LRO will spend the rest of its existence in a Moon-centered universe. This diagram illustrates that point of view. (Note that the distances between Earth, Moon, and Sun are not to scale, nor are their sizes.)
At present, Earth is in the lower left (Quadrant 2). The Sun is in the clear wedge at the right. Whenever the Sun is in Gemini (late June through late July), or in Sagittarius (six months later), LRO will receive sunlight throughout its entire lunar orbit, unblocked by the Moon. Earth is continuously visible to the Orbiter when located in Sagittarius (at the left) or Gemini (at the right).
The "ascending/descending" notation refers to LRO's path upward, out of the plane of the diagram (towards the viewer) or downward into the plane of the diagram. Readers with a knowledge of physics or mathematical notation will recognize the vector ("arrow") pointing out of the Moon towards the left. Align your right-hand thumb with the arrow, and then the rest of your fingers will point in the direction of orbital travel. (The "right-hand rule.")
"Eclipse Season" refers to times of the year when LRO will have its view of the Sun blocked by the Moon, ranging from moments (when the Sun is near the clear wedges) to 48 minutes (when the Sun is at the top or bottom of the diagram).
I think the diagram may be in error by using the term "lunar solstice." I think it should be "lunar equinox" (when the Sun is over the Moon's equator, as happens twice a year).
Occasionally, Earth will block all or part of the Sun as seen from LRO. Those events are what we on Earth see as lunar eclipses, when the Moon passes through Earth's shadow.
We've got a few of those coming up this year: July 7, August 6, and December 31. The first two are called "penumbral" eclipses because Earth will not completely block the Sun as seen from anywhere on the Moon. The latter event will be a "partial" eclipse because the Sun will be completely blocked, but only as seen from a part of the Moon (in this case, a relatively small area near the south pole).
Next year will have another partial (June 26, when the northern half of the Moon sees Earth completely cover the Sun) and a "total eclipse," when an observer anywhere on the lunar surface would see the entire Sun blocked for a time. That one is on December 21, lasting 83 minutes. Our power and thermal specialists designed LRO to withstand those conditions, but we will also take special steps to protect the spacecraft during that extended period of darkness, which will last longer than our usual worst-case 48 minutes (twice a month) caused by orbiting over the Moon's midnight longitude.
Note that June and December are when LRO's view of the Sun is perpetually unobstructed by the Moon. That means the shadows caused by Earth will not be extended in duration by LRO then having to pass into the Moon's shadow.
I believe this arrangement was intentionally made by our selection of launch date and lunar intercept point.
Friday, June 26, 2009
LRO's Orbit
Our burn completed successfully.
LRO's orbit passes over the Moon's north and south poles and is described as "inertially frozen." That means that it is unchanging in orientation with respect to the stars. The Moon rotates below, once each month, the Sun will circle it once a year, and Earth will circle it once a month, but the stars will remain fixed in LRO's sky.
I think the easiest way to picture this is:
Whenever the Moon is in the constellation Gemini, we see LRO orbiting the lunar disk counter-clockwise. When the Moon is at the opposite side of its orbit (180 degrees away in the sky, in the constellation Sagittarius), again we see LRO orbiting the lunar disk, but clockwise.
90 degrees to the east of Gemini is the constellation Virgo. When the Moon is there, LRO's orbit passes from south to north across the middle of the lunar disk as we see it. During half of LRO's 113-minute orbit, we can't see it from Earth because it's blocked by the Moon.
On the opposite side of the sky from Virgo is Pisces. When the Moon is there, LRO passes from north to south across the middle of the Moon's disk.
In between those four locations, you can interpolate where LRO's path would cross in front of or behind the Moon.
LRO's orbit passes over the Moon's north and south poles and is described as "inertially frozen." That means that it is unchanging in orientation with respect to the stars. The Moon rotates below, once each month, the Sun will circle it once a year, and Earth will circle it once a month, but the stars will remain fixed in LRO's sky.
I think the easiest way to picture this is:
Whenever the Moon is in the constellation Gemini, we see LRO orbiting the lunar disk counter-clockwise. When the Moon is at the opposite side of its orbit (180 degrees away in the sky, in the constellation Sagittarius), again we see LRO orbiting the lunar disk, but clockwise.
90 degrees to the east of Gemini is the constellation Virgo. When the Moon is there, LRO's orbit passes from south to north across the middle of the lunar disk as we see it. During half of LRO's 113-minute orbit, we can't see it from Earth because it's blocked by the Moon.
On the opposite side of the sky from Virgo is Pisces. When the Moon is there, LRO passes from north to south across the middle of the Moon's disk.
In between those four locations, you can interpolate where LRO's path would cross in front of or behind the Moon.
Today's Burn
Nearing today's orbit-adjustment burn, set for 8:25 AM EDT. Tomorrow morning will be the final one to get us into the commissioning orbit.
Around 6 this morning we did a reaction wheel momentum unload (entering "Delta-H Mode"), using thrusters to slow down the wheel speeds to keep them below specified thresholds.
Our colleagues at Arizona State University (home of the science operations center for the LRO Camera (LROC)) have posted a diagram showing where LRO is:
I've had some trouble on my home computer with it not showing the LRO path or position, but it displays fine on my work computer.
The projection of the lunar surface may be confusing to most readers. The far left and far right three-grid-wide segments are the far side (never seen from Earth) and the center six-square-wide segment is the near side, distinctive for its maria (the dark lava-bed plains, mostly absent from the far side). North is up.
Just a moment ago we reacquired contact with the Orbiter. This was my first shift during which the Orbiter passed behind the Moon. It emerged about 20 minutes later.
Wednesday, June 24, 2009
LRO and the Moon
I kept checking after sunset tonight to try to get my first glimpse of the Moon after LRO's LOI, but clouds covered all but a small strip of sky along the horizon. It wasn't until late (9:43 PM EDT, to be exact) that I finally spotted it in that strip from my mom's apartment window. I called my colleague Scott Walling (manning the flight software station in the LSR) to tell him to look for it when he went off shift at 10, and then we went outside to get a better view for ourselves and talked for a while.
If I'd thought ahead, I would've asked my Flight Dynamics colleagues where LRO was in its orbit at particular times. There's no chance of seeing it, but it's cool to have a rough idea of where it should be while you're looking at the Moon. I do know that LRO is orbiting the Moon counter-clockwise as we currently see it. The orbit (as of tonight) takes it as close as about 120 miles above the south pole, and as far as a thousand above the north. That would be about half the width of the lunar disk away from the northern edge.
As is often the case when the Moon is a crescent, we could faintly see some of the surface features on its night side. That's caused by Earthlight. A nearly full Earth (four times larger than the Moon appears in our sky) is shining in the Moon's (and LRO's) sky now, with only a sliver of darkness along its eastern edge. (The phase of Earth's disk as seen from the Moon is always a mirror image of the Moon's phase as we see it, with light and dark areas reversed.)
Milton
The LRO visualization lead is my friend Jennifer. She's several months pregnant with a son who will be named Noah. She and her husband are still mulling over middle names. She's been trying to find a Moon-related name, but most of those are feminine (e.g., Selena). Otherwise she's thinking of using her grandfather's name, Milton.
I pointed out that there's a crater on the Moon named Milton, so she was happy that her problem might be solved.
Unfortunately I learned later that the name was never officially approved by the International Astronomical Union! There is a crater named after John Milton on the planet Mercury, but that won't help Jennifer's cause.
Noah's big sister is named Marleyani, owed in part to Jennifer's husband being a fan of reggae performer Bob Marley. I love the sound of that name.
I pointed out that there's a crater on the Moon named Milton, so she was happy that her problem might be solved.
Unfortunately I learned later that the name was never officially approved by the International Astronomical Union! There is a crater named after John Milton on the planet Mercury, but that won't help Jennifer's cause.
Noah's big sister is named Marleyani, owed in part to Jennifer's husband being a fan of reggae performer Bob Marley. I love the sound of that name.
Review of Yesterday's Performance
Tonight at 11 PM EDT, NASA TV showed a replay of Tuesday morning's one-hour LRO LOI television coverage. The program was shown in both the MOC and LSR...our first chance to see how we came across on TV.
Darn it, I forgot to emote! My chance to be spotted by a talent agent has fallen to shreds...again.
The burn went so well that there wasn't much to show until it ended. My colleague Mike Blau commented to Bruce Trout about halfway through, "This is the most boring sim we've done."
Being up all night probably kept me pretty low key. Tension was probably the primary sensation I had through most of the burn. Not a lot, but some. Relief and a bit of incredulity came after it ended. A mix of other strong (good) emotions surfaced (mostly showing, others held back a bit as necessary) when I celebrated with the rest of the team.
Here's the big picture: my notes indicate that I first met with Mike Blau and Rick Saylor, the Ground Systems and Operations lead (and last night's flight director) when I joined LRO on March 1, 2007. The main question posed to me at that meeting...if an anomaly should impact LRO during its 3-5 day lunar cruise phase, can you create a flight software "patch" (a change to code or data) fast enough to fix the problem, so the LOI burn could take place as planned?
I still have a message I later wrote to management about this, excerpted here: "[They want to know if we can devise a ] "Lunar Cruise Emergency Patch Procedure." (Lunar Cruise is the five-day trip from Earth to the Moon...a mission phase that could lead to loss of mission if something prevents the Lunar Orbit Insertion Burn from going correctly at the end of Lunar Cruise, in which case the spacecraft will pass by the Moon and out into deep space.) I informed [them] that in principle we can accelerate our process, but the result would be increased risk introduced from each stage of the process. Some anomalies could take longer than five days to even understand, much less devise a fix for. I strongly recommended that their primary line of defense should be to test all nominal and contingency Lunar Cruise operations, and we (FSW) could provide only a secondary line of defense."
In a way, this has weighed on my mind for over two years. Finally that pressure is off now that we're safely in orbit. In another post I'll give a quick overview of what I might've done if an emergency had occurred before LOI.
Darn it, I forgot to emote! My chance to be spotted by a talent agent has fallen to shreds...again.
The burn went so well that there wasn't much to show until it ended. My colleague Mike Blau commented to Bruce Trout about halfway through, "This is the most boring sim we've done."
Being up all night probably kept me pretty low key. Tension was probably the primary sensation I had through most of the burn. Not a lot, but some. Relief and a bit of incredulity came after it ended. A mix of other strong (good) emotions surfaced (mostly showing, others held back a bit as necessary) when I celebrated with the rest of the team.
Here's the big picture: my notes indicate that I first met with Mike Blau and Rick Saylor, the Ground Systems and Operations lead (and last night's flight director) when I joined LRO on March 1, 2007. The main question posed to me at that meeting...if an anomaly should impact LRO during its 3-5 day lunar cruise phase, can you create a flight software "patch" (a change to code or data) fast enough to fix the problem, so the LOI burn could take place as planned?
I still have a message I later wrote to management about this, excerpted here: "[They want to know if we can devise a ] "Lunar Cruise Emergency Patch Procedure." (Lunar Cruise is the five-day trip from Earth to the Moon...a mission phase that could lead to loss of mission if something prevents the Lunar Orbit Insertion Burn from going correctly at the end of Lunar Cruise, in which case the spacecraft will pass by the Moon and out into deep space.) I informed [them] that in principle we can accelerate our process, but the result would be increased risk introduced from each stage of the process. Some anomalies could take longer than five days to even understand, much less devise a fix for. I strongly recommended that their primary line of defense should be to test all nominal and contingency Lunar Cruise operations, and we (FSW) could provide only a secondary line of defense."
In a way, this has weighed on my mind for over two years. Finally that pressure is off now that we're safely in orbit. In another post I'll give a quick overview of what I might've done if an emergency had occurred before LOI.
Orbit Adjustments
About an hour after my shift ends at 6 AM, LRO will perform another burn. This one will only last for 12 minutes. It's the first of four daily burns that will adjust our orbit into the profile desired during the "commissioning phase," when science instruments, the flight software, and attitude sensors will be modified, fine-tuned, and readied for the one-year exploration mission phase. When commissioning completes, LRO will be put into a circular and low (50-km) orbit that is harder (as in, consuming more fuel) to maintain than our commissioning orbit. But our science instruments require the more precise close-in orbit.
Earlier today, one of my colleagues generated the burn products for the onboard computer. About an hour ago I supervised their uplink to the Orbiter.
The four daily burns are called LOI burns, which is a misnomer. We have already "inserted" LRO into a lunar orbit with the true LOI yesterday.
Earlier today, one of my colleagues generated the burn products for the onboard computer. About an hour ago I supervised their uplink to the Orbiter.
The four daily burns are called LOI burns, which is a misnomer. We have already "inserted" LRO into a lunar orbit with the true LOI yesterday.
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