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Gravity Assists and the use of
the Slingshot method
By Morgan Welch
Principle
Gravity assists are the process of using a
planet's gravitational force to leech/seed
energy and momentum from the planet in
order to accelerate a spacecraft.
The reason that this is important, is that by
using the latent energy of celestial bodies, we
can conserve precious fuel and expand the
duration and reach of our current space
mission targets
As shown in the diagram (left) by variating
velocity, trajectory, position and mass a wide
range of effects can be achieved, beyond the
simplistic idea of speeding up.
Grav_Assist_Sim plays begins code initial
conditions for 2nd simulation is labeled and
commented
History
• Gravitational Assists have been at the forefront of all our
deep space exploration missions and should be considered a
technique of great beauty, complexity, and luck.
• Because of its high adaptability and great cost efficiency Grav.
Assists have been used in many space missions both short
and long term based. Voyager 2 for example used gravity
assists to visit all four of the outer planets:
Jupiter, Saturn, Uranus and Neptune.
Methods
• For this project I set out to model the efficiency of using the
slingshot method in multiple passes around the sun and orbiting
planets in order to launch observational crafts into extrasolar
trajectories rather using direct propulsion.
• In my programming I Implemented the RK4 method in order to
exact a more precise trajectory of multiple object tracking and
prediction.
• In order to speed up simulations I attempted to optimize my
code by vectorizing most of my code, a process that consists of
simplifying all looped parts of code so that it can be
implemented simultaneously in parallel rather than N linear
interations, cutting the total computational time down.
Animations
• A S.E.T.I. Orbital imaging Station residing just outside of Saturn’s orbit
will be in need of refueling, assuming we are still using standard rocket
fuel propulsion a direct refueling mission like this would be very costly
in terms of weight, fuel and time.
• However luckily for the Space agency, Venus is just about to pass Earth
on a lower orbit, by decelerating from earths orbit by approximately
9% of the shuttles velocity, the shuttle can then approach Venus from
behind and use Venus’ heavier mass and faster velocity to slingshot
the craft into a deep comet like orbit around the Sun that will intercept
the approaching Station. So by only changing the initial velocity of the
space shuttle sized craft leaving earth it was to achieve a maximum
orbit of ~10.11 Au exceeding Saturn with just one slingshot around
Venus taking 6.46 years.
Gravity assists can also be used to slow down celestial objects,
which would be useful for sending probes or stations to study
inner Solar system phenomena like the presence of a weak
electromagnetic field on Mercury.
In this animation The shuttle follows a similar trajectory to the
slingshot refueling mission, however instead of tailing Venus,
the shuttle attempts to pass and cross the Venus’ trajectory
and as a result the shuttle is slowed by the planet and is sent
into a lower energy elliptical orbit whereupon it will meet up
with pre-deposited station and then return to its maximal point
on the Venus Orbital path.
This method of slowing down is most notably used for the
orbital entry of satellites around large bodies
Limitations
• However, there is no such thing as a free lunch and this
technique is no exception; although its cost is time, by
using stellar bodies to propel a craft, a great amount of
effort is put into precisely planning, predicting, and
implementing each interaction.
• Long distance travel like for the Voyager missions are
limited by celestial body positioning, the Voyager two
mission for example was only made possibly by the
"Grand Tour" alignment of Jupiter, Saturn, Uranus and
Neptune. A similar alignment will not occur again until
the middle of the 22nd century.
• Even shorter missions can still be delayed by excessive
scattering of bodies though it is less common.
Sources
• Nasa.com
• http://www.planetary.org/blogs/guest-blogs/2013/20130926-gravityassist.html
• Pictures courteous of google
• Images are used for academic purposes only and are not owned by me.
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