Transit-1B, the first experimental navigational satellite has been launched on 13 April, 1960, laying the foundations of - the now ubiquitous - space-based navigation.

Events have started - as in other American space programmes - with Sputnik. The first satellite of the world started to beep on a Friday and only on Monday did the idea of measuring its orbit come to western researchers. Scientists at John Hopkins University tested their new receiver with success, measuring the Doppler-shift of the radio signals and from them proving mathematically that the broadcast indeed came from an object in low Earth orbit. That evening they made estimations for the orbital elements. The next few days were in fever of calculating the exact orbit. George Weiffenbach and William Guier developed an algorithm for the orbital elements using the Doppler-shift and the known position of the radio receiver. It did not take long to create the inverse theorem: knowing the satellite's orbit and measuring its radio signals we can determine the location of a receiver on Earth. The use of such a method? The most obvious use was for mobile receivers, of which the USA had several: ships, submarines, airplanes (as the military is usually the first to fund new ideas..). The Navy soon adopted the idea.

NASA would send a probe, where no one has sent before: directly into Sun’s outer atmosphere. The instruments of Solar Probe Plus have been chosen.

According to the current plans, the Solar Probe Plus would launch ‘til 2018. Last week the American space agency named that five scientific instruments, what they would deploy on the probe what will fly next to the sun, and what’s size is similar to a size of a car. The instruments would analyze the composition of solar wind, detect the impacting dust particles, measure the electromagnetic field of the star and would make 3D images of the corona. The experiments have been chosen from 13 suggestions presented in 2009. The pre-studies, planning, engineering and testing of the chosen instruments will cost 180 million dollars.

The Solar Probe Plus near the Sun (Fantasy: JHU APL)

As the probe will get close to the sun, it will have to endure more than 1400°C temperature and fierce bursts. It looks for the answer to two main questions: why is the corona hotter, than the visible “surface” of the sun - the photosphere - and how exactly gain the particles of the solar wind speed, which have an effect, among other things, on our Earth’s environment.

The scientific goals of Solar Probe Plus didn’t change since 2005, when the experts started to think about a probe, the Solar Probe, analyzing the Sun. The practical plans have altered though. It’s an idea since the 1970’s, that after a swinging maneuver around Jupiter a probe would go into a quasi-polar orbit around the Sun, where the smallest distance would have been 4 Sun radiuses. This would allow 2 flybys. In the current, newer plans the probe stays in the level of the ecliptics and nears the star much frequently – but the distances are larger and slowly decreasing too. The main program contains 24 perihelium-flybys in 35 Sun radiuses. 19 from that is even closer - 20 Sun radiuses. In the years following, after a swinging maneuver by Venus the 9,5 Sun radiuses are the goal. This will be the last, 88 days long orbit, and the probe would do it 3 times.

The changing orbit of the Solar Probe Plus around the Sun – In this image is the probe starts in the year 2015, but that altered to the July 2018. What didn’t change, that to reach reach the inner orbit will take 6,5 years. (Image: JHU APL)

The heat protection layer of the Solar Probe Plus is a 2,7 meters diameter shield. The power sources are two independent solar panels. The first will be used in a larger distance from the Sun, and when the probe gets closer, it will fold and will be pulled into the shade of the heat protection shield. During this part of the orbit they will use another, liquid-cooled solar panel. The scientific data will be stored on the deck, until the probe reaches again the 0,59 AU distance, then the data will be sent to Earth. (1 AU is the medium Sun-Earth distance, it’s roughly 150 million km - 215 times bigger, then the radius of the Sun.)

Frey Sándor

Translation by Márton Deák

http://www.urvilag.hu/amerika_es_az_urcsillagaszat/20100906_utazas_a_napba_indulas_2018ban