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\section{Reviewer A}

In the earlier stages of the project, we looked into formulating the path
planning as an energy minimization problem.  But we found that measuring
power consumption was extremely troublesome, and never got much empirical
data to use for testing.  

There has been some work on amplifiers that regenerate energy.
We looked into it far enough to conclude that they were expensive and long
lead items, and did not pursue it further.

In addition to being more energy efficient, revolute joints are generally
easier to seal than sliding joints.  The designers picked sliders 
primarily for simplicity.

\section{Reviewer B}

We took to heart the reviewer's observation that our prose
was, in places, long-winded and pompous.  We softened a
number of statements and tried to simplify where possible.  However, 
we were not satisfied with a
number of the simplifications suggested by the reviewer, because they were
over-simplifications.  For example, in the section where we talk about
behavior-based robots wasting energy, we do not think it is enough to say
``such rovers may be unable to recognize blind alleys and avoid getting
stuck or damaged.''  Because that statement only talks about particular
symptoms, and does not address the cause of the problem or the 
general symptoms of the problem.

Deleted sentence interpreted as impugning Rod Brooks.

The term ``natural terrain'' does not have a single meaning.  We add the
discussion of irregularity at various scales not to insult the reader, but
to focus on the partical aspect of the terrain that will be most important
in the paper.

Deleted the ``The Ambler integrated walking system \ldots'' and ``Our
strategy is \ldots'' sentences.

Replaced ``impacts,'' ``high-quality,'' ``position history,'' ``will
remain stable,'' ``terrain patch,'' ``energy-losing leg/terrain
interactions (collisions),'' ``time-efficient," ``cost-effective'' with
the suggested simpler terms.  

Recognized that ``data'' is a plural.

Added definition of pose after first usage.  (The definition of CSP was
already properly placed.)

Repetition.  We intentionally used the three challenges over and over
again because we wanted to use them as the organizing theme of the paper.
In each section (perception, planning, \ldots) we use the same
names for the challenges, but immediately address how the challenge
relates to the particular subsystem.  For us, the repetition is a virtue,
not a bug.

We did not conduct experiments to quantify the energy consumbed by
slipping, bumping, or soil work in general.  We formed our opinion that it
was significant after reading Bekker's Introduction to Terrain-Vehicle
Systems, in consultation with John Bares and Red Whittaker here at CMU.

Added reference to Figure 1 in description of orthogonal leg.

We agree that the treatment of systematic error in the dead reckoning
system is not very satisfying.  However, we reached a point in the project
where the costs of doing studies of beam deflection as a function of load (to
determine how much the body ``sagged'' so as to get the kinematics right)
far outweighed the benefits, so we gave up.  No change to the text.




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