Parking cargo in Mars orbit

Martinkh · 2004-01-17 22:04:06

Im familiar with satellite propulsion theories, Hohlman transfers and the like, but this is a bit much. Anyone here good with this stuff? I mean real good?

Good enough to figure out if you were to say, launch a 2 ton package from the moon, taking advantage of the appropriate forward momentum at certain times, how long would it take for that package to reach mars, where it could be placed in a parking orbit to await men? If a load was send every two months, even in sub-optimum conditions re earth-mars distance, how long would it take for say 6 bundles to get there? It could be a lfesaver to have emergency pods, ice chunks, fuel etc pre-positioned.

RobS · 2004-01-18 01:30:40

To answer your question, we have to assume a propulsion system. With chemical engines the amount of fuel to send something to Mars from the moon is reasonable about four months out of 26, and unreasonable the rest of the time (unless you can do a Venus gravity assist, which is possible for maybe three months out of nineteen). With nuclear thermal the window is longer; maybe six or seven months. With ion engines you can launch about any time, but travel times are more than a year always.

-- RobS

Martinkh · 2004-01-18 10:46:14

Is that constant thrust? What if the cargo was sent by timing the moons orbit, then launching from the moon to reach escape velovity from the moon, and allowing a big arc, with no further use of power until it is time to create the parking orbit.

Mundaka · 2004-01-18 14:29:02

Martinkh · 2004-01-18 14:42:48

Those orbits degraded because they were low enough to receive drag from the van allen belts (electrons and protons flying around, too fast to be taken to earth, too slow to excape). If we used a parking orbit well out of any Martian van allen belts, the orbits shouldn't degrade. I would imagine it would be easier to remotely deliver to orbit vs a moon, but then again, maybe a martian moon base instead of a martian space station would be a better starting point for Martian exploration.

dicktice · 2004-01-21 09:36:25

Martinkh: First off, I like your idea of contributing to a collection of useable "space junk" orbiting Mars, at least until it begins to be a navigational hazard. Simple capture by means of catching up gradually with the planet, to avoid aerobraking mechanisms, etc. Simply takes longer. But I would like to enlarge on your idea for launching the stuff (whatever it might happen to be) by means of a tether--not from Moon's surface, but piggy-back from a massive "smart rock," launched econimically from the surface just high enough to clear the highest peak in its orbit. The rock's mass and orbital speed would have to be great enough to sling the 1/10th (say) payload mass out to Mars, tangent to its orbit with just enough catch-up velocity. Some strap-on, mass produced communications, laser beacon, midcourse devices, etc. would add little to the cost, of say about once a Moon-day launch rate.

Martinkh · 2004-01-21 13:52:25

these rock/thether ideas all seem to me to violate the TANSTAAFL rule, otherwise known as Newtons third law.

I would imagine we would want to launch one package from the moon for every several delivered from earth, for economy sake, as the limiting factor in earh-moon deliveries will be mass, while the moon-mars parking orbit cost would be control systems, and missing the mark!!

Thus far, our space missions have been based on barely enough fuel to get the job done. The mars project has too many opportunities for variation in plan, and we need 2-3x as much fuel as is required to be on hand, in order to feel like it is not a suicide mission.

They have figured out "ideal" launch windows for Mars shots, so if we sent a package every 2 months for one year, how long before that window would we have to start the launch so that we would KNOW that all packages are in safe orbit before the men go? Hows that for a simple question!!!

dicktice · 2004-01-21 18:02:38

Martinkh: Here we go, again . . . the mass ramp-launched, or whatever, from Moon is simply a dumb mass to anchor the expendable tether's winch, which feeds 1,000 km or more twisted carbon ribbon, to be cut when the velocity vector is sufficient to coincide with Mars's orbit to be captured as a satellite in a highly eccentric orbit. Communication and beacon instrumentation devices accompany the valuable tons of payload, for location and mid-course correction reaction mass ejection(s), photon propulsive steering, etc. (Mere engineering details.) Your suggestion to use Moon was the key i.e., launching Moon-sourced materials and goods from Moon to Mars.. My contribution is to project into low (very low) orbit about Moon, a solidified mass of Moon regolith in whichever plane, and at whatever velocity required, from which to tether-launch the payload. The energy derived from the larger mass may be worked out to lower its altitude enough to smack into a Moon mountain, next revolution, to keep the nearspace clear of dangerous junk. Newton would have been proud! (Collecting and utilizing the payloads arriving in Mars-space every 30 sols or so, can be the subject of a next discussion--if you go along with the initial premise, that is.)

Martinkh · 2004-01-21 18:40:10

I was thinking launch the cargo in a direction that is tangental to the moons orbit such that the launch velocity is sufficient to escape the lunar pull (=> escape velocity), and timed such that the relative velocity in the direction of where mars will be at intercept is maximized. The escape velocity + the relative angular velocity would be quite a fast ride.

The energy of putting putting this cargo out on a "string" then cutting it at the right time is not a savings, as you must spend energy getting it up there to start with, Da? So why not just fire the darn thing at mars to start with? Sadly, if logic does not resolve this, math will have to. I'll let you start!!!!

Maybe I am being silly, but I am not a huge fan of applying forces to the moon itself that could eventually screw with it's stability. I realize we are talking about a small mass, but also a long moment arm.

dicktice · 2004-01-22 19:27:07

Martinkh: Last thing first--no matter how you accelerate an object on Moon's surface, it's going to cause an equal and opposite reaction. Digging minerals from which to manufacture rocket fuel constituents will affect the rotational rate and/or orbit of Moon about Earth. And a cockroach jumping into the ocean from Queen Mary 2 will change her draft and steering characteristics. But not enough to matter, right?
Next last and first thing--the string is merely a growth strategy to build on, when you run out of maglev track length enough to get up to velocity and/or need to change the plane of orbiting Moon, as Moon-Mars trip parameters change throughout their respective orbits about the Sun. Tethered accelerations can be as great as (1) materials and winch capacity allow (2) as lmassive a tether-anchor you can launch in whichever direction, to minimum-clearance Moon orbit.
But--how about doing a couple of test scenarios, beginning with what you might want to send, and take it from there, right out to Mars capture, and retrieval, say on Phobos?
Gotta go--to watch, and sympathize with those poor operators of the Mars rover that (unlike the little train that tried) just can't. At least for the moment. Real tough, but I have no faith in such slow, dumb remote-presence machines (not "robots" by any stretch) to obtain results in the brief professional lifetimes of people involved.
Gotta go now--to watch, and sympathize with those poor operators of the Mars rover that (unlike the little train that tried) just can't. At least for the moment. Real tough, but I have no faith in such slow, dumb remote-presence machines (not "robots" by any stretch) to obtain results in the brief professional lifetimes of people involved.

Pendragon · 2004-01-23 11:28:43

dicktice:

Maybe you could clarify for me, but what is the mechanism for momentum exchange between two tethered objects?

edit: Nevermind, I found a good explanation at tethers.com

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#1 2004-01-17 22:04:06

Re: Parking cargo in Mars orbit

#2 2004-01-18 01:30:40

Re: Parking cargo in Mars orbit

#3 2004-01-18 10:46:14

Re: Parking cargo in Mars orbit

#4 2004-01-18 14:29:02

Re: Parking cargo in Mars orbit

#5 2004-01-18 14:42:48

Re: Parking cargo in Mars orbit

#6 2004-01-21 09:36:25

Re: Parking cargo in Mars orbit

#7 2004-01-21 13:52:25

Re: Parking cargo in Mars orbit

#8 2004-01-21 18:02:38

Re: Parking cargo in Mars orbit

#9 2004-01-21 18:40:10

Re: Parking cargo in Mars orbit

#10 2004-01-22 19:27:07

Re: Parking cargo in Mars orbit

#11 2004-01-23 11:28:43

Re: Parking cargo in Mars orbit

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