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Date: 18 Jul 2007 16:33:29
From: Sam Wormley
Subject: The Mars Landing Approach: Getting Large Payloads to the Surface
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July 17th, 2007
http://www.universetoday.com/2007/07/17/the-mars-landing-approach-getting-large-payloads-to-the-surface-of-the-red-planet/
The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
Some proponents of human missions to Mars say we have the technology
today to send people to the Red Planet. But do we? Rob Manning of the
Jet Propulsion Laboratory discusses the intricacies of entry, descent
and landing and what needs to be done to make humans on Mars a
reality.
There's no comfort in the statistics for missions to Mars. To date
over 60% of the missions have failed. The scientists and engineers of
these undertakings use phrases like "Six Minutes of Terror," and "The
Great Galactic Ghoul" to illustrate their experiences, evidence of
the anxiety that's evoked by sending a robotic spacecraft to Mars
\u2014 even among those who have devoted their careers to the task.
But mention sending a human mission to land on the Red Planet, with
payloads several factors larger than an unmanned spacecraft and the
trepidation among that same group grows even larger. Why?
Nobody knows how to do it.
Surprised? Most people are, says Rob Manning the Chief Engineer for
the Mars Exploration Directorate and presently the only person who
has led teams to land three robotic spacecraft successfully on the
surface of Mars.
"It turns out that most people aren't aware of this problem and very
few have worried about the details of how you get something very
heavy safely to the surface of Mars," said Manning.
He believes many people immediately come to the conclusion that
landing humans on Mars should be easy. After all, humans have landed
successfully on the Moon and we can land our human-carrying vehicles
from space to Earth. And since Mars falls between the Earth and the
Moon in size, and also in the amount of atmosphere it has then the
middle ground of Mars should be easy. "There's the mindset that we
should just be able to connect the dots in between," said Manning.
But as of now, the dots will need to connect across a large abyss.
"We know what the problems are. I like to blame the god of war,"
quipped Manning. "This planet is not friendly or conducive for
landing."
The real problem is the combination of Mars' atmosphere and the size
of spacecraft needed for human missions. So far, our robotic
spacecraft have been small enough to enable at least some success in
reaching the surface safely. But while the Apollo lunar lander
weighed approximately 10 metric tons, a human mission to Mars will
require three to six times that mass, given the restraints of staying
on the planet for a year. Landing a payload that heavy on Mars is
currently impossible, using our existing capabilities. "There's too
much atmosphere on Mars to land heavy vehicles like we do on the
moon, using propulsive technology completely," said Manning, "and
there's too little atmosphere to land like we do on Earth. So, it's
in this ugly, grey zone."
But what about airbags, parachutes, or thrusters that have been used
on the previous successful robotic Mars missions, or a lifting body
vehicle similar to the space shuttle?
None of those will work, either on their own or in combination, to
land payloads of one metric ton and beyond on Mars. This problem
affects not only human missions to the Red Planet, but also larger
robotic missions such as a sample return. "Unfortunately, that's
where we are," said Manning. "Until we come up with a whole new
trick, a whole new system, landing humans on Mars will be an ugly and
scary proposition."
Road Mapping
In 2004 NASA organized a Road Mapping session to discuss the current
capabilities and future problems of landing humans on Mars. Manning
co-chaired this event along with Apollo 17 astronaut Harrison Schmitt
and Claude Graves, who has since passed away, from the Johnson Space
Center. Approximately 50 other people from across NASA, academia and
industry attended the session. "At that time the ability to explain
these problems in a coherent way was not as good," said Manning. "The
entry, descent and landing process is actually made up of people from
many different disciplines. Very few people really understood,
especially for large scale systems, what all of the issues were. At
the Road Mapping session we were able to put them all down and talk
about them."
The major conclusion that came from the session was that no one has
yet figured out how to safely get large masses from speeds of entry
and orbit down to the surface of Mars. "We call it the Supersonic
Transition Problem," said Manning. "Unique to Mars, there is a
velocity-altitude gap below Mach 5. The gap is between the delivery
capability of large entry systems at Mars and the capability of
super-and sub-sonic decelerator technologies to get below the speed
of sound."
Plainly put, with our current capabilities, a large, heavy vehicle,
streaking through Mars' thin, volatile atmosphere only has about
ninety seconds to slow from Mach 5 to under Mach 1, change and
re-orient itself from a being a spacecraft to a lander, deploy
parachutes to slow down further, then use thrusters to translate to
the landing site and finally, gently touch down.
No Airbags
When this problem is first presented to people, the most offered
solution, Manning says, is to use airbags, since they have been so
successful for the missions that he has been involved with; the
Pathfinder rover, Sojourner and the two Mars Exploration Rovers
(MER), Spirit and Opportunity.
But engineers feel they have reached the capacity of airbags with
MER. "It's not just the mass or the volume of the airbags, or the
size of the airbags themselves, but it's the mass of the beast inside
the airbags," Manning said. "This is about as big as we can take that
particular design."
In addition, an airbag landing subjects the payload to forces between
10-20 G's. While robots can withstand such force, humans can't. This
doesn't mean airbags will never be used again, only that airbag
landings can't be used for something human or heavy.
Even the 2009 Mars Science Laboratory (MSL) rover, weighing 775
kilograms (versus MER at 175.4 kilograms each) requires an entirely
new landing architecture. Too massive for airbags, the small-car
sized rover will use a landing system dubbed the Sky Crane. "Even
though some people laugh when they first see it, my personal view is
that the Sky Crane is actually the most elegant system we've come up
with yet, and the simplest," said Manning. MSL will use a combination
of a rocket-guided entry with a heat shield, a parachute, then
thrusters to slow the vehicle even more, followed by a crane-like
system that lowers the rover on a cable for a soft landing directly
on its wheels. Depending on the success of the Sky Crane with MSL,
it's likely that this system can be scaled for larger payloads, but
probably not the size needed to land humans on Mars.
Atmospheric Anxiety and Parachute Problems
"The great thing about Earth," said Manning "is the atmosphere."
Returning to Earth and entering the atmosphere at speeds between 7-10
kilometers per second, the space shuttle, Apollo and Soyuz capsules
and the proposed Crew Exploration Vehicle (CEV) will all decelerate
to less than Mach 1 at about twenty kilometers above the ground just
by skimming through Earth's luxuriously thick atmosphere and using a
heat shield. To reach slower speeds needed for landing, either a
parachute is deployed, or in the case of the space shuttle, drag and
lift allow the remainder of the speed to bleed away.
But Mars' atmosphere is only one per cent as dense as Earth's. For
comparison, Mars atmosphere at its thickest is equivalent to Earth's
atmosphere at about 35 kilometers above the surface The air is so
thin that a heavy vehicle like a CEV will basically plummet to the
surface; there's not enough air resistance to slow it down
sufficiently. Parachutes can only be opened at speeds less than Mach
2, and a heavy spacecraft on Mars would never go that slow by using
just a heat shield. "And there are no parachutes that you could use
to slow this vehicle down," said Manning. "That's it. You can't land
a CEV on Mars unless you don't mind it being a crater on the
surface."
That's not good news for the Vision for Space Exploration. Would a
higher lift vehicle like the space shuttle save the day? "Well, on
Mars, when you use a very high lift to weight to drag ratio like the
shuttle," said Manning, "in order to get good deceleration and use
the lift properly, you" need to cut low into the atmosphere. You"
still be going at Mach 2 or 3 fairly close to the ground. If you had
a good control system you could spread out your deceleration to
lengthen the time you are in the air. You" eventually slow down to
under Mach 2 to open a parachute, but you" be too close to the ground
and even an ultra large supersonic parachute would not save you."
Supersonic parachute experts have concluded that to sufficiently slow
a large shuttle-type vehicle on Mars and reach the ground at
reasonable speeds would require a parachute one hundred meters in
diameter.
"That's a good fraction of the Rose Bowl. That's huge," said Manning.
"We believe there's no way to make a 100-meter parachute that can be
opened safely supersonically, not to mention the time it takes to
inflate something that large. You'd be on the ground before it was
fully inflated. It would not be a good outcome."
Heat Shields and Thrusters
It's not that Mars' atmosphere is useless. Manning explained that
with robotic spacecraft, 99% of the kinetic energy of an incoming
vehicle is taken away using a heat shield in the atmosphere. "It's
not inconceivable that we can design larger, lighter heat shields,"
he said, "but the problem is that right now the heat shield diameter
for a human-capable spacecraft overwhelms any possibility of
launching that vehicle from Earth." Manning added that it would
almost be better if Mars were like the moon, with no atmosphere at
all.
If that were the case, an Apollo-type lunar lander with thrusters
could be used. "But that would cause another problem," said Manning,
"in that for every kilogram of stuff in orbit, it takes twice as much
fuel to get to the surface of Mars as the moon. Everything is twice
as bad since Mars is about twice as big as the moon." That would
entail a large amount of fuel, perhaps over 6 times the payload mass
in fuel, to get human-sized payloads to the surface, all of which
would have to be brought along from Earth. Even on a fictitious
air-less Mars that is not an option.
But using current thruster technology in Mars' real, existing
atmosphere poses aerodynamic problems. "Rocket plumes are notoriously
unstable, dynamic, chaotic systems," said Manning. "Basically flying
into the plume at supersonics speeds, the rocket plume is acting like
a nose cone; a nose cone that's moving around in front of you against
very high dynamic pressure. Even though the atmospheric density is
very low, because the velocity is so high, the forces are really
huge."
Manning likened theses forces to a Category Five hurricane. This
would cause extreme stress, with shaking and twisting that would
likely destroy the vehicle. Therefore using propulsive technology
alone is not an option.
Using thrusters in combination with a heat shield and parachute also
poses challenges. Assuming the vehicle has used some technique to
slow to under Mach 1, using propulsion just in last stages of descent
to gradually adjust the lander's trajectory would enable the vehicle
to arrive very precisely at the desired landing site. "We're looking
at firing thrusters less than 1 kilometer above the ground. Your
parachute has been discarded, and you see that you are perhaps 5
kilometers south of where you want to land," said Manning. "So now
you need the ability to turn the vehicle over sideways to try to get
to your landing spot. But this may be an expensive option, adding a
large tax in fuel to get to the desired landing rendezvous point."
Additionally, on the moon, with no atmosphere or weather, there is
nothing pushing against the vehicle, taking it off target, and a la
Neil Armstrong on Apollo 11, the pilot can "fly out the
uncertainties" as Manning called it, to reach a suitable or desired
landing site. On Mars, however, the large variations in the density
of the atmosphere coupled with high and unpredictable winds conspire
to push vehicles off course. "We need to have ways to fight those
forces or ways to make up for any mis-targeting using the propulsion
system," said Manning. "Right now, we don't have that ability and
we're a long way from making it happen."
Supersonic Decelerators
The best hope on the horizon for making the human enterprise on Mars
possible is a new type of supersonic decelerator that's only on the
drawing board. A few companies are developing a new inflatable
supersonic decelerator called a Hypercone.
Imagine a huge donut with a skin across its surface that girdles the
vehicle and inflates very quickly with gas rockets (like air bags) to
create a conical shape. This would inflate about 10 kilometers above
the ground while the vehicle is traveling at Mach 4 or 5, after peak
heating. The Hypercone would act as an aerodynamic anchor to slow the
vehicle to Mach 1.
Glen Brown, Chief Engineer at Vertigo, Inc. in Lake Elsinore,
California was also a participant in the Mars Road Mapping session.
Brown says Vertigo has been doing extensive analysis of the
Hypercone, including sizing and mass estimates for landers from four
to sixty metric tons. "A high pressure inflatable structure in the
form a of a torus is a logical way to support a membrane in a conical
shape, which is stable and has high drag at high Mach numbers," Brown
said, adding that the structure would likely be made of a coated
fabric such as silicon-Vectran matrix materials. Vertigo is currently
competing for funding from NASA for further research, as the next
step, deployment in a supersonic wind tunnel, is quite expensive.
The structure would need to be about thirty to forty meters in
diameter. The problem here is that large, flexible structures are
notoriously difficult to control. At this point in time there are
also several other unknowns of developing and using a Hypercone.
One train of thought is that if the Hypercone can get the vehicle
under Mach 1, then subsonic parachutes could be used, much like the
ones employed by Apollo, or that the CEV is projected to use to land
on Earth. However, it takes time for the parachutes to inflate, and
subsequently there would only be a matter of seconds of use, allowing
time to shed the parachutes before converting to a propulsive system.
"You" also need to use thrusters," said Manning. "You're falling 10
times faster because the density of Mars' atmosphere is 100 times
less than Earth's. That means that you can't just land with
parachutes and touch the ground. You" break people's bones, if not
the hardware. So you need to transition from a parachute system to an
Apollo-like lunar legged lander sometime before you get to the
ground."
Manning believes that those who are immersed in these matters, like
himself, see the various problems fighting each other. "It's hard to
get your brain around all these problems because all the pieces
connect in complex ways," he said. "It's very hard to see the right
answer in your mind's eye."
The additional issues of creating new lightweight but strong shapes
and structures, with the ability to come apart and transform from one
stage to another at just the right time means developing a rapid-fire
Rube Goldberg-like contraption.
"The honest truth of the matter," said Manning, "is that we don't
have a standard canonical form, a standard configuration of systems
that allows us to get to the ground, with the right size that
balances the forces, the loads, the people, and allows us to do all
the transformation that needs to be done in the very small amount of
time that we have to land."
Other Options and Issues
Another alternative discussed at the 2004 Mars Road Mapping session
was the space elevator.
"Mars is really begging for a space elevator," said Manning. "I think
it has great potential. That would solve a lot of problems, and Mars
would be an excellent platform to try it." But Manning admitted that
the technology needed to suspend a space elevator has not yet been
invented. The issues with space elevator technology may be vast, even
compared with the challenges of landing.
Despite these known obstacles, there are few at NASA currently
spending any quality time working on any of the issues of landing
humans on Mars.
Manning explained, "NASA does not yet have the resources to solve
this problem and also develop the CEV, complete the International
Space Station and do the lunar landing systems development at the
same time. But NASA knows that this is on its plate of things to do
in the future and is just beginning to get a handle on the needed
technology developments. I try to go out of my way to tell this story
because I'm encouraging young aeronautical engineering students,
particularly graduate students, to start working on this problem on
their own. There is no doubt in my mind that with their help, we can
figure out how to make reliable human-scale landing systems work on
Mars."
While there is much interest throughout NASA and the space sector to
try to tackle these issues in the ensuing years, technology also
needs a few more years to catch up to our dreams of landing humans on
Mars.
And this story, like all good engineering stories, will inevitably
read like a good detective novel with technical twist and turns,
scientific intrigue, and high adventure on another world.
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Date: 20 Jul 2007 10:22:47
From: John Savard
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
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On Wed, 18 Jul 2007 16:33:29 GMT, Sam Wormley <swormley1@mchsi.com >
quoted, in part:
> The real problem is the combination of Mars' atmosphere and the size
> of spacecraft needed for human missions. So far, our robotic
> spacecraft have been small enough to enable at least some success in
> reaching the surface safely. But while the Apollo lunar lander
> weighed approximately 10 metric tons, a human mission to Mars will
> require three to six times that mass, given the restraints of staying
> on the planet for a year.
As has been noted, this is a false assumption. We have to be able to
land one astronaut on the surface of Mars in one piece. We can always
land any supplies required in separate vehicles, and we can land more
than one astronaut in more than one craft.
But even landing one astronaut does involve some overhead. If I remember
correctly, the Mercury capsule weighed about 5,000 pounds, so that is 2
1/2 tons - or tonnes. That is still pretty heavy.
> Plainly put, with our current capabilities, a large, heavy vehicle,
> streaking through Mars' thin, volatile atmosphere only has about
> ninety seconds to slow from Mach 5 to under Mach 1, change and
> re-orient itself from a being a spacecraft to a lander, deploy
> parachutes to slow down further, then use thrusters to translate to
> the landing site and finally, gently touch down.
And this seems to suggest an obvious solution. Before gettting to the
atmosphere, where thrusters encounter these turbulence problems, slow to
under Mach 1. Then use thrusters to gently enter the atmosphere, and
deploy parachutes when needed.
> In addition, an airbag landing subjects the payload to forces between
> 10-20 G's. While robots can withstand such force, humans can't. This
> doesn't mean airbags will never be used again, only that airbag
> landings can't be used for something human or heavy.
That is quite right. Airbags as used for the Sojourner mission are
completely out for human missions. Even if the humans were immersed in
fluid, the sudden impacts involved would be far too dangerous.
> Even the 2009 Mars Science Laboratory (MSL) rover, weighing 775
> kilograms (versus MER at 175.4 kilograms each) requires an entirely
> new landing architecture. Too massive for airbags, the small-car
> sized rover will use a landing system dubbed the Sky Crane. "Even
> though some people laugh when they first see it, my personal view is
> that the Sky Crane is actually the most elegant system we've come up
> with yet, and the simplest," said Manning. MSL will use a combination
> of a rocket-guided entry with a heat shield, a parachute, then
> thrusters to slow the vehicle even more, followed by a crane-like
> system that lowers the rover on a cable for a soft landing directly
> on its wheels. Depending on the success of the Sky Crane with MSL,
> it's likely that this system can be scaled for larger payloads, but
> probably not the size needed to land humans on Mars.
Given that 775 kilograms is some 1,569 pounds, this is getting close to
what would be needed for a one-man landing craft.
> Using thrusters in combination with a heat shield and parachute also
> poses challenges. Assuming the vehicle has used some technique to
> slow to under Mach 1, using propulsion just in last stages of descent
> to gradually adjust the lander's trajectory would enable the vehicle
> to arrive very precisely at the desired landing site. "We're looking
> at firing thrusters less than 1 kilometer above the ground. Your
> parachute has been discarded, and you see that you are perhaps 5
> kilometers south of where you want to land," said Manning. "So now
> you need the ability to turn the vehicle over sideways to try to get
> to your landing spot. But this may be an expensive option, adding a
> large tax in fuel to get to the desired landing rendezvous point."
Getting to Mach 1 outside the atmosphere, and staying there all the way
down, then, is possible. Of course, it would involve a lot of fuel. But
that is about cost, not possibility.
> The best hope on the horizon for making the human enterprise on Mars
> possible is a new type of supersonic decelerator that's only on the
> drawing board. A few companies are developing a new inflatable
> supersonic decelerator called a Hypercone.
> The structure would need to be about thirty to forty meters in
> diameter. The problem here is that large, flexible structures are
> notoriously difficult to control. At this point in time there are
> also several other unknowns of developing and using a Hypercone.
More research may well yield more reasonable solutions to the problem of
landing on Mars than simply carrying along a lot of fuel.
One of the baseline assumptions in figuring out the fuel requirements
for a trip to Mars, though, at least in the early days, was that just as
one used enough fuel to go from standing still on Earth to entering the
Hohmann orbit at launch, one used enough fuel to match velocities with
Mars at the other end of the trip.
If air resistance at a slow velocity doesn't produce enough drag to
maintain a slow velocity, without impossibly large parachutes, then an
Apollo-style descent under rocket power becomes possible - no hypersonic
plume of air is present any longer. The only thing needed is a lot of
fuel.
So the only thing that's currently impossible is landing on Mars on the
cheap. Considering, though, that Dr. Zubrin's Mars Direct idea
eliminates the need to multiply by the total mass/payload mass ratio
*four* times, reducing that to two, this large mass penalty still
shouldn't make a Mars mission more difficult than it was believed to be
*before* Dr. Zubrin.
John Savard
http://www.quadibloc.com/index.html
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Date: 20 Jul 2007 19:49:32
From: MiKe T
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
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Look dude, just develop anti-gravity propusion and problem solved.
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Date: 21 Jul 2007 08:38:31
From: John Savard
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
On Fri, 20 Jul 2007 19:49:32 GMT, "MiKe T" <MT@nospamer.com > wrote, in
part:
>Look dude, just develop anti-gravity propusion and problem solved.
Well, yeah, but that doesn't really count. Because anti-gravity
propulsion, while it may be possible, may require knowledge we won't
discover for another thousand years. So we have to work with what we
have.
John Savard
http://www.quadibloc.com/index.html
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Date: 21 Jul 2007 14:12:18
From: MiKe T
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
"John Savard" <jsavard@excxn.aNOSPAMb.cdn.invalid > wrote in message
news:46a1c5d2.497538@news.aioe.org...
> On Fri, 20 Jul 2007 19:49:32 GMT, "MiKe T" <MT@nospamer.com> wrote, in
> part:
>
>>Look dude, just develop anti-gravity propusion and problem solved.
>
> Well, yeah, but that doesn't really count. Because anti-gravity
> propulsion, while it may be possible, may require knowledge we won't
> discover for another thousand years. So we have to work with what we
> have.
Of course, so what else? It seesm the problem is insurmountable unless you
can
come in at an incredibly shallow angle that takes you practically around the
planets atmosphere
a couple times like aerobraking but then it would have to be a Mars direct
thing. No decelerating
to orbit the planet. Just cruise straight into the planet. Maybe ion drive
engines that could slow the craft
way out in space. Go nuclear. Have an orbiting station ready.
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Date: 20 Jul 2007 01:52:04
From: thad@thadlabs.com
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
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On Jul 19, 7:59 pm, Chris L Peterson <c...@alumni.caltech.edu > wrote:
> On Thu, 19 Jul 2007 11:42:15 -0700, "t...@thadlabs.com"
>
> <t...@thadlabs.com> wrote:
> >Wernher von Braun did. In the 1950s. A large swing-out wing affair so
> >a vehicle could land like a plane even in Mars' thin atmosphere.
>
> The problem isn't generating lift, but losing several km per second of
> velocity (with an acceleration profile that is reasonable for somewhat
> delicate equipment... and people). If you can get near the ground and
> have a low speed, there are probably a variety of ways to actually land.
Precisely!
You hit the nail on the head.
So why cannot the "current NASA" evaluate what's been proposed
in the past (which seemed reasonable to me)? This isn't exactly
"rocket science" (or is it? :-)
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Date: 20 Jul 2007 13:40:12
From: Chris L Peterson
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
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On Fri, 20 Jul 2007 01:52:04 -0700, "thad@thadlabs.com"
<thad@thadlabs.com > wrote:
>So why cannot the "current NASA" evaluate what's been proposed
>in the past (which seemed reasonable to me)?
What proposal from the past? If you are talking about some sort of
landing employing a combination of aerobraking and lift surfaces, it
sounds as if that's one strategy that they've (that is, Manning et.al.)
analyzed closely. From the article, it sounds as if the approach has
possibilities, but remains very difficult in practice. We know a lot
more about the Martian atmosphere, and about heat shields and
aerobraking, than von Braun did 50 years ago.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 20 Jul 2007 02:41:01
From: John Savard
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
On Wed, 18 Jul 2007 16:33:29 GMT, Sam Wormley <swormley1@mchsi.com >
wrote, in part:
> If that were the case, an Apollo-type lunar lander with thrusters
> could be used. "But that would cause another problem," said Manning,
> "in that for every kilogram of stuff in orbit, it takes twice as much
> fuel to get to the surface of Mars as the moon. Everything is twice
> as bad since Mars is about twice as big as the moon." That would
> entail a large amount of fuel, perhaps over 6 times the payload mass
> in fuel, to get human-sized payloads to the surface, all of which
> would have to be brought along from Earth. Even on a fictitious
> air-less Mars that is not an option.
>
> But using current thruster technology in Mars' real, existing
> atmosphere poses aerodynamic problems. "Rocket plumes are notoriously
> unstable, dynamic, chaotic systems," said Manning. "Basically flying
> into the plume at supersonics speeds, the rocket plume is acting like
> a nose cone; a nose cone that's moving around in front of you against
> very high dynamic pressure. Even though the atmospheric density is
> very low, because the velocity is so high, the forces are really
> huge."
>
> Manning likened theses forces to a Category Five hurricane. This
> would cause extreme stress, with shaking and twisting that would
> likely destroy the vehicle. Therefore using propulsive technology
> alone is not an option.
Ah, here we are. In my simplicity, I would think the solution is
obvious.
Carry even *more* fuel, and slow down using rockets to subsonic speed...
in hard vacuum before even entering the atmosphere of Mars.
John Savard
http://www.quadibloc.com/index.html
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Date: 20 Jul 2007 02:56:21
From: Chris L Peterson
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
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On Fri, 20 Jul 2007 02:41:01 GMT, jsavard@excxn.aNOSPAMb.cdn.invalid
(John Savard) wrote:
>Carry even *more* fuel, and slow down using rockets to subsonic speed...
>in hard vacuum before even entering the atmosphere of Mars.
And then keep burning all the way down? Otherwise, you'll just start
falling and soon will be at a few km/s... this time in the atmosphere. I
don't think it's feasible to carry enough fuel for your strategy.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 20 Jul 2007 09:30:36
From: John Savard
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
On Fri, 20 Jul 2007 02:56:21 GMT, Chris L Peterson
<clp@alumni.caltech.edu > wrote, in part:
>On Fri, 20 Jul 2007 02:41:01 GMT, jsavard@excxn.aNOSPAMb.cdn.invalid
>(John Savard) wrote:
>
>>Carry even *more* fuel, and slow down using rockets to subsonic speed...
>>in hard vacuum before even entering the atmosphere of Mars.
>
>And then keep burning all the way down? Otherwise, you'll just start
>falling and soon will be at a few km/s... this time in the atmosphere. I
>don't think it's feasible to carry enough fuel for your strategy.
Well, since the need for gigantic parachutes and heat shields is due to
the high velocity to be shed, if the craft slows down outside the
atmosphere, and enters it under power, then the rockets will not have to
provide as much thrust within the atmosphere (reducing the one problem)
and a smaller parachute might be useful.
Yes, it will take a lot of fuel.
The other option, I suppose, would be to enter an elliptical orbit,
graze the atmosphere so as to lose only a little velocity each time,
somehow orienting a wing-like device so that grazing the atmosphere
won't deflect the landing vehicle completely out of orbit. I suppose
that is the sort of "advanced" solution they're working on.
John Savard
http://www.quadibloc.com/index.html
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| | | | |
Date: 20 Jul 2007 13:35:40
From: Chris L Peterson
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
On Fri, 20 Jul 2007 09:30:36 GMT, jsavard@excxn.aNOSPAMb.cdn.invalid
(John Savard) wrote:
>Yes, it will take a lot of fuel.
Pretty much an impossible amount, I'd think. It takes as much fuel to
get down at zero velocity as it takes to get up. On Earth, if you wanted
to land the shuttle on thrusters, for example, it would have to begin
its descent with its two solid boosters and huge liquid fuel tank. The
gravity well on Mars isn't as deep, of course, but it's still a nearly
unworkable amount of fuel you need to take with you (and of course, you
need a lot of fuel to take of again if it's a manned flight- all of
which is additional mass that needs to be landed softly).
>The other option, I suppose, would be to enter an elliptical orbit,
>graze the atmosphere so as to lose only a little velocity each time,
>somehow orienting a wing-like device so that grazing the atmosphere
>won't deflect the landing vehicle completely out of orbit. I suppose
>that is the sort of "advanced" solution they're working on.
I expect you're right- some sort of complex aerobraking will be the
solution. But it apparently remains a tricky problem... and a somewhat
risky approach.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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| | | | | |
Date: 21 Jul 2007 08:48:33
From: John Savard
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
On Fri, 20 Jul 2007 13:35:40 GMT, Chris L Peterson
<clp@alumni.caltech.edu > wrote, in part:
>(and of course, you
>need a lot of fuel to take of again if it's a manned flight- all of
>which is additional mass that needs to be landed softly).
No, Zubrin solved *that* problem.
The Viking lander, which didn't land by bouncing around, was 600 kg in
mass, while a Mercury capsule is about 1350 kg in mass.
Of course, the Viking lander was pretty lucky it didn't land right on
top of a boulder and get split in two. We wouldn't take that chance with
an astronaut, so something like a lunar lander, which can choose a
landing site, _is_ needed. But instead of something much more massive
than Apollo's lunar lander, you could put *each astronaut in his own
lander* if the mass of the landing vehicle is the problem.
The only thing that really needs to be landed in one piece is one
astronaut.
Basically, I'm just proposing a "brute-force" solution to show that it's
*possible* to land an astronaut safely. Not being an engineer, I'm
hesitant to go into more elegant solutions, which may or may not be
workable.
Perhaps a Mercury style capsule could work, if it also came with a
two-meter thick slab of very light honeycombed metal under it - and was
landed on a site carefully surveyed to be free of anything *but*
boulders as hazards. The idea being that slab would act like a slab of
wood, dented by the boulders below and resting on them, and protecting
the spaceship, perhaps even held above it by a truss structure.
John Savard
http://www.quadibloc.com/index.html
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Date: 21 Jul 2007 09:23:33
From: Greg Crinklaw
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface
|
John Savard wrote:
> On Fri, 20 Jul 2007 13:35:40 GMT, Chris L Peterson
> <clp@alumni.caltech.edu> wrote, in part:
>
>> (and of course, you
>> need a lot of fuel to take of again if it's a manned flight- all of
>> which is additional mass that needs to be landed softly).
>
> No, Zubrin solved *that* problem.
I actually solved the other problem a long time ago, but people are very
slow to come around to it. They will eventually though...
I believe the best approach to sending people to Mars is a one way trip.
Send volunteers for what amounts to a small colony. As long as we
also send everything they need to build underground shelters and keep
themselves alive on Mars indefinitely they could live out their lives
studying the planet. Barbaric? Crazy? Not if you look at how
Europeans settled the Americas or how humans have always migrated about
the planet (without the modern boundaries we are so obsessed with). In
an historical context it is quite a reasonable thing to do.
Yes, I know you all think it's a stupid idea, but it does solve the
larger, most important issue--what I call the "Apollo problem." Being
that do we really want to spend all these resources just so two people
can say they went there?
--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)
SkyTools: http://www.skyhound.com/cs.html
Observing: http://www.skyhound.com/sh/skyhound.html
Comets: http://comets.skyhound.com
To reply take out your eye
|
| | | | | | |
Date: 21 Jul 2007 13:50:14
From: Chris L Peterson
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
On Sat, 21 Jul 2007 08:48:33 GMT, jsavard@excxn.aNOSPAMb.cdn.invalid
(John Savard) wrote:
>Basically, I'm just proposing a "brute-force" solution to show that it's
>*possible* to land an astronaut safely. Not being an engineer, I'm
>hesitant to go into more elegant solutions, which may or may not be
>workable.
I don't think there's any question that it's possible to land an
astronaut safely. Certainly, there was nothing in the article to suggest
this is seen as anything other than a difficult engineering problem.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| |
Date: 20 Jul 2007 02:36:15
From: John Savard
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
On Wed, 18 Jul 2007 16:33:29 GMT, Sam Wormley <swormley1@mchsi.com >
quoted, in part:
> "There's too
> much atmosphere on Mars to land heavy vehicles like we do on the
> moon, using propulsive technology completely," said Manning, "and
> there's too little atmosphere to land like we do on Earth. So, it's
> in this ugly, grey zone."
While I'm sure he knows much more about this sort of stuff than I do, I
have to admit I find this a surprising statement.
I can see that a little atmosphere might give the temptation to make use
of it to save fuel, and do what aerobraking one can. But I'm baffled as
to how the thin atmosphere of Mars would interfere with using
retrorockets to slow the landing vehicle. Instead, I would see fuel
requirements, not Mars' atmosphere, as the problem with that approach.
John Savard
http://www.quadibloc.com/index.html
|
| | |
Date: 19 Jul 2007 21:14:43
From: Greg Crinklaw
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface
|
John Savard wrote:
> I can see that a little atmosphere might give the temptation to make use
> of it to save fuel, and do what aerobraking one can. But I'm baffled as
> to how the thin atmosphere of Mars would interfere with using
> retrorockets to slow the landing vehicle. Instead, I would see fuel
> requirements, not Mars' atmosphere, as the problem with that approach.
That was covered in the article, having to do with the aerodynamics of
nozzles. But he also said that fuels is the primary problem.
--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)
SkyTools: http://www.skyhound.com/cs.html
Observing: http://www.skyhound.com/sh/skyhound.html
Comets: http://comets.skyhound.com
To reply take out your eye
|
| |
Date: 19 Jul 2007 20:34:44
From: Holy Troller
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
As the record indicates, this human obsession with landing on humas on Mars
is completely out ta lunch.
|
| |
Date: 19 Jul 2007 18:54:08
From: TBerk
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
Why is the hang up on 'sending massive payloads to the surface of
Mars'? How about many smaller payloads waiting there when the Human
'package' shows up?
TBerk
|
| | |
Date: 20 Jul 2007 02:41:58
From: John Savard
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
On Thu, 19 Jul 2007 18:54:08 -0000, TBerk <bayareaberk@yahoo.com > wrote,
in part:
>Why is the hang up on 'sending massive payloads to the surface of
>Mars'? How about many smaller payloads waiting there when the Human
>'package' shows up?
The trouble is that even a Mercury capsule weighed more than a ton.
John Savard
http://www.quadibloc.com/index.html
|
| | | |
Date: 20 Jul 2007 05:09:57
From: Davoud
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
TBerk:
> >Why is the hang up on 'sending massive payloads to the surface of
> >Mars'? How about many smaller payloads waiting there when the Human
> >'package' shows up?
John Savard:
> The trouble is that even a Mercury capsule weighed more than a ton.
The trouble would be the vast cost of this meaningless publicity stunt.
How many robotic Mars missions could be carried out for just the cost
of carrying the life-support systems to and fro? The practice of
hatching grandiose schemes to divert people's attention from what is
happening to their country is standard fare in the third-world, and
unworthy of us. About the only thing good about the bankrupting of
America is that this mission isn't going to take place within the next
50 years, at least.
There is only one big question about Mars: does it have, or did it
have, life. If it /does/ we can find it with a robot and bring it back
and look at it or torture it or try to convert it to Christianity, or,
if it's not white in color, make it an object of hatred. If Mars /did/
have life we can bring back the evidence and ooh and aah over it.
The only possible reason for sending humans to Mars would be to
investigate artifacts found there by robotic explorers. Mars isn't
Barsoom, however, and those artifacts aren't there. Not that the idiot
who dreamed up this nonsense has read Burroughs, mind you. Just as
well; he's dumb enough to think "A Princess of Mars" is a history book.
Davoud
--
usenet *at* davidillig dawt com
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| | |
Date: 19 Jul 2007 22:15:25
From: Carsten A. Arnholm
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
TBerk wrote:
> Why is the hang up on 'sending massive payloads to the surface of
> Mars'? How about many smaller payloads waiting there when the Human
> 'package' shows up?
> TBerk
How many pieces of payload do you want to be? ;-)
|
| |
Date: 19 Jul 2007 11:42:15
From: thad@thadlabs.com
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
On Jul 18, 9:33 am, Sam Wormley <sworml...@mchsi.com > wrote:
> July 17th, 2007
>
> http://www.universetoday.com/2007/07/17/the-mars-landing-approach-get...
>
> The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
>
> Some proponents of human missions to Mars say we have the technology
> today to send people to the Red Planet. But do we? Rob Manning of the
> Jet Propulsion Laboratory discusses the intricacies of entry, descent
> and landing and what needs to be done to make humans on Mars a
> reality.
>
> There's no comfort in the statistics for missions to Mars. To date
> over 60% of the missions have failed. The scientists and engineers of
> these undertakings use phrases like "Six Minutes of Terror," and "The
> Great Galactic Ghoul" to illustrate their experiences, evidence of
> the anxiety that's evoked by sending a robotic spacecraft to Mars
> \u2014 even among those who have devoted their careers to the task.
> But mention sending a human mission to land on the Red Planet, with
> payloads several factors larger than an unmanned spacecraft and the
> trepidation among that same group grows even larger. Why?
>
> Nobody knows how to do it.
> [...]
Wernher von Braun did. In the 1950s. A large swing-out wing affair so
a vehicle could land like a plane even in Mars' thin atmosphere.
|
| | |
Date: 20 Jul 2007 02:59:56
From: Chris L Peterson
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
On Thu, 19 Jul 2007 11:42:15 -0700, "thad@thadlabs.com"
<thad@thadlabs.com > wrote:
>Wernher von Braun did. In the 1950s. A large swing-out wing affair so
>a vehicle could land like a plane even in Mars' thin atmosphere.
The problem isn't generating lift, but losing several km per second of
velocity (with an acceleration profile that is reasonable for somewhat
delicate equipment... and people). If you can get near the ground and
have a low speed, there are probably a variety of ways to actually land.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| |
Date: 18 Jul 2007 19:41:18
From: mitch
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
I'm not holding my breath.
"Sam Wormley" <swormley1@mchsi.com > wrote in message
news:thrni.31864$Fc.16905@attbi_s21...
> July 17th, 2007
>
> http://www.universetoday.com/2007/07/17/the-mars-landing-approach-getting-large-payloads-to-the-surface-of-the-red-planet/
>
> The Mars Landing Approach: Getting Large Payloads to the Surface of the
> Red Planet
>
> Some proponents of human missions to Mars say we have the technology
> today to send people to the Red Planet. But do we? Rob Manning of the
> Jet Propulsion Laboratory discusses the intricacies of entry, descent
> and landing and what needs to be done to make humans on Mars a
> reality.
>
> There's no comfort in the statistics for missions to Mars. To date
> over 60% of the missions have failed. The scientists and engineers of
> these undertakings use phrases like "Six Minutes of Terror," and "The
> Great Galactic Ghoul" to illustrate their experiences, evidence of
> the anxiety that's evoked by sending a robotic spacecraft to Mars
> \u2014 even among those who have devoted their careers to the task.
> But mention sending a human mission to land on the Red Planet, with
> payloads several factors larger than an unmanned spacecraft and the
> trepidation among that same group grows even larger. Why?
>
> Nobody knows how to do it.
>
> Surprised? Most people are, says Rob Manning the Chief Engineer for
> the Mars Exploration Directorate and presently the only person who
> has led teams to land three robotic spacecraft successfully on the
> surface of Mars.
>
> "It turns out that most people aren't aware of this problem and very
> few have worried about the details of how you get something very
> heavy safely to the surface of Mars," said Manning.
>
> He believes many people immediately come to the conclusion that
> landing humans on Mars should be easy. After all, humans have landed
> successfully on the Moon and we can land our human-carrying vehicles
> from space to Earth. And since Mars falls between the Earth and the
> Moon in size, and also in the amount of atmosphere it has then the
> middle ground of Mars should be easy. "There's the mindset that we
> should just be able to connect the dots in between," said Manning.
>
> But as of now, the dots will need to connect across a large abyss.
>
> "We know what the problems are. I like to blame the god of war,"
> quipped Manning. "This planet is not friendly or conducive for
> landing."
>
> The real problem is the combination of Mars' atmosphere and the size
> of spacecraft needed for human missions. So far, our robotic
> spacecraft have been small enough to enable at least some success in
> reaching the surface safely. But while the Apollo lunar lander
> weighed approximately 10 metric tons, a human mission to Mars will
> require three to six times that mass, given the restraints of staying
> on the planet for a year. Landing a payload that heavy on Mars is
> currently impossible, using our existing capabilities. "There's too
> much atmosphere on Mars to land heavy vehicles like we do on the
> moon, using propulsive technology completely," said Manning, "and
> there's too little atmosphere to land like we do on Earth. So, it's
> in this ugly, grey zone."
>
> But what about airbags, parachutes, or thrusters that have been used
> on the previous successful robotic Mars missions, or a lifting body
> vehicle similar to the space shuttle?
>
> None of those will work, either on their own or in combination, to
> land payloads of one metric ton and beyond on Mars. This problem
> affects not only human missions to the Red Planet, but also larger
> robotic missions such as a sample return. "Unfortunately, that's
> where we are," said Manning. "Until we come up with a whole new
> trick, a whole new system, landing humans on Mars will be an ugly and
> scary proposition."
>
> Road Mapping
>
> In 2004 NASA organized a Road Mapping session to discuss the current
> capabilities and future problems of landing humans on Mars. Manning
> co-chaired this event along with Apollo 17 astronaut Harrison Schmitt
> and Claude Graves, who has since passed away, from the Johnson Space
> Center. Approximately 50 other people from across NASA, academia and
> industry attended the session. "At that time the ability to explain
> these problems in a coherent way was not as good," said Manning. "The
> entry, descent and landing process is actually made up of people from
> many different disciplines. Very few people really understood,
> especially for large scale systems, what all of the issues were. At
> the Road Mapping session we were able to put them all down and talk
> about them."
>
> The major conclusion that came from the session was that no one has
> yet figured out how to safely get large masses from speeds of entry
> and orbit down to the surface of Mars. "We call it the Supersonic
> Transition Problem," said Manning. "Unique to Mars, there is a
> velocity-altitude gap below Mach 5. The gap is between the delivery
> capability of large entry systems at Mars and the capability of
> super-and sub-sonic decelerator technologies to get below the speed
> of sound."
>
> Plainly put, with our current capabilities, a large, heavy vehicle,
> streaking through Mars' thin, volatile atmosphere only has about
> ninety seconds to slow from Mach 5 to under Mach 1, change and
> re-orient itself from a being a spacecraft to a lander, deploy
> parachutes to slow down further, then use thrusters to translate to
> the landing site and finally, gently touch down.
>
> No Airbags
>
> When this problem is first presented to people, the most offered
> solution, Manning says, is to use airbags, since they have been so
> successful for the missions that he has been involved with; the
> Pathfinder rover, Sojourner and the two Mars Exploration Rovers
> (MER), Spirit and Opportunity.
>
> But engineers feel they have reached the capacity of airbags with
> MER. "It's not just the mass or the volume of the airbags, or the
> size of the airbags themselves, but it's the mass of the beast inside
> the airbags," Manning said. "This is about as big as we can take that
> particular design."
>
> In addition, an airbag landing subjects the payload to forces between
> 10-20 G's. While robots can withstand such force, humans can't. This
> doesn't mean airbags will never be used again, only that airbag
> landings can't be used for something human or heavy.
>
> Even the 2009 Mars Science Laboratory (MSL) rover, weighing 775
> kilograms (versus MER at 175.4 kilograms each) requires an entirely
> new landing architecture. Too massive for airbags, the small-car
> sized rover will use a landing system dubbed the Sky Crane. "Even
> though some people laugh when they first see it, my personal view is
> that the Sky Crane is actually the most elegant system we've come up
> with yet, and the simplest," said Manning. MSL will use a combination
> of a rocket-guided entry with a heat shield, a parachute, then
> thrusters to slow the vehicle even more, followed by a crane-like
> system that lowers the rover on a cable for a soft landing directly
> on its wheels. Depending on the success of the Sky Crane with MSL,
> it's likely that this system can be scaled for larger payloads, but
> probably not the size needed to land humans on Mars.
>
> Atmospheric Anxiety and Parachute Problems
>
> "The great thing about Earth," said Manning "is the atmosphere."
> Returning to Earth and entering the atmosphere at speeds between 7-10
> kilometers per second, the space shuttle, Apollo and Soyuz capsules
> and the proposed Crew Exploration Vehicle (CEV) will all decelerate
> to less than Mach 1 at about twenty kilometers above the ground just
> by skimming through Earth's luxuriously thick atmosphere and using a
> heat shield. To reach slower speeds needed for landing, either a
> parachute is deployed, or in the case of the space shuttle, drag and
> lift allow the remainder of the speed to bleed away.
>
> But Mars' atmosphere is only one per cent as dense as Earth's. For
> comparison, Mars atmosphere at its thickest is equivalent to Earth's
> atmosphere at about 35 kilometers above the surface The air is so
> thin that a heavy vehicle like a CEV will basically plummet to the
> surface; there's not enough air resistance to slow it down
> sufficiently. Parachutes can only be opened at speeds less than Mach
> 2, and a heavy spacecraft on Mars would never go that slow by using
> just a heat shield. "And there are no parachutes that you could use
> to slow this vehicle down," said Manning. "That's it. You can't land
> a CEV on Mars unless you don't mind it being a crater on the
> surface."
>
> That's not good news for the Vision for Space Exploration. Would a
> higher lift vehicle like the space shuttle save the day? "Well, on
> Mars, when you use a very high lift to weight to drag ratio like the
> shuttle," said Manning, "in order to get good deceleration and use
> the lift properly, you" need to cut low into the atmosphere. You"
> still be going at Mach 2 or 3 fairly close to the ground. If you had
> a good control system you could spread out your deceleration to
> lengthen the time you are in the air. You" eventually slow down to
> under Mach 2 to open a parachute, but you" be too close to the ground
> and even an ultra large supersonic parachute would not save you."
>
> Supersonic parachute experts have concluded that to sufficiently slow
> a large shuttle-type vehicle on Mars and reach the ground at
> reasonable speeds would require a parachute one hundred meters in
> diameter.
>
> "That's a good fraction of the Rose Bowl. That's huge," said Manning.
> "We believe there's no way to make a 100-meter parachute that can be
> opened safely supersonically, not to mention the time it takes to
> inflate something that large. You'd be on the ground before it was
> fully inflated. It would not be a good outcome."
>
> Heat Shields and Thrusters
>
> It's not that Mars' atmosphere is useless. Manning explained that
> with robotic spacecraft, 99% of the kinetic energy of an incoming
> vehicle is taken away using a heat shield in the atmosphere. "It's
> not inconceivable that we can design larger, lighter heat shields,"
> he said, "but the problem is that right now the heat shield diameter
> for a human-capable spacecraft overwhelms any possibility of
> launching that vehicle from Earth." Manning added that it would
> almost be better if Mars were like the moon, with no atmosphere at
> all.
>
> If that were the case, an Apollo-type lunar lander with thrusters
> could be used. "But that would cause another problem," said Manning,
> "in that for every kilogram of stuff in orbit, it takes twice as much
> fuel to get to the surface of Mars as the moon. Everything is twice
> as bad since Mars is about twice as big as the moon." That would
> entail a large amount of fuel, perhaps over 6 times the payload mass
> in fuel, to get human-sized payloads to the surface, all of which
> would have to be brought along from Earth. Even on a fictitious
> air-less Mars that is not an option.
>
> But using current thruster technology in Mars' real, existing
> atmosphere poses aerodynamic problems. "Rocket plumes are notoriously
> unstable, dynamic, chaotic systems," said Manning. "Basically flying
> into the plume at supersonics speeds, the rocket plume is acting like
> a nose cone; a nose cone that's moving around in front of you against
> very high dynamic pressure. Even though the atmospheric density is
> very low, because the velocity is so high, the forces are really
> huge."
>
> Manning likened theses forces to a Category Five hurricane. This
> would cause extreme stress, with shaking and twisting that would
> likely destroy the vehicle. Therefore using propulsive technology
> alone is not an option.
>
> Using thrusters in combination with a heat shield and parachute also
> poses challenges. Assuming the vehicle has used some technique to
> slow to under Mach 1, using propulsion just in last stages of descent
> to gradually adjust the lander's trajectory would enable the vehicle
> to arrive very precisely at the desired landing site. "We're looking
> at firing thrusters less than 1 kilometer above the ground. Your
> parachute has been discarded, and you see that you are perhaps 5
> kilometers south of where you want to land," said Manning. "So now
> you need the ability to turn the vehicle over sideways to try to get
> to your landing spot. But this may be an expensive option, adding a
> large tax in fuel to get to the desired landing rendezvous point."
>
> Additionally, on the moon, with no atmosphere or weather, there is
> nothing pushing against the vehicle, taking it off target, and a la
> Neil Armstrong on Apollo 11, the pilot can "fly out the
> uncertainties" as Manning called it, to reach a suitable or desired
> landing site. On Mars, however, the large variations in the density
> of the atmosphere coupled with high and unpredictable winds conspire
> to push vehicles off course. "We need to have ways to fight those
> forces or ways to make up for any mis-targeting using the propulsion
> system," said Manning. "Right now, we don't have that ability and
> we're a long way from making it happen."
>
> Supersonic Decelerators
>
> The best hope on the horizon for making the human enterprise on Mars
> possible is a new type of supersonic decelerator that's only on the
> drawing board. A few companies are developing a new inflatable
> supersonic decelerator called a Hypercone.
>
> Imagine a huge donut with a skin across its surface that girdles the
> vehicle and inflates very quickly with gas rockets (like air bags) to
> create a conical shape. This would inflate about 10 kilometers above
> the ground while the vehicle is traveling at Mach 4 or 5, after peak
> heating. The Hypercone would act as an aerodynamic anchor to slow the
> vehicle to Mach 1.
>
> Glen Brown, Chief Engineer at Vertigo, Inc. in Lake Elsinore,
> California was also a participant in the Mars Road Mapping session.
> Brown says Vertigo has been doing extensive analysis of the
> Hypercone, including sizing and mass estimates for landers from four
> to sixty metric tons. "A high pressure inflatable structure in the
> form a of a torus is a logical way to support a membrane in a conical
> shape, which is stable and has high drag at high Mach numbers," Brown
> said, adding that the structure would likely be made of a coated
> fabric such as silicon-Vectran matrix materials. Vertigo is currently
> competing for funding from NASA for further research, as the next
> step, deployment in a supersonic wind tunnel, is quite expensive.
>
> The structure would need to be about thirty to forty meters in
> diameter. The problem here is that large, flexible structures are
> notoriously difficult to control. At this point in time there are
> also several other unknowns of developing and using a Hypercone.
>
> One train of thought is that if the Hypercone can get the vehicle
> under Mach 1, then subsonic parachutes could be used, much like the
> ones employed by Apollo, or that the CEV is projected to use to land
> on Earth. However, it takes time for the parachutes to inflate, and
> subsequently there would only be a matter of seconds of use, allowing
> time to shed the parachutes before converting to a propulsive system.
>
> "You" also need to use thrusters," said Manning. "You're falling 10
> times faster because the density of Mars' atmosphere is 100 times
> less than Earth's. That means that you can't just land with
> parachutes and touch the ground. You" break people's bones, if not
> the hardware. So you need to transition from a parachute system to an
> Apollo-like lunar legged lander sometime before you get to the
> ground."
>
> Manning believes that those who are immersed in these matters, like
> himself, see the various problems fighting each other. "It's hard to
> get your brain around all these problems because all the pieces
> connect in complex ways," he said. "It's very hard to see the right
> answer in your mind's eye."
>
> The additional issues of creating new lightweight but strong shapes
> and structures, with the ability to come apart and transform from one
> stage to another at just the right time means developing a rapid-fire
> Rube Goldberg-like contraption.
>
> "The honest truth of the matter," said Manning, "is that we don't
> have a standard canonical form, a standard configuration of systems
> that allows us to get to the ground, with the right size that
> balances the forces, the loads, the people, and allows us to do all
> the transformation that needs to be done in the very small amount of
> time that we have to land."
>
> Other Options and Issues
>
> Another alternative discussed at the 2004 Mars Road Mapping session
> was the space elevator.
>
> "Mars is really begging for a space elevator," said Manning. "I think
> it has great potential. That would solve a lot of problems, and Mars
> would be an excellent platform to try it." But Manning admitted that
> the technology needed to suspend a space elevator has not yet been
> invented. The issues with space elevator technology may be vast, even
> compared with the challenges of landing.
>
> Despite these known obstacles, there are few at NASA currently
> spending any quality time working on any of the issues of landing
> humans on Mars.
>
> Manning explained, "NASA does not yet have the resources to solve
> this problem and also develop the CEV, complete the International
> Space Station and do the lunar landing systems development at the
> same time. But NASA knows that this is on its plate of things to do
> in the future and is just beginning to get a handle on the needed
> technology developments. I try to go out of my way to tell this story
> because I'm encouraging young aeronautical engineering students,
> particularly graduate students, to start working on this problem on
> their own. There is no doubt in my mind that with their help, we can
> figure out how to make reliable human-scale landing systems work on
> Mars."
>
> While there is much interest throughout NASA and the space sector to
> try to tackle these issues in the ensuing years, technology also
> needs a few more years to catch up to our dreams of landing humans on
> Mars.
>
> And this story, like all good engineering stories, will inevitably
> read like a good detective novel with technical twist and turns,
> scientific intrigue, and high adventure on another world.
|
| | |
Date: 18 Jul 2007 20:20:25
From: Greg Neill
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
"mitch" <mitch@nospam.com > wrote in message
news:y1uni.51753$xk5.7720@edtnps82...
> I'm not holding my breath.
[snip]
You quote the whole darned article to add this
one, practically information-free line? Yeesh.
How about some netiquette?
|
| | | |
Date: 19 Jul 2007 02:24:54
From: Sam Wormley
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface
|
Greg Neill wrote:
> "mitch" <mitch@nospam.com> wrote in message
> news:y1uni.51753$xk5.7720@edtnps82...
>> I'm not holding my breath.
>
> [snip]
>
> You quote the whole darned article to add this
> one, practically information-free line? Yeesh.
> How about some netiquette?
>
>
I put "mitch" the attention seeking troll in my kill file
a lot faster than it takes him to create another alias. Out
of sight out of mind.
|
| | | | |
Date: 21 Jul 2007 05:19:07
From: MiKe T
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
> I put "mitch" the attention seeking troll in my kill file
> a lot faster than it takes him to create another alias. Out
> of sight out of mind.
Right..
|
| | | | |
Date: 19 Jul 2007 04:34:14
From: mitch
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
"Sam Wormley" <swormley1@mchsi.com > wrote in message
news:WXzni.32182$Fc.15094@attbi_s21...
> Greg Neill wrote:
>> "mitch" <mitch@nospam.com> wrote in message
>> news:y1uni.51753$xk5.7720@edtnps82...
>>> I'm not holding my breath.
>>
>> [snip]
>>
>> You quote the whole darned article to add this
>> one, practically information-free line? Yeesh.
>> How about some netiquette?
>>
>>
>
> I put "mitch" the attention seeking troll in my kill file
> a lot faster than it takes him to create another alias. Out
> of sight out of mind.
You without guilt cast the first one...
|
| | | |
Date: 19 Jul 2007 00:23:41
From: mitch
Subject: Re: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet
|
"Greg Neill" <gneillREM@OVEsympatico.ca > wrote in message
news:469eacbd$0$335$9a6e19ea@news.newshosting.com...
> "mitch" <mitch@nospam.com> wrote in message
> news:y1uni.51753$xk5.7720@edtnps82...
>> I'm not holding my breath.
>
> [snip]
>
> You quote the whole darned article to add this
> one, practically information-free line? Yeesh.
> How about some netiquette?
Right.
|
|
