IPB

Welcome Guest ( Log In | Register )

12 Pages V  < 1 2 3 4 5 > »   
Reply to this topicStart new topic
Mro On Approach, TCM-3 not required
mcaplinger
post Feb 17 2006, 04:05 AM
Post #31


Senior Member
****

Group: Members
Posts: 1293
Joined: 13-September 05
Member No.: 497



QUOTE (jmknapp @ Feb 16 2006, 06:00 PM) *
Hmmm... using the "ideal" kernel gives periapsis on 15MAR2006 at 06:24UTC, 399km, at 67S 28E, although it's on the night side so the picture is dark. Pretty big difference there.

The software I'm using is a C program that I wrote to use the CSPICE library--so there could be a bug or three there. The same program works pretty well with Cassini, but at least in that case I have actual images to compare against for testing. Choice of kernels seems to be a big factor.


That result sounds pretty close to ours, so I'd say your code is working well. Those kernels just appeared on the NAIF website and I don't know what sort of burn performance differences they represent; it would surprise me if plausible burn variations would change the orbit timing so much.


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
Go to the top of the page
 
+Quote Post
Bob Shaw
post Feb 17 2006, 12:18 PM
Post #32


Senior Member
****

Group: Members
Posts: 2488
Joined: 17-April 05
From: Glasgow, Scotland, UK
Member No.: 239



QUOTE (mcaplinger @ Feb 17 2006, 04:05 AM) *
That result sounds pretty close to ours, so I'd say your code is working well. Those kernels just appeared on the NAIF website and I don't know what sort of burn performance differences they represent; it would surprise me if plausible burn variations would change the orbit timing so much.



Guys, can you *please* work out whoever is right, you're beginning to (gulp) worry me! MOI has already eaten several pretty toys...

Bob Shaw


--------------------
Remember: Time Flies like the wind - but Fruit Flies like bananas!
Go to the top of the page
 
+Quote Post
djellison
post Feb 17 2006, 12:47 PM
Post #33


Administrator
****

Group: Chairman
Posts: 13852
Joined: 8-February 04
Member No.: 1



Thing is - only a tiny tiny change in the altitiude at MOI, and the duration of MI will produce quite a large change at aphelion (it's a very eliptical orbit) and so a tiny fraction of a change to either of those numbers, will put quite a different bit of Mars under the spacecraft 5 days later smile.gif

Doug
Go to the top of the page
 
+Quote Post
Guest_AlexBlackwell_*
post Feb 17 2006, 06:13 PM
Post #34





Guests






QUOTE (Bob Shaw @ Feb 17 2006, 12:18 PM) *
Guys, can you *please* work out whoever is right, you're beginning to (gulp) worry me! MOI has already eaten several pretty toys...

You think Mike might be using metric figures, while jmknapp is using English units?

Hmm. That sounds vaguely familiar.
Go to the top of the page
 
+Quote Post
jmknapp
post Feb 17 2006, 06:28 PM
Post #35


Senior Member
****

Group: Members
Posts: 1428
Joined: 9-February 04
From: Columbus OH USA
Member No.: 13



QUOTE (AlexBlackwell @ Feb 17 2006, 01:13 PM) *
You think Mike might be using metric figures, while jmknapp is using English units?

Hmm. That sounds vaguely familiar.


I tend to prefer pixels per fortnight.

Be that as it may, any non-hyperbolic insertion orbit that doesn't intersect the surface is a good one.


--------------------
Go to the top of the page
 
+Quote Post
Guest_AlexBlackwell_*
post Feb 17 2006, 06:34 PM
Post #36





Guests






QUOTE (jmknapp @ Feb 17 2006, 06:28 PM) *
Be that as it may, any non-hyperbolic insertion orbit that doesn't intersect the surface is a good one.

That might be why the MRO mission designers baselined for aerobraking instead of lithobraking tongue.gif
Go to the top of the page
 
+Quote Post
elakdawalla
post Feb 17 2006, 06:36 PM
Post #37


Bloggette par Excellence
****

Group: Admin
Posts: 4503
Joined: 4-August 05
From: Pasadena, CA, USA, Earth
Member No.: 454



QUOTE (AlexBlackwell @ Feb 17 2006, 10:34 AM) *
That might be why the MRO mission designers baselined for aerobraking instead of lithobraking tongue.gif

I was going to crack that joke but I thought "Naw -- it's too old and tired." I guess no joke is too old and tired for an academic tongue.gif

--Emily


--------------------
My blog - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
Go to the top of the page
 
+Quote Post
Guest_AlexBlackwell_*
post Feb 17 2006, 06:50 PM
Post #38





Guests






QUOTE (elakdawalla @ Feb 17 2006, 06:36 PM) *
I was going to crack that joke but I thought "Naw -- it's too old and tired." I guess no joke is too old and tired for an academic tongue.gif
--Emily

Yeah, the joke was pretty stale.

In fact, as Mike has pointed out over the years, the public has gotten an incomplete if not distorted view of the MCO/MPL/DS2 losses, mainly that the root causes, especially of the MCO loss, can't be simply described as "Oh, they screwed up because they didn't know the difference between metric and English units."

For balance, I would also recommend the following:

Euler, Edward A., Steven D. Jolly, and H.H. Curtis; The Failures of the Mars Climate Orbiter and Mars Polar Lander: A Perspective From the People Involved; AAS 01-074, 24th Annual AAS Guidance and Control Conference, Breckenridge, CO, January 31-February 4, 2001.

A few years ago, Steve Jolly (of LMAO) also sent me some PowerPoint slides, prepared, I believe, for a subsequent conference. These offered some nice perspective, as well as being pretty instructive.

* EDIT - Before "[f]or balance" above, I should have inserted "In addition to the 'official' mishap investigation reports, which can downloaded, among other places, here, as well as the popular press coverage (of varying degrees of accuracy),..."

This post has been edited by AlexBlackwell: Feb 17 2006, 07:56 PM
Go to the top of the page
 
+Quote Post
Phil Stooke
post Feb 17 2006, 06:58 PM
Post #39


Senior Member
****

Group: Members
Posts: 5819
Joined: 5-April 05
From: Canada
Member No.: 227



Emily: "I guess no joke is too old and tired for an academic"

And no academic is too old and tired for a good joke.

Phil


--------------------
... because the Solar System ain't gonna map itself.
Go to the top of the page
 
+Quote Post
mcaplinger
post Feb 17 2006, 07:50 PM
Post #40


Senior Member
****

Group: Members
Posts: 1293
Joined: 13-September 05
Member No.: 497



QUOTE (AlexBlackwell @ Feb 17 2006, 10:13 AM) *
You think Mike might be using metric figures, while jmknapp is using English units?


Very funny, Alex. smile.gif If it makes anyone feel better, I don't have anything to do with planning MOI.

jmknapp has performed a valuable public service by highlighting that those three kernels produce significant orbital timing changes; I hadn't appreciated that the MOI performance could induce that large a change, but now we're prepared. We weren't given any context about what those kernels might mean -- they just showed up on the NAIF website. They may be for training purposes, or they may be physically realistic.


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
Go to the top of the page
 
+Quote Post
lyford
post Feb 17 2006, 08:06 PM
Post #41


Senior Member
****

Group: Members
Posts: 1264
Joined: 18-December 04
From: San Diego, CA
Member No.: 124



QUOTE (Phil Stooke @ Feb 17 2006, 10:58 AM) *
Emily: "I guess no joke is too old and tired for an academic"

And no academic is too old and tired for a good joke.

Phil

And I was going to crack that joke.....
It's getting to the point where I log on to UMSF and just nod in assent to almost every post tongue.gif


--------------------
Lyford Rome
"Zis is not nuts, zis is super-nuts!" Mathematician Richard Courant on viewing an Orion test
Go to the top of the page
 
+Quote Post
Guest_AlexBlackwell_*
post Feb 17 2006, 08:06 PM
Post #42





Guests






QUOTE (mcaplinger @ Feb 17 2006, 07:50 PM) *
Very funny, Alex. smile.gif If it makes anyone feel better, I don't have anything to do with planning MOI.

I couldn't resist the tweak, Mike, especially since I know the way the MCO/MPL/DS2 losses were reported has grated on you. It's not the same, though, as needling Bruce. Now that is fun tongue.gif

QUOTE (mcaplinger @ Feb 17 2006, 07:50 PM) *
jmknapp has performed a valuable public service by highlighting that those three kernels produce significant orbital timing changes; I hadn't appreciated that the MOI performance could induce that large a change, but now we're prepared. We weren't given any context about what those kernels might mean -- they just showed up on the NAIF website. They may be for training purposes, or they may be physically realistic.

Is this similar to the slight differences between MSSS-generated and JPL-designed targeting boxes that were evident early in MOC campaign? If I remember correctly, sometimes your orbit predicts disagreed with JPL's.
Go to the top of the page
 
+Quote Post
djellison
post Feb 17 2006, 08:09 PM
Post #43


Administrator
****

Group: Chairman
Posts: 13852
Joined: 8-February 04
Member No.: 1



QUOTE (AlexBlackwell @ Feb 17 2006, 08:06 PM) *
It's not the same, though, as needling Bruce. Now that is fun tongue.gif


Now that's actually a requirement for membership here, it's not a matter of humour - it's part of the process cool.gif

Doug
Go to the top of the page
 
+Quote Post
jmknapp
post Feb 17 2006, 09:39 PM
Post #44


Senior Member
****

Group: Members
Posts: 1428
Joined: 9-February 04
From: Columbus OH USA
Member No.: 13



QUOTE (mcaplinger @ Feb 17 2006, 02:50 PM) *
jmknapp has performed a valuable public service by highlighting that those three kernels produce significant orbital timing changes; I hadn't appreciated that the MOI performance could induce that large a change, but now we're prepared. We weren't given any context about what those kernels might mean -- they just showed up on the NAIF website. They may be for training purposes, or they may be physically realistic.


FWIW, here's the difference between the three kernels in terms of altitude. Looks like they are very different. Not sure of the context as you say--both high perf and low perf have shorter periods than ideal.



--------------------
Go to the top of the page
 
+Quote Post
djellison
post Feb 17 2006, 09:59 PM
Post #45


Administrator
****

Group: Chairman
Posts: 13852
Joined: 8-February 04
Member No.: 1



Being VERY unscientific, approx speed at periareion using Orbiter with these apareion's....

10000km - 4330 m/sec
18000km - 4460 m/sec
28000km - 4590 m/sec
38000km - 4650 m/sec
45000km - 4670 m/sec

So to vary between 28000 and 45000 is only a 80ish m/sec difference, in an MOI burn of I believe roughly 1000 m/sec over 25 minutes - so +/- 40m/sec is about a 4% error, or 1 minute of the burn

200 x 400km orbit is approx 3520 - 3320 m/sec ish -so aerobraking is giving us another 1000 m/sec of delta V.

All figures very VERY roughly done in orbiter.

Doug
Go to the top of the page
 
+Quote Post

12 Pages V  < 1 2 3 4 5 > » 
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 28th November 2014 - 01:25 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.