Justification for launching from French Guiana whichis near to equatorAswe all know near the equator, the surface of the Earth is traveling faster. Ifwe look at two spots from pole to pole, one spot on the equator and the other ishalfway to the pole, so each will make a complete revolution in 24 hours in aloop. But since the Earth’s shape is round, and the widest point is at theequator the spot on the equator would have to cover more miles in that twentyfour hours. That means that the land is moving faster at the equator than anyother place on the surface of the Earth. The land at the equator is moving 1670 km perhour whereas land halfway to the pole is only moving 1180 km per hour, so thisgives us an advantage by launching from the equator the spacecraft travels almost500 km/hour faster once it is launched.Hohman-transfer orbitThetransfer process to the final orbit will be perform by using a Hohman Transferorbit.
The parking orbit (200-300 Km) of the satellite will be a lower circularorbit. This maneuver is used to perform a transfer between two circular orbitsof different radii in the same plane. Two engine impulses will be used as seenin figure below.
Theorbit transfer process from the lower circular orbit occurs by firing the firstimpulse in the perigee section of the Earth to transfer it to the ellipticalorbit where it moves to the elliptical orbit where it performs the secondimpulse that will transfer the satellite from its elliptical orbit to thehigher circular orbit. InGEO position. Orbit maneuvers are necessary in order to decrease inclination ormove the satellite in emergency scenarios this movements will be perform bydelta-burns.
After operations and completion of the mission the satellite willuse the remaing fuel to deorbit or to move itself to the “disposal orbit”.Since a GEO orbit satellite is quite expensive to recover we deorbit it aroundthe earth and burn it in the atmosphere. That requires delta-v to move thesatellite into a graveyard orbit is about 11 m/s.
EnvironmentDueto the satellites location it is exposed to environmental effects such as highradiation. The satellite has to be protected from this effects, satellitedesign engineer has to take in to account the space weather and environment,with the use of radiation models we can determine how the satellite will beaffected to space weather. Cahoy study states that a satellite’s radiationexposure may vary depending on its orbit. For instance, some orbits are moredangerous than others; engineers needs to select components and materials thatcan survive and operate in such environmentsCahoyand Lohmeyer discovered that many amplifiers where affected during times ofhigh-energy electron activity, a phenomenon that occurs during the solar cycle,in which the sun’s activity fluctuates over a period of 11 years.
The high-energyelectrons flux is higher during the declining phase of the solar cycle. Takinginto account all these various effects our satellite has to be designed in orderto operate under such harsh conditions for a long time.PayloadsSatellitehas to receive all the buoys’ data and retransmit it in real time to thenearest ground station in our case it can be the Santiago de Chile’s. In orderto do that a repeater is needed on the satellite working at two frequencies foruplink and downlink.Thetotal latency will be the sum of the free-path (250ms), the computational delayof the satellite and the time response of the ground stations.
Its latencydepends mainly on the distance to the orbit and the ground equipment which canbe assumed as an instantaneous system.Havingthe sensors on the buoys the resolution is maximum and power consumption of thesatellite is just needed to operate the radio equipment, which can be obtainedvia solar panels.Additionally,buoys need energy which can be obtained by batteries and solar panels. As thelifetime of the mission is high (7 years) the need of alternative power sourcesis needed for the “Tsunameter” or may use different type of sensors attached tobuoys. We have checked that for a GEO and a buoy would be enough to cover inreal time.For meteorological purposes, wewould need to include a camera on the visible and the infrared spectrum and aHigh-resolution visible HRV imaging of half of the Earth’s disc and altimeter.
OperationDetectionof tsunamis by DART systemsThedetection of tsunamis is carried out by the Deep-ocean Assessment and Reportingof Tsunami (DART) solution. DART systems consist of an anchored seafloor bottompressure recorder (BPR) and a companion moored surface buoy for real-timecommunications. Sensors that measure the pressure at fixed points on theseafloor in a quiet environment of the deep waters.Whentsunami occurs, the change in pressure is observed on the seafloor and detectedby the sensors. An acoustic link transmits data from the BPR on the seafloor tothe surface buoy. The BPR collects temperature and pressure at 15-secondintervals.
The pressure values are corrected for temperature effects and thepressure is converted to an estimated sea-surface height (height of the oceansurface above the seafloor) by using a constant 670 mm Hg.Thesystem has two data reporting modes, standard and event. The system operatesroutinely in standard mode, in whichfour spot values (of the 15-s data) at 15-minute intervals of the estimated seasurface height are reported at scheduled transmission times the initial fewminutes, followed by 1-minute averages.Event mode messages also containthe time of the initial occurrence of the event.
The system returns to standardtransmission after 4 hours of 1-minute real-time transmissions if no furtherevents are detected.Underwater-to-surface data transmissionThisis realized by using mooring cable. In this system, data from sensor is transmittedto the surface by applying a signal to the internal winding of a cable coupler.This induces a signal in the single-turn secondary winding formed by themooring cable passing through the coupler. The signal is retrieved at thesurface by a similar configuration. This inductive modem technology provides aconvenient, economical, and reliable solution while still maintainingflexibility.
Ground stationsTheTSUSAT system will use two ground stations located in South America, the mainstation will work in Santiago, downloading the data collected by thegeostationary satellite. An algorithm for detecting variations in measurementsthat could be potentially dangerous might be implemented in near real time inorder to have enough time to alert at the related institutions. A backup groundstation located in Lima can be used in case that the main station has atechnical disruption.Thesubsystems will be redundant being able to use different combinations of them,just in case if one of them stops working due to technical disruptions. Thisconfigurations will be selected by setting different modes from ground control.