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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 about the feasibility of designing a probe to impact Pluto at XX km/sec and survive well enough to send back data.

Like, fire a (metaphorical) bullet full of scientific instruments directly into the surface of the planet.

Is it simply that we have no way to build something that could both survive such an impact and be complex enough to do anything useful afterwards? Or might it create too much destruction on Pluto's surface? Or some combination of those?

Edit:

I mean, it worked when we went to the Moon: http://gallerytpw.ca/wp-content/uploads/2011/09/Georges-M%C3...

Edit 2:

Not literally a bullet. I'm aware of the speed difference between NH and a bullet. ;-)

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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.

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/2015/0130080...

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.

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.

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.

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_...

wow.

How does new horizons survive? Space must be pretty empty.

That's why they call it space!

More seriously, there's a dust counter on the probe whose entire job is to be hit with stuff. But it's much tinier than a sand grain.

You would put something else in orbit and have high bandwidth communication to it and relay from there.

Putting something else in orbit is the hard part.

The relay doesn't have to be in orbit around Pluto, it could be trailing the impacter and fly by. Deep Impact did something like this with a comet.

A few million miles prior to arrival, jettison a 'probe from the probe', control this separately, beginning the negative acceleration of the mini-probe. This mini probe could enter a controlled orbit, and then launch a mini landing probe of even smaller size...etc.

Getting something to slow down enough to orbit is still a huge change in velocity. And even if it did, exactly how much bigger a transmitter could it carry considering it has to be hurled out to Pluto. At least with direct to Earth transmissions we can aim enormous[1] dishes at the signal source.

[1] http://deepspace.jpl.nasa.gov/about/DSNComplexes/70meter/

Ahhhh you said probe.

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.

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.

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.

The sensor will need to send data back, so it can't be too light weight.

The signal only needs to reach the mothership, not Earth.

Example: Philae communicated with Earth via Rosetta.

Yes but Rosetta orbited the comet, whereas in this case the probe would just zoom past the planet

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.

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)

> 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?

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.

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.

It is of course possible but difficultly and costs will probably explode ruining the cost benefit ratio. Fly by ten times or try landing once? Or fly by once and spend the remaining money exploring something else - there is so much else. And entering an orbit seems still vastly simpler than landing on the surface.

Yeah, but Saturn is at approx. 1/4 of the distance to Pluto and it used a different process to intersect to Saturn's orbit, taking more time to get there

New Horizons got to Jupiter after ONE year

There was a good xkcd what-if on this a while back. http://what-if.xkcd.com/38/

in part it's more dangerous than correction or passive braking system because you need a high twr motor and the explosive to go with it to have a way to correct for unforeseen consequences.

see what happened with philae, they got two redundant system to land and both failed.

if the scan reveal pluto to have an usable atmosphere, it will be much much easier to land

however, if you look at the trajectory they used it's an orthogonal encounter [1]

that means the speed they have relative one another is quite much more than when you approach calmly from behind using a hoffman transfer or the like - however if you go that route, instead of waiting 10 years you have to wait a load more, probably more like hundreds (exactly what they did with phila, they approached from the closest orbit possible to minimize the correction burn needed [2])

and let us not forget that having anything in space surviving for soo long is a challenge by itself, as having equipment on earth funded for so long to be maintained operational - remember this story about the other spacecraft that was sent to a comet flyby and was out of gas due leaks on its way back? [3] they had to work a great deal just to rebuild the communication equipement in time

[1] https://upload.wikimedia.org/wikipedia/commons/c/cb/New_Hori... [2] http://i.imgur.com/TUkKuhf.gif [3] http://blogs.nature.com/news/2014/07/attempt-to-retrieve-nas...

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.

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...

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.

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?

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.

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

[2] http://repository.tudelft.nl/view/ir/uuid%3Ae8c99c80-a25d-4c...

[3] http://courses.ae.utexas.edu/ase333t/past_projects/04spring/...

When mass parameter is big, use of WSBs is interesting. But mass parameters for sun-earth or sun-Mars are tiny. I've expressed my skepticism for ITN between earth and Mars: http://hopsblog-hop.blogspot.com/2015/04/potholes-on-interpl...

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.

> 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.

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.

I think that would be the most practical way. Nasa already launched Dawn, an ion drive probe, to visit Vesta and Ceres.

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.

If you were trying to land, you would use a different trajectory that doesn't result in you traveling 14 km/s to Pluto?

That would take a while to get there.

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.

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