astronomy

PAS-22

PAS-22 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 PAS-22 rather than just read about it. In short: AsiaSat 3, previously known as HGS-1 and then PAS-22, was a geosynchronous communications satellite, which was salvaged from an unusable geosynchronous transfer orbit (GTO) by means of the Moon's gravity. Launch of AsiaSat 3 AsiaSat 3 was launched for AsiaSat of Hong Kong to provide communications and television services in Asia by a Proton-K / DM-2M launch vehicle on 24 December 1997, destined for an orbital positi…

Key takeaways

PAS-22 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect PAS-22 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of PAS-22 from memory before moving on to harder problems.

Reference excerpt

Launch of AsiaSat 3 AsiaSat 3 was launched for AsiaSat of Hong Kong to provide communications and television services in Asia by a Proton-K / DM-2M launch vehicle on 24 December 1997, destined for an orbital position at 105.5° East. However, a failure of the Blok DM-2M fourth stage left it stranded in a highly inclined (51.6°) and elliptical orbit, although still fully functional. It was declared a total loss by its insurers.

HGS-1

The satellite was transferred to Hughes Global Services Inc., which was then a subsidiary of Hughes Space and Communications, with an agreement to share any profits with the consortium of 27 insurers. Edward Belbruno and Rex Ridenoure heard about the problem and proposed a 3–5 month low-energy transfer trajectory that would swing past the Moon and leave the satellite in geostationary orbit around the Earth. Hughes had no ability to track the satellite at such a distance and considered this trajectory concept unworkable. Instead, Hughes used an Apollo-style free-return trajectory that required only a few days to complete, a trajectory designed and subsequently patented by Hughes Chief Technologist Jerry Salvatore. This maneuver removed only 40° of orbital inclination and left the satellite in a geosynchronous orbit, whereas the Belbruno maneuver would have removed all 51° of inclination and left it in geostationary orbit. Although Hughes did not end up using the low-energy transfer trajectory, the insight to use a lunar swingby was key to the spacecraft rescue. According to Cesar Ocampo, Hughes had not considered this option until it was contacted by Ridenoure, although the Hughes engineers involved in the lunar flyby operations have stated that they were already working on the lunar swingby mission design before being contacted by him.

Rescue of satellite Using on-board propellant and lunar gravity, the orbit's apogee was gradually increased with several manoeuvres at perigee until it flew by the Moon at a distance of 6,200 km from its surface in May 1998, becoming in a sense the first commercial lunar spacecraft. Another lunar fly-by was performed later that month (6 June 1998) at a distance of 34,300 km to further improve the orbital inclination. These operations consumed most of the satellite's propellant, but still much less than it would take to remove the inclination without the Moon-assist manoeuvres. With the remaining fuel, the satellite could be controlled as a geosynchronous satellite, with half the life of a normal satellite – a huge gain, considering that it had been declared a total loss. The satellite was then maneuvered to geosynchronous orbit at 158° West. Once the satellite was in a stable orbit, it was commanded to release its solar panels, which had been stowed during takeoff and maneuvering. Of the satellite's two solar panels, only one released, and it became apparent that a tether was not operating correctly on board, which engineers attributed to heating and cooling cycles due to the satellite operating outside its design range while traveling to its final orbit.

PAS-22 In April 1999, Hughes filled to request authorization to operate the satellite at 60° West in C-band and in Ku-band. In 1999, HGS-1 was acquired by PanAmSat, and renamed as PAS-22, and moved to 60° West. It was deactivated in July 2002 and moved to a graveyard orbit.

Illustrations

Worked examples

Example 1 — a first encounter with PAS-22

Start with the simplest possible case. Write down what PAS-22 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 PAS-22 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 PAS-22 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 PAS-22

In research: PAS-22 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 PAS-22 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: PAS-22 is common in secondary-school and first-year university syllabi. It links to neighbouring topics AsiaSat satellites, Communications satellites in geostationary orbit, Missions to the Moon, so understanding it makes those chapters shorter.
In everyday life: Look for PAS-22 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 PAS-22 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PAS-22 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 PAS-22 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PAS-22 in simple terms?

AsiaSat 3, previously known as HGS-1 and then PAS-22, was a geosynchronous communications satellite, which was salvaged from an unusable geosynchronous transfer orbit (GTO) by means of the Moon's gravity. Launch of AsiaSat 3 AsiaSat 3 was launched for AsiaSat of Hong Kong to provide communications…

Why does PAS-22 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 PAS-22?

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 PAS-22.