Testing the GRACE follow-on triple mirror assembly

We report on the successful testing of the GRACE follow-on triple mirror assembly (TMA) prototype. This component serves to route the laser beam in a proposed follow-on mission to the Gravity Recovery and Climate Explorer (GRACE) mission, containing an optical instrument for space-based distance measurement between satellites. As part of this, the TMA has to meet a set of stringent requirements on both the optical and mechanical properties. The purpose of the TMA prototype testing is to establish the feasibility of the design, materials choice and fabrication techniques. Here we report on co-alignment testing of this device to the arc second (5 μrad) level and thermal alignment stability testing to 1 μ rad {{K}-1}

Effect of recess on cryogenic flame stabilization

National audienceAbstract: Mechanisms involved in cyrogenic flame stabilization are important in liquid rocker propulsion applications. These mechanisms are studied experimentally in this article by considering a single jet-flame formed by a coaxial injector fed by liquid oxygen (LOX) and gaseous hydrogen (GH(2)). The flame is analyzed by imaging the light emitted by hydroxyl (OH) radicals. To characterize the reaction zone structure one takes the average of the light emission signal. The result of this operation is then treated by numerical tomography (based on rite Abel transform) to get the local volumetric light intensity distribution. This method is used to study the effect of the LOX tube recess on the structure of the flame in the vicinity of the injection plane. It is shown that the recess augments the flame expansion angle and the size of the volume where the reaction takes place. (C) Academie des Sciences/Elsevier, Paris

Effects of a recess on cryogenic flame stabilization

International audienceAbstract: Flame stabilization is a central issue in propulsion applications. In cryogenic liquid rocket engines this process is controlled by a competition between liquid core breakup, atomization, vaporization, and reaction. It is known from practical experience that cryogenic flame stabilization is improved by recessing the liquid oxygen (LOX) tube with respect to the injection plane. This effect is investigated in this article using model scale experiments. A single jet-flame formed by a coaxial injector fed by LOX and gaseous hydrogen (GH(2)) is analyzed by imaging the light emitted by hydroxyl (OH) radicals. To characterize the mean reaction zone structure, the light emission images are averaged and the resulting image is treated by numerical tomography (based on the Abel transform). This yields the local volumetric light intensity distribution. This method is used to examine the modifications in the near flame structure due to the LOX tube recess. It is shown that when the LOX tube is recessed with respect to the injection plane, the flame is stabilized inside the injector, the flame expansion angle is augmented, the thickness of the flame brush and the size of the volume where reaction takes place is enhanced. Effects observed experimentally are quite significant. The phenomenon is interpreted with a simple model relying on a one-dimensional description. When the flame develops inside the duct, it produces hot gases which occupy a certain fraction of the available duct area, the hydrogen stream is accelerated, and consequently the gas to liquid momentum flux ratio J is augmented. The model provides the values of this quantity in terms of the fraction of vaporized oxygen. The augmented value of J, in turn, leads to a faster breakup of the liquid oxygen core, an improved primary atomization, and a corresponding augmentation of the flame blooming angle and combustion volume