Mars Science Laboratory (MSL) - "Curiosity"

[crosscountry]

No, the LM testing was done in Earth Orbit and in lunar orbit, with a lunar approach and abort. It was not able to fly near the Earth's surface. Are you thinking of the LLRV and LLTV?

Fred

There was landing testing done on Earth. The last part was to put the Apollo 10 near surface abort with the landing test done on Earth.

[ugordan]

NASA is partly to blame. To my eyes and ears the video describing the entry and landing seems to employ Hollywood drama.

People were freaking out about the skycrane method long before NASA put out that video.

[KaiYeves]

NASA is partly to blame. To my eyes and ears the video describing the entry and landing seems to employ Hollywood drama. Spooky music, dramatic voiceovers, "game over" comments. Heck NASA titled the durn thing The Seven Minutes of Terror.

ETA: Oops...looks like I was channeling iquestor's posts.

That exact same phrase ("Seven Minutes of Terror") was used during the Phoenix landing, as I recall.

[cjameshuff]

Too complicated. A simpler failsafe would be to simply make the bridle cutters dual redundant, if they aren't already.

First, that's not a failsafe, that's redundancy. Trying to prevent a failure is worthwhile, but so is designing the system to tolerate failure where possible.

Second, what exactly is "complicated" about this? Limiting thrust after the rover is down to levels that can't lift the rover off the ground is about as simple as you can get.

That exact same phrase ("Seven Minutes of Terror") was used during the Phoenix landing, as I recall.

That's right. A "Six Minutes of Terror" variant was also used for the MER rover landings. And people were freaking out about the crazy airbag landing scheme.

[Trebuchet]

Next weekend is looking interesting, fun, and scary! Saturday -- a tentative visit to Gillian's Renaissance Faire! Sunday, the Seafair hydro races AND Curiosity's landing! I'll be watching.

[ugordan]

First, that's not a failsafe, that's redundancy.

Fine, call it what you will. My point is it would still be more reliable than implementing some super precise evasive maneuver to land the descent stage within meters of the rover, yet without actually landing on top of it. You could take this paranoid approach to just about every phase of the EDL and have failsafes to be developed and then you would probably miss another Mars launch window because you just made the system even more complex.

Second, what exactly is "complicated" about this? Limiting thrust after the rover is down to levels that can't lift the rover off the ground is about as simple as you can get.

Software design and testing. Making especially sure you cut the lines *is* as simple as you get, your method requires new developments.

[Zvezdichko]

And people were freaking out about the crazy airbag landing scheme.

Yet we already knew that the airbag method has worked before - on Pathfinder.

They haven't tested it before. Personally I find ESA's approach much more convincing as they're going to run a test in 2016 with a landing demonstrator module, then (if it works) - send the rover in 2018

[cjameshuff]

Fine, call it what you will. My point is it would still be more reliable than implementing some super precise evasive maneuver to land the descent stage within meters of the rover, yet without actually landing on top of it.

What super-precise evasive maneuver? You only need to get the thing on the ground and its engines shut down without dragging the rover over!

You could take this paranoid approach to just about every phase of the EDL and have failsafes to be developed and then you would probably miss another Mars launch window because you just made the system even more complex.

But I'm not doing this. I'm suggesting a failsafe that they might have applied to make the system less likely to be lost if a failure occurs, at one particular point where it would be extremely simple to add such a failsafe.

Software design and testing. Making especially sure you cut the lines *is* as simple as you get, your method requires new developments.

So? There would be electronic, mechanical, and software design and testing behind adding redundancy to the line cutters.

They haven't tested it before.

What parts haven't been similarly tested as a landing technology? Controlled reentry is common practice on Earth. Chutes? Used on every vehicle that's re-entered an atmosphere. Tethered deceleration below a rocket pod? Done on the three preceding rover missions, and likely others. Controlled rocket-powered descent? Done, under even more difficult conditions and requirements, on Earth and the moon as well as Mars. There's nothing radically new here.

[ugordan]

What super-precise evasive maneuver? You only need to get the thing on the ground and its engines shut down without dragging the rover over!

The super-precise maneuver that would not "only" get the thing to the ground, but avoid doing it on top of the rover because that's precisely where the descent stage is at the time of rover touchdown. There would have to be a displacement maneuver of X meters performed by the descent stage. It takes software and a precise IMU to execute that flawlessly. It takes more software and testing to ensure that piece of code isn't inadvertently activated when it's not supposed to be. If you believe "latent" and otherwise unused code can't ruin your day, look up Ariane V maiden flight.

But I'm not doing this. I'm suggesting a failsafe that they might have applied to make the system less likely to be lost if a failure occurs, at one particular point where it would be extremely simple to add such a failsafe.

And I'm saying it's far from simple. If you're worried about dual-redundant bridle cutters failing to cut a line, you probably shouldn't have launched in the first place.

So? There would be electronic, mechanical, and software design and testing behind adding redundancy to the line cutters.

Not really. The same signal from the avionics would trigger both in parallel. There is very little added complexity. In fact, many pyro-actuated mechanisms are by design already dual redundant in that a signal fires two explosive charges, each of which is sufficient to do the job.

Really, there are many areas where EDL is more risky and failure prone than cutting some lines at the landing.

[cjameshuff]

The super-precise maneuver that would not "only" get the thing to the ground, but avoid doing it on top of the rover because that's precisely where the descent stage is at the time of rover touchdown. There would have to be a displacement maneuver of X meters performed by the descent stage. It takes software and a precise IMU to execute that flawlessly. It takes more software and testing to ensure that piece of code isn't inadvertently activated when it's not supposed to be. If you believe "latent" and otherwise unused code can't ruin your day, look up Ariane V maiden flight.

Ridiculous. You do not need to gently set the sky crane down precisely x meters away, you need to keep it from dragging the rover across the surface and terminate its flight without dropping it on the rover. It's likely the initial maneuver to move away will at least get the sky crane clear of the rover, so limiting maximum thrust after the rover is down is sufficient to greatly increase survivability following such a failure. A one time adjustment of a parameter in the existing control software, triggered at the same time as other post-landing events which will themselves likely doom the mission if they trigger early. That's it.

And this is nothing at all like what caused the Ariane 5 loss, which involved software reuse from a different system.

Not really. The same signal from the avionics would trigger both in parallel. There is very little added complexity. In fact, many pyro-actuated mechanisms are by design already dual redundant in that a signal fires two explosive charges, each of which is sufficient to do the job.

Very little, as compared to essentially zero added complexity to handle the possibility that the signal is for some reason prevented from being sent at all.

Really, there are many areas where EDL is more risky and failure prone than cutting some lines at the landing.

And few where a failsafe is practical to implement. This is one of those few.

[ugordan]

Ridiculous. <cut> A one time adjustment of a parameter in the existing control software, triggered at the same time as other post-landing events which will themselves likely doom the mission if they trigger early. That's it.

If you say so. Obviously, there is still time to suggest to JPL they implement this trivial improvement so why don't you contact them about it?

And few where a failsafe is practical to implement. This is one of those few.

See above.

[ToSeek]

There was landing testing done on Earth. The last part was to put the Apollo 10 near surface abort with the landing test done on Earth.

I'm not aware of any landing testing done on Earth. I don't even see how that would be possible.

[Trebuchet]

Here's a good video from Jorge Cham and PHD Comics showing a visit to the rover lab at JPL:

http://www.youtube.com/watch?v=sSpfJ...=youtu.be&hd=1

[cjameshuff]

If you say so. Obviously, there is still time to suggest to JPL they implement this trivial improvement so why don't you contact them about it?

Because they've most likely already done it, or something better! My whole point was that the nightmare scenario brought up by publiusr was unlikely because it was a situation that could easily be anticipated and a failsafe implemented!

[djellison]

o limiting maximum thrust after the rover is down is sufficient to greatly increase survivability following such a failure. A one time adjustment of a parameter in the existing control software, triggered at the same time as other post-landing events which will themselves likely doom the mission if they trigger early. That's it..

No. Just No. You want maximum thrust to get that descent stage away from the rover as far as possible.

What are you suggesting - that it touchdown, then sits there till the fuel runs out (potentially explosively) spewing hydrazine over the rover, probably destroying it in the process?

You are trying to find a solution to a problem that is so unlikely it's not worth trying to engineer around.

There is no 'fail safe' with failed pyros in EDL.

[cjameshuff]

No. Just No. You want maximum thrust to get that descent stage away from the rover as far as possible.

Ridiculous. It needs to get to a safe distance, it needn't go any further, and it doesn't need to drag the rover with it. Higher thrust increases the distance at which plume impingement can be an issue and increases the deviation from vertical required to achieve distance rather than altitude, complicating control. It's lighter by 900 kg of rover + much of the 390 kg of propellant (90 kg of propellant margin for the landing), a large percentage of the total descent stage mass, and doesn't need full thrust to move away.

What are you suggesting - that it touchdown, then sits there till the fuel runs out (potentially explosively) spewing hydrazine over the rover, probably destroying it in the process?

I'm not suggesting anything of the sort, or anything that can reasonably be confused with such a suggestion. What did you expect to achieve with such an obvious and absurd straw man?

You are trying to find a solution to a problem that is so unlikely it's not worth trying to engineer around.

No, I am pointing out that there is an outright trivial way to increase survivability of one particular failure mode, with essentially zero cost in risk or complexity. You and ugordon are fabricating bizarre schemes to argue against and doing whatever you can to take a solution that is likely just a particular choice of an already-existing parameter, or even just a factor to consider when selecting the thrust profile for the flyaway maneuver, and turn it into some kind of massive undertaking.

There is no 'fail safe' with failed pyros in EDL.

In some cases there is. I have given an example of one.

[djellison]

Ridiculous. It needs to get to a safe distance, it needn't go any further, and it doesn't need to drag the rover with it..

The bridle is 7.5 meters long. The rover is approx 3 meters on a side, and 1 meter tall to the deck. The descent stage is similarly about 3 meters on a side.

How do you get it a 'safe distance away' whilst still attached to a 7.5 meter bridle?

Explain - in detail - your example of a 'fail safe'.

[Superluminal]

I'm not aware of any landing testing done on Earth. I don't even see how that would be possible.

There was the LM trainer that nearly killed Armstrong.
http://videosift.com/video/Neil-Arms...der-Testflight

[Daggerstab]

There was the LM trainer that nearly killed Armstrong.
http://videosift.com/video/Neil-Arms...der-Testflight

That was landing training. We are talking about testing the hardware, i.e. the real Lunar Module in that case.

[cjameshuff]

How do you get it a 'safe distance away' whilst still attached to a 7.5 meter bridle?

More games. If the bridle's still attached, you're in a contingency where plume impingement is no longer the major concern, clearly not the situation where the descent stage is flying to a safe distance. You would have them apply maximum thrust and drag the rover across the landscape...care to explain how that's an improvement over some sandblasting, hydrazine contamination, and some chance of the descent stage ending up partially on the rover?

Explain - in detail - your example of a 'fail safe'.

I already did. Quit playing games and pretending to misunderstand it.

[swampyankee]

at least the LM has been tested in everything but landing, and that part was done on earth. There was only one step missing in the complete test. Besides, landing on an airless body is much easier.

Well, it wasn't tested for Lunar launch, either. The point remains that a full scale test was not, and could not, be done. So, the first full-scale LM test was Apollo XI. Apollo XII through XVII were the other six, but the Apollo XIII test was aborted because of service module problems. So, six full scale tests went to completion.

Component tests were obviously done, but system integration was, and remains, difficult for complex systems.

[djellison]

You would have them apply maximum thrust and drag the rover across the landscape....

No - I'd have the bridle separate....which it will. You're trying to engineer your way out of a box that enough testing has been done to guarantee we don't get into.

If those bridle's don't cut - it's game over. Same with dozens of other events during EDL. You can't fail graciously. Period.

I'll ask again - given the length of the bridle, the height and size of the rover, and the size of the descent stage...where does it end up?

You would probably kill the rover. The 900kg rover is not strong enough to withstand the descent stage landing on it. That's part of the reason the skycrane phase exists in the first place. Why do you think they want it a 'safe distance' away from the rover? Because there is significant risk of an explosive end to the descent stage's life. That safe distance (thru monte carlo sims) is several hundred meters. Infact, analysis lead to a change from letting the descent stage flame out thru fuel depletion to simply letting it burn for 4 seconds and shutting down. The balance being, if it flames out, the descent stage could well have a violent flame-out that could fling debris at the rover.

Moreover, in your cunning plan - how do you detect that the bridle hasn't cut? You are assuming that an event has occured where neither the descent stage umbilical nor the three bridles have cut - because the logic you are asking of the descent stage to put itself on the deck safely...it doesn't have. The flyaway controller on the descent stage has very very simple logic. Throttle one side up to 98%, one side up to 100%. Once the vehicle is at 50 degrees, 100% on both sides. After 4 seconds, kill the engines. That's it.

You are asking it to fly its way out of a situation it shouldn't be in, with abilities it doesn't have, into a situation that would kill the rover anyway.

[Swift]

I already did. Quit playing games and pretending to misunderstand it.

Moreover, in your cunning plan -

If you two don't knock off the sarcasm and the rudeness I'll suspend one or both of you.

[headrush]

Can someone ping this thread when there's some news? I don't watch tv and the net's a bit patchy around here.
Thanks

[djellison]

Pre landing fun starts tomorrow morning, 10 and 11 am Pacific time.
http://www.nasa.gov/multimedia/nasatv/index.html

1 p.m. - NASA Science News Conference – MSL Mission Science Overview – JPL (Public and Media Channels)
2 p.m. - NASA Science News Conference - Mission Engineering Overview - JPL (All Channels)

Keep an eye out for the final panelist on the second conference.

:-)

[SRH]

Question about Curiosity:

In terms of the distance at which Curiosity initiates the landing sequence:
is the distance being measured by how far Curiosity has traveled from Earth as determined by radio signals from Curiosity to NASA/Earth (based on redshift), or
is the distance being measured by onboard equipment telling Curiosity how far it is from the surface of Mars, or
is the distance being measured by onboard equipment telling Curiosity how far it has traveled from Earth (based on its motion/density of the medium/etc.)?

Thanks!

[Reality Check]

Question about Curiosity:

In terms of the distance at which Curiosity initiates the landing sequence:
is the distance being measured by how far Curiosity has traveled from Earth as determined by radio signals from Curiosity to NASA/Earth (based on redshift), or
is the distance being measured by onboard equipment telling Curiosity how far it is from the surface of Mars, or
is the distance being measured by onboard equipment telling Curiosity how far it has traveled from Earth (based on its motion/density of the medium/etc.)?

Thanks!

AFAIK the distance to Curiosity is measured from Earth using the standard techniques that are applied to all spacecraft besed on an imbedded ranging pulse in communications. See http://www2.jpl.nasa.gov/basics/bsf13-1.php

It looks like Curiosity has a certain time at which to start the landing sequence which will not be changed: MSL Remains on Track for Weekend Landing

Curiosity remains in good health, with no significant issues currently in work. There are no real-time activities planned today. The Mars Science Laboratory spacecraft remains on a consistent and stable course, well within the limits required to reach its target landing ellipse.

[Jeff Root]

Question about Curiosity:

In terms of the distance at which Curiosity initiates the
landing sequence:
is the distance being measured by how far Curiosity has
traveled from Earth as determined by radio signals from
Curiosity to NASA/Earth (based on redshift), or
is the distance being measured by onboard equipment
telling Curiosity how far it is from the surface of Mars, or
is the distance being measured by onboard equipment
telling Curiosity how far it has traveled from Earth (based
on its motion/density of the medium/etc.)?

Like most or probably all other deep-space spacecraft,
Curiosity has a star tracker. It takes images of Mars
and the star background and sends them to Earth where
they are analyzed to determine its position relative to
Mars. If it is in the right place, the onboard landing
program doesn't need to be adjusted. If it isn't in the
right place, it will most likely be commanded to use its
control jets to put it on track to land at the desired
time and location. In which case, again, the landing
program doesn't need to be changed. If for any reason
it can't land at the desired time or place, then the time
that the program uses to start the pre-landing activities
would be adjusted from Earth. The spacecraft needs to
orient itself, turn on some equipment and turn off other
equipment, and separate from the cruise stage which
I think has solar cells and stuff. After it enters Mars'
atmosphere, I think it determines when to deploy the
parachute with an accelerometer and probably a timer.
That is, it measures the deceleration as it enters the
atmosphere, then a fixed time after the deceleration
peaks, it deploys the parachute. After the heat shield
is jettisoned it uses radar to determine distance to
the ground.

Redshift in radio signals from Curiosity reveal its speed
relative to the receivers on Earth, but they don't tell the
distance. The time delay of returned signals should
reveal the distance.

-- Jeff, in Minneapolis

[Eadfrith]

So whats going to happen to Opportunity now?

[ugordan]

1 p.m. - NASA Science News Conference – MSL Mission Science Overview – JPL (Public and Media Channels)
2 p.m. - NASA Science News Conference - Mission Engineering Overview - JPL (All Channels)

For those of you who missed the conferences, they're posted at NASA's Youtube channel:

http://www.youtube.com/watch?v=KP-IR0MkZfs
http://www.youtube.com/watch?v=SwXe_X4UKoM