Hi all -
I have just uploaded to the Solar Thrust site a Java applet that will
calculate the required transfer orbit (and the delta-V and fuel) to move
between any two bodies of the Solar System (the planets are acceible from
drop-down lists, but you can input the orbital parameters for anything).
I am in the process of writing an article explaining what all the orbital
elements mean and the derivation of the equations, but I thought in the mean
time people could play with it and at least get some idea of the energy and
fuel costs involved in interplanetary travel. Very soon I'll make a similar
applet to go along with the engines article. The site URL
On Thu, 11 Mar 1999 11:51:18 -0500 (Eastern Standard Time), Keith Watt
writes:
> Hi all -
Boy, this leads straight into something I was going to ask about SolarThrust.
I was playing arround with some calculations about travel time between
planets last night, assuming the FT example on the page. So D-T
engines, 15 minute turns, etc. It seemed to me that using these rules it would
take about 25 months to travel from the earth to Mars, assuming you wanted to
stop at mars and then get home later. Very rough math.
So, when talking about SolarThrust, what kind of time delay are you thinking
about for inter planatary fights?
Calculate doesn't seem to work - no results for Orbit or Costs
The planet selection does work.
Whats a Semi-latus rectum - sounds kinky :-)
Tim -
Did you remember to put in an arrival time? The program has to know when you
want to get there...
> On Thu, 11 Mar 1999, Tim Jones wrote:
> Whats a Semi-latus rectum - sounds kinky :-)
Heh heh. It's rectum as in "rectilinear", I think. It's basically half
the width of the elliptical orbit - it's perpendicular to the semi-major
axis. Twice the semi-major axis is the length, twice the semi-latus
rectum is the width. With those two numbers you (or Adobe Illustrator, for
example) can draw the ellipse.
> Tim -
Slight user interface design flaw, but this does now work when you put in the
arrival time, you also have to enter
the rocket exhaust velocity to get mass / fuel ratio. Its
because I got defaults I didn't think I needed to add anything.
Making the entry fields more distinct and having a clue box describing the
need to enter values would help.
> On Thu, 11 Mar 1999, Matthew Seidl wrote:
> I was playing arround with some calculations about travel time between
For a Hohmann transfer (minimum-energy, longest time) orbit, it takes
about 8 months to get to Mars from Earth. For any other orbit the energy will
be higher. But also by increasing the energy you can get there faster, so
there are two variables in operation here. The program will let you play with
both. I should give a quick definition of the orbital elements, I think:
*Semi-major axis (a) = half the length of the elliptical orbit
*Eccentricity (e) = the shape of the orbit, 0=circle, 1=parabola
*Longitude of Perihelion (Pi) = the orientation of the orbit, this is the
angle between the semi-major axis and a reference line (for the Solar
System, that's the poition of the Earth on the spring equinox)
*Rotational velocity (omega) = how fast the planet revolves about the Sun
True Anomaly (nu) = where the planet currently is on its orbit at lauch (note:
for both target and origin), 0=perihelion, 180=aphelion
Arrival time (t2) = the number of years of flight time you want between origin
and target
The quantities marked with a * are constants for a given body, the program has
values for all the planets stored in it.
So, for example, on 9 March 2063, the true anomaly of the Earth is about 190
degrees and the true anomaly of Mars is about 224 degrees. If I want
to arrive in 3 months (0.25 years) I need a delta-V of 24.877 km/s (for
a
DT-fusion drive that means 68% of my rocket needs to be fuel; for a
He3-D
fusion drive it's only 0.3%). If I don't mind a little over 8 months of
travel time (0.7 years), I'll only need a delta-V of 5.78 km/s. This is
very close to a Hohmann orbit.
Hmm.. there actually may be a bug in the fuel calculations, I just noticed
an answer I didn't expect. I'll have to check that. The delta-V is
okay though.
> So, when talking about SolarThrust, what kind of time delay are you
I'm looking at strategic turns of 88 days (Mercury's orbital period, call it 3
months). That seems to make things work fairly well.
I'll let you know about the fuel calculations when I get a chance to check
it. That was a last-minute add - I should know better.
TTYL..
> On Thu, 11 Mar 1999, Tim Jones wrote:
> Slight user interface design flaw, but this does now
Okay, well I can have it calculate the time needed for a Hohmann transfer, I
think I'll have it use that as the default. I'll pick a reasonable engine to
default the exhaust velocity to.
> Making the entry fields more distinct and having a clue
As I mentioned, this is actually going to illustrate an article on the subject
I'm writing, so that will help a great deal. I just thought people might like
to play with it while I'm writing..
Thanks for the suggestions, they make good sense!
TTYL..
Okay, I've made the changes Tim suggested, plus corrected a couple of bugs (it
was trying to display scientific notation and I wasn't allowing it, so I was
losing the exponent!), please let me know if there are any problems.
By default, the program assumes a DT-Fusion drive (not the best for
interplanetary travel, mind you) and returns values for true anomaly for the
planets on 9 March 2063 (note: these numbers are corrected from my last post).
When you change either the origin or the target planet, it
automatically calculates the lowest-energy time (corresponding to a
Hohmann orbit) to that destination.
Oh, btw, I remembered two other terms from last post I should define:
*Perihelion (rp) = distance of closest approach of planet to Sun *Aphelion
(ra) = furthest distance of planet from Sun
TTYL..