

A New Way to Reach Mars Safely, Anytime and on the Cheap - softdev12
http://www.scientificamerican.com/article/a-new-way-to-reach-mars-safely-anytime-and-on-the-cheap/

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kartikkumar
The paper itself provides much more insight into the actual physics behind
this [1]. The article doesn't really do the paper justice in my mind, based on
my knowledge of the subject matter (although I appreciate the intent of
providing an accessible means to introduce the topic).

I wrote my MSc thesis on weak capture trajectories and the concept of the Weak
Stability Boundary [2] that was introduced by Ed Belbruno. It's a fantastic
aspect of the gravitational 3-body problem and has been probed from a number
of different perspectives over the last two decades, including tying in the
phenomenon of weak/ballistic capture into our understanding of the structure
of invariant manifolds and the periodic orbits about the Lagrange libration
points.

Disclaimer: Francesco is my boss but I haven't spoken to him yet about the
paper.

[1]
[http://arxiv.org/pdf/1410.8856v1.pdf](http://arxiv.org/pdf/1410.8856v1.pdf)

[2] [http://en.wikipedia.org/wiki/Low-
energy_transfer](http://en.wikipedia.org/wiki/Low-energy_transfer)

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r109
I hate all the fluff in this article.

TL;DR: Ballistic Capture aka "Low-energy transfer" is being rekindled by NASA,
Boeing, Belbruno, Topputo and colleagues. Fly the spacecraft ahead of Mars in
formation of the planets orbit relative to the sun allowing gravity to
gradually slow the spacecraft down. This saves on fuel/weight for entering
orbit at high velocity.

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iwwr
Unfortunately, Belbruno's work may stay unused because he has a penchant for
patenting it. The idea of low energy transfers aren't new and Belbruno didn't
invent them, but you can apparently patent individual trajectory strategies.
That also means any commercial venture would shy away from talking to him for
fear they may be litigated against (which has happened).

Another thing to notice is these trajectories are no good for manned travel as
they can take years or decades extra, they are even slower than the more
traditional multi-planet slingshot maneuvers.

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wallflower
Buzz Aldrin is very passionate about colonizing Mars [1]. He says there are
two big things that have to be accomplished before we can colonize Mars. The
first is to train astronauts to live in a confined isolated space for 260 days
(the length of a journey to Mars) [2]. This alternative journey trajectory
increases the 260 days.

The second is harder: We need to go to Mars at least three times and bring
back the men and women successfully. Once is not enough. Three proves we've
mastered the engineering, financial, physical, and physiological aspects.

[1] [http://www.pbs.org/wgbh/nova/space/aldrin-mars-
au.html](http://www.pbs.org/wgbh/nova/space/aldrin-mars-au.html)

[2] [http://www.guardian.co.uk/science/2010/jun/03/mock-
mission-m...](http://www.guardian.co.uk/science/2010/jun/03/mock-mission-mars-
moscow-hangar)

~~~
IshKebab
Wouldn't they have to live in a confined isolated space _on_ Mars too?

~~~
IndianAstronaut
Yes. Mars has an extremely thin atmosphere that would kill us if we did not
have pressurized suits and stations.

~~~
rjaco31
Don't forget the radiations. The main problem of the Mars atmosphere is that
it's too thin to stop enough of them for human beings.

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pavel_lishin
How much of a given total cost of a launch to Mars is the fuel? According to
the article, it shaves 25% off the fuel costs - but what percentage of the
total is that, let's say, for the past few missions?

It seems that the bigger advantage of this is adding a few months but doing
away with waiting for a launch window. Definitely great for equipment, though
it would put two months' worth of extra stress on actual human travelers.

~~~
tokenadult
_According to the article, it shaves 25% off the fuel costs_

Yes, by the facts and speculation reported in the article kindly submitted
here, the headline phrase "on the cheap" is plainly wrong, and "anytime" is an
exaggeration, as the overall trip time will tend to be longer for most such
missions. The article also notes, "The burn-free, capture altitude is also
quite high—some 20,000 kilometers above Mars, far beyond where science
satellites set up shop to scrutinize the planet up close. But taking along
just a little extra fuel can then gently lower a ballistically captured
spacecraft into scientifically valuable, standard orbits of around 100 to 200
kilometers like those achieved with Hohmann transfers—or even onward to the
Martian surface for a landing." So one part of the article says that the
mission will take less fuel (to leave the vicinity of earth), while another
part of the article says that the mission will have to carry along extra fuel
(in the Mars exploration modules) to arrive at a location where useful science
can be done. The bottom line here is that these missions will still be about
as expensive as current missions, and manned flight to Mars and back will be
staggeringly expensive.

~~~
pavel_lishin
But the trip time is only 2 additional months - which sure beats waiting over
two years for the next launch window!

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didgeoridoo
My KSP-fu is failing me here... how is it possible to match Mars' circular
solar orbit at a slower velocity? Wouldn't a different velocity imply a
different orbital distance from the sun?

~~~
Thrymr
Mars' orbit is not circular, and spacecraft's would not be, either. They would
be in slightly different (and intersecting, or nearly so) elliptical orbits,
which would allow Mars to gravitationally capture the spacecraft when it
approached closely enough.

~~~
ashark
Is performing a second burn to circularize a craft's orbit to near-sync with
Martian orbit really cheaper than a deceleration burn? In fact, that would
just be a complete Hohmann transfer.

I'd guess the target orbit for a craft performing this maneuver would still
have a periapsis in the neighborhood of Earth's orbit, meaning it'd still be
very unlike Mars' orbit until the craft was captured by Martian gravity.

(googles a bit)

It looks like these exploit Lagrange points somehow[1]. Precision maneuvers
and weird, long routes to the target body. I'm not quite following how this
works with only two bodies (Sun and Mars), versus the Sun-Earth-Moon trio.
Wikipedia claims the Mars Orbiter Mission used a low-energy transfer at some
point, but I can't figure out whether that was for the insertion into Martian
orbit or some earlier maneuver it performed.

[1]
[http://www.gg.caltech.edu/~mwl/publications/papers/lowEnergy...](http://www.gg.caltech.edu/~mwl/publications/papers/lowEnergy.pdf)

[edit] Hoffman -> Hohmann, because I'm an idiot.

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blisterpeanuts
[https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion](https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion)

With nuclear pulse propulsion, we could send a craft to Mars in 2-3 weeks,
safely, any time, and on the cheap.

The mass that can be transported is quite enormous, so we could piecemeal
launch the components of a huge habitat and vast amounts of supplies into an
outer orbit of Earth, robotically load them onto the pulse ship, and then
shoot that baby to Mars.

Probably the slowest part of the plan would be launching the stuff into orbit.
They scrubbed the idea of launching using nuclear pulse propulsion because of
the dangers of radioactive fallout. Too bad, because that would have made
things even simpler.

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kristianp
Web design tip (that I just made up). If you're going to have an annoying,
large header bar appear above the text when the user scrolls, don't put a
drop-shadow under it. It looks like an object is hiding the text, which it is,
but is very distracting compared to a flat border.

~~~
dwaltrip
I've gotten into the habit of doing: right click, inspect element, and then
"delete node" on these headers. I really should create a chrome extension to
reduce the friction in doing this.

~~~
kristianp
That would be cool. It would be nice to have an extension with a database of
sites to automatically remove these space-wasters.

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nicholasreed
For a fun (fictional) take about life on Mars, I'd recommend reading The
Martian by Andy Weir ( amazon link: [http://www.amazon.com/The-Martian-Novel-
Andy-Weir-ebook/dp/B...](http://www.amazon.com/The-Martian-Novel-Andy-Weir-
ebook/dp/B00EMXBDMA) ). The book was a wild read, and does a tremendous job
showing the myriad difficulties humanity must overcome in order to colonize
Mars.

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Animats
What this really means is that cargo deliveries to Mars can be made any time
in the orbital cycle; it's not necessary to wait for a close approach. The
trip takes a few months longer, but can be started at any time. Useful if
there are ever any significant operations on Mars.

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markbnj
I was surprised that they described a Hohmann Transfer as a "brute force
approach to attaining orbit." I would have described it as the non brute-force
approach to changing orbits.

~~~
theoh
Yeah, exactly. It also seems like this low energy technique is more or less a
Hohmann transfer to a different point in Mars's orbit. The energy is saved by
not arriving at Mars with a big velocity relative to the planet, which feels
kind of extraneous to the question of whether a Hohmann transfer is used or
not. Maybe it's the final Hohmann transfer into orbit around Mars they are
referring to? That would make sense. Or is that obvious?

~~~
markbnj
Honestly I think they just got the terminology wrong. The only difference
between this and a normal Hohmann is the means used to get the final change in
velocity at the end. By which time the whole "transfer" part of the show is
over. Otherwise it's just a normal transfer orbit.

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melling
Maybe now there will be a Mars X-Prize after we complete the Lunar X-Prize:
[http://lunar.xprize.org/](http://lunar.xprize.org/)

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nazca
Anyone have a gif/video of the 'ballistic capture' method?

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stefantalpalaru
No, but these static images describe it pretty well:
[http://ccar.colorado.edu/asen5050/projects/projects_2012/tru...](http://ccar.colorado.edu/asen5050/projects/projects_2012/truesdale/intro.html)

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japaget
This link describes "Halo Orbits" about the L1 Lagrangian point of the Earth's
orbit around the Sun. Mars isn't even mentioned.

~~~
stefantalpalaru
That's because using it with Mars is a novel concept. The mechanism, though,
is the same.

