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Space Science

How to Navigate a Spacecraft to Mars 67

Posted by Hemos from the fly-me-to-the-moon dept.
EccentricAnomaly writes "JPL has an article on how to design trajectories to Mars with the porkchop plot. They use an interesting analogy between reading these plots and divining the future from animal entrails. JPL also has the most excellent Basics of Spaceflight, which is an easy to understand tutorial on how to explore deep space."
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How to Navigate a Spacecraft to Mars More

How to Navigate a Spacecraft to Mars

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  • Step one of plotting a trajectory to Mars (Score:5, Funny)

    by kfg ( 145172 ) on Saturday November 03, 2001 @05:20AM (#2515860)
    Make sure everyone is using the SAME friggin' system of units.

    KFG

  • Oh no! (Score:1, Funny)

    by snake_dad ( 311844 )
    You know that the best vacation destinations always lose their attraction when people start publishing travelguides and maps and stuff... :-/

  • Basics of Space Flight [Hollywood version] (Score:5, Funny)

    by Anonymous Coward on Saturday November 03, 2001 @05:37AM (#2515888)
    • You need continuous thrust. Relying on Newton's 1st law to travel is for losers.
    • Always point toward your goal. Don't do a 180 and decelerate with your main engine, no need to match speeds.
    • Asteroid fields should look as dense as a forest, even if in reality asteroids rarely come within a mile of each other.
    • Shadows in space aren't totally black, because then we can't see.
    • Show stars through windows of well-lit spaceship rooms, because they're cool.
    • A gravity assist with the Sun will help you fly much faster.
    • Crescents of close bodies don't need to be oriented in the same way (oops, slashdot space logo?)
  • This is the best explanation of swingby manoever or gravity assist I have seen.
    And generally well done.

    • While the "Basics of Spaceflight" page is really nice, the "porkchop" page is quite lame - it wastes 5 pages to convince people that porkchop plots are nice and important tools, but when they show one of the plots [nasa.gov] on page 2 (!) they don't even explain what one can see there. So I'll try to do it myself:
      • The plot is for the two 2005 Earth-to-Mars transfer opportunities, using ballistic transfer (i.e. no propulsion during the flight except for orbital departure/insertion)
      • The horizontal axis is obviously the launch time from Earth, while the vertical axis is arrival time on Mars.
      • The two possible "windows" to Mars for 2005 seem to be the centers of the two blue coutour plots (if we only knew what the blue "C3L" lines mean!).
      • The red lines seem to be lines of constant travel time (labelled "TTIME"), so the lower window is for the shorter route (200 days TTIME as opposed to 400 days TTIME).

      The remaining questions are: What are the blue lines ? (very essential as they define the "windows". Maybe arrival velocity?) What are the magenta and green lines ?
      • > if we only knew what the blue "C3L" lines mean!

        C3L is the specific energy needed at launch to enter the transfer orbit from earth orbit. It's the square of the delta-V, I believe, and its a common number used to select a launch vehicle. Given a certain mass that you want to insert into Mars orbit, a Delta rocket, for example, would only provide a certain amount of C3, and if that isn't sufficient according to the porkchop plots, it's a no-go.

        The reason you have two local minimums on the plot is because one set is for a Type I orbit, traveling less than 180 degrees in the transfer orbit, and a Type II, traveling between 180 and 360 degrees.
      • OK, another reply to same parent. This page [cix.co.uk] gives a pretty good explanation of the equations and calculations for the hyperbolic escape orbit.
  • bah... all you need is a computer called HAL - he does it all for you :)

  • Sounds like software development to me (Score:5, Funny)

    by ColaMan ( 37550 ) on Saturday November 03, 2001 @07:51AM (#2515973) Journal
    Let's look at the similarities ...

    It costs a shitload.

    You normally have a few earlier versions that didn't perform to plan.

    You need to aim at a moving target that won't be there for two years, and of course you're own platform is moving as well.

    Not forgetting that if you're careless and not do your sums right , you'll crash and burn spectacularly and look like an idiot in front of the rest of the world.

    The major difference is of course (drumroll , please)

    In Space, no-one can hear your FUD.

  • Set pork chops to stun
  • It's a funny thing, I wget'ed (wgot?) that tutorial months ago... "Aha! At last a way to wile away the long gaps between new issues of TVGoHome [www.tvgohome] - I'll teach myself orbital mechanics! And there it sits, unread, along with everything else I [193.237.128.232] mirrored [193.237.128.232] for offline reading... unread whilst I just check Slashdot one more time... (Those links probably won't work unless I'm online. Goddam these UK phone charges... )

    • Brave man... (Score:4, Funny)

      by No Such Agency ( 136681 ) <abmackay@@@gmail...com> on Saturday November 03, 2001 @09:15AM (#2516064)
      Not only did you link to your home box on Slashdot (as we know, infamous for bringing even the largest websites to their knees), but now everybody knows your IP address too. That takes guts. Of course, if you're not online all the time, you'll be of much less interest to jerkwad scr1pt k1dd13z who want to run their personal pr0n site off your HD... Cheers!
      • heh! I didn't think of that... but, just to compound the risk - I'm pretty confident my properly secured NT4 box can take the heat. No, really, I am! OK, admittedly, I'm running low on medication, but still...
      • Wow, lotsa hits in fact... I'm surprised!


        andrew@INEGO% tail -100 access_log |grep -v
        192.168.0|awk '{print $1}'|sort|uniq
        127.0.0.1
        130.215.233.215
        160.36.81.191
        192.156.13.35
        192.156.13.36
        213.89.4.32
        216.165.42.86
        216.170.210.56
        61.136.15.233

        And anyway, skipt |1dd135?? On Slashdot??? Surely not...

  • >"which is an easy to understand tutorial on how to
    >explore deep space."

    every scout's need?
  • Since we're going to start having amatuer rocket scientists traveling into space ...

    It looks like JPL is helping people figure out how to get to mars on thier own. Tragically, I can see the fruit cakes now.

    I imagine it won't be so bad, so long as they leave a trail of bread crumbs,p.;-)

  • And this follows nasa releasing this [slashdot.org] stuff s little while ago. Are these guys (JPL and NASA) trying to get us to do their jobs for them? (By what else...sending pigs to mars! Pun intended.) Or is this just them clearing out old stuff to make way for new stuff. My bet is their magnetic tape media is getting unstable and they're too ashamed to admit it. Their sending it out to the world to let us mirror is in lots of places, under the allusion that it's actually worth something. It would be interesting though, to spend some time checking through these programs and tutorials to see if problems which led to the Challanger disater are apparent. Freynman said that the software development at JPL and NASA was tops, but he was comparing it to other parts of the organizations which were using orings for expansion joints which were designed as compression fittings. And other such problems. -=fshalor
  • I've always found that having a genius level set of twins, a cantankerous grandmother who writes Space Opera and a beset upon set of parents trying to raise a young child is a great way to get to mars. Sure, the bikes won't turn a profit post-tariff, but the flatcats will make serious money out in the belt.

    Failing that, just standing on the ground and looking up and wishing really hard sometimes works. You get scantily clad Martian princeses that way, too!

    --
    Evan "going through and rereading all his Trek novels, but may take a Barsoomian vacation for a bit" E.

    • IIRC they used Hazel's figures, as hers were the median...

      Would have been interesting if they had used Meade's...
      • Bless you... I've been making classic SF references (hint: I don't consider "Star Wars" classic SF) for a long long time on Slashdot - it used to be recognized and replied to way back when (before the great user purge), but hasn't in *years*.

        Ah, the glories of riding up on a tower of flame from your backyard, slipstick in one hand, the future ahead. It's a damn shame that we socialized space. It'll be there, though... it's been waiting for quite awhile.

        --
        Evan "Ad Astra Nauseum... but the Eagle has landed, tell your children when; Time won't drive us down to dust again" E.

  • Orbiter Simulator. (Score:1, Informative)

    by Anonymous Coward
    There's a great space-dynamics simulator called Orbiter [orbitersim.com].

    You can really get the feel for what's involved in plotting trajectories and getting to the right orbit. It's really good.

    And, it's free! (beer)

  • On the porkchop plot [nasa.gov], according to the legend at the top, the various curves are plots of the variables:
    • C3L
    • TTIME
    • SEP
    • Ls
    Can anyone tell us what those mean? Even just a few words that we can then go google. The body of the article mentioned a few things (like time-of-day orbital plane at Mars) but didn't explicitly correlate those ideas to the variable names.
    • C3L = C3 of Launch... C3 is (2*(Kinetic_energy/mass))^2 (or if you know orbit mechanics V-Infinity^2)

      TTIME = Transfer Time (days)... that is, how long it take to get to Mars

      SEP = Sun-Earth-Probe angle... that is, the angle on the corner of the triangle made by Sun-Earth-Probe... when this angle is too small you can't get a signal from the probe because of the noise from the Sun

      Ls --- I'm not sure on this one, it seems to be some sort of Launch angle
      • [other variables]

        Perfect! Thanks!

        Ls --- I'm not sure on this one, it seems to be some sort of Launch angle

        OK, with that hint I was able to figure it out. It's Earth-Sun-Mars angle, or, effectively, how far Mars is from Earth:

        1. Using a solar system simulator, I find that there is a Mars/Earth conjuction around 05-Nov-2005 (hmmm, 4 years from today) and around 25-Dec-2007 (hmmm, Christmas) -- those two dates are 2 years and 50 days apart, or 780 days.
        2. During that period, these two planets will swing through 360 degrees of Earth-Sun-Mars angle.
        3. Or, 180 degrees takes 390 days.
        4. Now, looking at the plot, the 0 Ls mark is at about 22-Jan-2006, and the 180 Ls mark is at about 10-Feb-2007. That's 384 days.
        Off by 1.5% just taking a guess and eyeballing the chart. Sounds like a confirmation to me :)

        Right?

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