“Dr. Joe Gurman of NASA’s Goddard Space Flight Center provides commentary on selected shots from SOHO’s 20 years in space.
After 20 years in space, ESA and NASA’s Solar and Heliospheric Observatory, or SOHO, is still going strong. Originally launched in 1995 to study the sun and its influence out to the very edges of the solar system, SOHO revolutionized this field of science, known as heliophysics, providing the basis for nearly 5,000 scientific papers. SOHO also found an unexpected role as the greatest comet hunter of all time—reaching 3,000 comet discoveries in September 2015.
When SOHO was launched on Dec. 2, 1995, the field of heliophysics looked very different than it does today. Questions about the interior of the sun, the origin of the constant outflow of material from the sun known as the solar wind, and the mysterious heating of the solar atmosphere were still unanswered. Twenty years later, not only do we have a much better idea about what powers the sun, but our entire understanding of how the sun behaves has changed.”
On March 6, 2009, the Delta II launch vehicle carrying the Kepler spacecraft lifted off from Launch Complex 17-B at Cape Canaveral Air Force Station in Florida.
Kepler is expected to be operational until at least November 2012. Scientists hope to discover exo-planets in the habitable zone of other stars. The habitable zone is a region around a star where water can exist in liquid form on the surface of a planet. You can find more information about Kepler on NASA’s Kepler Mission website.
Credits: NASA/Goddard Space Flight Center Scientific Visualization Studio
Predictions of space weather are important as the effects of magnetic storms can be very significant: disruptions in radio communications, radiation hazards to astronauts in LEO, and power lines surges, just to name a few. The goal of NASA’s Living With a Star (LWS) Program is to understand the changing Sun and its effects on the Solar System. The Solar Dynamics Observatory (SDO) is one of NASA’s LWS missions.
SDO will take measurements of the solar activity. There are seven science questions SDO will try to answer. Among them, what is the mechanism that drives the cycles of solar activity? How do the EUV variations relate to the magnetic activity of the Sun? Is it possible to make predictions regarding the space weather and climate? The last question, if answered, will make choosing the launch windows for future interplanetary manned missions an easier task.
The spacecraft is 2.2 x 2.2 x 4.5 m and 3-axis stabilized. At launch, it has a mass of 3200 kg (270 kg the payload and 1400 kg the fuel). The solar panels are 6.5 m across, cover 6.6 m2, and produce up to 1540 W of power.
Credits: NASA
SDO carries three instruments: the Atmospheric Imaging Assembly (AIA), EUV Variability Experiment (EVE), and the Helioseismic and Magnetic Imager (HMI). The instruments will take measurements that will reveal at a very high rate the variations of the Sun.
The HMI was developed at Stanford University and it will extend the SOHO/MDI instrument. The HMI will help to study the origin of variability and the various components of the magnetic activity of the Sun. The measurements aim at understanding the origin and evolution of sunspots, sources and drivers of solar activity and disturbances, connections between the internal processes and the dynamics of the corona and the heliosphere.
The AIA will capture images of the solar atmosphere in ten wavelengths every ten seconds. The data collected by the instrument will improve the understanding of the activity in the solar atmosphere. The instrument was developed by Lockheed Martin.
The SDO will launch aboard an Atlas V launch vehicle from SLC 41 at Cape Canaveral. SDO will operate on a geosynchronous orbit, which will allow continuous observations of the Sun. The orbit will also allow a continuous contact with a single dedicated ground station. The high data acquisition rate required such a mission profile, as a large on-board storage system would add to the overall complexity of the system.
Wide-field Infrared Survey Explorer or WISE is a NASA-funded scientific research project that will provide an all-sky survey in the mid-infrared wavelength range.
WISE will collect data that will allow scientists to compile an all-sky infrared image atlas and catalogue of over 300 million infrared sources. WISE will be able to measure the diameters of more than 100,000 asteroids that glow in the mid-infrared, and make observations of the coldest and nearest stars, regions of new star and planet formation, and the structure of our own galaxy.
WISE will only operate for seven to thirteen months. WISE will explore the entire Universe from a 523×523 km, 97.4-inclined orbit above the ground. The spacecraft will orbit in a Sun-synchronous orbit, so the solar panel will always be pointed at the Sun.
The cryostat will run for thirteen months. After a one-month in-orbit checkout period, the telescope will operate for six months. An additional pass of the sky (that would take another six months) is possible, if funded to do so by NASA.
Credits: UCLA/JPL
The spacecraft is 2.85 m long, 2.0 m wide, and 1.73 m deep. The spacecraft does not carry propellant. The telescope will make all pointing adjustments using reaction wheels and torque rods. Star trackers, sun sensors, a magnetometer, and gyroscopes will be the sensors used by the attitude control subsystem. The TDRSS (Tracking and Data Relay Satellite System) satellites will relay commands and data with ground stations.
The field of view is 47 arc minutes and it comes from a small telescope diameter (only 40 cm) and large detector arrays. The telescope has four infrared sensitive detector arrays, 1024×1024 pixels each. For the near-infrared bands, there are Mercury-Cadmium-Telluride (MCT) detectors, while for the mid-infrared bands, Arsenic-doped Silicon (Si:As) detectors are used.
Credits: UCLA/JPL
The optics instruments have to be cooled to very low temperatures in order to lower noise detection. The MCT detectors operate at 32 K, while the Si:As detectors will be cooled to less than 8 K.
The WISE launch is scheduled for November 2009. WISE will launch aboard a Delta II launch vehicle from Vandenberg Air Force Base, in California.
The WISE team consists of UCLA (University of California at Los Angeles), JPL (Jet Propulsion Laboratory), SDL (Space Dynamics Labs in Utah), BATC (Ball Aerospace & Technology Corporation), IPAC (Infrared Processing and Analysis Center), and UCB (University of California at Berkeley).
For more information about the WISE mission, you can visit the WISE mission homepage at the Space Science Laboratory, University of California, Berkeley, website.
STS-125 Space Shuttle Atlantis was the final Hubble Space Telescope servicing mission (SM4). The STS-125 crew consisted of Gregory C. Johnson, pilot; Scott D. Altman, commander; Michael J. Massimino, Michael T. Good, K. Megan McArthur, John M. Grunsfeld, and Andrew J. Feustel, all mission specialists.
STS-125 has some history behind it. In 2004, NASA head Sean O’Keefe cancelled the long-planned Hubble Space Telescope Servicing Mission 4, invoking new safety rules that were applied to space shuttle flights after the Columbia disaster. By June 2004, NASA was considering a robotic servicing mission, which was also cancelled due to prohibitive costs. A change in NASA policy came with the new head of NASA, Michael Griffin. The risks associated with the SM4 mission were reassessed, and by 2008 SM4 was back on track.
On May 11, 2009, STS-125 Space Shuttle Atlantis launched at 2:01 PM EDT. There were no obvious debris events during launch and after going through the post-launch checklist, the crew prepared the orbiter for in-orbit operations and conducted a survey of the payload bay and the crew cabin using the robotic arm.
On May 13, 2009, at 17:14 UTC, flight day #3, Hubble Space Telescope was grappled and by 18:12 UTC, the telescope was berthed in the payload bay of Atlantis.
There were a total of five EVAs performed by the STS-125 crew. During EVA#1 (John Grunsfeld/ Andrew Feustel), the Wide Field and Planetary Camera 2 (WFPC2) was replaced with the new Wide Field Camera 3 (WFC3), and the Science Instrument Command and Data Handling Unit were replaced. A Soft Capture Mechanism (SCM) was also installed on Hubble. SCM will be used to capture and de-orbit Hubble at the end of its operational life. EVA#2 (Michael Massimino/ Michael Good) replaced all three gyroscope rate sensing units (RSUs) and one of the battery unit modules. EVA#3 (John Grunsfeld/ Andrew Feustel) removed and replaced COSTAR with the Cosmic Origins Spectrograph, and replaced faulty electronics cards from the Advanced Camera for Surveys. EVA#4 (Michael Massimino/ Michael Good) removed and replaced electronics cards for the Space Telescope Imaging Spectrograph (STIS). EVA#5 (John Grunsfeld/ Andrew Feustel) replaced the second battery unit module, installed the Fine Guidance Sensor #3, replaced degraded insulation panels with New Outer Blanket Layer (NOBL)s, and also replaced a protective cover around Hubble’s low-gain antenna.
Hubble was released on May 19, 2009 (flight day #9). The telescope was lifted out of the orbiter’s payload bay using the robotic arm. After running through the release checklist, the STS-125 crew released Hubble at 12:57 UTC. The new equipment and the upgrades installed on Hubble will be tested for several months before resuming operation in early September.
Due to weather, which was less than favorable for landing, STS-125 had to delay the return to Earth for two days. The de-orbit burn was initiated on May 24, 2009, at 14:24 UTC.
STS-125 Space Shuttle Atlantis landed at Edwards Air Force Base in California, on Sunday May 24, 2009, at 11:39 AM EDT.
While the media has been busy with the launch of the STS-125 Atlantis for the Hubble Servicing Mission #4 from Cape Canaveral, another exciting launch is undergoing preparations further south, in Kourou, French Guiana.
Herschel and Planck are scheduled to launch on May 14, 2009. They will be stacked on the same Ariane 5 launch vehicle.
The two spacecraft will separate shortly after the launch (Herschel a couple of minutes before Planck) and will proceed independently to the L2 point of the Sun-Earth system. L2 is a point in space that has some special characteristics situated at 1.5 million kilometers from Earth in the opposite direction to the Sun. Herschel and Planck will operate from independent orbits around the L2 point.
Credits: ESA – D. Ducros, 2009
Stacked together, Herschel and Planck measure around 11 m in length, 4.5 m in diameter, and have a mass of approximately 5,700 kg. The piece that holds them together is called Sylda. Sylda is a support structure for Herschel and forms a protective cover for Planck.
The final orbit for Herschel will be a large, 900×500-thousand km, Lissajous orbit around the L2. There are three trajectory-correction maneuvers (TCM) planned for Herschel, during days L+1, L+2, and L+12. Planck will require a total of 5 TCMs that will enable it to operate from a 300×200-thousand km Lissajous orbit also around the L2 point.
The Lissajou orbits are inherently unstable, so both spacecraft will need regular thruster burns throughout their missions to stay on track.
“Without regular trajectory corrections, they would naturally drift off into a useless orbit about the Sun or Earth, with the rate of drift increasing with time,” says Gottlob Gienger, the senior flight dynamics advisor for the Herschel and Planck missions.
To read more about the launch of Herschel and Planck, you can visit the dedicated page on ESA’s website.
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