Showing papers by "Charles Swenson published in 2014"

Design, Development, Implementation, and On-orbit Performance of the Dynamic Ionosphere CubeSat Experiment Mission

Abstract: Funded by the NSF CubeSat and NASA ELaNa programs, the Dynamic Ionosphere CubeSat Experiment (DICE) mission consists of two 1.5U CubeSats which were launched into an eccentric low Earth orbit on October 28, 2011. Each identical spacecraft carries two Langmuir probes to measure ionospheric in-situ plasma densities, electric field probes to measure in-situ DC and AC electric fields, and a science grade magnetometer to measure in-situ DC and AC magnetic fields. Given the tight integration of these multiple sensors with the CubeSat platforms, each of the DICE spacecraft is effectively a “sensor-sat” capable of comprehensive ionospheric diagnostics. The use of two identical sensor-sats at slightly different orbiting velocities in nearly identical orbits permits the de-convolution of spatial and temporal ambiguities in the observations of the ionosphere from a moving platform. In addition to demonstrating nanosat-based constellation science, the DICE mission is advancing a number of groundbreaking CubeSat technologies including miniaturized mechanisms and high-speed downlink communications.

The Near Earth Object Scout Spacecraft: A Low Cost Approach to in-situ Characterization of the NEO Population

Abstract: In this paper we describe a micro/nano satellite spacecraft and a supporting mission profile and architecture designed to enable preliminary in-situ characterization of a significant number of Near Earth Objects (NEOs) at reasonable cost. The spacecraft will be referred to as the NEO Scout. NEO Scout spacecraft are to be placed in GTO, GEO, or cis-lunar space as secondary payloads on launch vehicles headed for GTO or beyond and will begin their mission after deployment from the launcher. A distinguishing key feature of the NEO scout system is to design the mission timeline and spacecraft to rendezvous with and land on the target NEOs during close approach to the Earth-Moon system using low-thrust/high- impulse propulsion systems. Mission feasibility and preliminary design analysis are presented along with detailed trajectory calculations. The use of micro/nano satellites in low-cost interplanetary exploration is attracting increasing attention and is the subject of several annual workshops and published design studies (1-4). The NEO population consists of those asteroids and short period comets orbiting the Sun with a perihelion of 1.3 astronomical units or less (5-8). As of July 30, 2013 10065 Near-Earth objects have been discovered. The spin rate, mass, density, surface physical (especially mechanical) properties, composition, and mineralogy of the vast majority of these objects are highly uncertain and the limited available telescopic remote sensing data imply a very diverse population (5-8). In-situ measurements by robotic spacecraft are urgently needed to provide the characterization data needed to support hardware and mission design for more ambitious human and robotic NEO operations. Large numbers of NEOs move into close proximity with the Earth-Moon system every year (9). The JPL Near-Earth Object Human Space Flight Accessible Targets Study (NHATS) (10) has produced detailed mission profile and delta V requirements for various NEO missions ranging from 30 to 420 days in duration and assuming chemical propulsion. Similar studies have been reported assuming high power electric propulsion for manned NEO rendezvous missions (11). The delta V requirement breakdown and mission profile data from references 10 and 11 are used as a basis for sizing the NEO Scout spacecraft and for conducting preliminary feasibility assessments using the Tsiokolvsky rocket equation, a (worst-case) delta V requirement of 10 km/sec, and a maximum spacecraft dry mass of 20 kg. Using chemical propellant for a 10 km/sec delta V drives spacecraft wet mass well above 300 kg so that chemical propulsion is a non-starter for the proposed mission profile and spacecraft wet mass limits. In contrast, a solar electric propulsion system needs only 8 kg of Xe propellant to accelerate the spacecraft to 10 km/sec in 163 days with 0.02 N of thrust and 500 W of power from1.6 sq m of 29% efficient solar panels. In a second example, accelerating a 4 kg payload to 7 km/sec over 180 days requires about 6.7 kg of propellant and 1.2 kg of solar panels (12 kg total spacecraft wet mass).

Hyperspectral Limb Scanner for the OPAL Mission

Abstract: The Earth’s lower thermosphere is an important interface region between the neutral atmosphere and the “space weather” environment. The NSF-sponsored Optical Profiling of the Atmospheric Limb (OPAL) mission is designed to map global thermospheric temperature variability at midand low-latitudes over the critical “thermospheric gap” region (~100-140 km altitude) where prior data are sparse. OPAL will profile the thermosphere temperature from 90 to 140 km altitude by observing the daytime O2 A-band emission. OPAL measures the thermosphere neutral temperature by spectroscopic analysis of molecular oxygen Aband emission (758 – 768 nm). This paper presents the OPAL mission science, instrument design, and measurement capabilities. OPAL is expected to launch in late 2016 with a mission duration > 9 months. The OPAL instrument is a grating-based imaging spectrometer with refractive optics and a high-efficiency volume holographic grating (VHG). The scene is sampled by 7 parallel slits that form non-overlapping spectral profiles at the focal plane with resolution of 0.5 nm (spectral), 1.5 km (limb profiling), and 60 km (horizontal sampling). A CCD camera at the instrument focal plane delivers low noise and high sensitivity. The instrument is designed to strongly reject stray light from daylight regions of the earth.

Auroral Spatial Structures Probe (ASSP)

Abstract: The Auroral Spatial Structures Probe (ASSP) is a NASA sounding rocket mission to be launched in the late January 2015 time frame that will be used to study both the spatial and temporal small scale variation of the electric and magnetic fields during active aurora and just before the onset of an auroral sub-storm. This will be accomplished through the use of a constellation of small payloads that separate relative to each other throughout a sounding rocket flight.

Measurement of lower thermosphere using The Optical Profiling of the Atmospheric Limb (OPAL) CubeSat experiment

Abstract: The Earth's lower thermosphere region between 90–140 Km is subjected to episodic energy and momentum forcing from the solar wind in the form of Joule heating and particle precipitation. This is believed to be the largest driver of global thermospheric temperature variability. In addition, this region is also subjected to the periodic and episodic energy and momentum forcing through tides, planetary waves and gravity waves generated in the lower atmosphere. These internal waves affect the temperature structure on many scales as they propagate up from the lower atmosphere into the thermosphere. However, the relative importance of these two coupling processes on the thermospheric temperature structure, on both regional and global-scales is poorly understood.

Orbit refinement for software defined radio for space applications

Abstract: Digital down-conversion in software defined radios in space-to-Earth and Earth-to-space communications is challenging due to potentially large Doppler frequency offsets. The predictability of satellite orbits suggests that a computed Doppler offset could be used to perform an orbit-informed down-conversion. However, publicly available orbital parameters and orbit propagator codes lack the accuracy required for fine Doppler removal. This paper proposes a technique to adjust the orbital parameters until the computed Doppler profile matches the Doppler profile in the received signal. This technique is applied to a real signal recorded from a satellite overpass and is shown to be able to very accurately estimate frequency offsets.