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djellison
Posted on: Jun 12 2012, 06:52 AM


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QUOTE (brellis @ Jun 11 2012, 09:32 PM) *
Is the scariest part getting into the atmosphere at the correct angle?


That's something we've done many times

QUOTE
Does the sky crane have a failure potential based on the fact that it's never been tried on Mars?


Yup. As has every landing system sent to Mars. When Viking went, it hadn't been tried on Mars. Nor had Pathfinder. Nor had MER ( which was similar to, but far from identical to Pathfinder ) And Phoenix's only previous test was a failure. There are many many ways in which MSL could fail during EDL.

QUOTE
Narrowing the landing ellipse eases my fears about the early parts of this process. The sky crane part has me all twisted up in concern!


Many many people seem to point at the Sky Crane and express concern, but no one's ever pointed out to me what it is that has them all concerned. Why does it make you any more or less concerned than Viking, Pathfinder, MER or Phoenix?

It's worth noting that the very same team that put Spirit and Opportunity on the surface of Mars - is the team responsible for MSL EDL.



  Forum: MSL · Post Preview: #184945 · Replies: 186 · Views: 168947

djellison
Posted on: Jun 10 2012, 12:17 AM


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Monday - 9am Pacific.
  Forum: MSL · Post Preview: #184915 · Replies: 186 · Views: 168947

djellison
Posted on: Jun 9 2012, 02:47 PM


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Look out for some landing ellipse news.
  Forum: MSL · Post Preview: #184900 · Replies: 186 · Views: 168947

djellison
Posted on: Jun 6 2012, 05:53 AM


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QUOTE (Sunspot @ Jun 5 2012, 01:37 PM) *
Cant beleive they have taken down access to the real time high res images, Venus has been visible in SDO cameras for over an hour.


This is probably the busiest event for SDO's website for half a decade. To make sure as many people as possible saw as much as possible, they obviously did crops of images so we could all track every phase of the transit in those amazing images.

Doing anything else would probably have seen their entire website go down for the duration of the event.

All the images will be online again soon.

Sometimes it amazes me that we are so astonishingly lucky to have the resources available to us, yet still people complain.

Shameful.





  Forum: Chit Chat · Post Preview: #184797 · Replies: 76 · Views: 45238

djellison
Posted on: Jun 4 2012, 03:54 PM


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Imagehost, XS and others have all gone away or have a policy of deleting older content. It's a shame, but that's the risk you run with free hosting facilities.
  Forum: Spirit · Post Preview: #184778 · Replies: 71 · Views: 170778

djellison
Posted on: Jun 4 2012, 12:39 AM


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It'll be about 10:35pm Pacific.
  Forum: Chit Chat · Post Preview: #184774 · Replies: 33 · Views: 22755

djellison
Posted on: May 22 2012, 07:52 PM


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It's hard to map project an image when two corners are in space.
  Forum: Past and Future · Post Preview: #184567 · Replies: 98 · Views: 268018

djellison
Posted on: May 21 2012, 08:47 PM


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It already has - http://en.wikipedia.org/wiki/File:MESSENGE...ly_Portrait.jpg
  Forum: Chit Chat · Post Preview: #184550 · Replies: 76 · Views: 45238

djellison
Posted on: May 21 2012, 06:11 AM


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Why would it? Venus doesn't care that the Earth's in opposition.
  Forum: Chit Chat · Post Preview: #184534 · Replies: 76 · Views: 45238

djellison
Posted on: May 20 2012, 12:24 AM


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QUOTE (PDP8E @ May 19 2012, 04:37 PM) *
There are a seven named peaks in Gusev in the vicinity of Spirit.


And they were named by the MER team.
  Forum: MSL · Post Preview: #184507 · Replies: 365 · Views: 228351

djellison
Posted on: May 19 2012, 11:11 PM


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The IAU could have just done nothing. What they've done is make this now a challenging issue for the project, for media relations etc etc.
  Forum: MSL · Post Preview: #184504 · Replies: 365 · Views: 228351

djellison
Posted on: May 19 2012, 08:06 AM


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It's disrespectful to the team that's put in the years of work who are about to explore it and most of all, disrespectful to Bob Sharp.
  Forum: MSL · Post Preview: #184495 · Replies: 365 · Views: 228351

djellison
Posted on: May 19 2012, 06:18 AM


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Got to say - this is a very silly move by the IAU.
  Forum: MSL · Post Preview: #184493 · Replies: 365 · Views: 228351

djellison
Posted on: May 17 2012, 05:58 PM


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I'm utterly addicted to Kerbal. Infact - right now I'm mapping Mun using this very addon. Running at 2x speed in a 4.5 x 45km orbit - I've gone about 31 orbits so far. You can see a few sections where I tried 10x speed, but the spacing became very bad ( call it, errr, low data rate season? )

Once this mapping cycle is finished - about another 15 orbits or so - I'll go to a high orbit, at 10x speed, to have a more scattergun approach and leave that running for a while.

D
  Forum: Chit Chat · Post Preview: #184441 · Replies: 5 · Views: 6705

djellison
Posted on: May 14 2012, 02:56 AM


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No - you didn't read my whole post - there are several other earth observing satellites that have that much ,or more power. Not to keep themselves warm - just to power their system, power their instruments, power their telecom gear etc.

  Forum: Earth Observations · Post Preview: #184372 · Replies: 3 · Views: 7033

djellison
Posted on: May 14 2012, 02:19 AM


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QUOTE (Blue Sky @ May 13 2012, 05:00 PM) *
What impressed me was it's power budget of 4000 watts. Yowza.


Very ordinary for an earth observing spacecraft. Aqua, Terra, Aura - all are over that.

The sadly dead Envisat was 50% more than that. Many geostationary communication satellites have 5 times that much.
  Forum: Earth Observations · Post Preview: #184370 · Replies: 3 · Views: 7033

djellison
Posted on: May 13 2012, 05:21 PM


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We know exactly how the MER chassis copes with real Mars. It's being used as calibration - a reality check - to help us figure out exactly how well the MSL chassis will handle Mars as well.
  Forum: MSL · Post Preview: #184359 · Replies: 50 · Views: 65647

djellison
Posted on: May 12 2012, 12:30 AM


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It's a 1909 penny. Had MSL launch in 2009 - it would have been 100 years old at the time.
  Forum: MSL · Post Preview: #184328 · Replies: 186 · Views: 168947

djellison
Posted on: May 11 2012, 06:11 AM


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I've looked at most of the publicly available MSL images and there isn't a close up of it - and certainly not when stowed.

It's visible here - http://photojournal.jpl.nasa.gov/jpeg/PIA14256.jpg

This is a poor image, from above, but you can see stowed MAHLI and stowed mobility and the bracket in question

http://photojournal.jpl.nasa.gov/jpeg/PIA15021.jpg


it's just behind the callout graphics in this one
http://photojournal.jpl.nasa.gov/jpeg/PIA15289.jpg

It's also on these...
http://photojournal.jpl.nasa.gov/jpeg/PIA14252.jpg
http://photojournal.jpl.nasa.gov/jpeg/PIA13980.jpg
http://photojournal.jpl.nasa.gov/jpeg/PIA13981.jpg
http://photojournal.jpl.nasa.gov/jpeg/PIA13808.jpg



  Forum: MSL · Post Preview: #184309 · Replies: 186 · Views: 168947

djellison
Posted on: May 10 2012, 04:39 PM


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You can see some of the carbon figre textures to the right of the LED reflections on the inside of the backshell as a slightly lineated checker like pattern
http://mars.jpl.nasa.gov/msl/images/msl201...1-4314-full.jpg

The actual spot we're looking at is not visible in that picture - but it's basically the same all the way around.

It's pretty warm in the backshell - typically room temperature. The CCD will be much happier once it's on Mars. Moreover - it will have been quite a long exposure to get that image, an order of magnitude or longer that will be done on Mars. We're talking a range of 20cm+, rather than the 2cm the LED's will typically be illuminating.
  Forum: MSL · Post Preview: #184291 · Replies: 186 · Views: 168947

djellison
Posted on: May 9 2012, 01:29 AM


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There's no soft way of doing it. Indeed, a more eccentric 'lobbed' orbit will involve higher speeds at perigee.
  Forum: Messenger · Post Preview: #184271 · Replies: 27 · Views: 80987

djellison
Posted on: May 6 2012, 05:41 PM


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QUOTE (Explorer1 @ May 5 2012, 09:24 PM) *
I doubt the camera is even designed to image the sun without being wrecked.


The whole spacecraft isn't designed to point that way - it would cook. The thermal blanket covering one side of the spacecraft is sun pointed at all times to avoid damage to the spacecraft.
  Forum: Messenger · Post Preview: #184230 · Replies: 27 · Views: 80987

djellison
Posted on: May 4 2012, 04:26 PM


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QUOTE (MahFL @ May 4 2012, 05:38 AM) *
I was under the impression the only actively guided part was the initial ballistic entry using the Nitrogen jets on the back shell.


Here's the best single document describing EDL
http://trs-new.jpl.nasa.gov/dspace/handle/2014/41629

Best section is this

QUOTE
The MSL entry guidance algorithm is divided into four phases. Entry interface marks the start of guided entry:
guidance is initialized in the pre-bank phase and the controller commands bank attitude hold until the sensed acceleration exceeds 0.5 Earth g’s.
Once the sensed acceleration exceeds the specified trigger limit, the range control phase begins. During the range control phase, the bank angle is commanded to minimize predicted downrange error at parachute deployment.
Throughout this phase, cross-range error is maintained with a manageable deadband limit by executing bank reversals as necessary.
Peak heating and peak deceleration occur during this guidance phase.
Once the navigated relative velocity drops below about 900 m/s, guidance transitions to a heading alignment phase to minimize residual cross-range error before parachute deployment.
Just prior to parachute deployment, the vehicle angle of attack is adjusted to 0° by ejecting balance masses while the azimuth is aligned for better radar performance later during parachute descent. Parachute deployment is triggered at a navigated velocity of over 450 m/s.


A small point - it's not nitrogen - it's hydrazine thrusters. Infact the 8 thrusters on the back of the backshell to control attitude / roll during guided entry are the same model of thruster used in clusters for Phoenix terminal descent ( Aerojet MR-107U )

This document is more specifically about the guided entry phase - including some nice charts of sim-runs
http://www.planetaryprobe.eu/IPPW7/proceed...ssion5/p453.pdf
  Forum: Chit Chat · Post Preview: #184192 · Replies: 33 · Views: 22755

djellison
Posted on: May 3 2012, 07:26 AM


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QUOTE (JohnVV @ May 2 2012, 11:03 PM) *
and our much thicker atmosphere
the air will play a much bigger role


As James points out - the softness is down to geometry alone.

  Forum: Chit Chat · Post Preview: #184154 · Replies: 33 · Views: 22755

djellison
Posted on: May 3 2012, 05:51 AM


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Note how soft the edge of the shadows are... a symptom of being closer to the sun, thus it's angular size being much larger.
  Forum: Chit Chat · Post Preview: #184150 · Replies: 33 · Views: 22755

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