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First exposure: blue and white GPS

A group of Israeli engineers is offering tiny satellites to Hagram that will do everything the big GPS satellites do

Summary of Raz Tamir's lecture, at a special event held at Tel Aviv University, 28/6/05 for the presentation of a program for tiny navigation satellites. The director of the Israel Space Agency, Zvi Kaplan, the previous director Avi Har-Evan, Dr. Noah Brosh and many others also took part in the conference.

One of the top brass in the space industry.

Introduction: What are CubeSat satellites
CubeSats are fully functional tiny satellites. These are satellites measuring 10 x 10 x 10 (when in each storage unit on the launcher you can place 3 satellites or one satellite measuring 10 x 10 x 30. For an amount of 3,500 dollars you can purchase the ready-made satellites that include a computer, an operating system and a transmitter. Just add a useful charger (Metad) and launch (which adds a cost of at least 40 thousand dollars).
CubeSat model pico-satellite standard
The satellites measuring 10 x 10 x 10 centimeters and weighing 1 kg, have today become the basis of one of the accepted Piko satellite families. The standard was originally proposed by Prof. Bob Twiggs from Stanford University and later developed in collaboration with Prof. Jordi Puig-Suari at California Polytechnic University and San Luis Obispo. To the levels of emphasis on simplicity and low price, CubeSat standards address all the critical issues required for the success of the mission, from the external dimension of the satellite to the P-POD launcher, to perform experiments and integration processes.
Compared to satellite missions that cost many millions of dollars, CubeSat projects have the potential for educational partnerships and successful integration into scientific and industrial missions at a much cheaper price.

Tamir: "When I came back from the tiny satellite conference last year, I asked if it was worth doing a competition between the universities in Israel to find uses for the satellite. One of the ideas was to feel earthquakes a few hours before they happen, there is a hypothesis that before the earthquakes there is an effect on the Earth's magnetic field. Several satellites were sent to find this coordinate.
"Instead of wasting resources and time on the development of the satellite, the consideration is that there is already a functioning satellite and we need to think about what scientific payload is placed inside it."
In the end, a group of about 15 engineers was formed who dedicate their free time to this. These are people who work at Mavet, MTA, the Ministry of Defense, the Air Force and Rafael. The team's mission is to build a GPS network based on these satellites.

How GPS satellites work
"A GPS satellite launches a beam and checks its distance to Earth. If we know where 4 such satellites are, we solve four equations with four vanishing points and we know where we are (if so, it gets complicated because of Doppler and a few other things. Basically, a GPS satellite is a flying clock. Our claim is that a small satellite can do the same actions as a GPS satellite does large. The CubeSat satellite has solar cells - two antennas that are GPS antennas and at the bottom there is a retro reflector - every ray of light that hits it returns exactly in the direction it came from. These satellites can replace any satellite the size of a room and its weight is 500 kilograms. Our goal is to simplify the the systems on the satellite and download to the ground stations what should not be on the satellite.

The current satellites have the ability to listen to the earth and their clock is accurate and updated. With us, on the other hand, the satellite is deaf. We need to make corrections to the location data of the satellites, including their drift, on Earth. For this, the SLR - SATLITE LASER RAGING station is used. The stations emit laser beams and hit the satellite and thus they receive data on its location. By picking it up and knowing where it is, I also know what the deviation of the clock is. At the same ground station, its drift from the position is estimated (due to drag and the activity of the sun and moon). We transmit this information instead to the Levin itself, to the end units. If I have a GPS receiver, I transmit the information to it either with the help of a communication satellite or with the help of the Internet. Instead of the patch file being on the satellite, a very small patch file is transmitted to the end unit. From this moment on, the end unit performs the same operation as before, except that it uses the patch file it has and is not transmitted from the satellite. The satellite does not need to know where it is. It transmits in all directions and reception on the ground is done by the unit.
The satellite includes a sun gauge - so that it orients itself so that the solar cells face the sun. Since the satellite has to rotate itself towards the sun, it is helped by the earth's magnetic flux. As soon as I pass electricity through the coil it becomes magnetic and tries to align itself with the magnetic field. Each such satellite has a battery (charged during the day and used to operate the satellite at night), a transmitter, a reflector and of course a computer. and a component that controls the rotation rate of the satellite.

Why do you need another GPS system?
As we know, the Russians, Europeans and Chinese are planning to launch navigation satellite systems. Tamir listed two reasons why more could be added. One: the removal of dependence on the Americans who, during a war, may paralyze, even regionally, the activity of the GPS system, which everyone already depends on on the one hand to operate weapons, and on the other hand also to assist the rescue forces. Plus there are benefits. Second reason: satellites switch to broadcasting on two frequencies. The ionosphere layer contains charged molecules that react with the electromagnetic wave, causing the wave to slow down or speed up. Broadcasting on several waves and several satellites will allow the error to be reduced from 10 per meter to one meter. Our system is pre-programmed to transmit on 2 frequencies.
"Additional reasons: we can add various tasks to the system - predicting earthquakes, we measure the earth's magnetic field in any case to direct the satellite. Scientific missions can be added and, in addition, there is no obstacle, if I put tiny cameras on all sides of the cubesats, it is possible to get continuous photographs of the Earth at a low resolution."

"We wanted to answer the question of whether such a system has a right to exist or not? Therefore, we did not continue with the final content, but faced the basic questions: at what height to place the satellites, how will we provide the exact information regarding the deviations of the satellite in terms of position and in terms of time. Is it possible to achieve total coverage if the satellites do not have a propulsion system and they may drift to one area and leave large parts of the earth uncovered, what is the required power, how do you maintain the orbit, and how do you maintain the satellite thermally. :
At what height should the satellites be placed?
"Like a GPS system, we want to cover as large an area as possible (up to 60 latitude), operate a minimum number of ground stations and maintain the concept of a smart ground station, a stupid satellite). The satellite has to get used to the space environment - a very extreme range of temperatures because there is no convection of the heat. The satellite is within the Earth's magnetic field, radiation emitted from the sun and cosmic radiation. We have to make an alternative between all kinds of considerations. I want the satellite to be high, because it has no propulsion system. On the other hand, the higher I go, the greater the required power. I want to be below the Van Allen belt, the higher I am I cover more of the earth and can be satisfied with fewer satellites. The number of satellites causes a choice of high altitude, radiation, drag - high, power - low. In the end we decided on 850 kilometers.
How many satellites?
Tamir: "We first calculated whether a constellation of 10 satellites in each of 10 orbits up to 60 degrees latitude would be sufficient. This arrangement is called the Walker constellation. We managed with 10 orbits and 10 satellites in each orbit and wanted to see if something like this could deliver what we wanted. This means: placing 100 satellites at an altitude of 850 km, so that 4 satellites can be covered at any moment, 85% of the time. We performed a simulation and came to the conclusion that we need 12 planes and 12 satellites in each plane when the satellite starts operating at a height of 5 degrees above the horizon if we were to increase the height to 7,000 even with 6 satellites in 6 orbits there is full coverage.
The problem will be solved precisely, if we continue the process. For now, we were content with that."

What about the accuracy of the clocks?
Tamir: "The satellite is a clock. The more accurate a satellite clock I have, the more accurately I can know the distance. Clocks that are on GPS satellites are cesium clocks that reach an accuracy of 10 minus 13. Today there are clocks for sale on the Internet with a maximum of 10 minus 12, based on ribidium atoms. With these watches I can allow the watch to drift for less than an hour and therefore the watch must be updated every 50 minutes. Today there are atomic clocks of 10 to the power of minus 13 in units of a few centimeters. It is estimated that by the time the launch date arrives, the technology will mature.

supply

"The satellite consumes 12-14 watts for its operation, including the computer, the transmission and charging the batteries for the night. We tested several configurations. A closed configuration delivers the same 14 watts, with panels at 14% efficiency. Since this is not enough because we also need to store energy for the night hours, we need to increase the surface area and point it in front of the sun. In this configuration we are able to provide 25 watts.
temperature differences
The temperature differences from side to side are high. But since the satellite is small, the solar radiation, the reflected radiation from the Earth and the internal power bring the maximum heat to 35 degrees during the day and 4 degrees at night, exactly the living area of ​​our electrical systems. We may need thermal control measures but these will be passive measures. We won't have to turn on heaters or remove the heat.

the ground station
The SATELLITE LASER RANGING station fires a green laser in the visible range. There are such stations for sale. The station shoots a laser beam at the satellite and it knows to a guess where the satellite was at any given moment. Accuracy of tens of centimeters. I know how to predict Levin in five hours. Two such stations, one at each end of the earth I am well arranged. It addresses track drifts, not clock drifts. The stations for drifting a clock are much simpler, these are stations with an accurate clock that receive the satellites. I know my time and my location, so I can solve other equations and use them to calculate the satellite's location.

Dispatch

"The satellite and the launch cost 50, but that's true if you're willing to compromise on a route that someone else chose, something that may be suitable for an experiment, but not for an operational system. A targeted launch for us is very expensive. And two alternatives are being considered - Ukrainian and Israeli.
We examined the Dnefer launcher, which has so far launched 15 cubesats in two different launches as hitchhikers. Initially we will do something like this, we will board an existing launch as hitchhikers, we will bring a mobile SLR station to Israel, we will perform the measurements on 5 satellites. If we want the system in full deployment, we will launch properly. This means that the missile will be launched into an 850 kilometer orbit, its third stage leaves one satellite, climbs, makes 3 laps, descends back and drops a second satellite. rising again. Within 9 hours, ten satellites are placed in this way. They have already done such launches where the public satellite constellations. In parallel with the activity of our group, this semester I am also guiding a group of students at the Technion whose project goal is to arrive at the initial planning of the system at the end of one semester, within a year for critical planning and after two years perhaps to reach a situation where the Technion will purchase several such units and make
A similar launcher was planned in Malam. There was a group of students who were thinking about the possibility of launching from an airplane. In the upper stage there is a system consisting of a motor and on its sides there are 10 tripods. Those pods each contain a satellite. This stage is put into orbit and performs the same exercise that the Dniper can perform. The price is not yet known.

The conclusions - the system is possible. The transmission power for a range of 3,000 kilometers is 4 watts. only. The weight of the satellite in the worst case is 4.5 kg. You can even lose a kilogram. An accuracy of 24 meters is reached, and it can be improved by using two frequencies.

The group continues to meet and the director of the Israel Space Agency, Zvi Kaplan, also promised to help it advance the project to carry out a more in-depth engineering examination.

A group of Israeli engineers is offering tiny satellites to Hagram that will do everything the big GPS satellites do

30.6.2005

By: Avi Blizovsky

Direct link to this page: https://www.hayadan.org.il/israelspace300605.html

Summary of Raz Tamir's lecture, at a special event held at Tel Aviv University, 28/6/05 for the presentation of a program for tiny navigation satellites. The director of the Israel Space Agency, Zvi Kaplan, the previous director Avi Har-Evan, Dr. Noach Brosh and many other top executives of the space industry also took part in the conference.
Introduction: What are CubeSat satellites
CubeSats are fully functional tiny satellites. These are satellites measuring 10 x 10 x 10 (when in each storage unit on the launcher you can place 3 satellites or one satellite measuring 10 x 10 x 30. For an amount of 3,500 dollars you can purchase the ready-made satellites that include a computer, an operating system and a transmitter. Just add a useful charger (Metad) and launch (which adds a cost of at least 40 thousand dollars).
CubeSat model pico-satellite standard
The satellites measuring 10 x 10 x 10 centimeters and weighing 1 kg, have today become the basis of one of the accepted Piko satellite families. The standard was originally proposed by Prof. Bob Twiggs from Stanford University and later developed in collaboration with Prof. Jordi Puig-Suari at California Polytechnic University and San Luis Obispo. To the levels of emphasis on simplicity and low price, CubeSat standards address all the critical issues required for the success of the mission, from the external dimension of the satellite to the P-POD launcher, to perform experiments and integration processes.
Compared to satellite missions that cost many millions of dollars, CubeSat projects have the potential for educational partnerships and successful integration into scientific and industrial missions at a much cheaper price.

Tamir: "When I came back from the tiny satellite conference last year, I asked if it was worth doing a competition between the universities in Israel to find uses for the satellite. One of the ideas was to feel earthquakes a few hours before they happen, there is a hypothesis that before the earthquakes there is an effect on the Earth's magnetic field. Several satellites were sent to find this coordinate.
"Instead of wasting resources and time on the development of the satellite, the consideration is that there is already a functioning satellite and we need to think about what scientific payload is placed inside it."
In the end, a group of about 15 engineers was formed who dedicate their free time to this. These are people who work at Mavet, MTA, the Ministry of Defense, the Air Force and Rafael. The team's mission is to build a GPS network based on these satellites.

How GPS satellites work
"A GPS satellite launches a beam and checks its distance to Earth. If we know where 4 such satellites are, we solve four equations with four vanishing points and we know where we are (if so, it gets complicated because of Doppler and a few other things. Basically, a GPS satellite is a flying clock. Our claim is that a small satellite can do the same actions as a GPS satellite does large. The CubeSat satellite has solar cells - two antennas that are GPS antennas and at the bottom there is a retro reflector - every ray of light that hits it returns exactly in the direction it came from. These satellites can replace any satellite the size of a room and its weight is 500 kilograms. Our goal is to simplify the the systems on the satellite and download to the ground stations what should not be on the satellite.

The current satellites have the ability to listen to the earth and their clock is accurate and updated. With us, on the other hand, the satellite is deaf. We need to make corrections to the location data of the satellites, including their drift, on Earth. For this, the SLR - SATLITE LASER RAGING station is used. The stations emit laser beams and hit the satellite and thus they receive data on its location. By picking it up and knowing where it is, I also know what the deviation of the clock is. At the same ground station, its drift from the position is estimated (due to drag and the activity of the sun and moon). We transmit this information instead to the Levin itself, to the end units. If I have a GPS receiver, I transmit the information to it either with the help of a communication satellite or with the help of the Internet. Instead of the patch file being on the satellite, a very small patch file is transmitted to the end unit. From this moment on, the end unit performs the same operation as before, except that it uses the patch file it has and is not transmitted from the satellite. The satellite does not need to know where it is. It transmits in all directions and reception on the ground is done by the unit.
The satellite includes a sun gauge - so that it orients itself so that the solar cells face the sun. Since the satellite has to rotate itself towards the sun, it is helped by the earth's magnetic flux. As soon as I pass electricity through the coil it becomes magnetic and tries to align itself with the magnetic field. Each such satellite has a battery (charged during the day and used to operate the satellite at night), a transmitter, a reflector and of course a computer. and a component that controls the rotation rate of the satellite.

Why do you need another GPS system?
As we know, the Russians, Europeans and Chinese are planning to launch navigation satellite systems. Tamir listed two reasons why more could be added. One: the removal of dependence on the Americans who, during a war, may paralyze, even regionally, the activity of the GPS system, which everyone already depends on on the one hand to operate weapons, and on the other hand also to assist the rescue forces. Plus there are benefits. Second reason: satellites switch to broadcasting on two frequencies. The ionosphere layer contains charged molecules that react with the electromagnetic wave, causing the wave to slow down or speed up. Broadcasting on several waves and several satellites will allow the error to be reduced from 10 per meter to one meter. Our system is pre-programmed to transmit on 2 frequencies.
"Additional reasons: we can add various tasks to the system - predicting earthquakes, we measure the earth's magnetic field in any case to direct the satellite. Scientific missions can be added and, in addition, there is no obstacle, if I put tiny cameras on all sides of the cubesats, it is possible to get continuous photographs of the Earth at a low resolution."

"We wanted to answer the question of whether such a system has a right to exist or not? Therefore, we did not continue with the final content, but faced the basic questions: at what height to place the satellites, how will we provide the exact information regarding the deviations of the satellite in terms of position and in terms of time. Is it possible to achieve total coverage if the satellites do not have a propulsion system and they may drift to one area and leave large parts of the earth uncovered, what is the required power, how do you maintain the orbit, and how do you maintain the satellite thermally. :
At what height should the satellites be placed?
"Like a GPS system, we want to cover as large an area as possible (up to 60 latitude), operate a minimum number of ground stations and maintain the concept of a smart ground station, a stupid satellite). The satellite has to get used to the space environment - a very extreme range of temperatures because there is no convection of the heat. The satellite is within the Earth's magnetic field, radiation emitted from the sun and cosmic radiation. We have to make an alternative between all kinds of considerations. I want the satellite to be high, because it has no propulsion system. On the other hand, the higher I go, the greater the required power. I want to be below the Van Allen belt, the higher I am I cover more of the earth and can be satisfied with fewer satellites. The number of satellites causes a choice of high altitude, radiation, drag - high, power - low. In the end we decided on 850 kilometers.
How many satellites?
Tamir: "We first calculated whether a constellation of 10 satellites in each of 10 orbits up to 60 degrees latitude would be sufficient. This arrangement is called the Walker constellation. We managed with 10 orbits and 10 satellites in each orbit and wanted to see if something like this could deliver what we wanted. This means: placing 100 satellites at an altitude of 850 km, so that 4 satellites can be covered at any moment, 85% of the time. We performed a simulation and came to the conclusion that we need 12 planes and 12 satellites in each plane when the satellite starts operating at a height of 5 degrees above the horizon if we were to increase the height to 7,000 even with 6 satellites in 6 orbits there is full coverage.
The problem will be solved precisely, if we continue the process. For now, we were content with that."

What about the accuracy of the clocks?
Tamir: "The satellite is a clock. The more accurate a satellite clock I have, the more accurately I can know the distance. Clocks that are on GPS satellites are cesium clocks that reach an accuracy of 10 minus 13. Today there are clocks for sale on the Internet with a maximum of 10 minus 12, based on ribidium atoms. With these watches I can allow the watch to drift for less than an hour and therefore the watch must be updated every 50 minutes. Today there are atomic clocks of 10 to the power of minus 13 in units of a few centimeters. It is estimated that by the time the launch date arrives, the technology will mature.

supply

"The satellite consumes 12-14 watts for its operation, including the computer, the transmission and charging the batteries for the night. We tested several configurations. A closed configuration delivers the same 14 watts, with panels at 14% efficiency. Since this is not enough because we also need to store energy for the night hours, we need to increase the surface area and point it in front of the sun. In this configuration we are able to provide 25 watts.
temperature differences
The temperature differences from side to side are high. But since the satellite is small, the solar radiation, the reflected radiation from the Earth and the internal power bring the maximum heat to 35 degrees during the day and 4 degrees at night, exactly the living area of ​​our electrical systems. We may need thermal control measures but these will be passive measures. We won't have to turn on heaters or remove the heat.

the ground station
The SATELLITE LASER RANGING station fires a green laser in the visible range. There are such stations for sale. The station shoots a laser beam at the satellite and it knows to a guess where the satellite was at any given moment. Accuracy of tens of centimeters. I know how to predict Levin in five hours. Two such stations, one at each end of the earth I am well arranged. It addresses track drifts, not clock drifts. The stations for drifting a clock are much simpler, these are stations with an accurate clock that receive the satellites. I know my time and my location, so I can solve other equations and use them to calculate the satellite's location.

Dispatch

"The satellite and the launch cost 50, but that's true if you're willing to compromise on a route that someone else chose, something that may be suitable for an experiment, but not for an operational system. A targeted launch for us is very expensive. And two alternatives are being considered - Ukrainian and Israeli.
We examined the Dnefer launcher, which has so far launched 15 cubesats in two different launches as hitchhikers. Initially we will do something like this, we will board an existing launch as hitchhikers, we will bring a mobile SLR station to Israel, we will perform the measurements on 5 satellites. If we want the system in full deployment, we will launch properly. This means that the missile will be launched into an 850 kilometer orbit, its third stage leaves one satellite, climbs, makes 3 laps, descends back and drops a second satellite. rising again. Within 9 hours, ten satellites are placed in this way. They have already done such launches where the public satellite constellations. In parallel with the activity of our group, this semester I am also guiding a group of students at the Technion whose project goal is to arrive at the initial planning of the system at the end of one semester, within a year for critical planning and after two years perhaps to reach a situation where the Technion will purchase several such units and make
A similar launcher was planned in Malam. There was a group of students who were thinking about the possibility of launching from an airplane. In the upper stage there is a system consisting of a motor and on its sides there are 10 tripods. Those pods each contain a satellite. This stage is put into orbit and performs the same exercise that the Dniper can perform. The price is not yet known.

The conclusions - the system is possible. The transmission power for a range of 3,000 kilometers is 4 watts. only. The weight of the satellite in the worst case is 4.5 kg. You can even lose a kilogram. An accuracy of 24 meters is reached, and it can be improved by using two frequencies.

The group continues to meet and the director of the Israel Space Agency, Zvi Kaplan, also promised to help it advance the project to carry out a more in-depth engineering examination.

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