Needle in a Haystack: Finding Two S-band CubeSats in a Swarm of 64 Within 24 Hours

In the past few years we have witnessed the ascension of rideshare missions, breaking records again and again for the total number of satellites released on a single launch. Such large swarms of spacecraft make it difficult for the Combined Space Operations Center (CSpOC) to identify satellite orbits until days to weeks after launch. For the SSO-A launch in December 2018, it took 11 days to catalog all 64 objects. While satellites should be designed to survive without ground contact for that long, for most missions, making contact and assessing vehicle state of health during early orbit operations is critical, and waiting for object cataloging is simply too risky. Furthermore, as CubeSats take on more operational roles, the amount of data needed to both uplink and downlink requires moving away from the traditional L-band frequencies to S-band and higher. While higher frequency bands allow faster data transmission it comes at a cost of smaller ground antenna footprints, requiring an order of magnitude better pointing knowledge in order to establish communications lock. With typical canister ejection speeds, spacecraft can drift away from the launch vehicle, whose orbit is typically known and provided by the launch integrator. Depending on ground antenna size, this implies the spacecraft will no longer be in the ground antenna field of view within a day or so of launch. This makes establishing communications with the spacecraft within the first 24 hours after launch paramount. This paper discusses how the ORS-7/DHS Polar Scout mission successfully achieved contact with its two 6U CubeSats and determined their orbital ephemerides in less than 24 hours after launching on the SSO-A mission on December 3, 2018. We present our spacecraft acquisition plan, which encompassed a number of different strategies that can be employed depending on the capabilities and equipment at the ground site

The Next Generation Solar Spectral Irradiance Monitor for the JPSS-TSIS Mission: Instrument Overview and Radiometric Performance

In order to advance understanding of how natural and anthropogenic processes affect Earth’s climate it is critically important to maintain accurate, long-term records of climate forcing. These climate-data records are a time series of measurements of sufficient length, consistency, and continuity to determine true climate variability and change. Quantifying the solar irradiance (both total and spectral) provides the necessary constraint on the total energy input. In particular, the long-term, continuous measurements of solar spectral irradiance (SSI) are needed to characterize poorly understood wavelength-dependent climate processes. The strong reliance on radiative transfer modeling for interpretation and quantification of the deposition of solar radiation in the atmosphere makes it imperative that the spectral distribution of radiant energy entering the atmosphere be known to a high degree of absolute accuracy (tied to international standards). Major measurement challenges in quantifying the influence of SSI variability on climate are achieving sufficient radiometric absolute accuracy and then maintaining (on-orbit) the long-term relative accuracy of the data record. The Total and Spectral Solar Irradiance Sensor (TSIS) Spectral Irradiance Monitor (SIM) is the next generation, space-borne SSI monitor that will fly as part of the dual agency (NASA/NOAA) Joint Polar Satellite System (JPSS) program scheduled for launch in late 2016. The instrument has been designed, characterized and calibrated to achieve unprecedented levels of measurement accuracy (\u3c0.25% absolute) and on-orbit stability (0.01-0.05%/yr.) required to meet the needs of establishing the SSI climate data record across a continuous wavelength region spanning 200 – 2400 nm (96% of the total solar irradiance). The full characterization and calibration follows a measurement equation approach at the unit-level for full validation of the end-to-end performance at the instrument-level. Following this approach, we characterize the SIM instrument as an “absolute” sensor tied to a cryogenic radiometer traceable to the NIST Primary Optical Watt Radiometer (POWR), the primary US standard for radiant power measurements

Calibration of the Spectral Irradiance Monitor in the LASP Spectral Radiometry Facility

The Total and Spectral Solar Irradiance Sensor (TSIS) Spectral Irradiance Monitor (SIM) is the next generation, space-borne SSI monitor that will fly as part of the joint agency (NASA/NOAA) Joint Polar Satellite System (JPSS) program scheduled for launch in late 2016. The instrument has been designed and calibrated to achieve unprecedented levels of measurement accuracy (less than 0.25%) and on-orbit stability required to meet the needs of establishing a complete solar spectral irradiance climate data record. The Spectral Radiometry Facility (SRF) at LASP was developed in order to validate the end-to-end performance of the SIM instrument. This facility includes a test chamber with a 5-axis manipulator that houses the SIM instrument. The illumination source is provided by a NIST Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) laser system. This laser system provides narrow tunable light from 210-2700 nm. The facility also includes a cryogenic radiometer with a precision aperture that is used to measure the absolute irradiance of the illumination light. This facility thus allows us to illuminate the instrument with a known irradiance, wavelength, and polarization. Additionally, the 5-axis manipulator permits us to test the pointing sensitivity and off-axis performance of the instrument. A series of detailed calibrations of the SIM instrument in this facility have allowed us to fully characterize the instrument wavelength scale, spectral response functions, pointing sensitivity, and radiometric accuracy to better than 0.25%

New Mission, New Orbit, No Problem - Applying the Responsive Space Capability to Meet the ORS-6 Mission

From a re-purposed Air Force bus, to a new reconfigurable NASA sensor, to the commercial ride-share launch service, the ORS-6 mission is a model of how flexible architecture, agile management, and creative engineering adjustments to heritage instruments can deliver first rate weather data with significant cost and schedule savings. The Compact Ocean Wind Vector Radiometer (COWVR) payload will measure ocean surface wind vectors at a comparable resolution and measurement accuracy to the WindSat radiometer on Coriolis, while using an order of magnitude lower power and mass. By adding polarimetric electronics and rotating capabilities to the Advanced Microwave Radiometer (AMR) flown on the Jason 1, 2, and 3 satellites, the COWVR instrument leverages years of heritage design, keeping non-recurring engineering costs down and reducing risk. Operationally Responsive Space will fly COWVR on a bus originally built for a mid-inclination, LEO, synthetic aperture radar mission. Because the bus was made with the Modular Space Vehicle architecture, a meld of both Space Plug-n-Play Avionics and Integrated System Engineering Team bus standards, it requires only a few moderate modifications to accommodate the new COWVR Payload in a higher altitude, high inclination, sun-synchronous orbit. Launching in the fall of 2017, ORS-6 will provide operational-like capabilities to the US Air Force weather program while space demonstrating the new bus and payload technology. This paper highlights how the modular construction of the bus allows for timely reconfiguration, assembly, and integration with the payload. Additionally, we present an overview of the COWVR instrument capabilities and how it will serve as a partial gap filler to the Air Force’s Weather System Follow-On program. We emphasize how ORS-6 represents exciting possibilities for future space missions in terms of adaptability, cost savings management, and technological innovation