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New Kind of Orbit Could Ease Mars Communications
Posted by
kdawson
on Fri Oct 16, 2009 10:02 AM
from the crossing-gravitational-gradients dept.
from the crossing-gravitational-gradients dept.
japan_dan writes "An interesting way to enable Earth-Mars communication when the Sun occludes the direct radio line-of-sight: ESA proposes placing a pair of continuous-thrusting relay satellites, using a solar electric propulsion system — one in front and ahead of Mars, the other behind and below — with both following non-Keplerian, so-called 'B-orbits'. This means the direction of thrust is perpendicular to the satellites' direction of flight, allowing them to 'hover' with both Earth and Mars in view. Quoting from the Q&A: 'We found that a pair of relay satellites would only have to switch on their thrusters for about 90 days out of every 2.13-year period, and this solution would only increase the one-way signal travel time by one minute, so it could be effective.'" Here is the paper describing non-Keplerian orbits (PDF).
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That's good news (Score:5, Funny)
Re: (Score:2, Funny)
You'd think, but the fools are assuming the extra minute of round-trip communication time isn't a problem because it doesn't seriously affect their reaction times. But they fail to understand that in the Martian language, time is a critical component of meaning! And extra minute of latency could make the difference between saying "We accept your offer of peaceful relations. We will begin transmitting cultural information immediately," and "We accept your offer of peaceful relations... Psych! We will beg
Re: (Score:2)
I don't think that we should attempt communication communication with the martians at all until they contact us. From what I've read [wikipedia.org], they can grok our meaning without much trouble (partially due to psychic abilities). However, their lack of adherence to our conservative moral platforms and religious dogma may doom our relations to tragic failure...
Re: (Score:3, Funny)
They're interior decorators so it looks great on the inside. If they can meet up with a race of landscape designers everything will be beautiful.
Re:Or their aesthetic sense. (Score:4, Funny)
Parent
Re: (Score:2)
Laugh, but just the fact that we're collectively trying to work out the problems of interplanetary communication now that we'll certainly have in the future (if we don't destroy ourselves) made my day.
Re:That's good news (Score:4, Funny)
As long as we don't go bombing their planet to look for water.... that's BAD for relations.
Parent
Wouldn't it make more sense.... (Score:5, Interesting)
Re: (Score:3, Informative)
I didn't know about L4 and L5 so looked it up:
http://en.wikipedia.org/wiki/Lagrangian_point [wikipedia.org]
I think any satellite requires some fuel for thrusters to correct the orbit.
Re: (Score:3, Informative)
L4 and L5 are actually the most stable lagrange points. The satellites would end up basically orbiting the lagrange point itself.
Re:Wouldn't it make more sense.... (Score:4, Informative)
Minor correction: they're the *only* stable Lagrange points. (And only then if the mass ratio of the primary and secondary body is high enough.)
Parent
Re: (Score:3, Funny)
...on the house outside LaGrange
Just let me know
If you want to go
To that home out on the range
They got a lot o' nice girls there...
-ZZ Top singing about outer space
Re:Wouldn't it make more sense.... (Score:4, Informative)
Doesn't matter. If the sun is between Mars-L4/5 and Earth, then Mars is visible from Earth. Likewise, if the Sun is between Earth-L4/5 and Mars, then Mars is visible from Earth.
The only case where you need these relays is if the Sun is between Mars and Earth (or close enough to a direct line to make a hash of radio communications between Mars and Earth), and in any such case, none of the L4/5 points (either Mars or Earth) will be blocked from either of the two planets.
Parent
Re: (Score:3, Interesting)
The idea isn't exactly new, you know. George O. Smith wrote a series of stories about a relay station in the L4 point of Venus, The Venus Equilateral series, [wikipedia.org] back in the '40s. It was a communications hub for the entire Solar System, and a hotbed of technological innovation. Great stories, still worth reading.
Re: (Score:3, Informative)
Wouldn't the Lagrange points also be occulted by the sun, though not at the same time as the planet? Also the distance would be a lot longer, as Nadaka said above.
Re: (Score:2)
I started to right the same message, but did some research first. The l4 and L5 points are 60 degrees off of the minor body's position. Therefore when Earth-Mars is out of sight, a communication satellite at this point could be used.
Re:Wouldn't it make more sense.... (Score:5, Informative)
Look up 1940's science fiction about the Venus Equilateral Relay Station by George O. Smith http://en.wikipedia.org/wiki/Venus_Equilateral [wikipedia.org]
Parent
Re: (Score:3, Insightful)
Re: (Score:3, Funny)
Witch ever way you slice there'd be no spell when both Earth and the satellites were blocked by the Sun so it's a wizard idea.
Re:Wouldn't it make more sense.... (Score:4, Insightful)
Also, to be pedantic, you would still need some fuel on a LaGrange spacecraft for station-keeping purposes. Though this amount would be minimal, you can't justifiably claim that you wouldn't need *ANY* fuel.
Cheers Mate.
Parent
Re: (Score:2, Funny)
~Your friendly RIAA rep
Re:Wouldn't it make more sense.... (Score:5, Informative)
The receiver/transmitter on these satellites and space probes are very small. Generally they transmit using only a few watts, and we rely on huge antennas like in the ubiquitous dishes in the Deep Space Network to gather enough of that minuscule signal to distinguish it from background noise. Going the other way, we use the same huge antennas to blast commands to these spacecraft at anywhere between 5-500 kW. By the time the signal reaches the spacecraft, it has dissipated substantially, but its original broadcast power was high enough that the spacecraft's relatively small antenna can still collect enough of it to distinguish the signal.
Putting a repeater spacecraft at the L4 or L5 points would place them a substantial distance from Mars. Consequently the repeater would need a very large antenna and large amounts of power (though not as big/much as earth-based antennas) in order to relay signals to/from a spacecraft on Mars. The idea presented in the paper is more akin to what we do right now with the two Mars Rovers and several of our Mars orbiters. The Rovers themselves have weak antennas and can't communicate directly with Earth except at low data rates. Instead, they transmit their data to the orbiters (same antenna can achieve higher bandwidth since the distance is much less), which then relay it to Earth using their much larger and more powerful antenna.
(Introduction to channel capacity [wikipedia.org] for those who may be wondering what the relationship is between data transmission speed and signal to noise ratio.)
Parent
Not quite (Score:5, Informative)
Would it?
Mars has an aphelion (maximum distance from sun) of 250 Gm, and the Earth has an aphelion of 150 Gm. So when the sun is occluding their line of sight, they are on opposite sides of the sun and are separated by at most 400 Gm. If you had a satellite in the Earth's L4 or L5 point, then this would form a 150,350,400 Gm triangle with Mars. Thus the total signal distance would be 500 Gm. This would add 100 Gm, increasing the transit time by 5.5 minutes (from 22.2 to 27.7 minutes). Not as good as the solution presented but not twice as long.
Placing these in the Earth's orbit, rather than Mars', would have the added advantage of solving the solar occlusion problem for anything we send out into the solar system, not just for things on Mars.
Parent
Re:Not quite (Score:4, Interesting)
The original article was mentioning satellites following/leading mars. With the satellites in mars Lagrange points, the distance would be longer, though not entirely double.
What the hell, I'll bother to do the math this time, using your figures of 150 Gm and 25 Gm that would result in a maximum distance from earth the a mars Lagrange point at about 350 Gm, plus the 250 Gm to mars gives a distance of ~600 Gm vs the strait line of 400 Gm. so its a ~50% increase in time.
Of course I could get pedantic and claim I was talking about the difference in time. But that would be fudging to cover my my lazy ass failing to math.
Parent
Re: (Score:3, Informative)
Satellites as a rule aren't maintained or refueled, they're simply shoved somewhere where their decrepit hulks can hit anything useful. Cheaper that way oddly enough.
Who needs full-time communications (Score:5, Funny)
Houston> We haven't talked for a day, what's up?
Mars rover> Hey, I moved one meter!
Houston> No shit!
Re:Who needs full-time communications (Score:5, Funny)
Parent
Cita tion need ed (Score:2, Informative)
FYI: there is no article on Wikipedia to describe a non-Keplerian orbit.
Even 2 simple diagrams describing the 2 orbits types would help.
Re: (Score:3, Insightful)
Orbital resonance, anyone? (Score:2)
Still, there may be something exotic that could be done.
Eh? (Score:3, Funny)
I understand "behind and below". WTF is "in front and ahead"?
Re: (Score:3, Insightful)
Yup, prolly should have been "in front and above".
Re: (Score:2)
Ah. I was only thinking in terms of Mars' orbital track.
Bandwidth (Score:5, Insightful)
This is slightly tangential, but worth noting I think:
This will be handy when we can't afford to lose contact with Mars for even a few days, but there's a bigger problem lurking in inter-planetary communications: bandwidth. We don't really have enough Deep Space Network dishes (particularly, the large 70-m ones) to talk to all of our missions as much as we should. We're sacrificing data collection on billion-dollar missions on a daily basis on the grounds that we don't have enough bandwidth to get it back. When we put people or even just more missions on Mars, that'll only get worse.
Re: (Score:3, Funny)
Immature (Score:5, Funny)
How about.... (Score:2)
...we let go of the harakiri you're supposed to commit if you ever go out of cell phone range? I mean, surely we can outfit an expedition that doesn't need 24/7 babysitting from mission control, It's not like Columbus had queen Isabella call him up every night to ask "Are you there yet? Food supply ok? Your blood sugar values are low, you should eat more."
Re: (Score:3, Insightful)
ANKOS... (Score:2, Funny)
A New Kind Of Science...er...Orbit. I wonder if Wolfram will try to take credit for this, too. Maybe there's an automata to describe it.
For those who don't RTFA (Score:4, Insightful)
To clarify - this sort of "orbital" motion (not really "orbital" since it actively powered) is hardly a new idea. What is relatively new is the fact that you have engines that permit you do do it without prohibitive fuel consumption. It's different from a hovering rocket-propelled lander (like the DC-X) only in scale. The key feature, not clear in the article, is that you are intentionally thrusting along the local vertical, in the direction of gravity, to modify its effects. That was possible and everybody knew about it since, well, Newton figured out gravity. What we haven't been able to do is to maintain it for more than the briefest periods due to excess fuel consumption.
The new part here is the Hall Current thruster, which is ~factor of 10 more efficient than traditional engines. The specific impulse of these is around 1800 seconds (lb-sec of impulse per lbm of fuel- hey I didn't invent the units, I just use them...) compared to maybe 180 for a hydrazine monopropellant thruster. These are not exactly "new" either, the Russkies have been using them for decades. Only recently has the western world begun to develop them, so it's new only in that sense. So the solution they are looking at is now looking reasonably practical, although no doubt still significantly limited by the fuel consumption.
Brett
Re: (Score:3, Informative)
Hey, ISP is in seconds, it's an industry standard. The SI version isn't any better - kgf-sec/kg. It makes more sense when you realize it's proportional to the exhaust velocity, which is in, say, feet/second.
Brett
Re:For those who don't RTFA (Score:5, Insightful)
Hey, ISP is in seconds, it's an industry standard.
But it shouldn't be. N*s/kg is the correct unit for specific impulse. "Seconds" is only used by American engineers who don't understand the difference between weight and mass.
When I was a kid I was deeply interested in space, but it wasn't until years later that I understood the meaning of Isp because of the idiotic convention of designating it in seconds, rather than force*time/mass, which makes its meaning completely obvious.
If you want to turn people off an understanding of the most basic aspects of space travel, by all means go ahead and keep using seconds for Isp. But it's really time for the United States to get with the rest of the world and abandon Imperial units, although I guess as an imperial power they seem like a natural fit.
[Ok, now wondering if this'll get more "troll" or "flamebait" mods. It should probably lean toward "flamebait", as the story is true: Isp in seconds really did confuse me for years. The egregious America-bashing is, well, egregious, so probably warrants a flamebait mod. But really, what's with the Imperial units, kids?]
Parent
Re: (Score:2)
Since there's barely anything useful on the Moon given the cost of getting it, and there's even LESS useful on Mars
Hmmm and what about the experience in design, contruction, operation and manteinance of ships, tools, environment and crews to get there?
how are we suppose to left this rock if don't start trying to get to the nearest, not so deadly rocks around here?
Egss in a basket on something like that i hear it's called...
Re:lets wake up here (Score:5, Funny)
I agree, even 6 year-olds are doing it.
Parent
Re:lets wake up here (Score:5, Insightful)
The only reason private enterprise is able to *think about* real space travel is because they are using the ~40 years of NASA knowledge and research.
http://science.howstuffworks.com/ten-nasa-inventions.htm [howstuffworks.com]
Ok so this is really basic, but also aerogel, and a laundry list of other things.
Being on Mars is really cool, and we have learned a lot about it. But as for usefulness it tells us maybe mining Mars wouldn't be that profitable (but did we know that before). But all the stuff they used to get to Mars, that shit trickels down FAST. I mean I personally believe that SSDs on the rovers are wat put them into the main stream. They lasted in a super harsh enviroment orders of magnitude longer than they were supposed to. So keep thinking all NASA produces is cool photos.
Parent
Re:lets wake up here (Score:5, Insightful)
What are you doing at a nerd site? Money is the LAST thing a nerd is thinking of when (s)he thinks of space. Space is for technological and scientific advancement. Sue, there will be money made in the future, but private enterprise operates on the next fiscal quarter.
NASA is doing ot because (duh) THERE'S NO MONEY IN SPACE EXPLORATION and money is the only reason for private enterprise to even exist.
Parent
Illudium Phosdex shortage! (Score:2)
"I have sent for you, Dodgers, because we are facing a crisis. The world supply of Illudium Phosdex, the shaving cream atom, is alarmingly low. Now we have reason to believe that the only remaining source is on Planet X, somewhere in this area."
"And you want me to find Planet X, eh?"
"Can you do it, Dodgers?
"Indubitubly, sir, because there's no one knows his way around outer space like... Duck Dodgers, in the twenty-fourth and a half
century!"
Re: (Score:3, Insightful)
Since there's barely anything useful on the Moon given the cost of getting it, and there's even LESS useful on Mars
Since you know the exact chemical composition of the entirety of the moon and Mars, would you mind sharing with the rest of us?
Re: (Score:2)
Booo, that paper was arcane but interesting.
Re:Why not above? (Score:5, Informative)
"Surely there is a stable point somewhere above the sun?"
No.
Gravity is always pulling you down, but there are places in the solar system where gravity balances out. These are called Lagrange points and space agencies use them as stable places to put spacecraft. If you're not in one of those places, you're happily going to fall on/in-to the object or end up in some sort of orbit going around the object, but you're not going to be motionless or synced up with anything.
All stable points within our solar system (L1/L5) are on the ecliptic plane iirc.
Parent