ERBS (Earth Radiation Budget Satellite)
ERBS is a pioneering Earth radiation budget satellite mission within NASA's ERBE (Earth Radiation Budget Experiment) Research Program - a three-satellite mission, designed to investigate how energy from the sun is absorbed and re-emitted by the Earth. The ERBE payload, three identical sets of two instruments each, represent a new generation radiometer of NASA/LaRC, first flown on ERBS (launch Oct. 5, 1984), then on NOAA-9 (launch Dec. 12, 1984), and on NOAA-10 (launch Sept. 17, 1986).
Objective: Measurement of reflected and emitted energy at various spatial levels (this process of absorption and re-radiation is one of the principal drivers of the Earth's weather patterns). The observations provided useful data for studies of geographical-seasonal variations of the Earth's radiation budget. In fact, the data of ERBS/ERBE were compared and combined with those ERBE data collected on the NOAA-9 and -10 spacecraft.
ERBS is a three-axis momentum-biased spacecraft (1º pointing using magnetic torquers and a hydrazine backup system) built for NASA/GSFC by Ball Aerospace Systems of Boulder, CO. The ERBS spacecraft structure is composed of three basic modules: the keel module, the base module, and the instrument module. The keel module is a torque-box structure providing structural support for the propulsion system, the solar array panels, and the antennas. The base module provided a direct interface to the Shuttle.
Figure 1: Line drawing of the ERBS spacecraft (image credit: Friedrich Porsch, DLR)
ERBS subsystems included TCS (Thermal Control Subsystem), EPS (Electrical Power Subsystem) which consisted of two 50 Ah, 22 cell NiCd batteries; PCU (Power Unit) for regulating electrical power; C&DH (Command and Data Handling Subsystem) for collection of instrument and S/C data for real-time transmission; CS (Communications Subsystem), which included NASA TDRSS transponders and antennas; ADCS (Attitude Determination and Control Subsystem), a three-axis, momentum system for attitude pointing, maneuvers, and thruster control; and OAPS (Orbit Adjust Propulsion System), a hydrazine propulsion system used for raising ERBS to its operating orbit after launch from the Shuttle.
ERBS was held primarily in the Earth-pointing mode for most of the mission. S/C size: 4.6 m x 3.5 m x 1.5 m. S/C mass = 2307 kg, nominal power = 470 W. Design life of 2 years with a goal of 3 years. 1) 2) 3) 4)
Figure 2: Functional diagram of the ADCS (image credit: NASA)
Figure 3: Functional block diagram of the C&DH subsystem (image credit: NASA)
Figure 4: Block diagram of the electric power subsystem (image credit: NASA)
Launch: The launch of the free-flyer ERBS satellite took place on Oct. 5, 1984 on Space Shuttle flight STS-41G from KSC (Kennedy Space Center), FLA. The ERBS spacecraft was deployed from Space Shuttle Challenger on October 5, 1984 (first day of flight) using the Canadian-built RMS (Remote Manipulator System), a mechanical arm of about 16 m in length. On deployment, one of the solar panels of ERBS failed initially to extend properly. Hence, mission specialist Sally Ride had to shake the satellite with the remotely-controlled robotic arm and then finally place the stuck panel into sunlight for the panel to extend.
The ERBS satellite was in fact the first spacecraft to be launched and deployed by a Space Shuttle mission.
Orbit: Non-sun-synchronous circular orbit, nominal altitude = 610 km, inclination = 57º, period = 96.8 min. Hence, ERBE coverage on ERBS is restricted to ±57º latitude (with regard to reflection and emitted measurements from Earth). - Note: The orbit of ERBS has slowly dropped to an altitude of 585 km over a period of 15 years (1999).
Figure 5: Time series of ERBS altitude (km) from 1985 to 2000 (image credit: NASA) 5)
RF communications: Downlink data rate at 128 kbit/s, uplink via TDRSS using an electrically steerable spherical array antenna (ESSA). The ERBS mission is being controlled and operated at NASA/GSFC; the ERBS data is being processed, archived and distributed at NASA/LaRC.
Figure 6: Artist's view of the deployed ERBS spacecraft in orbit (image credit: NASA)
• SAGE-II, built by the Ball Aerospace Systems Group, added 18 years to the original mission life of twenty-four months on ERBS and continues to give scientists a wealth of data on the chemistry and motions of the upper troposphere and stratosphere. 9)
• Of the ERBE instrument package only the nonscanner portion was still functioning (the scanner portion failed Feb. 28, 1990).
• The ERBE nonscanner instrument is operational at all times, except during spacecraft yaw maneuvers. At these times the ERBE nonscanner instrument is powered off to conserve spacecraft battery power. The yaw maneuvers take place approximately every 36 days to align the spacecraft solar panels with the sun.
• As of June 2001 the ERBS S/C was operational on only one battery. Thereafter, Ball Aerospace engineers were able to adjust the previously decommissioned NiCd battery and bring it back to service.
• ERBE is no longer capable of movement to the internal calibration position.
• The ERBE nonscanner unit is a real value, since it outlived it's design lifetime of 3 years by a factor of 5! Although the ERBS spacecraft would probably function beyond 2010, de-orbit plans were being developed for 2003. 10)
• In July-August 2003 a series of de-orbiting ΔV maneuvers were performed on the ERBS satellite in preparation for decommissioning. However, the decommissioning was halted, and the de-orbiting maneuvers ended on August 15, 2003, with the satellite in an orbit of 507 km x 559 km. Current NASA plans call for ERBS operations until the summer of 2005. 11)
• In particular, the ERBE observations have helped scientists world-wide to better understand how clouds and aerosols, as well as some chemical compounds in the atmosphere (so-called ”greenhouse” gases), affect the Earth's daily and long-term weather (the Earth's ”climate”). In addition, the ERBE data has helped scientists to better understand something as simple as how the amount of energy emitted by the Earth varies from day to night. These diurnal changes are also very important aspects of our daily weather and climate.
Sensor complement: (ERBE, SAGE-II)
Background: Although first measurements of Earth's radiation budget were gathered with the ERB (Earth Radiation Budget) instrument flown on NASA's Nimbus-6 and -7 spacecraft (launch June 12, 1975, launch Oct. 24, 1978, respectively) - however, the ERBE instruments were able to provide more accurate and systematic parameters for estimating the Earth's radiation budget.
Note: The analysis of the ERB data on Nimbus-6 failed to detect any irradiance variability due to degraded responses of the ERB radiometer. An improved version of ERB was subsequently flown on Nimbus-7. The TSI (Total Solar Irradiance) broadband data from ERB on Nimbus-7 are available for the period Oct. 1978 until the end of 1993. This radiometer (on Nimbus-7) was stable enough to detect short-term and long-term solar irradiance variability. ERB on Nimbus-7 was the first long term solar monitor utilizing the ESCC (Electrically Self Calibrating Cavity) technique.
ERBE (Earth Radiation Budget Experiment):
ERBE is a multimission instrument package of NASA/LaRC (PI: B. R. Barkstrom) with the objective to measure the Earth's radiation budget [i.e., the balance between incoming energy from the sun and outgoing thermal (longwave and reflected shortwave) energy from the Earth]. The goals of ERBE are: 1) to understand the radiation balance between the Sun, Earth, atmosphere, and space; and 2) to establish an accurate, long-term baseline data set for detection of climate changes. Earth radiation budget data are fundamental to the development of realistic climate models and to the understanding of natural and anthropogenic perturbations of the climate system. 12) 13) 14) 15) 16) 17) 18) 19) 20) 21) 22)
The instrument package was developed and built by TRW, Redondo Beach, CA. Each radiometric package (ERBE) contained four Earth-viewing nonscanning active-cavity radiometers, three scanning thermistor bolometer radiometers, and a solar monitor. The ERBE instrument has a mass of 61 kg, average power of 50 W, and an average data rate of 1.12 kbit/s.
ERBE consists of a `scanner' and a `nonscanner' unit, providing measurements on several spatial and temporal scales.
• The ERBE nonscanner unit features four Earth-viewing channels and a solar monitor used for solar calibration measurements. The Earth-viewing channels have two spatial resolutions: a horizon-to-horizon view (wide FOV or WFOV), and a FOV limited to about 1000 km in diameter (also referred to as medium FOV, or MFOV). For MFOF and WFOV there is a total spectral channel sensitive to all wavelengths, and a shortwave channel which uses a high purity, fused silica filter dome to transmit only the shortwave radiation from 0.2 to 5 µm. All five channels of the nonscanner are active cavity radiometers. Data rate: 160 bit/s.
Figure 7: Schematic diagram of the ERBE solar monitor (image credit: NASA)
• The ERBE scanner instrument unit contains three co-planar detectors (longwave, shortwave and total energy). Each detector scans the Earth perpendicular to the groundtrack from horizon to horizon. The detectors are thermistors (bolometers) which use space on every scan as a reference point to guard against drift. They are located at the focal point of a f/1.84 Cassegrain telescope whose aluminum-coated filters have been coated to enhance UV reflectivity. The IFOV for each channel is hexagonal, with an angular size of 3º (across track) x 4.5º (along track). Data rate = 960 bit/s.
Figure 8: Detection unit of the ERBE instrument (image credit: NASA)
Table 1: ERBE instrument parameters
Figure 9: Schematic view of the ERBE scanner unit (image credit: NASA)
Figure 10: Schematic view of the ERBE nonscanner unit (image credit: NASA)
Figure 11: Photo of the ERBE instrument with scanner unit (left) and nonscanner unit (right), image credit: NASA
ERBE instrument calibration: Inflight stability of all radiometric channels was monitored by internal calibration sources. An internal blackbody, evacuated tungsten lamps, and observations of the sun are used to check the stability and precision of the instruments. All seven of the Earth-viewing channels on ERBE have an inflight calibration capability.
In addition, a state-of-the-art ground calibration facility was used, coupled with the complete inflight calibration system. The ground facility contained a MRBB (Master Reference Blackbody), an integrating sphere, and a reference solar monitor - as well as windows through which a solar simulator may be directed at the appropriate instrument.
SAGE-II (Stratospheric Aerosol and Gas Experiment II):
SAGE-II was built by Ball Aerospace; PI: M. P. McCormick, Hampton University, Hampton, VA. SAGE-II is an Earth limb-scanning grating spectrometer (with a Dall-Kirkham telescope, two-axis gimbaled system capable of rotating in azimuth). Objective: monitoring of concentrations and distributions of stratospheric aerosols, nitrogen dioxide, and water vapor. SAGE II has measured the decline in the amount of stratospheric ozone globally and over the Antarctic since the ozone hole was first described in 1985. The limb measurements of the Earth's upper troposphere and stratosphere are taken in the altitude range of 10-40 km. 23) 24) 25)
The SAGE-II instrument is a seven-channel sun photometer using a Cassegrain-configured telescope, holographic grating, and seven silicon photodiodes, some with interference filters, to define the seven spectral channel bandpasses. Spectral range: 0.385 - 1.020 µm. Data rate = 6.3 kbit/s. Solar radiation is reflected off a pitch mirror into the telescope with an image of the Sun formed at the focal plane. The instrument's IFOV, defined by an aperture in the focal plane, is a 0.5 arcmin x 2.5 arcmin slit that produces a vertical resolution at the tangent point on the Earth's horizon of about 0.5 km. The SAGE-II instrument has a mass of 29.5 kg, average power consumption of 18 W, and a data rate of 6.3 kbit/s.
Radiation passing through the aperture is transferred to the spectrometer section of the instrument containing the holographic grating and seven separate detector systems. The holographic grating disperses the incoming radiation into the various spectral regions centered at the 1020, 940, 600, 525, 453, 448, and 385 nm wavelengths. Four channels (385, 454, 600, and 1020 nm) allow separation of atmospheric extinction along the line-of-sight due to Rayleigh scattering, aerosols, ozone, and nitrogen dioxide. The 940 nm channel allows concentration profiles of water vapor to be mapped. The 448 nm channel provides an additional channel for nitrogen dioxide detection, and the 525 nm channel is used for aerosol detection.
The spectrometer system is inside the azimuth gimbal to allow the instrument to be pointed at the sun without image rotation. The operation of the instrument during each sunrise and sunset measurement is totally automatic. Prior to each sunrise or sunset encounter, the instrument is rotated in azimuth to its predicted solar acquisition position. The radiometric channel data are sampled at a rate of 64 samples/s per channel, digitized to 12 bit resolution, and recorded for later transmission back to Earth. Sampling occurs twice per orbit for durations varying from 3 to 10 minutes each.
Figure 12: Illustration of the SAGE-II instrument (image credit: NASA)
The instrument provides self-calibrating near global measurements. Measurements taken from a tangent height of 150 km, where there is no attenuation, provide a self-calibration feature for every event. - The measurements are inverted using the “onion-peeling” approach to yield 1 km vertical resolution profiles of aerosol extinction (vertical resolution of 1 km below 25 km and a resolution of 5 km above 25 km). The focus of the measurements is on the lower and middle stratosphere.
SAGE-II stratospheric ozone data have become a standard long-record reference field for comparison with other stratospheric ozone measurements. SAGE-II data has been used to measure the decline in the amount of stratospheric ozone over the Antarctic since the ozone hole was first noted in 1985. The high-resolution SAGE-II measurements allow scientists to study the vertical structure of ozone in the Antarctic and, more importantly, allow scientists to study the correlations between various trace gases.
Status: In Oct. 2004, SAGE-II observations continued after 20 years in orbit providing the scientific community with a long-term, global depiction of the distribution of aerosol, ozone, water vapor, and nitrogen dioxide (NO2).
1) J.A.Dezio, C.A. Jensen, “Earth Radiation Budget Satellite,” in Monitoring Earth's Ocean, Land, and Atmosphere, Vol. 97 by AIAA, 1985, pp. 261-292
3) “Space Shuttle Mission STS-41G,” NASA Press Kit, October 1984, URL: http://www.jsc.nasa.gov/history/shuttle_pk/pk/Flight_013_STS-41G_Press_Kit.pdf
4) “Earth Radiation Budget Satellite- On-Orbit Reliability Investigation Final Report,” Hermandez Engineering Inc., Oct. 1996
5) Takmeng Wong, Bruce A. Wielicki, Robert B. Lee, III, “Decadal Variability of Earth Radiation Budget Deduced from Satellite Altitude Corrected ERBE/ERBS Nonscanning Data,” URL: http://ams.confex.com/ams/pdfpapers/79213.pdf
6) “Ball Aerospace Celebrates 21 Years of Ozone Research,” Oct. 20, 2005, URL: http://www.lexdon.com/article/Ball_Aerospace_Celebrates_21_Years/14704.html
7) Information provided by Kathryn A. Bush of NASA/LaRC, Hampton, VA
9) “The Battery Bunny Has Little on This Space SAGE,” October 6, 2004, URL: http://www.nasa.gov/vision/earth/lookingatearth/sage2.html
10) Information provided by Jack Paden and Bob Lee of NASA/LaRC
11) Information provided by William P. Chu of NASA/LaRC
12) Bruce R. Barkstrom, “The Earth Radiation Budget Experiment (ERBE),” Bulletin of the American Meteorological Society, Vol. 65, Issue 11, November 1984, URL: http://journals.ametsoc.org/doi/pdf/10.1175/1520-0477%281984%29065%3C1170%3ATERBE%3E2.0.CO%3B2
14) B. R. Barkstrom, J. B. Hall, Jr., “Earth Radiation Budget Experiment (ERBE): An Overview”, Journal of Energy, Vol. 6, 1982, pp. 141-146
15) B. R. Barkstrom, G. L. Smith, “The Earth Radiation Budget Experiment: science and implementation,” Review of Geophysics, Vol. 24, 1986, pp. 379-390.
16) L. P. Kopia, “Earth Radiation Budget Experiment scanner instrument,” Review of Geophysics, Vol. 24, 1986, pp. 400-406
17) R. B. Lee III, R. S. Wilson, “Accuracy and Precision of Earth Radiation Budget Experiment ERBE - Solar Monitor on the Earth Radiation Budget Satellite ERBE,” http://www.acrim.com/NASA_NIST%20TSI%20Workshop/Talks/RBLEEIII%20-%20TSI%20WORKSHOP%20NIST%20JULY%2018%202005%20REVISED.pdf
18) M. P. A. Haeffelin, J. R. Mahan, K. J. Priestley, ”Predicted dynamic electrothermal performance of thermistor bolometer radiometers for Earth radiation budget applications,” Applied Optics, Vol. 36, 1997, pp. 7129-7142
19) “Earth Radiation Budget,” URL: http://marine.rutgers.edu/mrs/education/class/yuri/erb.html#erbe
21) Robert B. Lee III, Robert S. Wilson, “1984-2003, Earth Radiation Budget Satellite (ERBS)/Earth Radiation Budget Experiment (ERBE) Total Solar Irradiance (TSI) measurements,” SORCE Meeting, Dec. 4-6, 2003, Sonoma, CA, URL: http://lasp.colorado.edu/sorce/news/2003ScienceMeeting/...
22) Takmeng Wong, Bruce A. Wielicki, Robert B. Lee III, G. Louis Smith, Kathryn A. Bush, Joshua K. Willis, “Reexamination of the Observed Decadal Variability of the Earth Radiation Budget Using Altitude-Corrected ERBE/ERBS Nonscanner WFOV Data,” Journal of Climate, Vol. 19, Aug. 15, 2006, pp. 4028-4040, URL: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.173.3459&rep=rep1&type=pdf
24) N. H. Zaun, L. E. Mauldin, M. P. McCormick III, “Design and performance of the stratospheric aerosol and gas experiment II (SAGE II) instrument,” Proceedings of SPIE, `Infrared Technology IX,' Edited by Richard A. Mollicone and Irving J. Spiro, Vol. 430, 1983, p. 99
25) “SAGE II: Understanding the Earth's Stratosphere,” NASA Facts, 1996, URL: http://www.nasa.gov/centers/langley/pdf/70813main_FS-1996-08-14-LaRC.pdf
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.