Solar Satellites

From Scholarpedia

This article has not been peer-reviewed or accepted for publication yet; It may be unfinished, contain inaccuracies, or unapproved changes.

Author: Dr. Brian Dennis, NASA/GSFC
Author: Dr. Ryan Milligan, NASA/GSFC

Dr. Brian Dennis accepted the invitation on 19 February 2008 (self-imposed deadline: 19 August 2008).

This article will briefly cover all solar-dedicated spacecraft plus others that carried solar instruments and made significant contributions to solar research.

First, we will generate a list of spacecraft to include and the names and capabilities of the instruments. Then we will review the main observations made by these instruments and their relevance to solar and heliospheric physics.

Contents

[edit]

Introduction


As pointed out by Sturrock (1979), it was not surprising that one of the first objects to be studied when space research commenced was the Sun. It is usually the brightest source in the sky at most electromagnetic wavelengths and its proximity to the Earth compared to all other astrophysical objects outside the solar system means that it can be studied in far greater detail. Also, considering the dominance of the Sun and its overwhelming importance for life on Earth, solar space observations have always had high priority. This is clear from the large number of spacecraft that have been dedicated to solar observations or which have carried some solar instrumentation. This great interest is, if anything, increasing as modern civilization relies more and more heavily on space-based technologies and their inherent vulnerabilities to the solar-controlled Space Weather. NASA is investing heavily in its Living With a Star program, and other nations are developing burgeoning space programs with significant solar objectives.

In preparing this article, it quickly became apparent that almost all spacecraft can be considered as solar satellites. All spacecraft must contend with the engineering consequences of the intense solar radiation in space, and even those not in Earth orbit can be considered as satellites in orbit about the Sun. The NSSDC Master Catalog (NMC) lists a total of 6404 spacecraft launched to date, an impossible number to review in this article. Even if we restrict ourselves to spacecraft identified in the NMC with Solar Physics, we still get 188 real spacecraft, starting with Sputnik 2 in 1957 and extending through STEREO A and B launched together in 2006. Space Physics has 632 spacecraft listed and Astronomy has 299. Certainly many of them have instruments making significant solar observations. We provide an edited version of the NMC list in Table 1 of spacecraft that have made or are making significant solar observations useful for research in solar physics.

For the purposes of this article, we have further restricted the number to those spacecraft whose primary objective was, or is, remote sensing of the Sun and those that, in the opinion of the authors, have made, or will make, observations of great significance to the development of solar physics. The list of past, present,and future missions selected is in the table of contents. A brief description is given of each selected mission with links to more detailed information. An attempt has also been made to summarize the major solar physics results from each mission, or at least provide links to published literature. A useful resource for finding publications of results from a given mission is the Aschwanden Solar Literature References Matrix.


After the first flights on captured V-2 rockets had paved the way with early observations in the far ultra-violet (UV) starting in 1946, NASA initiated the Orbiting Solar Observatory (OSO) series of dedicated unmanned solar satellites and undertook the first major manned solar mission from space called Skylab. Together, these early solar programs provided many outstanding observations in the UV, EUV, X-rays, and gamma-rays that provided the foundation of solar space science.

The biggest early manned program to study the Sun was Skylab with the Apollo Telescope Mount (ATM) as the main solar observatory. It operated from 1973 through 1979 and provided many outstanding observations made primarily during the three Shuttle flights when astronauts tended the instruments and returned the film used to record the images. The major results were presented in several reports from a series of workshops held to promote the study of these remarkable observations.

The OSO series obtained unprecedented UV and EUV imaging and spectroscopic observations together with X-ray, and gamma-ray spectroscopy. It eventually involved a total of eight spacecraft with OSO-1 launched in 1962 and OSO-8 launched in 1975 (OSO-C was not launched because of a failure during testing that damaged the spacecraft and resulted in the death of ? test engineers). The OSO spacecraft were given sequential letter names until launch (OSO-A through OSO-I) and then renamed with the next number in the sequence and referred to as OSO-1 through OSO-8. The first seven OSOs were built by Ball Brothers (later called Ball Aerospace) but Hughes Aircraft won the follow-on contract for OSO-I, J, and K. OSO-I became OSO-8 at launch on ? 197? but OSO-J and -K were combined together for budgetary reasons to become the Solar Maximum Mission (SMM), launched on a Delta rocket on 14 February, 1980. It operated successfully until November 1980, when the last of several fuses in the aspect control system failed and the spacecraft was no longer able to maintain the orientation towards the Sun with the arcsecond stability that was needed by the imaging instruments. The non-imaging instruments continued to operate as the spacecraft slowly spun about an axis pointed within a few degrees of Sun center. Then in April, 1984, in the first of many dramatic spacecraft rescue missions using the Space Shuttle, the aspect system was fixed by the astronauts, and SMM was able to provide 6 more years of excellent solar observations until it re-entered the Earth's atmosphere in December, 1989.

During this early period of solar space observations, the Russians also launched several spacecraft with instrumentation designed to look primarily at solar flares. Although less technically sophisticated than the NASA instrumentation, they still managed to make useful contributions to solar science.

The Japanese launched a highly innovative solar dedicated spacecraft called Hinotori in 1982 that was to rival SMM, especially in its hard X-ray imaging capability? It was the first mission to use modulation X-ray collimators on a spinning spacecraft to make X-ray images of solar flares using a Fourier-transform technique. This same technique was to be repeated almost 20 years later on NASA's High Energy Solar Spectroscopic Imager (HESSI) later renamed the Reuven Ramaty HESSI (RHESSI). The X-ray images made with Hinotori data at energies between ? and ? keV were the first to show clear evidence for footpoint brightening during impulsive flares.

[edit]

Timeline

Figure 1: caption goes here
Enlarge
Figure 1: caption goes here







Insert text here...






[edit]

Past Missions

[edit]

Skylab

Figure 2: Skylab
Enlarge
Figure 2: Skylab

The biggest early manned program to study the Sun was Skylab It operated from launch on 14 May 1973 through re-entry on 11 July 1979. A solar panel and part of its external shielding were was lost on launch, and the astronauts had to rig a "golden umbrella" to keep the temperature under control; this is visible in the picture.

Skylab carried many astrophysics instruments with eight separate solar instruments on the Apollo Telescope Mount (ATM). These are listed in Table 2. During its six years in orbit, Skylab provided many outstanding observations made primarily during the three Shuttle flights when astronauts tended the instruments and returned the film used to record the images. The major results were presented in several reports from a series of workshops held to promote the study of these remarkable observations.

[edit]

Orbiting Solar Observatories

Figure 3: OSO 8
Enlarge
Figure 3: OSO 8

Early in the space program, under the direction of John Lindsay, the head of the Solar Physics Branch at Goddard Space Flight Center, NASA initiated the Orbiting Solar Observatory (OSO) series of dedicated unmanned solar satellites. Eventually seven spacecraft were launched at the remarkable rate of about one per year, with the first launched in 196? and the last in 197? Together with Skylab, the solar instruments carried on these early spacecraft provided outstanding UV and EUV imaging and spectroscopic observations together with X-ray, and gamma-ray spectroscopy. The results of these pioneering observations still, to this day, provide the foundation of much of solar space science.

The OSO series eventually involved a total of seven spacecraft with OSO-1 launched in ? and OSO-8 launched in 197? (OSO-? was not launched because of a failure during testing that damaged the spacecraft and resulted in the death of ? test engineers). The spacecraft were initially given sequential letter names (OSO-A through OSO-I) and then renamed after launch with the next number in the sequence and became known as OSO-1 through OSO-8. The first seven OSOs were built by Ball Brothers (later called Ball Aerospace) but Hughes Aircraft won the follow-on contract for OSO-I, J, and K. OSO-I became OSO-8 at launch on ? 197? but OSO-J and -K were combined together for budgetary reasons to become the Solar Maximum Mission (SMM), launched on a Delta rocket on 14 February, 1980.

As shown in the figure, all the OSO spacecraft incorporated a "wheel" component spinning at up to 15 rpm to provide pointing stability, and a de-spun platform to carry the imaging instruments pointed at the Sun. This arrangement allowed for exquisite sub-arcsecond pointing accuracy and stability before the era of 3-axis stabilization techniques that are used today. Several other instruments that did not need to be constantly and precisely pointed at the Sun were mounted in the spinning "wheel" section. These included X-ray and gamma-ray spectrometers pointed perpendicular to the spin axis so that they scanned across the Sun each rotation, and similar instruments pointed parallel or near -parallel to the spin axis to view non-solar sources of astrophysical interest. Solar panels mounted on the de-spun platform provided the power, and slip-rings between the spinning and de-spun components were used for power and signal connections.

[edit]

Solar Maximum Mission (SMM)

Figure 4: SMM
Enlarge
Figure 4: SMM

In contrast with all of the OSO spacecraft, the Solar Maximum Mission was 3-axis stabilized so that all of the instruments were pointed at the Sun with arcsecond accuracy and stability. The payload was carefully selected to concentrate on obtaining observations that could further understanding of solar flares. These powerful phenomena had been revealed by earlier observations to be the most energetic explosions in the Solar System but the physical processes involved in the impulsive energy release and subsequent dissipation were largely unknown. To this end, imaging and spectroscopy was carried out at UV, EUV, and X-ray wavelengths to study the emission from plasma heated to temperatures as high as several tens of million Kelvin. The electrons accelerated during flares to suprathermal energies were detected through the bremsstrahlung X-rays that they produced. SMM included the first instrument capable of imaging these X-rays up to energies of 30 keV, well above the energies produced by all but the hottest plasma. The protons and heavier ions also accelerated during flares were detected through the nuclear gamma-rays that they generate as they interact in the solar atmosphere. SMM carried a sensitive gamma-ray spectrometer similar to the spectrometer that had made the first pioneering measurements of this high energy emission on OSO-7 back in 1972. Reviews of the scientific results from SMM can be found in the Springer publication, The Many Faces of the Sun : a summary of the results from NASA's Solar Maximum Mission by Strong et al. (1999).

SMM was launched on 14 February, 1980, on the rising phase of the 11-year cycle of activity. It operated successfully until November 1980, when the last of several fuses in the aspect control system failed and the spacecraft was no longer able to maintain the orientation towards the Sun with the arcsecond stability that was needed by the imaging instruments. The non-imaging instruments continued to operate as the spacecraft slowly spun about an axis pointed within a few degrees of Sun center. Then in April, 1984, in the first of many dramatic spacecraft rescue missions using the Space Shuttle, the aspect system was fixed by the astronauts, and SMM was able to provide 6 more years of excellent solar observations until it re-entered the Earth's atmosphere in December, 1989.

[edit]

Hinotori

Figure 5: Hinotori
Enlarge
Figure 5: Hinotori

The Japanese launched a highly innovative solar-dedicated spacecraft called Hinotori (meaning phoenix in Japanese) on 21 February 1981. It rivaled SMM, especially in its hard X-ray imaging capability. It was the first mission to use modulation X-ray collimators on a spinning spacecraft to make X-ray images of solar flares using a Fourier-transform technique. This same technique was to be repeated almost 20 years later on RHESSI. The X-ray images made with Hinotori data at energies between ? and ? keV were the first to show clear evidence for footpoint brightening during impulsive flares.








[edit]

Ulysses

Figure 6: Ulysses
Enlarge
Figure 6: Ulysses

The joint ESA-NASA Ulysses mission was launched in 1990 into a unique out-of-the-ecliptic orbit that goes over the Sun's poles every 6.2 years.

Figure 7: Ulysses Orbit
Enlarge
Figure 7: Ulysses Orbit

It is is the only mission capable of overcoming the limitations of all other measurements that are restricted to the vicinity of the ecliptic plane. Now on its third orbit about the Sun, Ulysses continues to provide new scientific results thanks to its different perspective.

Ulysses carries the following instruments:

  • Magnetometer (VHM/FGM)
  • Solar Wind Plasma Experiment (SWOOPS)
  • Solar Wind Ion Composition Instrument (SWICS)
  • Unified Radio and Plasma Wave Instrument (URAP)
  • Energetic Particle Instrument (EPAC)
  • Interstellar Neutral-Gas Experiment (GAS)
  • Low-Energy Ion and Electron Experiment (HISCALE)
  • Cosmic Ray and Solar Particle Instrument (COSPIN)
  • Solar X-ray and Cosmic Gamma-Ray Burst Instrument (GRB)
  • Dust Experiment (DUST)
  • Coronal-Sounding Experiment (SCE)
  • Gravitational Wave Experiment (GWE)
[edit]

Compton Gamma Ray Observatory (CGRO)

Figure 8: CGRO
Enlarge
Figure 8: CGRO

Although strictly speaking not a solar satellite, CGRO, the second of NASA's Great Observatories, made many important observations of solar flare X-rays and gamma-rays. Launched in April 1991 and re-entering the Earth's atmosphere in June 4 2000, CGRO covered almost a solar cycle with observations spanning an unprecedented six decades of the electromagnetic spectrum, from X-rays as low as 30 keV to gamma rays at 30 GeV.

The four instruments were as follows:

BATSE solar flare data are available at the Solar Data Analysis Center.

More recent Gamma-ray observations continue to be made with the even more sensitive ESA INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) in cooperation with Russia and the United States. The four instruments on INTEGRAL cover the energy range from 3kKeV to 10 MeV. Unfortunately, INTEGRAL cannot be pointed at the Sun, and so flare gamma-rays can only be detected through the thick anticoincidence shield around the high-resolution germanium detectors.

[edit]

Yohkoh (Sunbeam in Japanese)

Figure 9: Yohkoh
Enlarge
Figure 9: Yohkoh

Yohkoh, the second Japanese solar satellite with US and UK collaboration, was launched on August 30, 1991. All instruments operated successfully until an electrical failure ended the mission in 200? The four instruments were as follows:

Many scientific results from Yohkoh are summarized in the Nuggets.

[edit]

CORONAS

Figure 10: CORONAS
Enlarge
Figure 10: CORONAS

The Russian CORONAS project (Complex ORbital Observations Near-Earth of Activity of the Sun) was envisioned to include three missions to make observations during different phases of the 11-year solar cycle. The first mission in the series, CORONAS-I was launched on 2 March 1994 during solar minimum and re-entered on 4 March 2001. It carried a total of 12 science instruments including the Terek spectroheliometer, the RES-K solar x-ray spectrograph, the Helikon solar gamma-ray detector, the SUVR-SP-C ultraviolet radiometer, the DIFOS optical photometer, and other instruments. CORONAS-F was launched on 31 July 2001 near solar maximum and re-entered on 6 December 2005. It carried 15 instruments including UV, EUV, X-ray, and gamma-ray spectrometers, radio receivers, and particle counters.

The Coronas-F Instruments

  • DIFOS Multichannel Solar Photometer (IZMIRAN, GAO NANU, AIP)
  • SPIRIT Full Sun XUV spectroscopy imaging (FIAN, IAS, IAS)
  • SRT Solar X-Ray Telescope (FIAN, IAS)
  • RES X-Ray Spectroheliograph (FIAN, SAI)
  • DIOGENESS X-Ray Spectrometer and Fotometer (CBK PAN, IZMIRAN)
  • RESIK X-Ray Spectrometer (CBK PAN, IZMIRAN, MSSL, RAL, NRL)
  • SPR Solar Spectropolarimter (FIAN, NIIYaF)
  • IRIS Flare Spectrometer (FTI)
  • HELICON Gamma Spectrometer (FTI)
  • RPS X-Ray Spectrometer (IKI, MIFI)
  • AVS Time-Amplitude Spectrometer (MIFI, NIIYaF)
  • SUFR Solar UV Radiometer (IPG)
  • VUSS Solar UV Spectrophotometer (IPG)
  • SKL Solar Cosmic Rays Complex (NIIYaF, IEP)
  • MKL Cosmic Ray Monitor
  • SKI Spectrometer of Energy and Ion Chemical Composition
  • SONG Solar Neutron and Gamma Ray Spectrometer
  • PR-N: X-ray polarimeter


CORONAS-Photon is scheduled for launch in December 2008.

[edit]

Current Missions

[edit]

Geosynchronous Operational Environmental Satellites

Figure 11: GOES 8
Enlarge
Figure 11: GOES 8

The National Oceanic and Atmospheric Administration (NOAA) operates a series of meteorology observing satellites known as Geosynchronous Operational Environmental Satellites (GOES) which is a continuation of the Synchronous Meteorological Satellite (SMS) series. The GOES program formally began with the launch of the first operational spacecraft, GOES-A, in 1975, which was renamed GOES-1 when it reached orbit. The GOES spacecraft circle the Earth in a geosynchronous orbit, which means they orbit the equatorial plane of the Earth at a speed matching the Earth's rotation. This allows them to hover continuously over one position on the surface. The geosynchronous plane is about 35,800 km (22,300 miles) above the Earth.

As well providing systematic, continuous observations of terrestrial weather patterns, GOES also monitors space weather via its onboard Space Environment Monitor (SEM) system. The three main components of space weather monitored by GOES are: X-rays, energetic particles, and magnetic field. The initial series of satellites maintained attitude control by spinning. With the advent of GOES-8, launched in 1995, the basic platform design was changed to one called "3-axis stabilized." In 2001 GOES-12 was launched with a new X-ray instrument onboard -- the Solar X-ray Imager (SXI)**. This instrument creates images of the Sun, whereas the original XRS instrument only generated whole disk flux measurements.

X-ray Sensor (XRS) Ion chamber detectors provide whole-sun X-ray fluxes for the 0.5-to-4 and 1-to-8 Angstrom wavelength bands. These observations provide a sensitive means of detecting the start of solar flares. Two bands are measured to allow the hardness of the solar spectrum to be estimated.

Energetic Particle Sensor (EPS) Solid-state detectors with pulse-height discrimination measure proton, alpha-particle, and electron fluxes.

Magnetometer A twin-fluxgate spinning sensor allows Earth's magnetic field to be described by three mutually perpendicular components.

Soft X-ray Imager (SXI) [GOES-12 and 13 only] SXI was designed to obtain a continuous sequence of coronal X-ray images at a 1-minute cadence with a 512x512 intensified CCD. Broadband filters are employed to obtain images at several wavelength bands between about 6 and 60 Å.

Launch DateStatus
GOES-1 (A)October 16, 1975Decommissioned
GOES-2 (B)June 16, 1977Decommissioned
GOES-3 (C)June 16, 1978Decommissioned
GOES-4 (D)September 9, 1980Decommissioned
GOES-5 (E)May 22, 1981Decommissioned
GOES-6 (F)April 28, 1983Decommissioned
GOES-GMay 3, 1986Failed*
GOES-7 (H)February 26, 1987Decommissioned
GOES-8 (I)April 13, 1994Decommissioned
GOES-9 (J)May 23, 1995Decommissioned
GOES-10 (K)April 25, 1997In Operation
GOES-11 (L)May 3, 2000In Operation
GOES-12 (M)July 23, 2001In Operation**
GOES-13 (N)May 24, 2006In Orbit Storage***
GOES-ONovember 5, 2008
GOES-P2012?

* GOES-G failed to make it into orbit when its Delta rocket lost control after being struck by lightening shortly after liftoff.

**The SXI instrument is out of commission indefinitely due to a GOES 12 X-ray Sensor (XRS) anomaly on April 12, 2007.

***No GOES 13 SXI images available since December 2006 due to a detector anomaly that occurred in conjunction with an X-class flare.

[edit]

Solar and Heliospheric Observatory

Figure 12: The SOHO spacecraft
Enlarge
Figure 12: The SOHO spacecraft

SOHO, the Solar & Heliospheric Observatory, is a project of international collaboration between ESA and NASA to study the Sun from its deep core to the outer corona and the solar wind and was launched on December 2, 1995. SOHO moves around the Sun in step with the Earth, by slowly orbiting around the First Lagrangian Point (L1), where the combined gravity of the Earth and Sun keep SOHO in an orbit locked to the Earth-Sun line, approximately 1.5 million kilometers from Earth.

SOHO was designed for a nominal mission lifetime of two years. In 1997 the mission was extended until 2003 because of its spectacular success. In 2002, a second extension of another four years was granted, that is, through March 2007. This will allow SOHO to cover a complete 11-year solar cycle.

Control of the spacecraft was lost in June 1998, and only restored three months later through efforts of the SOHO recovery team. All 12 instruments were still us-able, most with no ill effects. Two of the three on-board gyroscopes failed immediately and a third in December 1998. After that, new on-board software that no longer relies on gyroscopes was installed in February 1999.

SOHO comprises a suite of 12 instruments:

Coronal Diagnostic Spectrometer (CDS) CDS detects emission lines from ions and atoms in the solar corona and transition region, providing diagnostic information on the solar atmosphere, especially of the plasma in the temperature range from 10 000 to more than 1 000 000°C.

Charge, Element, and Isotope Analysis System (CELIAS) CELIAS continuously samples the solar wind and energetic ions of solar, interplanetary and interstellar origin, as they sweep past SOHO. It analyses the density and composition of particles present in this solar wind. It warns of incoming solar storms that could damage satellites in Earth orbit.

Comprehensive Suprathermal and Energetic Particle Analyzer (COSTEP) The COSTEP instrument detects and classifies very energetic particle populations of solar, interplanetary, and galactic origin. It is a complementary instrument to ERNE (for more information, see below).

Extreme ultraviolet Imaging Telescope (EIT) EIT provides full disc images of the Sun at four selected colours in the extreme ultraviolet, mapping the plasma in the low corona and transition region at temperatures between 80 000 and 2 500 000°C.

Energetic and Relativistic Nuclei and Electron experiment (ERNE) ERNE measures high-energy particles originating from the Sun and the Milky Way. It is a complementary instrument to COSTEP.

Global Oscillations at Low Frequencies (GOLF) GOLF studies the internal structure of the Sun by measuring velocity oscillations over the entire solar disc.

Large Angle and Spectrometric Coronograph (LASCO) LASCO observes the outer solar atmosphere (corona) from near the solar limb to a distance of 21 million kilometres, that is, about one seventh of the distance between the Sun and the Earth. LASCO blocks direct light from the surface of the Sun with an occulter, creating an artificial eclipse, 24 hours a day, 7 days a week. LASCO has also become SOHO’s principal comet finder.

Michelson Doppler Imager/Solar Oscillations Investigation (MDI/SOI) MDI records the vertical motion (“tides”) of the Sun's surface at a million different points for each minute. By measuring the acoustic waves inside the Sun as they perturb the photosphere, scientists can study the structure and dynamics of the Sun’s interior. MDI also measures the longitudinal component of the Sun’s magnetic field.

Solar Ultraviolet Measurements of Emitted Radiation (SUMER) The SUMER instrument is used to perform detailed spectroscopic plasma diagnostics (flows, temperature, density, and dynamics) of the solar atmosphere, from the chromosphere through the transition region to the inner corona, over a temperature range from 10 000 to 2 000 000°C and above.

Solar Wind Anisotropies (SWAN) SWAN is the only remote sensing instrument on SOHO that does not look at the Sun. It watches the rest of the sky, measuring hydrogen that is ‘blowing’ into the Solar System from interstellar space. By studying the interaction between the solar wind and this hydrogen gas, SWAN determines how the solar wind is distributed. As such, it can be qualified as SOHO’s solar wind ’mapper’.

UltraViolet Coronograph Spectrometer (UVCS) UVCS makes measurements in ultraviolet light of the solar corona (between about 1.3 and 12 solar radii from the centre) by creating an artificial solar eclipse. It blocks the bright light from the solar disc and allows observation of the less intense emission from the extended corona. UVCS provides valuable information about the microscopic and macroscopic behaviour of the highly ionised coronal plasma.

Variability of Solar Irradiance and Gravity Oscillations (VIRGO) VIRGO characterises solar intensity oscillations and measures the total solar irradiance (known as the ‘solar constant’) to quantify its variability over periods of days to the duration of the mission.


[edit]

Transition Region And Coronal Explorer

Figure 13: The TRACE spacecraft
Enlarge
Figure 13: The TRACE spacecraft

TRACE, the Transition Region and Coronal Explorer, is the first US led solar research satellite since the Solar Maximum Mission and the first transition region and coronal satellite to observe the Sun during the rise to solar maximum. TRACE was launched on April 2, 1998 and was scheduled to allow joint observations with the Solar and Heliospheric Observatory (SOHO). Using TRACE, solar physicists are able to observe the solar surface (photosphere), through the transition region and into the corona. They are able to make these observations with a delay of a few seconds per image between the various wavelengths and with one arcsecond spatial resolution, corresponding to about 725 kilometers at the Earth-Sun distance. TRACE explores the connections between the different layers of the solar atmosphere, tracing the magnetic field from the photosphere, where it is buffeted by flows, into the corona, where it shapes and channels the plasma. A 1024 x 1024 CCD detector collects images over an 8.5 x 8.5 arcminute field-of-view.

TRACE Passbands
Wavelength (A) Width (A) Observed Temp (1000K)
5000broadcontinuum4-6.4
1700200continuum4-10
1600275C I, FE II, cnt4-10
155020C IV60-250
121684H I Ly-a10-30
1736.4Fe IX160-2000
1956.5Fe XII500-2000
28410.7Fe XV1250-4000


[edit]

Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI)

Figure 14: RHESSI
Enlarge
Figure 14: RHESSI

RHESSI is a NASA Small Explorer (SMEX) launched on 5 February 2002 to study solar flares through X-ray and gamma-ray imaging spectroscopy observations (Lin et al. 2002). RHESSI's primary mission is to explore the basic physics of particle acceleration and explosive energy release in solar flares. Based on previous observations, scientists believe that much of the energy released during a flare is used to accelerate, to very high energies, electrons (emitting primarily X-rays) and protons and other ions (emitting primarily gamma rays). The new approach of the RHESSI mission is to combine, for the first time, high-resolution imaging in hard X-rays and gamma rays with high-resolution spectroscopy, so that a detailed energy spectrum of the radiation can be obtained at each point of the image.

The RHESSI mission consists of a spin-stabilized spacecraft in a low-altitude orbit inclined at 38 degrees to the Earth's equator. The only instrument on board is an imaging spectrometer that allows high fidelity color movies to be made of solar flares in X-rays and gamma-rays between 3 keV and 17 MeV. This advanced capability is achieved by combining two complementary technologies -

  • Fourier-transform imaging (Hurford et al. 2002) using the spacecraft rotation at ~15 rpm and pairs of fine tungsten grids to modulate the solar X-ray and gamma-ray flux, and
  • High-resolution spectroscopy using cooled germanium detectors (Smith et al. 2002) to very precisely measure the energy of each photon that passes through the grids.

RHESSI has been operating successfully since launch and now has over 40,000 events listed in its flare catalog. Over 11,000 flares have been identified with detectable emission above 12 keV, ~950 above 25 keV, and 30 above 300 keV, with 18 showing gamma-ray line emission. A summary of the recent scientific results is given in the 2008 NASA Senior Review proposal. Further details an be found in the over 700 RHESSI-related publications listed in the Aschwanden Solar Literature Reference Matrix.

Following the NASA Senior Review recommendations, RHESSI has been approved for continuing operations for another two years. The germanium detectors were successfully annealed in November 2007 to remove the effects of radiation damage, thus restoring the detector energy resolutions and sensitive volumes to usable levels. Further anneals are planned as needed to maintain acceptable detector performance. Since the mission was designed with no expendables and the orbit decay has been minimal, RHESSI should be able to operate for years to come. Thus, RHESSI is ready for the rise from solar minimum to the expected maximum of the next activity cycle in 2009-2012.

References

  • Hurford, G. J., et al., 2002, The RHESSI Imaging Concept, Sol. Phys., 210, 61-86.
  • Lin, R. P., et al., 2002, The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI), Sol. Phys., 210, 3-32.
  • Smith, D. M., et al., 2002, The RHESSI Spectrometer, Sol. Phys., 210, 33-60.
[edit]

Solar Radition and Climate Experiment

Figure 15: SORCE
Enlarge
Figure 15: SORCE

The Solar Radiation and Climate Experiment (SORCE) is a NASA-sponsored satellite mission that provides measurements of incoming x-ray, ultraviolet, visible, near-infrared, and total solar radiation. The measurements provided by SORCE specifically address long-term climate change, natural variability and enhanced climate prediction, and atmospheric ozone and UV-B radiation. These measurements are critical to studies of the Sun, its effect on our Earth system and its influence on humankind. The SORCE spacecraft was launched on January 25, 2003 on a Pegasus XL launch vehicle to provide NASA's Earth Science Enterprise (ESE) with precise measurements of solar radiation. It launched into a 645 km, 40 degree orbit and is operated by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado (CU) in Boulder, Colorado, USA.

SORCE carries four intstuments:

Spectral Irradiance Monitor (SIM) SIM is a newly designed spectrometer that provides the first long-duration solar spectral irradiance measurements in the visible and near infrared (Vis/NIR). The wavelength coverage is primarily from 300 to 2400 nm, with an additional channel to cover the 200-300 nm ultraviolet spectral region to overlap with the SOLSTICE instrument.

SOLar STellar Irradiance Comparison Experiment (SOLSTICE) SOLSTICE makes daily solar ultraviolet (115-320 nm) irradiance measurements and compares them to the irradiance from an ensemble of 18 stable early-type stars. This approach provides an accurate monitor of instrument in-flight performance and provides a basis for solar-stellar irradiance comparison for future generations.

Total Irradiance Monitor (TIM) TIM measures the total solar irradiance (TSI), the integrated solar radiation incident at the top of the Earth's atmosphere. The TIM continues this climate record, which began in 1978 and is used to determine the sensitivity of the Earth's climate to the natural effects of solar forcing.

XUV Photometer System (XPS) XPS, which evolved from earlier versions flown on SNOE and TIMED, continue on these solar XUV irradiance measurements with improvements to accuracy, spectral image, and temporal change.


[edit]

Hinode

Figure 16: Hinode
Enlarge
Figure 16: Hinode

The Hinode mission (formerly known as Solar-B) is a follow-up to the highly successful Japan/US/UK Yohkoh (Solar-A) satellite, which operated between 1991 and 2001. Led by the Japanese Aerospace Exploration Agency's (JAXA) Space Science Research Division (formerly the Institute of Space and Astronautical Science (ISAS)), Hinode consists of a coordinated set of optical, EUV, and X-ray instruments that investigates the interaction between the Sun's magnetic field and its corona. Following the JAXA tradition, the mission was christened after the spacecraft’s first successful orbit – Hinode means sunrise in Japanese. Hinode was launched from Japan's Uchinoura Space Center on Friday, September 22 into a sun‑synchronous orbit at an altitude of about 600 km which means that it can observe the Sun continuously for nine months at a time. Around the summer (northern hemisphere) solstice each year, Hinode will experience an "eclipse season" during which the Sun will be eclipsed by Earth for a maximum of ten minutes in each 98 minute orbit. The first eclipse season is predicted to be May - July, 2007. During eclipse, the Solar Optical Telescope (SOT) will most probably be shut down because of thermal changes in the mirror. The set of three complementary instruments work together as a highly innovative solar observatory to explore the magnetic fields of the Sun, resulting in an improved understanding of the mechanisms that power the solar atmosphere and drive solar eruptions.

Solar Optical Telescope/Focal Plane Package (SOT/FPP) SOT is the first large optical telescope flown in space. Its aperture is 50cm and angular resolution achieved is 0.25" (175km on the Sun) covering a wavelength range of 480-650nm. SOT also includes the Focal Plane Package (FPP) vector magnetograph and spectrograph. The vector magnetograph will provide time series of photospheric vector magnetograms, Doppler velocity and photospheric intensity.

Extreme-ultraviolet Imaging Telescope (EIS) EIS is a two-channel, normal-incidence EUV spectrometer. Its two channels cover the ranges 170-210 Å and 250-290 Å, and are designed to observe solar coronal emission lines. It has a mirror which is tiltable in the Solar X direction, and is used to build up rastered spectral images of the Sun in up to 25 spectral ranges. Additionally, EIS has both narrow (one- and two-arcsecond wide) slits, and wider (40- and 266-arcsecond) imaging slots, all with 512 arcseconds in the cross-dispersion (Solar Y) direction. Under nominal conditions, the 40-arcsecond slot can be used to make simultaneous, separated, quasi-monochromatic images in up to twelve strong emission lines covering a temperature range from He II (log T 4.9) to Fe XXIV (log T 7.2). EIS is should be able to make slit images of active regions in 10 seconds, of quiet Sun in between 30 and 60 seconds, and of flares in approximately one second.

X-Ray Telescope (XRT) XRT is a high-resolution grazing-incidence telescope, which is a successor to the highly successful Yohkoh Soft X-Ray Telescope (SXT). High-resolution soft X-ray images reveal magnetic field configuration and its evolution, allowing the observation of energy buildup, storage and release process in the corona for any transient event. One of the unique features of XRT is its wide temperature coverage to see all the coronal features that are not seen with any normal incidence telescope.

[edit]

Solar Terrestrial Relations Observatory

Figure 17: STEREO A and B
Enlarge
Figure 17: STEREO A and B

STEREO (Solar TErrestrial RElations Observatory) is the third mission in NASA's Solar Terrestrial Probes program (STP). It is designed to view the three-dimensional (3D) and temporally varying heliosphere by means of an unprecedented combination of imaging and in situ experiments mounted on virtually identical spacecraft flanking the Earth in its orbit. This two-year mission will employ two nearly identical space-based observatories - one ahead of Earth, the other trailing behind - to provide the first-ever stereoscopic measurements to study the Sun and the nature of its coronal mass ejections (CMEs). The primary goal of the STEREO mission is to advance the understanding of the three-dimensional structure of the Sun's corona, especially regarding the origin of CMEs, their evolution in the interplanetary medium, and the dynamic coupling between CMEs and the Earth environment. The two near-identical spacecraft were launched together on a Delta II rocket from Cape Canaveral on October 25, 2006 and used a gravity assist from the moon to slingshot the spacecraft into a heliocentric orbit. The first to enter heliocentric orbit was the Ahead (STEREO-A) spacecraft and then two weeks later the Behind (STEREO-B) spacecraft. The two spacecraft drift away from Earth at an average rate of about 22.5 degrees per year. After the two year nominal operations phase the spacecraft will be about 90 degrees apart, each about 45 degrees from Earth. STEREO-A will drift ahead of Earth and STEREO-B behind. In order to accomplish this drift, STEREO-A will be traveling faster than Earth around the Sun and so must have an orbit slightly closer to the Sun than Earth's. Similarly, the STEREO-B must be traveling slower than Earth and must have an orbit slightly further than Earth. The spacecraft bus consists of six operational subsystems supporting two instruments and two instrument suites providing a total of 16 instruments per observatory.

Sun-Earth Connection and Coronal and Heliospheric Investigation (SECCHI) SECCHI is a suite of 5 scientific telescopes (EUVI, COR1, COR2, HI1 and HI2) that will observe the solar corona and inner heliosphere from the surface of the Sun to the orbit of Earth. SECCHI is named after one of the first astrophysicists, Angelo Pietro Secchi (1818-1878). Angelo Secchi was a Jesuit priest and was one of the first astrophysicists to use the new medium of photography to record solar eclipses. He photographed the 1860 eclipse, during which a CME is now thought to have occurred.

Coronagraphs COR1 and COR2 observe the inner (1.4-4. R_Sun) and outer (2-15 R_Sun) corona with greater frequency and polarization precision than ever before. COR1 will be the first space borne instrument to explore the inner corona in white light and pB down to 1.4 R_Sun. COR2 will image the corona with five times the spatial resolution and three times the temporal resolution of LASCO/C3.

Extreme Ultraviolet Imager (EUVI) provides full Sun coverage with twice the spatial resolution and dramatically improved cadence over SOHO/EIT. EUVI observes the photospheric magnetic field, chromosphere, and innermost corona underlying the same portions of the corona and the heliosphere observed by COR1, COR2, and HI.

Heliospheric Imager (HI) is the most novel instrument. It extends the concept of traditional externally occulted coronagraphs to a new regime, the heliosphere from the Sun to the Earth (12-318 R_Sun). HI has obtained the first direct imaging observations of coronal mass ejections in interplanetary space.

The Guide Telescope acts as a fine sun sensor for the EUVI and provides the error signal for the EUVI fine pointing system.

STEREO WAVE (SWAVES) SWAVES is an interplanetary radio burst tracker that traces the generation and evolution of traveling radio disturbances from the Sun to the orbit of Earth.

In-situ Measurements of Particles and CME Transients (IMPACT) IMPACT samples the 3-D distribution and provide plasma characteristics of solar energetic particles and the local vector magnetic field. IMPACT is a suite of seven instruments, three of which are located on a 6-meter deployable boom, with the others located on the main body of the spacecraft. The boom suite includes:

Solar Wind Experiment (SWEA) measures ~0.2 to 1 keV electrons with wide angle coverage.

Suprathermal Electron Telescope (STE) measures electrons from 5 to 100 keV with wide angle coverage.

Magnetometer Experiment (MAG) measures the vector magnetic fields in the range of ± 512 nT range with 0.1 nT accuracy.

The Solar Energetic Particle (SEP) suite in the main body includes:

Suprathermal Ion Telescope (SIT)

Solar Electron and Proton Telescope (SEPT)

Low Energy Telescope (LET)

High Energy Telescope (HET)

Plasma and Supra Thermal Ion and Composition (PLASTIC) PLASTIC provides plasma characteristics of protons, alpha particles and heavy ions. This experiment provides key diagnostic measurements of the form of mass and charge state composition of heavy ions and characterize the CME plasma from ambient coronal plasma. PLASTIC incorporates three science sensor functions into one package:

Solar Wind Sector (SWS) Proton Channel measures the distribution functions of solar wind protons and alphas, providing proton density, velocity, kinetic temperature and its anisotropy, and alpha to proton ratios with a time resolution up to about 1 minute.

Solar Wind Sector (SWS) Main (Composition) Channel measures the elemental composition, charge state distribution, kinetic temperature, and speed of the more abundant solar wind heavy ions (e.g., C, O, Mg, Si, and Fe) by using Electrostatic Analyzer (E/Q), Time-of-Flight (TOF), and Energy (E) measurement to determine Mass and M/Q. Typical time resolution for selected ions will be ~ 5 minutes.

Wide-Angle Partition (WAP) measures distribution functions of suprathermal ions, including inter-planetary shock-accelerated (IPS) particles associated with CME-related SEP events, recurrent particle events associated with Co-rotating Interaction Regions (CIRs), and heliospheric pickup ions. Typical time resolution for selected ions will be several minutes to hours.

[edit]

Future Missions

[edit]

Solar Dynamics Observatory

Figure 18: SDO
Enlarge
Figure 18: SDO

The Solar Dynamics Observatory will be the first mission to be launched for NASA's Living With a Star (LWS) Program, a program designed to understand the causes of solar variability and its impacts on Earth. SDO is designed to help understand the Sun's influence on Earth and Near-Earth space by studying the solar atmosphere on small scales of space and time and in many wavelengths simultaneously. SDO is a sun-pointing semi-autonomous spacecraft that will allow nearly continuous observations of the Sun with a continuous science data downlink rate of 130 Megabits per second. SDO's inclined geosynchronous orbit was chosen to allow continuous observations of the Sun and enable its exceptionally high data rate through the use of a single dedicated ground station. It is due to be launched in December 2008.

SDO will fly three scientific experiments:

Atmospheric Imaging Assembly (AIA) The Atmospheric Imaging Assembly will image the solar atmosphere in multiple wavelengths to link changes in the surface to interior changes. Data will include images of the Sun in 10 wavelengths every 10 seconds.

EUV Variability Experiment (EVE) The Extreme Ultraviolet Variablity Experiment will measure the solar EUV irradiance with unprecedented spectral resolution, temporal cadence, and precision. Measures the solar extreme ultraviolet spectral irradiance to understand variations on the timescales which influence Earth's climate and near-Earth space.

Helioseismic and Magnetic Imager (HMI) The Helioseismic and Magnetic Imager will extend the capabilities of the SOHO/MDI instrument with continuous full-disk coverage at higher spatial resolution.


[edit]

CORONAS-Photon

Figure 19: Coronas Photon
Enlarge
Figure 19: Coronas Photon

"CORONAS-PHOTON" is the third satellite in the CORONAS series and is scheduled for launch in December 2008. The main scientific goals of the project are as follows:

  • Investigate the energy accumulation and its transformation into energy of accelerated particles during solar flares.
  • Study the acceleration mechanisms, propagation and interaction of fast particles in the solar atmosphere.
  • Study the solar activity correlation with physical-chemical processes in the Earth's upper atmosphere.

The comprehensive instrument payload includes many UV, EUV, X-ray, gamma-ray, and cosmic ray instruments for a total payload weight of 540 kg.

[edit]

Solar Probe

Figure 20: Solar Probe
Enlarge
Figure 20: Solar Probe

Solar Probe will be a historic mission, flying into one of the last unexplored regions of the solar system, the Sun’s atmosphere or corona, for the first time. Approaching as close as 10 solar radii above the Sun’s surface, Solar Probe will employ a combination of in-situ measurements and imaging to understand how the Sun’s corona is heated and how the solar wind is accelerated. The closest ever approach previously made to the Sun, 0.31 AU (67 solar radii), by the Helios spacecraft in the 1970s. Solar Probe is currently scheduled for launch in 2015.

The baseline Solar Probe is a 3-axis stabilized spacecraft designed to survive and operate successfully in the intense thermal environment that it will encounter during its voyage around the Sun. The spacecraft’s most prominent feature is the Thermal Protection System (TPS), comprising a large 2.7-m diameter carbon–carbon conical primary shield with a low-conductivity, low-density secondary shield attached to its base. The TPS protects the spacecraft bus and instruments within its umbra during the solar encounter.

The in-situ instrument suite includes a Fast Ion Analyzer (FIA), two Fast Electron Analyzers (FEAs), an Ion Composition Analyzer (ICA), an Energetic Particle Instrument (EPI), a Magnetometer (MAG), a Plasma Wave Instrument (PWI), a Neutron/Gamma-ray Spectrometer (NGS), and a Coronal Dust Detector (CD).

[edit]

Solar Orbiter

Figure 21: Solar Orbiter
Enlarge
Figure 21: Solar Orbiter

By approaching as close as 48 solar radii, the Solar Orbiter will view the solar atmosphere with unprecedented spatial resolution. Over extended periods the Solar Orbiter will deliver images and data of the polar regions and the side of the Sun not visible from Earth. Following launch, Solar Orbiter will begin its journey to the Sun which will require a cruise phase lasting approximately 3.4 years. During this time, the spacecraft will use gravity assists from Venus and the Earth. This puts Solar Orbiter into a 150-day-long orbit from which it can begin its scientific mission.

Solar Orbiter is a specially designed three-axis stabilised spacecraft. It is designed to always point its smallest face to the Sun so the spacecraft is protected by a sunshield. At closest approach to the Sun, Solar Orbiter will receive 25 times the radiation per square metre that the Earth does. The spacecraft will also be kept cool by the positioning of special 'radiators', which will dissipate excess heat into space.

All Solar Orbiter's science instruments are currently in the concept phase. They will however be divided into three packages:

Field Package: 
Radio and Plasma Wave Analyser and Magnetometer.

Particle Package: 
Energetic Particle Detector, Dust Detector and Solar Wind Plasma Analyser.

Solar remote sensing instrumentation:
 Visible-light Imager and Magnetograph, EUV Imager and Spectrometer, EUV Imager, Coronagraph, and Spectrometer/Telescope for Imaging X-rays, as well as either a Generic Heliospheric Imager or a Wide Angle Coronograph.

The payload will be commissioned during the cruise phase and already be able to provide good science data. Upon entering the science orbit, closer encounters to the Sun will be achieved. Subsequent Venus gravity assist manouvres will increase the inclination providing a better view of the Sun's polar regions.

[edit]

Solar Sentinels

Figure 22: Solar Sentinels
Enlarge
Figure 22: Solar Sentinels









Insert text here...




[edit]

Bibliography


[edit]

Recommended reading

  • Sturrock, P. (1980) Solar flares: A monograph from SKYLAB Solar Workshop II. Colorado Associated University Press
  • Strong, Keith T.; Saba, Julia L. R.; Haisch, Bernhard M.; Schmelz, Joan T. (1999) The many faces of the sun : a summary of the results from NASA's Solar Maximum Mission. Springer
  • Aschwanden, M. (2005) Physics of the Solar Corona. Springer
[edit]

External links


Brian Dennis website

Ryan Milligan website


[edit]

See also

Solar telescopes, Cosmic X-ray sources, Solar flare simulations, Solar activity

Invited by: Dr. Søren Bertil F. Dorch, The Niels Bohr Institute and the Royal Library, Copenhagen, Denmark
Retrieved from "http://www.scholarpedia.org/article/Solar_Satellites"
For authors