"Orbital Mechanics for Dummies"

Can anyone recommend introductory
books on the subject?

The book "To Rise from Earth: An Easy to Understand
Guide to Space Flight" by Wayne Lee (a mission planner
at NASA) could serve as a good introduction. Very easy
to read and nicely illustrated.

Chapter 2 is "Above the Clouds: Orbital Mechanics
Without Math", and Chapter 3 is "Dancing in the Dark:
How to Perform Space Maneuvers."

Amazon.com carries the book, and your local library might
even have a copy.

James



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In article ,
Steve Mazerski wrote:
...What I am looking for now is a
basic but solid introduction into orbital / space flight
mechanics, e.g. how to calculate what energy is needed
to take an object from point A to point B, what is a delta V etc.
Can anyone recommend introductory books on the subject?

At the moment, I'm not aware of a gentle "For Dummies" introduction that
proceeds far enough to give you a useful technical grounding, alas.

The best introductory text I've seen is Prussing&Conway's "Orbital
Mechanics", but it is a university text, so it may be slow going for an
absolute beginner or someone short on math background.

If you have a good library on hand, you might look for Max Hunter's
"Thrust Into Space", but it is loooooong out of print (and essentially
impossible to find on the used market).

(And one unrecommendation: Bate/Mueller/White's "Fundamentals of
Astrodynamics" is popular but in my opinion not very good. Its sole
virtue is that it's cheap. Might be worth experimenting with if P&C
proves unsatisfactory.)
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

Steve Mazerski wrote:

Can anyone recommend introductory books on the subject?
I am imagining something along the lines of a none-existent
"Orbital Mechanics for Dummies".

Certainly:

Lee, Wayne: To Rise from Earth: An Easy-To-Understand Guide to Space Flight
http://tinyurl.com/lxxo

(http://www.amazon.com/exec/obidos/tg...1062501195/sr=
1-1/ref=sr_1_1/102-5726593-8558540?v=glance&s=books)

I think it's a great book!

From amazon.com:

"To Rise From Earth is a good introduction to the science of space flight. A
combination of history and science, this well illustrated book explains the
basic science of space flight, orbital mechanics and flying to other planets
at a level that should be understandable by a high school student.

The book is profusely illustrated, and full of marginal comments -
Historical facts, Scientific facts, Rules of thumb - which make it very
dippable. True to its intent, it explains the pricipals of space flight
clearly, without using a single equation.

As well as the theory, the book also gives a history of space flight, from
the first experiments with rockects by Goddard and von Braun, through the
American manned space programs (Mercury, Gemini, Apollo), with a large
chapter devoted to the Space Shuttle. A review of unmanned planetary probes
is also given, along with a final chapter on future exploration of Mars.

Throughout the book focuses on the American space program. One of its
shortcomings is that the Russian space program is almost completely ignored.
Also some of the Scientific and Historical facts given are wrong.

Overall, a very simple, readable and useful reference."

--
Steen Eiler Jørgensen
"No, I don't think I'll ever get over Macho Grande.
Those wounds run...pretty deep."

I HIGHLY recommend "Understanding Space: An Introduction to
Astronautics"
by Jerry Jon Sellers. This book is very readable and gives an
introductory but very detailed explanation of all aspects of
spaceflight including propulsion, spacecraft systems,
guidance/navigation, and a very detailed explanation of orbital
mechanics. Some of the orbital material covered include the
calculation of the six classical orbital elements from two observation
vectors, patched conic section flight paths for planetary missions,
and re-entry calculations using ballistic coefficients. The math used
is at an advanced high school or college freshman level (very little,
if any, calculus, lots of vector and matrix math clearly explained in
the appendix). To get the most out of this book, you MUST work the
chapter exercises. I had to because this was a textbook used for my
Masters in Space Systems Operations Management ;^)

It's a little pricey at around $70 but it is 110% worth it if you want
a solid introduction to real spaceflight. This book will definitely
separate you as a real layman rocket scientist from the techno-peasant
astronaut wannabes.

An alternate less expensive orbital book is the classic (and somewhat
dated) "Fundamentals of Astrodynamics" by Roger Bate, Donald Mueller,
and Jerry White.

Good luck with your studies!

Martin

OSPAM (JamesStep) wrote in message ...
Can anyone recommend introductory
books on the subject?

Here is a good start:

http://www.jpl.nasa.gov/basics/index.html

(Steve Mazerski) writes:

until recently I was of the vague impression that gravity diminishes
very quickly in space which is why occupants of orbiting vehicles
appeared weightless...

Gravity does not "diminish very quickly in space;" as Newton showed,
it obeys an inverse square law. Hence, at twice the Earth's raius,
the gravitational acceleration toward the Earth is still 1/4th gee,
at three earth radii, it is still 1/9th gee, etc. --- and the gravitational
accleration at the altitude of low earth orbit is so close to 1 gee as to
make no practical difference.

Astronauts _appear_ "weightless" because they are MOVING AT ORBITAL VELOCITY,
just like their spacecraft, and both they and they spacecraft have the _same_
acceleration toward the Earth. Since they are BOTH accelerating at the SAME
RATE in the SAME DIRECTION, their _RELATIVE_ acceleration is _ZERO_, and they
=APPEAR= to "float" _RELATIVE_ in the spacecraft cabin. However, in reality,
+BOTH= they and their spacecraft are falling toward the Earth at a about a gee.

For the same reason If you were in an elevator and the cable broke, both
the elevator =AND= you would fall toward the Earth at the local value of
the gravitational acceleration, and you would _FEEL_ "weightless."
This is =NOT= because gravity has "gone away," but because in a gravitational
field, =EVERYTHING= falls with _EXACTLY THE SAME ACCELERATION_.


-- Gordon D. Pusch

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In article ,
mcv wrote:
Other than that, I'm pretty much like you: an interested layman looking
for a clear explanation of principles with math that I can still understand
(and I'm only a computer scientist, and not a physicist or mathematician).

I've also always wanted to know why the Lagrange points work the way they
do. I have no idea.

The finer questions, like their stability and why there aren't any more of
them, get messy. But the basics of why they exist are not too hard.

Sloppily speaking, a circular orbit around an unaccompanied planet is a
balance between gravity and centrifugal force. But in (say) the
Earth-Moon system, there are three forces involved, one centrifugal and
two gravitational.

The "in-line" Lagrange points, along the axis joining the Earth and Moon,
are not too hard to grasp. They arise from various combinations of the
three forces adding up to zero by simple arithmetic. For example, the L1
point between Earth and Moon (caution, astronomers and space engineers
don't number the points the same way) is where centrifugal force *plus*
the Moon's gravity exactly balances Earth's gravity.

The "Trojan" Lagrange points, in the Moon's orbit 60deg ahead of and
behind it, are more subtle. At first glance, it looks like they shouldn't
work -- centrifugal force balances Earth's gravity just like it does for
the Moon, but nothing balances the Moon's gravity and it ought to pull
objects away from the point.

The key thing to understand is that objects in the Earth-Moon system don't
orbit the Earth. They orbit the barycenter of the system, basically the
system's overall center of mass, and that is displaced somewhat toward the
Moon from the Earth's center.

So an object at a Trojan point, at the same distance *from Earth's center*
as the Moon, is not quite at the same distance from the point it actually
orbits around -- it is slightly farther out than the Moon. And from its
viewpoint, the point it orbits is slightly to one side, the Moonward side,
of Earth's center. So to maintain its orbit, it needs to be pulled inward
a bit harder than Earth alone can manage, and it needs to be pulled off to
the Moonward side of Earth too.

The Moon's gravity obviously pulls to the Moonward side, and since the
Moon is only 60deg away from Earth as seen from the Trojan point, it also
pulls toward Earth a little bit. Here too the forces balance, but you
need to use vector addition rather than just arithmetic, and you must
remember that the center of rotation (which defines the centrifugal force)
is the barycenter, not Earth's center.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

mcv writes:

Henry Spencer wrote:
In article ,
mcv wrote:

I've also always wanted to know why the Lagrange points work the way
they do. I have no idea.
[...]
Sloppily speaking, a circular orbit around an unaccompanied planet is a
balance between gravity and centrifugal force. But in (say) the
Earth-Moon system, there are three forces involved, one centrifugal and
two gravitational.

The "in-line" Lagrange points, along the axis joining the Earth and Moon,
are not too hard to grasp. They arise from various combinations of the
three forces adding up to zero by simple arithmetic. For example, the L1
point between Earth and Moon (caution, astronomers and space engineers
don't number the points the same way) is where centrifugal force *plus*
the Moon's gravity exactly balances Earth's gravity.

This makes sense. And as I was reading this, I realised that the L2 point
(on the other side of the moon) is where the earth's gravity plus the
moon's gravity balances the centrifugal force, which is larger because
its orbital velocity is higher.

I still have no idea how L1 and L2 can possibly be stable, however.

Simple --- they _aren't_. L1, L2, and L3 are all "saddle points," unstable
to perturbations along the Earth-Moon line. (However, active station-keeping
to hold a body near L1, L2, or L3 costs less propellant than trying to "hover"
in a powered orbit anywhere else in the Earth-Moon system...)

[...]
So an object at a Trojan point, at the same distance *from Earth's
center* as the Moon, is not quite at the same distance from the point
it actually orbits around -- it is slightly farther out than the Moon.
And from its viewpoint, the point it orbits is slightly to one side,
the Moonward side, of Earth's center. So to maintain its orbit,
it needs to be pulled inward a bit harder than Earth alone can manage,
and it needs to be pulled off to the Moonward side of Earth too.

Alright, now I think I understand that too. It's easier than I thought.
But now I don't understand why this holds specifically for the L4 and
L5 points, and not for an infinite number of other points between those
and the L3 point.

At any point other than the Lagrange points, the acceleration due to gravity
has the wrong strength and direction for it to be possible for a body to
maintain a constant distance from both the Earth and the Moon, since it will
not point toward the barycenter and/or provide the correct centripetal
acceleration for the body to move in a 29.5 day circular orbit.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

I don't see a popular "Orbital Mechanics for Dummies" book getting
published into the everyday world, but I sure could use one here. I
turned up my nose at them when the first Dummies books came out, but
after a while I looked into one to see what it did and how it did it;
and I was impressed. I think the "Dummies" label is overdone,
probably as a sales point, and the idea of straightforward
unelaborated text is a winner.

Since we aren't going to see an "Orbital Mechanics for Dummies" book,
could we have an occasionally updated, annotated reading list? Like
what I see up this thread, but more compact and dedicated to its
Orbital Mechanics for Dummies topic? So that whoever couldn't find
one particular book could get ideas what others to try for? So that
the readers could find serious relevant information and *problem sets*
to work?

Thanks -- Martha Adams

"Martha H Adams" wrote in message
...
I don't see a popular "Orbital Mechanics for Dummies" book getting
published into the everyday world, but I sure could use one here. I
turned up my nose at them when the first Dummies books came out, but
after a while I looked into one to see what it did and how it did it;
and I was impressed.

I tend to grab one whenever I get a new program, then graduate to more
informative texts. Sometimes you don't know enough about a subject to even
know what questions to ask.

As an aside, I just happened to catch an episode of "Monarch of the Glen"
and saw poor Hector trying to figure out his computer. You couldn't see the
cover of the book, but it was obviously a Dummies book.
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