3/10 includes a lot of older missions and non-us missions. The US has quite a good track record for Mars missions. As time goes on we get better and better.
> So they completely beta tested this landing system on earth right?
That is not possible. Some things like gravity and atmospheric pressure/density cannot be replicated in the scale required to test here on earth. They have to rely on testing in parts and in some cases on calculations and data from previous visits and landings.
No. Mars having less atmosphere is exactly the point. Such an entry system hitting Earth's atmosphere would be like slamming into a brick wall--it wouldn't survive. And the greater density air on Earth would make the sky crane segment completely unstable. Not to mention that Earth's gravity is simply too large--components of the system would be crushed under their own weight.
I don't know about most of your points, but the components being crushed under their own weight doesn't seem right. The probe was built in Earth gravity and had to undergo 4-5G of acceleration during launch. Also, it's going to experience 13G of deceleration when entering the Martian atmosphere.
> Mars has LESS pressure. So the landing would be easier here, so it should have been tested?
No, having less atmosphere is a disadvantage in this case. This means just parachute wont work. Hence the whole sky crane thing. There is no feasible way to test the whole EDL (entry, descend, landing) phase here on this planet because simulating entry into mars's thin atmosphere is not possible out of computer simulations and whiteboards.
No need to test on earth as it would certainly fail. The crane probably couldn't even lift its own weight on earth with its almost three times higher gravity.
Here are some nice pictures, including testing the radar descent measurement system from a helicopter, testing the parachute in the largest wind tunnel in the world, and testing various assemblies in a large thermal/vacuum chamber:
http://www.theatlantic.com/infocus/2012/08/curiosity-just-da...
Worth a look, I promise. You get a sense of all the work to assemble a piece of hardware with this size and complexity.
I have been waiting for this for quite a while. Very excited about the potential for new discoveries.
Having said that, it still looks like the craziest Rube Goldberg set of hacked together systems I've ever seen for landing on a planet. Here's hoping it all comes off without a hitch. I have a feeling it'll become an object lesson in engineering whether it works or not.
It reminds me of the results of my highschool art class project 25 years ago. We were given a sheet of construction paper, a few straws, some glue and a couple of rubber bands. The challenge was to build something that would keep a light bulb from breaking when dropped from the top of a ten foot ladder.
I spent a week of class periods building what looked like a replica of the Lunar Module with fins - the legs were springs to absorb the impact. It worked great when I tested it but failed on the testing day because the teacher was holding it upside down when he dropped it.
My friend, who goofed off the whole week drawing comics in class spent 5 minutes wrapping his bulb in straws, then crumpled up the paper, uncrumpled it and then wrapped that around the straws. A couple of loops of tape and he made a landing "vehicle" that worked every time.
One of the things that came out of discussion with NASA scientists was a deliberate 'science of disaster' sort of thinking. There are a number of sensors in the landing shell, in curiosity, and in the sky crane, that start transmitting as soon as they can. Further the goal of having the Mars Odyssey in position was so that as much data could be collected as possible.
Basically you have to ask the question "What science can I do at this stage?" so that during every possible outcome you extract the most data you can.
I find that a fascinating way to structure your thinking about a project.
The review board analyzing the loss of MPL could not narrow down the cause for certain, although they did identify a most likely cause. It was resolved in the future to have as much data collected as possible so that an unexplained loss could not occur again.
One key ingredient in this is line of sight to a relay orbiter.
But this is not a science driver, it is an engineering driver.
At the top of the article, it says "Date: 05 August 2012 Time: 12:31 AM ET", lower in the article it says "Aug. 5; 1:31 a.m. EDT" but both of those seem to be mistakes since those times have already passed and nasa.gov says "Aug 6, 2012 1:31 a.m. Eastern". Sorry if this is pedantic, but I think the time is pretty important here.
What they meant was 10:30 PM pacific time on Aug. 05. For US East Coast and all areas east (Europe, Asia etc) this means Aug. 06. They posted the article early in the morning on Aug. 05 so they could have it up and relevant for a full 24 hours I guess!
Can someone explain to me why it isn't possible to steer the capsule with the heat shield such that it can be used to deplete virtually all of its speed?
I can imagine a system where the capsule pitches up near the end of its run so that it starts gaining altitude and then deploys a parachute for landing once it has reached its apogee.
I appreciate that their system probably is the best design as they are a smart bunch, however I haven't heard the reason's why some of the more conventional mechanisms weren't used.
Another thing is the crane mechanism, which is to protect the rover from the debris kicked up from the rocket motors. I was wondering why the rover couldn't just be encased in a simple lightweight protective box and then placed directly on the deck?
Does anyone have any links to the other designs that were considered and rejected?
I don't think the capsule has the right aerodynamic properties to allow it to work as a proper lifting body in the 0.01 ATM Martian atmosphere. We don't really have any experience about lifting bodies on Mars, even less than we have about huge supersonic parachutes.
You can't land on Mars with just a parachute anyway, not with a 900 kg payload. The main problem with Mars is that its atmosphere is just dense enough that it complicates things but not dense enough that it's really helpful.
Apparently according to this video [1] (about half way through) the capsule is a lifting body however I was thinking of something like a simple guided arrow, perhaps some fins that are extended on a telescopic shaft. You could possibly then put a tractor rocket at the end of this shaft to slow descent and keep the rocket plumes away from the main body and the ground.
Regarding parachutes, is it not the case that if you need more performance, that you simply increase their size?
Unless the atmosphere is so thin that the added weight of the parachute and it's support hurts more than it helps. 0.6 kPa is really that bad.
The effectiveness of a parachute grows at a square of your airspeed. This means that every planet has a minimum speed you can successfully slow down to using parachutes with a given system. For realistic loads and conventional materials, on Mars that is about 50m/s. Which is just too fast.
> I was thinking of something like a simple guided arrow, perhaps some fins that are extended on a telescopic shaft
It's one thing to say it, it's another to design it such it has a chance of working. Telescoping mechanisms with deployable aerodynamic structures sounds very complicated to me, compared to the thrusters they're using.
> You could possibly then put a tractor rocket at the end of this shaft to slow descent and keep the rocket plumes away from the main body and the ground.
The sky crane already does this.
> Regarding parachutes, is it not the case that if you need more performance, that you simply increase their size?
'Performance' is lots of things, presumably you mean drag. Increasing the diameter does increase the drag, but it also increases the opening forces, which requires a stronger structure, which means more mass. You don't have the luxury of much margin when every gram in your landing system has cost the us taxpayer thousands of dollars and is a gram that you can't use for science.
The capsule and heat shield do deplete virtually all of its speed. With Mars' thin atmosphere, the terminal velocity is still quite high and the parachute/rocket combination is needed to take it all the way down. AFAIK this is a relatively conventional system, with the exception of the very last moment of touchdown, which uses descent rockets and the sky crane.
Perhaps the most similar landing was by Viking, which made the final descent on rockets. Those thrusters were expressly designed (that is, compromised) to produce as little disturbance of the landing site as possible. The only thing Curiosity is doing that is really new is the sky crane. If there are any errors in understanding the dynamics of rocket plus lengthening pendulum in Mars gravity, then all is lost. I think it is likely that some extra attention has been paid to this part of the mission.
Everybody just watch this. It's Tom Rivellini, one of the lead mechanical designers of the landing mechanism, explaining how it works and how it evolved and what was considered and what was rejected. It's not a pithy over-produced 4 minute video, it's the real stuff for the technically interested. It answers all your questions.
> Can someone explain to me why it isn't possible to steer the capsule with the heat shield such that it can be used to deplete virtually all of its speed?
They do exactly that. But Mars' atmosphere is so thin that terminal velocity of the capsule is still supersonic.
> I can imagine a system where the capsule pitches up near the end of its run so that it starts gaining altitude and then deploys a parachute for landing once it has reached its apogee.
Parachutes don't help enough in 0.007atm. Even with the biggest chutes possible (remember: they're heavy!), you'd still be hurtling towards the ground like a missile.
> Another thing is the crane mechanism, which is to protect the rover from the debris kicked up from the rocket motors. I was wondering why the rover couldn't just be encased in a simple lightweight protective box and then placed directly on the deck?
Weight. Believe it or not, the sky crane delivers more payload to the surface.
> I appreciate that their system probably is the best design as they are a smart bunch, however I haven't heard the reason's why some of the more conventional mechanisms weren't used.
>
> Does anyone have any links to the other designs that were considered and rejected?
> They do exactly that. But Mars' atmosphere is so thin that terminal velocity of the capsule is still supersonic.
Also, that kind of blunt body is stable hypersonically, but unstable supersonically. As soon as you get to a mach number where a parachute can deploy stably (about mach 1.8 and below) you deploy it to stabilise the thing, and of course the drag is much greater than entry body alone.
>> Another thing is the crane mechanism, which is to protect the rover from the debris kicked up from the rocket motors. I was wondering why the rover couldn't just be encased in a simple lightweight protective box and then placed directly on the deck?
The point of the sky crane is not just to avoid kicking up dust, this notion seems to have become the received wisdom in the media though. The reasons include:
-Having rovers drive off from on top of things is difficult, it puts the CoG of the lander right up and if you have to drive off a sloped ramp having landed on a slope, the ramp can be really very sloped.
-Rocket forces nearer the ground can be quite an interesting control problem, in terms of the forces generated when you're near the ground and where all the exhaust goes.
-Having rocket fuel tanks landing on spikey rocks has the potential to really ruin your day.
-Knowing when to turn the rocket engines off (i.e. successfully detecting landing) is actually quite a hard problem. It's a very noisy problem, and getting it wrong was what destroyed Mars Polar Lander (i.e. it thought it landed when it was still up in the air, and so fell out of the sky). The skycrane has the rocket motors on the whole time and goes off an crashes.
Lots of this is explained in the video I linked to somewhere else in this family of comments.
>I can imagine a system where the capsule pitches up near the end of its run so that it starts gaining altitude and then deploys a parachute for landing once it has reached its apogee.
The martian atmosphere is really thin (I've heard it said that it would pass for vacuum in a high school science classroom). They've got that giant parachute doing as much deceleration-through-atmospheric-drag as possible, and it's still not enough. (And as a sibling post said, fancy atmospheric manoeuvring would require huge wings)
>Another thing is the crane mechanism, which is to protect the rover from the debris kicked up from the rocket motors. I was wondering why the rover couldn't just be encased in a simple lightweight protective box and then placed directly on the deck?
A box with rocket motors on? That'd still churn up the ground that the rover then has to drive through to go anywhere.
Or do you mean dropping it without the cable? The current rovers (MER) were deployed that way, with airbags, but this one's too big to do that with.
Yeah I was thinking of landing it without the cables, inside a protective box and then opening the box once all the dust and debris has settled or blown away. You wouldn't need any airbags as the current system is able to achieve a descent of only 1.5mph, meaning it could be placed gently on the surface.
You also need to consider that the landing may be successful but the vehicle's drive system may be rendered inoperable for any number of reasons. In that case, you'd want the surrounding ground to be as undisturbed/uncontaminated as possible so you could still do some science in that location without being able to move around.
I think that to do that maneuver you must have wings, and the atmosphere of Mars is thin, so you need bigger wings, and the structure to hold the wings in place give them enough strength. So I think it's easier to use a parachute.
* An overview on CosmoQuoest.org: http://cosmoquest.org/blog/2012/08/curiosity-landing-remembe...
* A Google+ hangout that'll be covering the landing: https://plus.google.com/events/c7c2fbd2gil25fjimln1jnr1134/1...
* Conversion of the landing time into various time zones: http://timeanddate.com/worldclock/fixedtime.html?msg=NASA+Cu...