Mro On Approach, TCM-3 not required Options

[Redstone]

MRO has shifted from the cruise phase to Approach phase. Apparently, the trajectory is so good that TCM-3 was cancelled. This is good news for the prospects for a long life for MRO supporting future missions. TCM-4 is on Feb 28, and MOI on March 10. Only 5 weeks away!

[RNeuhaus]

Good news. I seems that MRO has started to gain its speed due to Mars gravity tug, has not?

What is MOI? Mars Orbit Insertion.

http://mars.jpl.nasa.gov/mro/gallery/cruis...oach_200602.jpg

"It was a very busy time for the team. Many tests were conducted to ensure that the instruments onboard were functioning properly and our navigators performed trajectory correction maneuvers to keep us on a very precise path to Mars."

Speaking of that precision, the third of four possible course corrections was deemed unnecessary this week.

"The navigation solutions have shown a great consistency since the second trajectory correction maneuver was executed on November 18," said Han You, navigation team chief. "More importantly, the current data indicate that the spacecraft aim for insertion into Mars' orbit is well within the projected target. If the current trend continues, the spacecraft will require only a very small nudge to fine tune the final aim."

Rodolfo

[ugordan]

I seems that MRO has started to gain its speed due to Mars gravity tug, has not?

Where did you hear that? As far as I can see, MRO is sill on the elliptical transfer orbit and too far away to feel Mars' gravity influence. In fact, its heliocentric speed should be decreasing.
MRO won't begin to feel significant pull from Mars probably all the way until around a day or so before MOI.

[abalone]

MRO has shifted from the cruise phase to Approach phase. Apparently, the trajectory is so good that TCM-3 was cancelled. This is good news for the prospects for a long life for MRO supporting future missions. TCM-4 is on Feb 28, and MOI on March 10. Only 5 weeks away!

I hope they did a double ckeck in metrics and not just rely on the usual NASA units of ancient Kings appendages and Roman marching steps and bushels of wheat, but mistakes like that couldn't happen could they??

[djellison]

It's odd to think that from 'aboe' - MRO's burn which actually increase it's speed - but because it will being 'run over' by mars, it will be slowing down w.r.t. Mars itself

I hope they release the op-nav imagery - I'm sure it wont be particularly great, but it will make an interesting little movie watchign Phobos and Deimos doing their thing

Doug

[SFJCody]

How many pixels would HiRise get across the disc of Mars now?

[mcaplinger]

How many pixels would HiRise get across the disc of Mars now?

HiRISE has an IFOV of 1 microradian, so the pixel scale is the distance times 1e-6.
MRO is probably about 7 million km out right now (the simulations on the MRO site don't show the range) so that's 7 km/pixel. Mars is about 7000 km in diameter, so that's about 1000 pixels.

Of course, there are no plans to take such images that I'm aware of. The opnav camera is pointed in a direction almost 180 degrees away from the rest of the science instruments.

[djellison]

This is from a little PDF I found at the same place as the UHF tracking info

Attached thumbnail(s)

 

[crabbsaline]

This is from a little PDF I found at the same place as the UHF tracking info

Thanks Doug. I had to look up ONC to understand that part of the chart. I wonder what kind of "improved navigation capability" that they anticipate it will yield versus older methods?

I hope to see the ONC images soon.

[djellison]

I think they're using the ONC more as a tech-demonstrator to feed forward to future missions that will require that sort of accuracy. As it is for MRO, 'classical' navigation techniques are probably enough.

They wont be pretty pictures, but they'll be interesting none the less.

Doug

[jmknapp]

As far as I can see, MRO is sill on the elliptical transfer orbit and too far away to feel Mars' gravity influence. In fact, its heliocentric speed should be decreasing.
MRO won't begin to feel significant pull from Mars probably all the way until around a day or so before MOI.

True--MRO's speed relative to Mars won't start to increase until Feb. 25, & even then only very slightly until the day of MOI (per the SPICE kernel data).

Here's a chart of the speed for the month of March:

[jmknapp]

PS: Does anyone know what the field-of-view and resolution of the ONC are?

[djellison]

http://bookstore.spie.org/index.cfm?fuseac...d=619857&coden=

Abstract
The Optical Navigation Camera (ONC) is part of NASA's Mars Reconnaissance Orbiter (MRO) scheduled for an August 2005 launch. The design is a 500 mm focal length, F/8.3 Ritchey-Chretien with a refractive field corrector. Prior to flight, the off-axis performance of the ONC was measured at visible wavelengths in the off-axis scatter facility at the Space Dynamics Laboratory (SDL). This unique facility is designed to minimize scatter from the test setup to prevent data corruption. Testing was conducted in a clean room environment, and the results indicate that no detectable contamination of the optics occurred during testing. Measurements were taken in two time frames to correct an unanticipated stray light path, which occurred just outside of the sensor's field-of-view. The source of the offending path was identified as scatter from the edges of the field corrector lenses. Specifically, scatter from the interface between the flat ground glass and polished surfaces resulted in significant "humps" in the off-axis response centered at ± 1.5°. Retesting showed the removal of the humps, and an overall satisfactory performance of the ONC. The troubleshooting, correction, and lessons learned regarding the above stray light path was reported on in an earlier paper. This paper discusses the measurement process, results, and a comparison to a software prediction and other planetary sensors. The measurement validated the final stray light design and complemented the software analysis.

Very little info out there though. That's about all I could find.

[jmknapp]

http://bookstore.spie.org/index.cfm?fuseac...d=619857&coden=
Very little info out there though. That's about all I could find.

Thanks! That paper states that the FOV is 2.8 degrees (+/- 1.4 degees from the optical axis). I can see from the pointing (CK) SPICE kernels for the last few days that they are indeed periodically slewing the ONC across the position of Mars and Phobos/Deimos. Here's one predicted view from a few days ago:



The targets are in the FOV for about a minute. I gather from the paper that the intent is to have Mars outside the FOV for the science observations.

[Bob Shaw]

From the MRO website:

http://mars.jpl.nasa.gov/mro/mission/sc_instru_optical.html

"Optical Navigation Camera

This camera is being tested for improved navigation capability for future missions. If it performs well, similar cameras placed on orbiters of the future would be able to serve as high-precision interplanetary "eyes" to guide incoming spacecraft as they near Mars.

From 30 days to 2 days prior to Mars Orbit Insertion, the spacecraft will collect a series of images of Mars' moons Phobos and Deimos. By comparing the observed position of the moons to their predicted positions, relative to the background stars, the mission team will accurately determine the position of the orbiter in relation to Mars.

While not needed by Mars Reconnaissance Orbiter to navigate to Mars, the data from this experiment will be used to demonstrate that this technique can be used by future spacecraft to ensure their accurate arrival. Accuracy is important to some future landers and rovers that will need extremely precise navigation at Mars arrival to get to their landing sites safely."

So, some interesting images of the moons, perhaps?

Bob Shaw

[jmknapp]

I made an animation of the approach through the first orbit:

MRO approach movie (5.7MB MPG file)

It's from the point of view of a (fictitious) nadir-pointing camera with the same FOV (1.14 degrees) as HiRISE.

[djellison]

Given the addition of some post-moi-pre-aerobraking imaging, at what appears to be between about 0000 and 0600 on the 15th of March - any idea on a nadir target for that sort of time?

Doug

Attached thumbnail(s)

 

[jmknapp]

Given the addition of some post-moi-pre-aerobraking imaging, at what appears to be between about 0000 and 0600 on the 15th of March - any idea on a nadir target for that sort of time?

Doug

Looks like it's the north polar ice cap. Here's the view midway in that interval (+ marks the nadir point):



Note that the FOV above is 5 degrees. CTX has an FOV 0f 6 degrees; HiRISE 1.14 degrees.

[Guest_Sunspot_*]

I kept reading that they wouldn't be doing any imaging until after aerobraking was complete.. this is good news.

[mcaplinger]

Looks like it's the north polar ice cap. Here's the view midway in that interval (+ marks the nadir point):

Try looking (hint, hint) closer to 6:00 UTC.

[jmknapp]

Try looking (hint, hint) closer to 6:00 UTC.

Hmmm... here is the view at 0600:



Wondering what you are hinting at--perhaps this is targeted after one of the proposed Phoenix landing sites? The subpoint above is 75N 141W.

[helvick]

Wondering what you are hinting at--perhaps this is targeted after one of the proposed Phoenix landing sites? The subpoint above is 75N 141W.

Possibly - I had a placeholder for Phoenix @ 70N 120W but I'm not sure where I got that from. I didn't think the precise landing site had been chosen yet though.

[Phil Stooke]

It wouldn't be targeted, just whatever they are seeing as they pass by.

Phil

[babakm]

Some imaging of Phoenix candidate site D is on the MSSS site (roughly 71N 115-120W). The closest image I could find to 75N 141W is this one, but your nadir looks like it's ~180 degrees away from the projection here. Different coord systems?

[RNeuhaus]

Below is the Sout Pole Cap that looks different than the Nort Pole Cap. The MRO will orbit around poles?



A much better resolution and visibilty is below:


This is the south polar cap of Mars as it appeared to the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) on April 17, 2000. In winter and early spring, this entire scene would be covered by frost. In summer, the cap shrinks to its minimum size, as shown here. Even though it is summer, observations made by the Viking orbiters in the 1970s showed that the south polar cap remains cold enough that the polar frost (seen here as white) consists of carbon dioxide. Carbon dioxide freezes at temperatures around -125° C (-193° F). Mid-summer afternoon sunlight illuminates this scene from the upper left from about 11.2° above the horizon. Soon the cap will experience sunsets; by June 2000, this pole will be in autumn, and the area covered by frost will begin to grow. Winter will return to the south polar region in December 2000. The polar cap from left to right is about 420 km (260 mi) across

Rodolfo

[brianc]

A nice article about the MRO HIRISE camera system here

http://www.phim.unibe.ch/pig/HiRISE_IAF55.pdf

[mcaplinger]

Wondering what you are hinting at--perhaps this is targeted after one of the proposed Phoenix landing sites? The subpoint above is 75N 141W.

I think your software is confused, or ours is. What SPICE kernel are you using?

[jmknapp]

I think your software is confused, or ours is. What SPICE kernel are you using?

Could be. Here are the kernels I'm using:

CK:
'$KROOT/ck/DESAT_MOI_sc_20060103171803.bc',

SPK:
'$KROOT/spk/spk_c_tcm1-od006_050812_060315_p-v1.bsp',
'$KROOT/spk/spk_moi_lowperf_t2_051123_060320_p-v1.bsp',
'$KROOT/spk/spk_moi_ideal_051123_060320_p-v1.bsp',
'$KROOT/spk/spk_moi_highperf_t1_051123_060320_p-v1.bsp',

I notice there's a big difference whether highperf, ideal or lowperf is used, so maybe that's the difference. The projection above uses highperf (since it's the last listed in the config file).

[mcaplinger]

I notice there's a big difference whether highperf, ideal or lowperf is used, so maybe that's the difference. The projection above uses highperf (since it's the last listed in the config file).

We were doing this planning several weeks ago, so the kernel I used was from mid-January. In those kernels, we were near periapsis at 6:00 UTC. Looks like we're looking at some replanning if the MOI performance makes this much difference. I would try rerunning with ideal and see what that looks like.

BTW, what software are you using for this?

[jmknapp]

We were doing this planning several weeks ago, so the kernel I used was from mid-January. In those kernels, we were near periapsis at 6:00 UTC. Looks like we're looking at some replanning if the MOI performance makes this much difference. I would try rerunning with ideal and see what that looks like.

BTW, what software are you using for this?

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.

One kernel tells a cautionary tale:

spk_nomoi_051123_060320_p-v1.bsp

No MOI--gulp! That pessimistic kernel gives this view on 15MAR:

[mcaplinger]

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.

[Bob Shaw]

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

[djellison]

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

Doug

[Guest_AlexBlackwell_*]

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.

[jmknapp]

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.

[Guest_AlexBlackwell_*]

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

[elakdawalla]

That might be why the MRO mission designers baselined for aerobraking instead of lithobraking

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

--Emily

[Guest_AlexBlackwell_*]

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
--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

[Phil Stooke]

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

[mcaplinger]

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

Very funny, Alex. 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.

[lyford]

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

[Guest_AlexBlackwell_*]

Very funny, Alex. 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

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.

[djellison]

It's not the same, though, as needling Bruce. Now that is fun

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

Doug

[jmknapp]

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.

[djellison]

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

[Guest_AlexBlackwell_*]

Feb. 17, 2006

Dwayne Brown/Erica Hupp
Headquarters, Washington
(202) 358-1726\1237

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
(818) 354-6278

MEDIA ADVISORY: M06-029

NASA ANNOUNCES MARS MISSION BRIEFING

NASA will brief news media about the Mars Reconnaissance Orbiter
mission at 1 p.m. EST, Friday. The event is in NASA's auditorium, 300
E Street SW, Washington.

The NASA spacecraft is scheduled to arrive at Mars on March 10, 2006.
It will provide more information about the planet than all previous
NASA Mars missions combined. Participants will address mission goals
and the sequence of events necessary to successfully place the
vehicle into orbit around Mars.

Briefing Participants: Doug McCuistion, NASA Mars Exploration Program
Director, NASA Headquarters; Michael Meyer, NASA Mars Lead Scientist,
NASA Headquarters; James Graf, Mars Reconnaissance Orbiter Project
Manager, Jet Propulsion Laboratory, Pasadena, Calif.; Bob Berry,
Director, Space Exploration Systems, Lockheed Martin Space Systems
Co., Denver.

The briefing will air live on NASA TV, and the panel will take
questions from reporters at participating NASA centers. To ask phone
questions, reporters must call Jet Propulsion Laboratory media
relations by 5 p.m. EST, Tuesday at: (818) 354-5011 to obtain a
call-in number. To view a live webcast of the event and for more
mission information on the Web, visit: http://www.nasa.gov/mro

NASA TV's Public, Education and Media channels are available on an
MPEG-2 digital C-band signal accessed via satellite AMC-6, at 72
degrees west longitude, transponder 17C, 4040 MHz, vertical
polarization. In Alaska and Hawaii, they're on AMC-7 at 137 degrees
west longitude, transponder 18C, at 4060 MHz, horizontal
polarization. For digital downlink information on the Web, visit:
http://www.nasa.gov/ntv


-end-

[Bob Shaw]

The way I see it, almost *any* orbit is better than an unplanned landing mission. And I was, originally, really trying *not* to be cruel about the MCO trajectory, honest! I didn't *need* to be cruel, not with you lot aboard...

Bob Shaw

[Guest_AlexBlackwell_*]

I didn't *need* to be cruel, not with you lot aboard...

Hey, you forgot to include the appropriate emoticon. Or did you forget?

[RNeuhaus]

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

Also don't forget of Mars orbiter Nozomi, the japanese probe passed by 1000km above the Martian surface on December 14 and escaped from the gravitational sphere of Mars on December 16 to continue on traveling along the orbit around the sun. due to unrecoverable malfunction injection.

No more jokes of that kind, no matter of what old is that but not one as a good prediction . MRO is a very nice toy!

Rodolfo

[ElkGroveDan]

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.

OK now that we have figure out that there are problems with the Colonel's spices, the original question seems to have been lost. What was Mike referring to when he said "Try looking (hint, hint) closer to 6:00 UTC."?

[dvandorn]

It's getting to the point where I log on to UMSF and just nod in assent to almost every post

I've been doing that for quite a while... though, of course, there are a few posts every day that I certainly don't assent with. But, hey, as my father always used to tell me, it takes all kinds...

-the other Doug

[Bob Shaw]

I've been doing that for quite a while... though, of course, there are a few posts every day that I certainly don't assent with. But, hey, as my father always used to tell me, it takes all kinds...

-the other Doug

oDoug:

Was this outbreak of reasonableness PRE or POST medication?

Bob Shaw

[dvandorn]

I think it's probably safest to blame it all on the pain meds...

Actually, I don't feel exceptionally different from how I usually feel. A little lightheaded, but that's it. I *think* I'm still pretty sharp and clear when it comes to understanidng what I'm reading and being able to write in a coherent fashion. But y'all let me know if I start acting even more eccentric than normal...

-the other Doug

[yaohua2000]

Mars Reconnaissance Orbiter was only 5 million kilometers from Mars at 2006-Feb-18 12:41:54 UTC.

For Mac OS X users, you can download my widget to keep tracking the distance of the spacecraft to Mars on your Dashboard.

Download: http://magicnumber.sourceforge.net/MRO.zip

You can also make this distance as your signature on this forum, for the details, see http://magicnumber.sourceforge.net

[RNeuhaus]

After reading more details about MRO. I found it many interesting and surprises things:

As Mars Reconnaissance Orbiter approaches Mars traveling about 10,400 km per hour, it will need to fire six main engines for a long 25-minute burn, slowing the spacecraft down by about 3,584 km per hour! That reduction of speed relative to the planet will place the spacecraft into a long looping orbit around Mars.

The same as Doug has told us.

All subsystems and instruments on board (the so-called "dry mass") must weigh less than 1,031 kilograms (2,273 pounds) to allow room for 1,149 kilograms (2,533 pounds) of propellant for trajectory correction maneuvers that keep the spacecraft on target during the cruise to Mars and for burns that help capture the spacecraft into orbit around Mars.

The monopropellant hydrazine tank is big enough to hold 1187 kilograms (2617 pounds) of usable propellant. This amount of propellant, when used, will change the spacecraft's velocity by about 1.4 kilometers per second (3,100 miles per hour). Over 70% of the total propellant will be used during just one maneuver - Mars orbit insertion.

The propulsion combustible takes up more than 50% of spacecraft weigth.

Some way is needed to push the propellant to the thrusters. Mars Reconnaissance Orbiter feeds pressurized helium gas from a separate high- pressure tank, through a regulator, into the propellant tank where it puts the hydrazine propellant under pressure. Then, when any thruster is opened, the propellant will flow rapidly out, much like paint does from a can of spray paint.

Interesting, MRO uses HELIUM GAS to push Hydrazine away from the tank.
Pressurant Tank


About thrusters, a total of 20 rocket engine thrusters are onboard:

* Six large thrusters, each producing 170 Newtons* (38 pounds force) of thrust for performing the Mars orbit insertion burn. Together, all six produce 1,020 Newtons (104.5 kg 230 pounds force) of thrust. That's about the force you would feel if an NFL linebacker decided to sit on you.

* Six medium thrusters, each producing 22 Newtons* (5 pounds force) of thrust for performing trajectory correction maneuvers, and for helping to keep the spacecraft pointing in the right direction during the Mars orbit insertion burn.

* Eight small thrusters, each producing 0.9 Newtons* (0.2 pounds force) of thrust for controlling where the orbiter is pointed during normal operations as well as during Mars orbit insertion and trajectory correction maneuvers.

(*A Newton is a unit of force required to accelerate a mass of one kilogram one meter per second?every second!). One Newton is equivalent to 1.626 kg of push force.

So many thrusters! 20. I tought it had 7!!!

Spacecraft Configurations:

what the spacecraft will look like during various phases of the mission

During aerobraking, the solar panels have a special role to play. As the spacecraft skims through the upper layers of the martian atmosphere, the large, flat panels act a little like parachutes to slow the spacecraft down and reduce the size of its orbit.

The friction from the atmosphere passing over the spacecraft during aerobraking will heat it up, with the solar arrays heating up most of all. The solar arrays have to be designed to withstand temperatures of almost 200 Celsius (almost 400 degrees Fahrenheit!).

MRO will get very hot, up to 200 degree of centigrades at the perigee passing.

At Mars, the two panels together produce 1,000 Watts of power.

Nickel-hydrogen batteries

During each two-hour orbit around Mars the spacecraft will experience a "day" and a "night." During the "night," there is no sunlight because the planet is between the orbiter and the sun, and therefore blocks the sun's light from reaching the spacecraft. Astronauts on the shuttle experience this kind of pattern as well when they orbit the Earth.

During the nighttime periods, batteries are used to provide the necessary electrical power. The batteries charge during each "day" (using part of the electricity produced by the solar cells) and discharge during each "night' to keep the spacecraft supplied with electricity.

Mars Reconnaissance Orbiter uses two Nickel-Hydrogen rechargeable batteries, each with an energy storage capacity of 50 Ampere-hours - at 32 Volts that's 1,600 Watts for one hour. The spacecraft can't use this total capacity, because as a battery discharges its voltage drops. If the voltage ever drops below about 20 Volts then the computer will stop functioning - a very bad thing! So, to be safe, only about 40% of the battery capacity is ever planned to be used.
Comparing to MER, they have 1.2 M² of solar panel and its produces about 1000 wats when they had the best atmospheric conditions and about during the summer. The MRO has big solar panels, 10 M² and also produces about the same to MER? MRO will orbit Mars every two hours?, somewhat slower than ISS around Earth with 91 minutes.


There are three main mechanisms on board Mars Reconnaissance Orbiter:

* one that allows the high-gain antenna to move in order to point at earth
* two that allow the solar arrays to move to point at the sun

Each of these mechanisms, called gimbals, can move about two axes in much the same way that your wrist allows your hand to move in two axes: left/right and up/down. By contrast, your knee only has one axis of motion, but your neck has three.

As the spacecraft travels around Mars each orbit, these gimbals allow both solar arrays to be always pointed toward the sun, while the high-gain antenna can simultaneously always be pointed at earth.

What advanced is the space orientation software that the information from star tracker and sun sensors are feeding to the software in order to adjust constantly the solar panels and antenna pointing to Sun and Earth respectively.


The solar panels must be strong enough to survive launch, when the forces can exceed 5 g's. This means that the structure must be designed as if the spacecraft weighed five times what it does on earth! Extremely lightweight but strong materials are used to achieve this strength, including titanium, carbon composites, and aluminum honeycomb.

Any commercial airplane can withstand greater than 3 gravity but the military fighters can do up to 8 g's but the airman will be inconcient for that rather time.

Powerfull telecomunications
With its large-dish antenna, powerful amplifier, and fast computer, Mars Reconnaissance Orbiter can transmit data to earth at rates as high as 6 megabits per second, a rate ten times higher than previous Mars orbiters. This rate is quite high considering that Mars Reconnaissance Orbiter will achieve it while 100 million kilometers (62 million miles) from Earth.


Ten times faster than the previous Mars orbiters, which ones? I suppose it is refering to Odyssey?


High-gain Antenna
The high-gain antenna is a 3-meter diameter (10-foot) dish antenna for sending and receiving data at high rates.

The high-gain antenna will be deployed shortly after launch (see launch configuration), and will remain deployed for the remainder of the mission. It will serve as the primary means of communication to and from the orbiter.

The high-gain antenna must be pointed accurately and is therefore steered using the gimbal mechanism.

Low-gain Antennas

Two smaller antennas are present for lower-rate communication during emergencies and special events, such as launch and Mars Orbit Insertion. The data rate of these antennas is lower because they focus the radio beam much more broadly than the high gain antenna, so less of the signal reaches earth. But the Deep Space Network station on the earth can "see" the signal even when the spacecraft is not pointed at earth, and this is why these antennas are useful for emergencies. Think of how a flashlight works: with a tightly focused beam of light you can see farther directly ahead but not at all to the side. And with a wide beam you can see all around you but not very far. The low-gain antennas have the capability to transmit and receive.

The two low-gain antennas are mounted on the high-gain antenna dish - one on the front side and one on the back -- and are moved with it, although as just mentioned they do not require accurate pointing. Two are needed in that placement so that communication is possible at all times, no matter what the position of the spacecraft might be at a given time.

MRO has two LGA (front and back) and it has very good redundancy comparing to one of Hayabusa.


Mars Reconnaissance Orbiter uses a monopropellant propulsion system: there is fuel (hydrazine), but no oxidizer. Thrust is produced by passing the fuel over beds of catalyst material just before it enters the thruster, which causes the hydrazine to combust . (Other types of systems use bipropellant propulsion, where combustion is achieved by mixing a fuel with an oxidizer. The Space Shuttle, for example, uses liquid hydrogen as fuel and liquid oxygen as oxidizer, which spontaneously combust (explode) when they are mixed.)

Propellent: It is monopropellent. ONLY one : HYDRAZINE. It is a fuel. It does not need oxygen as an oxidizer to ignite. What is the catalyst material that causes the hydrazine to be fueled. Electrical ignition?



Reaction wheels:

While the reaction control system thrusters allow the spacecraft to turn quickly, they're not good at slow and steady turns. Slow and steady turns, however, are just what is required to take high-resolution images of Mars from orbit. Mars Reconnaissance Orbiter therefore has devices called reaction wheels. These are literally spinning wheels - four in total: one for each rotational axis plus a spare in case one of the three isn't working.



Good ones: 4 reactions wheels: one for three dimension axis plus one as a spare. Even better than Hayabusa.


Spacecraft Parts: Command and Data-Handling Systems

The Command and Data Handling subsystem is essentially the "brains" of the orbiter and controls all spacecraft functions. This system:

* manages all forms of data on the spacecraft;
* carries out commands sent from earth;
* prepares data for transmission to the earth;
* manages collection of solar power and charging of the batteries;
* collects and processes information about all subsystems and payloads;
* keeps and distribute the spacecraft time;
* calculates its position in orbit around Mars;
* carries out commanded maneuvers; and,
* autonomously monitors and responds to a wide range of onboard problems that might occur.

Space Flight Computer:
At the heart of the space flight computer, Mars Reconnaissance Orbiter employs the next generation of space-qualified processors, based on the 133 MHz PowerPC processor. While this speed may seem slow compared to the Gigahertz speed of the computer you're using to read this web site, it is fast by space standards. Commercial chips must be significantly enhanced and undergo long duration testing to prove they will survive the unforgiving radiation environment of space.

Flight Software:
The Flight Software is an integral part of the Space Flight Computer, and includes many applications running on top of an operating system, similar to the way your home computer has applications running on top of Microsoft Windows or MacOS. Mars Reconnaissance Orbiter's operating system is called VxWorks.
An example of an application is Fault Protection. Fault Protection continuously monitors hundreds of parts of the spacecraft for a wide range of problems, takes action to fix the problem if it can, and if it can't, keeps the spacecraft safe while it waits for instructions from Earth.


Smart enough to handle by itself during if there is a fault.

Solid State Recorder:

The Solid State Recorder is the primary storage for science instrument data onboard the spacecraft, with a total capacity of 160 Gigabits. That may seem like a lot, but not when you realize that a single image from HiRISE can be as big as 28 Gigabits!

The science data is stored on this recorder until it is ready for transmission to Earth, and then is overwritten with new science data.
The recorder is called a Solid State Recorder because it has no moving parts. Neither a tape recorder nor a hard disk drive, this device uses an array of over 700 memory chips, each with 256 Megabit capacity, to store Mars Reconnaissance Orbiter's data.

Whopping storage capacity in solid state record (RAM). The big computers has that amount storage. There very few computers have it.


Sensors

Sensors determine where the spacecraft is pointed, how fast it is turning, and how its speed is changing. They include:
sun sensors:

Sixteen sensors (eight are backups) deployed around the spacecraft body provide knowledge of where the sun is located. These sensors are pretty simple, and only give two answers: "I see the sun" or "I don't see the sun." The computer and flight software listen to all of the sensors and can deduce where the sun is from that information. Since the spacecraft relies on sunlight to create electrical power, this function is very important.

The sun sensors normally are used only when first waking up the spacecraft (for example, after launch) and during spacecraft emergencies - in both cases the spacecraft may not know where it is pointed.
The sun sensors give enough information so the spacecraft can continue to get power from the sun, but they don't give enough information for other things, like finding the earth, or a spot on Mars. For that, more sophisticated sensors coupled with computer software are required (see below).

Two star trackers are used to provide full knowledge of the spacecraft orientation, allowing the spacecraft to know not only where the sun is, but also where Earth and Mars are and how to point to any direction in the sky (which is necessary when doing a maneuver). As is the case with many components aboard Mars Reconnaissance Orbiter, the second star tracker is there as a back-up in case the first one fails.
The star tracker is a very smart camera. The star tracker takes a digital picture of the stars. Then, using its own catalog of thousands of stars, it compares the image with the catalog until it can identify the stars in the image. Once it does that, it knows exactly where it was pointing when it took the picture, and it sends a message to the computer with that information. And it does that ten times every second!

So many Sun sensors!!! up to 16??? (8 for backups) MRO has two star trackers which help to spacecraft ot only to know where the sun is located but also of Earth and Mars.


Sorry of that long post. It will permit us to be much better prepared to understand better of any MRO directions, movements, timing, so that we can discuss it better.

Rodolfo

P.D. More details, visit click here

[The Messenger]

Nice collection of details. Hydrazine (HN#NH) has been the fuel-of-choice for vectoring motors since Minuteman, which also uses the helium replacement system (The helium is stored in donuts wrapped around the nozzles, both cooling the nozzles and heating the replacement gas.) A monofuel allows simple valve trains and combustion chambers. Hydrazine is both toxic and corrosive - not surprising, as are most highly reactive chemicals.

[dilo]

Thanks for resuming all these infos, Rodolfo (perhaps the biggest post I saw in the Forum...).

A couple of considerations on the data storage/transmission.
They say: "Over its two-year primary science mission, the spacecraft is predicted to transmit more than 34 Terabits-that's more than all the data transmitted by all previous JPL spacecraft put together!"
This means an average transmission of 0.54 Mbit/sec if spacecraft is continuosly transmitting (obviously this is not true due to occultation and multiple DSN tasks); this figure is about one eleventh of real MRO antenna data rate (at 100 million Km).
Moreover, is a single image require 28 Gbit, this means only slightly more than 1000 images transmitted during primary mission, about 1.5 images/day...
I know we already spoken about bandwith bottleneck, this is just a remind...

[djellison]

[quote name='RNeuhaus' post='42269' date='Feb 19 2006, 06:14 AM']

Interesting, MRO uses HELIUM GAS to push Hydrazine away from the tank.
Pressurant Tank
[/quote]

I think just about every spacecraft I've ever seen does this.
[quote]
So many thrusters! 20. I tought it had 7!!!
[/quote]
Well - 7 main ones for the engine burn for MOI - but then lots of smaller ones for smaller manouvers and rotating the spacecraft to unload gyros.

[quote]
MRO will get very hot, up to 200 degree of centigrades at the perigee passing.
[/quote]

Ah - carefull - they say it's designed to withstand 200 degrees, not that they will nearly reach 200 degrees. They're get warm - but nothing like 200 deg. I think one of the tech papers I mentioned elsewhere shows CFD of how warm it might get.

[quote]
Comparing to MER, they have 1.2 M² of solar panel and its produces about 1000 wats when they had the best atmospheric conditions and about during the summer. The MRO has big solar panels, 10 M² and also produces about the same to MER? MRO will orbit Mars every two hours?, somewhat slower than ISS around Earth with 91 minutes.

[/quote]

Ahh - again, no - MER can produce up to about 1000 Watt-HOURS per sol, i.e. the equiv of 100 watts for 10 hours. Typically, the MER solar arrays would rarely produce more than 100 Watts at any one time - I'm not sure of the exact figures.

[quote]
Ten times faster than the previous Mars orbiters, which ones? I suppose it is refering to Odyssey?
[/quote]
and then some....

The very highest data rate I've seen quoted for Odyssey is 124425 bits per second - i.e. roughly 0.125 Mbits/sec

MRO's still a bit fluffy on quoted numbers - but the highest it can do is certainly around 5 Mbits/sec.

[quote]
Good ones: 4 reactions wheels: one for three dimension axis plus one as a spare. Even better than Hayabusa.

[/quote]
And the same as Cassini - which is already using its spare.
[quote]
Smart enough to handle by itself during if there is a fault.
[i]
[/quote]

Same as most spacecraft really.
[quote]
Whopping storage capacity in solid state record (RAM). The big computers has that amount storage. There very few computers have it.

[/quote]

Well - 160 Gbits is about 20 Gigabytes - and onboard that is equiv to the 'hard drive' for MRO - and I think we'd all be moaning if we only had that

Doug

[deglr6328]

Propellent: It is monopropellent. ONLY one : HYDRAZINE. It is a fuel. It does not need oxygen as an oxidizer to ignite. What is the catalyst material that causes the hydrazine to be fueled. Electrical ignition?

Hydrazine explodes on contact with many common metal oxides. Found this: "Most hydrazine thrusters use a catalyst bed made from iridium impregnated alumina (Al2O3) pellets 1.5 to 3 mm in diameter."

[helvick]

Ahh - again, no - MER can produce up to about 1000 Watt-HOURS per sol, i.e. the equiv of 100 watts for 10 hours. Typically, the MER solar arrays would rarely produce more than 100 Watts at any one time - I'm not sure of the exact figures.
and then some....

The instantaneous peak output of the MER Panels at mars would vary between ~146 and 214watts if they were in orbit rather than on the surface. Taking the atmosphere and seasonal Tau into account that changes to ~140 to 164 watts.
I thought MRO had 2x10m^2 panels which could peak at between 2.2 and 3.3kw but I presume that they are rarely optimally oriented so an average of 1000 watts over each orbit is probably right.

[Airbag]

Another interesting tidbit - MRO uses the same X-band uplink/downlink channel (32) as Spirit...an unexpected problem relating to Spirit's longevity. Expect to see much more UHF commanding of Spirit via Odyssey in the near future. Opportunity's channel (29) is shared with Deep Impact, but that has not been an issue so far because of their spatial separation.

Airbag.

[Bob Shaw]

Another interesting tidbit - MRO uses the same X-band uplink/downlink channel (32) as Spirit...an unexpected problem relating to Spirit's longevity. Expect to see much more UHF commanding of Spirit via Odyssey in the near future. Opportunity's channel (29) is shared with Deep Impact, but that has not been an issue so far because of their spatial separation.

Airbag.

Am I alone in thinking that this is, er, silly? Or was it too expensive to change the ground station gear?

Bob Shaw

[Guest_Myran_*]

Bob Shaw said Am I alone in thinking that this is, er, silly?

It doesnt sound like good planning to me. Not that I am as singleminded to think that any command from Earth intended for MRO will make Oppertunity to attempt spinning its nonexistant flywheels, or MRO to start evasive manuvers to avoid dangerously soft dunes.

Yet there could be a potential problem if any or both are programmed to stop and recieve when they catch a signal from Earth, and so might stop whatever work they do when the commands actually are for the other one. Are this a risk or do they really go completely 'mute' when they execute the set of commands they have gotten previously?

[djellison]

I imagine that a spacecraft that notices a signal on it's own channel, but can't understand it ( which is quite likely given the different bit rates the two spacecraft would be commanded with ) would probably go into a safe mode under the assumption that there is something wrong.


Doug

[SteveM]

I imagine that a spacecraft that notices a signal on it's own channel, but can't understand it ( which is quite likely given the different bit rates the two spacecraft would be commanded with ) would probably go into a safe mode under the assumption that there is something wrong.
Doug

Assuming intelligent design among the engineers at JPL (the pun was unintentional, but irresistable) can't we assume that they have a way to turn off Sprit's receiver when they plan to send signals to MRO and vice versa.

Steve

[Bob Shaw]

Assuming intelligent design among the engineers at JPL (the pun was unintentional, but irresistable) can't we assume that they have a way to turn off Sprit's receiver when they plan to send signals to MRO and vice versa.

Steve

Steve:

Please don't put that sort of idea into their heads!

Bob Shaw

[djellison]

I was thinking that, I imagine they can sequence things whereby the two dont listen in on one another, but there's still scope for cross talk at some point. For UHF commanding, as I understand it, you have quite a big latency, as they don't uplink to Odyssey as often as they would want to uplink to Spirit.

Doug

[belleraphon1]

Another interesting tidbit - MRO uses the same X-band uplink/downlink channel (32) as Spirit...an unexpected problem relating to Spirit's longevity. Expect to see much more UHF commanding of Spirit via Odyssey in the near future. Opportunity's channel (29) is shared with Deep Impact, but that has not been an issue so far because of their spatial separation.

Airbag.

Also.... these engineering decisions are made long before launch.... it is possible that no one anticipated Spirit still being functional in 2006.

Craig

[edstrick]

On it's second lunar day, JPL tried to get Surveyor 6 to wake up and transmit. Surveyor's 1 and 5 had operated successfully on the second (and for 5, later) lunar days, despite cold damage.

Surveyor 6 transmitted signal briefly, then went silent. While they were attempting various commands, switching systems in the blind, Surveyor 1 (which had the same receiver frequency) woke up instead on it's 7'th lunar day and briefly transmitted. I don't recall for sure, but I don't think they got interpretable telemetry from either of them during the attempts.

Surveyor 7 also was successfully operated during it's second lunar day.

Lunar Orbiter 1 was deliberately crashed at the end of it's extended mission to clear up a communications frequency.

[ugordan]

Don't the DSN uplink commands have a sort of digital signature as well as intended receiver "address" in their packet headers so that Spirit/MRO know the transmission is directed towards them specifically?
That would sure seem a logical and sensible thing to do. What would otherwise prevent, say, ESA's New Norcia DSN station to "accidentally" transmit garbage on channel 32 and screw up both probes at once?

[edstrick]

I think we're dealing with paleolithic technology standards, maybe from the 70's or 80's.
<grin>

[Airbag]

I think we're dealing with paleolithic technology standards, maybe from the 70's or 80's.
<grin>

Perhaps, but the Small Deep Space Transponders are new technology and used by many current missions. There are only so many X-band channels and they are simply all used up. This is all from the DESCANSO MER telecoms report (very interesting reading I thought).

The spacecraft do have their own IDs, but best not to tempt fate with multiple bit errors etc. and perhaps accidentally accept and decode a command not intended for that spacecraft. And yes, that can happen - Opportunity accidentally went into safe mode during a solar opposition experiment in which a bunch of NOPs was changed into something else as multiple bit errors slipped by the error checking etc.

There are several techniques (other than the obvious one of using Mars itself as a "blocker") that can be used to make sure X-band signals intended for MRO (and that is the important one during aerobraking) only get to MRO. From memory, I can recall these (there were others too):

- Change Opportunity's antennas' polarization (so that it is opposite to that of MRO)
- Doppler adjustment for specific target
- Reduce transmit power level (MRO has more gain)

Airbag

PS BTW, receivers are typically *never* turned off (except during Opportunity's Deep Sleep).

[Bob Shaw]

Can I patent interplanetary MAC addresses - they could be stored digitally in a small solid-state pod, perhaps?

We could call, them, oh, iMACs and iPods...

Seriously, if a $10 network card can have a unique identifier burned in, why don't spacecraft?

Bob Shaw

[Guest_Myran_*]

Airbag said: Change Opportunity's antennas' polarization

Of course! If they can do that relatively easy its a good solution. And delegate the problems to the communication engineers then who are more qualified in the first place.

[helvick]

Seriously, if a $10 network card can have a unique identifier burned in, why don't spacecraft?

I had a long boring waffle about bit rate, harmonics, the history of MAC addresses, Ethernet's emergence in the late 1980's and collisions on ARCNET networks in the early 1990's here but re-reading it made my eyes glaze over so I thought it would be better to simply point to the CCSDS website and in particular the Space Packet Protocol Blue Book Specification as an example of just hom much thought has to go into doing this sort of thing properly.

If only it was as simple as tagging each packet with a 12 byte target identifier.

[Bob Shaw]

I had a long boring waffle about bit rate, harmonics, the history of MAC addresses, Ethernet's emergence in the late 1980's and collisions on ARCNET networks in the early 1990's here but re-reading it made my eyes glaze over so I thought it would be better to simply point to the CCSDS website and in particular the Space Packet Protocol Blue Book Specification as an example of just hom much thought has to go into doing this sort of thing properly.

If only it was as simple as tagging each packet with a 12 byte target identifier.

I followed the links, and yes, there's a lot of work been put into the definition of the systems and architecture pertaining to Space Packets and wholly laudable commitments to international and interplanetary interoperability. But nowhere do I see such a thing as an analogue of a MAC address, which has historically provided a more-or-less fail-safe identifier for almost any bit of hardware. I still can't see why not...

...am I missing something?

Bob Shaw

[helvick]

But nowhere do I see such a thing as an analogue of a MAC address, which has historically provided a more-or-less fail-safe identifier for almost any bit of hardware. I still can't see why not...
...am I missing something?

Ah I get your point now - why not just have a unique hardware based ID per probe and leave it at that? Use something like a MAC address (12 bytes) so you can be pretty sure you'll never get a collision.

I don't think that the identity is the problem and that's all a MAC type idea will give you - an assured unique identity to enable specific devices to extract their data from a shared transmission medium. The spacecraft all have adequately unique identifiers at the moment in any case so the two main problems are firstly whether they are included in the command data packets that are transmitted at the moment and secondly if they are then what sort of error handling is in place to ensure that cross talk doesn't happen? Multiple bit flip errors seem to have made it possible for one asset to incorrectly intepret a signal intended for a different asset in the past so it would seem that the error codes being used by the MER's are not 100% perfect.

Another problem is just overall congestion of the system. If there is some need for complicated command sequencing on MRO and MER at the same time then one or other will have to back off in order to allow the other to finish.

[mcaplinger]

...am I missing something?

See the Global Spacecraft ID document: http://public.ccsds.org/publications/archive/320x0b1s.pdf

Of course, these are only 8 or 10 bits long.

But has been already pointed out, just relying on an ID field to reject commands would be foolish in the presence of bit errors. If you were designing a mission-critical system based on Ethernet (which probably wouldn't be a good idea anyway because of single point failures in the shared transmission medium) you would hopefully not rely on MAC uniqueness to keep the wrong receiver from doing something. It might be unlikely for a burst of errors to corrupt one MAC address into another in such a way to get past CRC checking, but it's not "fail-safe". Even with your home LAN, there are acknowledgement protocols in TCP/IP to keep such problems from happening.

[djellison]

As I understand it - spacecraft are all moving very quickly in different directions, so there is dopler to worry about, and they are scheduled to listen at particular upilnk rates, and so on and so forth.

If MRO's listening to it's uplink at X bps, and it's being sent at Y Hz off the specified frequency, it may be that Spirit interprets that as a bad uplink as it was expecting W bps and is moving in a way that is Z Hz of specified wavelength.

I'm fairly sure they'll be able to sequence things intelligently to sort this problem out.

Doug

[Toma B]

Is there any planed imaging with HiRISE on approach to Mars?
If not, why not?

[ugordan]

There's always a good reason for not performing observations shortly before orbit insertion. The latter is such a critical maneuver that the spacecraft team doesn't want to take any chances that might jeopardize the entire mission. When you use the instruments on board, they can always report a fault state due to various reasons and cause the S/C to go into safe mode which will then obviously just sit around and wait to hear from Earth.
Obviously, if a safing event happened shortly before orbit insertion the whole mission could go down the drain. That's why we typically get imaging after the maneuver and only on some missions a very distant image of the target well before the arrival.

[djellison]

--><div class='quotetop'>QUOTE(Toma B @ Feb 24 2006, 07:47 AM) </div><div class='quotemain'><!--quotec-->
Is there any planed imaging with HiRISE on approach to Mars?
If not, why not?
[/quote]

Not that I know of - because the optical navigation camera is not boresighted with HiRISE and needs to be aimed in that direction.

(ONC is the silver thing on the near side of the spacecraft - http://mars.jpl.nasa.gov/mro/gallery/space..._pre-launch.jpg )

Doug

[Guest_Sunspot_*]

The same was done with Cassini during the week or so before orbit insertion.

[Guest_AlexBlackwell_*]

The MRO arrival press kit is now up:

Mars Reconnaissance Orbiter Arrival at Mars
posted Feb. 24, 2006 (984 Kb)

[djellison]

And the press conf is in an hour and a bit as well

Doug

[jmknapp]

And the press conf is in an hour and a bit as well

One item from the press conference: other than the test images on March 14, there will be no images during the entire aerobraking phase--the instruments will be on "survival heaters" and the electronics will not be exercised at all.

[mcaplinger]

The MRO arrival press kit is now up...

"The three cameras from the science payload -- the High Resolution Imaging Science Experiment, the Context
Camera, and the Mars Color Imager -- will take their first test images of Mars as the orbiter passes low over the southern hemisphere near the end of the third orbit, on March 14."

Now that the press kit has let this out of the bag, I'll note that the timing and location moved by ~2 hours and ~30 degrees of longitude between the mid-January predict and the most recent one -- so the imaged areas will be in the southern hemisphere, but we probably won't know exactly where until after MOI.

I don't know yet when we can expect to have the image data back.

[RNeuhaus]

The MRO spacecraft will remain out of contact for a half hour. Lots of time of suspense. There will be a TV NASA coverage during this MOI?

The 109 km, I think it is the outside of ending of Martian atmosphere. Isn't it?



Rodolfo

[edstrick]

With apollo, for both orbit insertion and trans-earth-insertion burns, there were 2 important times. The times of expected AOS <acquisition of signal>times: for 1.) if the engine burn did not occur, and for 2.) If the engine burn did occur.

On orbit insertion, a no-burn signal would be early.. an improper burn later, a nominal burn at a specific time.. and an overburn or kablooie if no signal shortly after the optimum burn time.

On TEI, a nominal burn gets you back into view early, as you've sped up in orbit.

To some extent, the same will apply here. If AOS is within a few tens of seconds of the expected time, it's likely we're in a good orbit.

[jmknapp]

Does anyone know which DSN stations and/or other facilities will be listening for MRO's signal as it emerges from behind Mars at 22:16UTC on March 10th? Which one will likely be the first to report the signal?

[The Messenger]

The MRO spacecraft will remain out of contact for a half hour. Lots of time of suspense. There will be a TV NASA coverage during this MOI?

The 109 km, I think it is the outside of ending of Martian atmosphere. Isn't it?
Rodolfo

According to the press release, they will be monitoring live on NASA TV. 109 km is cutting it a little close to Mar's fickle atmosphere - I think this is near the final projected path of the Mars Climate Orbiter, but it actually went in somewhere between 95-80 km...

[Bob Shaw]

The 109 km, I think it is the outside of ending of Martian atmosphere. Isn't it?
Rodolfo

Rodilfo:

Not at all. Relatively speaking, the upper atmosphere of Mars extends *further* from the planet than does that of the Earth, and the pressure drops more slowly. So 109 km is well within the (very thin) upper atmosphere. Mars is particularly good for aerobraking, having a thin but extensive atmosphere which should be more forgiving than our own. But, after MCO and Mars Observer, there will be a certain tension in the (rarefied) air!.

Fingers, and all other appendages should be tightly crossed, chickens should be broken down into component parts, and any spare virgins kept neatly wrapped but ready for sacrifice - it's scawwwwwwy!

Bob Shaw

[djellison]

Of course - the reason for having such a low targetting point is because a periapsis that low invokes a fast orbital velocity - thus the ammount of engine braking required is less. If they targetted at say, 1500km, the orbital velocity at that altitude would be much slower so requiring much more delta V.

One day - I hope they'll be brave enough for Aero-capture at Mars. It's a very thin line to tred - +/- 10km will give you a bad day one way or the other, but they're getting to the point where it's possible, I'm sure.


Looking at this -
http://space.jpl.nasa.gov/cgi-bin/wspace?t...orbs=1&showsc=1

Goldstone will be the primary, with Madrid just setting.

Doug

[jmknapp]

Goldstone will be the primary, with Madrid just setting.

IIRC, with MER, some secondary facilities (Stanford) were also listening. Wonder if they might do the same with MRO.

[djellison]

Stanford was listening to MER because MER was also transmitting with its UHF antenna (to MGS), for which Stanford have a good facility, and indeed they caught Spirit, but not Opportunity as I understand it. No such transmission is planned for MRO as I understand it - just X-Band on the LGA which will be for the DSN to grab alone.

Doug

[mcaplinger]

Of course - the reason for having such a low targetting point is because a periapsis that low invokes a fast orbital velocity - thus the ammount of engine braking required is less. If they targetted at say, 1500km, the orbital velocity at that altitude would be much slower so requiring much more delta V.

I think there's some confusion. The aimpoint altitude at MOI is 400 km, not anything lower. After MCO, they're unlikely to try anything much lower.

[djellison]

Ahh - someone mis-quoted the press pdf previously then - it seemed a bit low to me

Doug

[Bob Shaw]

Ahh - someone mis-quoted the press pdf previously then - it seemed a bit low to me

Doug

Doug:

I was wondering, too - much lower than MGS!

Let's hope it *doesn't* go low...

Bob Shaw

[RNeuhaus]

Does anyone know which DSN stations and/or other facilities will be listening for MRO's signal as it emerges from behind Mars at 22:16UTC on March 10th? Which one will likely be the first to report the signal?

I am thinking about why any of three present Mars Orbiters, ODY, MGS and MEX aren't capable as a relay of any signal from a new member MRO to Earth and viceversa? The rovers might be the witnesers with their PANCAM. Not sure about its proper localization at the MOI critical moments.

I think there's some confusion. The aimpoint altitude at MOI is 400 km, not anything lower. After MCO, they're unlikely to try anything much lower.

Maybe, the space portal: spaceflightnow is confused. Below is the extract:

To take full advantage of atmospheric braking, the low point of the orbit will be carefully reduced to around 62 miles (100 km). It will be raised, or "walked out," later, with the ultimate goal being a roughly circular orbit with a high point of at most 199 miles (320 km) and a low point as close as 158 miles (254 km) to the surface.

http://www.spaceflightnow.com/mars/mro/060224moipreview.html

Rodolfo

[mcaplinger]

Maybe, the space portal: spaceflightnow is confused.

You're quoting the altitude during aerobraking, not the altitude at MOI, which is much higher.