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Philae Found

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Re: Philae Found

#101

Post by mikeash »

kordless wrote: post #94
newscracker wrote: post #26

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 b…

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.

Re: Philae Found

#102

Post by dfox »

kordless wrote: post #94
newscracker wrote: post #26

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 b…

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.

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.

Re: Philae Found

#103

Post by wcoenen »

spuz wrote: post #53
infodroid wrote: post #3

The hi-res image shows how just how unlucky a landing spot this was. http://www.esa.int/spaceinimages/Images/2016/09/OSIRIS_narro...

I'm surprised at how rugged the surface looks in these high-res images. Especially compared to the imagined flat landing areas we were used to seeing in the run up to the landing [1]. Just shows how difficult a task it was to land and keep the craft the right way up. [1] https://en.wikipedia.org/wiki/Philae_(spacecraft)#/media/Fil...

It was aimed at a flat spot, but when it failed to attach to the surface it bounced and floated for almost 2 hours, hitting the surface again 1 km away[1][2]. Its speed of 38 cm/s during that time was below escape velocity but not by much.

[1] https://www.youtube.com/watch?v=rJ2eqH3Bz4c

[2] http://blogs.esa.int/rosetta/2014/11/14/three-touchdowns-for...

Re: Philae Found

#104

Post by mastazi »

wolf550e wrote: post #86
edge17 wrote: post #83

Earlier quoted context omitted.

Scientifically speaking, a successful mission is one where you've gathered all the data for analysis and can work with it long after the mission is over. It's like, if SpaceX launches a rocket and it explodes - a real failure would be if they captured no telemetry and had no idea what happened vs knowing everything that happened and being able to replay the mission after the fact. Often times the data is far more imp…

The SpaceX comparison is bad because they don't do science missions. SpaceX do commercial launches for paying customers. Mission success is defined by whether the payload gets to its intended orbit, unharmed. Even if SpaceX learn a lot from a mission, if the payload is lost then the mission failed. While one can learn from failures, when the mission is not a test, learning is not enough for the mission to be called a…

> they don't do science missions true, but they do R&D like most large for-profit entities. However I agree with you that the comparison is not compelling. R&D is not SpaceX's main objective, hence the situation described doesn't compare to a scientific mission where you send a lander on a comet and you actually get the data from the lander.

Re: Philae Found

#105

Post by rm_-rf_slash »

spdegabrielle wrote: post #99
mturmon wrote: post #95

Earlier quoted context omitted.

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.

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?"

Re: Philae Found

#106

Post by pavel_lishin »

wcoenen wrote: post #103
spuz wrote: post #53

Earlier quoted context omitted.

I'm surprised at how rugged the surface looks in these high-res images. Especially compared to the imagined flat landing areas we were used to seeing in the run up to the landing [1]. Just shows how difficult a task it was to land and keep the craft the right way up. [1] https://en.wikipedia.org/wiki/Philae_(spacecraft)#/media/Fil...

It was aimed at a flat spot, but when it failed to attach to the surface it bounced and floated for almost 2 hours, hitting the surface again 1 km away[1][2]. Its speed of 38 cm/s during that time was below escape velocity but not by much. [1] https://www.youtube.com/watch?v=rJ2eqH3Bz4c [2] http://blogs.esa.int/rosetta/2014/11/14/three-touchdowns-for...

> it failed to attach to the surface it bounced and floated for almost 2 hours, hitting the surface again 1 km away[1][2]. Its speed of 38 cm/s during that time was below escape velocity but not by much.

These numbers sound completely ridiculous, unless you've played Kerbal Space Program, and know the visceral pain of bouncing above Minmus with a pixel of monopropellant left in the tanks.

Re: Philae Found

#107

Post by Cogito »

gokhan wrote: post #9

Unless other parts of the comet is more flat, that landing gear design seems clearly wrong. It included bolting itself to the surface, if I remember correctly, but it seems almost impossible to fixate three legs with almost no gravity on that surface.

There were three aspects to fixing the landing, to my understanding.

Legs keep it oriented, give a stable platform, and cushion the initial landing.

Top thruster pushes it into the surface, damping any bounce back from the impact.

Harpoons attach to the surface, affixing it permanently.

The top thruster was reported to not work at all, and the harpoons were unable to work by themselves. It's not clear if they would have worked if the top thruster was working as well.

Re: Philae Found

#108

Post by johncolanduoni »

spdegabrielle wrote: post #99
mturmon wrote: post #95

Earlier quoted context omitted.

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.

How do you figure? One of the biggest safety issues for manned space travel is radiation. Do you plan on outrunning it?

Re: Philae Found

#109

Post by johncolanduoni »

dfox wrote: post #102
kordless wrote: post #94

Earlier quoted context omitted.

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.

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.

Re: Philae Found

#110

Post by mturmon »

spdegabrielle wrote: post #99
mturmon wrote: post #95

Earlier quoted context omitted.

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.

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