Miniature X-ray Solar Spectrometer CubeSat
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The Miniature X-ray Solar Spectrometer (MinXSS) CubeSat was the first launched
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CubeSat with a science mission. It was designed, built, and operated primarily by students at the
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with professional mentorship and involvement from professors, scientists, and engineers in the Aerospace Engineering Sciences department and the Laboratory for Atmospheric and Space Physics, as well as
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,
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, and the National Center for Atmospheric Research's High Altitude Observatory. The mission principal investigator is Dr. Thomas N. Woods and co-investigators are Dr. Amir Caspi, Dr. Phil Chamberlin, Dr. Andrew Jones, Rick Kohnert, Professor Xinlin Li, Professor Scott Palo, and Dr. Stanley Solomon. The student lead (
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,
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) was Dr. James Paul Mason, who has since become a Co-I for the second flight model of MinXSS. MinXSS launched on 2015 December 6 to the
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as part of the Orbital ATK
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cargo resupply mission. The launch vehicle was a
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rocket in the 401 configuration. CubeSat ridesharing was organized as part of NASA ELaNa-IX. Deployment from the International Space Station was achieved with a NanoRacks CubeSat Deployer on 2016 May 16. Spacecraft beacons were picked up soon after by amateur radio operators around the world. Commissioning of the spacecraft was completed on 2016 June 14 and observations of solar flares captured nearly continuously since then. The altitude rapidly decayed in the last week of the mission as atmospheric drag increased exponentially with altitude. The last contact from MinXSS came on 2017-05-06 at 02:37:26 UTC from a HAM operator in Australia. At that time, some temperatures on the spacecraft were already in excess of 100 Â°C. (One temperature of >300 Â°C indicated that the solar panel had disconnected, suggesting this contact was only moments before disintegration.) Science data spanning the entire mission are publicly available.


Mission objective

The MinXSS mission is to measure the solar soft
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10  picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
spectrum from about 0.5 keV (25 Ã…) to 30 keV (0.4 Ã…) with ~0.15 keV
FWHM In a distribution, full width at half maximum (FWHM) is the difference between the two values of the independent variable at which the dependent variable is equal to half of its maximum value. In other words, it is the width of a spectrum curve mea ...
spectral resolution The spectral resolution of a spectrograph, or, more generally, of a frequency spectrum, is a measure of its ability to resolve features in the electromagnetic spectrum. It is usually denoted by \Delta\lambda, and is closely related to the resolvi ...
. This part of the solar
electromagnetic spectrum The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...
is where the largest enhancement from
solar flares A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other solar phe ...
is expected to occur. It also has an important impact on Earth
ionospheric The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an im ...
chemistry. Despite this, prior measurements have been either low-resolution broadband, or high-resolution but very narrow bandpass (see image below). The relatively recent creation of miniaturized
silicon drift detectors Silicon drift detectors (SDDs) are X-ray radiation detectors used in x-ray spectrometry ( XRF and EDS) and electron microscopy. Their chief characteristics compared with other X-ray detectors are: *high count rates *comparatively high energy resolu ...
has enabled the MinXSS measurements. MinXSS data will provide a means of probing the solar corona—especially in
active regions An active region is a temporary region in the Sun's atmosphere characterized by a strong and complex magnetic field. They are often associated with sunspots and are commonly the source of violent eruptions such as coronal mass ejections and sol ...
and
solar flares A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other solar phe ...
—and will be used as an input for models of the Earth's upper atmosphere, particularly the ionosphere,
thermosphere The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the ...
, and
mesosphere The mesosphere (; ) is the third layer of the atmosphere, directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as altitude increases. This characteristic is used to define its limits: it ...
. MinXSS is also the first flight of the Blue Canyon Technologies XACT attitude determination and control system (ADCS), one of the only commercially available 3-axis ADCSs for CubeSats. It is performing even better than its specification. This demonstrates that a critical technology for spacecraft has been successfully miniaturized and commercialized.


Science instrument

The primary science instrument onboard MinXSS is a modified Amptek X123 silicon drift detector. The instrument was modified to make it compatible with a space environment. Specifically, heat transfer pads were placed on the hottest components of the electronics boards to provide a conductive thermal path for heat transfer. In atmosphere, the electronics can cool convectively, but operation in vacuum requires cooling via conduction and hence an improved conductive path. Additionally, a small aperture made of
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolat ...
was attached to the front of the detector to reduce the likelihood of photon saturation and limit the field of view to ±4º. Finally, an additional
beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form mi ...
filter was mounted in front of the detector to reduce the number of
photoelectrons The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, and solid st ...
reaching the detector. There are two secondary science instruments: the X-ray Photometer (XP) and the Sun Position Sensor (SPS). XP is a single
photodiode A photodiode is a light-sensitive semiconductor diode. It produces current when it absorbs photons. The package of a photodiode allows light (or infrared or ultraviolet radiation, or X-rays) to reach the sensitive part of the device. The packag ...
with a beryllium filter in front of it of nearly identical thickness to the sum of the two beryllium filters in front of the X123. The purpose of XP is provide an on-orbit cross-calibration for the X123: the sum of the X123 spectrum should be approximately equal to the XP measurement. SPS is a fine sun sensor with 2.4 arcsec precision that consists of a planar quad-diode observing visible light, whose purpose is to provide fine knowledge of the solar position with respect to the X123 and XP optical axes to correct for any off-axis signal attenuation. All instruments were calibrated at the
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's Synchrotron Ultraviolet Radiation Facility (SURF III).


Pre-flight testing

Despite the loose requirements placed on CubeSats compared to larger spacecraft missions, MinXSS underwent the same rigorous tests that are considered standard in the aerospace industry. The X123 primary science instrument was fully flight-qualified on two
sounding rocket A sounding rocket or rocketsonde, sometimes called a research rocket or a suborbital rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The rockets are used to ...
flights. In addition to subsystem-level and system-level testing at the bench (i.e. in air at room temperature), the system also underwent thermal vacuum chamber cycle testing, thermal balance testing, vibration testing, and end-to-end communications testing. Mission simulations were performed during thermal vacuum cycling and at the bench using a solar array simulator that was autonomously power toggled with realistic orbital insolation and eclipse periods. This ensured that the spacecraft would be power-positive on orbit.


Communications

The spacecraft uses a measuring tape antenna and an AstroDev Li-1 radio. The spacecraft periodically beacons and its signal can be picked up with amateur ham radio operator equipment. Below are the communications specifications: * Frequency: 437.345
MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
* Data rate: 9600
baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulatio ...
* Modulation: GMSK * Beacon cadence: (as of 2016/07/04) 54 seconds Beacons recorded by ham radio operators can be sent to the MinXSS team (in
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format) to contribute to overall data capture.


On-Orbit success

The first critical hurdle for any deployed spacecraft is to establish communications with the ground. This was achieved on the first pass over the MinXSS ground station in
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. As a science mission, success is determined by receipt of useful scientific measurements. MinXSS first light was presented at a press briefing and a contributed poster during the
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's 47th Solar Physics Division Meeting in Boulder, Colorado. Over 40 GOES C-class and 7 M-class solar flares occurred in the first weeks of the MinXSS mission, and those observations were downlinked to the ground for analysis. The results of those analyses will be the subjects of several upcoming peer-review papers. Additionally, MinXSS was the first flight of the Blue Canyon Technologies XACT 3-axis attitude determination and control system (ADCS). It continuously performed exceptionally, with 8
arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
(1-sigma) pointing, where the specification was for 11 arcseconds.


Follow-on mission (MinXSS-2)

A second MinXSS spacecraft was built in parallel with the first. MinXSS-2 is identical to MinXSS-1 except for: * (1) an upgraded version of the X-ray spectrometer, the Amptek X123-FastSDD, vs. the X123-SDD on MinXSS-1; * (2) an upgraded version of the BCT XACT, using the current on-market hardware vs. the pre-release version used on MinXSS-1; * (3) addition of a circuit for in-flight "hard reset" power cycle; * (4) use of the AstroDev Lithium-2 radio vs. the Li-1 used on MinXSS-1; and * (5) minor software updates. MinXSS-2 is planned to deploy from the Spaceflight Industries SSO-A SmallSat Express mission, using a
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Falcon 9. Launch happened on 3 December 2018, and MinXSS2 was deployed to orbit. The MinXSS-2 orbit is
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and sun-synchronous at 10:30am LTDN, at approximately 575 km altitude, providing an estimated 4-year mission life. MinXSS-2 was selected for 2 years of funding by NASA under the 2016 Heliophysics Technology and Instrument Development for Science (H-TIDeS) program. MinXSS-2 also adds science involvement from the
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, with Dr. Harry Warren added as a co-investigator.


Awards

MinXSS was chosen as the 2016 AIAA Small Satellite Mission of the Year during the 30th Annual AIAA/USU
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in
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.


Project architecture

The MinXSS project was structured after the
Colorado Student Space Weather Experiment Colorado Student Space Weather Experiment (CSSWE) was the sixth National Science Foundation sponsored CubeSat mission. It was built by students at the University of Colorado at Boulder with advising from professionals at the Laboratory for Atmosp ...
CubeSat, which established the graduate projects course led by
Joseph R. Tanner Joseph Richard Tanner (born January 21, 1950) is an American instructor at the University of Colorado Boulder, mechanical engineer, a former naval officer and aviator, and a former NASA astronaut. He was born in Danville, Illinois. He is unusu ...
in the Aerospace Engineering Sciences department at the
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. Students in the department have the choice to either complete a Master's thesis or take two semesters of the graduate projects course. Typically, 10-20 students will be involved in each of the concurrent projects. CSSWE and MinXSS heavily leveraged professionals at the Laboratory for Atmospheric and Space Physics. As of 2018 March 8, 40 graduate, 5 undergraduate, and two high school students have worked on the project. Roughly 40 professionals have contributed with varying levels of involvement, from providing feedback at design reviews to writing flight software.


References


External links


MinXSS official sitePhotos of deployment from the International Space Station compiled into a movie
(courtesy Tim Peake)
XACT Data Sheet
{{Use American English, date=August 2016 Student satellites CubeSats Spacecraft launched in 2015 Satellites deployed from the International Space Station Spacecraft decommissioned in 2017