Hacker News Reader

Comment by grinich | Hacker News Reader

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.

View on HN

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

Reply on news.ycombinator.com