Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stecf.org/conferences/adass/adassVII/reprints/antunesa.ps.gz Äàòà èçìåíåíèÿ: Mon Jun 12 18:51:42 2006 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 03:46:03 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: rainbow

Astronomical Data Analysis Software and Systems VII
ASP Conference Series, Vol. 145, 1998
R. Albrecht, R. N. Hook and H. A. Bushouse, e
Ö Copyright 1998 Astronomical Society of the Pacific. All rights reserved.
ds.
Astro­E's Mission Independent Scheduling Suite
A. Antunes and A. Saunders
Hughes­STX, Goddard Space Flight Center, Greenbelt, MD 20707,
Email: antunes@lheamail.gsfc.nasa.gov
P. Hilton
Hughes International/ISAS, 3­1­1 Yoshinodai, Sagamihara, Kanagawa
229, Japan
Abstract. The next generation of Mission Scheduling software will
be cheaper, easier to customize for a mission, and faster than current
planning systems. TAKO (``Timeline Assembler, Keyword Oriented'',
or in Japanese, ``octopus'') is our in­progress suite of software that takes
database input and produces mission timelines. Our approach uses openly
available hardware, software, and compilers, and applies current schedul­
ing and N­body methods to reduce the scope of the problem. A flexible
set of keywords lets the user define mission­wide and individual target
constraints, and alter them on­the­fly. Our goal is that TAKO will be
easily adapted for many missions, and will be usable with a minimum of
training. The especially pertinent deadline of Astro­E's launch motivates
us to convert theory into software within 2 years. The design choices,
methods for reducing the data and providing flexibility, and steps to get
TAKO up and running for any mission are discussed.
1. Scheduling Defined
The basic concept of scheduling is simple. You take a list of targets, and make
a calendar. The rest is e#ciency and bookkeeping, which is akin to saying
``to make a painting, just put paint on a canvas.'' In reality, it is a bit more
complicated. The three main factors to consider are calculated quantities (i.e.,
unchangeable facts of the situation), derived quantities (soft constraints, ratings
of good and bad events, and politics), and capacity constraints (such as time
and telemetry).
For mission scheduling, the general calculated quantities are based on the
platform. For satellites, this includes: sun angle, orbital position, earth limb
angle, roll angle, and others. For ground based, several analogs are day/night,
latitude/longitude, and elevation angle. These have no particular weight to
them, but are simply physical facts about the observing situation.
From these, we create the derived quantities, which determine whether a
given observation is feasible. This includes (for satellites) issues like allowable
sun condition, occultation, thermal profile, in­SAA region, bright/dark earth,
ground­station contacts, and star tracker acquisition. Some of these are func­
263

264 Antunes and Saunders
tions of the calculated quantities, and others are qualitative opinions based on
the calculated quantities. Some derived quantities can be entirely political, and
imposed from the outside (scientific priority, for example).
Capacity constraints include, first and foremost, time, generally defined as
``you can only look at one thing at a time.'' Telemetry is a large concern for
satellites, and other user­defined resources vary from mission to mission.
Tracking all of these is the principal task of scheduling, that is, to place
targets such that no constraints are violated and all resources are used to max­
imum e#ciency without overbooking. The goal is ultimately to maximize the
scientific routine.
So tools to manipulate this output not just ``a schedule'', but also an eval­
uation of its overall suitability (and stability) for the problem at hand. The
interface must present all the quantities above to the user when hand­editing is
required. Finally, the automatic scheduling routines (ranging from simple ``good
time bad time'' limiting, to AI routines that make sequences) must interface with
the editing options available to the user.
TAKO (``Timeline Assembler, Keyword Oriented'') is our multimission soft­
ware suite for achieving this goal while simplifying training and operations (and
thus saving time and expenses). Our goal is that TAKO will be easily adapted
for many missions, and will be usable with a minimum of training. Rather than
having a single monolithic program, we are building an integrated suite (similar
to the FTOOLs/XANADU approach) that handles all input, parameterization,
scheduling, and output. This provides flexibility both for a variety of missions,
and for changes during an mission lifetime.
Further, our design is modular to allow customization of relevant sections
for di#erent missions. Feedback from the Astro­E science team and from other
schedulers has been crucial in determining the necessary capabilities for this
suite. The first benchmark goal for the Astro­E first edition is to be able to
schedule at least 400 items over a 1­year baseline at 1 minute resolution, and to
manipulate this schedule in real time without alienating the user.
2. TAKO Design
The focus for users is the intuitive GUI for interaction and scheduling. Schedul­
ing is an intensely visual task, and much of the development time is for this GUI.
The actual scheduling engine deals only with the generic time­ordered quality
function and header, without having restrictions on what the header elements
are. The intermediary code between this flexible GUI and generic scheduler is
what makes TAKO specifically useful for satellite and observational scheduling.
For a given mission, the input file currently specifies how to custom­build
single observations in a highly flexible way. It uses ASCII files for storage and
output, allowing filters to be written and input/output to be integrated with
other packages (including spreadsheets). Thus the entire suite can be dropped
as a single unit into the mission's science operations center, with pre­ and post­
processors written to make the linkage.
TAKO uses standard hardware, operating systems, and compilers (i.e., any
workstation with gcc and Tcl/Tk 8.0). And, TAKO is modular by design, to
allow for use with di#erent missions. Switching missions or handling updated

Astro­E's Mission Independent Scheduling Suite 265
requirements requires adjustments to a handful of the discrete modules, rather
than an entire code overhaul. And much of the mission­specific specifications
can be done at the user level, in the input files, rather than requiring a recompile.
To improve communication, all our documentation is produced as the mod­
ules are written, in HTML, so that the entire package design can be understood
and easily accessed by Web. The design work and user manuals alike will be
available from the Web. After integration, training manuals will also be avail­
able. In the absence of dense technical details within this paper, we therefore
refer you to these Web pages (URL given below).
3. TAKO Implementation
For TAKO, we set several basic design precepts. The GUI is an on­screen editor
that ties it all together. Keyword­value pairs are used to define data elements
and relations generically. Each data element has a header, and acts like an ob­
ject. This object­oriented design means that new elements can be defined on the
fly, much as with a database. And, parameters can be adjusted during runtime
or before each run, with saved definitions allowing mission customization.
Mission­specific code is largely in orbital prediction routines (``calculated
quantities''). Derived quantities are specified in terms of these, using the keyword­
value pair schema. There are four primary types of structures (``target informa­
tion'', ``constraints'', ``resources'', and ``event list''). ``Target information'' is the
information from the science proposals. ``Constraints'' is the interpretation of
the science objectives into operations terms, i.e., ``avoid SAA'' in people­speak
becomes an on­screen curve showing what times are allowed. Constraint curves
are very similar to SPIKE ``suitabilities'' (for those familiar with HST's pack­
age). ``Resources'' includes items like the actual schedule (how much time is
spent on target) and telemetry. And ``event lists'' are outputs like the mission
timeline itself, lists of calibration observations, and so on.
4. TAKO Buy­In
To work for many missions, a scheduling tool must be flexible, accept post­launch
changes, be able to handle many situations, and be better/faster/cheaper 1 . In
the past, it took as long to customize an old tool as to write a new one, and
most solutions required post­launch customization. Also, each mission required
new training for new tools, often at a programmer level, increasing costs and
time spent doing everything except actually scheduling. So TAKO is designed
to be easily adapted for many missions, and to require a minimum of training
at the user level (substituting ``common sense'' instead) 2 .
Buy­in assumes that the software is subject­oriented rather than focusing
on the specific algorithms or performance benchmarks. In short, the user comes
1 NASA motto
2 It takes an engineer to design a car and a mechanic to fix it, but anyone can drive. R. A.
Heinlein

266 Antunes and Saunders
first. A good design is presumed to already use appropriately chosen algorithms
and to achieve requisite benchmarks; what matters most is that the software
not merely function, but be genuinely usable. Therefore, the problem it solves
is ``maximize science return''-- to consistently produce good mission schedules
over a long period of operations.
Looking at it from a system perspective, again focusing on the user base,
we find that it must install easily and require no special software, must pro­
vide immediate functionality, and be easily integrated with familiar tools and
files. From a long­term perspective, it should be flexible, adaptable, and easily
modified. And, it should be evolutionary (taking the best of previous packages)
rather than implementing new ideas simply to be di#erent-- there should be a
familiarity to the overall methodology.
To achieve these goals, we've defined two approaches, ``internal'' and ``exter­
nal''. Internally, the base­level algorithm and programming work is being done
with standard professional methodologies, to select the best approach for the
given precepts and implement it (nothing terribly novel there). Externally, the
GUI is the predominant way the user will interact with TAKO, and is being de­
signed by a programmer/analyst (p/a), receiving constant feedback from three
di#erent mission schedulers. Thus the interface is essentially being designed
by the users, with the p/a acting as adjudicator and implementer. TAKO was
designed in detail before coding began, so that ad hoc coding and integration
problems are generally minimized.
Astro­E launches early in 2000. For more information, visit the Astro­
E URL (http://lheawww.gsfc.nasa.gov/docs/xray/astroe) and the TAKO sub­
pages (http://lheawww.gsfc.nasa.gov/docs/xray/astroe/tako).
Acknowledgments. We are grateful to Pamela Jenkins for scheduling ad­
vice, Larry Brown for programming support, and Glenn Miller for moral support.