I am writing a science fiction novel that includes several
orbital missions and sub-orbital trajectory problems. It
has a space-war component that requires me to figure out how
to hit a number of targets on the ground from points in orbit.

There is no need for anything approaching military precision.
The Earth can be considered as a perfect sphere. All orbits
and orbital sections can be computed as a two-body problem.
Atmospheric effects can be ignored. Any acceleration due to
use of spacecraft engines (boost) can be considered
instantaneous. The only reason that I even want a solution
is to get the science close enough so that I don't get a
bunch of "you fool, your wrong, ha ha ha" letters from
irate readers.

The idea solution would be a computer program (preferably
as a set of Java classes) that I could plug partial initial
conditions and partial target conditions into. Complete
conditions include latitude, longitude, altitude, velocity
vector and available boost (to modify velocity vector).
Partial conditions includes any subset of the above.

Solution should compute or iterate to deviation at closest
approach so that I can adjust initial conditions until an
acceptably accurate solution is achieved.

The types of problems I want to solve include:

Reentry: Given initial latitude, longitude, altitude and
velocity vector solve for point of impact (target altitude
= radius of Earth).

Targeted Reentry: Given target latitude, longitude and
altitude (target altitude = radius of Earth) and initial
latitude and longitude, compute initial altitude, velocity
vector and available boost required to hit the target.

Orbital Rendezvous: Given initial latitude, longitude,
altitude and velocity vector, solve for rendezvous at
target latitude, longitude, altitude and velocity vector.
This could require chaining several solutions together to
simulate several boosts as in boost to high apogee, boost
for orbital plane change, boost to close approach, boost
to matching orbit.

Orbital Fly By: Like Orbital Rendezvous, but with no
requirement to match orbits. Think of ship A getting
close enough to shoot at ship B.

Initial price is a fair amount for someone to find a
solution that I have not found. I can re-price the question
upward if someone want to tailor a solution to my specific
needs.

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Request for Question Clarification by arimathea-ga on 11 Mar 2003 12:26 PST

vernmcgeorge-ga,

There are several software packages, some free for hobbyists, that can
perform this task or derivations of it.  Would links to several such
packages be an acceptable answer to this question?

Thanks,
arimathea-ga

---

Clarification of Question by vernmcgeorge-ga on 12 Mar 2003 14:07 PST

It is possible that such a software packages referenced by arimathia-ga
could form the basis for a solution if and only if it is possible for
to automate the input of initial conditions, the output of results,
comparison with desired results and input of revised initial conditions.
The easiest path to this is Java source code. Anything else will cause
me to spend more time programming and less time writing.

Re mathtalk-ga's comment, I have no intention of boring the readers with
the details of this process. My intention is only to include specific
results that are not provably wrong. Unlike "The Moon is a Harsh Mistress"
(one of my all time favorite novels) where the distance from the Earth to
the Moon is fixed by nature, in my novel, I get to pick the orbital
parameters of the space ship bombarding the Earth (within constraints that
I don't want to talk about because I'm not ready to share the plot with
the outside world).

If I never get a solution, then I will fall back on the vague handwaving
that Heinlein may have used in TMisHM, although I suspect he did in fact
do his homework to come up with the transit times and impact energies that
he sprinkled throughout the book.

A "back of the envelope" solution might help me or might not. BTW what is
"syzygy"? In terms of a space opera game, I have yet to find one that will
do what I want. I haven't looked very hard and what I really need from
cush a game would be the mission planning part and what I suspect I would
find in a game would be the "pulling the trigger and blowing stuff up"
part.

Thanks seizer-ga for the NASA pointer. Entertaining but not ultimately
useful, at least not without major work.

-- Vern

---

Request for Question Clarification by arimathea-ga on 13 Mar 2003 11:02 PST

vernmcgeorge,

I'm posting this as a request for clarification rather than an answer.

The tool I have in mind is Satellite Tool Kit (STK).  The tool is
designed for satellite tracking, but has a ton of different modules
available for it which may help your query.  I'd call the tool fairly
easy to use.  The basic software is free for hobbyist and
non-commercial purposes, and I have a feeling that that if you
contacted the authors of STK, Analytical Graphics, they would be happy
to provide you a license for the software.

Without drawing together about 25-30 disparate java classes, I am
aware of no other convenient way to accomplish your problem.

If you'll accept this as an answer, i'll post it.  I think STK will
solve your problems.  If STK does not end up solving your problems, I
will follow the issue diligently to its end and continue working on
the question.

Best of luck.

STK is available at http://www.stk.com/

arimathea-ga

---

Clarification of Question by vernmcgeorge-ga on 15 Mar 2003 17:02 PST

arimathea-ga,

I have sent an email to AGI (the makers of STK) and will let you know
as soon as I get a response. At least on the surface, STK looks
promising. The biggest
question on my mind is will they grant me a license that I can afford
(free or cheap). If the STK solution requires a multi-product full
time aerospace engineer type discount, it won't be a solution that I
can use.

-- Vern

Hello vernmcgeorge!

I wonder if you've already come across NASA's wonderful collection of
applets available at:

http://spaceflight.nasa.gov/realdata/

While they certainly don't begin to address all your requirements,
perhaps you'll find them useful (or at least amusing)!

Best of luck with the novel,

--seizer-ga

I'm unclear on how such computations so detailed as to be falsifiable
would make a palatable appearance in science fiction.  Heinlein's Moon
is a Harsh Mistress employs a plot device of bombardment of Earth by
projectiles launched from the Moon, but without tedious exactitude.

A computer game/simulation of "space opera" on the other hand might
well require the sort of simplified ("Atmospheric effects can be
ignored.") computations you describe.

I might have thought you were interested, for the writing perspective,
in a helpful "back of the envelope" approach to apogee and syzygy
calculations, but the "Java Class" and other detailed requirements
suggest otherwise.

regards, mathtalk

Hi, vernmcgeorge:

While apogee and perigee refer to the highest and lowest points of an
orbit, and hence to the length of the major axis of an elliptic orbit
for a simply 2-body system, the term syzygy properly refers to a
linear alignment of three bodies, esp. the Earth, Sun and Moon.  I was
using it in a very loose sense, to suggest the problems of "aligning"
the target, the missile, and the spaceship.

regards, mathtalk

I will post few links here, including link which points to a
program which can be used to solve listed scenarios.

Program is described here:

G.O.D. 0.81
Date: May 24th, 1995 License: GPL
Size: 40.7K Rating: ***
Information:
G.O.D. stands for Gravitational Orbits Dynamics. It simulates interactions
between n-bodies in 3D or 2D space, based on the Newton physic model.
Download
http://linux.tucows.com/home/preview/9227.html

 I am posting this  as a comment,  for possible benefit of
  the asker and use of my colleague   arimathea-ga,
  because in my humble opinion, computer program,
  any program, is not an answer and google
  answers is not a good vehicle for finding an answer
  in this case.

  Author wants to write and not play with a program.
  Running such program, tweaking it, is a skilled job,
  it takes time to come to speed.
  In this case author needs somebody with more
  then technician level skills since what needs to be
  calculated, how it should be used and described is
  not well defined.
  Sci_Fi writer can create scenarios which differ from
  current practice, he can create UFOs which change
  directions instantly for any mass, as in

  ".. Any acceleration due to
use of spacecraft engines (boost) can be considered 
instantaneous .."

but he should be consistent.
 If he has created engines which can provide unusual
 thrust on negligeable amount of fuel,
 then he may need not any program, since path may
be arbitrary (like path of a pedestrian, who may change direction
instantly).

Current programs arrive to a unique path because they impose
conditions, usually 'limited engine thrust' and fuel-optimality.
See e.g

... The Role of Fuel-Optimal Flight Plans in Maintaining Regular Operations.

www.informs.org/Conf/NO95/TALKS/SE15.1.html

or

... Vadali et al. 13 present a method to compute fuel- optimal multi-impulse
maneuvers for formation flying using the chief-deputy concept. ...
jungfrau.tamu.edu/~html/alfriend/alfriendpublications/ 
FormationFlying/OrbitEstablishment.pdf


 Minimum Fuel Optimal Control For A Scalar System A. Problem Statement
The first-order, continuous-time system for this example and the minimum fuel

ece.gmu.edu/~gbeale/ece_620/xmpl-620-min-fuel-01.pdf - Similar pages

and other link which come for

SEARCH TERM

fuel optimal

CONCLUSION

 This author  requires (still In My Humble Opinion) a technical consultant, who
 will interact with him over time, and will eventually proofread the manuscript.

Google Answers is not set up to deal with that, but GA researcher can find a
suitable consultant or  consultant broker, once question is formulated that way.


Good luck with your book,
Perhaps you can let us know when it is published,
by asking some question about something like
'what to wear to book signing tour'

hedgie

make you rich.

I like the one where Gene Simmons plays the assassin that has the gun
that shoots the little missle bullets that attache to a heat/infrared
fingerprint of the intended victim. I can imagine even boring old
sites on a planet will have at minimum latitudinal and longitudinal
"crosshairs" to extinguish them by...

Sgt. Shultz, as usual, knows "Nuthing!"

Hi, Vern...

I ran your question past a friend of mine, who does that sort of thing
as a day job.  The solution to it, he observed mildly, is
"non-trivial."

He says that if you want to go into it seriously, a comprehensive text
is "An
Intoduction to the Mathematics and Methods of Astrodynamics" by Dr.
Richard Battin of MIT.  He points out, however, that Dr. Battin
teaches this material over a two-semester graduate course which is
notoriously intense.

If you just want to figure out a quick and dirty solution to your
problem, he too recommends STK.  Perhaps the publishers might bend a
little to offer a (discounted) demo or student copy?  Or have someone
in their promotions department run the calculations for you in
exchange for a credit in the book?

Best of luck,

-Chromedome

Have you considered using...









THE FORCE?

arimathea-ga,

AGI has granted me a license to STK.

Please post an answer so I can accept it and you can be paid.

-- Vern

vernmcgeorge-ga on 12 Mar 2003 14:07 PST wrote:

>If I never get a solution, then I will fall back on the vague handwaving
>that Heinlein may have used in TMisHM, although I suspect he did in fact
>do his homework to come up with the transit times and impact energies that
>he sprinkled throughout the book.

As an ardent Heinlein fan I can tell you this: Heinlein always did his
homework.  He worked out those problems himself by hand, with his
skillful wife checking his work.  Any and all technical information in
all Heinlein novels was up to date and as accurate as possible at the
time it was written.  He is a great example of how a sci-fi author
should write, and I am quite content that contemporary writers like
you follow in the same path.