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\begin{document}

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\twocolumn[
\Large 
\centerline {\bf Project Description}
\normalsize
\vspace{0.5cm}
]


\section{Results from Prior NSF Support}
Over the past few years, the PI's group at the University of Arizona
has built two spectroscopic heterodyne array receivers;
{\it PoleSTAR}, a 4 pixel 810 GHz
receiver now in operation on the 1.7~m AST/RO telescope at the South
Pole and {\it DesertSTAR}, a 7 pixel 345~GHz array receiver for the
10-meter Heinrich Hertz Telescope (HHT) on Mt. Graham,
Arizona.  Both instruments are the very first of their kind.  PoleSTAR
has been fully integrated with the AST/RO telescope and offers excellent 
($T_{\rm rec}<700$K) receiver performance on all
4 pixels (Figure~\ref{polestar}).  
DesertSTAR went into routine operation on the HHT with an
initial complement of 3 pixels in October 2003 and has recently been expanded
to the final hexagonal array of 7 pixels.   Both
instruments were funded by NSF programs; work on PoleSTAR 
was funded by the NSF Office of Polar Programs (A. Stark--PI: OPP-0126090),
and DesertSTAR 
development has been a joint effort between the University of Arizona,
the University of Massachusetts, and the University of Virginia with
partial funding through the NSF ATI program (AST-9622569).  
More recently, a multi-institutional team led by the PI was awarded an
NSF MRI grant (AST-0421499) to construct {\it SuperCam}, a 64 pixel,
heterodyne array for the Heinrich Hertz Telescope.  

The experience and heritage gained through these efforts will be
invaluable in making HEAT a reality. 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.31,angle=0]{../figures/ngc6334-final.eps}
\caption{\label{polestar} {\small Simultaneous 4-channel spectra from
    PoleSTAR, the PI's 810~GHz array
    receiver, now in operation at the AST/RO telescope at the South
    Pole.  Every imaged point in a heterodyne map also
    represents a high-resolution ($\lambda/\Delta \lambda \approx
    10^6$) spectrum.}} 
\end{figure}

\vspace{-0.25cm}

\section{Research Activities}

The proposed High Elevation Antarctic Terahertz Telescope (HEAT) will
forge entirely new capabilities for ground based infrared and submillimeter
astronomy, by providing a window on the Universe which otherwise would be
unavailable except via airborne or space-based platforms. The
pioneering surveys to be performed by HEAT will be made
available to the entire astronomical community.  HEAT represents a
true international pioneering effort in keeping with the spirit of the
International Polar Year 2007-2008.  Here, we outline
HEAT's ``key project'', a THz survey of the Galactic Plane observable from
Dome~A, Antarctica.  

\subsection{Introduction}

From the Milky Way to the highest-redshift protogalaxies at the onset
of galaxy formation, the internal evolution of galaxies is defined by
processes closely related to their interstellar contents: 
\begin{enumerate}
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\item the transformation of neutral, molecular 
gas clouds into stars \& clusters (star formation). 

\item the interaction of the interstellar medium
(ISM) with the young stars that are born from it, a regulator of
further star formation. 

\item the return of enriched stellar material to the
  ISM by stellar death, eventually to form future generations of stars.

\end{enumerate}

\noindent The evolution of galaxies is
therefore determined to a large extent by the life cycles of
interstellar clouds: their creation, star-forming properties, and
subsequent destruction by young (hot) stars.  


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.38,angle=0]{../figures/LifeCycle-ISM.eps}
\caption{\label{cycles} {\small Life Cycles of the ISM}} 
\end{figure}

The life cycle of interstellar clouds is summarized pictorially in
Figure~\ref{cycles}. These clouds are largely comprised of
atomic \& molecular hydrogen and atomic helium. These
species are notoriously difficult to detect under normal interstellar
conditions.  Atomic hydrogen is detectable via the
21~cm spin-flip transition and provides the observational basis for
current models of a multiphase Galactic ISM.  Its emission
is insensitive to gas density and does not always discriminate between 
cold (T$\sim$70K) atomic clouds and the warm (T$\sim$8000K) neutral medium
that is thought to pervade the Galaxy. 
Furthermore, neither atomic helium nor molecular hydrogen
(H$_2$) have accessible emission line spectra in the prevailing
physical conditions in cold interstellar clouds.   Thus, it is important
to probe the nature of the ISM via rarer trace elements. 
Carbon, for example, is found in ionized form (C$^+$) in neutral clouds,
eventually becoming atomic (C), then molecular as carbon monoxide (CO)
in dark molecular clouds. 

Although we are now beginning to understand star formation, the
formation, evolution and destruction of molecular clouds remains
shrouded in uncertainty. 
The need to understand the evolution of interstellar clouds in the context 
of star formation has become a central theme of contemporary
astrophysics.  The National Research Council's
most recent {\it Decadal Survey} has identified the study of star
formation as one of the key recommendations for new initiatives in
this decade. Similarly, understanding the processes that give rise to
star and planet formation represent the central theme of NASA's
ongoing Origins program. 

\noindent A new, comprehensive survey of the
Galaxy must address the following questions to make significant progress
toward a complete and comprehensive view of Galactic star formation:
\begin{itemize}
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\item How do molecular clouds form, evolve, and become disrupted?  How
  do typical atoms and grains cycle through the ISM?

\item How and under what conditions do molecular clouds form stars?

\item   How do the energetic byproducts of stellar birth, UV radiation
  fields and outflows regulate further star formation
  in clouds?

\item How does the Galactic environment impact the formation of clouds
  and stars?   What are the specific roles of spiral arms, central
  bars, infall and other influences from outside the Galaxy?

\end{itemize}

\subsection{HEAT Science Goals}
\label{goals}

Via resolved C$^+$, C, CO, and N$^+$ line emission, HEAT uniquely probes
the pivotal formative and disruptive stages in the {\bf life cycles of
interstellar
clouds} and sheds crucial light on the {\bf formation of stars} by
providing new insight into the relationship between
interstellar clouds and the stars that form in them; a central
component of {\bf galactic evolution}.  A detailed study
of the ISM of the Milky Way is used to construct a template
to {\bf interpret global star formation in other spiral galaxies}.

Joined with CO, HI and IR surveys, HEAT will:
\begin{enumerate}
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\item Map as a function of Galactic
position the size and mass distribution and internal velocity
dispersion of interstellar clouds in the Galaxy.
\item Construct the first barometric map in the Galactic Plane, 
the first map of the
gas heating rate, and a detailed map of the star formation rate.
\item Probe the relation between the mass surface density
(on kpc scales) and the star formation rate, so that we may be able to
understand the empirical Schmidt Law used to estimate the star
formation rate in external galaxies. 
\item Reveal clouds clustering and forming in spiral arms
and supershells, and follow the growth of clouds to eventually shield
molecules and become gravitationally bound. 
\item  Observe the formation
and destruction of clouds throughout the Galaxy, and directly observe
the feedback caused by supernovae and the ultraviolet
radiation from massive stars.
\item Ultimately construct a Milky Way template connecting the line
  emission from C$^+$, 
  N$^+$, C, CO, and dust continuum to star formation
  properties and state of the ISM. This template will be applied to nearby
  star-forming galaxies. 
\end{enumerate}

The {\bf minimum science mission} of HEAT is to make significant
contributions to achieving the three major science goals described 
below. Using the proposed instrument and observing methodology,
this mission is expected to be achievable in {\it two years} of survey
operation from Dome~A.

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.58,angle=0]{../figures/m33.eps}
\caption{\label{m33} {\small The location of GMCs in the nearby
    spiral galaxy M33 are overlaid upon an integrated intensity map of
    the HI 21~cm line \citep{enga03}.  These observations show that
    GMCs are formed from large structure of atomic gas, foreshadowing
    the detailed study of GMC formation that HEAT will provide in the
    Milky Way.}} 
\end{figure}

\subsubsection{Goal 1:  The Life Cycle of Interstellar Clouds}

{\bf The formation of interstellar clouds is a prerequisite for star
formation, yet the process has not yet been observed! HEAT is designed
with the unique combination of sensitivity and resolution needed to
observe atomic clouds in the process of becoming giant molecular
clouds (GMCs).}

Theories of cloud formation are guided and constrained by observations
of the atomic and molecular gas components. Based primarily on HI and
CO observations, several mechanisms have been proposed to consolidate gas
into GMC complexes (Figure~\ref{m33}).  HEAT can distinguish these
processes by:  
\vspace{-0.2cm}
\begin{enumerate}
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\item Accounting for the entire H$_2$ mass (including H$_2$ clouds with
  little CO) when computing global measures of the interstellar medium. 
\item  Making a more complete \& characterized catalog of
  interstellar clouds than CO or HI surveys alone. 
\item Constructing spatial and kinematic comparisons of
sufficient resolution, spatial coverage and dynamic range to probe a
wide range of interstellar phases and environments. 
\end{enumerate}

\vspace{-0.1cm}
\noindent Since the C$^+$ (and to a lesser degree, C$^0$) line emissivity 
barometrically selects
clouds of atomic gas and H$_2$ clouds with little CO, regions of GMC
formation may therefore be tracked by a large density of clouds per beam, 
or regions with individual
clouds with higher than average columns or pressures. With HEAT's
superlative spectral resolution, these regions can be identified with
superrings or spiral arms or convergent parts of a turbulent
medium.  With guidance from 2MASS extinction mapping, 
HEAT will follow cold HI clouds and H$_2$ clouds as they transit
the spiral potential, and will witness the process of cloud formation
directly from the atomic substrate or small H$_2$ clouds. 
These clouds will be seen in C$^+$ and C line
emission by HEAT.  Similarly, 
N$^+$ observations of ionized gas survey the location and rate of star
formation in the Galaxy. The rate of star formation is determined by
using the N$^+$ luminosity to determine the ionizing luminosity of OB
stars, a standard metric for the star formation rate.  

{\it HEAT's high spectral resolution enables crucial
kinematic studies of the Galaxy to be made}. HEAT will determine
the kinematics and thermal pressures of most supershells, fossil
superrings, and new molecular clouds condensing via gravitational
instability of old superrings and supershells. HEAT can detect 
the H$_2$ clouds which
determine the role of OB association-driven supershells and superrings
in the production of molecular clouds and the cycling of gas between
the various phases of the ISM. Since N$^+$ measures the flux of
ionizing photons, and C$^+$ measures 
their impact upon neighboring cloud surfaces, HEAT will measure the
resolved photoevaporating atomic or ionized gas driven from clouds
with UV-illuminated surfaces, thereby determining the rate of
mass loss from all cataloged clouds, and their destruction
timescales. HEAT's survey will correlate the star formation rate in a
given OB association with the rate of destruction of any nearby
(within 30 pc) natal GMC.  Such
measurements are crucial for models of star formation feedback and
global galactic evolution. 


\subsubsection{Goal 2: The Galactic Star Formation Rate}

Star formation within galaxies is commonly described by two empirical
relationships: the variation of the star formation rate per unit area
with the  (atomic + molecular) gas surface density \citep{schm59,kenn98} and a
surface density threshold below which star formation is
suppressed \citep{mart01}.  The Schmidt Law has been evaluated from the radial
profiles of H and HI, CO emissions for tens of galaxies. The mean
value of the Schmidt index, $n$, is $1.4 \pm 0.15$ \citep{kenn98}, 
valid for kpc
scales. This empirical relationship is used in most models of galaxy
evolution with surprising success given its simplicity. Oddly, there
has been little effort to evaluate the Schmidt Law in the Milky Way
owing to the difficulty in deriving the star formation rate as a
function of radius within the plane. 

The HEAT survey of CO, C, C$^+$ and N$^+$
emission provides the optimum set of data to calculate the Schmidt Law
in the Galaxy. The N$^+$ line is an excellent tracer of the star
formation rate as it measures ionizing luminosity with unmatched
sensitivity, angular and spectral resolution, and is unaffected by
extinction. The C$^0$ and C$^+$ lines, in conjunction with HI~21cm and CO line
emission, provide the first coherent 
map of the neutral interstellar gas surface density and its variation
with radius. HEAT's high spectral resolution allows one to assign a
radial location of any emission feature assuming a rotation curve. The
Schmidt Law is constructed from the radial profiles of the star
formation rate derived from N$^+$ emission and the gas surface
density.  The column density threshold
is inferred from the absence of star formation activity in the outer
radii of galaxies where there is still a significant reservoir of
gas \citep{kenn98}.  The velocity-resolved star
formation rate indicators 
provided by HEAT will be invaluable in interpreting more traditional
indicators, like the far-infrared continuum.
With its resolution and ability to gauge
thermal ISM pressure, HEAT evaluates this critical, regulatory process
in the Milky Way. 

\subsubsection{Goal 3: Constructing a Milky Way Template}

C$^+$ and N$^+$ will be the premier
diagnostic tools for submillimeter studies of external galaxies 
with large redshifts (e.g. with ALMA). In
such spatially unresolved galaxies, however, only global properties
can be measured.  
Detailed interstellar studies of the widely varying
conditions in our own Milky Way Galaxy
serve as a crucial diagnostic template or ``Rosetta
Stone'' that can be used to translate the global properties of more distant
galaxies into reliable estimators of star formation rate and state of
the ISM.  The HEAT mission covers a
broad range of density and UV intensity, establishing the relationship
between physical properties, C$^+$, C, CO, N$^+$, HI, FIR
emission, and star formation.  

\subsection{Properties of the Proposed Survey}

HEAT's science drivers represent a definitive
survey that would not only provide the clearest view of interstellar
clouds and their evolution in the Galaxy, but would also serve as the reference
map for contemporary focused studies with Herschel, SOFIA, APEX, and the
ALMA interferometer.  The following properties define the science
needs for HEAT.

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.38,angle=0]{../figures/footprint.eps}
\caption{\label{beams} {\small The power of HEAT: Each of the 3
    heterodyne beams of HEAT are overlaid upon
    a 2MASS infrared image of NGC~6334.  The beams will measure
    high-resolution spectra in the 0.81, 1.46, and 1.90~THz bands
    respectively, a
    small portion (25\%) of each is shown as synthetic spectra of
    NGC~6334.}}
\end{figure}

\subsubsection{High Resolution Spectroscopic Imaging}

Techniques commonly used to diagnose the molecular ISM 
include submillimeter continuum mapping of dust
emission \citep{hild83} and dust extinction mapping at optical and
near-infrared wavelengths \citep{lada94}.  Large format detector
arrays in the infrared are now 
commonplace, and with the advent of bolometer arrays like SCUBA at the
JCMT and SHARC at the CSO, both techniques have performed degree-scale
maps of molecular material.  However, these techniques have limited
applicability to the study of the large-scale evolution of molecular
clouds due to the complete lack of kinematic information.   

The confluence of many clouds along most Galactic lines of sight can only 
be disentangled with spectral line techniques.  Fitting to a model of
Galactic rotation is often the
only way to determine each cloud's distance and location within the
Galaxy.  With
resolution finer than 1~\kms, a cloud's kinematic location can
be even distinguished from other phenomena that alter the lineshape, such as 
turbulence, rotation, and local effects such as protostellar
outflows.  These kinematic components play a vital role in the
sculpting of interstellar clouds, and a survey that has the goal of
understanding their evolution {\bf must} be able to measure them.  
{\bf HEAT will easily resolve the
intrinsic profiles of Galactic interstellar lines, 
with a per-channel
resolution of 0.4~\kms\ over 370~\kms\ of spectrometer
bandwidth, in excess of the Galactic rotational velocity. }


\subsubsection{A Terahertz Galactic Plane Survey}

Molecular line surveys have been performed over the entire sky in the
light of the 2.6~mm 
J=1-0 line of \co, and have been used to synthesize our
best understanding of the molecular content of the Galaxy.  Still, our
understanding of the evolution of Galactic molecular clouds is
woefully incomplete.  The CO~J=7$\rightarrow$6 line measured by
HEAT is a better probe of the energetic gas that plays a role in
stellar/interstellar feedback mechanisms. It probes gas that 1) participates
in molecular outflows, 2) senses radiation fields at the
photodissociated surfaces of clouds, and 3) is warmed by 
star-formation in cloud cores.  It will help 
interpret even basic properties of clouds derived from 
existing mm-wave observations by constraining excitation conditions. 

As already described in Section~\ref{goals}, the dominant spectral
lines of the Galaxy are the fine structure far-infrared and
submillimeter lines of C, CO, C$^+$ and N$^+$.  They probe and regulate 
all aspects of the formation and destruction of star forming clouds.
They will provide the first barometric maps of the Galaxy, and illuminate
the properties of clouds and their life cycles in relation to their
location in the Galaxy.   They will highlight the delicate interplay
between (massive) stars and the clouds which form them, a critical
component of galactic evolution. 

\subsubsection{Angular Resolution and Full Sampled Maps}

Good angular resolution is a critical aspect of improvement for a new
Galactic survey.  Previous surveys of [N~II] and [C~II] were limited
to very small regions (KAO, ISO) or had low angular resolution (COBE,
BICE) \citep{benn94,naka98}.  HEAT will fully sample both species over
large regions of sky 
to their diffraction limited resolution of 1.7$'$ and 1.3$'$,
respectively.  Arcminute resolution with proper sampling 
is crucial to disentangling
different clouds and cloud components over large distances in the
Galaxy.  For example, the Jeans length for star formation in a GMC is
approximately 0.5~pc.   This length scale is resolved by HEAT to a
distance of 500~pc at CO~J=7$\rightarrow$6 \& [C~I], and 1200~pc at
[C~II].  Warm and cold HI clouds and GMCs can be resolved well past
10~kpc. 


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.32,angle=-90]{../figures/resolution.eps}
\caption{\label{resolution} {\small {\bf The need for high angular
    resolution: } HEAT has the unique blend of wide field-of-view
    and good angular resolution to easily resolve GMCs throughout the
    Galaxy, even to the LMC and SMC.  HEAT will 
    study all star forming regions in detail within a distance of
    1~kpc, and all interstellar components to a distance of $>$10~kpc.}} 
\end{figure}


\subsubsection{High Sensitivity}
\label{sensitivity}

HEAT's high sensitivity is owed mostly to
the superlative atmospheric conditions above Dome~A, Antarctica.  The
extreme cold and exceptional dryness allow ground-based observations
into the otherwise forbidden THz windows.  A plot of the expected
atmospheric transmission for excellent winter observing
conditions at Dome~A versus the comparable opacity at the South Pole 
is plotted in Figure~\ref{atmo}.  {\bf The high elevation of Dome~A
definitively opens the Terahertz windows to ground-based observatories and 
cannot be matched anywhere else on Earth.}  The implications for the
sensitivity to each spectral line is discussed below.

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.32,angle=-90]{../figures/transplot.eps}
\caption{\label{atmo} {\small Terahertz atmospheric transmission for good 
    ($\sim$25th percentile)
    winter conditions for South Pole (bottom) and Dome~A (top),
    derived from PWV measurements at Pole and estimates from 
    Lawrence (2004) for Dome~A.  The pwv content 
    for each model atmosphere is 220 and 70 microns respectively,
    Arrows indicate the
    wavelengths of the [N~II], [C~II], and CO/[C~I] lines.}}
\end{figure}

\medskip

\noindent {\it CO $J=7\rightarrow6$}
\smallskip

We aim to detect all CO to A$_V$=1,
where most hydrogen has formed H$_2$ and CO is just
forming.  This extinction limit corresponds to
N($^{12}$CO)$\sim 2 \times 10^{15}$~cm$^{-2}$, or 
an integrated intensity 
(T$_k \sim$ 70K) of 1.5~K~\kms\ in the
J=7$\rightarrow$6 transition at $n_H=10^5$~cm$^{-3}$. 
This sensitivity limit is achievable (3$\sigma$) within 4 seconds of
integration time at 806~GHz in {\it median} winter atmospheric
conditions (T$_{sys}\sim$1500K) on Dome~A.  Limits on
J=7$\rightarrow$6 in that time would constrain the gas density, based
upon the line brightness of millimeter wave transitions. 

\medskip

\noindent {\it Atomic carbon $J=2\rightarrow1$}

The same extinction limit (A$_V$=1 mag) set for CO will also be applied to
the J=2$\rightarrow$1 fine structure line of atomic carbon at 809~GHz.
The corresponding column density of atomic carbon is $N(C)=1\times
10^{16}$~cm$^{-2}$, yielding a line intensity of 0.7 K~\kms\ at $T_k =
50$K and $n_{\rm H} = 10^4$~cm$^{-3}$, achievable (3$\sigma$) in 15 seconds of
integration time with HEAT during winter on Dome~A.  

\medskip
\noindent {\it N$^+$ and C$^+$}
\smallskip

The fine structure lines of ionized carbon and nitrogen represent the
dominant coolants of the interstellar medium of the Galaxy and
starforming galaxies.  Indeed, the integrated intensity of the
158~\micron\ C$^+$ line alone represents 1\% of the bolometric
luminosity of the Galaxy!  As such, these lines are relatively easy
to detect in the ISM.  
Our most demanding requirements for detection of C$^+$ and N$^+$
lie in the search for the formation of giant molecular clouds
(via C$^+$) and the measurement of the diffuse warm ionized medium in the
Galaxy (via N$^+$).  A flux limit of 1~K~\kms\ will detect N$^+$ in
warm HI as far away as the Molecular Ring, achievable in median winter
weather in 30 seconds with velocity smoothing to
2~\kms, appropriate for hot ionized gas. 
Similarly, the accumulation of GMCs from
many cold neutral clouds of atomic hydrogen occurs at low relative
column densities of $\sim 5\times 10^{20}$~cm$^{-2}$.  Since essentially all
carbon in such clouds is ionized, $N(C^+) \sim
10^{17}$~cm$^{-2}$.  At the $T=70$K common in cold atomic clouds and
$n_{\rm H} = 10^3$~cm$^{-3}$, the expected C$^+$ line emission would
be 2.4~K~\kms, detectable in 30 seconds in excellent winter weather on
Dome~A.  The 3$\sigma$ limit achievable with deep
integrations (15 minutes) with HEAT would reach $n_{\rm
 H} = 10^2$~cm$^{-3}$.  This limit would readily determine whether
interstellar material causing significant
infrared extinction but without CO
is gravitationally bound and likely to be a forming
molecular cloud, or is simply a line of sight with numerous
overlapping diffuse HI clouds.  


\subsubsection{Mapping Coverage of the Galactic Plane}

\begin{figure*}[!hbt]
\centering
\includegraphics[scale=0.9,angle=0]{../figures/FigDame.eps}
\caption{\label{area} {\small Plotted atop the Dame et al. (1987)
    CO~J=1$\rightarrow$0 map of the Galactic plane, is the coverage of
    the surveyed region to be mapped by HEAT in the first two years. 
    A definitive chemical and kinematic survey of star forming clouds in C$^0$~J=2-1,
    \co\ J=7$\rightarrow$6, and [N~II] of 120
    square degrees ($\sim$30~square degrees in [C~II] emission) 
    can be performed in a single season.  
    No other site on Earth allows routine access to both
    far-infrared lines. }}
\end{figure*}

Figure~\ref{area} demonstrates the sky coverage of HEAT's
Galactic plane survey.  From previous CO surveys it
is known that the scale height of CO emission toward the inner Galaxy 
is less than one degree \citep{dame87,dame01}.  The BICE experiment
demonstrated that the C$^+$ distribution is more extended, but still
is confined to $|b| < 1$. 
Interstellar pressure, abundances, and physical
conditions vary strongly as a function of Galactocentric radius, so it is
necessary to probe the inner Galaxy, the outer Galaxy, and the
$l=\pm 100^o$ tangent arms to obtain a statistically meaningful survey
that encompasses the broad dynamic range of physical conditions in the
Galaxy.  We propose therefore to 
probe the entire Galactic plane as seen from Dome~A ($0
> l > -120^o$).  A {\it completely unbiased survey} will be
undertaken, covering up to 240 square degrees ($-1^o < b < 1^o$).  
The ``inner'' Galaxy survey will coincide
with GLIMPSE, a Spitzer Space Telescope (SST) Legacy Program \citep{benj03}. 
Above $l=90^o$, most of the CO emission is located at
higher Galactic latitude, so $l$ and $b$ strip mapping will locate
the best regions to map, generally following the CO J=1$\rightarrow$0
distribution\citep{dame87,dame01} and the best characterized star
forming regions in the Galaxy -- while maximizing
synergies with the ``Cores to Disks'' SST Legacy program
\citep{evans}, and other SST GTO programs.  

%As discussed in Section~\ref{instrument}, 
HEAT exceeds all of these needs and constitutes
an exceptional Galactic survey instrument.


\subsection{Survey Activities}

\subsubsection{Mapping Strategy}

The most efficient mode of data collection 
which produces the highest fidelity images is 
On-the-Fly (OTF) mapping.  In this mode, the telescope continuously 
scans back and forth across a field while the backends are 
read-out at a sufficient rate to eliminate aliasing and beam smearing.  

The broad coverage of the HEAT survey and the circumpolar
nature of the sky rotation over Antarctica lends itself naturally
to efficient, 24-hr/day mapping. HEAT can reach the requisite sensitivity of
1$\sigma$=0.15~K~\kms\ per beam at 810~GHz (1$\sigma$=0.5~K~\kms\ at
1.4~THz) over a fully sampled (at 1.4~THz) square degree in 20 hours,
assuming median winter conditions of $\tau_{810}\sim$1. 
120 square degrees from $0 > l > -60^o$ will be mapped 
in $\approx$160 days. Further 
mapping of the Outer Galaxy will follow in Seasons~2 and 3. 
When the atmospheric opacity at 1.9~THz drops below $\sim$1.5, 
focused surveys including C$^+$ will begin.  Of the best
35 days of winter weather, 3-4 weeks will be devoted to
a medium-sensitivity C$^+$ survey (1$\sigma \sim$1~K~\kms), with each square
degree of mapping requiring about 20 hours each, for a total of up to 20-30
square degrees of coverage per season.  
7-10 days will be devoted to deep C$^+$ surveys
of selected regions guided by 2MASS and GLIMPSE for the formation of
molecular clouds -- a total of 0.5~square degrees will be mapped to
1$\sigma \sim 0.2$~K~\kms\ per season.

HEAT's IF bandwidth, coupled with chopping OTF techniques, 
allows detection of the 370~$\mu$m dust continuum emission, and,
stability permitting, also in the 205 and 158 \micron\ HEB bands.  Thus, we
will also simultaneously record total power scans and construct dust
continuum maps.  

\begin{table*}[!hbt]
\centering
\small
\begin{tabular}{|l|c|c|l|}
\hline
{\bf Participant} & {\bf Team} & {\bf Affiliation} & {\bf Participation
  Activity} \\
\hline \hline
Christopher Walker & I, S & Univ. Arizona &  Project PI \\
\hline
Michael Ashley & I, S & UNSW & AASTINO Systems and site testing \\
\hline
Michael Burton & S & UNSW & Star formation, ISM physics \\
\hline
Ed Churchwell & S & Wisconsin & Synergy with GLIMPSE survey (Spitzer) \\
\hline 
Neal Erickson & I &  Univ. Mass. & (sub)mm and THz receivers, molecular clouds\\
\hline
J. R. Gao & I & SRON & THz HEB mixers \\
\hline
David Glaister & I & Ball Aerospace & Cryogenic Systems \\ 
\hline
Willy Gully & I & Ball Aerospace & Cryogenic Systems \\ 
\hline
Chris Groppi & I, S & NRAO & Receiver systems, submm star formation studies\\ 
\hline
Abby Hedden & I, S & Arizona & Receiver systems, star and cloud
formation \\
\hline
Frank Helmich & S & SRON & Physics and Chemistry of Cloud Cores \\
\hline
Karl Jacobs & I & U. K\"{o}ln & (SIS) receiver Systems, SIS mixers \\
\hline 
Jon Lawrence & I & UNSW & Antarctic Aeronomy and Astronomy \\
\hline
Bob Lowenstein & I & Univ. Chicago & Satellite communications \\
\hline
Jacob Kooi & I & Caltech & Receiver Systems and Telescope Integration\\
\hline
Craig Kulesa & I, S &  Univ. Arizona &  Deputy PI, software integration, ISM physics \& chemistry \\
\hline
Imran Mehdi & I & JPL & THz LO sources \\
\hline
Gopal Narayanan & I, S & Univ. Mass. & Star formation, molecular clouds\\
\hline
Robert Pernic & I &  Univ. Chicago & Telescope Implementation \& Polar Operations \\
\hline
Tom Phillips & I, S & Caltech & Synergy with Herschel/HIFI \\
\hline
Patrick P\"{u}tz & I & Arizona/K\"{o}ln & Receiver systems, SIS mixers \\
\hline
Gordon Stacey & I, S & Cornell & Far-infrared Instrumentation \& spectroscopy\\
\hline
Antony Stark & I, S & SAO/CfA & Telescope Optics \& Systems; Synergy w/ AST/RO \\ 
\hline
John Storey & I, S & UNSW & AASTINO Systems, Site testing, Polar Operations \\
\hline
J\"{u}rgen Stutzki & S &  Univ. K\"{o}ln & Physics \& Chemistry of the ISM \\
\hline
Wilfred Walsh & S & UNSW & Polar astrophysics, star formation \\
\hline
Sander Weinreb & I & JPL & IF amplifiers \& processors; correlator system \\
\hline
\end{tabular}
\caption{\label{roles} \small Activities of the Science ({\bf S}) and
  Instrumentation ({\bf I}) Teams}
\end{table*}

\subsubsection{Science Products and Dissemination}

A primary challenge of OTF mapping is data management.
We therefore plan to adopt a scheme akin to that 
developed at FCRAO, whereby
coadded and regridded data is written as FITS \&
CLASS files, and headers for 
each scan are written into a MySQL relational database, which 
facilitates efficient logging and retrieval of the data.
The most demanding storage
requirements for 240 square degree maps, regridded to 50$''$ spacing,
with 1024 spectral points per grid position, is 7~GB.  Even today,
this volume can be readily handled by embedded computers with
disk arrays and/or nonvolatile memory.  

Access to these data products to the greater scientific community
will be provided through a web browser interface that will
interface with MySQL and the FITS data cubes.  Preprocessed data cubes
will be transferred over Iridium and a possible TDRSS-1 link, whereas
the raw data will be collected from the telescope annually during
maintenance.  There will be biannual data products -- a
preliminary release midseason, and a final release in January.  The
final release will be fully calibrated and will include all science
products.  

\smallskip
\noindent \fbox{\parbox{3.0in}{All science tools, packaged reduction software,
    data products and 
    science products will be made available from the HEAT web
    page.}}

\smallskip

\noindent  {\bf Important science tools include the following: }

\smallskip

\noindent {\it Clumpfinder} and {\it Outflowfinder}:  All Galactic
  cloud cores and star forming 
  regions will be separated,
  identified and analyzed from the master dataset as a function of
  position in the Galaxy.  An unbiased survey of 
  Galactic outflows, superrings, supershells, and their energy inputs
  to the ISM will be tabulated.  

\smallskip

\noindent {\it Analysis Package and Cloud Models}:  Tools used to
  extract physical properties of clouds will be released.  These tools
  will include statistical equilibrium calculations, 
  NLTE radiative transfer codes, a basic chemical network
  capable of following H and C chemistries, and foundational 
  models of molecular clouds and PDRs.

\smallskip 

\noindent {\it 2MASS Extinction Maps and the Formation of Molecular
  Clouds}:  The release of the 
  2~$\mu$m All Sky Survey will be used to make extinction maps over
  the surveyed regions to be
  compared with the measured CO emission and used to guide our
  selection of regions to map in C$^+$ emission.  The extinction maps 
  will be calibrated to an N(H$_2$) scale using high
  resolution infrared absorption line 
  spectroscopy of H$_2$ and \co\ at the 6.5-meter MMT. 
 
\subsubsection{Synergies with Spitzer, SOFIA and Herschel}

{\bf HEAT is timely}.  The Spitzer Space Telescope Legacy program GLIMPSE, 
headed by E. Churchwell, will provide a thermal infrared survey of the
Galactic plane that provides a complete census of star formation, the
stellar structure of the molecular ring, will map the warm
interstellar dust, constrain extinction laws as a function of
galactocentric radius and will detect all young embedded O and B
stars.   HEAT will provide the best corresponding
interstellar cloud survey that will account for the 
dense cloud material that forms stars,  cloud interaction with
formed stars, and kinematic disruption by mass ejection, outflow, and supernova
remnants.  Collaborator E.~Churchwell will provide guidance in
accessing and interpreting this data for comparison with HEAT data
products.  

HEAT naturally complements the capabilities of heterodyne receivers on
SOFIA and Herschel.  The higher angular resolution
afforded by larger telescopes necessarily reduces their field of
view and mapping speed.  The HEAT survey would require 
many months of dedicated observing time on either Herschel or SOFIA,
inconsistent with their
use as general purpose observatories.  HEAT is a dedicated mapping
instrument with a focused mission and a lifetime that exceeds the
grasp of long duration balloons.  HEAT will provide
ideal reference maps of THz line emission for more detailed
followup with SOFIA and Herschel.  Indeed, the HEAT data distribution and
databasing system will be aligned as much as possible with that of 
Herschel/HIFI (HEAT Co-PI T.~Phillips is also a Co-PI on HIFI). 

\begin{figure*}[!hbt]
\centering
\includegraphics[scale=1.3,angle=0]{../figures/concept.eps}
\caption{\label{concept} {\small HEAT concept: The telescope has an effective
collecting area of 0.5m. Elevation tracking is accomplished by
rotating the $45^\circ$ flat reflector. The entire telescope structure
rotates for azimuth tracking and is warmed well above ambient by waste heat 
from the AASTINO module below. The HEB and SIS mixers used in
the instrument package are cooled to $\sim 4$~K using closed-cycled
cryo-cooler technology developed for space-based applications.}} 
\end{figure*}

\subsubsection{Roles of the Collaboration Participants}

Personnel who will initially develop and use HEAT
comprise the Science~(S) and Instrument~(I) Teams tabulated in
Table~\ref{roles}.  They are also represented in an organization
chart, Figure~\ref{orgchart} in Section~\ref{management}.  {\it 
At least 4 graduate students and 2 undergraduates will participate in
the instrument and science development. }



\section{Research Instrumentation and Needs}
\label{instrument}

\subsection{Overview}

HEAT will be a fully automated, state-of-the-art THz observatory
designed to operate autonomously from Dome A in Antarctica. The
combination of high altitude (4,200~m), low precipitation, and extreme
cold make the far-IR atmospheric transmission exceptionally good
from this site. In Figure~\ref{atmo} we present a plot of the
expected atmospheric transmission above Dome A as a function of
wavelength (Lawrence 2004), indicating that winter weather at Dome~A
approaches (to order of magnitude) the quality of that achieved
by SOFIA.  The wavelengths of several important
astrophysical lines are indicated with arrows. HEAT is designed to
take advantage of these unique atmospheric conditions and observe
simultaneously in [C~II](158 $\mu$m), [N~II](205 $\mu$m), and CO 
J=7$\rightarrow$6/[C~I] (370 $\mu$m). 

\smallskip
A conceptual drawing of HEAT is shown in Figure~\ref{concept}. For
robustness and efficiency, the telescope and instrument are integrated
into a common optical support structure (OSS). 
HEAT will be mounted on top of a University of New South Wales AASTINO
(Automated Astrophysical Site-Testing InterNational Observatory). The
AASTINO provides power and communications for the HEAT telescope and
instrument. The total power budget for HEAT (including cryogenics, telescope 
drive system, and instrument control system is $\sim 550$~W, which can
be readily provided by efficient, high reliability generators 
within the AASTINO. Data
transfer and command and control of HEAT will be done via satellite and is
described in more detail in Section~\ref{control}. 
The University of New South Wales will provide an  
AASTINO specifically for HEAT and participate in all aspects of design,
integration, deployment, and operation (see Support Letter from J. Storey).
The HEAT/AASTINO facility is functionally equivalent to a
space-based observatory. Indeed, many of the key components used in
the instrument were originally developed for space applications. A 3D
rendering of HEAT mounted atop an AASTINO is shown in
Figure~\ref{AASTINOHEAT}.  

\subsection{Telescope}

The telescope is designed to have maximum efficiency and the minimum
number of optical components. Its design is similar to that of Kraus
(1966) and utilizes an off-axis, Gregorian configuration. Incoming
light is reflected horizontally off a 45$^\circ$, $0.5 
\times 0.7$~m flat reflector to an f/2.2 off-axis parabolic mirror. The
converging beam is intercepted by hyperbolic tertiary mirror that
directs it from a flat quaternary into the receiver. The tertiary 
mirror can chop the incoming beam between source and reference
positions ($\Delta {\rm az} \sim 10^\prime$) at a rate of 0 to 4~Hz. The
mirrors are fabricated from aluminum on a numerical milling
machine and have a surface roughness $\le 3\,\mu$m rms.  Elevation
tracking is achieved by rotating the first flat reflector. Azimuth
tracking is achieved by rotating the OSS on a bearing attached to the
roof of the AASTINO. The absolute pointing accuracy will be
15$^{\prime\prime}$, 1/5 of the smallest diffraction-limited beam. The
slew speed will be 1$^\circ$/sec.  The University of Arizona has a
long history of building state-of-the-art telescopes. Vertex/RSI will
provide the additional expertise required to optimize the telescope
for operation in a Polar environment. The telescope cost estimate,
which includes detailed design, fabrication, and testing of the
telescope and drive system, is provided in the budget. R. Pernic will
provide technical oversight of the telescope design and implementation. 

To prevent ice accumulation, the telescope is
enclosed and warmed to $\sim$0$^\circ$C by waste heat forced up through the
azimuth bearing from the AASTINO. A small radome made of a low-loss
dielectric (e.g. Goretex or polyethylene) encircles the first flat
reflector. This optical configuration provides an unobstructed view of
the sky. A CCD and near-IR camera are mounted just
outside the radome on an extension of the elevation axis. The cameras
provide pointing and site testing data. 

\subsection{Receiver}

\subsubsection{Design Approach}

Heterodyne receivers are needed to achieve the sensitive, high
spectral resolution ($R=\lambda/\Delta\lambda > 10^6$) observations of
[N~II], [C~II], and CO/[C~I]
required for the proposed Galactic plane survey. The key components of a
submillimeter-wave heterodyne receiver are the mixer and local
oscillator (LO). The mixers and LOs that will be used in HEAT were
originally developed for use in the HIFI instrument for the {\it
Hershel Space Observatory}. There are 3 types of mixers in common
use; the Schottky diode mixer, the SIS mixer, and, more recently, the
Hot Electron Bolometer (HEB) mixer. The Schottky diode mixer is
less sensitive than either SIS or HEB mixers and requires orders of
magnitude more LO power. Their principal advantages are robustness and
ability to operate at room temperature. 
Below $\sim$1~THz SIS mixers provide the lowest
receiver noise temperatures ($T_{rec} \le 400$~K). Above 1~THz HEB
mixers have the best performance ($T_{rec} \le 900$~K). The $\sim1$~THz
upper limit to SIS mixer performance is currently set by the
availability of suitable superconducting materials. Therefore, HEAT
will use SIS mixers for the CO/[C~I] channel and HEB mixers for the
[N~II] and [C~II] channels. Two mixers (one for each polarization) will
be used at each frequency to increase sensitivity and provide
redundancy. At 810~GHz it is possible to sub-harmonically pump a
Schottky diode mixer with a low frequency LO source (available LO
power is insufficient at THz frequencies). The
expected $T_{rec}$ is $\sim$3000~K. We will include one such
mixer (provided by UMass) in the HEAT instrument package to permit
limited operation of the observatory in an uncooled state.    

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.52,angle=0]{../figures/AASTINO.eps}
\caption{\label{AASTINOHEAT} {\small Rendering of HEAT atop a UNSW AASTINO}}
\end{figure}

\subsubsection{Receiver Optics}

A close-up of the receiver optics is shown in Figure~\ref{optics}. The
incoming beam from the quartenary encounters two bandpass filters,
the first centered on the [N~II] (1.459~THz) line and the second on the
[C~II] (1.9~THz) line.  

Outside of their nominal passband, the filters are highly
reflective. Therefore, when the incoming beam encounters the first
filter, all but a narrow range of frequencies around the [C~II] line
are reflected to the [N~II] filter. The light reflected off the [N~II]
filter contains the CO J=7$\rightarrow$6 and [$^{12}$C~I] and
[$^{13}$C~I] J=2-1 lines. The three emerging beams are
collimated and directed into the instrument cryostat. Before entering
the cryostat, the corresponding LO signals are injected into the
collimated beams using Mylar (for the 810~GHz mixer) and silicon (for
the 1.45 and 1.9~THz mixers) beam splitters. The Mylar is used to
inject the 810~GHz LO because it is both low-loss and wideband,
permitting DSB operation at the IF frequency (1.5~GHz) required for
simultaneous observations of CO and [CI] lines. Silicon etalons can
serve as efficient LO diplexers, passing $>$95\% of the signal while
reflecting $>$50\% of the LO power (Mueller and Waldman 1994). These
properties make silicon etalons attractive beam splitters for THz
mixers where LO power is precious and the size and
complexity of Martin-Puplett diplexers can be prohibitive.
One polarization of the 810~GHz signal is directed via a wire grid
into the ambient temperature, Schottky receiver before the beam enters
the cryostat.  
Upon entering the cryostat, the beams pass through infrared blocking
filters. For the HEB mixers, the same type of bandpass filters used
for frequency diplexing will be used at the entrance window of the 4~K
radiation shield. Here the filters not only prevent infrared loading on the
4~K stage, they also help to prevent the HEB mixers from being
saturated by the incoming radiation field.  Wire grids direct the
horizontal and vertical polarization components of the incoming light
into the 1.45 and 1.9~THz mixer pairs.

\begin{figure}[!hbt]
\centering
\includegraphics[scale=1.99, angle=0]{../figures/optics.eps}
\caption{\label{optics} {\small Optical subsystem and LO injection for
    HEAT's HEB, SIS and Shottky mixers.}}
\end{figure}


\subsubsection{Mixer Performance}

The HEB mixers for HEAT will be provided by SRON/Delft (see support letter from
J. R. Gao) and follow the successful quasi-optically coupled, NbN
phonon-cooled design of Gao et. al. (2004). {\it These mixers
have the lowest noise 
temperatures and LO power requirements of any mixers measured to
date ($T_{rec}= 940$~K and $P_{LO} = 0.17\,\mu$W at 1.89~THz).} 
Allan variance measurements (Kooi
2004) of HEB stability (Figure~\ref{AllanResultJB}) show excellent
performance can be achieved if the incoming beam is chopped at $\ge
1$~Hz. The HEAT telescope will accommodate sky chopping at
frequencies up to 4~Hz.) Gas cell measurements of the 1.32~THz line of
water were recently made by the HEAT instrument team. The measurements
(see Figure~\ref{mixers} for a typical spectrum) confirm both the stability
results of Kooi (2004) and the low noise performance of HEB mixers. 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.44,angle=0]{../figures/HEBH2Ospectrum.eps}
\caption{\label{mixers} {\small Laboratory measurement of gas cell
    H$_2$O using SRON/Delft HEB mixers.}} 
\end{figure}

The SIS mixer will be provided by the University of Cologne (see
Support Letter from K. Jacobs). The
design and fabrication of the SIS mixer is described by Puetz {\it
et al.} (2004) and has been successfully used on the
AST/RO telescope at the South Pole for several years. $T_{rec}$ is expected to be $\sim$500K. 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.65,angle=0]{../figures/Allanresult.eps}
\caption{\label{AllanResultJB} {\small Allan variance stability tests for
    Delft HEBs are in accordance with the radiometer equation when
    a chopping mirror is used \citep{kooi05}, as proposed for HEAT.}}
\end{figure}


\subsubsection{Local Oscillators}

HEAT will employ 3 solid-state local oscillator chains built by the
Jet Propulsion Laboratory (see Support Letter from R. Cox). The
809~GHz chain will consist of three doublers. The 1.45 THz chain will
have four doublers, and the 1.9~THz chain will be comprised of  
one doubler and two triplers. {\it These chains leverage heavily
from the technology developed for {\it Herschel} and have had their
performance validated in lab measurements.} All three chains easily
meet our LO power requirements of $> 100$~$\mu$W at 809~GHz and $>
7$~$\mu$W at 1.46 and 1.9~THz, sufficient to pump two mixers at each 
frequency (the Schottky mixer at 810~GHz will have its own LO chain,
see discussion above). The JPL LO chains will be pumped by
CTI/Millitech DRO (dielectric resonant oscillator)/active multiplier
chains that can source $\sim 3$~dBm of power between 90-106~GHz. Each
of the phase-locked DROs is fixed tuned to a single frequency, that
when up-converted, corresponds to one of the three target
astrophysical lines. A CAD drawing illustrating the integration of
the LOs is provided in Figure~\ref{optics}. Since each of the three
receivers acts independently, any increase in phase-noise that might
occur by using an active multiplier chain has minimal, if any, impact
on the quality of the collected data. The frequency stability of the
LO chains will be better than $\pm 0.5\,$MHz at 809~GHz and $\pm
1.0\,$MHz at 1.46 and 1.9~THz.  


\subsubsection{IF Processing \& Spectrometers}

The IF output of the HEB mixers is centered at 2~GHz. In order to
simultaneously detect the CO J=7$\rightarrow$6 line in the lower
sideband and the [C~I] line in the upper sideband, the SIS mixer will
have an IF center frequency of 1.5~GHz.  
The IF output of each mixer is amplified by a low-noise MMIC amplifier
and downconverted to baseband for processing by three, 1024 lag
autocorrelators. The autocorrelators for the [N~II] and [C~II] channels
will each have 2~GHz of instantaneous bandwidth and $\sim 2$~MHz
resolution. The autocorrelator for the lower frequency CO/[C~I] channel
will run at half the clockspeed of the other two channels, yielding an
instantaneous bandwidth of 1~GHz and frequency resolution of $\sim
1$~MHz resolution. These correlators provide velocity coverage in
access of 316~km/s at a resolution $\le 0.4$~km/s, enabling all three
lines to be resolved and observed throughout the Milky Way without
needing to retune. Spaceborne Inc. of La Canada, CA has demonstrated a
2~GHz wide, 1024 lag correlator that meets our design specifications 
(see Figure~\ref{correlator}) and provided a quote for the complete
HEAT correlator system.  Co-I Weinreb (Caltech) will provide the MMIC modules
and oversee the construction of the IF processor and integration with the
Spaceborne spectrometer system.  

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.35,angle=0]{../figures/correlator.eps}
\caption{\label{correlator} {\small The Spaceborne digital
  autocorrelator provides an ideal ``off-the-shelf'' multichannel
  spectrometer for HEAT. a) 2~GHz Spaceborne correlator chip.  b)
  Laboratory measurement of spectral response.}} 
\end{figure}


\subsubsection{Cryogenics}

A reliable, efficient, low-vibration 4~K cryogenic system is essential
to the success of HEAT. Experience has shown that care must be taken
to insure the 
uninterrupted operation of cryogenic systems over extended
periods. This philosophy is crucial for the proposed remote,
automated facility at Dome~A. Indeed, the system requirements for
HEAT are more like those of a 
spacecraft than a ground-based observatory. It is for this reason that
we have a teamed with Ball Aerospace (see Ball support letter) to adapt
one of their successful space-based cryogenic systems to work for HEAT.  

\medskip

\noindent{\it HEAT Cryogenic Subsystem Trades and Approach}

The cryogenic subsystem for HEAT must maintain the detectors
at 4~K. A number of approaches, including off-the-shelf
commercial cryocoolers (or mechanical refrigerators), were
evaluated against the system requirements. The need for
unattended operation for at least 1 year eliminates the
possibility of using liquid expendable cryogens. The remote
and harsh Antarctic environment prevents the use of
off-the-shelf commercial cryocoolers primarily due to limited
power ($<$600~W) provided by the AASTINO. High
cost prevents the use of fully space qualified cryocoolers for
HEAT. The optimum cryogenic system that meets both
technical and cost requirements is a combination of
commercial and aerospace cryocooler hardware. 
The HEAT cryogenic system requirements are shown in
Table~\ref{cryoreq}. 

\begin{table}[!hbt]
\centering
\begin{tabular}{cc}
\hline \hline
{\bf Requirement} & {\bf Specification} \\
\hline
4K cooling capacity  &  4 mW \\ 
14 K cooling capacity  &  220 mW \\ 
70 K cooling capacity  &  3.6 W \\ 
4 K temperature stability  &  $\pm$0.01 K \\ 
Input power  &  $<$500 W \\ 
Lifetime  &  $>$2 years \\
Vibration  &  Low \\ 
Vacuum level  &  $< 10^{-5}$ Torr (at 1 yr) \\ 
Cost  &  Low to Moderate \\ 
\hline
\end{tabular}
\caption{\label{cryoreq} Cryogenic system requirements for HEAT}
\end{table}

Table~\ref{cryoopts} shows a compilation of cryocooler approaches and their
power consumption. Only the hybrid system can consume less than the
500~W requirement.  While a Pulse Tube G-M features low maintenance
and vibration, its power consumption is unsuitable for 
HEAT. The extra cost of the semi-custom cryosystem enables the
reduction in input power needed for operation from a remote site. 

\begin{table*}[!hbt]
\centering
\begin{tabular}{cccc}
\hline \hline
{\bf Capacity at 4K} & {\bf Manufacturer} & {\bf Input power (W)} &
{\bf Meets Requirement?} \\
\hline
0.1 W (G-M)  & Sumitomo SRDK-101D  & 1300  & No \\ 
0.5 W (G-M)  &  Sumitomo SRDK-205D  & 3500  & No \\ 
0.5 W (Pulse Tube G-M)  & Sumitomo SRP-052A  & 7500  & No \\ 
20 mW (Hybrid G-M/J-T)  & Ball Aerospace - HEAT  & 400 &  Yes \\ 
\hline
\end{tabular}
\caption{\label{cryoopts} Cryocooler approaches and applicability
to HEAT}
\end{table*}

\medskip

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.35,angle=0]{../figures/cryoblock.eps}
\caption{\label{cryoblock} {\small The cryocooler supporting the HEAT
    cryogenic system is a hybrid cooler consisting of a modified
    Gifford McMahon precooler and a Joule-Thomson cooler.}} 
\end{figure}

\noindent {\it Cryo System Implementation}

The proposed cooler has a high degree of technology maturity. {\it All
of the cryocooler components and their integration have been proven
in test.} Cooling capacities in excess of 25~mW were
measured for temperatures down to 5~K. Tests with $^3$He as the J-T
working fluid extended the temperatures down to 3.5~K, and
demonstrated 12~mW of cooling at 3.8~K, more than adequate for cooling
HEAT's complement of mixers.  
Leveraging off Ball Aerospace's system and instrument expertise, the
cryogenic system has been designed to meet the HEAT's unique
requirements (Figure~\ref{cryoblock}). 

\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.85,angle=0]{../figures/balldewar.eps}
\caption{\label{balldewar} {\small Cut-away views of low-vibration, long-life, 4~K closed-cycle cryostat designed by Ball.}} 
\end{figure}

The 4~K temperature control as well as the cryocooler on/off and a
safety defrost heater will be handled by a commercial temperature
controller from Lakeshore Cryotronics. A mW-level trim heater 
will maintain 4~K with
changing environmental conditions. The analog output will provide
remote operation and access to a safety defrost heater used in case the JT
orifice plugs.

Extremely low vibration operation is essential on a spacecraft. Ball
brings this expertise to HEAT. To comply with the tight vibration and
thermal requirements, Ball will 
provide a separate structural mount for the detector package, and use
the J-T to refrigerate the isolated system (see
Figure~\ref{balldewar}). The temperature of the cold plate will be
actively regulated to within 10~mK. To meet the tight power
constraints, Ball has designed a special dewar that uses the cold
Antarctic environment to minimize power consumption. This type of
optimization and design strategy is common for space missions where
power conservation and reliability are essential. To our knowledge
this is the first time this philosophy is being employed to such a
degree on a ground-based instrument. 


\begin{figure}[!hbt]
\centering
\includegraphics[scale=0.5,angle=0]{../figures/computer.eps}
\caption{\label{computer} {\small The HEAT instrument and telescope 
    control system is a network of several low-power embedded
    computers with redundant arrays of nonvolatile memory.}} 
\end{figure}

\subsubsection{Calibration}

HEAT will be able to calibrate observations through several means. 1)
A vane with an ambient temperature absorbing load will be located at
the dewar entrance window, allowing standard chopper wheel calibration
to be performed. 2) HEAT will routinely perform sky-dips to
compute the atmospheric optical depth in each of its three wavelength
bands. 3) HEAT will regularly observe a standard list of calibration
sources. 4) The AASTINO will also host a Fourier Transform Spectrometer
(funded through the Australian program) that will measure
atmospheric transmission throughout the FIR. These measurements will be
coordinated with HEAT spectral line observations to provide cross
calibration. 

\subsubsection{Control System and Communication}
\label{control}

The HEAT control system will consist of a distributed computer control
system where the telescope drive system, receiver frontend
({\it e.g.} mixers, LOs, and cryostat) computer, backend
(spectrometer) computer, and the AASTINO communicate via Ethernet
(Figure~\ref{computer}).  The prototype system is based on a
Technologic Systems TS-7200 ARM-based embedded computer that draws
less than 2 watts of power and runs Linux or NetBSD.  HEAT will be
designed to work 
autonomously for up to a week at a time, performing pre-programmed
observational programs and storing astronomical and housekeeping data
in non-volatile memory.  Preprocessed sample data will be uploaded to
control centers at the Universities of Arizona and New South Wales
via (1-3) dedicated Iridium satellite channels.  Raw data will be recovered
from HEAT each year during maintenance and processed into the released
data products.

\section{Project Management}
\label{management}

\subsection{Organization}
HEAT is an exciting, challenging project that requires the coordinated 
participation of scientists and engineers from several academic institutions
and leading-edge companies to succeed. We have developed an organizational
structure (shown in Figure~\ref{orgchart}) 
to meet this task. Collectively the HEAT
team members represent many years of successful telescope and
instrument development in Antarctica. The organizational structure of
the HEAT project
provides effective control of the project while allowing the delegation 
of authority to be made at the proper level within the organization.
The main components of the organization are (1) the PI, who has overall 
responsibility for the project and coordinates the activities of the 
participants, (2) the DP-I (Kulesa) who assists the PI and is responsible 
for instrument control and data products, (3) the Project engineer
(PE) responsible for system integration, (4) the Project Manager 
(PM-McMahon) who oversees the fiscal realities of the project, and (5)
the Science and Instrument Teams who will provide extensive scientific and
technical guidance throughout 
the course of the project. Table~\ref{roles} provides a listing of the
roles and responsibilities of each member in the
organization. Postdocs, graduate students, and technical staff at the
collaborating institutions will participate in developing the hardware
and software for HEAT.  

\begin{figure}[!htb]
\centering
\includegraphics[angle=0,scale=0.35]{../figures/OrganizationChart.eps}
\caption{\small \label{orgchart} HEAT Organizational Chart}
\end{figure}


A schedule of key project milestones and tasks is provided in
Figure~\ref{gantt}.  During the first 3 months of the
project a reference design for HEAT will be completed, followed by a
design review by the instrument and science teams. Procurement of key
components will begin soon after following the spending profile
outlined in the budget. Integration and test of the receiver system
will take place at Ball Aerospace in December-January 2006/2007. Acceptance
tests of the telescope will take place in February-April 2007. The receiver
and telescope will be shipped to the University of New South Wales in
May 2007, where an extended period of integration and testing with the
AASTINO module will occur, including system evaluation in a large -85C
environmental chamber (see Support Letter from J. Storey). Our goal is 
to ship HEAT to the South Pole in August-November 2007,
with subsequent deployment to Dome~A in January 2008.  This schedule
enables a one year margin for the two-year minimum science mission. 

Routine communications between project participants is essential.
There will be quarterly telecons between Science and Instrument team
members to monitor progress, provide insight into solutions to
emerging problems, and redefine priorities as needed. There will
be weekly telecons and quarterly meeting (primarily through
teleconferencing) between the PI, D-PI, PE, PM, and Technical Leads
(Storey - AASTINO, Pernic - Telescope, Glaister - Cryogenics, Gao -
Mixers, Mehdi - LOs, Weinreb -IF/Correlators, and Kulesa - software).  

The ability to meet the proposed schedule is made possible by the heavy
leveraging of receiver technology funded through NASA and ESA for HIFI, 
past NASA and Internal Research \& Development funds for developing 
closed-cycle cryocoolers for JWST at Ball, and the experience of team
members and Vertex/RSI in building telescopes for Antarctica. {\it
Indeed, the HEAT instrument team officially formed over a year ago
and has been optimizing component technologies and system designs
for HEAT since.}   

\begin{figure*}[!htb]
\centering
\begin{minipage}{6.5in}
{\parbox{5.2in}{\includegraphics[angle=0,scale=0.85]{../figures/gantt.eps}}}
{\parbox{1.2in}{\caption{\small \label{gantt} Timeline: two years
of development, 
integration and testing is followed by three years of survey
work at Dome~A.  The two year minimum science mission allows for one year of
margin.  Leverage of technologies from Herschel/HIFI and the PI's
SuperCam instrument development makes this timeline realistic. 
}}}
\end{minipage}
\end{figure*}

\subsection{Logistics: Deployment to Dome A}
 
Antarctic science has reached a level of maturity where several options exist
for fielding instruments on remote sites. In the case of Dome A these include:

\begin{enumerate}
\setlength{\topsep}{-1ex}
\setlength{\partopsep}{-1ex}
\setlength{\itemsep}{-0.4ex}
\setlength{\parsep}{-0.4ex}

\item  {\bf Traverse from Pole}: By 2007 it is expected that the overland
route from McMurdo to the South Pole will be well established, and the
necessary infrastructure such as tractors and sleds will be routinely
available at South Pole. A single overland expedition from Pole to
Dome A could bring in all the equipment and supplies needed for the
HEAT experiment. Twin Otter flights (2) from Pole could bring in and
retrieve additional personnel if needed. 

\item {\bf CASA 212} (Australian Antarctic Division): J. Storey (see Support
   Letter) will be requesting one CASA 212 cargo flight directly from
   South Pole to Dome A for transport of the HEAT experiment.  In
   addition, he will ask for a flight (from Mawson or Pole) to bring
   in personnel to install HEAT, and a third flight
   a few days later to bring in remaining fuel and to
   retrieve the science team from Dome A. 

\item {\bf LC-130/Twin Otters}: Raytheon Polar has developed a flight
  plan to deploy the HEAT experiment on Dome A
  using an LC-130 flight from McMurdo (put-in)
  and three Twin Otter flights from Pole (personnel). 

\item {\bf IPY Traverse from Dome C} (Multinational): There is
   considerable interest amongst the international community
   in exploring the astronomical potential of Dome A by deploying a
   set of experiments to monitor site conditions there. HEAT is
   included in the international IPY proposal for the Dome A traverse.  

\end{enumerate}

A Chinese traverse reached Dome A during the recent 2004-5 season; a Twin Otter
from Pole provided assistance near the summit of Dome A. 
The HEAT team will continue to work closely with the NSF, Raytheon
Polar, and the International Community to implement an optimal plan
for deployment to Dome A during the IPY. 

\section{Educational Impact}

The development and establishment of the first astrophysical observatory on 
Dome~A offers many opportunities to tap into the imagination of students of 
all ages. Below we highlight two examples.

\medskip

\noindent {\bf Instrument Development Experience}

\smallskip

The training of students in the development of state-of-the-art
instrumentation is essential to the future of science. This is
particularly true in mm/submm astronomy where technological advances
are happening so rapidly. 
Ironically, there are only a handful of laboratories in the world
where students gain hands-on experience in the design, fabrication,
and fielding of radio astronomy instrumentation. In the PI's lab we
have had a number of students (both graduate and undergraduate)
participate in the development of submm-wave instrumentation
for Antarctica (i.e. AST/RO) and the Heinrich Hertz Telescope
(HHT) on Mt. Graham, Arizona. This work, and the astronomy that has
come from it, has been a major component of 5 Ph.D. dissertations and
numerous undergraduate research projects. HEAT is a natural extension
of these research efforts. In the proposed budget for HEAT, funds for
one full-time graduate student are requested. However, as is customary in
the PI's lab, many other students will also participate in making the
program a success. Indeed, one of the most important aspects of
training students in instrument development is experience in working
in teams. Astronomical instrumentation is becoming ever more complex,
and requires the talents of many individuals. Providing students with
both technical training and team-work experience increases their
probability of success.  The HEAT grant will also support two half-time 
graduate students at Caltech working with Co-I Weinreb in the
fabrication of the HEAT IF amplifiers and processor.

\medskip

\noindent {\bf K-12 Outreach: A Student Radio Telescope}
\smallskip

In support of education and public outreach activities the PI and his students 
have constructed a remotely operable, steerable, 3.5~m
Student Radio Telescope 
(SRT) for observing the HI line in the Milky Way. The SRT has been used as 
a instructional tool in undergraduate courses (both major and
non-major).  Students from on and off
campus will soon be able to monitor and control
observations with the SRT. Unlike optical telescopes, the SRT can be
used day and night, making it ideal for classroom instruction.  Like
HEAT, the SRT is a spectroscopic Galactic Plane survey
telescope. During the course of developing and operating HEAT we will
develop instructional modules for various age groups that focus on the
science and technology of HEAT and use the SRT as a ``hands-on''
laboratory with the goal of providing students with an intuitive
understanding of underlying physical concepts.  

\clearpage

\pagestyle{empty}

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\end{document}
