David Mauro

Heterogeneous Spacecraft Networks: Performance analysis for low-cost Earth Observation missions

Heterogeneous Spacecraft Networks (HSNs) are network environments in which spacecraft from different missions and institutions can communicate with each other at low cost and with low impact on overall system resources. The Mission Design Center (MDC) at NASA Ames Research Center has been studying solutions for low cost multi-spacecraft systems for a number of years. One may now build on the idea to interconnect clusters of spacecraft with each other to have them act as mobile nodes belonging to the same collaborative mission. Recent progress in small satellite technology is significant, and one of the advantages of small satellites lies precisely in the large quantity of spacecraft that can be produced at accessible costs. It follows naturally that small satellites are an interesting candidate platform for development and demonstration of the HSN concept. This paper is the second in a series of three companion papers. The general concept of operations for HSNs in LEO and a number of future applications are proposed in the first paper [6], while enabling technology such as devices and lower layer protocols are discussed in paper three [7]. In this paper, we pick up the scenario of a low-cost and multi-institutional network of Earth Observation (EO) missions in LEO and conduct network performance analysis using the AGI System Tool Kit (STK) and the open-source Network Simulator (NS-3). A multi-spacecraft network consolidates the individual capabilities of each spacecraft from different institutions by combining benefits of both frequent revisit and concentrated observation. Complementary and correlated data could be collected simultaneously from a large set of distributed spacecraft utilizing HSN capability. In this specific configuration, communication distance between spacecraft, related delays and error rate are the major factors in network performance. Also, average duration of communication opportunities between spacecraft is usually very limited. Thus, it is important to simulate orbital dynamics, link margins, and protocols simultaneously to analyze network performances. In this paper, we compare some existing protocols to obtain a measure for the practical performance of the candidate network. We focus on best-effort data delivery, an approach necessitated by the severe constraints on communications resulting from low-cost and low system resource small spacecraft. In the application layer, we show that packet size and data rate of a source node also affect overall performance of the network. We present the resulting figures of merit from our simulations. The paper concludes with a summary of the simulation results.

Heterogeneous Spacecraft Networks: Wireless network technology assessment

Constellations of small satellites are useful for a number of earth observation and space exploration missions. The Heterogeneous Spacecraft Network project is defining operations concepts and promising technology that can provide greater capability at lower cost. Typically, such spacecraft can communicate with each other in orbit and with ground stations for spacecraft operation and downlink of science data. However, small spacecraft often cannot utilize the capability delivered by networks such as the Universal Space Network, even if the mission could afford the cost. Small spacecraft have significant constraints in terms of power availability, attitude stability and overall mass and volume, requiring innovative technology for implementing highly functional satellites. A major challenge for such missions is selecting communications technology able to function in the space environment, able to meet the requirements for both inter-satellite and space-to-ground data links and fit within the resources available on small satellites. Moreover, the cost of the technology needs to be as low as possible to facilitate participation by a broad range of organizations. Finally, the communications networks should conform to standards allowing broad adoption and the use of common infrastructure for multiple missions. Communications technology based on the IEEE 802 family of local area and metropolitan area network standards can be adapted to meet the needs of such missions. This paper will identify possible development paths for improved communication between small satellites and to the ground by reviewing and evaluating standards-based technology for use by small satellite missions. Methods for greatly extending both range and data rate will be proposed and analyzed. It will review and evaluate the IEEE 802.11 wireless network standards, the ITU WCDMA 3G cell phone standard and the IEEE 802.15.4 Personal Area Network standard. A simple set of communication requirements will define the trade offs between standards and identify the technical capability needed for such missions. Specifically, the improvements needed to the Physical Layer to extend range to 1200 Km and the ability to comply with spectrum management constraints will be investigated. Authentication and encryption will be addressed along 1with adjustments to the Media Access Control layer that can optimize data transfer rates over a broad range of distances and conditions. The paper concludes with recommendations for standards-based communication technology development for small satellites supported by the results of this trade study. The primary objective is to greatly reduce the cost of data communication for small satellites by establishing a common infrastructure able to meet the needs of most missions.

CHARM: A CubeSat water vapor radiometer for earth science

The Jet Propulsion Laboratory (JPL) and Ames Research Center (ARC) are partnering in the CubeSat Hydrometric Atmospheric Radiometer Mission (CHARM), a water vapor radiometer integrated on a 3U CubeSat platform, selected for implementation under NASA Hands-On Project Experience (HOPE-3). CHARM will measure 4 channels at 183 GHz water vapor line, subsets of measurements currently performed by larger and more costly spacecraft (e.g. ATMS, AMSU-B and SSMI/S). While flying a payload that supports SMD science objectives, CHARM provides a hands-on opportunity to develop technical, leadership, and project skills. CHARM will furthermore advance the technology readiness level (TRL) of the 183 GHz receiver subsystem from TRL 4 to TRL 6 and the CubeSat 183 GHz radiometer system from TRL 4 to TRL 7.

Heterogeneous Spacecraft Networks: General concept and case study of a cost-effective, multi-institutional Earth observation platform

In recent years the Mission Design Center (MDC) at NASA Ames Research Center has been studying mission concepts involving clusters of small spacecraft capable of providing cost-effective solutions in orbit compared to space missions involving only a single larger spacecraft. Low-cost networks of small spacecraft can be a viable alternative to large budget Earth observation or space exploration missions producing significant scientific return for often moderate development efforts and short lead times. This paper is the first in a series of 3 companion papers in which we make the point that the scientific value (and hence the cost effectiveness) of small multi-spacecraft missions can be further increased if the network of spacecraft is allowed to be heterogeneous. We define Heterogeneous Spacecraft Networks (HSNs) to be networks of spacecraft having different operators or originating from different missions that are able to communicate with each other in a low-cost manner and with low impact on overall system resources. HSN incorporates both the space segment and ground segment for an end-to-end solution. In this contribution we illustrate the strength of the HSN approach by presenting a general concept for a HSN in LEO as well as a case study showcasing the value of such a network. In particular, we present a case study where we examine the feasibility of a low-cost, multi-institutional network of small spacecraft acting as a next-generation Earth Observation (EO) platform and focusing on ad-hoc data relay to maximize throughput. In the simulation we show that the downlink throughput of an HSN can be larger by an order of magnitude compared to the conventional scenario where no networking capability exists. Other benefits of using a HSN as a next-generation increment of existing capabilities include increased revisit frequencies as well as the ability to collect correlated data simultaneously from distributed locations around the globe using either conventional or fractionated spacecraft. We list key performance requirements for a HSN in order to produce a desirable scientific return and present a concept of operations (ConOps) for the practical implementation. In the ConOps we discuss the required performance of the inter-satellite and space-to-ground links and give an overview of the associated ground station network. We give an overview of the network management techniques required to operate and control the network on a day-to-day basis and address the issues of network configuration, network discovery and security, as well as fault and performance management. The paper ends with an outlook on the paradigm shift HSNs may introduce in the domain of space operations. We also list a number of promising applications making use of the strength of the concept.