三菱電機： イオンエンジンを採用：超低高度衛星（SLATS）（動画）：
Mitsubishi : Ion engine adopted: Ultra Low Altitude Test Sat (SLATS)：
三菱电机：使用离子发动机：超低空卫星（SLATS）
超低高度軌道への挑戦：
通常の地球観測衛星の軌道高度（600～800km）には微量の大気が存在。
多くの地球観測衛星は、微小な大気抵抗による軌道の低下を、補う必要があります。
定期的にガスジェットを噴射することで、高度を、維持します。
さらに、超低高度軌道（300～180km）では、
600～800kmの軌道高度と比べて約1000倍もの大気抵抗を受けます。
イオンエンジンを採用：
そのため、「つばめ」は通常のガスジェットよりも燃料効率が10倍良いイオンエンジンを採用しました。
大気抵抗が少ない小型衛星により、
継続的に高度を維持する
超低高度衛星技術の開拓に挑みます。
http://www.mitsubishielectric.co.jp/society/space/satellite/observation/slats.html
JAXA | Super Low Altitude Test Satellite (SLATS) “TSUBAME” has set a GUINESS WORLD RECORDS(R)
1. Details on the Guinness World Record set by the Super Low Altitude Test Satellite “TSUBAME” (SLATS) URL：https://www.guinnessworldrecords.jp/world-records/592663-lowest-altitude-earth-observation-satellite-in-orbit
Name of record:
Lowest altitude by an Earth observation satellite in orbit
Record values: Orbital altitude of 167.4 km*2
Record Text: The lowest altitude by an Earth observation satellite in orbit is 167.4 km (104 mi) and was achieved by JAXA’s TSUBAME (JAPAN) during its mission from 23 December 2017 to 1 October 2019.
Further info： TSUBAME was a Super Low Altitude Test Satellite operated by Japan Aerospace Exploration Agency, or JAXA.
With its ion engine, TSUBAME
was able to capture high-resolution satellite images despite the atmospheric drag and density of atomic oxygen present in super low altitudes.
It maintained seven different orbital altitudes, with 167.4 km being the lowest.
At 167.4 km altitude, Tsubame used both its ion engine system and gas-jet thrusters.
2. Achievements made by “TSUBAME” (SLATS) and future prospects A super low altitude satellite has the merit of being able to take high resolution satellite images using a small sensor.
However, when in orbit at an altitude that is categorized as being super low—at an altitude between 200 km and 300 km—the satellite
will be exposed to 1,000 times more atmospheric resistance and concentrated atomic oxygen that would cause it to deteriorate as compared to other Earth observation satellites orbiting at the usual altitudes.
Thus, super low altitude
has been considered as being unsuitable for Earth observation satellites that require precise positioning, orbit control and long-term satellite operations.
“TSUBAME” first maintained an orbital altitude of 271.5 km, which was gradually lowered to finally reach the 167.4 km altitude that was recognized as a world record this time by the Guinness World Records.
This orbit in super low altitude was maintained for a period of seven days.
During its time orbiting in the record-breaking altitude, “TSUBAME” conducted tests on taking high resolution satellite images, and succeeded in obtaining good results.
The test satellite also succeeded in acquiring data of
atmospheric density,
atomic oxygen density, and
the level of deterioration of material samples
that were exposed to the atmosphere. Furthermore, the satellite also succeeded in demonstrating that the material developed by JAXA has the ability to withstand exposure to atomic oxygen for a long period of time.
https://global.jaxa.jp/press/2019/12/20191224a.html