Excellent New Book
Jim Varney (sat_watcher@rocketmail.com)
Thu, 15 Jan 1998 12:12:54 -0800 (PST)
I have been enjoying an outstanding new book called "Fundamentals of
Astrodynamics and Applications" by David A. Vallado (McGraw Hill ISBN
0-07-066834-5). If you are interested in orbital mechanics and have had
a few classes of calculus in college, then you'll enjoy this book too.
What sets this book apart is that nearly all of the theoretical
mathematics is followed up by discussions of practical application. For
example, after introducing a simplified analytical technique based on
Kepler's equations and using the time rate of change in mean motion to
model drag, Vallado writes
"We prefer numerical techniques to find n-dot and n-dot-dot, but we
often use 2-line element sets because of their current availability. Be
very careful when using these relations. For decades 2-line element
sets from Space Command have transmitted the mean-motion rate already
divided by two. Don't divide twice!"
That's what I like about this book. It isn't just an academic textbook
-- Vallado likes to get into the nuts-and-bolts of actually using the
theories. How many textbooks warn you not to divide by 2 twice? Each
chapter includes a look back (history of the theories) and looks forward
(discussions about the thinking contained in the academic journals).
Another example of practical discussion is this passage on how B-star
isn't really a drag term:
"Be aware that the value of B* is always modified. It's really an
arbitrary free parameter... The estimated value of B* may be completely
unrelated to drag effects in the presence of satellite maneuvers,
significant solar pressure and atmospheric perturbations, large
third-body effects from the Sun or Moon, or large deflections caused by
mismodeling of the Earth's gravitational field."
The book includes 67 "algorithms" which show how computer code could be
structured to calculate various problems. The preface states that there
will be a CD-ROM available with source code in FORTRAN, C++ and Pascal.
This book contains the most detailed treatments of time (UTC, TAI, TDT,
TDB, etc.), coordinate frames (B1950, J2000, nutation, precession,
etc.), gravity models (zonal, sectoral and tesseral harmonics) and
atmospheric models (exponential, Harris-Priester, Jacchia-Roberts and
Soviet Cosmos) that I have seen in one book.
Reading between the lines I detect some criticism of the current state
of affairs with 2-line elsets and SGP4, a topic about which Mr. Vallado
and I discussed by e-mail several months ago. Referring to NORAD 2-line
elements Vallado writes
"Many people often incorrectly assume these element sets have no errors.
In fact, ALL element sets contain errors based on their mathematical
formation. ...errors in the formation of (2-line) element sets can be
on the order of a kilometer or more." (People using COLA to predict
satellite collisions should note this!)
This book is rich with a lot more: a good treatment of orbital maneuvers
(plane changes, Hohmann transfers, orbit-raising); mission requirements
("frozen" orbits, sun-synchronous, repeating groundtracks,
reconnaisance); coordinate system transformations. The appendices
include the JGM-2 gravity model and planetary epherimedes.
If you're comfortable with some higher math like vector operations and
partial derivatives, then this book a "must have" for the advanced
satellite observer. I think Vallado's book will replace Bate, Mueller
and White's "Fundamentals of Astrodynamics" as the "classic" reference
book for astrodynamics. It's going to take a long time for me to absorb
this book -- if I'm capable of absorbing all of it, that is.
This is not an easy book to find. I obtained mine by doing a web search
and found that the University of Texas was requiring the book for a
course, and luckily I was able to purchase the last available copy from
the university bookstore. It's now a new semester so they may have
restocked. Or try Microcosm Books in California at
www.smad.com/ds/home_dab.htm. Expect to pay about $35 for the soft
cover. 922 pages.
__________________________________________________
Jim Varney 121.398W 38.458N 8m Sacramento, CA
jamesv@softcom.net, sat_watcher@rocketmail.com
_________________________________________________________
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