5 ms·

I don't understand why they need the skycrane. Why did Viking land ok without this complexity? Why can't they reuse whatever they did for Viking?

dag11 14y ago
I'm pretty sure one of the reasons is its unprecedented size: http://upload.wikimedia.org/wikipedia/commons/0/0d/Mars_Science_Laboratory_wheels.jpg http://upload.wikimedia.org/wikipedia/commons/0/0d/Mars_Scie...
raverbashing 14y ago
Size + required landing precision It certainly looks like overly complex. The simplest system, that is, airbags, are unusable because of the size (it's almost like the difference between a big toy car and a regular car) You probably can't brake it only with retrorockets, and as this mission is aiming to be the most precise landing on Mars ever (and I'm not even sorry for the pun) they need a way to get the lander to an exact location (by deploying it from the crane)
- Sharlin 14y ago
  People seem to forget/not realize that the EDL (entry, descent and landing) of Spirit and Opportunity had pretty much all the elements that the Curiosity EDL does PLUS the airbags and the airbag cocoon: http://www.youtube.com/watch?v=Ij33yhdGn_g http://www.youtube.com/watch?v=Ij33yhdGn_g
  - CamperBob2 14y ago
    Leaving out the sky crane means that the comparison doesn't involve "pretty much all the same elements." The MSL sky crane is insanely complicated. Not much can go wrong with an airbag, relatively speaking. I'd compare it to Cassini-Huygens, more than Spirit and Opportunity.
    - mturmon 14y ago
      "not much can go wrong with an airbag" -- not true. The mission designers for MER (Spirit/Opportunity) admitted that a wrong bounce or an initial collision with a sharp rock could spell doom. I think the airbag relies considerably more on good luck. You can't really model collisions the way you can a descent on a cable. The latter is 100% engineered.
    - Sharlin 14y ago
      But as the video shows, the MERs did have a similar system - after the parachute phase, the rover in its cocoon was lowered from the aeroshell at the end of a tether. Then, the retrorockets in the aeroshell fired, bringing the whole thing to a full stop some tens of meters above the ground. After that, the airbags inflated, the tether was severed, and the rover dropped the rest of the way to the surface.
ddbeck 14y ago
One of the reasons for the skycrane is that it minimizes the area of the Martian surface that will be disturbed by the landing rockets. The skycrane approach moves less surface soil around the landing site (decreasing travel distance to pristine subjects for geological study) and deposits less rocket exhaust (which complicates chemical and biological studies). NASA has an excellent and free ebook, _When Biospheres Collide_ [1], which goes into great detail about the problems posed by biological contamination (both forward and back). The book dedicates a long chapter to the great lengths taken with the Viking landers to avoid contamination problems. Having read it, I'm not at all surprised NASA is giving alternatives a try. [1]: http://www.nasa.gov/connect/ebooks/when_biospheres_collide_detail.html http://www.nasa.gov/connect/ebooks/when_biospheres_collide_d...
- tocomment 14y ago
  Why didn't Viking worry about disturbing the landing site? Also If it can drive why does it matter what happens to the landing site?
  - ricardobeat 14y ago
    They drive at mm/s speeds. Moving over a few meters because the soil is stirred up is a huge waste of energy and time, not to mention the risk of failure.
    - mturmon 14y ago
      No, not for curiosity. That robot is expected to drive many kms as part of its planned activities. Its nominal speed is 30 m per hour.
      - dredmorbius 14y ago
        Which is 120 mm/sec -- about 4.75 inches, as parent noted.
        mturmon 14y ago

dag11 14y ago

I'm pretty sure one of the reasons is its unprecedented size: http://upload.wikimedia.org/wikipedia/commons/0/0d/Mars_Science_Laboratory_wheels.jpg http://upload.wikimedia.org/wikipedia/commons/0/0d/Mars_Scie...

raverbashing 14y ago

Size + required landing precision It certainly looks like overly complex. The simplest system, that is, airbags, are unusable because of the size (it's almost like the difference between a big toy car and a regular car) You probably can't brake it only with retrorockets, and as this mission is aiming to be the most precise landing on Mars ever (and I'm not even sorry for the pun) they need a way to get the lander to an exact location (by deploying it from the crane)

Sharlin 14y ago
People seem to forget/not realize that the EDL (entry, descent and landing) of Spirit and Opportunity had pretty much all the elements that the Curiosity EDL does PLUS the airbags and the airbag cocoon: http://www.youtube.com/watch?v=Ij33yhdGn_g http://www.youtube.com/watch?v=Ij33yhdGn_g
- CamperBob2 14y ago
  Leaving out the sky crane means that the comparison doesn't involve "pretty much all the same elements." The MSL sky crane is insanely complicated. Not much can go wrong with an airbag, relatively speaking. I'd compare it to Cassini-Huygens, more than Spirit and Opportunity.
  - mturmon 14y ago
    "not much can go wrong with an airbag" -- not true. The mission designers for MER (Spirit/Opportunity) admitted that a wrong bounce or an initial collision with a sharp rock could spell doom. I think the airbag relies considerably more on good luck. You can't really model collisions the way you can a descent on a cable. The latter is 100% engineered.
  - Sharlin 14y ago
    But as the video shows, the MERs did have a similar system - after the parachute phase, the rover in its cocoon was lowered from the aeroshell at the end of a tether. Then, the retrorockets in the aeroshell fired, bringing the whole thing to a full stop some tens of meters above the ground. After that, the airbags inflated, the tether was severed, and the rover dropped the rest of the way to the surface.

ddbeck 14y ago

One of the reasons for the skycrane is that it minimizes the area of the Martian surface that will be disturbed by the landing rockets. The skycrane approach moves less surface soil around the landing site (decreasing travel distance to pristine subjects for geological study) and deposits less rocket exhaust (which complicates chemical and biological studies). NASA has an excellent and free ebook, _When Biospheres Collide_ [1], which goes into great detail about the problems posed by biological contamination (both forward and back). The book dedicates a long chapter to the great lengths taken with the Viking landers to avoid contamination problems. Having read it, I'm not at all surprised NASA is giving alternatives a try. [1]: http://www.nasa.gov/connect/ebooks/when_biospheres_collide_detail.html http://www.nasa.gov/connect/ebooks/when_biospheres_collide_d...

tocomment 14y ago
Why didn't Viking worry about disturbing the landing site? Also If it can drive why does it matter what happens to the landing site?
- ricardobeat 14y ago
  They drive at mm/s speeds. Moving over a few meters because the soil is stirred up is a huge waste of energy and time, not to mention the risk of failure.
  - mturmon 14y ago
    No, not for curiosity. That robot is expected to drive many kms as part of its planned activities. Its nominal speed is 30 m per hour.
    - dredmorbius 14y ago
      Which is 120 mm/sec -- about 4.75 inches, as parent noted.
      - mturmon 14y ago