Archive for the Observatories Category

SDO Launch Coming Soon! – Feb 3rd

Posted in Astronomy, Launches, Mission Operations, Observatories on 01/18/2010 by clairdeluna

Shortlink: http://wp.me/pJisQ-3e

The Solar Dynamics Observatory (SDO) is the next robotic scientific mission NASA will launch. Currently it is scheduled to launch from Cape Canaveral’s SLC-41 on an Atlas 5 rocket on February 3, 2010 with a one hour launch window (10:53-11:53 a.m. Eastern Time). The mission will nominally last for 5 years. After the success of the SOHO, STEREO, and TRACE missions, having another active solar observatory will be an incredible leap in capability for solar science.

And what a leap! SDO will have the fastest time resolution ever flown for solar imaging: 8 full disk images covering 8 different wavelengths every 10 seconds. This means SDO will generate an absolutely phenomenal amount of data. One major challenge for missions in orbit is finding a way to transmit large amounts of data to the ground. Often, spaceborne instruments are capable of generating much more data, but must choose to produce less so that the data storage and transmission requirements are met.

SDO’s solution to this issue is to place the observatory in a geosynchronous orbit over the White Sands ground terminal in Las Cruces, New Mexico. Geosynchronous orbits are special because the satellite orbits the Earth at the same rate that the Earth itself is rotating. These are the orbits used by the satellites that monitor weather, or provide your satellite TV. In this case, the geosynchronous orbit will allow SDO to have very long continuous communications directly with the ground. Direct link to the ground allows for transmission of more data per second than using data relay satellites. So this orbit absolutely maximizes the transmission rate for SDO.

Why does SDO need so much data? Well, because the mission is designed to perform very precise helioseismology measurements. Seismology, the study of how waves travel through an object, is used on Earth to study tectonic disturbances such as earthquakes and volcanos. For large, deep earthquakes, seismic measurements of such disturbances tell geologists much about the inner structure of the Earth. By using SDO to watch waves travel across the surface of the Sun, helioseismologists hope to gain similar knowledge of what is occuring deep below the Sun’s surface.

In fact, observations made from the ground have already demonstrated the feasibility of such science. But ground based solar observatories have significant disadvantages over orbiting spacecraft. For example, SDO will only experience nighttime twice each year, with each being about 3 weeks long. This means the rest of the year SDO will have non-stop viewing of the Sun, giving solar scientists an unprecedented dataset just as we start a new solar cycle.

In addition, SDO hopes to uncover much more about the solar magnetic cycle. After the long solar minimum we have just experienced, it is evident that our understanding of the Sun’s intrinsic magnetic field is still in its infancy. SDO’s monitoring of the Sun’s complex magnetic structure will give us an opportunity to better understand how it interacts internally and with the rest of the solar system; from sunspots, prominences, and coronal mass ejections from the Sun’s surface to solar wind and auroras experienced here on Earth.

I’m so excited to see what new science this observatory unlocks! Of course it still has to go through that last big leap to get it into orbit. Let’s just hope the rocket doesn’t blow up!

WISE: Deployments coming soon

Posted in Astronomy, Mission Operations, Observatories on 12/24/2009 by clairdeluna

It looks like the WISE observatory is happily working through the early checkout phase. During the first few days/weeks of a mission, the engineers verify the basic functionality of a newly launched spacecraft, essentially making sure nothing broke during the extreme environment associated with launch.

During launch, the observatory experiences extreme vibration, acoustic, thermal and space (vacuum) environments either simultaneously or in rapid succession. Prior to launch we test each of these individual environments as best we can, but nothing can really prepare for the intensity of the launch. As a result, the post-launch checkout is a very slow, careful process that exercises each bit of spacecraft functionality one tiny step at a time. That way, if anything has broken, it can be identified early, troubleshot, and either recovered, or changed to a redundant piece of hardware. NASA prefers for all spacecraft to be fully redundant (that is, have a spare bit of hardware for everything in case the primary one breaks) but the reality is that full redundancy is cost prohibitive.

Instruments are often not fully redundant. Almost every single instrument on a NASA mission is one-of-a-kind hardware, designed specifically and solely for the science goal of that mission. Instrument designers do their best to provide redundancy where possible. But there are always parts on the instrument that, should they fail, will end the mission for that instrument.

In addition, many missions have hardware that must be deployed. For example, a solar array may need to be driven from a folded to an extended position, or a door may need to be opened to provide a sun-shade to an instrument. For WISE, the sole instrument on board has a cover protecting the cryogenically cooled interior. The cover keeps out water that would freeze to the interior surfaces, possibly obscuring the detectors. This water originates on Earth, but is carried into space on various surfaces of the observatory, such as within the thermal blankets protecting portions of the spacecraft. Once the observatory has had sufficient time in space for the water to have sublimated away (outgas time), the cover can be removed. In this case, the cover deployment currently scheduled for December 29th will be carried out by firing three explosive fasteners.

Should a deployment fail to occur, it can often mean a mission-ending situation. There is no redundancy in the WISE cover (i.e. you cannot remove an alternate cover and get science data). As a result, this is a very critical activity. In addition, ground testing typically does not exercise the firing of pyrotechnics. Rather, the signal used to release the nuts can be tested prior to installation, and the response of the nuts to such a signal can be tested on duplicate hardware. The upshot is that this deployment is likely the first and only time the entire system has ever been tried all together.

It may seem like this is a foolish method, but unfortunately some systems are simply untestable on the ground. Spacecraft engineers work to test such hardware as thoroughly as possible. However, when deployment time comes, we are all holding our breath until the pyros blow correctly and the cover comes off…

It’s Alive…..Alive!!!

Posted in Astronomy, Mission Operations, Observatories on 12/22/2009 by clairdeluna

Finally, after much consternation among solar scientists everywhere (okay, that’s a bit of an exaggeration) the Sun has awaked from one of the deepest solar minima in recent history. You can see a total of five, FIVE, active regions in this extreme ultraviolet picture from SOHO:

The SOHO observatory has monitored solar activity since 1995, sitting at the L1 Lagrangian point between the Earth and the Sun. This stable position, four times farther than the Moon’s orbit, offers an unimpeded view of the solar disk. The science return from this observatory has been incredible, drastically increasing our understanding of the star that powers our planet and lives.

This feat is even more amazing considering SOHO’s history. In 1998, a problem on the observatory ended with the failure of all gyroscopes. For a mission designed around the ability to self-stabilize at the L1 gravitational minimum, such a loss seems mission-ending. However, operations engineers learn early that it’s necessary to work with what is available, even though the situation isn’t optimal. In this case, an amazing effort to rescue the SOHO observatory ensued, and the spacecraft engineers devised a method to use the observatory successfully without gyroscopic stabilization.

The extreme environment of space eventually degrades or destroys the spacecraft we launch. But until we are forced to accept that an observatory is irretrievable, operations engineers will work to keep the mission going. As a result, most missions end due to funding cuts, not hardware failure.

WISE Launching!

Posted in Launches, Observatories on 12/14/2009 by clairdeluna

Go check out the launch on NASA TV! (Now that the launch is complete, this link is no longer showing the WISE launch. However, you can watch the replay below.)

Update: Once again, despite my constant expectations, the rocket didn’t blow up! Don’t believe me? Here’s the replay…

Words have meaning: Hold (Hold Hold)

Posted in Launches, Mission Operations, Observatories, Word Meanings on 12/13/2009 by clairdeluna

The last few minutes of a launch are very critical. It is at this time that systems on the launch vehichle, and (for some missions) the payload, are switched from using an external power source to using their internal batteries. For Delta launches, this switch usually occurs four minutes before launch, and gives the final insight into the complete health of the system. At this point, if any data indicates a possible problem it is necessary to quickly stop the launch.

In mission operations, words that indicate a specific, time-critical action must be very precise. In this situation, the words used by an engineer to the launch director to stop the launch are:

Preparing to launch a multi-million to multi-billion dollar observatory requires practice. So the last six months prior to launch are filled with practices. “Mission rehearsals” that exercise the post-launch and activation process are very complicated, and are run repeatedly by the mission operations team. “Launch rehearsals” that practice the pre-launch process are performed jointly with the launch vehicle operations team several times before launch. During launch rehearsals, one of the hardest things for me to learn was never to say the word “hold.”

Saying “hold hold hold” only has consequences if you say it on the particular communications channel (voice loop) that is connected to the launch operations team, and I never had any reason to be on that loop. Even so, I spend the last few months finding alternative words to use. “Please carry this for me,” rather than “Please hold this.” “Can you wait a minute,” rather than “Can you hold on.” And the list goes on…

It seems like such an innocuous word, hold, until you realize that with that one word you have the power to stop a launch. And right before launch, even a one day delay is a LOT of manpower, and money. But that’s not nearly as painful as the investigation that would follow a failed launch.

You hope you never have to say “hold hold hold.” But if something’s not right, it’s absolutely the right thing to do…

WISE Launch Slips to Saturday

Posted in Launches, Mission Operations, Observatories on 12/11/2009 by clairdeluna

Note: As palmerin mentions below, the launch is now scheduled for Monday. Enjoy the free weekend! I bet the mission team is frustrated!

The WISE launch, originally scheduled for yesterday, has slipped to Saturday morning. The current WISE mission launch page indicates that the reason for the slip is a “problem with a booster steering engine.” Such a problem could range from relatively minor (two sensors giving incompatible readings) to serious (some hardware failure could make the booster unsteerable). But with a 24 hour hold, it’s probably a minor issue.

When your launch window is less than 14 minutes (6:09:33 – 6:23:51 a.m. PST for Saturday), you only get one shot at launching. The typical Delta-II recycle time (how long it takes to get a second try) is about 20 minutes. I’ve seen it done in 17 minutes, and that was very fast. If the problem requires more than a few moments to figure out, the launch is usually scrubbed (postponed) and rescheduled for a later time. How long they wait depends on the severity of the problem. The minimum time is however long it takes to get to the next launch window that will put the spacecraft into the proper orbit. For a mission like WISE, that time is probably 24 hours, hence the 24-hour delay.

Sadly, that means those of us who are launch junkies have to actually drag ourselves out of bed on Saturday morning if we want to watch the launch. But hey, at least we aren’t gonna have to work the weekend!

Words have meaning: Satellite, Spacecraft, Observatory, Payload

Posted in Mission Operations, Observatories, Word Meanings on 12/07/2009 by clairdeluna

Ever look up in the sky and see a star moving slowly across the sky, passing the other stars around it? What you are seeing is a satellite, an object orbiting another object, reflecting sunlight off its surface.

In this case, the satellite is man-made. However, the moon is also a satellite, just like that little dot you saw. It is an object orbiting the Earth. The Earth itself is a satellite, since it orbits the Sun. And there are man-made satellites that also orbit Mars (e.g. Mars Odyssey), Saturn (Cassini), the Sun (SOHO) and many other solar system bodies. Even those observatories that are no longer functioning (like Mars Global Surveyor) are still satellites, they still are in orbit. I find that many people think of satellites only as man-made objects, even though nature made them first. And we tend to forget that the word satellite has little meaning without knowing what body the object is orbiting.

If you watch NASA TV (and who doesn’t, right?) and listen to those engineers and scientists talking about their satellite it can seem like they are using a lot of different words for what seems like a simple subject. However, in the space industry there are certain very specific terms that we use that have specific meanings. So while it may seem that we are spouting lots of words to just sound extra-super-duper-smart, in reality we are using those terms in order to be precise. Take, for example, the terms “spacecraft,” “observatory,” and “payload.”

A spacecraft is a support structure. It contains the hardware necessary to power, command, and control the “payload” that is connected to it. Often the term “spacecraft bus” is used to indicate the fact that this structure is the support for the payload. When the spacecraft and payload have been mated together, the whole unit (at least for a science mission) is the “observatory.”

Hardware that has been connected to support hardware is a “payload.” The instruments (scientific sensors) are the spacecraft’s payload. (For commercial satellites, the payload may be an antenna/transmitter for relaying cell phone signals, or digital TV.) The observatory is the launch vehicle’s payload. A spacecraft bus without its payload is like a person’s brain with only rudimentary sensory input. It can function, and even receive and respond to commands, but it has a hard time interacting with the world around it and will not be very productive. Likewise, it is unusual to expend a launch vehicle without a payload (though this situation does happen sometimes in testing a new launcher).

So, the next time you see that small speck of light moving among the stars, remember: that observatory in space, that satellite of the Earth, is a complex system made up of multiple functional parts, each with their own precise terms. And it has gone through many phases to become what may seem to you to be a simple “satellite.”