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by newscracker 3572 days ago
I watched this documentary called "To catch a comet" about the Rosette/Philae mission to comet Churyumov–Gerasimenko. The achievement of getting to the comet and landing Philae, like many other achievements in space, is really phenomenal. So many things could've gone wrong, but the fact that the worst was Philae bouncing and getting stuck in a dark place (and not being able to perform fully) is a huge success beset by an issue of a smaller magnitude.

The description of the documentary says [1]:

> Unable to carry enough fuel owing to weight restrictions, the Rosetta scientists devised a delicate cat and mouse trajectory to reach their distant destination. In the ten years Rosetta had been in space she flew around the Earth three times, Mars once and the asteroid belt twice, to gain the momentum she needed to reach her destination. In the months before landing, the team navigated Rosetta safely to a world never before observed at such distances or accuracy. Rosetta orbited the comet before releasing Philae onto the surface.

Quoting from the article of this thread:

> “We were beginning to think that Philae would remain lost forever. It is incredible we have captured this at the final hour.”

This brings a much better ending for the people who worked on the mission for more than 30 years. [1] We tend to anthropomorphize things like spacecrafts, landers, rovers and many other inanimate objects. I think for the team (and many others following this news), this photo would be like being able to see a dear friend one last time, say goodbye in their minds and have some kind of closure.

The Wikipedia article, and especially the section titled "Landing and surface operations" [2], is also quite interesting to read.

[1]: http://www.pbs.org/program/catch-comet/

[2]: https://en.wikipedia.org/wiki/Philae_(spacecraft)#Landing_an...

3 comments

I tried to find the full version of the PBS "To catch a comet" about the Rosette/Philae mission but came up empty handed. Searching google, I was able to find a talk by Mark McCaughrean (ESA) called "Rosetta: to Catch a Comet". Been watching it for about 30 minutes and it's awesome. So, for anyone else looking for something to watch, this worked out great. Pretty amazing talk!

https://www.youtube.com/watch?v=KOiY-OCCRjs

I would recommend everyone who hasn't done so already watch the trajectory of Rosette[1].

1. https://youtu.be/ktrtvCvZb28

Also available in handy gif form : http://i.imgur.com/TUkKuhf.gif
There's also the argument for doing things a better way. Our propulsion systems suck, which is why we're having to send robots to comets instead of humans. Humans don't get stuck in cracks. Robots get stuck in cracks because they have no clue how to measure things they've never seen before.
What exactly is your point? Better propulsion would solve a ton of problems with space flight all at once, but how do you achieve it? This is nearly as bad as saying that gravity sucks, if we could just turn it off then it would all be so much simpler.
> Humans don't get stuck in cracks.

https://duckduckgo.com/?q=trapped+in+a+crevasse

Come on. Propulsion is far from the first reason we're not sending humans to comets -- safety, risk, mass, need for return, habitability.
All those things are inseparable from propulsion.
Again, clearly not true. Crewed implies habitable implies need for O2 implies more complexity. This complexity could not be carried on the budget, schedule, and risk allocated for this asteroid lander.

You could say the same thing about safety, and the need for return.

How do you figure? One of the biggest safety issues for manned space travel is radiation. Do you plan on outrunning it?
If you have awesome propulsion then you can just bring a shitload of shielding mass.
But use of such a system requires development, testing, and flight qualification, affecting cost, schedule, and risk. It will also affect other variables, like volume.

Focusing on a point solution like "propulsion" is not even the right kind of question to answer "why not solve this problem with humans?".

That's a fair point. That's like saying "we have the best medical facilities in the world for any treatment imaginable, but the hospital is five miles away. How will we carry you there in time to be treated?"
Yeah I'm surprised there aren't more humans volunteering to get blasted onto a moving comet with no way to get back off it, seems very safe.
With our current understanding of physics, chemical rockets have one giant engineering advantage: the same mass that is consumed for energy production is also the reaction mass. So anything better for imparting large delta-Vs has to be non-newtonian and our current understanding of physics does not allow existence of any such thing.
That's a big oversimplification. Project Orion-style propulsion is certainly not ruled out by our current understanding of physics. There's no non-Newtonian mechanics involved, just the substitution of a nuclear reaction instead of a chemical one. Not to mention that we have lots of evidence of non-Newtonian mechanics (e.g. Special and general relativity), even if whether GR can assist in space travel is an open question.
If look at it the other way around: burning the reaction mass is the only source of energy you use to accelerate the reaction mass — it doesn't sound obviously optimal.

Nuclear thermal, and nuclear/solar electric (aka ion) rockets achieve better specific impulse despite carrying separate weight for power. Some nuclear designs (e.g. Orion as johncolanduoni said) do have overlap between reaction mass and energy source mass. Solar sails, ground lasers, and gravity assists avoid some of the need for carrying reaction mass. All these are perfectly newtonian.

Chemical does win among currently working designs at accelerating quickly, which is critical for human exploration, and to some degree for getting to orbit. There is no inherent physical reason alternatives can't achieve that.

I must recommend the extremely fun Project Rho site though I'm just started reading it: http://www.projectrho.com/public_html/rocket/enginelist.php It's not always clear where existing science ends and Sci-Fi begins, but that's generally on technology barriers (e.g. we haven't yet managed break-even contained fusion), not mythical "entirely new understanding of physics". And the amount of actual science — detailed papers, prototypes etc — on diverse and bizzare drive designs is way more than I expected!