DAS Reentry Survivability Analysis

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Evaluating and Addressing Potential Hazards of Fuel Tanks Surviving Atmospheric Reentry

In order to ensure reentering spacecraft do not pose an undue risk to the Earth's population it is important to design satellites and rocket bodies with end of life considerations in mind. In addition to considering the possible consequences of deorbiting a vehicle, consideration must also be given to the possible risks associated with a vehicle failing to become operational or reach its intended orbit. Based on recovered space debris and numerous reentry survivability analyses, fuel tanks are of particular concern in both of these considerations. Most spacecraft utilize some type of fuel tank as part of their propulsion system. These fuel tanks are most often constructed using stainless steel or titanium and are filled with potentially hazardous substances such as hydrazine and nitrogen tetroxide. For a vehicle which has reached its scheduled end of mission the contents of the tanks are typically depleted. In this scenario the use of stainless steel and titanium results in the tanks posing a risk to people and property do to the high melting point and large heat of ablation of these materials leading to likely survival of the tank during reentry. If a large portion of the fuel is not depleted prior to reentry, there is the added risk of hazardous substance being released when the tank impact the ground. This paper presents a discussion of proactive methods which have been utilized by NASA satellite projects to address the risks associated with fuel tanks reentering the atmosphere. In particular it will address the design of a demiseable fuel tank as well as the evaluation of off the shelf designs which are selected to burst during reentry

A Flight Study of the Conversion Maneuver of a Tilt-Duct VTOL Aircraft

Flight records are presented from an early flight test of a wing-tip mounted tilting-ducted-fan, vertical-take-off and landing (VTOL) aircraft configuration. Time histories of the aircraft motions, control positions, and duct pitching-moment variation are presented to illustrate the characteristics of the aircraft in hovering, in conversion from hovering to forward flight, and in conversion from forward flight to hovering. The results indicate that during essentially continuous slow level- flight conversions, this aircraft experiences excessive longitudinal trim changes. Studies have shown that the large trim changes are caused primarily by the variation of aerodynamic moments acting on the duct units. Action of the duct-induced downwash on the horizontal stabilizer during the conversion also contributes to the longitudinal trim variations. Time histories of hovering and slow vertical descent in the final stages of landing in calm air show angular motions of the aircraft as great as +/- 10 deg. about all axes. Stick and pedal displacements required to control the aircraft during the landing maneuver were on the order of 50 to 60 percent of the total travel available

Eastward Ho: Issues and Options in Regional Development for the Metropolitan Boston Region

Conventional wisdom suggests that the basic job of public policy studies (and public institutions, for that matter) is to deal in a timely and practical fashion with pressing public issues of the day. The focus typically is on \u27ripe\u27 topics, \u27hot\u27 political problems. If a study can be ahead of the curve, in John Kingdon\u27s apt phrase an idea whose time has come, so much the better. But unlike more traditional academic research, where the focus is timeless — i.e., an explanation of previously inexplicable phenomena, timeliness is a prime reason for initiating a policy study. In this context, analyzing the prospects for regional governance in Massachusetts and New England and suggesting the creation of any new arrangement for metropolitan regions for the Commonwealth seems premature or, at best, wishful thinking. But these are not conventional times. Wrenching changes in welfare, education, and health care are accelerating in a nation being demographically transformed. Three important forces are at work which suggest that regional goverment may be a timely topic after all. First, as we will describe, the academic community is giving some priority to the subject after two generations of neglect. Second, in a time of budgetary constraints, the economic development strategies of metropolitan communities increasingly require a global perspective that emphasizes the interdependence of central city and surrounding suburbs in achieving and maintaining an international competitive advantage. Especially in Massachusetts, given the effects of Proposition 2 1/2 and pressures on the costs of land and home ownership, the need to develop and articulate a common metropolitan economic strategy grows. Third, political forces speak increasingly to the ineffectiveness of local governments in coping with the critical issues of the day. In the midst of the Big Dig and a long-term inability to site a new convention center and a stadium within the metropolitan Boston region, how to plan and provide key metropolitan infrastructure is definitely a \u27hot\u27 political issue

High-dose rate brachytherapy (HDRB) for primary or recurrent cancer in the vagina

PURPOSE: The purpose of this study was to evaluate the efficacy of HDR brachytherapy for primary or recurrent vaginal cancer. METHODS: Between the years 2000 to 2006, 18 patients with primary or recurrent vaginal cancer were treated with brachytherapy (HDRB). Six patients had primary vaginal cancer (stage II to IVA) while 12 were treated for isolated vaginal recurrence (primary cervix = 4, vulva = 1 and endometrium = 7). Five patients had previous pelvic radiation therapy. All except one patient received external beam radiation therapy to a median dose of 45 Gy (range 31.2–55.8 Gy). The HDRB was intracavitary using a vaginal cylinder in 5 patients and interstitial using a modified Syed-Nesblett template in 13 patients. The dose of interstitial brachytherapy was 18.75 Gy in 5 fractions delivered twice daily. The median follow-up was 18 months (range 6–66 months). RESULTS: Complete response (CR) was achieved in all but one patient (94%). Of these 17 patients achieving a CR, 1 had local recurrence and 3 had systemic recurrence at a median time of 6 months (range 6–22 months). The 2-year actuarial local control and cause-specific survival for the entire group were 88% and 82.5%, respectively. In subset analysis, the crude local control was 100% for primary vaginal cancer, 100% for the group with recurrence without any prior radiation and 67% for group with recurrence and prior radiation therapy. Two patients had late grade 3 or higher morbidity (rectovaginal fistula in one patient and chronic vaginal ulcer resulting in bleeding in one patient). Both these patients had prior radiation therapy. CONCLUSION: Our small series suggests that HDRB is efficacious for primary or recurrent vaginal cancer. Patients treated with primary disease and those with recurrent disease without prior irradiation have the greatest benefit from HDRB in this setting. The salvage rate for patients with prior radiation therapy is lower with a higher risk of significant complications. Additional patients and follow-up are ongoing to determine the long-term efficacy of this approach