back to article ESA proposes ion drive Sun-dodge Mars commsat ploy

Experts in interplanetary navigation have hit upon a novel scheme for maintaining communications with Mars, should a need to do so eventuate - as in the case of a manned mission to the red planet, for instance. Diagram of the proposed Mars commsat orbits, looking in the plane of the ecliptic. Credit: Universities of …


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  1. rpjs

    Lagrange points

    Wouldn't putting a commsat in one of the Eart/Sun or Mars/Sun L4 or L5 points be easier?

  2. M7S

    The Ice Warriors cometh

    after all, they wouldnt be the first to use our own satellites against us.

  3. frank ly

    Signal Delay?

    "...the time taken for messages to travel back and forth - already some hours when Earth and Mars are far apart."

    The Earth is 'only' 8 light minutes from the Sun and is 1 AU from the Sun.

    Mars orbit is about 1.5 AU from the Sun (you're getting the sense of scale here...).

    So, how come it takes 'some hours' for a signal return trip Earth-Mars when Mars is at the other side of the Sun? It should take about 40 minutes. (I've drawn a diagram, I think I know what I'm doing here). Even allowing for elliptical orbits and wobbles etc, I don't see how they can say 'some hours'.

  4. Gianni Straniero

    Re: Lagrange points

    Interesting idea. It seems Mars-Sun L4 and L5 have asteroids, which might be a bit inconvenient. they're both 750 light seconds from Mars, so radio links would still be slow.

    I don't have a chart to hand, so I'm not sure if Earth-Sun L4 and L5 would also be occluded during conjunction.

  5. Cameron Colley

    I'm still not playing

    Counterstrike with those HPB Martians.

  6. Bernard Lyons


    "Eventuate" IS NOT A WORD. I don't care if it's used in Australian English, it's STILL not a word.

  7. Anonymous Coward
    Anonymous Coward

    Radio times to Mars

    "...the time taken for messages to travel back and forth - already some hours when Earth and Mars are far apart."

    No they don't - trip times to Mars vary from just over 3 minutes when Earth is closest to the planet to about 22 minutes when they're on opposite sides of the Sun. Double that for a round trip. If you're being put on hold for 'some hours' when calling Mars you should consider changing your operator.

  8. The Mighty Spang

    witches in space?

    don't you mean occluded rather than occulted?

  9. Anonymous Coward

    @frank ly

    The problem isn't the time it takes to get the information there, it's the amount you can get. Ever watched a video on youtube using dialup? Well, dialup is fast compared to what you can get

    when you comunications over this long a distance, because signal strench will cause serious problems. That's why getting a message there takes a long time.

  10. frank ly

    @AC 00:53 re. @frank ly

    Time taken for a signal to travel back and forth - about 40 minutes. (speed of light limited)

    Time taken for a 'message' to be transferred - some hours. (channel bandwidth limited)

    Ok, that should make it more understandable.

  11. DJV Silver badge


    Blimey, I've got a couple of collections of SF stories by George O Smith based on similar (but scaled up) ideas. They were written in the late 1940s and all the technology was based on valves! Fantastic.

    Mines the one with the Venus Equilateral collections in the pocket...

  12. D. M

    Did I remember

    TIE standards for Twin Ion Drive?

    *it is no moon, it is a space station*

  13. frank ly

    @ The Mighty Spang re. witches in space

    He means 'occulted'. Dictionaries are so useful, check it out.

  14. Ken Hagan Gold badge

    Re: @frank ly

    "Well, dialup is fast compared to what you can get when you comunications over this long a distance..."

    Case in point, during the recent LCROSS mission, the controllers clearly dropped the bandwidth they were prepared to allocate to one of their live cameras to 0.1Mbps. And the moon is several hundred times closer than Mars, and radio signal strength falls off with distance squared (which is another reason why Lagrange points aren't as useful as they might seem).

    Second case: the transmitter on Voyager 2 is about 30 watts and can still be picked up by the Deep Space Network, but only at very low bandwidths. During the fly past Neptune, they needed more bandwidth and had to use the Very Large Array instead. According to, Voyager 2 is currently managing 7.2 kilobits per second (so yes, less than dial-up) when the weather is nice. (What NASA really needs is a whacking great receiver dish in Earth orbit, but that's not sexy.)

    You have to extract signal from noise, so you can either send less signal (more clearly) or send a louder signal. The theoretical limit is given by the Shannon-Hartley theorem.

  15. Tim Cockburn

    Better latent than never

    "signal strench will cause serious problems." I assume the strench is caused by the methane in the martian atmosphere .

  16. Andus McCoatover

    Tales of the bleeding obvious?

    Sodding hell. Aint that why we have satellites?? And, which Lagrange Points (LP's)? Earth's, or Mars'? . How about parking the repeaters in moon's LP's? More sunlight == more power, Shirley.

    (Oh, yep, I always wondered how NASA got a well-panned shot of the Apollo 11 LEM launching from the moon. Their explanation went something like "Camera operator anticipated the 4 seconds signal transmit time". Except, it ain't 4 seconds. It's 2.7. Only, that's return time, so it's really about 1.35. One way. Maybe moon seconds. Yo, that'll do it. NOT.

    Not one to doubt Armstrong and Aldrin didn't come back with green cheese on their boots, but...)

  17. Peter Stone

    Fact copying fiction?

    Wasn't this problem solved in the 18940's? In the Venus Equlaterial series of stories?

  18. TeeCee Gold badge

    @Tim Cockburn

    Nah, everyone knows that as these conditionalities commence to excurse the eventuation of strench is unavoidablized.

  19. Anonymous Coward
    IT Angle


    Yes, 'eventuate' is a word; an ugly, unneccessary word like 'bachelorette', 'burglarize', etc.

  20. Bounty

    inclined orbint around sun?

    Why not just put a relay in an inclined orbit close to, and around the sun? The delay would be short. Only need 1 sat. As a bonus, it could work as a relay for all planets. (Something like Venus to sun relay sat to Earth would be better than bouncing it off of the Mars sat.) I think the chances of Mars behind the sun and an inclined relay sat in a close orbit to the sun transiting or also being behind the sun are like, super rare.

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