No abstract

This study describes a computer simulation that provides an accurate calculation of the touchdown conditions. The program is small enough to operate on a personal computer. The program simulates the Orbiter trajectory from an altitude of 10,000 ft to the Earth's surface. It assumes the Orbiter flies close to its reference altitude profile, with negligible crosswind effects. Flight data have proven both assumptions to be valid. By incorporating these assumptions with the Shuttle guidance logic, a quick approximation can be made of the touchdown speed and downrange distance to an accuracy within 400 ft of the mainframe prediction. Nomenclature= change in C D due to elevens Q?ge = change in C D due to the ground effects Q>i g = change in C D due to the landing gear C Dsb = change in C D due to the speedbrake C £>ref = CD corresponding to reference speedbrake position Q/SB = C D to speedbrake deflection ratio D = ground relative drag Z>oo = drag relative to the freestreem F = total aerodynamic force on the vehicle g = gravitational constants, =32.174ft/s 2 h = vehicle altitude h = vehicle altitude ratê sb = speedbrake control constant, = 2 deg x s/ft sbi = speedbrake integral multiplicative constant, = 0.1 deg/ft L = ground relative lift LOO = freestream lift force m = mass of the vehicle <7 = dynamic pressure 5 = vehicle wing area, = 2690 ft 2 SBDEF = commanded speedbrake deflection SB ref = reference speedbrake position, = 65 deg S bi = integral multiplicative factor V = ground relative velocitŷ eas = equivalent airspeed error = equivalent airspeed error, = F eas -490 KOO = freestream Orbiter velocity at altitude V = ground relative deceleration K 2 = updated ground relative velocity V w = velocity of the wind j8 = constant for air density calculation F = landing gear deployment angle 7 = ground relative flight-path angle 7 = ground relative flight-path angle rate 700 = freestream flight-path angle AS = vehicle displacement At = time step 0 = vehicle pitch angle p a = air density of the freestream at altitude P 0 = air density at sea level for 62 standard atmosphere $ = angle between the relative drag and the total aerodynamic force on the vehicle

4x6 m elli ptic al (pa rab olic) prim ary cold stop se co nd ar y (el lip so ida l) focal plane instrument package

No abstract

With a final decision on the mission still pending, renewed preparations for a fifth Space Shuttle-based Servicing Mission (SM4) to the Hubble Space Telescope (HST) began in 2005. Since inception, HST was designed to be serviced, not only to refurbish or replace degraded and nonfunctional components, but also to infuse new technology into the Observatory. Over its 15-year span, HST has experienced all of the above cases. Its long life has necessitated the installation of new hardware such as a solid-state recorder, gyros, and instruments. At the same time, the spacecraft has pioneered technological advances in spacebased electronics and instruments. These advances range from a space-qualified 486 computer to state-of-the art imaging cameras and spectrographs spanning a range of wavelengths. For this upcoming servicing mission, HST will experience this two-fold process again with the replacement of hardware such as a new complement of six gyros, six new batteries, a refurbished fine guidance sensor, and three new outer blanket panels. Two new scientific instruments --Wide Field Camera 3 (WFC3) and Cosmic Origins Spectrograph (COS) will also be installed. With these improvements, the Observatory will continue to provide cutting edge capabilities with an extended lifetime well into the next decade. This paper will provide an overview of the planning and unique challenges of the SM-4 mission from an operational aspect, and describe in more detail the hardware to be installed. Additionally, the greatly expanded and unique scientific opportunities enabled by the installation of the new scientific instruments will be discussed.