ENVISAT likely dead in the sky

More bad satellite news: ENVISAT seems to have stopped phoning home. ENVISAT is a giant satellite managed by the European Space Agency, and has been collecting a ton of environmental data since 2002. It has 10 different instruments, and has been used extensively in climate research over the past decade.

Sometime on 8 April, ENVISAT stopped communicating with controllers at the ESA. There has been a concerted effort to determine the cause of the failure and re-establish communication of the satellite. This effort is impressive, with the French satellite Pleiades even being turned away from Earth to try to capture images of ENVISAT to determine the state of the solar panels. Other observations of the satellite are also being used to make sure that ENVISAT is -- and is staying -- in a stable orbit. There is some hope that a connection can be reestablished if ENVISAT has gone into -- or could be cajoled into switching to --  "safe mode." Otherwise, it is likely that there has been catastrophic failure of the main computer or power source on board, and there's no hope of recovery. 

ENVISAT's estimated lifetime was just 5 years, so again over-engineering paid off (like the Mars rovers, SeaWiFS, etc). Unfortunately, the Sentinel satellites that are planned to replace ENVISAT have not been put into orbit yet, so there is likely to be a gap in the data record for some of the quantities that ENVISAT monitors. These even include CO2; the launch failure of the Orbiting Carbon Observatory (NASA) in 2009 left just ENVISAT and a Japanese satellite with capabilities to monitor CO2 from space. Now there is just the Japanese satellite, the Greenhouse Gases Observing Satellite. Apparently there is a lot of controversy and arguing about how to pay for the Sentinels, making the ESA's commitment to climate monitoring just as shaky as NASA and NOAA's in the USA.

SOURCES:
Geoff Brumfiel, 

Nature

 

484,

 

423–424

 

(26 April 2012)

 

doi:10.1038/484423a

, 
ESA [link]

Glory of the sea?

I recently wrote about the Glory satellite mission [LINK]. Early this morning, the rocket carrying Glory to orbit was launched from Vandenberg Air Force Base. Unfortunately Glory will only be studying the particles in the south Pacific, because the rocket was unable to attain orbit and crashed into the ocean. [LINK]. This is very similar, at least superficially, to the failure of the Orbiting Carbon Observatory, which I also blogged about [LINK]. This is supposed to be the "golden age" of satellite observations of the climate system, but it is hard to believe when we struggle to get the satellites into orbit. Glory has been over a decade in the making, and I imagine there are a lot of people around the country right now who are wondering what they are going to do in the next couple of years.

There may be hope, though. The Orbiting Carbon Observatory 2 is a go, scheduled to be put into orbit in February 2013. Except that they are planning to use yet another Taurus rocket [LINK]. So, yeah.

RealClimate also picked up this story [LINK].

Glory Be.

Well, it might be, depends how the launch goes. Glory is the new NASA "A-Train" satellite that is supposed to be launched on 23 February [LINK]. The launch vehicle is a Taurus XL 3110; I know what you're thinking, but no this is not a Ford model. It is, however, a similar rocket to the one that delivered the Orbiting Carbon Observatory to the bottom of the ocean [LINK]. So let's hope for a little better luck with this one.

The satellite is really going to be doing two things once it is functional. First, it is going to measure the solar output. Put another way, it is going to measure how much sunshine reaches the top of the atmosphere. Second, it is going to use the Aerosol Polarimetry Sensor (APS) to measure properties of suspended particles in the atmosphere (aerosol). According the the overview, "this instrument will measure the size, quantity, refractive index, and shape of aerosols."[NASA]. This isn't the first time aerosol will be observed from space, but it is the first time that detailed properties will be retrieved (as opposed to bulk or geometric properties, as from CALIPSO).

If you are thinking, but isn't the A-Train lifetime actually nearly over? Well, yes, it sure is getting there. Because of the lack of funded missions on the horizon, I have heard our present period referred to as the golden age of satellite observations. The A-Train has been up for a while, except that everything has been delayed. Glory was scheduled to launch in 2008, and here we are years later. The OCO did launch, but crashed; there is an OCO2 planned, but it will be some time before they can build, test, and launch the replacement. The French companion to the A-Train, PARASOL, is heading toward end of life (probably this year), and has had to leave the train because it doesn't have enough fuel to maintain synchronous observations. I think it is safe to say that the original picture of the A-Train never came to fruition, but there has been a lot of overlap which is providing a better view from space than ever could have been achieved with a single satellite.

An interesting aspect of this mission is that the APS is measuring parameters that I don't think have ever been measured from space. It is a passive instrument, which just means that it looks at the light coming up from Earth, and then analyzes that light. Often satellites just measure the brightness (intensity) of the light, and might do that for several frequencies. Glory will measure the other "Stokes parameters" to get information about the polarization of the light, and will do it in 9 different spectral bands. It is quite an impressive piece of optical equipment, even more so when you think it is in a box 705 km above the earth traveling at 24,000 kph or so. Basically a small section of the Earth is seen by the satellite, and the light goes through a refractive telescope and then something called a Wollaston prism before reaching the detectors. The prism separates two orthogonal linearly polarized beams, each beam then impacts a detector. The instrument also contains a motor that rotates the mirrors and allows views of the scene at multiple angles. My knowledge of optics to too rusty to be able to say anything useful about this, but it amazes me that such a complex, delicate instrument can be put into orbit.

But don't forget that Glory is also measuring the Total Solar Irradiance. This is a critical parameter as it represents the energy source for the climate system. There have been continuous space-based measurements of the sunshine for about 30 years. The good news is that the measurements show the variability in solar output and are consistent with theory about what the solar constant should be. The bad news is that different instruments have shown slightly different values (ranging from 360-370 W/m2). That doesn't sound too bad, but 10W/m2 of incoming sunlight makes a substantial difference in the global energy budget. Glory will hopefully provide the accuracy and stability needed to better constrain the average solar output.

Details of Glory can be found in an overview paper from BAMS [LINK], but keep in mind that this was written by the scientists. Despite being for the general atmospheric science community, they don't do a great job of explaining things in simple non-jargony language.