Meteoroids are the historians of space, hurtling through the cosmos with clues about primitive solar nebula and even the precursors to life itself. These travelers ablate as they enter the Earth’s atmosphere, appearing as a “shooting star” or meteor and giving off emission spectra that indicate their composition. Unfortunately, the ultraviolet light emitted never reaches the ground, being first absorbed by the Earth’s atmosphere before it can be studied. A new student-led mission seeks to change all that by launching a CubeSat into the upper atmosphere to collect UV spectral data over the span of one year1.
With an estimated 44 metric tons of meteoritic material falling on the Earth each day2, we are constantly being bombarded with information from space. Meteors are chunks of rock and metal varying from 10 μm to 10 m in size, originating from asteroids and other planetary bodies. Traveling at up to 42 kilometers per second3, they experience tremendous friction from atmospheric gases as they enter the Earth’s atmosphere, causing them to ablate and glow, trailing ionized gases in their wake. While the eye sees the glow as a streak of light (hence the term “shooting star”), it is actually composed of many atomic and molecular emission lines.
Observatories and amateur astronomers have been collecting meteor spectra for years as a method of characterizing meteor composition and gaining clues about the formation of the planets, properties of primitive solar nebula, and even the origin of prebiotic molecules on earth. The inherent absorption of light below 310 nm by the atmosphere, however, limits the lower wavelength range of meteor observation from Earth. If the spectra from meteors could be collected from space, additional UV spectral lines could be seen, providing information about volatile species like OH, C, C2, CH, NO, SiO, AlO, and CN.
A Lofty Goal
A group at the Université Pierre et Marie Curie (UPMC, Paris, France) has begun a 5-year project to develop a 3U CubeSat capable of performing a statistical count of meteor entry into the Earth’s atmosphere, and to collect UV spectra as they do so. Project METEOR was initiated by UPMC and the Institute of Celestial Mechanics and Ephemeris Calculations (IMCCE – Paris Observatory) as part of the JANUS projects4. It is also supported by collaborations with the Laboratoire d’Informatique de Paris (LIP6), the Laboratoire Atmosphères, Milieux et Observations Spatiales (LATMOS) and the French Space Agency – Centre Nationale d’Etudes Spatiales (CNES).
This educational project enlists students to perform the design and build of a CubeSat equipped with a visible camera capable of 20-30 frames per second, and a high resolution UV spectrometer (≤0.8 nm). This work will complement the Fireball Recovery and InterPlanetary Observation Network (FRIPON) project, a network of 100 cameras watching for meteorites entering the atmosphere above France with the goal of tracking their origin. Data collected by the CubeSat will be much less vulnerable to weather conditions and atmospheric attenuation of spectral lines than traditional ground-based studies. Additionally, the CubeSat will allow observation of many more meteors, and provide access to their UV spectra at close range. Given that only a few meteor spectra have ever been collected from space, the increase in UV spectral information that could come from METEOR is significant.
At 300 km from Earth’s surface, an incoming meteoroid begins interacting with the upper atmosphere and begins to heat. As it approaches 120 km out, it begins to fragment, and temperatures reach 500-900 K. After that, the body (now a meteor) can reach temperatures of 2500 K, and the surrounding air ionizes to generate a plasma trail, emitting light for 0.3-5 seconds5. Light captured by the UV spectrometer during this time could show evidence of carbon (C) or radical hydroxyl (OH-), which can be traced back to the primordial solar nebula. Presence of OH- could also be evidence for the hypothesis that water on Earth is of extraterrestrial origin. Silicon (Si) and iron (Fe) are among the other species of interest that could be seen in the 200-400 nm spectral range planned for the instrument.
Though the project is still in the early planning stages, the METEOR team is looking at Ocean Optics spectrometers as models for size, power, and data budget on the mission. With a total mass of <4 kg, a compact spectrometer is needed. The spectrometer requirements include <1.5 nm resolution, an integration time range half that of the emission window (preferably 0.1-2.5 s), and high sensitivity, as some phenomena may yield as few as 50 photons/cm2/s/nm.
For initial models, the group considered the Maya2000 Pro and USB2000+ spectrometers. While the Maya2000 Pro offers higher sensitivity, the USB2000+ is lower in mass and power budget. It was also important to consider the quantity of data created, for which the Maya2000 Pro was considered as an upper limit (it using a 2D detector with vertical binning as compared to the USB2000+’s 2048 pixels).
The Maya2000 Pro detector is 2048 x 64 pixels, with 16-bit output, yielding a total spectrum data size of: Bs= 2048 pixels x 64 x 16 bit/pixel = 2.10 Mbit
When combined with the camera data at 30 fps, the total data to be collected for a single meteor event is 21.57 Mbit. Several events will need to be stored in memory for up to several consecutive orbits until contact with the ground station can be made, then sent with a high data rate communication link. Power will be provided via solar panels with storage and a control unit. Active thermal control will likely be needed in conjunction with passive thermal design measures to ensure all components remain within operating temperature range. The team is still deciding whether to use a vertical or horizontal configuration for the CubeSat (see below)1.
More Challenges Ahead
The METEOR mission will undoubtedly encounter more challenges as it prepares for deployment in 2020, including the customization of a UV spectrometer for space environments. Silicon-based detectors are prone to damage by cosmic radiation, which can significantly shorten their lifetime. The team may need to consider a radiation-hardened detector and electronics. With Ocean Optics applications scientists advising on the relative benefits of the Maya2000 Pro versus the Flame and EMBED spectrometer designs, they are sure to find the right solution.
- Ortega Varela De Seijas, M. “Design of a 3U Cubesat for Meteor Detection and Characterization.” Proc. of 67th International Astronautical Congress (IAC), , 26-30 September 2016. N.p.: International Astronautical Federation (IAF), 2016.
- Jeunes en Apprentissage pour la réalisation de Nanosatellites au sein des Universités et des écoles de l’enseignement Supérieur (JANUS).
- J. Vaubaillon, Dynamique Des Météoroides Dans Le Système Solaire. Application A La Prevision Des Pluies Météoritiques, Observatoire de Paris, October 2003.