.
Apologies in advance for any lack of civility - it's unintended

Offline Pipcard

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Re: Mars Direct - Problems and Solutions
« Reply #186 on: 04/02/2015 03:52 am »
By smaller, I mean, the minimal launcher that can carry the Mars vehicle (however large it may be) and/or departure stage into LEO before departing for Mars. Something that can carry the same capacity as Falcon Heavy but with wider stages and fairings.

The Mars vehicles may have to be larger due to "optimistic/underestimated mass budgets," so a direct-to-Mars SHLV may become harder to develop or manage.

But I am curious as to what people think that masses should really be.

Why multiple launches with refueling (not a depot - direct refueling)? As it was said before, if you fly a super-heavy launcher only 1 time every two years, the fixed costs get divided over less launches, resulting in more cost per flight.

Maybe it will involve one launch to carry the ERV/Hab/(probably MAV?) with an unfueled departure stage into LEO. The alternative is to have several stages that link up to perform the TMI burn, but that involves more orbital assembly.
« Last Edit: 04/02/2015 04:12 am by Pipcard »

Offline Dalhousie

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Re: Mars Direct - Problems and Solutions
« Reply #187 on: 04/02/2015 04:52 am »
By smaller, I mean, the minimal launcher that can carry the Mars vehicle (however large it may be) and/or departure stage into LEO before departing for Mars. Something that can carry the same capacity as Falcon Heavy but with wider stages and fairings.

The Mars vehicles may have to be larger due to "optimistic/underestimated mass budgets," so a direct-to-Mars SHLV may become harder to develop or manage.

But I am curious as to what people think that masses should really be.

Why multiple launches with refueling (not a depot - direct refueling)? As it was said before, if you fly a super-heavy launcher only 1 time every two years, the fixed costs get divided over less launches, resulting in more cost per flight.

Maybe it will involve one launch to carry the ERV/Hab/(probably MAV?) with an unfueled departure stage into LEO. The alternative is to have several stages that link up to perform the TMI burn, but that involves more orbital assembly.

Falcon Heavy is too small without multiple missions, six to 12 to duplicate MD.  Even with ISRU you can't get away from needing about 15 tonnes per person on the surface of Mars.
Apologies in advance for any lack of civility - it's unintended

Offline Pipcard

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Re: Mars Direct - Problems and Solutions
« Reply #188 on: 04/02/2015 05:32 am »
So you're saying that a 60 tonne payload on the Martian surface is needed at least?
« Last Edit: 04/02/2015 05:33 am by Pipcard »

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