6 ms·

Any actual engineer will probably find this comment painfully naive, but here we go: If it's infeasible to slow down to get into orbit or land on Pluto, what a

• unclebucknasty 11y ago
  Wonder if there would have been any way to use Neptune to slow the probe? Probably would have been travelling too fast, I'm guessing.
• trothamel 11y ago
  It's probably the former. It's been tried before, with Deep Space Two at mars - but didn't work. There's also a sense that if you're going to spend tons of money to send a once-in-a-generation probe to an outer planet, it has to work.
• grinich 11y ago
  A bullet travels about 1,700 MPH. New Horizons is going about 36,300 MPH. The probe weighs 480 kilograms, so it's kinetic energy is approximately 63.2 Gigajoules. For reference, this is like 15 tonnes of TNT released on impact. Hard to make something that survives those kind of conditions.
  • ceejayoz 11y ago
    Plus, probes that far out have worse-than-dialup transmission rates. It takes 42 minutes to return a single photo from the LORRI camera. Bursting large amounts of data out in a short period of time before impact isn't feasible. http://www.planetary.org/blogs/emily-lakdawalla/2015/01300800-talking-to-pluto-is-hard.html http://www.planetary.org/blogs/emily-lakdawalla/2015/0130080...
    • chc 11y ago
      I think the suggestion was to send the data after impact. I guess the idea is to basically fire a shock-absorbing crate full of scientific instruments, let the impact destroy the crate, and hope the instruments survive and get to work.
      • chasing 11y ago
        Yup, that was my idea. Or to have NH itself fire off some very tiny instruments that might weight little enough to not go off like an atom bomb when hitting the ground. A GoPro, for example. (I KNOW: NOT AN ACTUAL GOPRO. A small armored camera.) Or a thermometer. The constraint there, though, might be designing equipment that is both very low mass and also capable of talking back to either Earth or the rest of NH as it zips away.
        • danbruc 11y ago
          I fear that won't work. The speed relative to Pluto during closest approach was 13.78 meters every millisecond, I can't imagine that anything larger than a grain of sand will not behave like a liquid upon impact.
          • idlewords 11y ago
            Even a grain of sand will go boom. Here's what a particle of similar size did to the space shuttle windshield, traveling at half the speed of New Horizons. https://commons.wikimedia.org/wiki/File:Space_debris_impact_on_Space_Shuttle_window.jpg https://commons.wikimedia.org/wiki/File:Space_debris_impact_...
            • socceroos 11y ago
              wow.
            • blazespin 11y ago
              How does new horizons survive? Space must be pretty empty.
  • mmagin 11y ago
    I wonder if it would be more interesting to fire a sizable dumb projectile into Pluto and then after you've past it a bit (with proper alignment of the spacecraft, sun, and pluto) observe the absorption spectrum of the gas/dust cloud produced.
    • kartikkumar 11y ago
      That's kinda what Deep Impact did. LRO & LCROSS did something similar, but the problem is that for a larger body, you need an impactor with a fair amount of energy before you'd be able to likely generate anything that is observable. Also, there's the planetary protection issue, which makes the design of impactors A LOT more expensive.
  • murbard2 11y ago
    You don't have to crash/land the entire probe, you could land a lightweight sensor that was carried by the probe and which requires little fuel to decelerate.
    • umeshunni 11y ago
      The sensor will need to send data back, so it can't be too light weight.
      • kijin 11y ago
        The signal only needs to reach the mothership, not Earth. Example: Philae communicated with Earth via Rosetta.
        • murbard2 11y ago
          Yes but Rosetta orbited the comet, whereas in this case the probe would just zoom past the planet
• jccooper 11y ago
  Bullet goes about 1.2 km/s at best. New Horizons is going ~14 km/s relative to Pluto. That's a heck of an impact to survive. You could do it on Earth by braking in the atmosphere, but there's not a lot of that on Pluto.
  • jsprogrammer 11y ago
    If you were trying to land, you would use a different trajectory that doesn't result in you traveling 14 km/s to Pluto?
    • ebetica 11y ago
      That would take a while to get there.
• deleted 11y ago
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• Cthulhu_ 11y ago
  It's theoretically possible, it'd just require a lot of fuel to slow the craft down enough to survive a landing. source: I've played Kerbal Space Program. If you speak maths (I don't), you could probably do them; the calculations are relatively simple: https://en.wikipedia.org/wiki/Delta-v https://en.wikipedia.org/wiki/Delta-v.
  • raverbashing 11y ago
    No, it is much much harder. Especially the survival part Delta-v is literally Physics 101 Landing on Mars is hard, but feasible. Because it has a thick atmosphere to help with the braking Sure, it adds a lot of complications as well, but it is a very good way of slowing your craft enough for other braking systems to work (like rockets, parachutes, etc) Of course, bodies with little atmosphere also have a small gravity, so that makes things easier as well (like landing on the Moon)
    • drjesusphd 11y ago
      > No, it is much much harder. Especially the survival part Please elaborate. What is dangerous about a braking burn? Sure, it's harder (because you need to carry that fuel), but not impossible in principle. > Sure, it adds a lot of complications as well, but it is a very good way of slowing your craft enough for other braking systems to work (like rockets, parachutes, etc) I'm sorry, when do rockets not work?
      • danbruc 11y ago
        But it is not some fuel, it is more or less the same amount of fuel you need to accelerate the thing. And now you have to accelerate twice as much mass at liftoff requiring even more fuel. Of course requiring even more fuel itself. The tyranny of the rocket equation.
        • drjesusphd 11y ago
          Yes, it's hard. I understand that. But not impossible. Same arguments apply to Saturn, but "we" managed to get Cassini in orbit. It's a matter of scale, not principle.
• deleted 11y ago
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• eastbayjake 11y ago
  A few months ago someone posted on HN about "ballistic capture" to enter a Martian orbit with far less fuel, and I've spent the last few months wondering if you could do that to mosey into a Plutonian orbit: http://www.scientificamerican.com/article/a-new-way-to-reach-mars-safely-anytime-and-on-the-cheap/ http://www.scientificamerican.com/article/a-new-way-to-reach...
  • skykooler 11y ago
    Part of the reason New Horizons is going so fast is to reach Pluto in "only" ten years. A Hohmann transfer (which you would need to make a ballistic capture) would take about 124 years just to reach Pluto.
    • eastbayjake 11y ago
      The article led me to believe you would avoid a Hohmann transfer with ballistic capture by flying it into a similar orbit and letting the planet slowly creep up on the probe and pull it into orbit. Am I misreading that?
      • Dylan16807 11y ago
        You're cutting the final burn but you're still pulling roughly the same maneuver, by taking an orbit that peaks at about the same altitude as pluto, and that is a slow orbit.
  • kartikkumar 11y ago
    My boss co-authored that paper [1] :) Ballistic capture is interesting: makes use of fuzzy/chaotic dynamics in the 3-Body Problem. I worked on analysis of the Weak Stability Boundary, which is the mathematical set of all points in phase-space that lie at this fuzzy boundary, for my Masters thesis [2]. It has been used in a few missions, including SMART-1, Stardust, and Hiten. ESA's Bepi-Colombo mission will also be using it to ensure that there isn't a single point-of-failure to enter orbit around Mercury. The big problem with ballistic capture is that it doesn't guarantee a more optimal solution. Transfers can take a lot longer, and in theory even require more fuel. So it's very much a case of having to perform mission analysis on a case-by-case basis. Nevertheless, it's an interesting prospect to send unmanned missions to Mars carrying habitat elements, before a manned mission, since they can be sent well in advance. I analyzed the prospect of potentially using a cycler [3] for this in my thesis. [1] http://arxiv.org/abs/1410.8856 http://arxiv.org/abs/1410.8856 [2] http://repository.tudelft.nl/view/ir/uuid%3Ae8c99c80-a25d-4c7b-b8c2-f0f27c69fc32/ http://repository.tudelft.nl/view/ir/uuid%3Ae8c99c80-a25d-4c... [3] http://courses.ae.utexas.edu/ase333t/past_projects/04spring/Cycler%20Website/cyclers.html http://courses.ae.utexas.edu/ase333t/past_projects/04spring/...
• liquidise 11y ago
  So, for such an impact, you would almost certainly need the strongest bouncing lander ever produced. However, Pluto's escape velocity only is about 1/10th the speed of NH. This means that if that first bounce upon impact would result in even 10% of the initial velocity, it will literally bounce out of the system and back towards the sun.
• Florin_Andrei 11y ago
  > If it's infeasible to slow down to get into orbit or land on Pluto, what about the feasibility of designing a probe to impact Pluto at XX km/sec and survive well enough to send back data That's actually harder to do. To insert in orbit, you can still have some residual speed, you don't have to slow all the way down. To land on the surface and survive, you would have to brake even harder. Anything near orbital speed would be a non-survivable impact, even for hardened electronics. Not to mention interactions with the atmosphere on the way down.
• tyho 11y ago
  I am not an engineer, but it might be easier to launch a spacecraft with an ion engine that over years manages to reduce the speed relative to Pluto to something human scale.
  • tim333 11y ago
    I think that would be the most practical way. Nasa already launched Dawn, an ion drive probe, to visit Vesta and Ceres.