Seiko Astron’s Next Stage of Practicality and Beauty
Twelve years have passed since the birth of the Seiko Astron GPS solar watch in 2012, when it was touted as the “second revolution” following the quartz watch. While its appearance and movement have continued to undergo updates ever since its debut, a major advancement in performance and aesthetics came with the new Caliber 5X83 in 2024. Along with greater convenience from added functionality, a vertical layout of the sub-dials at the 12, 9, and 6 o’clock positions has been achieved, something not possible with earlier GPS models, as the level of perfection of a GPS solar watch has been exponentially raised.
The next-generation Seiko Astron GPS Solar, adding new functionality while raising performance
The first Seiko Astron with a Caliber 5X movement came out in the fall of 2018. The Caliber 5X53, which was developed at that time, was a major advancement on the Caliber 8X series movements that came before it, incorporating functions such as fast time zone adjustment, a time-transfer function for instantly switching between home and local time zones, and automatic time correction, all in a compact case size. For a long time, it was the foundation of Seiko Astron performance.
Then, in 2024, the Caliber 5X series movements received their first update in around five and a half years in the form of Caliber 5X83. Among its highlights are a dual-time display, showing the time in two time zones at once, and a newly added stopwatch function that measures elapsed time in increments of 1/20th of a second. What’s more, the switchover time of the time transfer function implemented in Caliber 5X53 has been greatly shortened, and battery charging efficiency has been improved, in these and other ways making the Seiko Astron even more multifunctional while substantially improving ease of use.
In spring of 2024, the Seiko Astron GPS Solar Dual-Time Chronograph was released with this new movement. Three models including the SSH151 have a ceramic bezel and carry over the solid case design characteristic of the Seiko Astron GPS Solar Series. The Seiko Astron appearance also underwent a notable change, adopting a vertical three-eye layout. Then in fall of this year, three models were added, led by the SSH159. Featuring a titanium bezel along with a sharply angular exterior design, the modern styling has been further refined.
Seiko Astron GPS Solar Dual-Time Chronograph SSH159
GPS Solar (Caliber 5X83). When fully charged, power reserve of up to two years (in power save mode). Titanium with super-hard coating (diameter 42 mm, thickness 12.4 mm). Water resistance to 10 bars.
Seiko Astron GPS Solar Dual-Time Chronograph SSH151
GPS Solar (Caliber 5X83). When fully charged, power reserve of up to two years (in power save mode). Titanium with super-hard coating (diameter 43.3 mm, thickness 13.4 mm). Water resistance to 10 bars.
The new 2024 models with Caliber 5X83 add a dual-time display along with new chronograph functionality. The layout features a sub-dial at 12 o'clock that measures elapsed time in increments of 1/20th of a second (left), and a sub-dial at the 6 o’clock position for displaying a second time zone. The time shown at the 6 o’clock position can be switched instantly to and from the main time display by means of the time transfer function.
How the new Caliber 5X83 has advanced the Seiko Astron
The new Caliber 5X83 movement was developed with the aim of expanding the variations of multifunction GPS solar models with a metal bezel. While the Caliber 5X83 came to be the heart of a dual-time chronograph, a major goal with a chronograph is to achieve full-scale functionality, including that for timing in increments of 1/20th of a second in addition to the timekeeping by the center seconds hand. In seeking to realize this, Seiko Epson, which was in charge of the watch’s development, focused on the antenna shape.
The earlier Caliber 5X53 adopted a box-shaped patch antenna. Use of a patch antenna did allow the case size to be made smaller and enabled support for a metal bezel, but the antenna position proved to be a hindrance to further advances in multifunctionality. For the sake of antenna directionality and design balance, the patch antenna was positioned at 12 o'clock, which meant that no more than six motors could be accommodated for moving the hands. The result was that Caliber 5X53 models came to have a dual-time function with a horizontal three-eye design.
To resolve this issue, Caliber 5X83 adopts a flat antenna with the addition of a dielectric antenna. This is the same antenna configuration adopted for Caliber 3X62, announced in 2023, and allows for greater design freedom in the movement space. Where the patch antenna had been located, a motor was added; that is, an additional function could be accommodated, which in this case meant putting a sub-dial at the 12 o'clock position for a vertical three-eye layout, something that up to now was difficult in a GPS solar model.
On the left is Caliber 5X53 released in 2018, while on the right is the newly developed Caliber 5X83. The gold part covering the top of Caliber 5X83 is the flat antenna, which also plays the role of holding the date indicator in place.
What’s more, the addition of another motor improves the watch’s usability. Since Caliber 5X53 had six motors, the hand indicating each mode and the calendar were operated by one motor. Now that the new movement has replaced the patch antenna with a flat one, freeing up more space, there are seven motors, enabling the multi-indicator and calendar to be driven by independent motors. This eliminates the complex motion of the mode hand that occurred when the time transfer function was executed. It also makes switching between home and local times around 40% faster than before.
Antenna performance is of course guaranteed in Caliber 5X83. To confirm the reception performance of signals transmitted by GPS satellites, Seiko Epson conducted field tests not only in Japan but in the world’s major municipalities. The testing confirmed the signal reception success rate in environments crisscrossed with radio waves of various kinds and in locations obstructed by buildings.
Thoroughgoing assessment of the new Seiko Astron GPS Solar Dual-Time Chronograph was carried out, so that the finished product is a watch that can be used with assurance all over the world.
On the left is the patch antenna used in Caliber 5X53. Caliber 5X83 freed up movement space by changing to a flat antenna as shown on the right, enabling the addition of one more motor. However, since GPS signals are picked up from the periphery of the watch, only a ceramic bezel can be used with a flat antenna. The dielectric antenna shown at the lower right was used to improve the capture performance. It has the role of shifting directionality to the dial side, thereby making it possible to use a metal bezel.
How steps to improve charging efficiency made it possible to improve the look and feel of the dial
As noted earlier, models adopting a patch antenna were unable to accommodate a sub-dial at the 12 o'clock position; moreover, the need to keep the antenna from showing through the dial imposed limits on the appearance. With Caliber 5X83 and its flat antenna, however, it became possible not only to adopt a vertical three-eye layout but to enhance the dial look and feel, transforming the appearance of a GPS solar watch.
This is most notable in the dial of the SSH159 model, with its silver motif. Adopting a silver or other light-colored dial is highly difficult in the first place with the Seiko Astron or other GPS solar watch. One reason is that such colors tend to disperse the light that is the power source of a solar watch, hindering it from reaching the solar cell under the dial. Another is that the solar cell, antenna, and other internal parts tend to show through the dial. The new models adopt a bright silver color for the entire dial, while creating a hard texture that is in synch with the Seiko Astron GPS Solar Series solid exterior.
The SSH159 dial adopts a silver motif along with vertical striations, for a metal-like finish. At the same time, the circular patterns on the three sub-dials give an accent to the dial design.
On the left is the solar cell used in Caliber 5X53. Comparing it to the Caliber 5X83 solar cell (right) makes clear that the need for antenna space at the 12 o'clock position imposed restrictions not just on multifunctionality but on the dial design as well. Since GPS signals are blocked by the solar cell power generation region, Caliber 5X53 is designed not to generate power in the antenna space at the 12 o'clock position. With Caliber 5X83, switching to a flat antenna made it possible to expand the solar cell generation area, which resulted in improved charging efficiency. With the black dial Caliber 5X83 model, a blue solar cell is used to obtain a deeper black and express a dark blue.
This is made possible by a newly devised dial structure, having as base a reflector plate with a metal-like luster and achieving both light reflection and transparency. A transparent polycarbonate dial part is overlaid on the reflector plate. If it were simply overlaid, however, the texture of the reflector plate would show through directly, not the desired look and feel of luxury. Vertical striations are therefore stamped on the surface of the dial parts, and the back side is given a translucent matte coating. While drawing out the silver color of the reflector plate, this also enhances the sense of quality.
Seiko Epson explains that “A solar dial can easily take on a plastic-like texture, and this is particularly true with white colors. An issue with solar calibers is therefore how to realize a metallic-looking dial.” The SSH159 model, however, has cleared this major hurdle, coming close to a metal-like appearance, and in this respect would seem to have done away with a negative factor that had dogged solar watches.
The three parts making up the SSH159 dial. The reflector plate on the left, made of polyester and acrylic composite material, is the base on which the dial part (center) and ring-shaped part are overlaid to form the dial. Vertical striations are stamped deeply into the surface of the dial, which is given a translucent coating on the back, thereby achieving a solid, metal-like texture.
Two designs born of bezels with different materials
The Seiko Astron GPS Solar Dual-Time Chronograph was released in spring 2024 as a ceramic bezel model, followed in November by a second model with a titanium bezel. Since a hybrid approach combining a flat antenna with dielectric antenna was decided at the movement development stage, a bezel of either material was already supported; but the exterior design needed to be rethought. That is, because ceramics and titanium differ in material properties, the exterior design values are different.
While ceramics are materials with excellent hardness, resistant to scratching, their lack of viscosity makes them breakable. For this reason, a ceramic bezel needs to be thick for fixing it to the case, and an adequate case size is necessary. The first series, including the SSH151, was made taking these requirements into account. Combining a titanium bezel with the same exterior design, however, inevitably results in a heavy impression.
The second series accordingly narrowed the top of the bezel and made it more angular, for a silhouette that makes the case appear thinner. In addition, whereas the ceramic bezel models have a dual-curve sapphire watch glass, the titanium bezel models changed to a flat sapphire watch glass. This results in a case diameter of 42 mm for the second series, 1.3 mm smaller than the first series, and a case thickness 1 mm thinner at 12.4 mm. Even while based on the solid modern form of the Seiko Astron GPS Solar Series, models were created each with their own distinctive impressions.
Whereas the ceramic bezel (left) has a broad top surface space, the titanium bezel (right) top surface is much narrower and more sharply sloped, resulting in a solid, light appearance befitting a fully titanium exterior. The appeal of each model is enhanced by adopting a shape matched to the material texture.
The case has a sharply angular, powerful form common to the Seiko Astron GPS Solar Series. The SSH159 in particular with its silver-colored dial is strongly imbued with a cool atmosphere like modern architecture.
The Seiko Astron GPS Solar Dual-Time Chronograph with new Caliber 5X83 movement was not designed simply for multifunctionality. Achieving a vertical three-eye layout, which previously seemed unattainable in a GPS solar watch, while dramatically enhancing the design, including the texture of the dial, it is a masterwork that takes the GPS solar watch to the next stage.