A Dumb MER question
Japperm
few months only because Mars dust will cover top of the solar panels. If
this is the case, why didn't the MERs include a little automated air blower?
It seems like a simple solution. Does any knowledgeable person know the
answer?
Henry Spencer
Japperm <schu...@rochester.rr.com> wrote:
>From what I've read and heard about the MERs, they will stop working after a
>few months only because Mars dust will cover top of the solar panels. If
>this is the case, why didn't the MERs include a little automated air blower?
It's not so easy in extremely thin air, especially when nobody is really
sure how hard you'd have to blow.
By that time, the MERs will also be losing power because of deteriorating
Sun angles (which couldn't be fixed short of making the solar arrays
movable), and the deepening cold will be starting to damage their
electronics, so the incentive to stretch things out a little longer is
limited.
Long-term operations on the Martian surface really need nuclear power, so
that there's plenty of heat available during the night.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. | he...@spsystems.net
MSu1049321
panel issue as one of the very wicked night cold and it's effect on battery
performance. I read it had a few small capsules of radioisotopes in it just to
create internal heat to keep it going longer, but these were small and only
lasted a short time. Had the mobile probes been powered by RTG's, I daresay
they could ahve run far far longer, but they would have been heavier and more
complicated. Everything's a tradeoff. Dust could be blown off solar panels by
an ultrasonic vibrator as well as by electrostatic means... both would require
power, though, which is where the panels came in, in the first place;-)
.spade.
.spade.
"Japperm" <Nos...@eaatmespammeranddie.com> wrote in message news:fGGJb.45658$q55....@twister.nyroc.rr.com...
Henry Spencer
.spade. <arbit...@ihug.com.au> wrote:
>A windscreen wiper?
Could be a really bad idea if the Martian dust is as abrasive as lunar dust.
David Brower
>In article <bt8mk2$d8p$1...@lust.ihug.co.nz>,
>.spade. <arbit...@ihug.com.au> wrote:
>>A windscreen wiper?
>Could be a really bad idea if the Martian dust is as abrasive as lunar dust.
Mechanized "tear off", as used by onboard cameras during formula car
events. Weight and reliability issues would abound, but if you
could double your useful life with one...
-dB
--
Butterflies tell me to say:
"The statements and opinions expressed here are my own and do not necessarily
represent those of Oracle Corporation."
OM
wrote:
>In article <bt8mk2$d8p$1...@lust.ihug.co.nz>,
>.spade. <arbit...@ihug.com.au> wrote:
>>A windscreen wiper?
>
>Could be a really bad idea if the Martian dust is as abrasive as lunar dust.
...It might not be, considering that it does get blown around by the
Martian air, unlike the soil on the airless Moon. Then again, how
difficult would it have been to have brought along an air compressor
to blow the dust off?
OM
--
"No bastard ever won a war by dying for | http://www.io.com/~o_m
his country. He won it by making the other | Sergeant-At-Arms
poor dumb bastard die for his country." | Human O-Ring Society
- General George S. Patton, Jr
Scott Lowther
>
> On Sun, 4 Jan 2004 18:53:58 GMT, he...@spsystems.net (Henry Spencer)
> wrote:
>
> >In article <bt8mk2$d8p$1...@lust.ihug.co.nz>,
> >.spade. <arbit...@ihug.com.au> wrote:
> >>A windscreen wiper?
> >
> >Could be a really bad idea if the Martian dust is as abrasive as lunar dust.
>
> ...It might not be, considering that it does get blown around by the
> Martian air, unlike the soil on the airless Moon. Then again, how
> difficult would it have been to have brought along an air compressor
> to blow the dust off?
Oh, come now. You've read Dietz... we don't have that kind of
technology.
;P
--
Scott Lowther, Engineer
Remove the obvious (capitalized) anti-spam
gibberish from the reply-to e-mail address
Paul F. Dietz
> Oh, come now. You've read Dietz... we don't have that kind of
> technology.
Ah, your wit continues to inform us of the quality of both
your arguments and your character.
Paul
Scott Lowther
Oh boo-hoo. So which is it: do we have the technology to put an air
compressor on a Mars over, or not? We have not done this yet, so your
arguement, based on recent posts by *you*, would be that we do not have
that technology. Thus my previous post would be in complete agreement
with your position on this matter.
So, you don't like it when people disagree with you, and you don't like
it when people *do* agree with you.
Paul F. Dietz
> Oh boo-hoo. So which is it: do we have the technology to put an air
> compressor on a Mars over, or not? We have not done this yet, so your
> arguement, based on recent posts by *you*, would be that we do not have
> that technology. Thus my previous post would be in complete agreement
> with your position on this matter.
We haven't demonstrated that we do, but I'd expect it wouldn't
be that hard. Some development would be required. I would be
concerned about filtering dust, the lifetime of the air filters,
the lubricants used in the compressor, cooling the motor, and operating
the unit in extreme cold.
I would not be willing to say we had this technology until
it had been demonstrated.
Paul
Scott Lowther
> I would not be willing to say we had this technology until
> it had been demonstrated.
Then you DO agree with the following:
---
> Then again, how
> difficult would it have been to have brought along an air compressor
> to blow the dust off?
Oh, come now. You've read Dietz... we don't have that kind of
technology.
---
Since you agreed with me... "your wit continues to inform us of the
quality of both your arguments and your character" would thus imply that
you either think very highly of my arguement/character, or very
poorly... and thus you think very poorly of your *own* character.
Do not accuse someone else of having poor arguements or character when
they espouse YOUR arguements.
Paul F. Dietz
> Paul F. Dietz wrote:
>
>
>>I would not be willing to say we had this technology until
>>it had been demonstrated.
>
>
> Then you DO agree with the following:
> ---
>
>>Then again, how
>>difficult would it have been to have brought along an air compressor
>>to blow the dust off?
>
>
> Oh, come now. You've read Dietz... we don't have that kind of
> technology.
> ---
>
> Since you agreed with me... "your wit continues to inform us of the
> quality of both your arguments and your character" would thus imply that
> you either think very highly of my arguement/character, or very
> poorly... and thus you think very poorly of your *own* character.
>
> Do not accuse someone else of having poor arguements or character when
> they espouse YOUR arguements.
You wrote (with great implied sarcasm) the 'Oh, come now...'
statement.
I *agree* with that statement. The wit I was criticizing was
your sarcasm.
And, in fact, we don't have that technology in a form that
the rover designers were willing to use. Maybe it was mass
budget, maybe it was safety concerns (unwillingness to store
too much compressed gas) or maybe it was one of the several
issues I mentioned. Spacecraft designers don't like to pioneer
too many new things.
Paul
Scott Lowther
> You wrote (with great implied sarcasm)
You choose to read what you choose to read.
> And, in fact, we don't have that technology in a form that
> the rover designers were willing to use.
HA! There, now THAT is a reasonable statement, much more so than your
previous blanket statements. The world ISN'T as black-white, is-ain't as
your "We don't" nonsense.
We HAVE the technology to do a great many things in space. But, they
cost too much, weigh too much, scare the wrong set of protestors. But
that is NOT the same thing as "We don't have it."
Paul F. Dietz
> We HAVE the technology to do a great many things in space. But, they
> cost too much, weigh too much, scare the wrong set of protestors. But
> that is NOT the same thing as "We don't have it."
The fact remains that the technology that is available did not satisfy
the needs of the customer. If one is willing to drop that constraint,
then many supposed technologies become available. They don't even have
to be reliable, or even workable.
Paul
Scott Lowther
>
> Scott Lowther wrote:
>
> > We HAVE the technology to do a great many things in space. But, they
> > cost too much, weigh too much, scare the wrong set of protestors. But
> > that is NOT the same thing as "We don't have it."
>
> The fact remains that the technology that is available did not satisfy
> the needs of the customer. If one is willing to drop that constraint,
> then many supposed technologies become available.
Yes. The technologies are, again, extant. And, as I've repeatedly
pointed out, mods would be advisable. But the technologies are extant,
and can be used as-is if you're willing to be non-optimised.
Your previous reply "We don't" to the claim that "we have the technology
in hand to do a good start at it" was, at best, not accurate. Many
things in life and engineering do not need to be completely or even
approximately optimized to be damned useful. The mindset that all things
DO need to be perfectly optimized has led to a NASA that can't do a
damend thing without thousands of man-hours spent poring over Powerpoint
presentations, and, in the end, spending lots of money and building
nothing.
Paul F. Dietz
> Your previous reply "We don't" to the claim that "we have the technology
> in hand to do a good start at it" was, at best, not accurate.
I disagree with this statement. To not rehash the previous argument,
I will offer up another one.
'Settlement' implies the ability of a community to exist and sustain
itself. This need not necessarily imply they can be completely self-sufficient,
(although for the purpose described at the beginning of the other
thread it might have to be) but it does imply that they be able to be
economically self-sustaining.
This implies they must be sufficiently productive that each person can (on
average) produce enough value to pay for all the equipment and supplies
they need.
We are *not* close to being able to do that. Anything we build now would
be a pitiful imitation of a sustainable settlement. Maybe that would be
a step toward better technologies that would make the settlement more
sustainable, but perhaps the technology has to move in other directions
to make the goal achievable (Dyson suggests focusing on biotechnology, for
example, with space settlement beginning in about 50 years.)
I consider the ultimate goal sufficiently far away that a linear
approach is probably not the right one.
Paul
Scott Lowther
> 'Settlement' implies the ability of a community to exist and sustain
> itself. This need not necessarily imply they can be completely self-sufficient,
> (although for the purpose described at the beginning of the other
> thread it might have to be) but it does imply that they be able to be
> economically self-sustaining.
>
> This implies they must be sufficiently productive that each person can (on
> average) produce enough value to pay for all the equipment and supplies
> they need.
>
> We are *not* close to being able to do that. Anything we build now would
> be a pitiful imitation of a sustainable settlement.
Nobody is suggesting that with what we have now we could make a fully
self-sufficient, happy little colony. What is suggested is that we could
make "a good start at it."
While historical analogies are dubious at best as far as space
settlement... consider North America. First european settlers were the
Vikings. They made, to all accounts, "a good start at it," and were only
driven away because of conflict with the Skraelings and the Little Ice
Age. However... they made "a good start at it" with the technology they
had. Had the Injuns not been there (and, as far as I'm aware, there
aren't Injun-analogs on the Moon or Mars), it's entirely possible that a
Viking society would have been awaiting Cortez... even though Viking
tech was considerably less advanced than 16th-century Spanish tech. In
the end, North American Vikings faield not because their technology
wasn't up to it, but because their colonization infrastructure wasn't up
to it. It was too long of a journey for people so poor.
And of course, North America was settled considerably earlier by the
Injuns themselves, with technology vastly lesser than what even the
Vikings had. In their case, they *did* have the requisite
infrastructure: enough bodies simply swarmed across the land bridge.
Kevin Willoughby
om@our_blessed_lady_mary_of_the_holy_NASA_research_facility.org says...
> On Sun, 4 Jan 2004 18:53:58 GMT, he...@spsystems.net (Henry Spencer)
> wrote:
> >In article <bt8mk2$d8p$1...@lust.ihug.co.nz>,
> >.spade. <arbit...@ihug.com.au> wrote:
> >>A windscreen wiper?
> >Could be a really bad idea if the Martian dust is as abrasive as lunar dust.
> ...It might not be, considering that it does get blown around by the
> Martian air, unlike the soil on the airless Moon. Then again, how
> difficult would it have been to have brought along an air compressor
> to blow the dust off?
Or use a trick that is common on the little video cameras strapped to
race cars for TV coverage of car races: a spool of clear plastic that
unwinds in front of the lens. Given the extraordinary contortions of the
MER rovers, a little motor to wind away the dirty plastic, pulling clean
plastic over the lens should be trivial.
--
Kevin Willoughby kevinwi...@acm.orgNoSpam.invalid
Imagine that, a FROG ON-OFF switch, hardly the work
for test pilots. -- Mike Collins
MSu1049321
MER rovers, a little motor to wind away the dirty plastic, pulling clean
plastic over the lens should be trivial.
-- >>
Not to be contrary, but the tear-aways and roll-aways on NASCAR cameras and
helmets have a MUCH more benign environment to work in than Mars, and a pitcrew
of humans ready to fix or replace things at a minute's notice. On Mars, if it
jams or breaks, it may kill the mission. I can't begin to list all the problems
the same mechanism would face on Mars, but some would include:
0ver 150 degree cold at night, unholy UV radiation, a trip thru 8 months of
deep space and zero-g and a firey reentry, plus heavy g-shock on landing and
abrasive dust that will stick to bearings, rollers, and lubricants.
I would not be surprised to learn it would take a very special and new plastic
formulation and a very hardy and tested deployment mechanism to make this a
foolproof solution.
Henry Spencer
OM <om@our_blessed_lady_mary_of_the_holy_NASA_research_facility.org> wrote:
>>>A windscreen wiper?
>>Could be a really bad idea if the Martian dust is as abrasive as lunar dust.
>
>...It might not be, considering that it does get blown around by the
>Martian air, unlike the soil on the airless Moon.
Possibly not, but nobody's sure. There is also thought to be a strong
possibility that the particles are small and the adhesion to the surface
fairly strong, in which case a wiper just won't work (although a brush
might perhaps do better).
>Then again, how
>difficult would it have been to have brought along an air compressor
>to blow the dust off?
In the thin air, it probably requires fairly high gas velocities, not
trivial to achieve.
Last I heard (a paper by Geoff Landis, I think), electrostatic dust
removal was considered probably the best bet.
Keith F. Lynch
> Then again, how difficult would it have been to have brought along
> an air compressor to blow the dust off?
Henry Spencer <he...@spsystems.net> wrote:
> In the thin air, it probably requires fairly high gas velocities,
> not trivial to achieve.
The air coming out of a compressor needn't be thin.
Of course that might just substitute one problem (dust blocking the
solar panels) for another (dust clogging the compressor's air intake,
or abrading its pump).
--
Keith F. Lynch - k...@keithlynch.net - http://keithlynch.net/
I always welcome replies to my e-mail, postings, and web pages, but
unsolicited bulk e-mail (spam) is not acceptable. Please do not send me
HTML, "rich text," or attachments, as all such email is discarded unread.
Henry Spencer
Keith F. Lynch <k...@KeithLynch.net> wrote:
>>> an air compressor to blow the dust off?
>> not trivial to achieve.
>
>The air coming out of a compressor needn't be thin.
It will be by the time it reaches the solar arrays. It'll expand to match
ambient pressure (and thus, more or less, ambient density) before it
covers any significant distance.
Paul F. Dietz
> It will be by the time it reaches the solar arrays. It'll expand to match
> ambient pressure (and thus, more or less, ambient density) before it
> covers any significant distance.
It will also cool, though. I suspect you'd get a mixture of cold gas
and CO2 snow. What will supersonic CO2 snowflakes do to the solar
arrays?
Paul
Pat Flannery
Henry Spencer wrote:
>It will be by the time it reaches the solar arrays. It'll expand to match
>ambient pressure (and thus, more or less, ambient density) before it
>covers any significant distance.
>
Years and years ago, when I was a kid ( this happened around 1970) and
had carte blanche to tear apart any household appliance that went on the
fritz, my dad brought home my granddad's burnt out big television set,
with the monster picture tube (for those days)- anyway, the thing was a
good 2 1/2 to 3 feet from the end of the cathode ray gun to the front
of the screen; at the end of the cathode ray gun stood the little dollop
of glass where it had been sealed after if had been vacuumated. This
intrigued me, so I set the tube face-down on the floor, worked up my
nerve, and snapped off the little curlicue of glass with a lock wrench
while looking away from the tube in case it imploded; the glass snapped
off cleanly- leaving a hole about two to three millimeters in diameter-
a prolonged whooshing sound followed and faded away after around fifteen
seconds, as the interior pressure equaled ambient air pressure.
When I turned the tube upright, I got quite a surprise; the phosphors
were blown off the middle of the front screen. It took a second to
figure out what happened... the air entering at the back had nothing to
slow it down for the first few seconds, so it continued on at high
velocity to the front screen. Until the air pressure rose enough inside
the tube for turbulence to abate its forward momentum.
In much the same way, control jet exhaust from RCS systems in space
continues on for quite some distance at high velocity, enough to strike
objects and cause them to move (remember how the Shuttle's RCS firing
blew the HST's jettisoned solar array about, and how the Apollo's SM
thrusters made the solar parasol on Skylab ripple badly)
I would think that the thin atmosphere of Mars would act in much the
same manner; the gas jet would spread as you say; but the low
atmospheric pressure would mean that the kinetic energy of the jet
would remain high to a fairly good distance from the nozzle, due to the
lack of impact between itself and enough atmospheric gas molecules to
slow it down.
Pat
Pat Flannery
Paul F. Dietz wrote:
>
> It will also cool, though. I suspect you'd get a mixture of cold gas
> and CO2 snow. What will supersonic CO2 snowflakes do to the solar
> arrays?
Oddly enough, we recently got in a frozen cake down at work that was
packed in dry ice, we went to a website on the uses of dry ice- and one
of them is this: http://www.dryiceclean.com/Overview.htm
...this sounds like a bad thing to do to a solar panel.
Pat
Paul Blay
>
> [...] one
> ...this sounds like a bad thing to do to a solar panel.
I don't know. Might have been useful on a certain solar-
concentrator utilising design ;-)
jeff findley
>
> Henry Spencer wrote:
> >It will be by the time it reaches the solar arrays. It'll expand to match
> >ambient pressure (and thus, more or less, ambient density) before it
> >covers any significant distance.
>
> same manner; the gas jet would spread as you say; but the low
> atmospheric pressure would mean that the kinetic energy of the jet
> would remain high to a fairly good distance from the nozzle, due to the
> lack of impact between itself and enough atmospheric gas molecules to
> slow it down.
Your experiment with the TV tube was essentially a proof of
concept of how to blow dust off of a glass surface.
While I can "see" both sides of the issue, all the arguing back and
forth doesn't mean much until someone actually does an experiment like
this as a proof of concept.
A "real" proof of concept wouldn't take much. You need a piece of
solar panel, a vacuum chamber, and a small diameter tube leading to
supply of compressed gas of similar composition to Martian atmosphere
(perhaps just CO2 for the proof of concept). The biggest challenge
would be to find "dust" which closely mimicked the properties of
Martian dust, since the properties of said dust may not be known well.
Repeatedly dust the solar panel and blow the dust off and see how the
panel performs after each dust/blow cycle.
Jeff
--
Remove "no" and "spam" from email address to reply.
If it says "This is not spam!", it's surely a lie.
jeff findley
> Oddly enough, we recently got in a frozen cake down at work that was
> packed in dry ice, we went to a website on the uses of dry ice- and one
> of them is this: http://www.dryiceclean.com/Overview.htm
> ...this sounds like a bad thing to do to a solar panel.
Depends on the durability of the solar panel and how often, and how
vigorously, you blow the panel clean. Such issues can readily be
investigated with a few properly conducted science experiments.
Herb Schaltegger
> Your experiment with the TV tube was essentially a proof of
> concept of how to blow dust off of a glass surface.
>
> While I can "see" both sides of the issue, all the arguing back and
> forth doesn't mean much until someone actually does an experiment like
> this as a proof of concept.
>
> A "real" proof of concept wouldn't take much. You need a piece of
> solar panel, a vacuum chamber, and a small diameter tube leading to
> supply of compressed gas of similar composition to Martian atmosphere
> (perhaps just CO2 for the proof of concept). The biggest challenge
> would be to find "dust" which closely mimicked the properties of
> Martian dust, since the properties of said dust may not be known well.
>
> Repeatedly dust the solar panel and blow the dust off and see how the
> panel performs after each dust/blow cycle.
>
> Jeff
All you'd need to do is design a neat little con-di (convergent-divergent)
nozzle optimized for Martian ambient conditions. Depending on the gas
properties of the Martian air used, the throat conditions of the nozzle
(determined mostly by diameter) and the shape of the nozzle, you can tailor
the resulting jet of air pretty easily, actually. You end up with a
supersonic flow of not-necessarily dense gases which should nonetheless
work quite well to remove dust and loose grit from the surface in question.
--
Herb Schaltegger, B.S., J.D.
Reformed Aerospace Engineer
Remove invalid nonsense for email.
Henry Spencer
Pat Flannery <fla...@daktel.com> wrote:
>>It will be by the time it reaches the solar arrays. It'll expand to match
>>ambient pressure (and thus, more or less, ambient density) before it
>>covers any significant distance.
>
>atmospheric pressure would mean that the kinetic energy of the jet
Yes, you'd get a substantial jet velocity, which is how such a
dust-blowing system would work. But although the gas will be moving
fairly briskly, it won't be much denser than the surrounding gas (and what
added density it has will be due to temperature drop during expansion).
Henry Spencer
Note that they need to compress the dry ice into pellets beforehand to
make this work -- snow would be a rather milder case.
Although, of course, if you're compressing Martian air to do this, it's
already got some dust in it, and *that* dust is going to hit the panels
at high speed...
Pat Flannery
jeff findley wrote:
>
>While I can "see" both sides of the issue, all the arguing back and
>forth doesn't mean much until someone actually does an experiment like
>this as a proof of concept.
>
>A "real" proof of concept wouldn't take much. You need a piece of
>solar panel, a vacuum chamber, and a small diameter tube leading to
>supply of compressed gas of similar composition to Martian atmosphere
>(perhaps just CO2 for the proof of concept). The biggest challenge
>would be to find "dust" which closely mimicked the properties of
>Martian dust, since the properties of said dust may not be known well.
>
>Repeatedly dust the solar panel and blow the dust off and see how the
>panel performs after each dust/blow cycle.
>
This would certainly be the ideal solution; one thing that might affect
the result is if the dust were to stick to the panel via a static
charge... can a solar panel develop a static charge?
Pat
>
>Jeff
>
>
Pat Flannery
Henry Spencer wrote:
>Yes, you'd get a substantial jet velocity, which is how such a
>dust-blowing system would work. But although the gas will be moving
>fairly briskly, it won't be much denser than the surrounding gas (and what
>added density it has will be due to temperature drop during expansion).
>
First off, I'd use either compressed helium or nitrogen over the
compressor/Martian atmosphere solution for the sake of simplicity;
second I'd put a De Laval nozzle on the end of the gas tube so as to try
to focus the gas jet.
Pat
Pat Flannery
Henry Spencer wrote:
>Note that they need to compress the dry ice into pellets beforehand to
>make this work -- snow would be a rather milder case.
>
>Although, of course, if you're compressing Martian air to do this, it's
>already got some dust in it, and *that* dust is going to hit the panels
>at high speed...
>
The other problem is that the dry ice formation may plug the nozzle as
it exits, due to the temperature drop.
I'll stick with helium or nitrogen. also there is the matter of power
consumption to drive the atmospheric compressor.
An alternative idea might be to borrow a page from dirt-bike riders- who
wear goggles with multiple peel-off layers. Simply cover the panels with
four or five layers of thin transparent material that can be flipped
upwards and outwards as it is jettisoned after it becomes excessively
dusty. I remember every one of Telstar's( or was it Tiros?) solar cells
were individually covered with a thin sheet of synthetic
sapphire...this sound a bit on the expensive side, but there must be
something fairly cheap that could be used that would still pass the
wavelengths of light that the cells need.
Pat
Phil Fraering
>In article <btd9bs$f5n$1...@panix3.panix.com>,
>Keith F. Lynch <k...@KeithLynch.net> wrote:
>>>> an air compressor to blow the dust off?
>>> In the thin air, it probably requires fairly high gas velocities,
>>> not trivial to achieve.
>>
>>The air coming out of a compressor needn't be thin.
>It will be by the time it reaches the solar arrays. It'll expand to match
>ambient pressure (and thus, more or less, ambient density) before it
>covers any significant distance.
If you design the nozzle right, the speed will increace as it expands,
right?
--
Phil Fraering
http://newsfromthefridge.typepad.com
Henry Spencer
Phil Fraering <pgf@AUTO> wrote:
>>>> In the thin air, it probably requires fairly high gas velocities,
>>>> not trivial to achieve.
>>>The air coming out of a compressor needn't be thin.
>>It will be by the time it reaches the solar arrays. It'll expand to match
>
>If you design the nozzle right, the speed will increace as it expands,
>right?
Correct. But in that thin air, it'll be a significant effort to get the
velocity up to what's needed to remove fine, well-adhering dust.
Herb Schaltegger
> In article <iumsc1-...@lungold.cox-internet.com>,
> Phil Fraering <pgf@AUTO> wrote:
>>>>> In the thin air, it probably requires fairly high gas velocities,
>>>>> not trivial to achieve.
>>>>The air coming out of a compressor needn't be thin.
>>>It will be by the time it reaches the solar arrays. It'll expand to
>>>match ambient pressure...
>>
>>If you design the nozzle right, the speed will increace as it expands,
>>right?
>
> Correct. But in that thin air, it'll be a significant effort to get the
> velocity up to what's needed to remove fine, well-adhering dust.
With all due respect to Henry, I disagree. As I pointed out a couple of
days ago, a decently-designed con-di (convergent-divergent) nozzle at the
end of a compressor hose will result in supersonic flow at the exit; that
is a function of compressible gas dynamics, period. If you know the nozzle
exit conditions you're designing for (e.g., the mean daylight surface
temperature, pressure, density, specific heat, etc. of the Martian
atmosphere at the landing site) this is not a difficult task.
jeff findley
>
> With all due respect to Henry, I disagree. As I pointed out a couple of
> days ago, a decently-designed con-di (convergent-divergent) nozzle at the
> end of a compressor hose will result in supersonic flow at the exit; that
> is a function of compressible gas dynamics, period. If you know the nozzle
> exit conditions you're designing for (e.g., the mean daylight surface
> temperature, pressure, density, specific heat, etc. of the Martian
> atmosphere at the landing site) this is not a difficult task.
I tend to agree with Herb. This is the sort of thing you give to
college students in an undergraduate aerodynamics classes (also gas
dynamics). This is something a college graduate (in an appropriate
engineering field) ought to be able to do without much difficulty.
Dick Morris
If the flow reaches sonic velocity at the throat, it will continue to
accelerate as it expands through the diverging section.
Kaido Kert
> From what I've read and heard about the MERs, they will stop working after a
> few months only because Mars dust will cover top of the solar panels. If
> this is the case, why didn't the MERs include a little automated air blower?
> It seems like a simple solution. Does any knowledgeable person know the
> answer?
Heres another dumb MER question. Id assume that airbag landing
approach will not be suitable for possible future human martian
landings.
So are further developments of such landing technique actually worth
it ? Why not perfect thruster-powered landings instead ? Because
otherwise if and when the need arises we'd have to start from a clean
sheet again.
Does it actually offer any significant mass savings, or are there less
potential failure modes or what ?
-kert
Marvin
news:693cff74.04010...@posting.google.com:
> approach will not be suitable for possible future human martian
> landings.
> So are further developments of such landing technique actually worth
> it ? Why not perfect thruster-powered landings instead ? Because
> otherwise if and when the need arises we'd have to start from a clean
> sheet again.
> Does it actually offer any significant mass savings, or are there less
> potential failure modes or what ?
>
> -kert
>
Airbags have a lowish upper mass limit they can handle, the rovers are
close to that limit. Humans would not like the 40G-bounces that go along
with this landing mode.
Why airbags? As compared to thruster-powered landings, you have lots less
failure modes, medium-big mass savings and huge complexity savings. Of
course the few failure modes that airbags do have tend to be lethal and
unpredictable. (things like landing on a sharp rock. the airbag system is
virtually unguided as to final approach, and totally unguided once bouncing
begins)
Why not perfect thruster-powered landings instead?
Been there, done that. We know exactly how to do these in a safe way,
including some backups to handle several of the possible failure modes,
etc. Its just that the whole package of thrusters, surface-sensors, control
mechanisms, etc.. makes for a very heavy package. Not something you can
launch on a mere Delta. The high complexity also leads to longish
development times, nasty budgets, etc.
Henry Spencer
Marvin <kitfox@die_spam_die.pixie.co.za> wrote:
>Why airbags? As compared to thruster-powered landings, you have lots less
Not really. The airbag systems have a bunch of failure modes all their
own, including failure of their braking rockets. (Beagle 2 is the only
probe to ever attempt landing on Mars with no rocket braking, unless
possibly the Russians tried it way back when.) It's particularly bad for
the MER landing system, which relies on rocket thrust not just for braking
but also for canceling side motion due to wind, based on real-time
analysis of descent-camera images (!).
>medium-big mass savings, and huge complexity savings.
Sorry, simply not true. That's why the MESUR project, which eventually
begat Mars Pathfinder, baselined airbags -- in the *expectation* that the
result would be a simple, robust, lightweight landing system. But that is
*NOT* how it turned out. The airbag systems are, in fact, heavy and
complex compared to rocket landing, and they also constrain you to land in
relatively low areas (they need relatively dense air for their parachutes).
The one real technical advantage airbags have is that in rough terrain,
they have a rather better chance of a safe landing, because they cope much
better with a touchdown point that isn't flat and level.
For MER, they also had a programmatic advantage in that the US currently
has no flight-qualified rocket-landing system, given the lingering worries
about MPL's hardware design. However, adapting the MP airbag system to
handle the heavy rovers was a lot harder than people first expected; the
MER team has been worked to death for the last 18 months or so. Quite
probably it would not have been attempted if folks had known then what
they know now.
>Why not perfect thruster-powered landings instead?
>Been there, done that. We know exactly how to do these in a safe way,
>including some backups to handle several of the possible failure modes,
>etc. Its just that the whole package of thrusters, surface-sensors, control
>mechanisms, etc.. makes for a very heavy package. Not something you can
>launch on a mere Delta.
Nonsense. MPL was launched on a Delta. Phoenix, which is using the copy
of the MPL hardware built for the cancelled 2001 lander, will also launch
on a Delta. As noted above, a rocket landing system is actually lighter
than the airbags for a given payload. It's also simpler (!) and more
versatile, and gives a much gentler ride. The one price you do pay is
that the current systems are not smart enough to notice that they're about
to set down on a boulder that will wreck them.
Henry Spencer
Kaido Kert <kaido...@hotmail.com> wrote:
>So are further developments of such landing technique actually worth it ?
Probably not. All future landers are planned to use rocket landing.
Phil Fraering
>Correct. But in that thin air, it'll be a significant effort to get the
>velocity up to what's needed to remove fine, well-adhering dust.
I'm thinking that if you design the nozzle right, you might keep the same
momentum-per-cross-sectional-area, or at least keep the loss of same to
acceptable levels.
Keep in mind the thinner atmosphere may cut both ways: there's less
back pressure on the nozzle, and there will be less drag induced
on the compressed stream of, er, air. (For lack of a better term).