Author Topic: NASA - MSL Updates  (Read 83243 times)

Offline Lee Jay

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Re: NASA - MSL Updates
« Reply #20 on: 12/02/2011 04:31 PM »
When is the landing?  I heard on the NASA Tweetup that it is at 10:00pm or so PDT, but they didn't say a date (maybe August 6th)?  But the update says it's the 5th, but not the 5th where.  Anyone have the truth?

Offline Apollo-phill

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Re: NASA - MSL Updates
« Reply #21 on: 12/02/2011 04:37 PM »
Anyone have any data for MSL TCM-1 due 10 December 2011 yet ?

Rumor has it that MSL entered safemode due to a thruster issue and the first TCM has been pushed back.  Anyone here have insight into this?

If you read the press release from the beginning till the end, both your questions will be answered.


UMSF reports that the TCM was canceled because of an accurate launch, and the TCM was not needed.  The safemode was caused by a star-tracker software issue.  They have recovered from safemode, with the exception of the start-tracker problem, which does not appear to be serious.

No need to quoted secondary sources. All that information is in the press release if, again, you read it till the end.

pechisbeque

I only asked about TCM-1 BEFORE JPL/NASA issued news release and did not add the 'safe-mode' info that was posted by another poster. :D

A-P


Offline Apollo-phill

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Re: NASA - MSL Updates
« Reply #22 on: 12/02/2011 04:41 PM »
was the velocity sun relative or earth relative?

Jim

From press release this is what JPL/NASA said:-

"....As of 9 a.m. PST (noon EST) on Friday, Dec. 2, the spacecraft will have traveled 10.8 million miles (17.3 million kilometers) of its 352-million-mile (567-million-kilometer) flight to Mars, and will be moving at 7,500 mph (12,000 kilometers per hour) relative to Earth and at 73,800 mph (118,700 kilometers per hour) relative to the sun....."

Its the "travelled distance" I am 'confused' over .

Have written to JPL direct for answer but guy is out of office till Monday (he's the one who issued release - thought he'd have hung around answer any media calls !!).


A-P

Offline Apollo-phill

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Re: NASA - MSL Updates
« Reply #23 on: 12/02/2011 04:58 PM »
When MSL attempts to land on Mars using the Skycrane I understand that the distance from the ground to Skycrane - when MSL is released - will be 8.8 metres.

Could, however, the kick-up of martian regolith during firing of the 'Skycane thrusters' confuse' the altitude attitude sensors perhaps - therefore - releasing MSL too high from ground even if only a few centimtres? Could it withstand a 'free fall ' of just a few centimtres ? Any limit for a free fall ?


A-P


Offline ugordan

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Re: NASA - MSL Updates
« Reply #24 on: 12/02/2011 05:03 PM »
They measure the arc of the transfer trajectory in the sun-relative frame so it makes sense to measure the travelled distance in the same frame.

Offline ugordan

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Re: NASA - MSL Updates
« Reply #25 on: 12/02/2011 05:08 PM »
Could, however, the kick-up of martian regolith during firing of the 'Skycane thrusters' confuse' the altitude attitude sensors perhaps - therefore - releasing MSL too high from ground even if only a few centimtres?

The dust kicked up is not that thick to overwhelm the significantly higher radar ground reflection. The last few meters might even be IMU driven based on radar readings up until that point.

Why would several centimeters be of any issue, anyway?

Offline Apollo-phill

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Re: NASA - MSL Updates
« Reply #26 on: 12/02/2011 05:21 PM »
On a flat ground scenario a few centimetre fall may be OK but if the ground is on a slight slope (and this is a crater floor area emember so slopes may be more abundant ) a drop of a few centimetres may be more 'damaging' that could invoke rollover/tipover ?

I'm sure the guys/gals over at JPL have thought about this but would like see (PDF?) what their planning and final choice was on it ?

A-P

Offline ugordan

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Re: NASA - MSL Updates
« Reply #27 on: 12/02/2011 05:25 PM »
What drop are you talking about? Look at the EDL sim video. It's basically going to be a constant velocity phase landing similar to what Phoenix executed. The vehicle suspension and wheels are there to provide shock absorption. As Rob Manning said, it should be the smoothest planetary landing to date.

Offline Nomadd

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Re: NASA - MSL Updates
« Reply #28 on: 12/02/2011 05:33 PM »
They measure the arc of the transfer trajectory in the sun-relative frame so it makes sense to measure the travelled distance in the same frame.
I wonder if I can get accounting to fall for that when I turn my mileage report in.

Offline Apollo-phill

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Re: NASA - MSL Updates
« Reply #29 on: 12/02/2011 05:37 PM »
What drop are you talking about? Look at the EDL sim video. It's basically going to be a constant velocity phase landing similar to what Phoenix executed. The vehicle suspension and wheels are there to provide shock absorption. As Rob Manning said, it should be the smoothest planetary landing to date.

I wondered whether the sensors detecting 'ground surface' could be 'confused' by any dust kickup and thereby releasing the skycrane deployment vehicle before it actually touched hard surface leaving a few centimetres fall .If on flattis ground probably not a problem with - as you say - it has suspension but if on a sloping ground might be more a problem.

Are any MSL EDL PDFs around in public domain describing the process in detail ?

A-P







Offline Apollo-phill

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Re: NASA - MSL Updates
« Reply #30 on: 12/02/2011 05:56 PM »
Since my last post re MSL skycrane landing, I have found a PDF called :-

The MSL SkyCrane Landing Architecture
A GN&C Perspective
by
Miguel San Martin
Jet Propulsion Laboratory, California Institute of Technology
presented at the  International Planetary Probe Conference Barcelona, Spain June 14-18, 2010

Not yet read it but looks very interesting and I did quickly note that he stated:-

"...Ground thruster plume interaction  requires large vertical approach speeds to
deal with:
Trenching effects
Dust effects
Ground pressure effects....."

So,yes,as I  suspected they have thought about it :-)

A lot of good technical data on the landing seems to be in this PDF for those who like techie stuff

A-P

Offline Apollo-phill

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Re: NASA - MSL Updates
« Reply #31 on: 12/02/2011 06:13 PM »
Another skycrane landing PDF just found is called:-

"The Mars Science Laboatory"
"EDL Mode Commander"
by
Paul Brugarolas,Kim Gostelow,Miguel San Martin,Fred Sirrecchio and Gurkipal Singh
JPL

Again,not ye digested these techie PPT presentation frames.

A-P

Offline zeke01

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Re: NASA - MSL Updates
« Reply #32 on: 12/02/2011 06:28 PM »
What drop are you talking about? Look at the EDL sim video. It's basically going to be a constant velocity phase landing similar to what Phoenix executed. The vehicle suspension and wheels are there to provide shock absorption. As Rob Manning said, it should be the smoothest planetary landing to date.

I wondered whether the sensors detecting 'ground surface' could be 'confused' by any dust kickup and thereby releasing the skycrane deployment vehicle before it actually touched hard surface leaving a few centimetres fall .If on flattis ground probably not a problem with - as you say - it has suspension but if on a sloping ground might be more a problem.

Are any MSL EDL PDFs around in public domain describing the process in detail ?

A-P

Yes.  See attachment
« Last Edit: 12/02/2011 06:31 PM by zeke01 »

Offline joncz

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Re: NASA - MSL Updates
« Reply #33 on: 12/02/2011 06:47 PM »
They measure the arc of the transfer trajectory in the sun-relative frame so it makes sense to measure the travelled distance in the same frame.
I wonder if I can get accounting to fall for that when I turn my mileage report in.

Only if the Judge gets to use the sun-relative velocity when determining your speeding fine.  :o

Offline Apollo-phill

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Re: NASA - MSL Updates
« Reply #34 on: 12/02/2011 07:23 PM »
Here is a very ggod description of the last few seconds of when MSL Skycrane will be operating and you will read that it is the sensing f the "bridle going slack" that triggers - in effect - touchdown :-

"........As planned, MSL does not have a direct means of sensing Rover touchdown; a software logic is employed instead.  Consider what happens as the Descent Stage (DS) and Rover, separated by the triple-bridle continue to descend at a constant rate during the SC segment of the mission.  Actually it is the DS which is forced to follow this constant velocity vertical trajectory. 
It is forced to remain on this path until the touchdown has been confirmed.  As the system continues its descent, at some point in time the Rover will make contact with the surface, eventually causing the bridle to go slack as long as the DS can be made to continue on its downwards constant
rate motion.  A continuation of the DS motion requires less force.  It is this change in the force command which is monitored (with a persistence check) to declare touchdown.  Upon receiving this indication,  a bridle cut is performed to sever the DS Rover connection.  The DS, in order to land at a far enough distance from the Rover, throttles up while executing a turn to place the velocity vector at an optimum angle with respect to the local horizontal.  All engines are shut down after a fixed time interval, and the DS coasts eventually crashing on the surface. ......."


from
"Guidance and Control Design for Powered Descent and Landing on Mars "
by Gurkirpal Singh, Alejandro M. SanMartin  , Edward C. Wong 
Jet Propulsion Laboratory"



Apollo-phill

Offline Apollo-phill

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Re: NASA - MSL Updates
« Reply #35 on: 12/02/2011 07:25 PM »
In the previous post SC is SkyCrane

So,dust kickup will probably not be a major concern unles of curse it affects the triple bridal to a very great effect (doubtful).

A-P

Offline Jim

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Re: NASA - MSL Updates
« Reply #36 on: 12/02/2011 07:47 PM »
There is no physical object called sky crane. MSL uses a descent stage to lower the rover.   Skycrane is a methodology. 

Offline Jim

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Re: NASA - MSL Updates
« Reply #37 on: 12/02/2011 07:49 PM »
What drop are you talking about? Look at the EDL sim video. It's basically going to be a constant velocity phase landing similar to what Phoenix executed. The vehicle suspension and wheels are there to provide shock absorption. As Rob Manning said, it should be the smoothest planetary landing to date.

I wondered whether the sensors detecting 'ground surface' could be 'confused' by any dust kickup and thereby releasing the skycrane deployment vehicle before it actually touched hard surface leaving a few centimetres fall .If on flattis ground probably not a problem with - as you say - it has suspension but if on a sloping ground might be more a problem.

Are any MSL EDL PDFs around in public domain describing the process in detail ?

A-P

No, the sensors detect the weight on the bridle which determines landing

Offline Lee Jay

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Re: NASA - MSL Updates
« Reply #38 on: 12/02/2011 08:00 PM »
"........As planned, MSL does not have a direct means of sensing Rover touchdown; a software logic is employed instead.

No, the sensors detect the weight on the bridle which determines landing

Can both of these be correct in some way I'm not seeing?

Offline Pheogh

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Re: NASA - MSL Updates
« Reply #39 on: 12/02/2011 08:32 PM »
Ok so if I understand this correctly what actually causes the bridle cut is that the DS senses a difference in thrust requirement based on the when the lander touches the surface it is no longer carrying that load, correct?

Makes me wonder though if there are any bumps in deployment of the bridle that could inadvertently cause a slack reading? Of course I am sure they have covered all anomalies, still would love to a ton more about the systems development.

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