Jeff Greason - Academia.edu (original) (raw)

Papers by Jeff Greason

SAE technical paper series, Sep 17, 2007

Progress toward developing an evaluation process for interstellar propulsion and power options is... more Progress toward developing an evaluation process for interstellar propulsion and power options is described. The goal is to contrast the challenges, mission choices, and emerging prospects for propulsion and power, to identify which prospects might be more advantageous and under what circumstances, and to identify which technology details might have greater impacts. Unlike prior studies, the infrastructure expenses and prospects for breakthrough advances are included. This first year's focus is on determining the key questions to enable the analysis. Accordingly, a work breakdown structure to organize the information and associated list of variables is offered. A flow diagram of the basic analysis is presented, as well as more detailed methods to convert the performance measures of disparate propulsion methods into common measures of energy, mass, time, and power. Other methods for equitable comparisons include evaluating the prospects under the same assumptions of payload, mission trajectory, and available energy. Missions are divided into three eras of readiness (precursors, era of infrastructure, and era of breakthroughs) as a first step before proceeding to include comparisons of technology advancement rates. Final evaluation "figures of merit" are offered. Preliminary lists of mission architectures and propulsion prospects are provided.

48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Apr 23, 2007

[Abstract] XCOR Aerospace has progressed in making fluoropolymer composite material suitable for ... more [Abstract] XCOR Aerospace has progressed in making fluoropolymer composite material suitable for lightweight, oxygen compatible, linerless LOX tanks for propulsion, fuel cell, and life support applications. A twelve-month NASA program assisted us in the development of a composite liquid oxygen tank that can serve as an integral part of vehicle structure, in a skin-foam-skin structural sandwich, as compared to a tank that has to be suspended within the vehicle structure. The principal benefit of this material over graphite/epoxy is its non-combustibility. Also, compared to aluminum it has lower density, lower coefficient of thermal expansion (CTE), and higher strength. This paper discusses the results of XCOR’s efforts to make and test skin coupons, sandwich coupons, and cylinders made of this new thermoplastic fluoropolymer composite material.

IEEE Journal of Solid-State Circuits, 1992

A microprocessor clock generator based upon an analog phase-locked loop (PLL) is described for de... more A microprocessor clock generator based upon an analog phase-locked loop (PLL) is described for deskewing the internal logic control clock to an external system clock. This PLL is fully integrated onto a 1.2-million-transistor microprocessor in 0. 8-p CMOS technology without the need for external components. It operates with a lock range from 5 up to 110 MHz. The clock skew is less than 0.1 ns, with a peak-to-peak jitter of less than 0.3 ns for a 50-MHz system clock frequency.

Journal of the British Interplanetary Society

A new class of reaction drive is discussed, in which reaction mass is expelled from a vehicle usi... more A new class of reaction drive is discussed, in which reaction mass is expelled from a vehicle using power extracted from the relative motion of the vehicle and the surrounding medium, such as the solar wind. The physics of this type of drive are reviewed and shown to permit high velocity changes with modest mass ratio while conserving energy and momentum according to well-established physical principles. A comparison to past propulsion methods and propulsion classification studies suggests new mission possibilities for this type of drive. An example of how this principle might be embodied in hardware suggests accelerations sufficient for outer solar system missions, with shorter trip times and lower mass ratios than chemical rockets. Keywords: Propulsion, Reaction drive, Solar wind, External power, Dynamic pressure

AIAA Nuclear & Future Flight Propulsion Committee ‐ Practical Interplanetary Propulsion (... more AIAA Nuclear & Future Flight Propulsion Committee ‐ Practical Interplanetary Propulsion (PIP) Group: The trajectory to the Trappist‐1 Solar Gravity Lens (SGL)was initially modeled in an internal seed code and then designed in Thinking Systems' Astrodynamics Workbench, as shown in Figure 1. The 6.9 year trajectory to the SGL, along with its projection on the celestial sphere, is shown on the left. Pathfinder reaches its 390 km/s cruising speed quickly. Once the trajectory model was complete, the PIP Group searched for targets of opportunity along its path. The right side of Figure 1 shows a collection of Trans‐Neptunian Objects (along with Centaur asteroids) considered for flyby opportunities along the trajectory, and includes a modeled close approach to fly‐by one of those objects.

Publications of the Astronomical Society of the Pacific, 134:023001 (11pp), 2022 February, 2022

The Jupiter Observing Velocity Experiment (JOVE) is a solar-powered technology demonstration of r... more The Jupiter Observing Velocity Experiment (JOVE) is a solar-powered technology demonstration of rapid flight to outer solar system targets, performing a flyby of Jupiter 30 days after launch. This is achieved using a magnetic drag device to accelerate with the solar wind plasma. This "Wind Rider" propulsion system can potentially also decelerate against the Jovian magnetosphere dawn eddy, to enable Jupiter orbital insertion in future missions. The 16U cubesat bus contains scientific instruments to record the plasma parameters from the vicinity of the spacecraft, with principal measurements coming from a SPAN-I ion velocity sensor. This paper includes a description of the propulsive mechanisms and supporting subsystems and trajectory simulation results derived from solar wind measurements over the past two solar cycles. The objectives of the JOVE technology demonstrator design include: (1) verify Wind Rider stability and control; (2) characterize loss mechanisms in the solar wind, such as resistive losses in the plasma, as well as the magnetic field transient interaction time; (3) operate onboard instruments to measure the velocity and direction of the solar wind (SPAN-Ai) and speed of the spacecraft relative to the Earth (radio Doppler shift), to enable precision navigation on future science missions; and (4) characterize the Lift-to-Drag ratio of the plasma magnetic field. (The lift force enables lateral course control and maneuvering within the solar wind.) Applying existing scientific data from Voyagers and other deep space probes into new engineering models was important for enabling new insights about Wind Rider propulsion. It enables more science to be performed in a shorter amount of time, across the Jovian system.

Publications of the Astronomical Society of the Pacific, 2022

Solid State Technology, 1992

The scalability of partially depleted (PD) SO1 with a floating body has been evaluated to below t... more The scalability of partially depleted (PD) SO1 with a floating body has been evaluated to below the sub-0.25ym regime using transistors, ring oscillators and 4 Mb SRAMs as test vehicles. In this piaper the speed and power performance of PD-SO1 are compared to those of bulk for 1.8V/sub-0.25pm logic applications. In addition, the 4Mb SO1 SRAM yield issues are revealid. Using the same transistor off-state leakage current limit criterion for both bulk and SOI, we conclude that PDSOI with a floating body will provide no speed and insignificant power advantage over bulk for sub0.25pm logic applications.

1991 Symposium on VLSI Circuits, 1991

Solid-State Circuits IEEE International Conference, 1992

The authors describe a phase-locked-loop (PLL)-based deskewed clock generator that is fully integ... more The authors describe a phase-locked-loop (PLL)-based deskewed clock generator that is fully integrated with a microprocessor and achieves a skew of less than 0.1 ns with peak-to-peak jitter of 0.45 ns using an 0.8-μm CMOS technology. The block diagram of the deskewed clock generator is shown along with the measured schmoo diagram of the PLL clock generator functionality frequency versus

VLSI Technology, Symposium, 1997

... to NMOS leakage since if all the inputs to the NMOS devices are low, the high ... Figure 2 sh... more ... to NMOS leakage since if all the inputs to the NMOS devices are low, the high ... Figure 2 shows the delay versus power for static and dynamic implementations of two circuits in ... Deep SubmicronTransistor Leakage It is the poor tolerance to deep sub-micron transistors leakage in ...

VLSI Circuits, 1997. …, 1997

15 4-93081 3-76-X 1997 Symposium on VLSI Circuits Digest of Technical Papers ... This timing can ... more 15 4-93081 3-76-X 1997 Symposium on VLSI Circuits Digest of Technical Papers ... This timing can tolerate some phase uncertainty, and is timed by a simple chain of inverters from the sense amp enable. Acknowledgments The authors wish to thank Angie Bell, Bill Benefiel, ...

Electron Devices …, 1996

A 0.25\ μm generation logic technology has been developed with high performance transistors and f... more A 0.25\ μm generation logic technology has been developed with high performance transistors and five layers of planarized interconnect. The transistors are optimized for 1.8 V operation to provide high performance, low power and good reliability. The interconnects ...

SAE technical paper series, Sep 17, 2007

48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Apr 23, 2007

IEEE Journal of Solid-State Circuits, 1992

Journal of the British Interplanetary Society

Publications of the Astronomical Society of the Pacific, 134:023001 (11pp), 2022 February, 2022

Publications of the Astronomical Society of the Pacific, 2022

Solid State Technology, 1992

1991 Symposium on VLSI Circuits, 1991

Solid-State Circuits IEEE International Conference, 1992

VLSI Technology, Symposium, 1997

VLSI Circuits, 1997. …, 1997

Electron Devices …, 1996

AGU 2021 Fall Meeting, 2021

AIAA Nuclear & Future Flight Propulsion Committee ‐ Practical Interplanetary Propulsion (PIP) Gro... more AIAA Nuclear & Future Flight Propulsion Committee ‐ Practical Interplanetary Propulsion (PIP) Group: The trajectory to the Trappist‐1 Solar Gravity Lens (SGL)was initially modeled in an internal seed code and then designed in Thinking Systems' Astrodynamics Workbench, as shown in Figure 1. The 6.9 year trajectory to the SGL, along with its projection on the celestial sphere, is shown on the left. Pathfinder reaches its 390 km/s cruising speed quickly. Once the trajectory model was complete, the PIP Group searched for targets of opportunity along its path. The right side of Figure 1 shows a collection of Trans‐Neptunian Objects (along with Centaur asteroids) considered for flyby opportunities along the trajectory, and includes a modeled close approach to fly‐by one of those objects.