back to article Mars needs TRAFFIC COP to stop probe prangs, says NASA

NASA has “beefed up” the processes it uses to stop orbiters around Mars from colliding with each other, after two orbiters came within two kilometres of each other in early January. Humanity currently has five live orbiters around the red planet, namely NASA's MAVEN, Mars Odyssey and the Mars Reconnaissance Orbiter (MRO), plus …

  1. I Am Spartacus
    Headmaster

    Just add SPICE

    NASA JPL has a suite of programs that go under the name of SPICE. Once you have all the space craft orbits (and manoeuvres) defined as a data files, it is relatively easy to to compute proximity at any point in advance. What would be needed is to refine these data files (known as kernels) on a regular basis,

    1. David Harper 1

      Re: Just add SPICE

      It may be easy to calculate a spacecraft position far into the future from a SPICE kernel, but that doesn't mean that the calculated position will be accurate. SPICE is just a data format and a set of subroutines to interpret that data. It's not a panacea for the fundamental difficulty of accurately modelling the orbit of spacecraft around Mars.

      I'm guessing that the major stumbling blocks are uncertainties in the gravity field of the planet and the atmospheric drag -- remember that MAVEN is actually sampling the Martian upper atmosphere. Both of these uncertainties severely limit the accuracy of a long-term ephemeris of a spacecraft in an orbit like MAVEN's.

      1. Michael H.F. Wilkinson Silver badge

        Re: Just add SPICE

        In principle, SPICE should work. However, to work accurately SPICE needs an accurate model of the gravitational field around the planet. For Earth, decades of data gathering have yielded a good model, but it is still being refined. For Mars, the data are far more sparse, I would assume, so the model is not nearly as good, I would assume. It might be good enough, of course

        SNAP ;-)

  2. frank ly

    "... the odd orbits we've selected ..."

    I hope they were selected because they're useful/sensible/logical?

    1. This post has been deleted by its author

    2. x 7

      Re: "... the odd orbits we've selected ..."

      They were selected to avoid the spitting range of the Martian Rock Snakes

    3. Anonymous Coward
      Anonymous Coward

      Re: "... the odd orbits we've selected ..."

      To some extent they were 'selected' by fuel limitations to get the orbiter out of Earth's gravity, to Mars, but stopping at Mars. Different orbiters were launched at different points in Earth's and Mars' orbits, taking different amounts of time to get there, so the delta x / delta y velocities relative to Mars were different. It is easier to brake into an eccentric orbit than into a circular orbit.

  3. jake Silver badge

    Serious question ...

    What kind of dumb-ass space program would spend megabucks trying to get into orbit around another rock, other than the Earth, without checking with other space programs about the current state of the orbit situation on that other rock?

    I mean, really? Are they that stupid? The mind boggles.

    1. phuzz Silver badge
      Facepalm

      Re: Serious question ...

      The thing is, you can't really predict the orbits of all the spacecraft around Mars that far in advance. Things like, exactly how high up the atmosphere is extending this week, have an affect on some or all of the orbits. Also, some of the Mars orbiters have shifted their orbits, most notably to avoid the dust cloud from comet Sliding Spring last year.

      This means that when a space probe is being planned and built (typically years before it'll even get near space) they can make a rough calculation of how likely a collision is, but actually predicting a near pass can only be done a few weeks in advance.

      tl/dr Yes of course they calculated it, but situations change.

    2. Shrimpling

      Re: Serious question ...

      You notice the main issue reported was a NASA probe avoiding another NASA probe...

      It is not a problem of communications between agencies, it is a problem of communication between different teams within the same agency. They even admit in their press release that only 2 of the 3 NASA missions were event talking to each other before they made the recent changes.

    3. cray74

      Re: Serious question ...

      "I mean, really? Are they that stupid? The mind boggles."

      The rate of accidental collisions between intact satellites in crowded Earth orbits remains small after almost 6 decades. The average satellite wrecking debris impacts happens about once per year, and collisions between intact satellites or complete upper stages are very rare: There are four significant recorded collisions in that time: Cerise; Iridium 33/Kosmos 2251; BLITS; and NEE-01 Pegaso.

      Because of that low rate of collision the primary means of satellite navigation in Earth orbit is based on the Big Sky theory: space is so big that you're unlikely to hit another satellite during the operating life of the satellite, so don't worry about it.

      For example, while the Iridium constellation gets 400 collision warnings per week ("something will pass within 5 km") the estimated probability of a collision for the fleet is only 1 in 50 million per conjunction. Only manned spacecraft regularly dodge debris, and lately satellite builders have grudgingly taken precautions like "safing" spent stages and moving satellites to graveyard orbits at the end of their life.

      When you pack thousands of spent stages and satellites into Earth orbit, "navigate" them by flying blind, and get so few satellite-wrecking accidental collisions, then it's might be worth rethinking the level of stupidity involved.

      And remember Adams' words: "Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."

    4. MyffyW Silver badge
      Coat

      Re: Serious question ...

      I mean, really? Are they that stupid? The mind boggles.

      Well it's not rocket science, is it?

      Sorry couldn't resist, I'll get my coat.

  4. Vulch

    Older orbiters still there

    Mariner 9, one of the Viking orbiters and possibly a couple of Soviet orbiters are still whizzing round out there too. With no communications for decades their exact orbits are a matter for speculation.

  5. Winkypop Silver badge
    Alert

    Americans, Indians and Europeans....

    So, is it give way to the right or give way to the left?

    1. DocJames
      Mushroom

      Re: Americans, Indians and Europeans....

      Just coming straight through. You should move....

      Oops.

      1. Anonymous Coward
        Anonymous Coward

        Re: Americans, Indians and Europeans....

        I expect the American's will have guns on theirs to blast their way through....shoot first, ask questions later!

        1. jake Silver badge

          @AC "7 mins"" (whatever that means, ElReg) Re: Americans, Indians and Europeans....

          "I expect the American's will have guns on theirs"

          I think you mean the Soviets. See: Nudelman-Rikhter NR-23. Nice little rifle round.

          1. x 7

            Re: @AC "7 mins"" (whatever that means, ElReg) Americans, Indians and Europeans....

            If you read the Wiki page about the Almaz capsules, it would seem the NR-23 guns flown there were actually branded as "Shchit-1" and "Shchit-2"

            Probably what you would feel if you were onboard when they started firing....

            http://en.wikipedia.org/wiki/Almaz

            1. CaptSmeg

              Re: @AC "7 mins"" (whatever that means, ElReg) Americans, Indians and Europeans....

              This made me wonder about two things...

              One, and I haven't done the maths, I'd imagine you'd have to start doing some orbital corrections if you fired one of those for any length of time. I guess that is why they aligned it with the thrust axis?

              Two, if they did test fire the one on the Almaz, where did they point it? Either there is a nasty burst of 32 slugs in orbit waiting for some poor sod to wander into their line of fire - which is rather irresponsible, or they fired it at the planet which might be an act of war?

              Oh what fun the military have when nobody is looking.

              1. cray74

                Re: @AC "7 mins"" (whatever that means, ElReg) Americans, Indians and Europeans....

                "One, and I haven't done the maths, I'd imagine you'd have to start doing some orbital corrections if you fired one of those for any length of time"

                The 23mm Rikhter fired 0.168kg shells at 850m/s (no idea of propellant gas mass), and the gun had 32 rounds. At launch, the station was 18,900kg; I don't know how much mass was lost due to maneuvering and life support requirements. The guns were only fired near the end of the station's life.

                By conservation of momentum, 32 x 0.168kg shells at 850m/s would recoil the 18,900kg station at 0.24m/s. That's not a major course correction, but something to be noted in the long run.

                "Two, if they did test fire the one on the Almaz, where did they point it?"

                Well, the Salyuts ran in low orbits - about 210km in the case of Salyut-3 - so orbital life times were short. If the guns were fired against the orbit direction (or within the 180-degree stern arc), then the shells would have even shorter lifetimes. If fired within 75 degrees of either side of dead astern (i.e., over a 150-degree rear arc) then the 220 to 850m/s reduction in the shells' orbital velocities means they'd hit atmosphere pretty soon - minutes, at a guess. Even firing within 76 to 87 degrees of dead astern imparts a large de-orbit kick of 45 to 205m/s, which is as stiff as any spacecraft's intentional de-orbit burn. (The velocity imparted to the shells perpendicularly - up, down, left, or right - to the station's orbital track is less relevant for determining orbital life times.)

                "or they fired it at the planet which might be an act of war?"

                Whatever bits of the shells survived re-entry wouldn't be much of a threat. The explosives would've cooked off and the shrapnel would be falling at a modest terminal velocity. Considering Canada didn't go Rambo on Russia for spraying radioactive satellite fuel over it, I don't think anyone was going to declare war over some scorched, small bits of metal.

                "Either there is a nasty burst of 32 slugs in orbit waiting for some poor sod to wander into their line of fire - which is rather irresponsible"

                Firing forward gets trickier, but I can make one general statement about any Salyut shells fired ahead of the station: they're always going to return to their point of origin, which is a low perigee of 210km. An 850m/s boost straight forward would extend the shells' orbital lives by putting them into an elliptical orbital with an apogee of several thousand kilometers (I think), but their perigee is going to remain c210km since they have no motors to alter the perigee. Assuming they didn't actually hit the station at some point, the shells' low perigee would mean they'd re-enter pretty soon, under a few years, though they'd be in orbit longer than the station.

                Of course, the risk of the shells hitting the station - which was doing useful work even while unmanned - is a good basis to assume the gun was only fired backwards.

      2. Anonymous Coward
        Anonymous Coward

        Re: Americans, Indians and Europeans....

        >>>Just coming straight through. You should move....

        Mexico doesn't have an orbiter up yet. ;)

    2. The elephant in the room

      Re: Americans, Indians and Europeans....

      "He is intelligent but not experienced. His pattern indicates 2-dimensional thinking"

      https://www.youtube.com/watch?v=RbTUTNenvCY

    3. Martin Budden Silver badge

      Re: Americans, Indians and Europeans....

      It doesn't matter how many guns you have, you still have to give way to the lighthouse.

  6. Annihilator
    Boffin

    2D

    "Many of the orbiters' orbits intersect: the image at the top of this story shows that India's MOM, for example, cuts across the orbit of three other craft and Mars' two moons."

    It doesn't show anything, as it's a 2D projection of a 4D system. For example, MOM could be orbiting at a 45 degree angle to the Martian system's plane and passing around Phobos and Deimos.

  7. ben kendim

    Your pattern indicates two dimensional thinking.

    Please show us the inclinations of those 'overlapping' orbits, then we will see how close they really are.

  8. FozzyBear

    Just declare an orbit a tow away zone.

    An Aussie tow truck driver would have the offending satelite wheel clamped, towed and impounded before the paint was dry on the sign.

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