Mars Rovers Landing ???

When I have a thought you know I'm going to tell you "ALL" what it is.
We know the rovers are inside a bag,and when this bag hits the ground it
is going to bounce up and down till finally it comes to rest,and out the
rovers come. It is that first impact bounce that bothers me. The bag
has to make a sudden stop hitting Mars hard surface. It is always the
sudden stop that is the killer. Now the bag and all that's in it has to
change direction. Here we have inertia coming into play. That is the
reason I like light stuff. What if the bag inclosing the rovers were
made out of a light marshmallow material. When it hit it would plop. The
soft material could be made much thicker on its bottom to cushion the
force of impact. No bounce means less chance of rolling into a deep
gulley. Less chance of landing upside down. Easier engineering. Would
like to throw a marshmallow of the Sears Tower,and I'll bet it would not
even change its shape hitting the sidewalk. Well now I can go to bed.
I got that thought of my mind. Bert

Bert posted:

We know the rovers are inside a bag,

No Bert, the rovers are inside a *lander*. Go to the following URL:
http://mars.jpl.nasa.gov/mer/mission/spacecraft.html

The lander's strong tetrahedral frame both encloses and holds the rover,
helping to protect it. The airbags (there are more than one Bert) inflate on
the *outside* of the lander structure. Once the lander stops bouncing or
rolling, the airbags deflate, the lander unfolds its petals to expose the
rover, the rover is released by triggering explosive bolts, and the rover
drives off the lander and onto the surface.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Bert posted:

We know the rovers are inside a bag,

No Bert, the rovers are inside a *lander*. Go to the following URL:
http://mars.jpl.nasa.gov/mer/mission/spacecraft.html

The lander's strong tetrahedral frame both encloses and holds the rover,
helping to protect it. The airbags (there are more than one Bert) inflate on
the *outside* of the lander structure. Once the lander stops bouncing or
rolling, the airbags deflate, the lander unfolds its petals to expose the
rover, the rover is released by triggering explosive bolts, and the rover
drives off the lander and onto the surface.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

"David Knisely" wrote in message
...
No Bert, the rovers are inside a *lander*. Go to the following URL:
http://mars.jpl.nasa.gov/mer/mission/spacecraft.html
Bert's comment has got me to thinking about the bouncing airbag concept.

After the RAD motors and 'chutes have done their job the airbags are
intended to reduce spacecraft residual velocity to zero. Let us call the
velocity just before impact V.

Scenario 1.
The inflated airbag/spacecraft assembly hits the surface and bounces. It now
will have an upward velocity. Assume around ten bounces are expected then
the new upward velocity will be very approximately 0.9V. The spacecraft will
be subjected to a deltaV of 1.9V within a fraction of a second. After
reaching some height it will return to the surface with a velocity of a bit
less than 0.9V and will again bounce to give a second deltaV of 0.9+0.8 =
1.7V. This will continue with the assembly bouncing around at random, maybe
hitting a few rocks on some bounces. Numbers here are approximate, but you
get the general idea...the craft is subjected to a number of deltaV's that
exceed the initial velocity.

Now let let us surround the craft with bags of sticky viscous goo. Very
light sticky viscous goo. It would need to be generated at around the same
time that the bags would have been inflated with gas. Let us run through the
impact scenario again.

Scenario 2.
The inflated airbag/spacecraft assembly hits the surface and....plop,
squelch! It stays put. All of the kinetic energy has been converted to heat
in the goo. Total deltaV is from V to zero = V. Assuming that the time from
V to zero with the goo is roughly the same time that the airbags would cause
a reversal of V, the goo method subjects the craft to around half of the
airbag stresses at first impact...and there are *no* secondary impacts. For
another bonus...the airbags would not need to be pressurised to hold the
goo. In fact bags may not even be needed if a suitable self-skinning goo
could be engineered.

OK...what is the telephone number for NASA?

Sally

"David Knisely" wrote in message
...
No Bert, the rovers are inside a *lander*. Go to the following URL:
http://mars.jpl.nasa.gov/mer/mission/spacecraft.html
Bert's comment has got me to thinking about the bouncing airbag concept.

After the RAD motors and 'chutes have done their job the airbags are
intended to reduce spacecraft residual velocity to zero. Let us call the
velocity just before impact V.

Scenario 1.
The inflated airbag/spacecraft assembly hits the surface and bounces. It now
will have an upward velocity. Assume around ten bounces are expected then
the new upward velocity will be very approximately 0.9V. The spacecraft will
be subjected to a deltaV of 1.9V within a fraction of a second. After
reaching some height it will return to the surface with a velocity of a bit
less than 0.9V and will again bounce to give a second deltaV of 0.9+0.8 =
1.7V. This will continue with the assembly bouncing around at random, maybe
hitting a few rocks on some bounces. Numbers here are approximate, but you
get the general idea...the craft is subjected to a number of deltaV's that
exceed the initial velocity.

Now let let us surround the craft with bags of sticky viscous goo. Very
light sticky viscous goo. It would need to be generated at around the same
time that the bags would have been inflated with gas. Let us run through the
impact scenario again.

Scenario 2.
The inflated airbag/spacecraft assembly hits the surface and....plop,
squelch! It stays put. All of the kinetic energy has been converted to heat
in the goo. Total deltaV is from V to zero = V. Assuming that the time from
V to zero with the goo is roughly the same time that the airbags would cause
a reversal of V, the goo method subjects the craft to around half of the
airbag stresses at first impact...and there are *no* secondary impacts. For
another bonus...the airbags would not need to be pressurised to hold the
goo. In fact bags may not even be needed if a suitable self-skinning goo
could be engineered.

OK...what is the telephone number for NASA?

Sally

"Sally" wrote in message
...
"David Knisely" wrote in message
...
No Bert, the rovers are inside a *lander*. Go to the following URL:
http://mars.jpl.nasa.gov/mer/mission/spacecraft.html
Bert's comment has got me to thinking about the bouncing airbag concept.

After the RAD motors and 'chutes have done their job the airbags are
intended to reduce spacecraft residual velocity to zero. Let us call the
velocity just before impact V.

Scenario 1.
The inflated airbag/spacecraft assembly hits the surface and bounces. It
now
will have an upward velocity. Assume around ten bounces are expected then
the new upward velocity will be very approximately 0.9V. The spacecraft
will
be subjected to a deltaV of 1.9V within a fraction of a second. After
reaching some height it will return to the surface with a velocity of a
bit
less than 0.9V and will again bounce to give a second deltaV of 0.9+0.8 =
1.7V. This will continue with the assembly bouncing around at random,
maybe
hitting a few rocks on some bounces. Numbers here are approximate, but you
get the general idea...the craft is subjected to a number of deltaV's that
exceed the initial velocity.

Now let let us surround the craft with bags of sticky viscous goo. Very
light sticky viscous goo. It would need to be generated at around the same
time that the bags would have been inflated with gas. Let us run through
the
impact scenario again.

Scenario 2.
The inflated airbag/spacecraft assembly hits the surface and....plop,
squelch! It stays put. All of the kinetic energy has been converted to
heat
in the goo. Total deltaV is from V to zero = V. Assuming that the time
from
V to zero with the goo is roughly the same time that the airbags would
cause
a reversal of V, the goo method subjects the craft to around half of the
airbag stresses at first impact...and there are *no* secondary impacts.
For
another bonus...the airbags would not need to be pressurised to hold the
goo. In fact bags may not even be needed if a suitable self-skinning goo
could be engineered.

OK...what is the telephone number for NASA?
You are missing one thing.
The spacecraft itself, is not the airbag, but is inside the airbag. Hence,
though the delta V, will behave as you describe, the time involved for the
ship is stretched significantly. If you watch a bouncing ball in slow
motion, the bottom starts to move up off the surface, before the upper
surface responds. The ship, actually decelerates, from the instant the
surface of the bag touches the ground, while it travels allmost the entire
radius of the airbag towards the ground. The time taken for the change in
velocity, determines the peak acceleration involved. So though the delta V
is lower in the 'absorbent' material, the acceleration perceived by the ship
inside the goo is higher. You also have to carry the 'goo' from Earth (the
gas can be stored at high pressure, or created from a chemical reaction, and
hence involves carrying far less mass). Building systems to survive high-G,
is a relatively well understood technology. Even in the second world war,
electro/mechanical fuses were routinely being built (using valves!), to
handle accelerations of hundreds of G.

Best Wishes

"Sally" wrote in message
...
"David Knisely" wrote in message
...
No Bert, the rovers are inside a *lander*. Go to the following URL:
http://mars.jpl.nasa.gov/mer/mission/spacecraft.html
Bert's comment has got me to thinking about the bouncing airbag concept.

After the RAD motors and 'chutes have done their job the airbags are
intended to reduce spacecraft residual velocity to zero. Let us call the
velocity just before impact V.

Scenario 1.
The inflated airbag/spacecraft assembly hits the surface and bounces. It
now
will have an upward velocity. Assume around ten bounces are expected then
the new upward velocity will be very approximately 0.9V. The spacecraft
will
be subjected to a deltaV of 1.9V within a fraction of a second. After
reaching some height it will return to the surface with a velocity of a
bit
less than 0.9V and will again bounce to give a second deltaV of 0.9+0.8 =
1.7V. This will continue with the assembly bouncing around at random,
maybe
hitting a few rocks on some bounces. Numbers here are approximate, but you
get the general idea...the craft is subjected to a number of deltaV's that
exceed the initial velocity.

Now let let us surround the craft with bags of sticky viscous goo. Very
light sticky viscous goo. It would need to be generated at around the same
time that the bags would have been inflated with gas. Let us run through
the
impact scenario again.

Scenario 2.
The inflated airbag/spacecraft assembly hits the surface and....plop,
squelch! It stays put. All of the kinetic energy has been converted to
heat
in the goo. Total deltaV is from V to zero = V. Assuming that the time
from
V to zero with the goo is roughly the same time that the airbags would
cause
a reversal of V, the goo method subjects the craft to around half of the
airbag stresses at first impact...and there are *no* secondary impacts.
For
another bonus...the airbags would not need to be pressurised to hold the
goo. In fact bags may not even be needed if a suitable self-skinning goo
could be engineered.

OK...what is the telephone number for NASA?
You are missing one thing.
The spacecraft itself, is not the airbag, but is inside the airbag. Hence,
though the delta V, will behave as you describe, the time involved for the
ship is stretched significantly. If you watch a bouncing ball in slow
motion, the bottom starts to move up off the surface, before the upper
surface responds. The ship, actually decelerates, from the instant the
surface of the bag touches the ground, while it travels allmost the entire
radius of the airbag towards the ground. The time taken for the change in
velocity, determines the peak acceleration involved. So though the delta V
is lower in the 'absorbent' material, the acceleration perceived by the ship
inside the goo is higher. You also have to carry the 'goo' from Earth (the
gas can be stored at high pressure, or created from a chemical reaction, and
hence involves carrying far less mass). Building systems to survive high-G,
is a relatively well understood technology. Even in the second world war,
electro/mechanical fuses were routinely being built (using valves!), to
handle accelerations of hundreds of G.

Best Wishes

"Roger Hamlett" wrote in message
...
You are missing one thing.
The spacecraft itself, is not the airbag, but is inside the airbag. Hence,
I do understand that there are multiple airbags attached to the outside of
the spacecraft and that they have connections between them. This is why I
referred to the "spacecraft assembly"...meaning the spacecraft plus airbags.

though the delta V, will behave as you describe, the time involved for the
ship is stretched significantly. If you watch a bouncing ball in slow
motion, the bottom starts to move up off the surface, before the upper
surface responds.
Yes, understood.

The ship, actually decelerates, from the instant the
surface of the bag touches the ground, while it travels allmost the entire
radius of the airbag towards the ground.
The same thing could happen with a goo filled bag with the correct goo
design.

The time taken for the change in
velocity, determines the peak acceleration involved. So though the delta V
is lower in the 'absorbent' material, the acceleration perceived by the
ship
inside the goo is higher.
I can't see this. Surely, the time taken for maximum bag deformation can be
just the same with the goo filled bags, depending on the "stiffness" of the
goo.

The conventional airbag "un-deforms" as it returns the deformation energy
back into kinetic energy and launches the craft assembly onto its second
bounce. In contrast, the goo bag would not do this, it would stay deformed
because the energy would have been absorbed as heat. Therefore, the craft
assembly would not be subject to second and subsequent accelerations. My
whole argument is that the rebound and subsequent bounces are unnecessary
and detrimental to the spacecraft.

You also have to carry the 'goo' from Earth (the
gas can be stored at high pressure, or created from a chemical reaction,
and
hence involves carrying far less mass).
Yes, some extra mass would be needed for the goo in undeployed form.
However, I have seen some very light formaldehyde foams where a minute
amount of liquid transforms into a *lot* of foam. And that is just off the
shelf stuff from DIY stores. Cutting edge technology could produce foam goo
with very low density and containing its own propellant. Remember, the foam
goo would be in a 0.01 bar environment so a small amount of propellant gas
would expand the foam by a large amount. The extra mass would be offset by
the reduced requirements of the airbags themselves, they would not need to
be so sturdy. I doubt if the bags would need to be interconnected so less
pipework would be required.


Building systems to survive high-G,
is a relatively well understood technology. Even in the second world war,
electro/mechanical fuses were routinely being built (using valves!), to
handle accelerations of hundreds of G.
Agreed, but the apparent maturity of a technology does not preclude the
arrival of new and innovative ideas.

Sally

"Roger Hamlett" wrote in message
...
You are missing one thing.
The spacecraft itself, is not the airbag, but is inside the airbag. Hence,
I do understand that there are multiple airbags attached to the outside of
the spacecraft and that they have connections between them. This is why I
referred to the "spacecraft assembly"...meaning the spacecraft plus airbags.

though the delta V, will behave as you describe, the time involved for the
ship is stretched significantly. If you watch a bouncing ball in slow
motion, the bottom starts to move up off the surface, before the upper
surface responds.
Yes, understood.

The ship, actually decelerates, from the instant the
surface of the bag touches the ground, while it travels allmost the entire
radius of the airbag towards the ground.
The same thing could happen with a goo filled bag with the correct goo
design.

The time taken for the change in
velocity, determines the peak acceleration involved. So though the delta V
is lower in the 'absorbent' material, the acceleration perceived by the
ship
inside the goo is higher.
I can't see this. Surely, the time taken for maximum bag deformation can be
just the same with the goo filled bags, depending on the "stiffness" of the
goo.

The conventional airbag "un-deforms" as it returns the deformation energy
back into kinetic energy and launches the craft assembly onto its second
bounce. In contrast, the goo bag would not do this, it would stay deformed
because the energy would have been absorbed as heat. Therefore, the craft
assembly would not be subject to second and subsequent accelerations. My
whole argument is that the rebound and subsequent bounces are unnecessary
and detrimental to the spacecraft.

You also have to carry the 'goo' from Earth (the
gas can be stored at high pressure, or created from a chemical reaction,
and
hence involves carrying far less mass).
Yes, some extra mass would be needed for the goo in undeployed form.
However, I have seen some very light formaldehyde foams where a minute
amount of liquid transforms into a *lot* of foam. And that is just off the
shelf stuff from DIY stores. Cutting edge technology could produce foam goo
with very low density and containing its own propellant. Remember, the foam
goo would be in a 0.01 bar environment so a small amount of propellant gas
would expand the foam by a large amount. The extra mass would be offset by
the reduced requirements of the airbags themselves, they would not need to
be so sturdy. I doubt if the bags would need to be interconnected so less
pipework would be required.


Building systems to survive high-G,
is a relatively well understood technology. Even in the second world war,
electro/mechanical fuses were routinely being built (using valves!), to
handle accelerations of hundreds of G.
Agreed, but the apparent maturity of a technology does not preclude the
arrival of new and innovative ideas.

Sally

Sally posted:

Numbers here are approximate, but you
get the general idea...the craft is subjected to a number of deltaV's that
exceed the initial velocity.

No, the first impact will have the greatest velocity. The airbags are
designed to cushion the impact force and to dissipate the energy of impact.
These bags are not tremendously elastic, so the bounces will be less and less
velocity change as the lander bounces or rolls along the surface.

For
another bonus...the airbags would not need to be pressurised to hold the
goo. In fact bags may not even be needed if a suitable self-skinning goo
could be engineered.


Any "goo" which could do this would be heavy. The airbags are not highly
pressurized (I believe the pressure is around 1 psi). They are light and
disipate the energy fairly effectively as was seen with the Pathfinder lander.
With this heavier probe, I doubt it will bounce as high or as often as the
Pathfinder did. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************