Re: Joint Russian/Chinese manned flyby mission to Mars

On Oct 5, 3:45 pm, Quadibloc <jsav...@xxxxxxxxx> wrote:
On Sep 29, 2:13 am, "Jim Relsh" <jrel...@xxxxxxxxx> wrote:

I keep wondering whether this is a possibillity in the not so distant future
as the rewards for them would be great, whilst the cost and engineering
challenges are within their realm.

I can't imagine anyone wanting to do a manned flyby of Mars instead of
a manned landing.

John Savard

Lack of imagination then.

A spacecraft in orbit is naturally less than a light second away from
the surface, which will make A) teleoperation of surface based
equipment practical. B) make it much easier to give instructions to
robotic equipment on ground, erc.


Naturally, many quite mistakenly assume that manned landing on Mars
will be easilly acievable thing, but those do neglect quite a few
facts.

Below, a bit on the problems with a Manned landing:

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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

Written by Nancy Atkinson

Mars. Landing here is going to be hard. Image credit: NASA/JPLSome
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 - 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'd need to cut low into the atmosphere. You'd 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'd eventually slow down to under Mach 2 to
open a parachute, but you'd 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'd 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'd 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.

Written by Nancy Atkinson

Filed under: Space Exploration, Mars
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Einar

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