To Mars and Back With Less Fuel

One of the facts about space travel, when done with rockets, is that if
you need to execute a manoeuver requiring a large delta-V in order to
come back from where you went, then the amount of fuel needed to send
you there has been multiplied many times over because your return fuel
had to be sent with you.

We are all familiar with the plan of Dr. Robert Zubrin to alleviate this
issue by sending only hydrogen to Mars, which can be used to produce
oxygen and methane by reacting with the carbon dioxide in the Martian
atmosphere.

NASA proposed a Mars Reference Mission, in which production of fuel on
Mars was scaled down, to just enough to launch a capsule into orbit to
rendezvous with the return craft.

Originally, I proposed a modification of Dr. Zubrin's original plan to
cut it up into smaller pieces. But now I think that a plan with even
smaller fuel requirements can be constructed using the Mars Reference
Mission as a basis.

The amount of fuel produced on Mars is increased, however; to a level
greater than that required to put a small ship into Mars orbit, but less
than that required to send a large ship, on which astronauts can be
provided life-support for the long journey home, on a Hohmann orbit back
to Earth.

I propose that the asronauts begin their journey home by using the fuel
produced on Mars to launch a small craft into an orbit that would return
it to Earth.

But in that craft, they would rendezvous with a larger craft, launched
*three years previously* from Earth, in a 1.5 year free-return orbit,
which would have the supplies they need to survive on the long journey
back.

This avoids sending to Mars the fuel needed to provide a large delta-V
to a large ship. It does pose risks, as making the return rendezvous is
critical. The fuel savings may be enough as not to be entirely offset by
launching two return ships.

John Savard
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isn't this just Aldrins 'Mars Express'

http://www.popularmechanics.com/scie...tml?page=5&c=y

John Savard wrote:


But in that craft, they would rendezvous with a larger craft, launched
*three years previously* from Earth, in a 1.5 year free-return orbit,
which would have the supplies they need to survive on the long journey
back.

This avoids sending to Mars the fuel needed to provide a large delta-V
to a large ship. It does pose risks, as making the return rendezvous is
critical. The fuel savings may be enough as not to be entirely offset by
launching two return ships.

The 1.5 year orbit would make it a Niehoff cycler. Niehoff cyclers
exploit the fact that 8 Martian years are very close to 15
Earth years. There are two types of Niehoff cyclers: the VISIT 1 and
VISIT 2.

The VISIT 1 has a 1.25 year period and passes earth every 5 years and
Mars every 3.75 years.

The VISIT 2 has a 1.5 year period, passes earth every 3 years and Mars
every 7.5 years.

Mars doesn't have a period of _exactly_ 15/8 years, so it will slowly
drift from the rendesvous point. However, this can be compensated for by
using Earth or Mars gravity assists to slightly rotate the line of apsides.

The Aldrin cycler passes both planets much more frequently, close to the
Earth Mars synodic period 2 1/7 years. However the Aldrin apohelion is
clear out in the asteroid belt. IIRC the Martian and Aldrin cycler
velocity vectors are at about an 80 degree angle when the cycler passes
Mars. This results in horrendous delta vee requirements to match Mars
velocity. The Aldrin cycler also needs to rotate it's line of apsides to
keep synchronized with Mars. However the apside rotation requires more
delta vee than the Niehoff rotation. Considerable fuel must be spent for
this while the Niehoff rotation can be accomplished almost completely
with Earth or Mars gravity assists.

The Niehoff cyclers consume much less fuel than Aldrin because they're a
lot closer to the Earth/Mars Hohmann orbit.

In the March 2000 issue of Scienfific American there is an article on
Mars Cyclers by James Oberg and Buzz Aldrin. It is well worth reading IMHO.

Hop

BlagooBlanaa wrote:

isn't this just Aldrins 'Mars Express'

http://www.popularmechanics.com/scie...tml?page=5&c=y



Thanks for a good link!

As I mentioned in my reply to Savard, Aldrin's cycler passes earth and
Mars more frequently, but delta vee requirements are higher as the 1.5
and 1.25 year cyclers are much more Hohmann like.

Hop

On Wed, 07 Jun 2006 07:17:17 -0700, Hop David wrote,
in part:

As I mentioned in my reply to Savard, Aldrin's cycler passes earth and
Mars more frequently, but delta vee requirements are higher as the 1.5
and 1.25 year cyclers are much more Hohmann like.

Since Mars' orbit is elliptical, it is possible for something with an
orbital period of less than 1.41 years, that of the Hohmann orbit, to
reach Mars. At first I thought that 1.25 years was pushing it, but then
I realized that one could achieve this with an orbit part of which was
spent closer to the Sun than Earth is.

I was wondering about the originality of this idea - for all I knew, von
Braun might have suggested it first, or Oberth - but I had thought it
distinct from the concept of a cycler.

A cycler would have to be a fairly big installation, since it would be
envisaged as remaining useful indefinitely. I'm envisaging the launch of
two craft, one to bring the astronauts to Mars, and one to take them
back, that are not much larger than what would be required to provide
the astronauts with life support on their journey anyways. The goal, of
course, is actually to *shrink* them, by not having to provide enough
fuel to obtain any significant delta-V at Mars or elsewhere in space.

Anything that can sit around for three years and still support
astronauts, though, may well wind up being very close to usable as a
cycler in any event. If that's the case, it just goes to show how
daunting a journey to Mars really is.

John Savard
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On Wed, 07 Jun 2006 07:07:25 -0700, Hop David wrote,
in part:

The Aldrin cycler passes both planets much more frequently, close to the
Earth Mars synodic period 2 1/7 years. However the Aldrin apohelion is
clear out in the asteroid belt. IIRC the Martian and Aldrin cycler
velocity vectors are at about an 80 degree angle when the cycler passes
Mars. This results in horrendous delta vee requirements to match Mars
velocity.

Looking at the Popular Mechanics article, I see he addressed that with a
proposal for a "Semi-Cycler", which, except for being smaller, has at
least a superficial resemblance to the type of return craft I'm
proposing.

At least, though, it should be clear my goals are very different. Dr.
Edwin Aldrin is aiming at setting up, with a major initial expense,
something that will make exporation of Mars at least a semi-permanent
activity. I'm trying to reduce the minimum *entry* cost for a single
initial mission to Mars - which will differ from a "flags and
footprints" mission in the sense that the astronauts will spend months,
rather than years collecting rock samples and the like.

Given that a module which will support the astronauts for three years
will also be going with them to Mars (in case of a lander failure)
(assuming a 2-year orbit's higher fuel requirements are worse than
making it last for 3 years instead of 2), not only might such a module
be close to what is required for a cycler, it might be such as to permit
permanent colonization of Mars. But I'm assuming that bottled water and
canned food, rather than an O'Neill colony with a functioning ecosystem,
would be what was sent at least for the return journey (there, 3 year
survival time of the ship is required, but not 3 years of supplies:
failure to land on Earth does not bear thinking about).

John Savard
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Silly question: are there any asteroids in cycler-like orbits?
--
http://www.cic.gc.ca/english/immigrate/
http://www.livejournal.com/users/james_nicoll

John Savard wrote:

On Wed, 07 Jun 2006 07:17:17 -0700, Hop David wrote,
in part:


As I mentioned in my reply to Savard, Aldrin's cycler passes earth and
Mars more frequently, but delta vee requirements are higher as the 1.5
and 1.25 year cyclers are much more Hohmann like.


Since Mars' orbit is elliptical, it is possible for something with an
orbital period of less than 1.41 years, that of the Hohmann orbit, to
reach Mars. At first I thought that 1.25 years was pushing it, but then
I realized that one could achieve this with an orbit part of which was
spent closer to the Sun than Earth is.

When the perihelion is less than 1 A.U., the cycler crosses earth's
orbit twice. This might make for more frequent fly bys and decrease the
need for rotating the line of apsides.

On the negative side, the cycler's velocity vector wouldn't be parallel
with earth's velocity vector during fly by. This would increase the
taxi's (to borrow Aldrin's term) delta vee expense.


I was wondering about the originality of this idea - for all I knew, von
Braun might have suggested it first, or Oberth - but I had thought it
distinct from the concept of a cycler.

A cycler would have to be a fairly big installation, since it would be
envisaged as remaining useful indefinitely.

I don't think it'd have to start out big. At first it need not be much
more elaborate than a Zubrin Mars Return Vehicle. It could be added onto
over time.

I'm envisaging the launch of
two craft, one to bring the astronauts to Mars, and one to take them
back, that are not much larger than what would be required to provide
the astronauts with life support on their journey anyways. The goal, of
course, is actually to *shrink* them, by not having to provide enough
fuel to obtain any significant delta-V at Mars or elsewhere in space.

Anything that can sit around for three years and still support
astronauts, though, may well wind up being very close to usable as a
cycler in any event. If that's the case, it just goes to show how
daunting a journey to Mars really is.

Aldrin calls the main body of the cycler a "Castle". And I believe
they could well evolve into huge castle like structures. But like I said
earlier, the first incarnation would resemble a more ordinary MRV.


John Savard
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John Savard wrote:

Dr. Edwin Aldrin is aiming at setting up...

Minor nitpick.

Aldrin has legally changed his name to "Buzz" so he is now both
formally and informally "Dr. Buzz Aldrin", not "Dr. Edwin Aldrin".

Jim Davis

James Nicoll wrote:

Silly question: are there any asteroids in cycler-like orbits?

Strange coincidence - I just started playing with asteroids again.

Excel isn't exporting these web pages very well

Asteroid Orbit
blue dot - perihelion
red dot - apohelion

Earth Orbit
Darkest blue dot - Earth position at asteroid perihelion.
Lighter blue dots - Later earth positions at asteroid perihelions.

Mars Orbit
Red slash mark - Mars position at asteroid apohelion
Lighter pink slash marks - Later Mars positions at asteroid apohelions

Blue line - Asteroid ascending & descending node.

http://clowder.net/hop/Visit1/1993PC.htm
http://clowder.net/hop/Visit1/1998KG3.htm
http://clowder.net/hop/Visit1/1999VT25.htm
http://clowder.net/hop/Visit1/2000WG10.htm
http://clowder.net/hop/Visit1/2003UD22.htm
http://clowder.net/hop/Visit1/2003UX26.htm

It is interesting that earth positions during perihelion
form slowly rotating squares. Mars positions during apohelion
form slowly rotating triangles.

NEO search programs NEAT and LINEAR have been charged with finding
potential Chicxulubs. But some are lobbying that the search be widened
to find potential Tunguskas. Hope they get funding for that.

I think it's a safe bet that when they get a thorough inventory of the
smaller asteroids, the above list will be larger. A smaller asteroid can
provide radiation shielding but is much more amenable to having its
orbit changed.

Also it would be an easier political sell to have have a 30 meter
asteroid tweaked for frequent earth fly bys. If it happened to hit the
earth, it'd burn up harmlessly in the upper atmosphere. I wouldn't want
a 1 kilometer asteroid tweaked for frequent earth fly bys.

Later I will put up some possible Visit2 asteroids.

Hop