Engineering topics

Merkowitz, Stephen

Publications and source records attributed to Merkowitz, Stephen.

5 records

NASA NTRS2019

The NASA Space Geodesy Network

NASA successfully demonstrated next generation SLR, VLBI, and GNSS using the GGAO prototypes.Tier 1 deployment of next generation stations is underway: KPGO (Kokee Park, Hawaii); VGOS station operational; VGOS station at McDonald Observatory, Texas nearly operational; build of long-lead items for first 3 SLR stations underway. Planning and discussions with international partners for Tier 2 deployment underway. Plan for Decadal Survey responsive deployment acceleration under review by NASA.

Merkowitz, Stephen↗

NASA NTRS2008

Current LISA Spacecraft Design

The Laser Interferometer Space Antenna (LISA) mission, a space based gravitational wave detector, uses laser metrology to measure distance fluctuations between proof masses aboard three spacecraft. LISA is unique from a mission design perspective in that three spacecraft and their associated operations form one distributed science instrument, unlike more conventional missions where an instrument is a component of an individual spacecraft. The design of the LiSA spacecraft is also tightly coupled to the design and requirements of the scientific payload; for this reason it is often referred to as a "sciencecraft." A detailed discussion will be presented that describes the current spacecraft design and mission architecture needed to meet the LISA science requirements.

Merkowitz, Stephen↗

NASA NTRS2004

LISA Propulsion Module Separation Study

The Laser Interferometer Space Antenna (LISA) mission is a space-borne gravitational wave detector consisting of three spacecraft in heliocentric orbit. Each spacecraft is delivered to it operational orbit by a propulsion module. Because of the strict thermal and mass balancing requirements of LISA, the baseline mission concept requires that the propulsion module separate from the sciencecraft after delivery. The only propulsion system currently baselined for the sciencecraft are micronewton level thrusters, such as FEEP or colloid thrusters, that are used to balance the 30-40 microN of solar radiation pressure and provide the drag-free and attitude control of the spacecraft. Due to these thrusters limited authority, the separation of the propulsion module from the sciencecraft must be well controlled to not induce a large tip-off rotation of the sciencecraft. We present here the results of a design study of the propulsion module separation system that is shown to safely deliver the LISA sciencecraft to its final operational orbit.

Merkowitz, Stephen↗

NASA NTRS2004

LISA Thermal Design

The Laser Interferometer Space Antenna (LISA) mission, a space based gravitational wave detector, uses laser metrology to measure distance fluctuations between proof masses aboard three spacecraft. The total acceleration disturbance to each proof mass is required to be below 3 x 10(exp -15) meters per second squared per the square root of Hertz. Optical path length variations on each optical bench must be kept below about 3 pm per the square root of Hertz. Noise due to spacecraft thermal distortions, temperature difference variations across proof mass housing, and other thermal effects are expected to be a significant contributors to these noise budgets. The LISA Integrated Modeling team developed a detailed thermal model that is currently being used to drive the design of LISA. Several new thermal analysis techniques are also being developed in order to achieve model accuracies to LISA levels. We present here an overview of the LISA thermal design and modeling efforts. The latest thermal results calculated using the current baseline design of LISA are also discussed.

Merkowitz, Stephen↗

NASA NTRS2004

Self-Gravity Modeling for LISA

The Laser Interferometer Space Antenna (LISA) mission, a space based gravitational wave detector, uses laser metrology to measure distance fluctuations between proof masses aboard three spacecraft. The total acceleration disturbance to each proof mass is required to be below 3 x 10(exp 15) m/sq square root of Hz. Self-gravity noise due to spacecraft distortion and spacecraft motion is expected to be a significant contributor to the acceleration noise budget. To minimize these effects, the gravitational field at each proof mass must be kept as small, flat, and constant as possible. It is estimated that the static field must be kept below 5 x 10(exp -10) m/sq s with a gradient below 3 x 10(exp -8)/sq s in order to meet the required noise levels. Most likely it will not be possible to directly verify by measurements that the LISA spacecraft meets these requirements; they must be verified by models. The LISA Integrated Modeling team developed a new self-gravity tool that calculates the gravitational forces and moments on the proof masses to aid in the design and verification of the LISA spacecraft. We present here an overview of&e tool and the latest self-gravity results calculated using the current baseline design of LISA. We also present results of a self-gravity analysis of the ST-7 DRS package that will fly on the LISA Pathfinder mission.

Merkowitz, Stephen↗