A Proposed International Tropical Reference Atmosphere up to 1000 km

Motivated by the need in many aerospace applications for a meaningful reference atmosphere characteristic of the whole of the tropics in both the northern and southern hemispheres of the globe, a proposal was made earlier by the authors for altitudes up to 80 km. This proposal is here based on balloonsonde, rocketsonde, grenade, falling sphere and satellite data in the range 0 to 100 km, and on the MSIS- 83 model from 100 to 1000 km. The proposal consists of linear segments in the temperature distribution with values in degrees Celsius of 27, −9, −74, −5,−5, −74 and −80.4 at geopotential altitudes of 0, 6, 16, 46, 51, 74 and 84.69 km (= 86 km geometric altitude) respectively, beyond which the description is in terms of geometric altitude. A linear segment between 86 and 97 km with a lapse rate of $0.6^0C/km$ is followed by an elliptic variation commencing with atemperature gradient of zero at 97 km to reach at 110 km a temperature of $−45^0C$ with a gradient of $15^0C/km$. This gradient remains constant up to 120 km where the temperature is $105^0C$. Beyond 120 km the temperature distribution follows a Bates type of profile up to 1000 km to reach a value there of $760^0C$. A sea level pressure of 1010 mb and an acceleration due to gravity of $9.78852 ms^{-2}$ corresponding to the Tropic of Cancer are used in the preparation of the atmospheric tables

Simulation and modelling of orbital debris environment by equivalent breakups

It is well known that the increasing space activities pose a serious threat to future missions. This is mainly due to the presence of spent stages, rockets spacecraft and fragments which can lead to collisions. The calculation of the collision probability of future space vehicles with the orbital debris is necessary for estimating the risk. There is lack of adequately catalogued and openly available detailed information on the explosion characteristics of trackable and untrackable debris data. Such a situation compels one to develop suitable mathematical modelling of the explosion and the resultant debris environment. Based on a study of the available information regarding the fragmentation, subsequent evolution and observation, it turns out to be possible to develop such a mathematical model connecting the dynamical features of the fragmentation with the geometrical/orbital characteristics of the debris and representing the environment through the idea of equivalent breakup. (C) 1997 COSPAR

Relative position and attitude estimation and control schemes for the final phase of an autonomous docking mission of spacecraft

This paper describe schemes for onboard relative position and attitude estimation and control for the final translational phase of an autonomous space rendezvous and docking system. Different estimators for attitude and position parameters based on a vision system-outputs are given. Relative position control based on-phase-plane control technique and relative attitude control based on relative quaternion feedback scheme are described. Based on the study, it turns out that fixed gain observers are sufficient for the estimation of position and attitude. Sensitivity of different parameters on these estimators and controllers are also described. A detailed computer simulation provides the,expected range of parameters for which a successful maneuver towards the target can be achieved

Engine Control in Hybrid Applications

Den strängare emissionslagstiftning har drivit motorutvecklingen till att förbättra utsläppen från förbränningsmotorn. Ett effektivt sätt att minska utsläppen motorutsläppen är att använda en elmotor, d.v.s. hybridisera fordonet. Transienta emissioner är ett område där en minskning av utsläppen kan uppnås. Denna studie kommer att fokusera på hur transienta emissioner och specifik bränsleförbrukning kan minskas och hur körbarheten kan förbättras med hjälp av en elmotor som ett stöd vid transient körningar av förbränningsmotorn. Genom att låta lastuppbyggnaden av förbränningsmotorn rampas upp till den begärda lasten och låta den elmotorn ta den resterande belastningen, skulle en reducering av emissioner ske. Målet är att finna en strategi hur förbränningsmotorn och elmotorn bör kontrolleras för att reducera utsläppen, den specifik bränsleförbrukningen och körbarheten. Datainsamlingen genomfördes genom ett automattest innan examensarbetet påbörjades. Testet simulerar en elektrisk motor och är baserad på en transientcykel bestående av tre stegsvar. Sju olika ramptider och sju motorhastigheter tillsammans med nio olika laststeg användes under provet. Resultaten visade att de transienta NOx-emissionerna är den begränsande faktorn för strategin av styrningen. Det visades att NOx- och PM-emissioner under positiva transienter kan minskas vid varvtal under 1000 rpm och vid långsamma turbo responser för ramptider på två till tio sekunder. Den negativa transienten minskar eller påverkas inte vid dessa situationer. För situationer med snabba turbo responser, kunde ingen vinst ses. Tillsammans med resultaten och parametrar såsom, luftmassflödet, motorbelastning och varvtal, utvecklades en strategi för hur man kan styra förbränningsmotorn och elmotorn.Stricter legislation of emissions has forced the engine developers to improve the ICE emissions. One effective way to reducing the engine-out emissions is to utilize an electric motor, i.e. hybridize the vehicle. Transient emissions are an area where a gain in emissions can be achieved. This study will focus on how transient emissions and specific fuel consumption can be reduced, and how the driveability can be improved by using an electric motor as a support during transient operating of the ICE. By letting the load build up of the ICE be ramped up to the demanded load and letting the electric motor taking the remaining load, this could be achieved. The goal is to find a strategy how the ICE and the electric motor should be controlled to fulfill the reduction in emissions and specific fuel consumption, and the driveability. The data acquisition was conducted through an automatic test before the thesis began. The test simulates an electric motor and is based on a transient cycle consisting of three step responses. Seven different ramp times and seven engine speeds, together with nine different load steps was used during the test. The results showed that transient NOx-emissions is the limiting factor for the control strategy. It was showed that the NOx- and PM-emissioins during positive transients could be reduced at engine speeds below 1000 rpm and at slow turbo responses for ramp times of two to ten seconds. The negative transient will decrease or not be effected at all during these situations. For situations with high turbo boost responses, no gain could be seen. Together with the results and inputs such as; air mass flow, engine load and engine speed, a strategy of how to control the ICE and the electric motor was developed

Reference annual atmospheres for midlatitude and tropics

Many aerospace and scientific applications require the specification of the atmospheric properties at various locations, UT and seasons for a range of solar and geomagnetic activity. The nature and mechanisms of the lower and upper atmospheres are different so also their models. Further there is a need to match these models and this is accomplished here in a simple way. In the revision of CIRA 1972 in 1986, the reference middle atmospheres is not yet complete. Two annual reference atmospheres from sea level up to 2000 km for the midlatitude and the tropics is proposed. Other monthly reference atmospheres as also the structure of the atmospheric tables to be provided in the above document is also indicated

A posterior semi-stochastic low Earth debris on-orbit breakup simulation model

A posterior modeling approach for on-orbit breakup, named ASSEMBLE (ASemi-Stochastic Environment Modeling of Breakup in LEO), is proposed.The main objectives of this paper are the statistical characterization of the orbital and physical parameters of the fragments generated by a non-orbit breakup. The analysis of two line element (TLE) data of the fragments of some fragmentation events, such as the Indian PSLV-TES rocket body breakup, showed their orbital parameters obey statistical distributions. The apogee or perigee height, limited by breakup altitude, and the inclination follow Laplace distributions, while the eccentricity a Lognormal distribution. Subsequently, suitable empirical relations in the literature help to expand the fragmentation scenario to mass, effective area, and ballistic coefficient. Lastly, the simulation of well-known historical breakups of (i) SPOT I rocket body,(ii) COSMOS 1813, (iii) STEP II rocket body, and (iv) CBERS I/ SAC Iprovide further confidence in the present model for orbital debrisstudies

Single-resolution and multiresolution extended-Kalman-filter-based reconstruction approaches to optical refraction tomography

The problem of reconstruction of a refractive-index distribution (RID) in optical refraction tomography (ORT) with optical path-length difference (OPD) data is solved using two adaptive-estimation-based extended-Kalman-filter (EKF) approaches. First, a basic single-resolution EKF (SR-EKF) is applied to a state variable model describing the tomographic process, to estimate the RID of an optically transparent refracting object from noisy OPD data. The initialization of the biases and covariances corresponding to the state and measurement noise is discussed. The state and measurement noise biases and covariances are adaptively estimated. An EKF is then applied to the wavelet-transformed state variable model to yield a wavelet-based multiresolution EKF (MR-EKF) solution approach. To numerically validate the adaptive EKF approaches, we evaluate them with benchmark studies of standard stationary cases, where comparative results with commonly used efficient deterministic approaches can be obtained. Detailed reconstruction studies for the SR-EKF and two versions of the MR-EKF (with Haar and Daubechies-4 wavelets) compare well with those obtained from a typically used variant of the (deterministic) algebraic reconstruction technique, the average correction per projection method, thus establishing the capability of the EKF for ORT. To the best of our knowledge, the present work contains unique reconstruction studies encompassing the use of EKF for ORT in single-resolution and multiresolution formulations, and also in the use of adaptive estimation of the EKF's noise covariances. (C) 2010 Optical Society of Americ

Relook into the historical progress and philosophy of Indian space exploration

A study of the history and philosophy of the contribution of India towards the exploration of space since antiquity provides interesting insights. The contributions are described during the three periods namely: (1) the ten millenniums from 10,000 BC with a twilight period up to 900 AD; (2) the ten centuries from 900 AD to 1900 AD; and (3) the ten decades from 1900 AD to 2000 AD; called mythological, medieval, and modern respectively. Some important events during the above periods provide a reference view of the progress. The Vedas during the mythological period and the Siddhantas during the medieval periods, which are based on astronomical observations, indicate that the Indian contribution preceded other cultures. But most Western historians ignore this fact time and again in spite of many proofs provided to the contrary. This chapter also shows that Indians had the proper scientific attitude of developing any physical theory through the triplet of mind, model, and measurements. It is this same triplet that forms the basis of the present day well known Kalman filter technique. Up to about 1500 BC the Indian contribution was leading but during foreign invasion and occupation it lagged and has been improving only after independence

A constant gain Kalman filter approach for the prediction of re-entry of risk objects

The accurate estimation of the predicted re-entry time of decaying space debris objects is very important for proper planning of mitigation strategies and hazard assessment. This paper highlights the implementation strategies adopted for the online reentry prediction using Kalman filter approach with constant gains with the states being the semi-major axis, eccentricity and ballistic coefficient and using the measurements of the apogee height and perigee height derived from the Two Line Elements provided by agencies like USSPACECOM. Only a very simple model is utilised for the orbit propagation and a basic feature of the present approach is that any unmodellable state and measurement errors can be accounted for by adjusting the Kalman gains which are chosen based on a suitable cost function. In this paper we provide the details of validating this approach by utilising three re-entries of debris objects, namely, US Sat. No. 25947, SROSS-C2 Satellite and COSMOS 1043 rocket body. These three objects re-entered the Earth's atmosphere on 4th March 2000, 12th July 2001 and 19th January 2002, respectively

New Approach for the Evolution and Expansion of Space Debris Scenario

The evolution of the space debris scenario consisting of a very large number of fragments is described using the propagation of the characteristics of equivalent fragments without propagating each and every individual debris fragment. This is similar to characterizing a fluid in terms of the average density, pressure, and temperature without considering the velocities of individual molecules in a fluid element. The space debris fragments are assigned to a three-dimensional bin of semimajor axis, eccentricity, and ballistic coefficient. A suitably defined representative semimajor axis, eccentricity, and an equivalent ballistic coefficient (a, e, B) are defined for the equivalent fragments in each of the bins.Aconstant gain Kalman filtering technique based on 1) propagating the above characteristics, and 2) updating them as and when further measurements become available, has been proposed. Further the assimilation of the information from other breakups with the passage of time is also possible. The robustness of the constant Kalman gain approach instead of using the Kalman filter statistics helps to handle better the unmodeled or unmodelable errors due to the finite bin size and the environmental perturbations. This methodology is also suggested to handle massive atmospheric data assimilation problems