IPB

Welcome Guest ( Log In | Register )

MSL Cruise Phase
nprev
post Nov 26 2011, 03:50 PM
Post #1


Merciless Robot
****

Group: Admin
Posts: 8789
Joined: 8-December 05
From: Los Angeles
Member No.: 602



Okay, we're off and running! Please post all comments relating to MSL's transit to Mars here.


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
 
Start new topic
Replies
tanjent
post Nov 27 2011, 03:34 AM
Post #2


Member
***

Group: Members
Posts: 214
Joined: 30-December 05
Member No.: 628



I'm having some trouble with "data dropouts" myself while trying to view the videos - I wanted to review the telemetry data on the evolution of perigee and apogee during the second Centaur burn, because the first time through I did not understand what I was seeing. My recollection is that after a steady increase the apogee figures dropped abruptly somewhere over Madagascar. This may have simply indicated a move to a higher power of 10 on the display but it was too blurry to be sure. The perigee seemed to be stuck somewhere in the 80's or -80's (couldn't tell if it was a negative sign or a "star" in the simulation). This I really did not understand because it persisted even after the spacecraft was well on its way to Mars. Is it just that after a certain point the perigee ceased to update? Maybe some rocket scientist here can explain how the perigee figure would be expected to evolve if we actually continued to track it as the spacecraft approaches escape velocity. Seems to me both apogee and perigee would eventually have to go to infinity at the point where the vehicle transitions to a solar orbit but when it becomes possible to view the video without a "please try again later" message I am sure it will confirm that this is not what we actually saw.
Go to the top of the page
 
+Quote Post
kwan3217
post Nov 27 2011, 02:23 PM
Post #3


Junior Member
**

Group: Members
Posts: 89
Joined: 27-August 05
From: Eccentric Mars orbit
Member No.: 477



(Full inline quote removed- Mod)

The apogee for a perfect parabola is infinite, but if you run the formulas to find the perigee and apogee of an ellipse, on a hyperbola, you will get the correct perigee but a finite, negative apogee. Obviously a distance can never be negative (you can never be closer to me than at my same position, with zero distance) but you can run all the formulas in reverse with this negative apogee and get the correct position and velocity of the spacecraft.

Which brings me to my second point: There is in theory enough information in the elements to get the position and velocity of the spacecraft during the burns, if they are all consistent. One thing I don't know is how they handle "altitude". A really common way to do it is to take the radius distance from the center and subtract the equatorial radius of the Earth, but since the Earth is not a perfect sphere, this would result in a negative altitude at launch. So I don't know what you have to add to get back the radius vector, and it may be two different things for different altitudes. I remember seeing one of these simulations where the altitude wasn't in between periapse and apoapse.

Back to the original point: Since the apogee took one value and stuck with it after escape velocity was achieved, maybe they just put in some fill value, like -9999999 meters, and translated it to nautical miles. In which case, after escape, the orbital elements become insufficient to reconstruct position and velocity.
Go to the top of the page
 
+Quote Post
scalbers
post Nov 27 2011, 04:08 PM
Post #4


Senior Member
****

Group: Members
Posts: 1670
Joined: 5-March 05
From: Boulder, CO
Member No.: 184



QUOTE (kwan3217 @ Nov 27 2011, 03:23 PM) *
Back to the original point: Since the apogee took one value and stuck with it after escape velocity was achieved, maybe they just put in some fill value, like -9999999 meters, and translated it to nautical miles. In which case, after escape, the orbital elements become insufficient to reconstruct position and velocity.

Yes those numbers were fascinating. I assumed we just had one look at the numbers after the orbit went hyperbolic (eccentricity > 1). It seemed a reasonable value of negative apogee for a hyperbolic orbit. Osculating orbital elements of course can always be converted to an instantaneous position and velocity. I wrote a FORTRAN subroutine a long time ago that does this conversion - at least for heliocentric orbits.

I wonder what the earth-relative velocity and eccentricity values were when the engines cut off? It takes about 3.2 km/sec delta-V to go from low-Earth orbit to reach escape velocity (11.3 km/sec). Another 0.6 km/sec or so is needed to get to a Mars transfer orbit, though it looks from this press-kit excerpt that the actual excess velocity is more like 3.3 km/sec.

Orbit at SC Separation
Perigee: 104.0 km
Inclination: 35.5 deg
Hyperbolic Departure
Hyperbolic Excess Velocity Squared (C3): 10.78 km2/sec2
Declination of the Launch Asymtote (DLA): -1.10 deg
Right Ascention of the Launch Asymtote (RLA): 126.6 deg

Approximate Values
Orbit parameters shown for launch on 25 Nov 2011 at 10:25 a.m. EST.

And the following velocity equation from Wikipedia can help get back the semimajor axis, and then the eccentricity:

http://en.wikipedia.org/wiki/Elliptic_orbit

Steve
Go to the top of the page
 
+Quote Post
kwan3217
post Nov 28 2011, 08:58 PM
Post #5


Junior Member
**

Group: Members
Posts: 89
Joined: 27-August 05
From: Eccentric Mars orbit
Member No.: 477



(Full inline quote removed- Mod)

The guys at JPL SSD (that do the Horizons ephemeris program) got the spice kernel for a projected launch at what happened to be the actual launch time, 26 Nov at start of window. Since the launch was accurate (<0.1 sigma) this is probably pretty good. You can't get the kernel from them, but you can run Horizons and get any form of vectors or elements you want, which may be even better than a kernel.

Earth departure according to the kernel:
Kernel starts at 2011-NOV-26 15:52:12.3830 CT (not UTC, about a minute difference. UTC is 2011-11-26T15:51:06.200 at kernel start)
Periapse was 798.736 seconds before this, 13m18.736 seconds, so periapse was at 2011-Nov-26 15:38:53.647 CT (15:37:47.464 UTC)
Periapse distance: 6572.438km from the center of the Earth, or about 194km altitude
Eccentricity: 1.17677
From this, velocity at periapse was 11.490km/s. This was 476m/s above escape speed at this altitude. Hyperbolic excess speed (v_inf, eventual speed of departure from Earth) is 3.274km/s, for a C3 of 10.721

Spaceflightnow reported centaur main engine start 2 at 32:40 MET (15:34:40 UTC) and cutoff at 40:30 MET(15:42:30 UTC) so theoretical periapse is during the centaur burn, which is kind of as expected.

The second burn also was used to increase the inclination, so it was not purely in plane. The parking orbit was something like 28deg inclination, while departure was at 34.5deg. This is weird, since you should be able to launch at an azimuth such that no plane change is needed in the second burn.
Go to the top of the page
 
+Quote Post

Posts in this topic
- nprev   MSL Cruise Phase   Nov 26 2011, 03:50 PM
- - Oersted   The live footage of the first couple of kilomete...   Nov 26 2011, 03:52 PM
- - climber   Oppy, here I come ! Waiting for post launch co...   Nov 26 2011, 04:07 PM
|- - Oersted   QUOTE (climber @ Nov 26 2011, 05:07 PM) O...   Nov 26 2011, 04:34 PM
|- - climber   QUOTE (Oersted @ Nov 26 2011, 05:34 PM) W...   Nov 26 2011, 04:48 PM
- - nprev   Yeah, that was indeed a beautiful sight to behold,...   Nov 26 2011, 04:08 PM
- - vikingmars   ... and we just had champagne at home near Paris t...   Nov 26 2011, 04:14 PM
- - DEChengst   They just started showing the title card for the p...   Nov 26 2011, 05:34 PM
|- - sgendreau   EDIT2: Not much news. No news is good news for ...   Nov 26 2011, 06:01 PM
- - dmg   Anyone know why the telemetry pickup from the laun...   Nov 26 2011, 07:07 PM
- - MarsEngineer   No news is good news indeed! We are watching...   Nov 26 2011, 09:51 PM
|- - Pando   QUOTE (MarsEngineer @ Nov 26 2011, 02:51 ...   Nov 26 2011, 11:16 PM
|- - Oersted   QUOTE (MarsEngineer @ Nov 26 2011, 10:51 ...   Nov 27 2011, 12:20 AM
- - climber   Tanks Rob, I was browsing like mad to get any news...   Nov 26 2011, 10:11 PM
- - MERovingian   Bravo to all the teams involved, JPL, ULA, NASA, K...   Nov 26 2011, 10:52 PM
- - nprev   Rob, thanks very much for taking the trouble durin...   Nov 27 2011, 12:01 AM
- - Explorer1   Actually the last EDL was in 2008 with the Phoenix...   Nov 27 2011, 12:01 AM
- - Oersted   I uploaded footage of the launch and spacecraft se...   Nov 27 2011, 12:44 AM
|- - Syrinx   Thank you sir for the videos. I was unable to wat...   Nov 27 2011, 02:02 AM
- - tanjent   I'm having some trouble with "data dropou...   Nov 27 2011, 03:34 AM
|- - kwan3217   (Full inline quote removed- Mod) The apogee for a...   Nov 27 2011, 02:23 PM
|- - scalbers   QUOTE (kwan3217 @ Nov 27 2011, 03:23 PM) ...   Nov 27 2011, 04:08 PM
|- - kwan3217   (Full inline quote removed- Mod) The guys at JPL ...   Nov 28 2011, 08:58 PM
- - john_s   I was watching those numbers too. The apogee shou...   Nov 27 2011, 03:54 AM
- - tanjent   OK - I bet it actually finds the perigee by lookin...   Nov 27 2011, 04:04 AM
|- - MahFL   The separation video was just awesome, although I ...   Nov 27 2011, 04:49 AM
|- - OKB001   QUOTE (MahFL @ Nov 26 2011, 08:49 PM) The...   Nov 27 2011, 05:59 AM
- - tanjent   Well, the altitude should be directly observable b...   Nov 27 2011, 02:50 PM
- - Astro0   A little late to the party I guess. My weekend was...   Nov 27 2011, 10:05 PM
|- - MarsEngineer   QUOTE (Astro0 @ Nov 27 2011, 02:05 PM) A ...   Nov 28 2011, 12:36 AM
- - Oersted   Oh, a rainbow to boot! Lovely panorama and tha...   Nov 27 2011, 10:30 PM
- - MarsEngineer   Hi all, Please take a look at the observations ma...   Nov 28 2011, 12:54 AM
- - nprev   ...words utterly fail me. Just remarkable. Many t...   Nov 28 2011, 12:59 AM
- - eoincampbell   WOW! Thanks for sharing another "Heimdall...   Nov 28 2011, 03:05 AM
- - tanjent   Quote: http://www.facebook.com/BrisbanePlanetarium...   Nov 28 2011, 08:36 AM
- - Oersted   That is an amazing timelapse! http://www.yout...   Nov 28 2011, 01:12 PM
- - Oersted   On my youtube page of MSL launch movies I am getti...   Nov 28 2011, 03:10 PM
|- - Greg Hullender   QUOTE (Oersted @ Nov 28 2011, 07:10 AM) ...   Nov 28 2011, 03:57 PM
- - Roby72   Here you could see Curiosity 10 hours 30 minutes a...   Nov 28 2011, 09:51 PM
- - Bobby   Question? Is there a site either through JPL or a...   Nov 29 2011, 12:40 AM
- - punkboi   http://space.jpl.nasa.gov/ MSL's position sho...   Nov 29 2011, 12:49 AM
- - Astro0   As usual, Eyes on the Solar System can take us all...   Nov 30 2011, 04:12 AM
- - Explorer1   Is the cruise stage's spin in real-time? Great...   Nov 30 2011, 05:57 AM
|- - MahFL   Don't forget, the whole Rover is spinning....l...   Nov 30 2011, 12:08 PM
- - MahFL   I am not sure how accurate the model is but it loo...   Nov 30 2011, 12:13 PM
- - ilbasso   Should we bring her back for repairs?   Nov 30 2011, 12:18 PM
|- - MahFL   I just read that the hand lens imager can take pic...   Nov 30 2011, 01:52 PM
|- - eoincampbell   QUOTE (MahFL @ Nov 30 2011, 05:52 AM) ......   Nov 30 2011, 04:19 PM
|- - Deimos   http://msl-scicorner.jpl.nasa.gov/Instruments/MAHL...   Nov 30 2011, 04:50 PM
- - pospa   Also VERY cool would be any MAHLI picture from ins...   Nov 30 2011, 02:22 PM
- - climber   You can even dream of a shot of Spacecraft separat...   Nov 30 2011, 03:05 PM
- - ElkGroveDan   The next images we'll see from MSL will likely...   Nov 30 2011, 03:46 PM
- - djellison   QUOTE (pospa @ Nov 30 2011, 06:22 AM) Als...   Nov 30 2011, 04:40 PM
|- - MarsEngineer   QUOTE (djellison @ Nov 30 2011, 08:40 AM)...   Nov 30 2011, 04:57 PM
- - john_s   I love the idea of the rover doing an "arms-l...   Nov 30 2011, 05:21 PM
- - djellison   It took all the way until working on the MSL anima...   Nov 30 2011, 05:23 PM
- - climber   I noticed on a previous video that legs extended a...   Nov 30 2011, 06:18 PM
- - djellison   Actually - the descent stage thrusters do start be...   Nov 30 2011, 07:25 PM
- - john_s   That "hard drop", with the rover falling...   Nov 30 2011, 07:38 PM
|- - climber   I read, where?, that, as soon as released, Curiosi...   Nov 30 2011, 07:53 PM
- - Ron Hobbs   From what I thought was a very informative article...   Nov 30 2011, 08:17 PM
|- - djellison   Ron - as far as I know, that article has it about ...   Nov 30 2011, 10:33 PM
|- - MahFL   Well I should have known better the tragectory man...   Dec 1 2011, 12:23 AM
- - Syrinx   http://www.sciencedaily.com/releases/2011/...11201...   Dec 2 2011, 07:42 AM
- - stevesliva   Seems to be regurgitating the same source: http://...   Dec 2 2011, 07:56 AM
|- - MahFL   The Eyes on the Solar System make my IE 8 crash af...   Dec 2 2011, 03:10 PM
|- - djellison   QUOTE (MahFL @ Dec 2 2011, 07:10 AM) The ...   Dec 2 2011, 06:52 PM
- - B Bernatchez   No problems for me (that wouldn't be fixed by ...   Dec 2 2011, 05:42 PM
- - Mars Attack   I'm a bit concerned about the reported reset o...   Dec 4 2011, 02:57 PM
|- - stevesliva   QUOTE (Mars Attack @ Dec 4 2011, 10:57 AM...   Dec 4 2011, 04:55 PM
||- - Mars Attack   QUOTE (stevesliva @ Dec 4 2011, 04:55 PM)...   Dec 4 2011, 05:20 PM
|- - Paolo   QUOTE (Mars Attack @ Dec 4 2011, 03:57 PM...   Dec 4 2011, 07:04 PM
- - ElkGroveDan   There is extra fuel aboard and my understanding is...   Dec 4 2011, 03:42 PM
|- - centsworth_II   QUOTE (ElkGroveDan @ Dec 4 2011, 10:42 AM...   Dec 4 2011, 07:18 PM
- - Hiwayman   Sorry for this being posted in the wrong forum, bu...   Dec 4 2011, 03:56 PM
|- - Oersted   QUOTE (Hiwayman @ Dec 4 2011, 04:56 PM) S...   Dec 4 2011, 08:43 PM
- - elakdawalla   Someone else pointed this out to me on the Atlas f...   Dec 4 2011, 04:19 PM
|- - Hiwayman   QUOTE (elakdawalla @ Dec 4 2011, 09:19 AM...   Dec 4 2011, 04:28 PM
|- - climber   QUOTE (elakdawalla @ Dec 4 2011, 05:19 PM...   Dec 4 2011, 06:52 PM
- - djellison   From http://trs-new.jpl.nasa.gov/dspace/handle/201...   Dec 4 2011, 08:23 PM
- - nprev   Yeah, it really was a sweet launch...and major kud...   Dec 4 2011, 08:49 PM
- - Mars Attack   Mr. Doug Djellison, any chance that you could expa...   Dec 4 2011, 11:00 PM
- - djellison   We hope to - but it's entirely a matter of bud...   Dec 4 2011, 11:12 PM
|- - climber   QUOTE (djellison @ Dec 5 2011, 12:12 AM) ...   Dec 5 2011, 11:38 AM
- - punkboi   You can now view MSL's current position in spa...   Dec 7 2011, 05:57 AM
- - Syrinx   http://space.jpl.nasa.gov/cgi-bin/wspace?t...=1...   Dec 7 2011, 07:56 AM
- - Lucas   For the impatient among us... http://space.jpl...   Dec 7 2011, 02:56 PM
- - pospa   T +18 days - MSL has about 9% of its cruise done a...   Dec 14 2011, 02:32 PM
- - punkboi   Where is Curiosity now? There's now a dedicate...   Dec 14 2011, 10:27 PM
- - Lunik9   New sunspot 1387 erupted during the late hours of ...   Dec 26 2011, 09:28 AM
- - Explorer1   How large would an event have to be to seriously i...   Dec 26 2011, 11:40 PM
|- - centsworth_II   According to Curiosity and the Solar Storm, CMEs p...   Dec 27 2011, 08:05 AM
- - pospa   TCM-1 scheduled for Jan 11th, dv 5,5 m/s. Then eq...   Jan 6 2012, 11:03 PM
- - pospa   TCM-1 completed successfully. Rob Manning describ...   Jan 13 2012, 10:01 AM
- - Phil Stooke   "By the time a CME reaches the Earth-Mars exp...   Jan 13 2012, 12:12 PM
- - climber   According to AW&ST next trajectory correction ...   Jan 31 2012, 06:53 PM
- - pospa   Not sure if mentioned here before, but radio amate...   Feb 6 2012, 09:53 AM
- - MahFL   Software fix for Star Tracker problem. Tracker   Feb 10 2012, 01:37 PM
- - Mars Attack   The computer that received the software fix, is i...   Mar 1 2012, 03:36 PM
- - MahFL   QUOTE (Mars Attack @ Mar 1 2012, 03:36 PM...   Mar 2 2012, 12:20 AM
2 Pages V   1 2 >


Closed TopicStart new topic

 



RSS Lo-Fi Version Time is now: 31st October 2024 - 11:18 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 funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member.