astronomy

OKEANOS

OKEANOS is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand OKEANOS rather than just read about it. In short: OKEANOS (Oversize Kite-craft for Exploration and Astronautics in the Outer Solar system) was a proposed mission concept to Trojan asteroids, which share Jupiter's orbit, using a hybrid solar sail for propulsion; the sail was planned to be covered with thin solar panels to power an ion engine. In situ analysis of the collected samples would have been performed by either direct contact or using a lander carrying a hig…

Key takeaways

OKEANOS belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect OKEANOS to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of OKEANOS from memory before moving on to harder problems.

Reference excerpt

OKEANOS (Oversize Kite-craft for Exploration and Astronautics in the Outer Solar system) was a proposed mission concept to Trojan asteroids, which share Jupiter's orbit, using a hybrid solar sail for propulsion; the sail was planned to be covered with thin solar panels to power an ion engine. In situ analysis of the collected samples would have been performed by either direct contact or using a lander carrying a high-resolution mass spectrometer. A sample-return to Earth was an option under study. OKEANOS was a finalist for Japan's Institute of Space and Astronautical Science (ISAS)' 2nd Large Mission Class to be launched in 2026, and possibly return Trojan asteroid samples to Earth in the 2050s. The winning mission was LiteBIRD.

Overview The OKEANOS mission was a concept first proposed in 2010 to fly together with the Jupiter Magnetospheric Orbiter (JMO) as part of the cancelled Europa Jupiter System Mission – Laplace. In its latest formulation, the OKEANOS mission and LiteBIRD were the two finalists of Japan's Large Mission Class by the Ministry of Education, Culture, Sports, Science and Technology. LiteBIRD, a cosmic microwave background astronomy telescope, was selected. Analyzing the composition of the Jupiter Trojans may help scientists understand how the Solar System was formed. It would also help determine which of the competing formation hypotheses is right: remnant planetesimals during the formation of Jupiter, or fossils of building blocks of Jupiter, or captured trans-Neptunian objects by planetary migration. The latest proposal included a lander to perform in situ analyses. There were several options for this mission, and the most ambitious one proposed to retrieve and send samples to Earth for extensive investigations. Had it been selected in April 2019 for development, the spacecraft would have launched in 2026, and may had offered some synergy with Lucy spacecraft that will flyby multiple Jupiter Trojans in 2027.

Spacecraft The spacecraft was projected to have a mass of about 1,285 kg (2,833 lb) including a possible lander and would have been equipped with solar electric ion engines. The 1600 m2 sail would have had a dual purpose of solar sail propulsion and solar panel for power generation. If a lander had been included, its mass would have been no greater than 100 kg. The lander would have collected and analyzed samples from the asteroid. A more complex suggested concept would have had the lander take off again, rendezvous with the mothership and transfer the samples for their transport to Earth.

Solar sail and solar panels The unique proposed sail was a hybrid that would have provided both photon propulsion and electric power. JAXA referred to the system as a Solar Power Sail. The sail would have been made of a 10 μm-thick polyimide film measuring 40 × 40 meters (1600 m2), covered with 30,000 solar panels 25 μm thick, capable of generating up to 5 kW at the distance of Jupiter, 5.2 Astronomical Units from the Sun. The main spacecraft would have been located at the center of the sail, equipped with a solar-electric ion engine for maneuvering and propulsion, especially for a possible sample-return trip to Earth. The spacecraft would have used solar sail technology initially developed for the successful IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun) that launched in 2010, whose solar sail was 14 m × 14 m in size. As with the IKAROS, the solar angle of the sail would have been changed by dynamically controlling the reflectivity of liquid crystal displays (LCD) on the outer edge of the sail so that the sunlight pressure would produce torque to change its orientation.

Ion engine The ion engine intended for the mission was called μ10 HIsp. It was planned to have a specific impulse of 10,000 seconds, power of 2.5 kW, and a maximum thrust magnitude of 27 mN for each of the four engines. The electric engine system would have been an improved version of the engine from the Hayabusa mission, used for maneuvering, and especially for an optional sample-return trip to Earth. A study indicated the need for 191 kg of xenon propellant if it had been decided to bring a sample back to Earth.

Lander

The mission concept considered several scenarios, targets, and architectures. The most ambitious scenario contemplated in situ analysis and a sample-return using a lander. This lander concept was a collaboration among the German Aerospace Center (DLR) and Japan's JAXA, starting in 2014. The spacecraft would have deployed a 100 kg lander on the surface of a 20–30 km Trojan asteroid to analyze its subsurface volatile constituents, such as water ice, using a 1-meter pneumatic drill powered by pressurized nitrogen gas. Some subsurface samples would have been transferred to the on board mass spectrometer for volatile analysis. The lander's scientific payload mass, including the sampling system, would not have exceeded 20 kg. The lander would have been powered by batteries and was planned to perform an autonomous descent, landing, sampling and analysis. Some samples were to be heated up to 1000 °C for pyrolysis for isotopic analysis. The conceptual payload for the lander would have included a panoramic camera (visible and infrared), an infrared microscope, a Raman spectrometer, a magnetometer, and a thermal radiometer. The lander would have operated for about 20 hours using battery power. If a sample-return was to be performed, the lander would have taken off then, rendezvous and deliver the surface and subsurface samples to the mothership hovering above (at 50 km) for subsequent delivery to Earth within a reentry capsule. The lander would have been discarded after the sample transfer.

Conceptual scientific payload On the lander

Mass spectrometer Hyperspectral microscope Hyperspectral panoramic imager Optical navigation camera Laser rangefinder Fluxgate 3-axis magnetometer Alpha particle X-ray spectrometer (APXS) Surface and subsurface sampler On the spacecraft

Exo-Zodiacal Infrared Telescope (EXZIT) is a 10 cm-diameter telescope. Gamma-ray burst polarimeter (GAP-2) Monostatic radar to image the body's internal structures Attached to the sail

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with OKEANOS

Start with the simplest possible case. Write down what OKEANOS claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to OKEANOS before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about OKEANOS ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of OKEANOS

In research: OKEANOS appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses OKEANOS in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: OKEANOS is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cancelled missions to Jupiter, Japanese inventions, Japanese space probes, so understanding it makes those chapters shorter.
In everyday life: Look for OKEANOS outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study OKEANOS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what OKEANOS means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain OKEANOS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is OKEANOS in simple terms?

Why does OKEANOS matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study OKEANOS?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on OKEANOS.