Did NASA really make it to Mars?

Dear Bill:

If you were in front of me on a PhD Qual Oral, you bet I'd can your ass too,
if this is any example of your know-nothing 'understanding' of spaceflight
basics.

Mars's lower gravity doesn't squeeze the air down so tightly, so above about
100-200 km,
it's actually thicker than earth's. That's where aerobraking (and natural
meteors) mostly occur.

It's not "at most a mile thick". You must have been confusing it with your
head.

"Such a small, thin atmosphere would require such a huge parachute to slow
the descent
appreciably over such a short difference in altitude that it seems obvious
that the weight
of such a parachute would make it impractical." And -- correct me if I'm
wrong -- you
whine that you were UNFAIRLY denied entry to a PhD program in space science
at the University of Texas? Bill, you're lucky you were given an 8th grade
certificate.

Find something to do that you're competent at, and make yourself -- and
us -- happier.

Your 'tough love' friend,

JimO



"Bill Clark" wrote in message
om...
It is my understanding that the atmosphere of Mars is so thin that the
winds that always go hundreds of miles per hour would only feel like a
light breeze. Also, Mars being such a small planet, the atmosphere
itself is a much thinner than on Earth, being at most a mile thick.

This makes me doubt the efficacy of the recent Mars missions that have
supposedly used aerobraking to save fuel, using the friction of the
Martian atmosphere to slowly bring the spacecraft into a low Mars
orbit. I almost wonder if aerobraking is possible at all; except NASA
claims to have used it successfully on the satellites currently
orbiting Mars.

I also wonder how the Mars landers use parachutes to effectively slow
the descent of the latest Mars landers. Such a small, thin atmosphere
would require such a huge parachute to slow the descent appreciably
over such a short difference in altitude that it seems obvious that
the weight of such a parachute would make it impractical. Yet, the
NASA missions that have landed on Mars claim to use parachutes quite
effectively - even for the latest two landers which are monster robots
compared to little sojourner which was the size of a PC box, versus
the refrigerator sized landers there now.

These simple notions make it seem like the whole thing is a hoax, and
that we never made it to Mars at all but just some remote desert in
Arizona . . .

Just curious

I don't want to get in the middle of your fight, Jim, but it's pretty well
known that the air (if you could call it that) on Mars is actually quite a
bit thinner than what we're accustomed to on earth. Aerobraking isn't so
exotic a technique as many might think, but that aside, the point about the
parachutes is well made. And BTW, that's no longer an issue of space flight.

Wasn't that a beer can I saw under one of those rocks?


Mars's lower gravity doesn't squeeze the air down so tightly, so above
about
100-200 km,
it's actually thicker than earth's. That's where aerobraking (and natural
meteors) mostly occur.



---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.637 / Virus Database: 408 - Release Date: 3/20/04

On Wed, 24 Mar 2004 17:38:19 GMT, in a place far, far away, "ashlar"
made the phosphor on my monitor glow in
such a way as to indicate that:

I don't want to get in the middle of your fight, Jim, but it's pretty well
known that the air (if you could call it that) on Mars is actually quite a
bit thinner than what we're accustomed to on earth.

Reread what he wrote. The air at the surface is thinner, but at
higher altitude it's actually thicker, because it's compressed less.

the point about the parachutes is well made.

No, it's not.

On Wed, 24 Mar 2004 17:57:12 GMT, h (Rand
Simberg) wrote:

On Wed, 24 Mar 2004 17:38:19 GMT, in a place far, far away, "ashlar"
made the phosphor on my monitor glow in
such a way as to indicate that:

I don't want to get in the middle of your fight, Jim, but it's pretty well
known that the air (if you could call it that) on Mars is actually quite a
bit thinner than what we're accustomed to on earth.

Reread what he wrote. The air at the surface is thinner, but at
higher altitude it's actually thicker, because it's compressed less.

Wow, that's nifty!

the point about the parachutes is well made.

No, it's not.

In article ,
h (Rand Simberg) wrote:

Reread what he wrote. The air at the surface is thinner, but at
higher altitude it's actually thicker, because it's compressed less.

Let's not be sloppy in our terminology lest Stuffie show up and start
castigating us once more. "Thicker" in terms of linear distance, or
"thicker" in terms of density?

--
Herb Schaltegger, B.S., J.D.
Reformed Aerospace Engineer
Columbia Loss FAQ:
http://www.io.com/~o_m/columbia_loss_faq_x.html

On Wed, 24 Mar 2004 13:02:42 -0600, in a place far, far away, Herb
Schaltegger made the phosphor on my
monitor glow in such a way as to indicate that:

In article ,
h (Rand Simberg) wrote:

Reread what he wrote. The air at the surface is thinner, but at
higher altitude it's actually thicker, because it's compressed less.

Let's not be sloppy in our terminology lest Stuffie show up and start
castigating us once more. "Thicker" in terms of linear distance, or
"thicker" in terms of density?

I meant in terms of density, but it may be in the other sense of the
word as well--I'd have to go look it up.

"Rand Simberg" wrote in message
...
On Wed, 24 Mar 2004 13:02:42 -0600, in a place far, far away, Herb
Schaltegger made the phosphor on my
monitor glow in such a way as to indicate that:

In article ,
h (Rand Simberg) wrote:

Reread what he wrote. The air at the surface is thinner, but at
higher altitude it's actually thicker, because it's compressed less.

Let's not be sloppy in our terminology lest Stuffie show up and start
castigating us once more. "Thicker" in terms of linear distance, or
"thicker" in terms of density?

I meant in terms of density, but it may be in the other sense of the
word as well--I'd have to go look it up.

How about: the rate of density decrease with altitude is lower on Mars than
on Earth?

On Wed, 24 Mar 2004 14:51:45 -0500, in a place far, far away, "Scott
Hedrick" made the phosphor on my monitor glow in
such a way as to indicate that:

In article ,
h (Rand Simberg) wrote:

Reread what he wrote. The air at the surface is thinner, but at
higher altitude it's actually thicker, because it's compressed less.

Let's not be sloppy in our terminology lest Stuffie show up and start
castigating us once more. "Thicker" in terms of linear distance, or
"thicker" in terms of density?

I meant in terms of density, but it may be in the other sense of the
word as well--I'd have to go look it up.

How about: the rate of density decrease with altitude is lower on Mars than
on Earth?

Yes, but I should clarify that when I say "thinner" and "thicker"
above, I mean relative to earth's profile, not to each other. The
Martian atmosphere 's definitely thinner at altitude than it is at the
surface, but it's thicker than earth's at (some) altitude.

"Rand Simberg" wrote in message
...
On Wed, 24 Mar 2004 17:38:19 GMT, in a place far, far away, "ashlar"
made the phosphor on my monitor glow in
such a way as to indicate that:

I don't want to get in the middle of your fight, Jim, but it's pretty
well
known that the air (if you could call it that) on Mars is actually quite
a
bit thinner than what we're accustomed to on earth.

Reread what he wrote. The air at the surface is thinner, but at
higher altitude it's actually thicker, because it's compressed less.


Compared to the same altitude on Earth. Just to be clear, neither Rand nor
Jim are saying that the atmosphere magically gets denser as you get higher.

(at least not until you hit the ether.:-)

the point about the parachutes is well made.

No, it's not.

The air is still sufficient to provide lift for an airplane. There are lots
of designs
for a UAV that would fly in the martian atmosphere, very nicely, thank you.


"ashlar" wrote in
I got a laugh out of the goose story and thought I'd share that. This
brings
me back to the earlier thought the guy had about the size of a chute large
enough to land a large robotic craft, "refrigerator size" I think he said,
on the surface of the planet without scattering its innards across several
kilometers.

Even if the density is greater at higher altitudes, it remains that at the
surface it's very thin by our standards. In either case I'd say that
that's
gotta be one colossus of a chute. To my thinking the simple chute is a
very
big (pun intended) issue.