Charlotte Gerhart

Comparison between analytical predictions and experimental data for a loop heat pipe

Comparisons between steady-state temperature predictions obtained from a loop heat pipe thermal model, developed by Dynatherm Corporation and modified by the authors, with experimental data obtained from an 800W, titanium wick, loop heat pipe located at the Air Force Research Laboratory (AFRL) thermal facility in Albuquerque, NM are discussed. Model predictions are compared with experimentally determined temperature values for several power levels between 50W and 600W and for condenser temperatures between 233 K and 293 K.

Characterization of a high capacity, dual compensation chamber loop heat pipe

Results of acceptance tests at the Institute of Thermal Physics (ITP) in Russia and initial performance tests at the Air Force Research Laboratory (AFRL) of a dual compensation chamber (CC) loop heat pipe (LHP) are compared for three orientations. At steady state, temperatures were higher and heat transfer coefficients and conductance were lower at AFRL. These differences are attributed to higher resistance due to usage, rather than test, mounting and more complex insulation lay-up at AFRL. For the horizontal orientation power (W) and heat flux (W /cm2) reached at IPT and AFRL were 1500 and 10.5, and 900 and 6.3, respectively. AFRL transient data showed brief reverse flow on startup for some runs with power at or below 50 W, at times marked temperature fluctuations, and response to chiller temperature change.

Vibro‐acoustic launch protection experiment (VALPE)

Launch acoustic and vibration loads have the potential to damage sensitive payloads within a payload fairing, often requiring more structural mass to withstand these loads than would otherwise be necessary to survive launch. Experiments demonstrating several vibro‐acoustic mitigation technologies developed by AFRL/VS and its contractors flew on the Vibro‐Acoustic Launch Protection Experiment 2 (VALPE‐2) aboard a Terrier‐Improved Orion sounding rocket from Wallops Island Flight Facility in August 2003. Flight data collected in November 2002 from a nearly identical launch (VALPE‐1) was used to characterize the fairing environment for comparison. Preparations for the flight experiments are discussed along with the performance of the various experiments in flight. The several experiments include an Adaptive Vibro‐Acoustic Device (AVAD) to mitigate acoustic loads, an active/passive hybrid vibration isolation system using voice‐coil actuation and a ShockRing passive component, a voice‐coil regenerative electron...

Variable Emittance Materials Based on Conducting Polymers for Spacecraft Thermal Control

Ashwin‐Ushas has developed a unique, patented Variable Emittance technology based on the infrared (IR) electrochromism of unique Conducting Polymers. This has features of: very thin ( 104 cycles; low power consumption ( 104 cycles; low power consumption (< 40 μW/ cm2); and most importantly, space environment durability (space vacuum and −40 °C to + 75 °C, Solar Wind, gamma radiation to 7.6 Mrad). A demonstrator spaceflight is tentatively planned on NASA‐Goddard’s ST5 mission. This paper describes the features and current status of the technology, including results from the most recent tests. It is shown that the technology is the most promising among proposed new Variable Emittance technologies, and possibly one of the only technologies applicable to microspacecraft, besides also being applicable to large spacecraft, space bas...

Active vibration isolation system for launch load alleviation

Payloads delivered to orbit by expendable launch vehicles experience high levels of vibration. This vibration can cause component failures, or more frequently, lead to extra weight that would otherwise be useful for added functions on orbit. Vibration isolation systems have been flown to protect various components as well as entire spacecraft, dramatically reducing launch loads and saving costs in redesign and tests. Future spacecraft and components may benefit from further load reduction through the use of higher performance active isolation systems. These active systems are capable of introducing compliance in selected axes, while maintaining required rigidity in others. They can also produce excellent isolation without large amplification. Passive and active vibration isolation systems were developed for the Vibro Acoustic Launch Protection Experiment (VALPE) and flew aboard sounding rockets. The paper describes the design and development of the isolation systems, actuation and isolation architectures and control strategies. Integration of two flight experiments is summarized. Ground test results are presented for passive and active systems. Results of the experiments are provided, and recommendations for active vibration isolation are offered.

Initial characterization results of metal wick capillary pumps

In the past 5 years considerable effort has been invested in understanding and improving capillary pumped loop (CPL) technology and many advances have been made, particularly with respect to evaporator designs. With the development of looped heat pipe (LHP) manufacturing capability and expertise outside the former Soviet Union there has been a push to incorporate LHP technology in CPLs to improve their performance. Of particular interest has been the application of sintered metal wicks in the evaporators. Conventional CPL evaporators used polyethene wicks that are generally limited to a minimum pore size of 10 to 15 microns, which severely limited the wicking height of a system against gravity. Metal wicks allow pore sizes to 1 micron and sometimes even less, potentially increasing the wicking height by orders of magnitude. Not only can metal wicks increase the wicking height of the CPL, easing the ground testing restrictions, but they can also theoretically increase the heat flux density of an evaporator...

Overview of the Vibro-Acoustic Launch Protection Experiment at the Air Force Research Laboratory

Experiments demonstrating several vibro-acoustic mitigation technologies will be tested on the Vibro-Acoustic Launch Protection Experiment 2 (VALPE-2) aboard a Terrier-Improved Orion sounding rocket slated for launch from Wallops Island Flight Facility in May 2003. Flight data collected in November 2002 from a nearly identical launch (VALPE-1) is being used to characterize the fairing environment and design the prototype hardware for the second flight. This paper discusses the various experiments that will be tested on the VALPE-2 flight, and presents some of the measured results and lessons learned from the first flight.

University Nanosat System thermal design, analysis, and testing

Thermal design for space systems is an iterative process that balances the temperature requirements for all mission phases with the available resources. Secondary payloads often have to be designed for a wide range of conditions available on various launch platforms, without the benefit of additional resources such as power or thermal shielding. This paper will discuss the thermal design, analysis, and thermal vacuum testing of a small satellite payload that was initially intended for launch from the US Space Shuttle and eventually launched on the EELV Heavy demonstration in December 2004.

The vibro-acoustic launch protection experiment overview and flight results summary

The cost of performing any mission on orbit is a strong function of the cost of getting the mass into orbit and the mass of a spacecraft is driven by the launch loads that the components must be deigned to survive. Additionally, these design loads vary between launch vehicles so if circumstances arise that require a change in launch vehicle significant time and money can be spent in modifying and testing to meet different requirements. Technologies that reduce both the vibration and acoustic environments during launch have the potential to both reduce the design load levels, and eventually equalize them between boosters. To this end the Air Force Research Laboratory, Space Vehicles Directorate in cooperation with the Space Test Program, Boeing SVS, CSA Engineering, and Delta Velocity have been investigating methods to decrease the acoustic and vibration loads induced on payloads by the launch environment and demonstrating them on a sounding rocket launch. The Vibro-Acoustic Launch Protection Experiment (VALPE) mission included an acoustically designed Chamber-Core skin, two passive/active vibration isolation experiments, a passive/active acoustic damping experiment, and an energy recovery experiment integrated onto a Terrier-Improved Orion sounding rocket and launched from NASA Wallops Island. A description of the overall mission, experiments, and general results from the flight test are discussed.