Tetsuo Yasaka

Low-velocity projectile impact on spacecraft

Abstract Various impact phenomena are encountered in space, among which debris impacts are of most concern. In terms of velocity range of the impacts, structural hazard at very large velocity of over a few km/s is much investigated. However, lower velocity impacts can also be encountered, with similar fatal effects to spacecraft. Examples are debris impacts in geostationary altitude and those onto rear side of spacecraft in low earth orbit. It should be pointed out that debris shield like Whipple bumper system is not effective at low velocities, and no other effective means are known to protect spacecraft from projectiles encounted at less than 1 km / s . A series of laboratory impact tests are conducted to find out characteristics of both structural damages and fragments created and released into space. The major items made clear are that characteristics of fragments are similar to those of hypervelocity impacts. Structural damage to honeycomb panels and mesh-type parabola dishes will be described as examples of debris impact in geostationary orbit. Another example to be investigated is impacts of rocks and steel projectile onto structure of sampling mechanism on a surface of an asteroid, a mission to fly in the year 2002.

Analytical and experimental investigations for satellite antenna deployment mechanisms

This paper deals with the prediction of deployment dynamics , a n t e n n a v ib ra t ion cha rac te r i s t i c a n d reliability evaluation related with ADM necessary for large satellite an tenna development. A stat ist ical analysis is proposed to predict deployment dynamics of a n antenna based on the driving and friction torques of mechanical parts whose statistical distributions a re f i t ted to normal d i s t r ibu t ions . Tes t r e s u l t s a r e comprised within a range of + o (standard deviation) predicted by the analys is . Vibration analys is i s performed to clarify t h e effect of ADM bend ing stiffness. The effect of ADM bending st iffness on antenna natural frequencies was studied analytically to establish a guideline for determination of the ADM bending stiffness. The first natural frequency of the antenna was lessened by 5Hz due to the effect of ADM bending stiffness. A procedure is proposed to evaluate the reliability of the ADM. The failure Mode and Effects Analysis is conducted to identify al l possible failure modes, among which the critical modes are selected for fu r the r inves t igat ions . Deployment reliability is calculated assuming that the deployment r e l i ab i l i t y of t h e ADM m a i n l y d e p e n d s on t h e magnitude of difference between the dr iv ing and friction torque.

Breakup in geostationary orbit: A possible creation of a debris ring

Abstract Fragment creation process due to a possible breakup in geostationary orbit is analyzed. The fragment cloud will cover the whole geostationary ring in a short period and will be hazardous to all geostationary satellites alike for a long period.

Geo debris environment: A model to forecast the next 100 years

Abstract The geostationary orbit is a unique natural resource that mankind will find useful for many generations to come. During a little over than 30 years, more than 600 objects have been placed into this region. Most of these objects were left in stable orbits to remain there for many thousands of years. At least three of these objects experienced fragmentation, whose fragments are too small to be detected from the earth, but are large enough to damage or destroy other satellites. The motion of these objects was analyzed to find out potential collision hazards including longitudinal clustering and sun-moon gravity effects. A breakup model was adopted partly reflecting laboratory experiments. With a simple object accumulation model the debris environment evolution was evaluated, under realistic debris mitigation scenarios to be adopted in the near future.

Orbital debris environment model in the geosynchronous region

The Kyushu University orbital debris environment model in the geosynchronous region has been updated to provide a better and more accurate description and understanding of orbital debris environment than the previous model. The main advantage of the present model over the previous model is to introduce more realistic breakup dispersion to estimate collision hazards to other spacecraft caused by breakup fragments. The results from the new model indicate that all aged satellites should move into a disposal orbit at the end of mission to reduce potential hazards to operational satellites. However, boosting up all aged satellites cannot preserve the current orbital environment sufficiently because debris fragments from explosions are still hazardous to operational satellites. The results also indicate that safekeeping procedures for all rocket bodies and spacecraft that remain in the geosynchronous region after completion of their mission are required as well as in low Earth orbit.

Using NASA Standard Breakup Model to Describe Low-Velocity Impacts on Spacecraft

The applicability is examined of the hypervelocity collision model included in the NASA standard breakup model 2000 revision to low-velocity collisions possible in space, especially in the geosynchronous regime. The analytic method used in the standard breakup model is applied to experimental data from low-velocity impact experiments previously performed at Kyushu University at a velocity range less than 300 oils. The projectiles and target specimens used were stainless steel balls and aluminum honeycomb sandwich panels with face sheets of carbon fiber reinforced plastic, respectively. It is concluded that the hypervelocity collision model in the standard breakup model can be applied to low-velocity collisions with some simple modifications.

Orbital Evolution of Cloud Particles from Explosions of Geosynchronous Objects

Current orbital debris search strategies for telescopes observing in geosynchronous Earth orbit are designed around the known orbital distributions of cataloged objects. However, the majority of cataloged objects are believed to be intact spacecraft and rocket bodies, not the debris particles the searches are intended to locate. If there have been breakups in geosynchronous Earth orbit, the explosions may have put the debris into orbits that are significantly different from those in the catalog. Consequently, observation plans optimized for the catalog population may not be optimized for any unseen debris populations. Some hypothetical cases and a real near-synchronous U.S. Titan IIIC transtage explosion will be presented to demonstrate this effect. Perturbing accelerations to be considered for orbital evolution are the nonspherical part of the Earth’s gravitational attraction and gravitational attractions due to the sun and moon. Solar radiation pressure effects are omitted in this analysis, not because they are unimportant for this type of analysis, but to concentrate on the primary orbit perturbations.

Space debris protection: A standard procedure in future?

Abstract The near earth orbital environment is getting hazardous due to increasing space debris accumulated as a result of human space activities. Man tended facility is being designed so that the main structure may be protected from a collision with a limited size debris. Other space systems are generally found inadequate to possess protection shields because of functional requirement of space-viewing faces and cost burden in terms of added mass. In the future, where the debris hazard is expected to become severer, the situation is not expected to change and most space systems will be left unprotected. The present situation and future projection of the orbital debris environment will be first reviewed. The possible hazard to space systems will be described in terms of colliding debris size at various orbits. Some of the measures to secure safety of the system will be then proposed for future application.

Remarks on orbital environment protection at geostationary altitude: Results from long term breakup simulation

Abstract A program “GEO-Evol” was developed to simulate orbital object population growth in geostationary orbit, taking into consideration the launch rate, re-orbiting rate of satellite at their end-of-life and other fragment production processes. Two parameters are found to be remarkably influential, the re-orbiting rate and explosion rate. Present explosion rate is judged far too large to be accepted. It is strongly suggested that the explosion rate should be reduced by at least two orders of magnitude. Assuming the low explosion rate and high re-orbiting rate, the fragment population at geostationary altitude will be kept sufficiently low for next 200 years and only two operational satellite will be lost due to collision during this period.

The structural feasibility of a gravity stabilized antenna

Abstract A very large Earth oriented antenna structure which is stabilized by the gravity gradient force is analyzed and its feasibility is discussed. Stresses caused by gravity forces are analytically obtained by assuming that the antenna reflector is a spherical membrane. It is shown that a compression membered flexible reflector maintains its contour by adjusting the length of tethers which connect the reflector and the spacecraft main body.