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#20
by
MB123
on 10 Mar, 2008 09:43
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These proposed architectures, are they available online? Will I be able to find many of them on the NASA techhnical reports server?
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#21
by
Kaputnik
on 10 Mar, 2008 11:18
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Look for Mars Direct, Mars For Less, NASA's 'Design Referece Mission version 1 to 3, amongst others.
Another example was published recently and details are discussed on the Ares-V part of the forum.
Yet another is JPL's NEP-AG study, although that didn't look at operations outside of Mars transit itself.
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#22
by
iamlucky13
on 12 Mar, 2008 22:35
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scienceguy - 8/3/2008 10:07 AM
Does anyone here know the maximum amount of mass that one could bring to Mars and still use aerobraking?
Does anyone here know the maximum amount of mass that one could bring to Mars and still use propellant to achieve Mars orbit?
The basic question has already been answered, but I thought I'd point out that aerobraking and achieving orbit are two separate actions. Aerobraking is used to circularize an orbit, such as the Mars Reconnaissance Orbiter did after its orbital insertion burn. This involves repeated dips through the upper atmosphere to lower the apogee of the highly elliptical insertion orbit. The final step is another engine burn to raise the perigee so the orbit is nearly circular.
Rather than a burn, aero-capture is another potential option for entering orbit. This is involves passing even lower into the atmosphere to bleed off a large amount of velocity in a single pass, entering an elliptical orbit that way. If desired, aerobraking or engine firing can then be used to circularize the orbit.
Aero-capture has never been done before. As I understand, it requires greater navigational precision, and a heat shield approximately as capable as one designed for direct entry.
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#23
by
A_M_Swallow
on 12 Mar, 2008 23:01
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iamlucky13 - 13/3/2008 12:35 AM
Aero-capture has never been done before. As I understand, it requires greater navigational precision, and a heat shield approximately as capable as one designed for direct entry.
To be viable the aero-capture heat shied only has to save its own weight in fuel, larger savings are even better. Is the Mars breaking delta-v of approx 3.3 km/s sufficiently low that a reusable heat sheild made out of say titanium possible?
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#24
by
A_M_Swallow
on 12 Mar, 2008 23:07
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Is there an elliptical/ballistic Earth orbit that can be used to test aero-capture?
To develop the techniques and heat shields we only need a small payload.
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#25
by
Kaputnik
on 13 Mar, 2008 11:55
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Is the MOI delta-v really as much as 3.3km/s? I thought it was more like a third of that. Oh well.
I believe that ESA are talking about an aerocapture demonstrator. I don't know the flight profile but you'd think an elliptical orbit or a lunar flyby would do the job.
Until we have a reliable network of guidance beacons at Mars (similar to GPS) I doubt that a manned spacecraft or even an unmanned one if it were mission critical would be allowed to use aerocapture, but that's just IMHO.
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#26
by
meiza
on 13 Mar, 2008 14:11
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Depends how many passes you can do. You're going to need some propulsion maneuvers anyway too. So it's not strictly an either-or-problem.
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#27
by
A_M_Swallow
on 13 Mar, 2008 16:05
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Kaputnik - 13/3/2008 1:55 PM
Is the MOI delta-v really as much as 3.3km/s? I thought it was more like a third of that. Oh well.
No. Rechecking that figure includes visiting both of Mars's moons.
Earth C3 to Mars transfer is 0.6 km/s
Mars transfer to Mars C3 is 0.9 km/s
Mars C3 to low Mars orbit = 0.2 + 0.3 + 0.9 = 1.4 km/s
So Mars transfer to low Mars orbit = 0.9 + 1.4 = 2.3 km/s
http://en.wikipedia.org/wiki/Delta-v_budget
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#28
by
iamlucky13
on 13 Mar, 2008 19:12
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A_M_Swallow - 12/3/2008 5:01 PM
iamlucky13 - 13/3/2008 12:35 AM
Aero-capture has never been done before. As I understand, it requires greater navigational precision, and a heat shield approximately as capable as one designed for direct entry.
To be viable the aero-capture heat shied only has to save its own weight in fuel, larger savings are even better. Is the Mars breaking delta-v of approx 3.3 km/s sufficiently low that a reusable heat sheild made out of say titanium possible?
A metal probably isn't a great material choice, and I'm not aware of any reason a ceramic or similar shield couldn't be used for both capture and entry. Still, some of the things I've read have suggested a two stage heat shield to reduce entry mass (less fuel to de-orbit, better mass/surface area ratio) and to reduce risk of heat soak from the capture from damaging anything. Ceramic heat shields have very low thermal conductivity, so over the relatively short time of the capture they may heat up quite a bit, but you'd have a fair amount of time to jettison it before the heat soaked into the rest of the craft.
The heating from the capture manuever is actually greater than that for the following entry from low orbit.
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#29
by
Suzy
on 15 Mar, 2008 20:04
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tnphysics - 10/3/2008 10:11 AMThe second method may not work owing to speed-of-light communication delays (up to 20 minutes+)
It's a 40-minute delay (20 minutes each way) when Mars & Earth are furthest apart
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#30
by
jcopella
on 16 Mar, 2008 14:51
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What is the current thinking (plans, designs, revised risk assessments) regarding radiation shielding? I had a casual association with someone in the Navy (somehow he got involved thru knowing Bill Readdy, IIRC) who worked on a Mars study group in the mid-90s. At the time he told me the radiation problem was a (the) show-stopper.
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#31
by
Podkayne
on 16 Mar, 2008 15:31
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For published reports on human missions to Mars, search David Portree's excellent compendium "Romance to Reality"
You could also try The Mars Society and NASA's technical reports library .
Many of the answers to questions on this thread can be found in scholarly, researched, and peer-reviewed papers. There is no need for speculative, incomplete, or shoot-from-the-hip answers - unless that's what you are looking for.
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#32
by
Podkayne
on 16 Mar, 2008 16:03
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jcopella - 16/3/2008 10:51 AM
What is the current thinking (plans, designs, revised risk assessments) regarding radiation shielding? I had a casual association with someone in the Navy (somehow he got involved thru knowing Bill Readdy, IIRC) who worked on a Mars study group in the mid-90s. At the time he told me the radiation problem was a (the) show-stopper.
For a
scholarly discussion of the risks of radiation exposure and other hazards to humans on Mars, see "
Safe on Mars: Precursor Measurements Necessary to Support Human Operations on the Martian Surface (2002) " from the National Research Council.
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#33
by
jcopella
on 16 Mar, 2008 16:35
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Podkayne - 16/3/2008 1:03 PM
jcopella - 16/3/2008 10:51 AM
What is the current thinking (plans, designs, revised risk assessments) regarding radiation shielding? I had a casual association with someone in the Navy (somehow he got involved thru knowing Bill Readdy, IIRC) who worked on a Mars study group in the mid-90s. At the time he told me the radiation problem was a (the) show-stopper.
For a scholarly discussion of the risks of radiation exposure and other hazards to humans on Mars, see " Safe on Mars: Precursor Measurements Necessary to Support Human Operations on the Martian Surface (2002) " from the National Research Council.
LOL
I've actually read that paper. It doesn't answer the question I posed (which I should clarify), but thanks -- it does deal with radiation impacts but the focus is on risks to Mars surface operations.
To clarify:
My question related to the shielding-related design impacts for a Mars Transfer Vehicle. The last I heard from someone actively working on a precursor project to VSE/Cx, the shielding requirements were a show-stopper.
I'm just wondering if there's been any evolution in that position since VSE/Cx, and if so, what the current thinking is.
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#34
by
Podkayne
on 16 Mar, 2008 18:27
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As you probably know, it takes a while for the results of NASA studies to make their way into publication. You might check the proceedings from the AIAA Space 2007 Conference or the 2008 Space Technologies and Applications International Forum for the most recent results that have made it past the technical and management reviews.
I haven't seen much on Constellation studies of human Mars missions since the House threatened to forbid NASA to fund any studies related to the subject. (This is not the first time Congress has forbid NASA to even think about human missions to Mars.)
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#35
by
Jason
on 16 Mar, 2008 23:02
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How well would a book like Red Mars hold up to reality? Do the ideas in it have any basis in the scientific community or is it misleading?
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#36
by
Podkayne
on 17 Mar, 2008 14:20
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#37
by
Garrett
on 17 Mar, 2008 15:06
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Where can we get reliable (scholarly) information on launch windows, journey times and total mission durations for human Mars missions? From Wikipedia it appears that the minimum energy launch window is about every 2.135 years (780 days)
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#38
by
Jim
on 17 Mar, 2008 15:17
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Garrett - 17/3/2008 12:06 PM
Where can we get reliable (scholarly) information on launch windows, journey times and total mission durations for human Mars missions? From Wikipedia it appears that the minimum energy launch window is about every 2.135 years (780 days)
They aren't fixed numbers. They are interrelated variables
Launch vehicle performance drives many of this numbers (launch windows, journey times, etc )
mission duration is a function of the mission architecture, which will or be affected Launch vehicle performance
the only thing fixed is the muinimum energy launch window of 26 months
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#39
by
Garrett
on 17 Mar, 2008 15:40
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Cheers for the quick reply. I actually hadn't finished my post - I pressed the "Submit" button by accident!
I understand that journey times and mission durations are not very closely correlated to launch windows, but I imagine that actual launches will be preferably close to the minimum energy launch window? An author on Wikipedia also suggested another, longer trajectory going into Venus.
I would still have believed that the mission duration will not be completely independent of these launch windows. Likewise, I imagine that the journey times will be optimised not only as a function of the launch vehicle but also of the launch window. What I'm wondering is whether the variables are as interrelated as you say or whether the situation is actually closer to a few "eigenvalues" so to speak?
I suppose the best answer is that I should probably start reading a "rocket science" book and work out the equations myself! :-p