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| SPARTAN 201-5 |
| Payload Bay |
| 2,978 |
| Prime: Scott Parazynski |  |
| Backup: Stephen Robinson | |
| Overview |
 SPARTAN 201 is a free-flying payload that will study the solar wind and the sun's corona to increase our knowledge of our star's effects on the Earth. The satellite will be deployed and retrieved by the shuttle orbiter Discovery.The SPARTAN carrier is a simple, reusable vehicle that can carry a variety of scientific instruments at a relatively low cost. After it is deployed from the orbiter in space, it provides its own power, pointing, and data recording as it performs a preprogrammed mission. In addition to solar experiments, the SPARTAN spacecraft can be programmed to conduct stellar astronomy, Earth fine pointing, spacecraft technology experiments and demonstrations, and microgravity science and technology experiments. The SPARTAN project offers the scientific community an intermediate capability for conducting investigations in space between that afforded by small payloads that remain in the orbiter and larger satellites that orbit the Earth for long periods of time. SPARTAN 201: Studying the Sun's Corona The SPARTAN 201 series is investigating the solar corona--the thin upper layers of the sun's atmosphere, which reach temperatures of about 2 million degrees Fahrenheit. Scientists hope to determine the mechanisms that cause the heating of the corona and the acceleration of the solar wind, which originates in the corona, and explain why the corona is so much hotter than the rest of the sun. The first three SPARTAN 201 flights have already advanced our understanding of the solar wind and its origin. SPARTAN 201-05 observations will be coordinated with observations made from the Solar and Heliospheric Observatory (SOHO) satellite, a cooperative mission of the European Space Agency (ESA) and NASA. The second and third missions were coordinated with the passage of the Ulysses spacecraft over the sun's south and north poles. The sun's corona is difficult to study because its light is relatively dim compared to the sun's total luminance. The white light corona can be viewed from Earth only during a solar eclipse, which strongly reduces the brightness of the scattered sunlight. Ground-based astronomers are never able to see the ultraviolet radiation because of interference from the Earth's atmosphere. (For more information on SPARTAN Solar Studies see EXPERIMENTS) SPARTAN Solar Telescopes SPARTAN 201 is equipped with two complementary telescopes that can measure these emissions from the sun's corona. The white light coronagraph (WLC), provided by the High-Altitude Observatory in Boulder, Colo., will measure the density of the electrons in the coronal white light. The ultraviolet coronal spectrometer (UVCS) from the Smithsonian Astrophysical Observatory at Harvard will measure the velocities, temperatures, and densities of the coronal plasmas. The ultraviolet instrument and the WLC are housed in an evacuated cylinder with an aperture door that is opened after SPARTAN is released from the shuttle. By comparing the data collected by the two telescopes and combining the observations of the SPARTAN 201 missions and Ulysses and observations made by ground-based instruments, scientists expect to gain a much more complete picture of the origin of the solar wind. (For more information on SPARTAN Solar Telescopes, see EXPERIMENTS) Solar Disk Studies In addition to observing the solar corona, SPARTAN will take a look at the solar disk on two orbits and record background/geocoronal measurements during nighttime portions of each orbit. The solar disk observations will be used to probe the Earth's exosphere in order to correct for its absorption and scattering effects on the spectral data. SPARTAN Secondary Experiments SPARTAN 201-05 will also carry three secondary experiments: SPAM, TEXAS, and VGS. (For more information on SPARTAN Secondary Experiments, see EXPERIMENTS) The SPARTAN Spacecraft The rectangular SPARTAN 201 spacecraft consists of a service module that contains attitude control, thermal control, payload function control, and power distribution systems and an instrument carrier, a cylindrical container that holds the telescopes. On the bottom of the spacecraft is the upper portion of the release/engage mechanism, or REM. The lower half of the REM is attached to the spacecraft's payload bay support structure. The two halves of the REM mate to hold the spacecraft rigidly in place on the support structure and unlatch to allow SPARTAN to be deployed. SPARTAN Operations SPARTAN will be deployed from Discovery's cargo bay on flight day 2. A crew member will use the orbiter's 50-foot robot arm to lift the free-flying satellite from its support structure and release it in space. After SPARTAN is released, it must perform a 45-degree pirouette to confirm that it is functioning properly before its mission can begin. (For more information on SPARTAN rendezvous ops, see RENDEZVOUS) SPARTAN will conduct its operations 70 to 100 miles from Discovery. Once the spacecraft is a safe distance from the orbiter, it will be activated by an internal timer and will initiate its preprogrammed mission. This program cannot be changed after SPARTAN has been deployed from the orbiter because there is no command or telemetry link between the two spacecraft. SPARTAN is completely autonomous while deployed: a battery supplies electrical power, and it has its own pointing system and a tape recorder for storing science data. |
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| History/Background |
| This is a reflight of the STS-87 SPARTAN 201-04, which developed problems shortly after being deployed from the shuttle in November 1987. After it was released, SPARTAN failed to perform a pirouette maneuver because of an incomplete initialization sequence. The spacecraft was sent into a spin when Columbia's robotic arm bumped it during a retrieval attempt. After spacewalking astronauts recaptured the free flyer four days after its deployment, NASA was cautiously optimistic that SPARTAN could be deployed for a shortened mission. In the end, however, the mission had to be canceled because Columbia would not have had enough propellant for the rendezvous and capture activities. Postflight testing and reviews of data tapes at KSC in January confirmed that the SPARTAN satellite was healthy and had performed as expected. All flight data correlated well with in-flight predictions and assessments. This is the fourth SPARTAN 201 mission. SPARTAN 201-01 flew on STS-56 in April 1993 April, 201-02 on STS-64 in September 1994, and 201-03 on STS-69 in September 1995. The SPARTAN astrophysics experiments evolved from NASA's sounding-rocket science program. The SPARTAN project was conceived in the late 1970s to take advantage of the opportunity offered by the space shuttle to provide more observation time for the increasingly more sophisticated experiments than the five to 10 minutes allowed by sounding rocket flights. On this flight, for example, SPARTAN 201 will conduct observations of the sun for about 43 hours. Externally occulted coronagraphs have been used on U.S. space missions since the technology was perfected in 1966 by Gordon Newkirk of the High-Altitude Observatory. The WLC is the third design produced by the High-Altitude Observatory and is 10 times more sensitive than the versions that were used on the Skylab mission in 1973-74 and the Solar Maximum Mission from 1980 to 1989. The coronagraph was developed by French astronomer B. Lyot around 1932 to allow astronomers to study the sun's corona without having to wait for a total solar eclipse. The externally occulted coronagraph is an improved design that significantly reduces the scattered light generated by the telescope. The WLC also contains a polarimeter, which removes the effect of the light of the solar corona and the scattering in the cloud of dust, called the ecliptic cloud, left when the solar system was formed. A filter blocks the glow caused by atmospheric molecules colliding with the SPARTAN spacecraft. |
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| Benefits |
| Discoveries about the unknown source of the energy that heats the solar corona and accelerates the solar wind may help scientists understand the winds that carry mass and momentum away from other stars and why the sun's rotation has slowed. The results may also help them to explain how the Earth's magnetism and, ultimately, its climate and weather are affected by variations in the radiation and particles emitted by the sun. The results will also benefit the designers of Earth-orbiting spacecraft. The torrent of electrons, protons, and ions streaming from the sun at speeds of almost 1 million miles per hour causes the spectacular Northern and Southern lights, but it also is responsible for degrading the performance and reliability of spacecraft in Earth orbit. |
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